Hi Larry, although containing a nominal 2% silver and despite that we normally see silver as a shiny metal, it doesn't go necessarily that a 62/36/2 alloy will give better cosmetics. In fact in some cases it will exhibit 'worse' cosmetics by exhibiting a rougher surface. A 62/36/2 alloy won't be eutectic it will be off eutectic, melting and solidifying over a temperature range. Albeit there is a tight range, any deviation from the nominal 62/36/2 through over charge of the elements or through contamination (Sb, Ce, Fe .... yes there are limits but they're changed or overlooked, sometimes for good reasons), will potentially increase the likelihood for cosmetic deterioration. With respect to palladium finishes, it's been shown that the joint produced over palladium alloys/plating is formed through the soldering alloy dissolving the component finish and hence wetting the component. Note that it's also know that silver finishes give a nicer joint with silver containing alloys, work I was involved in indicated that even with the limited contamination of the silver finish into e.g. 63/376 solder alloy can create a differential cooling profile in the joint producing a solder joint with a rough surface. Strictly speaking as 'scientist' I don't have the info on other finishes (OK maybe I know a little about soldering to an alloy 42 finish), however the dissolution of gold pad finishes into solder joints is well known, therefore I draw a similar conclusion of dissolution of gold in the formation of solder joints over gold. With respect to joint strength being better with 62/36/2, there is a lot of data available apparently showing this to be the case. I state 'apparently' since 'joint strength' is a very vague statement. Alloys tested under one set of conditions can exhibit the reverse or inverse results under different test conditions, so it's a bit of a 'mythological fact', docusoap style, not exactly incorrect, but not the whole truth. Now here's my myth for the record, I believe the thick film story is the correct one, however it was before my time so can't categorically state it's true. You also might find that someone has spec'd 62/36/2 alloy to overcome some apparent soldering issue that disappeared through using this alloy, it is significantly different that 63/37. A lot of specs come about through chasing down a solution rather than an explanation. Does that help you? Probably not eh? Andrew Hoggan BBA Associates Ltd www.bba-associates.com -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Larry Koens Sent: 26 July 2001 15:05 To: [log in to unmask] Subject: Re: [TN] solder paste with 2% silver Thanks for the input you guys have given me. I had heard some of the same things, that the 2% is used in the Hybrid industry and that the 2% is suppose to give shinier (cosmetic) solder joints. But, I guess my question is, does the 2% give me a just a better cosmetic joint? Is there no real mechanical benefit? Thanks, Larry -----Original Message----- From: d. terstegge [mailto:[log in to unmask]] Sent: Thursday, July 26, 2001 8:32 AM To: [log in to unmask] Subject: Re: [TN] solder paste with 2% silver 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 > > ------------------------------------------------------------------------ -- > ------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt delivery of Technet send the following message: SET > Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > > E-mail Archives > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for > additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 > ext.5315 > ------------------------------------------------------------------------ -- > ------- ------------------------------------------------------------------------ --------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ --------- ------------------------------------------------------------------------ --------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ --------- ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------