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July 2001

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Subject:
From:
John Nelson <[log in to unmask]>
Reply To:
Date:
Thu, 26 Jul 2001 12:33:00 -0400
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Gosh, we've got some real technical expertise out there,
not just us old seat of the pants engineers.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ed Hare
Sent: July 26, 2001 11:06 AM
To: [log in to unmask]
Subject: Re: [TN] solder paste with 2% silver


I did my PhD thesis on the creep behavior of SN62 versus SN63 (UW - 1995).
SN62 (62Sn-36Pb-2Ag) was significantly more creep resistant and had a higher
elastic modulus than SN63.  This might make it more resistant to creep
rupture failure and thermal fatigue (due to creep-fatigue interactions).
Much of this research is published as cited below.

Best regards,
Ed Hare

1995    "Stress Relaxation Behavior of Eutectic Tin-Lead Solder", Journal of
Electronic Materials, October 1995.

1994    "Stress Relaxation Behavior of Eutectic Tin-Lead Solder with Silver
and
Copper Additions",  Ph.D. Dissertation, University of Washington, 1994.

1993    "The Effect of Ag Additions on the Stress Relaxation Behavior of
Eutectic Tin-Lead Solder", TMS Annual Meeting, Denver, CO.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Peter Barton
Sent: Thursday, July 26, 2001 7:35 AM
To: [log in to unmask]
Subject: Re: [TN] solder paste with 2% silver


One other reason given for preference of 62Sn/36Pb/2Ag is that it is a
ternary alloy with a 'pasty' range between 177deg C and 189 deg. C as
opposed to 63Sn/37Pb which is a eutectic. This slower transition from
solidus to liquidous is helpful when soldering low mass parts that are prone
to tombstoning such as 0402 and 0201.

Also according to the data published by the International Tin Research
Institute the 2% silver version gives a stronger soldered joint.

Pete Barton
ACW Technology Ltd

===== Original Message from "TechNet E-Mail Forum." <[log in to unmask]> at
26/07/01 14:31
>From "Soldering in Electronics" by Klein Wassink:
>
>"Note on solder alloy composition:
>Solder paste in hybrid circuit technology (for thick-film circuits) usually
has a metal
composition of tin62-lead36-silver2. It should be realised that the addition
of silver is not at all necessary for the silver (-palladium) metallisation
of the
>components, but for the much thinner silver-palladium conductors on the
tick-film substrates.
The use of the more expensive silver containing alloy, instead of the common
tin60-lead40 alloy, for (relow) soldering on printed boards with copper
>solder lands is not based on technological necessity, but sometimes on
>better availability of this alloy (in the form of paste) and in most cases
merely on habit.
For the rest: with silver loaded alloy no harm is done !"
>
>Kind regards,
>
>Daan Terstegge
>SMT Centre
>Thales Communications
>Unclassified mail
>Personal Website: http://www.smtinfo.net
>
>
>
>
>>>> "Kasprzak, Bill (sys) USX" <[log in to unmask]> 07/26 1:54 pm >>>
>To all:
>
>I've been reading, with great interest, the responses so far to the use of
>2% silver paste. I am not being critical of the folks who responded so far
>but, each one cites a "reported" or "understood" advantage to using 2%
>paste.
>
>I have also heard some of same reasons for considering a switch to a 2%
>silver paste. Can any of the metallurgists on this forum confirm some of
>these reported advantages and perhaps recommend that given x,y, and z, one
>should consider using 2% silver solder alloys?
>
>Good topic.
>
>Bill Kasprzak
>Moog Inc., Electronic Assembly Engineering
>
>
>> -----Original Message-----
>> From: Eric Christison [SMTP:[log in to unmask]]
>> Sent: Thursday, July 26, 2001 4:20 AM
>> To:   [log in to unmask]
>> Subject:      Re: [TN] solder paste with 2% silver
>>
>> > I always understood that you had to use a paste with 2% silver if you
>> >  were using components
>> > with terminations containing Palladium. The 2% silver is also supposed
>> to
>> >  five you a shinier
>> > finished solder joint.
>> >
>> > Steve.
>> >
>> > Larry Koens wrote:
>> >
>> > > Got a question for everyone,
>> > >
>> > > I just switched companies and the new company that I'm with now uses
a
>> > > 62/36/2 solder paste. I've always used the 63/37 formula. The guys
who
>> > > decided to use the 2% silver are no longer with the company. My
>> >  question
>> > > to you is, why would they want the 2% silver in the paste? They know
>> > > something I don't?!
>> > >
>>
>> The silver should give the alloy higher strength, better creep resistance
>> and a higher melting point. Perhaps your application benefits from one of
>> these differences?
>>
>> Regards,
>>
>>
>>
>> Eric Christison
>>
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