Soft brazing is widely used in electronic packaging, solder has become the interconnection material of all three levels of connection, in addition, tin lead material as a surface coating is also widely used in components and PCB surface coating.Electronic packaging technology can be divided into through-hole assembly technology and surface assembly technology.Through hole assembly technology is characterized by perforated insert printed circuit board assembly, which adopts the traditional wave-soldering technology. Surface assembly technology mainly applies the principles of science and co-formation to place components and components on the surface of printed circuit board for board assembly, instead of inserting them into the circuit board.Compared with through-hole instrumentation, surface mount technology increased circuit density, reduced size components, circuit boards, reduce the device quality, shorten the wire interconnection, along with the development of the electronics manufacturing, and surface mount technology has been gradually replaced the hole instrumentation technology, according to authoritative organization predicts that by 2012 the global use of instrumentation components, will fall to 10%, the surface of the assembled elements of utilization rate will rise to 90%.At the same time, this also brings solder joints, PCB boards, components and other aspects of reliability problems.
Soft brazing according to the classification of process methods, there are lead-free hand orno soldering, lead-free dip welding, lead-free wave soldering and lead-free reflow welding.In terms of energy supply;There are vapor condensation, hot gas, convection, induction, laser, focused infrared, white beam, vertical reflow and other ways.The reaction process of soft brazing is generally;The substrate and solder paste are preheated first, then the volatile substance evaporates, the brazing agent generates permeation activation, the substrate is cleaned and the solder is infiltrated through chemical pyrolysis, then the solder melts and infiltrates into the substrate, the brazing agent carrier protects the substrate during soft brazing, and the brazing agent carrier escapes from the molten solder, the chemical pyrolysis is over, and the solder solidifies.
Infrared emission and convection reflow are the main methods in electron assembly soft brazing.Key process parameters affecting product yield and solder joint integrity are as follows.Preheating temperature, preheating time, peak temperature, duration at peak temperature, cooling rate;The flow curve based on slower heating rate and lower temperature will be more suitable for today's complex assembly, which can reduce the exposure time of peak temperature zone and reduce residual stress. However, the process curve designed for multiple reflux in soft brazing needs to be further designed and improved.