Steve,

I didn't check the spreadsheet, but that sounds about right.
My rule of thumb is that (roughly) 30 uin thickness or more of Au is probably trouble, and you got about 25 times that!

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, June 29, 2012 2:06 PM
To: [log in to unmask]
Subject: EXTERNAL: [TN] Gold Embrittlement Calculator

Hi All,

 

Gonna' be another hot weekend here in the Northeast! Mid 90's all weekend long with heat index up around 100.

 

Anyways, I found this excel spreadsheet calculating percentage of gold in a solder joint that was created by Melissa Lau of Lockheed Martin. The link to it is here:

 

http://circuitsassembly.com/cms/magazine/95/3630_

 

I'm just wondering if I'm using it right. For instance I'm trying to determine what the gold percent is for an 0402 resistor pad on a board that has 19 microns of gold on it and using a 4-mil thick stencil.

 

I looked at a Vishay data sheet and I get a lead termination of roughly 10-mils long X 20-mils wide X 14-mils high. The next input is for lead plating, there's already a .5-mil input there so I'm just going to leave it at that. I can't find what the lead plating thickness should be in the datasheet.

 

The opening in the stencil is 23-mils X 25-mils and it's a 4-mil thick stencil, so I have to change the formula in the cell under the column "Solder Paste Wt" since it's based on a 6-mil thick deposit. The gold is 19-microns thick, so that converts over to .748-mils.

 

What I wind-up with is a solder joint with 36.5% wt in gold! Does that sound right?

 

Steve



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