Paul,
What you are saying sounds "strange", as more details would require. You can contact me off line if you wish, as I'm in GTA area.
Regarding your questions, then;
1. If all Sn is consumed to form intermetallics, then you end up with only Pb in the former solder.
2. Intermetallics formation occurs only at the interface, BUT once Sn at the interface is consumed, the one from the rest of solder "rush-in"
3. It's a problem if instead of ductile Cu you have a brittle material as a wall of a PTH.
Regards,
Vladimir
SENTEC
------Original Message------
From: Paul Reid
Sender: TechNet
To: [log in to unmask]
ReplyTo: TechNet E-Mail Forum
ReplyTo: Paul Reid
Sent: Jun 16, 2009 11:09
Subject: [TN] Copper Dissolution Questions continued
To continue my quest to understand copper dissolution.
I have a coupon where the copper in the PTH is dissolved by the solder
during thermal excursions. I notice a metallic interface against the
copper. I assume the interface is a tin copper concentration but then
again I don't know. Understand that this is thermal excursions on a
coupon without any solder paste, component etc. The solder volume
consists of the solder associated with a surface finish. In other words
a low fixed solder volume.
1. Can copper dissolution change the tin/lead ratio of the solder that
is above the intermetallic?
2. Is copper dissolved throughout the solder or only at the
intermetallic layer?
3. Would this be a significant concern for assembly?
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
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