Hi Jim- Dave's concerns are quite legitimate. It won't work. You will have to use alternate materials. The thick film gold will dissolve into the solder instantaneously. It's the tin. Tin/gold eutectic could work, but it is darned hot--about 270C, which means about 290C reflow temp, and it's real strong, so differential TCE could lead to huge stresses. Probably an indium based alloy could help you out for prototypes, but Indium forms bad intermetallics with copper, so if that's the metal on the BGA, you're stuck. Wayne ________________________________________ From: TechNet [[log in to unmask]] On Behalf Of David D. Hillman [[log in to unmask]] Sent: Thursday, January 06, 2011 10:24 AM To: [log in to unmask] Subject: Re: [TN] Solder Ball Attachment to Thick Film Gold Hi Jim - welcome back! A couple of things you should be concern about: (1) gold embrittlement - you need to make sure that the gold content of the final solder joint is less than 3 weight % or you will form a gold/tin intermetallic phase which degrades the solder joint integrity; (2) dissolution of the thick film gold plating - you need to make sure that the soldering process doesn't completely leach/diffuse the thick film gold plating from the package substrate. This may not be an issue depending on what type of plating is between the gold and the package substrate (i.e. do you have a nickel subplating layer). Dave Hillman Rockwell Collins [log in to unmask] "Marsico, James - ES" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 01/06/2011 08:52 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Marsico, James - ES" <[log in to unmask]> To [log in to unmask] cc Subject [TN] Solder Ball Attachment to Thick Film Gold Good Day Technet: I've been a way from Technet for a number of years, but now I'm glad to be back. Not being all that familiar with the thick-film process, maybe someone can help. We are in the process of designing a BGA multichip module where we're working with a supplier who will supply the empty package. The supplier wants to use thick-film gold for the external I/O pads, where we will be attaching solder balls after the component is assembled. I have no experience soldering tin-lead solder balls to thick-film gold and was wondering if this is a standard practice or if we're breaking new ground. Although this is a developmental program, this assembly will eventually be flight-worthy for a military avionics project. Thanks in advance for your help, Jim Marsico ITT Corporation 1500 New Horizons Blvd. North Amityville, NY 11701 631-630-5079 [log in to unmask]<mailto:[log in to unmask]> ________________________________ This e-mail and any files transmitted with it may be proprietary and are intended solely for the use of the individual or entity to whom they are addressed. If you have received this e-mail in error please notify the sender. Please note that any views or opinions presented in this e-mail are solely those of the author and do not necessarily represent those of ITT Corporation. The recipient should check this e-mail and any attachments for the presence of viruses. 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For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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