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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?
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