Hand soldering and rework is required excellent technique and a good tool operator process steps ; an inexperienced operator may have nightmares reliability . When equipped with adequate tools and training , the operator should be able to creation of a reliable solder joints. Sometimes more than hand soldering surface mount through-hole (through-hole) welding more challenging because of the smaller pitch and higher pin count . Rework process, must be careful not to overheat the printed circuit board ; otherwise plated through holes and pads are easily damaged. This article will review the contact welding and heating gas welding , the two most common manual welding. Contact with the contact welding is completed when welding in a heated iron mouth (tip) or ring (collar) in direct contact with the welding point . Iron ring mounted on the mouth or welding tools . A single nozzle for heating the welding point of the welding , the welding ring for simultaneously heating a plurality of welding points . Single nozzle welding tools and welding nozzles , a variety of design structure.
Soldering iron ring forms on the mouth also has a variety of design structure. There are two or four discrete rings , mainly for components removed. Ring is designed primarily for multi -pin components, such as integrated circuits ((IC); However , they can also be used to disassemble the rectangle and cylindrical elements iron rings have been used to remove adhesive junction components useful in the solder melts . after screwing the element iron ring can break glue connections. quadrilateral element , such as a plastic pin chip carrier (PLCC), a problem arises because the iron ring is difficult to simultaneously contact all the pins , if not in contact with all arguments iron ring feet, heat conduction does not occur , which means that some of the solder does not melt , especially in the J- leaded components , all pins may not be the same reference plane , which makes it impossible to simultaneously contact all the iron ring pin this situation could be disastrous , because there are welded to the pin pad when removing components from the operator to pull out of the PCB .
Welding tip and ring requires regular preventive maintenance. They need to be cleaned , sometimes on the tin . May require regular replacement , especially when using a small soldering iron tip . Contact with the contact welding systems welding systems can be classified as low price to high price , often limit or control the temperature. Selected depending on the application . For example , surface-mount applications are usually fewer calories than through-hole applications.
Constant temperature system to provide a continuous , constant output , continuously transferring heat . For surface mount applications , these systems should be run in the 335 ~ 365 ° C temperature range.
Limiting temperature of the system , the system has helped to keep the temperature at an optimum temperature limit the ability range . These systems do not continuously transmit heat, which prevents overheating, but heat recovery may be slow . This may cause the operator to set a higher temperature than desired , speed welding. Surface mount applications operating temperature range is 285 ~ 315 ° C.
Temperature control system to provide high output capability. These systems, such as the temperature of the restriction system , the heat is not transmitted continuously . Response timing and temperature control system to be superior than the limit temperature . Surface mount applications operating temperature range is 285 ~ 315 ° C. These systems also provide the ability to better deviation is usually 10 ° C. Contact welding system related features include: in most cases , the contact welding is welding (touch-up) and the component removal and replacement of the easiest and cheapest way . Can be easily removed with a welded ring attached with plastic components . Relatively low cost resistance welding equipment , readily available. Problems associated with the resistance welding system comprising: a nozzle without limitation iron or ring system is easy to temperature shock , the mouth or the iron ring raised above the desired temperature range. Iron must be in direct contact with weld ring and pin , reach efficiency. Temperature shock may damage the ceramic components, especially multilayer capacitors. Heated gas ( hot air ) Welding
Hot air welding nozzle by the heated air or an inert gas , such as nitrogen, and the pin point to the welding point is completed . Hot air heating equipment options include a single location from simple handheld units to complex automatic unit designed to heat multiple locations. Remove and replace the hand-held system of rectangular , cylindrical, and other small components. Remove the replacement of complex automated system components together , such as foot and dense area array components.
Hot air system to avoid the contact with the local thermal stresses welding system may occur, which makes it even heating is critical in applications of choice. Air temperature generally in the range 300 ~ 400 ° C. The time required to melt the solder depends on the amount of hot air . Larger components can be removed or replaced before , may require more than 60 seconds of heating .
Nozzle design is very important ; nozzle must be hot air soldering point to point , and sometimes to avoid the elements of the body . Nozzles may be complicated and expensive. Adequate preventive maintenance is necessary ; nozzle must be regularly cleaned and properly stored to prevent damage. Heat -related features include: hot air as a heat transfer medium low efficiency , reduce thermal shock due to the slow heating rate generated . It is an advantage of certain elements , such as ceramic capacitors. Use hot air as the heat transfer medium , eliminating the need direct contact with iron mouth . Temperature and heating rate can be controlled , repeatable and predictable . Heat -related problems include : hot air welding equipment prices range from high . Automatic systems are quite complex, requiring high-tech level of operation. Flux and solder fluxes can be used to drop the vial , you can use the seal or reusable full flux pen. Often, the operator using too much flux. I prefer to use a flux pen , because they limit the amount of flux used . I also prefer to use solder with flux core containing flux and solder alloys. When using liquid solder and flux-cored with flux , flux ensure compatibility .
Surface Mount Solder usually require smaller diameter solder wire , typically in the range of 0.50 ~ 0.75mm . Welding usually requires a large through-hole solder wire diameter , in the range of 1.20 ~ 1.50mm. Solder (solder paste) can be used to drop a syringe , although many manual welding paste is heated too fast , causing splashing of tin and solder ball . Flux gum instead of solder , arranged in the area for replacement element is useful .
