TODAY'S VAPOR PHASE SOLDERING: AN OPTIMIZED REFLOW TECHNOLOGY FOR LEAD FREE SOLDERING

摘要

In the beginning of SMT, Vapor Phase Soldering was the preferred reflow soldering technology because of its excellent heat transfer capabilities. There were also some disadvantages like fast temperature rise, nearly no influence on the temperature profiles and high costs. So the use of Vapor Phase Soldering was reduced to special applications with high mass or complex boards in low numbers (e.g. for military or aerospace use). Over the last years a new Vapor Phase procedure and new machines were developed. So Vapor Phase Soldering now offers new features for soldering, especially helpful when changing to lead free soldering. The main advantages of a state of the art vapor phase system are low process temperatures, freely adjustable temperature gradients and profiles, automatically controlled time above liquidus and a perfect automatic inert gas atmosphere. Soldering always means to heat up everything good enough that soldering can be accomplished even on sockets or large BGAs but at the same time to be sure that nothing is overheated or delaminated. So especially for lead free soldering the process window becomes pretty small. With Vapor Phase Soldering even FR4 boards, double sided densely packed, can be soldered reliable and with no danger of overheating since the maximum board temperature is physically limited to the vapor temperature (e.g. 230°C for lead-free SnAgCu). Because of its perfect inert gas atmosphere the wetting with lead free solder paste, is almost as good as with leaded solder alloys. Latest developments in vapor phase soldering technology provide a combination of Vapor Phase and vacuum soldering to get void free solder joints. This vacuum soldering technology becomes increasingly important since more and more power electronics need to be soldered on SMT boards. The advantages of the Vapor Phase heat transfer in combination with new machines and options offer an excellent tool for easy and defect free reflow soldering, independent whether lead free or leaded solders are used.