Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Reliability testing of lead-free solder joint

This result consists of a new reliability testing method for lead-free solder joints and a model for the reliable assembly of PWBs.

The reliability test can assess the reliability impacts of different solder/finish combinations and solder joint gap geometries. This is a clear progress compared to the bulk tests that have been widely used so far. The new test is an adaptation to the requirements of lead-free soldering with its variety of solder/finish combinations on one hand. On the other hand it allows reliability assessments of fine pitch solder joints and thus enters new dimensions for reliability testing following the permanent trend of miniaturization and ever smaller solder joints.

Additionally to testing, the proper assembly especially of complex and miniaturized PWBs requires a deeper knowledge on how to design and assemble such boards. A model was therefore developed and tested to achieve highly reliable PWBs in production and later use.

Reliability at 0 h (quality of solder joints and ppm level of failures after board assembly) was modelled. Modelling results show that simultaneous reduction of tomb-stoning and bridging, and an increase in self-alignment, are incompatible.

A theoretical model was also developed for each of the three phenomena. Therefore, intermediate settings are recommended, until the occurrence of a particular defect in the reflow process requires shifting the settings to correct for this phenomenon to optimize the ppm reject level. The combination of the model outcomes and the experimental results led to new insights for each phenomenon. The most important of these is that dynamic processes, such as the formation of an oxide layer on fillet surfaces, during reflow, play a major role.

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Reported by

Fraunhofer IZM
Gustav-Meyer-Allee 25
13355 Berlin
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