Don't use Au/Sn eutectics if you want long term reliability in cyclic environment....
Experimented with Au/Sn for TAB interfaces and found that in a cyclic thermal environment the cracks in the Au/Sn eutectic propagated all the way through the Au bump and annealed OFHC Cu leads...
Had to develop special gang T/C bonder to meet bond reliability requirements...
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
Sent: Thursday, January 06, 2011 7:43 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Ball Attachment to Thick Film Gold - Found word(s) list error in the Text body
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
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"Marsico, James - ES" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
01/06/2011 08:52 AM
Please respond to
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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
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