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September 2018

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Subject:
From:
Yuan-chia Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Yuan-chia Joyce Koo <[log in to unmask]>
Date:
Wed, 5 Sep 2018 15:01:59 -0400
Content-Type:
text/plain
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text/plain (32 lines)
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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