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.
Generally translated into circuit board components, simply is to install the components of the circuit board. It is made up of PCB, components and electronic accessories, and other components are formed by must combine two.
Pcb assembly
A, in order to better complete SMT processing, want to do the communication:
1, the size of the PCB: 50 x 50-508 x 440, such as plate is small, suggest to do makeup.
2, the plate thickness: 0.5 3.2 mm. So the flexible plate, need the tray, the best is around 1.6 mm.
3, recently components from the edge of 5 mm.
4, should have more than two best PCB MARK points. Precision components diagonal also had better have a MARK, MARK cannot be oxidation, etc.
5, board face top components 15 mm.
6, the heaviest PCB board for 4 kg.
7, the repeat precision 3 sigma. 15 um.
8, the actual patch speed per hour 15000 chip components.
9, SMD components in the range of: 0201-56 x x 15 mm to 56. 80 g in weight.
10, can post the components as: 0201, SOIC, PLCC, QFP, TSOP, QFN, the LGA, BGA, flip chip, high-density connector, heterosexual, CSP, CCGA.
11 and precision components of post pack as follows: IC minimum distance of 0.2 mm; Minimum pin width 0.1 MM BGA minimum distance of 0.2 MM; Minimum ball diameter 0.1 MM
B, in order to better provide welding quality, we suggest to do the following:
1, because of your components on the PCB near edge (less than 5 mm), suggest to do so the edge. The width of the edge for 5-10 mm.
2, if the plate is small (less than 80 x 80 mm), suggest make a puzzle, the number of puzzles (according to the size of the plate and plate thickness.
3, in order to provide the precision of welding, it is recommended that each small diagonal all make a mark points on the board. General is straight for the 1 mm - 2 mm circle.
4, if there is a high precision SMT components, it is recommended that the diagonal do two components in the high precision of the mark. The diameter of 1 mm.
5, is a still a whole roll of material provided, we can do, a minimum of 30 cm length, but the longer we do better.
6, special requirements to communicate well, such as material for lead-free, element and heat-resistant, materials, oxide materials and PCB for baking.
7, you do the installation position of welding is components and polarity have special requirements, such as designing PCB solder, 0402 two welding disc distance of 0.4 or 0.5 mm, outside from 1.6 mm; 0603 two welding inside the distance between 0.6 0.7 mm, outside the span 2.5 mm; 0805 welding disc spacing is 0.8-0.9 mm; Outside the span 3.2 mm; 1206 for the welding of the disk spacing: 1.6 mm, outside the spacing of 4.6 mm; Welding plate or BGA welding plate to go on line, which is the best the welding plate hole is blind hole or holes in the green oil.
8, BGA, QFN and other precision components, generally 24 hours to 120 degrees bake, resistance capacity materials than the materials more than 30, convenient patch on machine, otherwise only hand swing or manual welding.
SMT and PCB assembly
The surface coating
Selective surface coating equipment manufacturers from mass production to the online high yields the production level provides a great advantage. Flexible and integration of the coating and curing function of the system to provide the accurate surface coating, at the same time has a good ability of process control and traceability, configuration of various patented dispensing head, thus saving cost, increasing production and productivity.
On the coating the surface of the problem, manufacturers always face the balance production of printed circuit boards, the challenge of material and labor force investment, but also must consider process involved in the regulations and environmental problems. Traditional method of surface coating, such as impregnated and pressure spray gun, usually require expensive materials and artificial cost. Does not contain solvent surface coating material make cost becomes higher.
SMT adhesives
Jet surface-mount adhesive than traditional techniques such as needle type dispensing and silk screen printing, provides a more technical advantages. Many PCB design requirements than the traditional time/pressure has a higher point glue dispensing system speed and accuracy, also calls for more flexible than screen printing.
Some printed circuit board design requirements is quicker than the traditional time/pressure dispensing system of dispensing speed and higher precision of dispensing, also calls for more flexible than silk screen printing technology. Non-contact jetting dispensing technology to eliminate some glue Z axis movement, in the process of height detection device and a needle problem, so as to realize the precise dispensing. In the field of SMT production, injection dispensing valve provides the following advantages:
Incomparable production, dispensing per hour up to 55000 points
Drip/residue
Bending have higher tolerance to the board
Components around spraying has more flexibility
Solder paste dispensing technology
Discrete device for quick accurate solder paste deposition. As you evolve of packaging design, the type and amount of discrete device will change.
Lower the height of the contact force detector provides accurate and consistent dispensing height control, to ensure that the excellent adhesive repeat precision.
The solder paste dispensing technology is suitable for multiple production scene: Sag area of PCB solder paste deposition
Additional solder paste dot coating after printing, common rf shielding and the need of different sizes sedimentary plank
BGA and QFN device maintenance
Half a circuit board assembly solder paste deposition
Before printing halftone design research and development testing
High mixing degree, low yield of production environment, do not need to screen printing
In order to ensure a successful solder paste dispensing process, please note the following items:
Solder paste ideal metal filling ratio: metal weight ratio of 84-86%
Glue point number less than 300 microns usually need to paste shape is 5 or 6 and specifications for the needles of 28 to 30.
It is very important to control point glue clearance. If the PCB bending deformation, will require additional process control, such as increasing height detectors.
Czech state system provided solder paste can be more rubber is widely used in various kinds of operation work including production, laboratory and research and development, and may include a variety of surface concave area.
The system can be adopted according to the specific application of solder paste DV - 7000 screw valve valve or piezoelectric driving SV - 100.
Also can choose to select the most able to meet the needs of your production platform - from batch type (such as SpectrumTM S - 820) to the linear system (SpectrumTM S - 910 n)
At the bottom of the CSP or BGA
Non-contact injection dispensing technology is in the circuit board to the chip level (CSP), BGA, and cascade packaging (PoP) to the bottom of the best way to fill.
When using the bottom after filling for solder joint seal, when CSP components used in portable electronic devices has better reliability.
Mass production of electronic components need high speed and precision of dispensing. In many of the CSP application, how to spray the precise amount to provide protection, at the same time, do not waste expensive sealing material, is critical. Dispensing need material can automatically compensate for lifetime colloid viscosity changes.
Selective flux injection
With the flip chip and chip scale packaging (CSP) technology is gradually applied to such as high capacity production line, continuous output and stable quality is the key factor of success. Through precise control of very thin design application flux effectively, is the key to maximum capacity and quality.
Using selective production of flux injection can be increased by 30%, at the bottom of the filling can be optimized at the same time, the reliability of increase production capacity and equipment utilization.
Conductive adhesive
Heat conduction and conductive epoxy resin colloid chips are used to bond on the substrate, so as to ensure the safety of electrical grounding and heat dissipation of the chip. The glue material usually canned life is very short, sensitive to temperature. The filler in the rubber material is apt to jam.
Conductive adhesive can point or thin line of glue, change for hybrid element, solder paste, RFID equipment, such as assembly, or MEM form electrical connection. Conductive adhesive are usually used in hard disk drive components, hearing elements and other electronic components used in medical equipment.
Resistance welding membrane dispensing
Resistance welding membrane dispensing technology is high mixing degree, low yield production environment cost effect options. When the circuit board has been part of the assembly components and silk screen printing is no longer available, usually use online resistance welding film adhesive technology. At the same time, the membrane resistance welding dispensing provided under the condition of high conventional low yields a high cost effect of alternatives, this assembly are developed for each screen printing fixture may be unable to bear the cost.
Edge bonding
Edge bonding is filling at the bottom of the alternative, for BGA and similar chip scale packaging (CSPs) increased mechanical strength and reliability.
Similar game systems, laptops, netbooks and other consumer products often require active components on the PCB for the four corners and edges of adhesive bonding point. These products in the process of transportation or operation, easily affected by vibration or impact mechanical orce. Through to the BGA corners or edges for dispensing operation, interconnection between devices and PCB pressure is minimized.
Regardless of the colloid spraying is between the component placement Angle of "bonding", or after the "edge bonding", automatic dispensing system can be in the fastest speed to ensure accurate deposition.
Cascading packaging (PoP)
PoP device at the bottom of the filling material injection can achieve high capacity per hour and infiltration area is lesser, but also achieve the synchronization at the bottom of the packaging at the top and bottom fill.
3 d packaging and assembly to promote the use of the surface area and volume within the product. As more and more functions are added, the surface of the PCB assembly density is higher and higher, so that the passive and active components are not assembled in the same surface.
Through packages storage stack above the logic encapsulated, known as the "laminated packaging", the area of the PCB can be greatly narrowed, to produce smaller products. Jet technology can realize synchronous filling at the bottom of the packaging at the top and bottom, to protect components from the impact and vibration damage.
Embedded components
3 d packaging and assembly to promote the use of the surface area and volume within the product. As more and more functions are added, the surface of the PCB assembly density is higher and higher, so that the passive and active components are not assembled in the same surface.Through embedding passive components and active components under the surface of the PCB, without increasing the size of the PCB can gain more features.
Embedded assembly dispensing solution:
In hollow cavity between the chip and injection of hole wall at the bottom of the filling material Cavity of unable to print solder paste dot coating.
The cavity spray adhesive, in order to minimize the movement of the passive components
Non-current fill at the bottom of the board level
Non-current filling glue in traditional needles at the bottom of the glue dispensing technology for operation, also can through our award-winning
DispenseJet injection valve, coaxial with patented air pressure assist device.
Illiquid filling can be used to improve the flip chip and at the bottom of the CSP (chip scale packaging) of the reliability of the printed circuit board.
The use of illiquid fill at the bottom of the circuit board design more flexible, because to fill at the bottom of the components and the interval of the adjacent components required for small.
Application of filling at the bottom of illiquid, spray head located above device is a very short distance (usually 1 mm), spray out of the colloid.
According to the requirement of the production of precision and speed, but the injection points or lines.
PCB assembly testing techniques
Detection of assembled printed circuit board could end up or done by automation system by using the method of to move, and often use two ways. "Manual" means an operator using the optical instruments through visual inspection board, and make a correct judgment about the defect.
Automation system is the use of computer aided graphic analysis to determine the defects, many people also think automation system includes all except the light of the manual testing of test methods.
X-ray technology provides an assessment of the thickness of the solder, distribution, internal hole, crack, take off the welding and welding method to test the existence of the ball (Markstein, 1993). Ultrasonics will detect holes, cracks and did not post the interface. Automatic optical inspection assessment external features, such as bridge, tin melting volume and shape. Laser detection can provide the external characteristics of three-dimensional images. Infrared detection by comparing and a known good welding point weld thermal signal, to detect the internal welding point of failure.
It is worth noting that have already found the automatic detection technology for detecting assembly of printed circuit board co., LTD. Can't find all the defects. Manual visual inspection method, therefore, be sure to use, and the method of automatically detecting the joint especially for those small amounts of applications. X-ray inspection and manual optical combination is the optimal way to detect the plate assembly defects.
Assembling and welding of printed circuit board is easy to exist the following defects:
1) lack of components;
2) component failure;
3) components exist installation error, misalignment;
4) invalidation;
5) poor wetting;
6) bridge;
7) insufficient solder;
8) too much solder form tin ball;
9) formation of weld pinhole (bubble);
10) pollutants;
11) are not appropriate welding plate.
12) polarity error;
13) pins float;
14) pin out too long;
15) in cold welding contact;
16) solder too much;
17) solder hole;
18) open holes;
19) printing lines within the circle of the fillet structure is poor.
The repair of lead-free solder in the PCB assembly
Due to insufficient suction, wettability and core as it is difficult to realize lead-free welding rework is to implement various components of lead-free soldering is impossible? This paper introduces a kind of the method can easily implement lead-free solder repair.
Rework is in the process of mass production of lead-free PCB assembly is an important part of the initial period of transition, when the information curve of each link in the supply chain, in particular. However, due to the need to guarantee, so in the entire product life cycle is still within the scope of the rework.
People found, lead-free solder alloys usually don't like Sn/Pb solder wetting and core, as a result, the lead-free solder rework is difficult, its application in the QFP is an obvious example. Despite these differences, through the use of the flux gel, pen type suction solder flux and core is used for discrete component, such as surface grid array of different components such as lead-free solder (Sn/Ag/Cu/Sn/Ag) developed successful rework method (i.e., manual and semi-automatic). For most of the Sn/Pb rework equipment can still be used in lead-free solder. The welding parameters must be regulated so that suitable for lead-free solder higher melting temperature and lower the wettability. Sn/Pb rework and other prevention method adopted in the board (such as a necessary drying) is still applicable to lead-free solder rework. Studies have shown that using the appropriate rework process can make appropriate particle structure and formation of the intermetallic compound of reliable lead-free solder joints.
Special attention should be paid to reduce the rework process of solder joints, the possibility of components and PCB have a negative impact.
Due to welding temperature rise, laminated material, glass fiber between Cu and Z axis, coefficient of thermal expansion (CTE) mismatch, to put more stress on the Cu layer, will likely plating in the hole Cu cracking, leading to failure. This is a fairly complex problems, because it is decided by many variables, such as PCB layers and thickness, laminated materials, rework temperature curve, Cu layout and the guide hole geometry (such as aperture ratio). To determine what kind of conditions in the lower pressure material (such as high Tg and low CTE) to replace traditional FR4, meet the requirements of lead-free welding, have a lot of work to do. This is not to say that the low cost of materials (such as CEM, FR2, etc.) can not be used in lead-free soldering. In fact, have been applied in the mass production of these methods, and on the basis of each application situation of the application examination. Must to rework pads and mask the effect of viscous carefully assessed.
Similarly, also cope with the effects of the rework on the element reliability for serious study. Warp and layer is off some of the problems that may occur. The recently released the IPC - 020 - b standard points out that it should be rework for high temperature components in lead-free soldering the focus of the rating into consideration.
The reliability of electrochemical is another important issue should be considered. When the moisture condensation on the flux residue dissolved in the board, under the electric bias of conductor can produce electrochemical reaction between traces, which led to the decrease of the surface insulation resistance (SIR). If produce electromigration and dendritic growth, due to "short circuit", formed between conductor tracks will generate more serious fault. The reliability of the electrochemical by no clean application of flux residues to resist electromigration and dendritic growth performance to decide. , therefore, must implement the IPC (according to the TM - 650 2.6.3.3) on the basis of SIR or Telecordia testing, in order to ensure the rework using flux and flow flux/peak flux and the flux of rework any of the reactant will not bring electricity to no clean application migration and the risk of dendritic growth.
"Element mix" problem is involved to ensure the quality of the special problems, especially during the period of transition of this technique.
Through lead to long-term reliability of lead-free solder the preliminary study shows that the influence of different due to the content of lead in solder joints, so influence is also different, when the content of lead in the middle range of values of the impact of its is one of the biggest, because in the last solidification between the tendrils of the formation of tin in the grain boundary segregation phase (for example, rough lead particles), in this position began to crack, and spread under cyclic load. For example; It shows 2 ~ 5% lead content will give the fatigue life of lead-free solder brings adverse effect, but it may not be worse than the effect of Sn/Pb solders. Therefore, if the use of lead-free solder repair lead of the board, from the Angle of the solder, the lead-free solder and Sn/Pb solder together may not affect the reliability of Sn/Pb solders.
However, the influence of temperature on the components (especially the laminate components) is a concern. On the other hand, using Sn/Pb solder lead-free solder board repair the reliability of solder joints may be inferior to other board as well as the reliability of lead-free solder joints.
In terms of supply system, during the transition period, should be used for welding of lead-free soldering irons and welding material (core solder and flux gel, etc.) to do the clear mark is key.
And repair must lead time cost and the increase of the economic costs, repair just mend measures, the key lies in strengthening the operator technology training, try to be less rework.
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.
For more information about PCB, or to learn more about the online quote and ordering process, please visit //www.PCBway.com.
