I've seen this kind of etching (usually called erosion) when I have a big
through-hole part and try to rework it with a Pb-free solder fountain. If
you don't do it VERY quickly, the corner between the via barrels and the
pads can get completely removed. I haven't done solder float at the
temperature you're talking about. Presumably the fact that you're not
agitating the situation (such as the solder fountain does) should lead to
far less erosion.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, August 19, 2014 11:40 AM
To: [log in to unmask]
Subject: Re: [TN] Query on Copper dissolution

20-25 micron are excessive.. normally, you form intermetallic layers, you
stop the dissolution somewhat, unless, the plating quality is poor (porous
or high current density).  my guess.
 jk
> My apologies for answering your question with a question, but how do 
> you know the reduction is 20-25 microns?  I presume a measurement 
> before the floats is not possible.  I'm interested to see what the 
> experts have to say. Louis Hart
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Nagaraj U
> Sent: Tuesday, August 19, 2014 1:59 AM
> To: [log in to unmask]
> Subject: [TN] Query on Copper dissolution
>
> Hi All,
>
> We have a few customers asking for 6x solder float at 288°C, 10 
> seconds (IPC-TM-650, 2.6.8, Condition A). After completion of 6x 
> solder float (using SnPb 63/37 solder) we typically see reduction of 
> Copper in PTH (due to copper dissolution) in the range of 20 to 25µm. 
> The reduction in Cu thickness is maximum at the PTH knee area.
>
> Can I have some inputs if this level of copper dissolution is normal?
> If it is not normal, how do we reduce this?
>
> Thanks in advance!
>
> Best Regards,
> U.Nagaraj
> MICROPACK, India.
> [Logo]<http://www.micro-pack.com>
>
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