This is just an Excerpt from a larger document, click here to view the entire document.Conclusions and Ongoing Work
As the lead-free process development for these capacitor filter assemblies has progressed, the results of reliability testing (thermal shock test and burn-in test) for the baseline (Pb-bearing assemblies) are presented. Hypothesizing that the intermetallics formed in the SnPb solders are similar to the initial findings (Figure 3) there is a presence of more AuSn4 intermetallics in samples reflowed using the large profile as compared with samples using the medium profile. By reducing the time at reflow temperature, medium vs. large profile, solder reflow appears to reduce the intermetallics, improves the number of solder grains, and reduces the size and magnitude of gas bubbles formed from the trapped organics. The excessive number of AuSn4 intermetallics would likely make the solder brittle and, hence, lead to failure of these samples during the reliability analysis. As a result, our ongoing efforts are focusing on reducing the TAL for all capacitor sizes. The intermetallic study of the Pb-free samples displayed some promising features mainly the effect of low Cu concentration on the Ni finish pins.
As a side-note, a production-based objective is also met wherein, with the different-sized assemblies, the same reflow profile can be achieved by only changing belt speed (and not temperature settings). Thus far, we have begun to establish reliability data for lead-free assembly and have made initial investigations into intermetallic determinations of species. Thermal cycling for our lead-free samples is underway.