Question posed by the Moderator to all three presenters:
We have covered a lot of ground today, ranging from metallurgical advancements in laboratory studies to the design and performance of tomorrow’s electronic packaging. I would like to ask each of you to comment on the critical gap areas and needs for lead-free solder technologies for which the materials community should pay special attention.
The responses were:
Handwerker: From the point of view of tin-whisker growth, I think there’s a lot of fundamental science that really needs to be done. A very careful fundamental science that would help link the observations of whether whiskers grow or not to the risks associated with using those particular processes or techniques in actual systems. There’s a huge gap there. The other gap is that with respect to the behavior of materials in the field—and this is going back to what Dave Hillman and Dongkai Shangguan said—is that we have a lot of test results, but we really don’t know how good is “good enough” for lead-free in all the different use conditions that are out there. And that’s particularly important when we start to trade off things like accelerated thermocycling performance with drop and shock. And so until we really have a better idea of what actual performance we need from lead-free in use applications, there’s more risk there than needs to be. It could be that all the lead-free solders we’ve looked at so far are perfectly fine in a wide range of applications, but we just don’t know it yet because of the acceleration factor issue that Dongkai has talked about.
Hillman: I think I’d echo Carol’s words. If you look at just solder alloy selection itself, we’ve got a baseline, we’re seeing the small additions and refinements. Yet as a process engineer, I’m trying to tie down and wrap a process so it’s repeatable, consistent. And if you look at the things that Carol and Dongkai talked about today, we need some stability even though it’s inherent in our nature to keep trying to optimize and find the best thing out there. And so I think from my viewpoint I’d like to see us hold the line for a little while and understand what we’ve got.
Shangguan: I agree with everything that David and Carol just mentioned. One of the areas that I would like to highlight is the study of solder, not just solder product reliability and the complex loading conditions. Because in actual applications, the loading condition is not just thermocycle or bending or tensile or corrosion, it’s all of these conditions simultaneously imposed.
These conditions and the failure mechanism often interact with each other; they may accelerate each other. Therefore, our understanding of the solder behavior, reliability behavior, fatigue behavior, creep behavior, and electrochemical behavior under these complex loading conditions that are simultaneously imposed would be very, very critical to the reliability of the product in actual applications. That is an area I would like to see more research on from the industry as well as the academic.
