Eric, I don't know for sure, but I believe it is a combination of solid solution strengthening of the tin phase and a more macro mechanism involving pinning of grain boundaries by the Ag3Sn intermetallic phase. I did not resolve the deformation mechanisms as part of my research. I was more interested in empirical constitutive relationships of Ag (& Cu) concentration versus creep rate because that data was not available at the time to support finite element modeling of solder joints. Best regards. Ed -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Eric Christison Sent: Thursday, July 26, 2001 10:02 AM To: [log in to unmask] Subject: Re: [TN] solder paste with 2% silver Ed, As a matter of interest. Are the improved mechanical properties a result of the silver atoms limiting dislocations in the Xtal structure? Regards, > > 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) metallisatio > n > 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 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 ---------------------------------------------------------------------------------