New application fields and recent innovations in the manufacture of electronic assemblies have increased thermal and mechanical requirements on solder joints. The reasons are the continual broadening of areas of application, the integration of different functions on an electronic board and the combination of electronical and mechanical systems on a minimum possible space. This leads to increasing thermal and mechanical stresses on solder joints. One example for higher temperature requirements are automotive applications. Particularly in the region of the motor the average working temperature reaches 140 deg C. Therefore tin-lead-solders with a melting point of 183 deg are no longer suitable for these applications. Other solder alloys are necessary which are reliable at higher temperatures and which can be manufactured using standard soldering processes, standard substrates and conventional electronical parts. Furthermore, lead-free solders are gaining in importance as the WEEE directive is expected to go into effect on 01.01.2004. This directive contains a strict program concerning the elimination of toxic substances including in electronic equipment. The lead-free solder alloys Sn95.5Ag3.8Cu0.7 and Sn96.2Ag2.5Cu0.8Sb0.5 were chosen for this investigations. The reason for this alloy selection was the good availability on the market in form of pastes and bars. In addition, previous investigations on lead-free solders favoured the SnAgCu-solder-alloy. lt may be concluded from both these and earlier results that the solder materials Sn95.5Ag3.8Cu0.7 and Sn96.2Ag2.5Cu0.8Sb0.5 can be processed using slightly modified reflow and wave soldering processes. Of course, the reliability achieved for chip solder joints using Sn95.5Ag3.8Cu0.7 under temperature shock stress are somewhat below the expected figures. The causes for this fact may be the new polyimide material and the increased temperature gradient. All of the solder joints investigated on the other components show evidence of external damage, but are not completely broken. At present, testing the printed circuit boards in combined thermal cycling- / vibration test is being carried out.
Behaviour of lead-free solder joints under thermal and mechanical stresses
Die Eigenschaften von bleifreien Lötverbindungen unter thermischen und mechanischen Belastungen
2000
9 Seiten, 10 Bilder, 3 Tabellen, 3 Quellen
Conference paper
English
Effects of Thermal and Vibrational Cycles on Stresses in Lead-Free Solder Joints AIAA Paper
British Library Conference Proceedings | 2007
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