See, it just starts ( I like arguing with Werner ). I made some investigation on leadless components after 8000 cycles -20 / 100deg.C; 2degr./min; dwell time30 min. where we polished the solder so that we where able to see the grains. What we saw was the breakdown of the coarse solder structure after soldering into smaller grains. This refinement occurred between pad and component as well as along the caps in the meniscus. In my understanding the first due to the CTE mismatch of component and board the latter due to the local mismatch of component and solder. We observed the refinement in the meniscus also in kind of a slip band. It had the shape of a wedge with the tip heading to the PCB. The cracks we saw where always growing within that zone. The slip bands that are approx. 15um thick occurred in shear test specimen with a solder layer that was 50um thick. On some occasions I was able to see a similar effect in SMT solder joints when they where around 50um thick. The refined bands measured between 10 and 20 plus something um. Due to these findings I believe that the enhancing of the solder thickness for better reliability has a limit of roughly 30um. Thicker joints will not contribute to the joint reliability. Well, that's what I think but I would never dare to contradict Werner in public (HeHe). Regarding ETH Werner, I must say that every student does some reliability investigations on an appropriate level. No research is done in that field in ETH. We transferred it all to EMPA and also the lecture at ETH is held by us. Well, anyway EMPA is part of ETH. My job at EMPA is not very different from before exempt one thing. We are now allowed to perform failure analysis for money and we drown in work. Luckily I still have research projects ( reliability of lead less solder, Reuse Repair Recycling of electronic waste ) which enable me to escape the everyday hassle and to do work which is intellectually satisfying and gives room for scientific thoughts. All in all I like my job. Best regards Guenter ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################