In April last year I met in Munich (Muenchen) with a senior engineer from a major automotive components supplier, who told me flat out that "there [were] no polymer-based solutions for under-the-hood electronics" die-attach, due to the severe thermal-cycling and vibration/shock conditions experienced. Absent any recent advances in metal-filled polymer technology, the use of solder seems to be the only way forward here.
Indium Corporation is working with several different customers on different approaches to the problem of Pb-free Power die-attach, and there are two schools of thought:
1/ Solidus must be above 260degC: which limits us to the few options available. These options are either expensive, low conductivity, poor wetting, high tensile strength, low malleability, highly reactive, or any combination of these.
2/ Liquidus must be well above 260degC and solidus must be "fairly high" (>215degC ballpark)
We naturally can't say anything detailed about the approaches we are taking here, but the fact that customers are considering the use of materials that are partially liquid at temperatures lower than the MSL1 pretreatment requirement of 260degC, is an interesting paradigm-shift.
Indium Corporation's R&D group, under the guidance of Dr Ning-Cheng Lee, is also currently working on other high-melting alloys and some novel processes. We anticipate more news by Q3/Q4 this year.