Unless you want to use AuSn eutectic preform and reflow it. Costly. They better pay you arms and legs.
--------------------------
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----- Original Message -----
From: Mike Fenner [mailto:[log in to unmask]]
Sent: Thursday, January 06, 2011 11:16 AM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Solder Ball Attachment to Thick Film Gold
Welcome back to the fold!
Conventional wisdom is that Sn based solders are not used on gold surfaces.
Specifically on gold thickfilm there is a tendency for all the gold to leach
off. Alumina is not solderable. Even if you have a non soluble under layer
such as nickel (as In gold thin film) joints tend to be very
brittle/inflexible
So if you can't not use gold, you have to dump the tin.
Non Tin based alternatives would be
- high lead alloys, but these come with high melting points [>280C], the
cost penalty is not great.
- gold/tin alloys, nice alloys but very high price.
- In based to replace Sn. Intermediate in price, MP similar to analogous
Sn/Pb alloys.
When looking at the high Pb and 80Au/Sn alloys you need to recall - apart
from possible damage to your parts - that you will need temperature stable
fluxes, you will be on the edge of the performance range for normal fluxes.
Similarly In solders should ideally be used with special fluxes to cater for
the different (mainly slower) behaviour of indium during soldering compared
to Sn based alloys.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Marsico, James - ES
Sent: Thursday, January 06, 2011 2:53 PM
To: [log in to unmask]
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]>
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