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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