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June 2012

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Fri, 29 Jun 2012 14:05:33 -0400
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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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