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Subject:	Re: goldfinish on PC boards
From:	Pratap Singh <[log in to unmask]>
Date:	Sun, 03 Nov 1996 17:27:04 -0800
Content-Type:	text/plain
Parts/Attachments:	text/plain (43 lines)

Wolfgang ERAT wrote:
> 
> Would appreciate any source for info on effects on solderjoint
> reliability when assembling (solderpaste / IR Reflow ) a full gold
> (approx 30 microinches thick) finished board. What are the effects of
> the gold alloying with the tinlead in the joint ? / Thank you.
> 
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> ***************************************************************************30 microinch gold is excessive and will result in gold-tin intermetallic. Gold continues 
to react with solder even at room temperature. If gold can be finely dispersed in solder 
bodyand limited to 2-4 % by weight, then it may be OK. The joint relaibility is also 
dependent upon the component lead compliancy.

Further solder joints with more than 1 wt % will produce grainy looking joints and not 
the shiny joint you see otherwise.

A large body of literaure is available on the subject. Some references are:

1. Soldering to Gold Films by F.G. Yost, Sandia Labs, Gold Bulletin, Vol. 10, No. 4, 
1977.

2. Dissolution Rtaes and Relaibility Effects Of Au, Ag, Ni and Cu in Lead Based Solders 
by H Berg and E.L. Hall, 5005 E McDowell Road Motorola, Phoenix, AZ, 85008.

Each of these papers have further references.
-- 
Pratap Singh
Tel./Fax: 512-255-6820
e-mail: [log in to unmask]

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