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April 2007

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Subject:
From:
Liang Yin <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Liang Yin <[log in to unmask]>
Date:
Tue, 1 May 2007 01:32:04 +0000
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Scott,

One drawback of Cu DIG could be the degradation of solderability over time. 
The interdiffusion of Cu and Au might lead to exposed Cu patches on the pad 
surface, especially the Au thickness is thin. High temperatures will speed 
up the diffusion substantially. For example, some bake processes before the 
soldering. Exposed Cu will be oxidized if no additional oxidation 
protection, and the pads become less wettable if the flux selection is not 
aggressive. Thick Au thickness helps to delay the time for Cu to reach the 
surface, but sometimes excess Au might lead to solder joint embrittlement.

Liang

Liang Yin

Process Research Engineer
Advanced Process Lab
Unovis Solutions
Binghamton, NY





>From: Scott Lefebvre <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Scott 
>Lefebvre <[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] ENIG vs. IG over Copper DIG.
>Date: Mon, 30 Apr 2007 17:50:33 -0700
>
>Currently I have been using ENIG as my primary lead free solder finish
>but I've been reading about Direct Immersion Gold "DIG".  Direct
>immersion gold is deposited directly on the copper surface to a
>thickness of 1-2 uins.  I want to know if anyone in Technet has any
>experience with this finish.
>
>
>
>I use both water soluble solder and no clean solder flux in our current
>process.  The lead free solder is SAC305 for both SMT and through-hole.
>
>
>
>One of the drawbacks I could think of is copper dissolution when
>soldering the boards with SAC305 solder.  I have not had any issues
>using our existing ENIG solder finish but one of our new PCB shops have
>asked if we could switch.
>
>
>
>Scott Lefebvre
>
>
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