Vladimir,
I refer to Sn-rich and Pb-rich phases in eutectic SnPb. In cross-section showing a contact angle, the Sn-rich phase always leads the Pb-rich phase. SnPb wets very well to Au or Ag. If we eliminate any capillary action (as in solder flowing between plates), the leading edge of the Sn-phase on polished Au or Ag can approach zero - certainly below 5 degrees. If you add surface roughness, contamination, dust, oxides, or anything else, then the angle grows.
A simple measurement would be to take an Au-plated bare board, put it on a hot plate and lightly drop some very small drops of molten SnPb solder onto the surface. If you are delicate and produce small drops (perhaps about 5 mm across, you should be able to assume spherical caps. Measure the diameter and height of the drop. From that, you can calculate contact angles for your surface. I've done this with flip-chip underfills. It works remarkably well.
Regards,
Andy
Andrew C. Giamis
Andrew Solutions
FMA / Reliability Engineer
40 Technology Drive,
Warren, NJ 07059
(908) 546-4686 [Office]
(908) 938-7945 [Cell]
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-----Original Message-----
From: vladimir Igoshev [mailto:[log in to unmask]]
Sent: Friday, April 13, 2012 1:30 PM
To: Giamis, Andy; [log in to unmask]
Subject: Re: [TN] Wetting angles
Thank you Andy,
Two questions, though. Do you know the actual values, as they should be far higher than 0 (it's not liquid He we are talking about :-)).
Secondly, do you refer to pure Pb and Sn or Pb-rich and Sn-rich phases?
------Original Message------
From: Giamis, Andy
To: [log in to unmask]
To: [log in to unmask]
Subject: RE: [TN] Wetting angles
Sent: Apr 13, 2012 12:47
Typically the Sn phase wets out farther than the Pb phase. On a good clean Au surface, the contact angle approaches zero.
Regards,
Andy
Andrew C. Giamis
Andrew Solutions
FMA / Reliability Engineer
40 Technology Drive,
Warren, NJ 07059
(908) 546-4686 [Office]
(908) 938-7945 [Cell]
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev
Sent: Friday, April 13, 2012 12:43 PM
To: [log in to unmask]
Subject: [TN] Wetting angles
Technetters,
I have a simple question.
Does anyone know what the wetting angles of the two phases of the Pb-Sn eutectic on a Au surface are.
Or at least which one is lower?
Any direct answer (number/reference) will be greatly appreciated.
Regards,
Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
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Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
______________________________________________________________________
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