Well, it's not exactly like that. Yes, with Pb-free solders it's possible to see a thicker layer of intermetallic (and most probably not because of the higher content of Sn, but the temperature), HOWEVER, it will be in the same range of 3-7 (roughly) microns, as with PB/Sn ones. Otherwise, the joints won't be reliable (too thick intermetallics). Considering that Cu layer half an ounce (at least< or 15 microns), I wouldn't say that Pb-solders can eat it up.
Regards,
Vladimir
Vladimir Igoshev, Ph. D.
Manager, Metallurgical Lab
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of stephen gregory
Sent: Monday, March 27, 2006 12:09 PM
To: [log in to unmask]
Subject: Re: [TN] Lead free solders
Steve,
Are you sure that it was the flux? What I have heard is that the copper will dissolve because of the high tin content of lead free solders. This was further illustrated to me when I asked the question about removing insulation and tinning Litz wire. One of the recommendations that was made to me was to use a low tin content solder (70Pb/30Sn) to avoid "necking", or dissolving the copper wire.
I have also heard about problems with trying to rework lead free solder joints...small pads will sometimes just disappear.
-Steve Gregory-
Steve Kelly <[log in to unmask]> wrote:
Good Morning,
Can any one point me to some papers showing problems with no-clean lead
free flux. I just returned from a customer who did some extensive
thermal cycling on some parts we soldered with no -clean lead free 96.5%
tin, 3% silver, and .5% copper. The flux was so active it started to eat
through the copper. Not a pretty sight. Thanks in advance. Steve Kelly
Steve Kelly
PH: (416) 750-8433
FAX: (416) 750-0016
CELL: (416) 577-8433
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