On Thu, May 19, 2011 at 12:09 PM, wrote: > > The parts I'm talking about here are the "SEM" series connectors from > Samtec. The pins coming out the > bottom of the connector are a rectangular post shape. I see no sort of > strain relief of the pin iself. > I noticed that the pins are gold plated. When you solder a joint that has gold in it, you can get what's called "gold embrittlement". Basically, the gold dissolves in the solder, migrates through it and becomes part of the joint structure. This causes the solder to be weaker mechanically than normally so the solder joint becomes brittle. Higher temperatures accelerate the embrittlement process as is true for many reactions. The brittleness depends on the resulting concentration of gold in the joint. I think the small surface area of a SMT pad also means that you'll have a higher gold/solder concentration than a through hole joint and this may mak= e matters worse. Joints with AU embrittlement that are subjected to stress, e.g. connectors, are more likely to fail than unstressed joints. For space work, we always wicked off the gold, per a NASA spec, using solder before soldering a pin. I think the small surface area of a SMT pad also means that you'll have a higher gold/solder ratio than a through hole joint and this may make matters worse. Here's some reading material on the subject: http://www.semlab.com/goldembrittlementofsolderjoints.pdf http://www.eng-tips.com/viewthread.cfm?qid=3D7370&page=3D70 http://hdl.handle.net/2060/19720017872 http://nepp.nasa.gov/files/15502/06_295_Plante_Report_AFL2828_SolderJoints%= 20Evaluation_121206.doc Hope this helps. Carey Fisher --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .