Hi, Keith Thank you for your input on this. It raises five questions: 1. Does the elimination of such a small amount of silver from the alloy contribute to any significant increase in the solder's ductility after soldering is completed? 2.Specifically, can you provide data as to exactly what the ductility delta is between all three alloys? I would expect a significant difference between 63/37 and SN100 or SAC305, due to the percentage of lead. 3. Also, with the understanding that VPS would probably provide better wetting, how would it otherwise affect the ductility of the alloy after soldering is completed? The profile used is essentially the same. 4. For a given assembly that has inherently high CTE stresses due to design issues as Amol's assembly presumably has, are you saying that using SN100 and VPS rather than SAC305 and convection reflow will cure his problems? 5. How do the long-term creep fatigue rates of Sn100 compare with SAC305 and SN63Pb37? I am not a metallurgist, and I am at a loss as to where to find this information. -----Original Message----- From: Leadfree [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: Wednesday, July 16, 2008 5:03 AM To: [log in to unmask] Subject: Re: [LF] [TN] SN100 for Reflow Application Although the correspondence under this title has been very interesting and informative this string drifted somewhat from the original question, which was: From: "Kane, Amol (349)" <[log in to unmask]> Subject: SN100 for Reflow Application X-To: TechNet E-Mail Forum <[log in to unmask]>, Dear technetters, Is anybody using SN100 (or other high Sn alloys) for SMT reflow soldering applications? what have your experiences been with this alloy? I have a PCB with a BGA, that is cracking due to mechanical stress (that is not SMT process related), we have a combination of solder cracking, and pad cratering. The PCB currently uses SAC305. We also build a SnPb variant of the same exact board with no issues (the bare board material is different for SnPb and LF versions). I was therefore wondering whether SCA305 alloy properties could be a contributing factor this defect. How does the ductility and shear strength of SN100C compare to SAC305 and 67-37SNPb alloy? To return to the original question, since it has not been clear from the correspondence exactly what the nature of the crack was I cannot say with any certainty whether the result would be any better with SN100C than with SAC305. However, to answer the specific question on the ductility and shear strength of SN100C, it is a more ductile alloy than SAC305 and has a lower flow stress and in that regard is more like 63/37 SnPb. If the cracking occurred in a situation where the joint was subjected to substantial strain then the greater compliance of the SN100C could mean that the solder would accommodate that strain without cracking and without transmitting the stress to the substrate or the component. Cratering can be a symptom of unrelieved stress being transmitted into the laminate instead of being absorbed by deformation of the solder itself, e.g. the cratering failure with area array devices in dropped cell phones with SAC305 joints. Cracking of chip capacitors can be another consequence of strain being transmitted rather than accommodated by the solder. In regard to a later comment on the poor results obtained in reflow with the 99C alloy (Sn-0.7Cu), although SN100C is based on that same alloy microalloying with Ni and Ge substantially changes the behaviour of the alloy, as has been well documented in several peer-reviewed scientific papers. Reflowed SN100C joints are smooth, bright and generally free of shrinkage defects and can be difficult to distinguish from 63/37SnPb joints. The higher melting point of SN100C (227C/440F compared with the 215-220C/419-428F of SAC305) has been raised as a concern but the experience of the increasing number of lines running with SN100C paste indicates that because of the modifying effect of the microalloying additions the alloy needs less superheat (excess of the peak temperature over the melting point) than SAC305. For reflow lines reflowing SAC305 with a peak temperature around 240-245C/464-473F, which seems to be a profile very commonly used with that alloy, SN100C has proved to a "drop-in-replacement". However, depending on the Delta T, we would be more cautious about suggesting SN100C would be a drop-in-replacement for SAC305 for lines running with a peak temperature 230-235C/446-455F. However, results obtained with the new generation of vapour phase reflow systems indicate that good results can be achieved with SN100C with a liquid with a boiling point of 235C/455F. Keith Sweatman Nihon Superior Co., Ltd ------------------------------------------------------------------------ -------Leadfee Mail List provided as a 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 Leadfree To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL) Search previous postings at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ------------------------------------------------------------------------ ------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------