A printed circuit board (pcb) mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. pcb's can be single sided (one copper layer), double sided (two copper layers) or multi-layer. Conductor on different layers are connected with plated-through holes called vias. Advanced pcb's may contain components - capacitors, resistors or active devices - embedded in the substrate.
circuit board soldering
BGA Ball Grid Array Package ball grid array package is widely used in integrated circuit packaging .
As FPGA / CPLD motherboard Northbridge and Southbridge , mobile chip, which is good soldering directly related to the production of films made by the reliability and life , I soldered the chip BGA package soon , and wanted to write thoughts , we hope the exhibitions.
Technology principles
Principles adopted BGA solder reflow . But here is what the mechanism of the solder ball reflow soldering process .
When the solder balls As a heated environment , solder ball reflow divided into three stages :
Preheat:
First , the viscosity of the solvent used and the desired properties of the screen starts to evaporate , the temperature rise must slow ( about 5 sec ° C), boiling and splashing to limit , prevent the formation of the tin beads , and some of the internal stress of the element of Comparative sensitive to external temperature rises too quickly if the component will cause breakage .
Flux ( cream ) active, chemical cleaning operation began , water-soluble flux ( paste ) and leave- flux ( paste ) the same cleaning action will occur , but the temperature is slightly different . The metal oxides and some pollution removed from the upcoming combination of metal and solder particles. Tin solder requires a "clean" surface on the good metallurgy .When the temperature continues to rise , melting the solder particles are first individually , and the surface and began to suck liquefied tin " Dengcao " procedure. So that the surface coverage of all possible and begin forming a tin solder .
Reflux :
The most important at this stage , when all the individual solder particles melt , combined together to form a liquid tin , then the surface tension began to form fillet surface , if the gap between the component lead and PCB pad over 4mil (1 mil = thousandths one inch ) , is very likely due to the surface tension so that the pins and pads separately , that is causing the tin open.
Cooling:
Cooling stage , if the cooling fast , tin point strength will be slightly bigger , but not too quickly may cause the internal temperature stress components .
1 . Process principles adopted
For BGA soldering , we are using the BGA Rework Station (BGA rework station ) to be welded . Process Principle different manufacturers BGA rework station uses slightly different, but roughly the same. Here to introduce the concept of temperature curve. BGA solder balls on the unleaded and leaded into two . Lead solder ball melting point 183 ℃ ~ 220 ℃, melting point lead-free solder ball 235 ℃ ~ 245 ℃.
Here are solder balls have a temperature curve and no shot used during welding .
As can be seen from the above two curves, welding roughly divided into preheating, insulation , reflux, cooled four intervals ( different BGA rework station work to do slightly different ) with or lead solder or lead-free solder , solder melting stage in the recirculation zone , except that the temperature is different , the previous curve reflux as a slow heating and holding process. Understand this basic principle , any BGA rework station can be so . Here introduce several temperature zones:
Preheating zone : also called slope area for the PCB temperature from ambient temperature to be raised to a temperature of activity . In this area, the heat capacity of the circuit boards and components is different, different temperatures enhance their actual rate . Temperature circuit boards and components shall not exceed 2 ~ 5 ℃ per second speed continuous rise , if excessive , will produce thermal shock, circuit boards and components are likely to damage, such as minor cracks ceramic capacitors . The temperature rise is too slow , the paste will feel warm excessive solvent evaporation is not sufficient, affect the quality of welding . Furnace preheating zone will generally comprise 15 to 25 % of the entire length of the heating zone .
Insulation zones : sometimes called dry or wet area, this area usually accounts for 30 to 50% of the heating zone . The main purpose is to make the temperature of the active region of the stabilizing elements on the PCB , to minimize the temperature difference . In this region given enough time for the heat capacity of the large temperature components to catch smaller components , and to ensure that the solder paste flux fully evaporate. To the end of the active region , the pad , the solder balls on the pin member and the oxide is removed , the temperature of the balance board . It is noted that all components on the PCB at the same temperature when the end of this area, otherwise go to the reflux temperature zone will be because of the unevenness generates various parts faulty welding . Generally the activation temperature range is generally 120 ~ 150 ℃, if the temperature of the active region is set too high, the flux ( ointment ) is not enough time activated, and a temperature slope is incremented upward slope. Although some manufacturers allow the paste to add some temperature activation period , but the ideal temperature curve should be stable temperature.
Reflux zones: zone or sometimes called final temperature peak area, the role of this region is to increase the temperature of the PCB from the active peak temperature to a recommended temperature. Active temperature is always a little lower than the melting temperature of the alloy, while the peak temperature of the melting point is always on . Typical temperature range around the peak melting temperature of the alloy paste plus 40 ℃, work time is the recirculation zone 20 - 50s. This zone temperature set too high so that the slope of the temperature rise over per 2 ~ 5 ℃, or to reflow peak temperature higher than recommended , or working too long may cause excessive curl PCB delamination or burning, and undermine the integrity of the components. Reflow peak temperature is lower than recommended , it may appear cold welding defects such as working time is too short. Cooling zone : this zone paste and solder alloy powder has melted sufficiently wet surfaces to be connected , should be as fast as possible for cooling , which would contribute to the formation of an alloy crystal obtained bright solder joints, and a better appearance and a low contact angle. Slow cooling will result in the decomposition of impurities of the circuit board into the more tin to produce dark coarse joints. In extreme cases, it may cause poor wetting and binding force weakened joints . Cooling section cooling rate is usually 3 ~ 10 ℃ / S.
2 Process in
Before soldering BGA, PCB and BGA be at 80 ℃ ~ 90 ℃, 10 to 20 hours under conditions of constant temperature baking in the oven , the purpose is in addition to the influx of different , more appropriate to adjust the degree of damp baking temperature and time. Not opened the PCB and BGA can be welded. In particular , when all of the following operations , to wear a wrist strap or antistatic gloves to prevent electrostatic damage to the chip may cause. Before welding BGA, To accurately aligned on the BGA pads on the PCB . Here are two methods: optical alignment and manual alignment. At present, the use of hand- on position, coming around the BGA and the PCB pads around the screen line alignment. Here is a orifices : in the BGA and the printing process of the alignment line , is not completely aligned in time , even if the solder ball and pad shift of about 30% can still be welded. Because the solder ball melting process, because of the tension between it and the pad and the pad is automatically aligned. After completing the alignment operation on the PCB on BGA rework station stand, will be fixed so that it and BGA rework station level. Select the appropriate hot air nozzle ( ie, nozzle size slightly larger than the size BGA) , and then select the corresponding temperature curve , start welding until the temperature curve is completed, cooling , will complete the BGA soldering.
In the production and debugging process , it is inevitable because of other reasons to replace damaged or BGA BGA. BGA rework station BGA can also complete the demolition work . Removing the BGA soldering process can be seen as the reverse of BGA . The difference is that , until the temperature curve is completed, use the vacuum suction pen BGA sucked , why do not other tools , such as tweezers, because they want to avoid damage due to excessive force pads . Remove the BGA PCB will be in addition to hot tin operation ( removal of the tin pads ), why does it have to be hot ? Because of heat and preheat the PCB is quite functional , in addition to tin can guarantee job easier. Here to use suction-line , during the operation do not use excessive force to avoid damage to the pad , the pad on the PCB to ensure smooth, it can be operated soldering BGA 's .
Can be removed BGA soldering it again ? The answer is yes. But before that there is a critical step , and that is bumping . The purpose is to bumping solder ball BGA re- planted on the pads and the new BGA can achieve the same effect arrangement . Details here under bumping . Here are two tools to use steel mesh and suction-line.
First, we want the dross removing excess BGA , BGA requirement is to make the surface smooth, without any glitches ( tin formation ) .
Step 1- Apply flux paste ( agent )
Conductive mat on the BGA , apply a small amount of the surface of the BGA help paste ( agents ) .
Step 2 - removing the solder ball
Tin and iron with suction to remove the solder ball from the BGA. Placed on the suction-line help paste the iron on the suction-line .
Before you wash paddling in BGA solder wire surface , so that iron absorption is heated to melt the solder ball and solder wire .
Note: Do not let the iron pressed on the surface. Cracks were scraped too much pressure on the pads will surface. In order to achieve the best results , it is best to use suction-line once through BGA surface. Leave a small amount of solder paste on pads help make bumping easier.
Step 3 - cleaning
Immediately clean up BGA surface with industrial alcohol ( washer water ) , at this time to help clean up the residual solder paste to make it easier to remove .
Movement by friction surface to help remove the BGA solder paste . Keep moving cleaning. When cleaning always start from the edge , do not forget the corner .
Use a clean solvent cleaning every BGA
Step 4 - Check the
Recommended examination under a microscope. Observe a clean pad , pads and solder ball damage did not remove.
Note: Due to the corrosive flux is recommended if there is no immediate bumping to additional cleaning.
Step 5 - excessive cleaning
Deionized water and scrub brush in the BGA surface .
Note : For best cleaning results , with a brush in one corner of the back and forth from one direction to wash the surface of the package . Cycle scrub.
Step 6 - Rinse
And deionized water to wash the brush surface of the BGA . This helps to remove solder paste residues from the BGA surface.
Let BGA dry in the air. Step 4 repeatedly check with BGA surface.
If the BGA is placed for a period of time before planting the ball , you can basically make sure they are nice and clean up . BGA is not recommended to be placed in the water to soak for too long.
After performing the above operations , you can plant the ball up . Here to use stencils and vegetation units.
The role of the stencil is that it can easily be placed on the BGA solder balls corresponding pads. Role is to plant tables on BGA solder ball melting , it is fixed on the pad . Bumping when the first BGA surface ( there are pads that side ) evenly spread a layer of flux paste ( agent ) , the amount applied to do no less. Apply the amount of more or less bumping may have resulted in failure . Each pad will be a hole in steel mesh ( here is universal steel mesh ) on each and BGA alignment. Then solder ball pads were poured with steel mesh , with a brush or other tool to dial into the ball every hole in the stencil , solder ball BGA will arrive on down the hole . After completion of this step , carefully check there and not aligned solder ball pads , if any, to be set right with a needle . Carefully remove the stencil , BGA on the high-temperature paper , bumping into the table . Plant tables have temperature setting is based solder ball 220 ℃, 235 ℃ to lead-free solder ball set . Bumping time is not fixed. Is actually based on when the BGA solder balls are melted and shiny surface , into a complete sphere to determine when these observed by the naked eye. Can reach a state in which the recording time , the next time bumping according to this .
BGA ball is a need for patience and careful work , time for the operation to be careful and earnest .
3 . Level home and abroad
BGA (Ball Grid Array Package) is this years most popular package
Its appearance can greatly enhance integration of the chip and manufacturability . Due to a late start in China BGA soldering technology, the domestic manufacturing BGA rework station can not many manufacturers , therefore , BGA rework station in the country is relatively small , especially in the west. With optical alignment , X-RAY BGA rework station features even more rare, perhaps late Chinese in X-RAY rework station can build a lot , there is currently IAC eastern detection provides detection detects this regard , see the following technical aspects of it !
4 . Technical difficulties resolved
In the actual work which will encounter different sizes, different thicknesses of different sizes PC BGA, have also adopted the use of lead-free soldering with lead solder . They use the temperature curve is different . Therefore , it is impossible to weld in a temperature curve all the BGA. Depending on the conditions of how to set a different temperature curve , which is the key to the BGA soldering process . Here are several groups of pictures to illustrate this. Causes the temperature does not have a lot , there is a reason for this is when the test temperature curve , are carried out in air-conditioned environment , that is not a normal temperature. Summer and winter temperatures and temperature caused by air-conditioning does not comply , so the set temperature curve when the BGA will be high or low. So every time when welding , should test whether the actual temperature set temperature value . First, the principle is based on the temperature setting is lead solder or lead-free soldering set the appropriate temperature , then use a thermometer ( or thermocouple ) test the actual temperature, and then adjust the actual temperature set temperature , so as to reach the ideal temperature welding. In the welding process , we must ensure BGA rework station , PCB, BGA at the same level, vibration welding process can not happen , or it will melt the solder ball bridging occurs , causing a short circuit . PCB board design is generally a good board only to save material and electrical characteristics are also very good in all aspects , such as heat, anti- interference.
Welding points:
1. choice of electric iron
Electric iron power should be determined by the size of welding points , solder joint area, spot cooling speed is fast, so use the electric iron power should be bigger. General electric iron power has 20W 25W 30W 35W 50W and so on. In the process of making the choice about 30W of power more appropriate.
After prolonged use electric iron , iron head will generate a layer of oxide , then it is not easy to eat tin, then you can file away the oxide layer with a file , such as a soldering iron after the iron is energized when the head is inserted rosin fever , coated with solder can continue to use , bought a new electric iron must also be on the tin before use.
2. solder and flux
Selection of solder flux and low melting corrosive , such as rosin , solder should not be used industrial welding and corrosive acid oil , preferably containing rosin solder , very convenient to use .
3 . Welding method
Element must be clean and tin , the electronic component stored in the air , the oxidation of the element with a layer of oxide film on the pin , as well as other soils , before welding knife scrape an oxide film can be used , and immediately coated Solder ( commonly known as the lining of tin ) , and then welding. After these processing elements easily weld , not prone to Weld phenomenon .
Soldering temperature and soldering time
Soldering temperature should be higher than the electric soldering iron temperature , but not too high to tip in contact rosin just smoke as well. Welding time is too short , too low temperature solder , solder melting inadequate , likely to cause rough Weld joints , whereas prolonged welding , soldering easy flowing, and easy to make components from overheating damage to components .
The number of soldered points
Number of soldering point can not be too little, too little welding is not strong, the mechanical strength is also bad . And too easily lead to the appearance of a lot and is not connected internally . Solder should just weld the component pin on all submerged , outline looming as well.
Note the location of the soldering iron and solder
Beginners in welding , soldering iron will generally move back and forth in the weld or squeeze , this approach is wrong. The correct way is to keep out of the tin surface electric iron to reach the welding points, so the heat transfer area, welding speed .
4 . Inspection after welding
There must be checked after welding seamless welding , Weld and components caused by a short circuit due to the solder flow . Weld difficult to find , you can clamp the clamping device pin gently pull , shake immediately if found welding .
PCB soldering techniques basic content
Circuit boards, circuit boards , PCB board , pcb welding technology in recent years, the electronics industry technology development process , you can notice a very obvious trend is the reflow technology. Cartridge principle of traditional reflow process can also be used , which is commonly referred to through-hole reflow soldering. Its advantage is that it is possible to complete all of the joints at the same time , so that production costs to a minimum . However, it limits the temperature-sensitive element reflow soldering applications , either Cartridge or SMD. Then people turn to select welding. Most applications can be adopted after reflow soldering choice . This will become an economic and efficient completion of welding residual Cartridge , and is fully compatible with future lead-free soldering .
Selective soldering process characteristics can be compared with the wave soldering process to understand the characteristics of selective soldering . The most obvious difference between the two lies in the lower part of the wave soldering PCB is completely immersed in the liquid solder , and in selective soldering , only part of the specific area in contact with the solder wave . Since the PCB itself is a poor heat conduction medium , so it does not heat to melt the welding of components and PCB area adjacent solder joints . Before welding must also be pre- coated with flux. Compared with the soldering flux is coated on only the lower portion of the PCB to be welded, rather than the entire PCB. Selective soldering additional plug-in component only for welding. Selective soldering is a new approach , a thorough understanding of the selective soldering process and equipment are required for successful welding .
Selective soldering processes typical selective soldering process include : the flux coating , PCB preheating, dip soldering and drag soldering .
In selective soldering flux coating process , the flux coating process plays an important role . At the end of the heating and welding welding , flux activity should be sufficient to prevent the generation of the bridge and prevent PCB oxidation . Fluxing by the X / Y robot carrying PCB flux through the top of the nozzle , spray flux to be soldered to the PCB position . Flux has a single mouth spray , micro -jet , synchronized multi-point / graphics spray a variety of ways . Microwave peak reflow soldering process after the election , the most important is accurate spray flux . Microporous jet never soiled area outside the joints . Lightly spray dot pattern diameter greater than the minimum flux 2mm, so the spray deposition flux on the PCB position accuracy of ± 0.5mm, in order to ensure the flux is always covered in welded parts of the above , spray welding dose tolerance provided by the supplier , technical specifications should prescribed amount of flux is generally recommended 100% safe tolerances.
The main purpose of the preheating process in the preheating process is not selective soldering reduce thermal stress , but the pre- dried to remove the solvent flux, prior to entering the solder wave , such that the flux has the correct viscosity. When welding , preheating is not critical influence of heat brought to the welding quality , PCB material thickness , the device determines the type of package specifications and flux preheat temperature setting. In selective soldering , there are different theories to explain the warm-up : Some process engineers think PCB should be conducted before fluxing , preheating ; another point of view does not require preheating and soldering directly . Users can be arranged according to the specific circumstances of the selective soldering process .
Circuit board soldering methods
Welding is one of the important aspects of the manufacture of electronic products , if there is no corresponding process quality assurance , any well-designed electronic products are difficult to meet the design requirements . In research and development, trial design , technical innovation process to produce a , two circuit boards, possible nor necessary to use automated equipment often requires manual assembly and welding . In mass production , from the screening test components to the circuit board assembly welding , are done by automated machinery , such as automatic test machines , component cleaning machines , boring tin, plastic machine , plug machines, wave soldering machines , cut leg machines, PCB cleaning machines. These computer-controlled manufacturing equipment , electronic products in the modern mass production played an important role in helping to ensure consistency of process conditions and assembly and welding operations , improve product quality.
1 . Welding and soldering conditions classification
1.1 Classification of welding
Welding technology in the electronics industry is very broad , in electronics manufacturing process, to be used in almost all kinds of welding methods , but the most common, the most representative is soldering methods. A solder welding , the welding member which is lower than the melting point of solder and solder joint member is heated to soldering temperature , in the case of the weldment is not melted , the solder is melted and welded surface infiltration , both relying on the diffusion of atoms form a connection weldment . Its main features are the following three points :
⑴ solder melting point lower than the weldment ;
⑵ solder when soldering and welding parts together will be heated to a temperature solder , the solder melts and the weldment does not melt ;
⑶ weld molten state to form solder wetting rely on the welding surface by capillary action into the gap between the solder weldment , an alloy layer is formed , thereby achieving the coupling of the weldment .
Except for some alloys contain large amounts of chromium , aluminum and other elements should not be used soldered , other metal materials may be used mostly soldered . Soldering method is simple, just use simple tools ( such as electric iron ) to complete the weld , solder refurbished, removable components , re- welding process . In addition, solder also has a low cost , easy to automate , etc., in electronic engineering technology , the use of which is the oldest , most widely used, accounting for the largest proportion of welding methods.
1.2 soldering must have the condition
Welding is the physical basis of " infiltration " infiltration also called " wet ." To explain the invasion , starting with drops of water on a lotus leaf Speaking : lotus leaf surface wax layer of impermeable material , the surface tension of water to keep it beads rolling on the leaves and can not spread out , this state can not be called infiltration ; Conversely, if the liquid contact surface of the spread with the solid , fully spread contact called infiltration. Soldering process, is heated , so that the welding surface of the molten tin solder flow , infiltration, tin atoms penetrate into the surface of the copper base material ( conductor pad ) , and the contact surface between the two formation of brittle alloy layer Cu6-Sn5 's .
During the welding process , the contact angle between the solder and the base material is called the wetting angle formed , as shown in 5.13 . (a) the figure, then , there is no infiltration of the solder and the base material , can not form a good joint ; (b) in FIG , when the solder and the base metal infiltration, can form a good solder joint. Carefully observe the wetting angle joints , we can judge the quality of solder joints.
Circuit board soldering methods
Welding is one of the important aspects of the manufacture of electronic products, if there is no corresponding process quality assurance, any well-designed electronic products are difficult to meet the design requirements. In research and development, trial design, technical innovation process to produce a, two circuit boards, possible nor necessary to use automated equipment often requires manual assembly and welding. In mass production, from the screening test components to the circuit board assembly welding, are done by automated machinery, such as automatic test machines, component cleaning machines, boring tin, plastic machine, plug machines, wave soldering machines , cut leg machines, PCB cleaning machines. These computer-controlled manufacturing equipment, electronic products in the modern mass production played an important role in helping to ensure consistency of process conditions and assembly and welding operations, improve product quality.
1. Welding and soldering conditions classification
1.1 Classification of welding
Welding technology in the electronics industry is very broad, in electronics manufacturing process, to be used in almost all kinds of welding methods, but the most common, the most representative is soldering methods. A solder welding, the welding member which is lower than the melting point of solder and solder joint member is heated to soldering temperature, in the case of the weldment is not melted, the solder is melted and welded surface infiltration, both relying on the diffusion of atoms form a connection weldment. Its main features are the following three points:
⑴ solder melting point lower than the weldment;
⑵ solder when soldering and welding parts together will be heated to a temperature solder, the solder melts and the weldment does not melt;
⑶ weld molten state to form solder wetting rely on the welding surface by capillary action into the gap between the solder weldment, an alloy layer is formed, thereby achieving the coupling of the weldment.
Except for some alloys contain large amounts of chromium, aluminum and other elements should not be used soldered, other metal materials may be used mostly soldered. Soldering method is simple, just use simple tools (such as electric iron) to complete the weld, solder refurbished, removable components, re-welding process. In addition, solder also has a low cost, easy to automate, etc., in electronic engineering technology, the use of which is the oldest, most widely used, accounting for the largest proportion of welding methods.
1.2 soldering must have the condition
Welding is the physical basis of "infiltration" infiltration also called "wet." To explain the invasion, starting with drops of water on a lotus leaf Speaking: lotus leaf surface wax layer of impermeable material, the surface tension of water to keep it beads rolling on the leaves and can not spread out, this state can not be called infiltration; Conversely, if the liquid contact surface of the spread with the solid, fully spread contact called infiltration. Soldering process, is heated, so that the welding surface of the molten tin solder flow, infiltration, tin atoms penetrate into the surface of the copper base material (conductor pad), and the contact surface between the two formation of brittle alloy layer Cu6-Sn5's.
During the welding process, the contact angle between the solder and the base material is called the wetting angle formed, as shown in 5.13. (A) the figure, then, there is no infiltration of the solder and the base material, can not form a good joint; (b) in FIG, when the solder and the base metal infiltration, can form a good solder joint. Carefully observe the wetting angle joints, we can judge the quality of solder joints.
Obviously, if the welding surface of a barrier layer of oxide or dirt infiltration, an alloy layer can not be generated in two metallic materials, or the temperature sufficiently high enough to melt the solder not, do not make solder wetting. Soldered, must have the following conditions:
⑴ weldment must have good weldability
Solderability is the so-called at an appropriate temperature, the metal material to be welded with a good combination of properties can form the solder alloy. Not all metals having good weldability, and some metals such as chromium, molybdenum, tungsten, etc. is very poor weldability; some metals and relatively good weldability, such as copper, brass, etc.. In welding, the metal surface at a high temperature oxide film material can affect weldability. In order to improve weldability, surface tin, silver and other measures can be used to prevent oxidation of the surface material.
⑵ weldment surfaces must be kept clean
In order to achieve good soldering and welding parts combination welding surface must be kept clean. Even good weldability weldments, as storage or contaminated, are likely to produce harmful infiltration oxide film and the surface of the oil in the weldment. Be sure to put dirt in front of the welding film clean, otherwise it is impossible to ensure the welding quality. Mild oxidation of the metal surface layer may be cleared by the flux effect, the severity of oxidation of the metal surface by mechanical or chemical methods should be clear, for example, curettage or pickling.
To use an appropriate flux ⑶
Role is to remove solder flux surface of the oxide film. Different welding processes, should choose a different flux, such as nickel-chromium alloy, stainless steel, aluminum and other materials, there is no dedicated special flux soldering is difficult to implement. When soldering printed circuit boards and other sophisticated electronic products for reliable and stable welding, usually with rosin-based flux. Alcohol is generally used to dissolve the rosin into the pine fragrance use.
⑷ weldment to be heated to the proper temperature
When soldering, the solder melting heat and the heating effect of the welding object, so that the tin, lead atoms sufficient energy to penetrate the metal surface to be welded is formed in the alloy lattice. Soldering temperature is too low, the solder penetration unfavorable atomic unable to form an alloy, can easily form Weld; soldering temperature is too high, in a non-eutectic solder state, accelerated decomposition and evaporation rate of flux, solder quality decline, serious cases cause the pad off the printed circuit board.
It is emphasized that, not only to be heated to melt the solder, and should also be heated to a temperature to melt the solder weldment.
⑸ suitable welding time
Welding time is the whole welding process, the physical and chemical changes in the time required. It consists of welded metal welding temperature reaches the time the solder melting time, flux of time to play a role and generate metal alloys several parts. When soldering temperature is determined, it should be to determine the appropriate time according to the shape to be welded weldments, nature, characteristics and so on. Welding time is too long, easily damaged components or welded parts; too short, not up welding. In general, each spot weld the longest time not exceeding 5s.
2. Preparation before welding - tin
To improve the quality and speed of welding, to avoid Weld defects, before assembly of the weld should be solderable surface treatment - tin. Has not been cleaned and coated with flux printed circuit board, to be processed in accordance with Chapter 5 of the method described. In the face of the electronic components to be welded (the need for welding leads or other places) on the solder plating, is a very important step before welding, especially for some of the components poor weldability, tin is crucial. Professional electronics manufacturers are equipped with specialized equipment for handling weldability.
Tinned also called "sugar tin" is actually liquid solder on the metal surface to be welded infiltration, forming a layer of metal to be welded is different from the binding is different from the solder layer. The bonding layer by the solder and the metal to be welded two properties, the component is not securely connected to the same material.
3. Basic skills of hand soldering iron
Use electric iron for manual welding, it is not difficult to master, but there are some technical essentials. People engaged in the production of electronic products is to improve the quality of welded from four aspects: materials, tools, methods, operator.
The most important of course, people skills. Without welding practices and intentions of experience for quite some time, comprehend, can not grasp the essentials of welding technology; Even skilled workers engaged in welding work longer period of time, we can not guarantee consistent quality of each solder joint. Only by fully understanding the intentions welding principle plus practice, will it be possible to learn the basic skills of welding in a short period of time. Some specific methods and conventions described below, are the practical lessons learned, beginners quickly master the skills of welding shortcut.
Beginners should practice diligently and continuously improve operational skills, can not leave the welding quality problems when debugging the whole circuit again resolved.
Correct posture 3.1 welding operation
Master the correct operating position, the operator can guarantee the physical and mental health, reduce labor injuries. To reduce the heat flux when the volatile substances hazardous to human, reduce the amount of harmful gases inhaled, under normal circumstances, the iron should be less than the distance to the nose, 20cm, 30cm usually appropriate.
There are three types of electric iron grip as shown in the following figure
Schematic way electric iron grip
Solder take law
Anti-grip action stable, long operation fatigue, suitable for high-power soldering operation; positive grip in power for operation with elbow iron or electric iron; general operating table welding weldment PCB etc. , the multi-use method to hold a pen.
There are two general take solder method, as shown in Figure 5.16. As the solder contains a certain percentage of lead, but lead is a heavy metal harmful and therefore should be worn when operating gloves or wash their hands after the operation, to avoid ingestion of lead dust.
After the electric iron use, must be securely plugged on iron shelves, and pay attention to the wire and other debris not to touch the tip to avoid burns wires, causing leakage and other accidents.
3.2 The basic steps of hand soldering operations
Master electric iron soldering temperature and time, select the appropriate contact position of the tip and solder joints, it may get a good spot. Right hand during welding operations can be divided into five steps, as shown in FIG.
⑴ Step one: Prepare welding (Figure (a))
Wire left hand, right hand soldering, welding equipment into the state. Required to keep the tip clean, no welding slag and other oxides, and coated with a layer of solder.
⑵ Step two: heating welding (figure (b))
Tip against the junction of two weldments, heat the entire weldment all, time is about 1 to 2 seconds. For soldering components on the printed circuit board, it should pay attention to the tip simultaneously contact both to be welded. For example, Figure (b) of the wire and terminal, while component leads to uniform heating of the pad.
⑶ Step Three: fed wire (Figure (c))
When welding surface weldment is heated to a certain temperature, solder contacts from across the iron weldments. Note: Do not put solder iron to the head!
⑷ Step Four: Remove the wire (Figure (d))
When the wire melting a certain amount, immediately left the 45 ° direction to remove the wire.
⑸ Step Five: Remove the soldering iron (Figure (e))
Solder pads and infiltration weldments after welding site, right on the 45 ° direction away iron, welding ends. The third step from start to finish fifth step, the time is also about 1 ~ 2s.
Five-step method of soldering operation
For small heat capacity weldment, such as connecting wires on the printed board smaller, the three steps can be simplified.
① preparation: with the above steps one;
② heating and wire: iron head on into the weldment after welding.
③ to shift iron wire: solder diffusion welding surface infiltration after reaching the expected range, and immediately removed the wire and remove the iron, and note the time of removal of the wire must not lag in time to remove iron.
For low-calorie absorption weldment, the whole process but these times 2 ~ 4s, accurate rhythm control each step, the order of the master, skilled coordinated movements are carefully through a lot of practice and experience to solve problems. It was summed up in five steps approach control method using a few seconds of time: the number of contact pads after a soldering iron, two (about 2s), the number of wire into three, four, remove the soldering iron, wire melting amount depends on observation decision. This way you can refer to, but because of the power soldering iron, solder heat capacity differences and other factors, there is no real grasp of welding heat given chapter to follow, specific conditions must be specific treatment. Imagine, for a larger heat capacity joints, if the use of smaller power soldering iron, in these times, it may not make the heating temperature to melt the solder, soldering impossible.
3.3 soldering temperature and heating time
In introducing the mechanism and conditions for soldering has been repeatedly mentioned, the appropriate temperature to form a good solder joint is essential. How exactly this temperature control it? Of course, according to the relevant data, you can clearly identify the optimum temperature of different weldment material needed to obtain the relevant curve. However, in the welding process in general, possible to use a thermometer to any kind of instrument is detected, but to a more intuitive way to understand clearly the weldment temperatures.
After the test results, the tip on the weldment weldment residence time and temperature rise is directly proportional relationship. The same iron, when heated thermal capacity of different weldments, to achieve the same soldering temperature can be achieved by controlling the heating time. But in practice they can not determine the relationship between the heating time and so only. For example, when using low-power soldering iron heating large weldments, regardless of how long to stay soldering iron temperature weldment also does not rise up because of the heat capacity is less than iron and iron weldments loss of heat in the air. In addition, to prevent internal damage from overheating, and some components do not allow long-term heating.
What impact its external features and weldment joints heating time is it? If the heating time is less, the solder will not fully infiltration weldments, rosin slag formation and Weld. Conversely, excessive heat may cause damage to the components in addition to outside, as well as the hazards and external features:
⑴ weld appearance is deteriorated. If the solder has infiltrated weldment later also continue to excess heat, would make all the volatile flux, causing molten solder overheating, reduce infiltration performance; easy to pull out when leaving tin soldering tip, and solder surface white, appears rough particles lose their luster.
⑵ flux decomposition temperature carbonization caused by Hong Gason. Rosin generally begins to decompose at 210 ℃, not only lost the role of flux, and the formation of carbon residue in the joints become slag defects. If it is found rosin black, long heating time is certainly caused in the welding process
⑶ excess heat will destroy the adhesive layer on the PCB copper foil, lead foil pad peeling. Therefore, the appropriate heating time, the heating furnace is critical to accurately grasp the welding quality.
3.4 Specific methods of manual welding operations
Under the guarantee of high-quality solder joint objectives, specific welding operation practices can vary, but the following summary of these previous methods, guidance for beginners is not negligible.
⑴ to keep the tip clean
When welding, the tip of long-term high temperature state, came in contact with a weak acid flux and other substances, and its surface is very susceptible to oxidation and corrosion coated layer of black impurities. These impurities form the insulating layer, preventing heat conduction between the tip and the weldment. So, pay attention with a damp cloth or wet sponge ready to wipe wood fiber tip. For general tip, when you can use the rasp polluting corrosion repair to the surface oxide layer. For long-life tip, you absolutely can not use this method it.
⑵ to speed by increasing the heat transfer area of contact
When heated, so that each part should be on the need to solder infiltration weldment heat evenly, rather than just heating part weldments, not by increasing the pressure of the iron weldments way, so as to avoid damage or imperceptible risks. Some beginners tip pressure applied to the welding surface, an attempt to speed up the welding, it is not right. The correct way is to use different tip according to the shape of the weldment, or their own dressing tip, so that the tip is brought into contact with the surface of the weldment contacts instead of dots or lines. In this way, we can greatly improve the heat transfer efficiency.
⑶ heating rely solder bridge
In the non-pipelined operations, welded joints shapes are varied, are unlikely ever to replace the tip. To increase the heating efficiency of the heat transfer needed for solder bridges. The so-called solder bridge is retained by the head of a small soldering iron, as the heat transfer between the tip and the bridge of the weldment. Since the thermal efficiency of the molten metal is much higher than the air, so that the weldment is heated quickly to the welding temperature. It should be noted, as tin solder bridge can not keep too much, not only because of prolonged retention in the solder iron head is overheated, actually have reduced the quality, but also may cause a short circuit between the joints even by mistake.
⑷ iron evacuated with stress
To timely evacuation of iron, and the angle and direction of the solder joints formed on the evacuation. Shows the different effects of the withdrawal direction iron tin solder Figure 5.18.
The relationship between the direction and solder iron evacuation of tin
⑸ not move until the solder solidification
Do not move or make weldment subjected to vibration, especially when forceps weldments, we have to wait before removing the solidified solder tweezers, otherwise easily cause loose structure or soldered joints.
⑹ to moderate amount of solder
Tubular hand soldering solder wire commonly used, has been fitted with an internal flux rosin and activator made. Solder wire diameter 0.5,0.8,1.0, ..., 5.0mm and other specifications, to be selected according to the size of the solder joints. Generally, you should make a diameter slightly smaller than the diameter of the solder pads.
, The Figure, only the excess solder of the solder unnecessarily consumed, but also increase the welding time, reduce the operating speed. More seriously, the excess solder can easily cause a s, hort circuit fault imperceptible. Too little solder can not form a strong bond, is also disadvantageous. Especially when soldering PCB lead wire, solder amount insuffi, cient, causing wires to fall off very easily.
Tin solder mastery
⑺ to moderate amount of flux
The amount of flux for welding very favorable. Excessive use of rosin flux, wipe off any excess will be needed after welding flux, and extend the heating time, reducing efficiency. When insufficient heating time, and easy to form defects "slag" is. Welding switches, connectors, when the excess solder flow easily on contact, can cause poor contact. Suitable welding dose should be wetted parts pine fragrance can only be formed solder will not flow away through the through-holes on the PCB. Using rosin core solder wire, basically do not need to apply a flux. Currently, PCB circuit board manufacturing plant in front of the factory are mostly conducted pine fragrance spray treatment, without further flux.
⑻ Do not use as a tool tip solder delivery
Some people used to be welded to the welding surface, resulting in oxidation of the solder. Because the soldering iron tip temperature is generally above 300 ℃, solder flux in easily decomposed at high temperatures fail, overheating the solder is also in a state of low quality. In particular it should be noted that, in some old books and also introduced the method of delivery of the solder with the tip, the reader noted that identification.
4 solder joint quality and inspection
Solder joint quality requirements should include good electrical contact, mechanical and aesthetic combined with a solid three. Solder joint quality assurance most important thing is that you must avoid Weld.
4.1 Weld reason and the harm arising
Weld is dominated by the metal surface to be welded oxides and dirt caused it to make contact resistance joints become connected, causing the circuit is not working properly, the connection is good and bad instability phenomena, without an increase in noise regularity, to commissioning, use and maintenance of circuits significant risks. In addition, there are over a long period beginning part of Weld points in the circuit to work, keep in touch is still good, it is not easy to find. However, under the effect of temperature, humidity and other environmental conditions of vibration, the contact surface is gradually oxidized in contact together slowly becomes incomplete. Weld point of contact resistance causes localized heating, the local temperature rise has prompted endless Keys further deterioration of joints, eventually even to spot off the circuit completely unable to work properly. This process can sometimes up to a year or two, the principle can be explained by the concept of "original battery": When joints so that water vapor into the gap after wet, the water molecules dissolve metal oxides and dirt to form the electrolyte, Weld Point Copper and tin-lead solder on both sides of the battery equivalent to the original two electrodes, tin solder loses electrons is oxidized copper gains electrons is reduced. In such a galvanic cell structure, point occurred in Weld metal loss corrosion, increased local temperature chemical reaction, mechanical vibration to let them continue to expand the gap until a vicious cycle to Weld breaking point eventually formed.
According to the statistics show that the failure of electronic machine products, nearly half are caused due to poor welding. However, there are tens of thousands from a spot where electronic equipment to identify what caused the failure Weld point, it is not easy. So, Weld circuit reliability is a major hazard and must be strictly avoided. When manual welding operations, in particular, should be noted.
In general, the main cause of Weld are: poor solder quality; poor or reducing the amount of flux is not enough; are not pre-clean the surface of the weld is good, tin is not strong; tip temperature is too high or too low, surface oxide layer; welding time control is not good, too long or too short; solder when soldering not yet solidified, welded components loose.
4.2 pairs of solder requirements
⑴ reliable electrical connection
Welding is achieved from the main electronic circuit means electrically connected physically. Solder connection does not depend on pressure, but firmly connected to the alloy layer formed by the welding process to achieve the purpose of the electrical connection. If the solder is just piled on the surface of the weldment or alloy layer formed only a small part, perhaps in the initial test and the work will not find a problem spot, but with the passage of time and changes in condition, the contact layer oxidation, from appeared, breaking through when the circuit generates or simply do not work, and then observe the solder appearance, still connected as ever. This is the electronic products work most troublesome issue, but also must attach great importance to product manufacturing problems.
Sufficient mechanical strength
Welded electrical connections not only play a role, but also the fixed components to ensure the means of mechanical connection. This problem has a mechanical strength. As a pewter solder material itself is relatively low intensity, often tin solder tensile strength of about 3 ~ 4.7kgf/cm, only 10% of the ordinary steel. To increase the strength, there should be sufficient connection area. If Weld point, just pile on the solder pads, naturally, can not talk about the intensity of it. In addition, after the insertion of the lead bending components, the implementation of the hooking, stranded around the web after welding, but also increase the mechanical strength and effective measures.
Common causes of lower intensity due to defects does not flow over the solder joints, or too little solder, solder may also be crystallized as the welding member yet solidified solder caused by vibration occurred coarse (like tofu-like) or cracks.
⑶ clean and neat appearance
Good solder joints requires just the right amount, rounded surface, a metallic luster. Appearance is a reflection of the quality of welding, attention: solder joint is welded metallic luster surface temperature suitable to generate signs alloy layer, this is not just aesthetic requirements.
Other than visual inspection of solder joints, in addition to visually (or with a magnifying glass, microscope) solder is in compliance with the above criteria, but also to check the quality of welding from the following aspects of the entire printed circuit board:
No weld;
No solder pull the tip;
No solder causing a short circuit between the conductors (the so-called "bridge");
Does not damage the wires and insulation components;
No solder splash.
Examination, in addition to visual but also with finger touch outside, tweezers toggle, cable and other ways to check for broken wires, pads peeling and other defects.
Formation of solder joints and the appearance of a typical 4.3
In the single-sided and double-sided (multilayer) printed circuit board solder joint formation is different: Figure 5.20 (a), the single-sided board, solder pads formed only above the weld surface; yet In the double-sided or multilayer, not only infiltrated the top of the molten solder pads, but also due to capillary action, penetrate into the metal of the hole, including the formation of regional spot above the hole and the component side metallization pad welding face pad portion A of FIG. 5.20 (b) in Fig.
Regardless of manual welding equipment welding or double-sided printed circuit boards, solder may flow through hole components metal surfaces: After manual welding when welding dual panel facing up, the infiltration of molten solder pads, solder due gravity flow along the metal component side of the hole; using soldering time, dual-panel welding face down, plug wire hole peak pressure and capillary action also cause the solder to flow spewing component side. After solidification of the solder, the solder pads on the component side of the hole, and help to improve the electrical connection and mechanical strength. Therefore, the design of the double-sided printed circuit board pad, the diameter can be smaller, thereby increasing the mounting density and wiring density dual panel. However, the component side of the solder does not flow too much, so as not to cause a short circuit in the component surface.
Solder joint formation
Typical solder joint appearance
See the chart, from the appearance of a typical solder intuitive look, its requirements are:
① approximately conical shape and the surface is slightly concave, showing diffuse sloping to the welding wire as the center of symmetry into a flared skirt. Weld points are often surface projecting outwardly, it can be identified.
② the solder, the solder connection is concave natural transition, smooth solder and solder junction member, the contact angle as small as possible.
③ smooth surface with a metallic luster.
④ no cracks, pinholes, slag.
4.4 powered inspection
After the appearance of the check is finished think the connection is correct before energizing check, which is the key test circuit performance. If you do not undergo a rigorous visual inspection, check the power not only more difficult, and may damage the equipment and instruments, resulting in accidents. For example Weld power cable, then you will find the device when power is not applied on the power, of course, can not be checked.
Power may reveal many tiny defects, for example, a bridge circuit is not observed visually, but the interior is not easy to perceive the hidden Weld. Therefore, the fundamental problem is to improve the skill level of the welding operation, the problem can not be left to the weld inspection process to complete.
Mainly due to the circuit board welding defects
1, can affect the weldability of the welding quality circuit board aperture
Circuit board hole good weldability, the defect will be generated Weld parameters affect the circuit element and the inner lead wire multilayer conductive components is unstable, causing the circuit function fail. Called solderable metal surface is wetted by molten solder in nature, i.e., where the metal surface to form a solder layer of a relatively uniform and smooth continuous film is attached. Effect of the printed circuit board solderability main factors: (a) component and the solder of the solder properties. Chemical solder soldering process is an important part of it by the chemical composition of the flux-containing material, commonly used for low-melting metal is eutectic Sn-Pb or Sn-Pb-Ag. Wherein the impurity content of the control to have a certain ratio of prevent oxide impurities generated by the flux dissolved. Flux through the heat transfer function, the solder wettability to help remove rust is soldered circuit board surface. Generally use white rosin and isopropanol solvent. (2) soldering temperature and the surface of the metal plate cleanliness also affect solderability. Temperature, the faster the diffusion of solder, having a high activity at this time, the circuit board and the solder will melt rapidly oxidized surface, welding defects, the circuit board surface contamination can affect weldability resulting defects that including tin beads, balls, open, good gloss and so on.
2, warpage resulting weld defects
Warp circuit boards and components in the welding process, due to the stress deformation of the Weld, short circuit defects. Warping is often due to the temperature of the upper and lower parts of the circuit board imbalance. For large PCB, since the plate is warped by its own weight will fall. Common PBGA device from the printed circuit board about 0.5mm, if the board as the device is large, with the normal shape of the cooling circuit boards, solder joints will be under stress for a long time, if the device is sufficient cause to raise 0.1mm Weld open.
3, the circuit board design affects the quality of welding
In the layout, the size of the circuit board is too large, although the welding easier to control, but the length of the printed lines, impedance increases, decrease noise immunity, increased costs; too small, the heat decreased, difficult to control welding, the adjacent lines prone interfere with each other, such as circuit boards electromagnetic interference and so on. Therefore, we must optimize the PCB board design: (1) shorten the connection between high-frequency components to reduce EMI interference. (2) The weight of a large (e.g., exceeding 20g) component should be fixed to the bracket, and welding. (3) heating elements heat issues should be considered to prevent a larger ΔT element surface defects and rework, thermal elements away from heat sources. (4) Arrangement components as parallel as possible, so not only beautiful but also easy to weld, should be for mass production. 4:3 rectangular circuit board design best. Conductor width not mutated to avoid discontinuities in the wiring. When the circuit board for a long time to heat, swelling and falling copper prone, therefore, should avoid the use of a large area of copper foil.
About PCBway
Since 2003 PCBWAY has been the leading PCB quick turn manufacturer specializing in both Prototype and Production quantities, Initially produced single-sided and double-sided printed circuit boards for the consumer electronics market. PCBWAY is ranked among the top 4 board fabricators in asia and is well-known for its expedited turn time capabilities and its reliable best on-time shipping record.
Today, we have over 450 operators with high modern facilities to manufacture multi-layer PCB up to 12 layers. Backing up with a group of professional engineers, and well established quality system. PCBWay has grown to become a major PCB manufacturer in Asia to serve in diverse customers base such as electronics appliance, communication, educational electronics, power supplies, Automationsetc.
Our mission is to become one of leading PCB manufacturer that provide in high quality product with total customer satisfaction.
