Guy, my book is: for proper wetting and reliable solder joints, the uniform IMC (continues layer) must be present at the solder/pad and solder/part interconnect interface. depend upon the plating quality and aging of the surface finishing, the wetting might be different using same reflow profile. Not sure what the author intended to address (may be photo would tell you the story). to me, the continues layer is key... the thickness is 2ndary... (some times, the poor solder mask will wet to the pad causes some sections = edge has thin or almost nothing IMC, that would be a problem as stress concentration point causes reliability failure - have seen that before...similarly, old board with patch oxide causes poor wetting of solder, non-uniform formation of IMC, also a reliability risk... cross section few rows of SJ might needed if you suspect problematic combination of board/part/solder paste... etc.etc.). IMHO. jk On Sep 5, 2018, at 12:58 PM, Guy Ramsey wrote: > Recently, I was reviewing a lab report. It concluded that the > manufacturer > should increase the IMC thickness as a part of process changes . . . > It stated that, while there are no industry specifications for IMC > thickness it s generally accepted that for Pb-free assemblies the IMC > thickness should be in the 20 to 120 uin range. It seems to be > critical of > a process that produces IMC between 10 and 70 uin on pads across a > single > device. > Does anybody have reference papers or texts that would support this > target > and process critique?