Case Studies in Quality and Reliability Analysis of Fine Pitch Solder Joints

Rapid feedback on the effect of changes in materials or assembly process parameters on solder joint quality is essential in process optimisation for fine pitch surface mount solder assembly. This is particularly the case where the demands of high volume production do not allow lengthy experimentation to be carried out on the production line. The greater precision and care required in analysis of fine pitch solder joints places a further constraint on the speed at which the analysis can be carried out. The techniques of microstructural analysis, solder joint mechanical strength testing and short duration environmental stress testing must be used to meet a rapid turnaround quality and reliability analysis requirement and to maximise the amount of information obtained from each stage of the analysis. Three case studies are detailed which demonstrate the use of these techniques in a high volume production context to provide rapid feedback on joint quality. The case studies have been selected for presentation not only to demonstrate the analysis techniques but also because they address issues which are of current interest due to the increased usage of fine pitch packages in production and the constraints on the use of solvents for cleaning of circuit boards. The studies are: A: A comparison between the use of standard and stagger printing techniques for solder paste B: A comparison between the use of standard and no-clean solder pastes C: Analysis of solder joint failures seen on topside fine pitch components after wave soldering In addition, results are presented on the effect of prolonged temperature cycling on the boards from Case Study A which show that the solder joints, although visually very much deteriorated, maintained mechanical strength after the temperature cycling.