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July 2012

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From:
Mike Fenner <[log in to unmask]>
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Date:
Sun, 1 Jul 2012 17:01:48 +0100
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I just gave the spreadsheet a quick look over (not an audit). Based on that
glance I suggest it needs to be treated with a little caution.
Assuming I have not been thrown off by the (to me) unfamiliar units there
are some built in assumptions which may not apply.

1) The solder paste data used assumes Sn 63 type 3 powder at 90% by weight
and that should be stated. It may not be true for all users.

More importantly 
2) I think it assumes 100% transmission efficiency on printing and that is
not going to be the case even with the best pastes.  
So if I'm right overall the spreadsheet will give a number which understates
the gold.


Regards


Mike Fenner

Bonding Services & Products
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663
E: [log in to unmask]

 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: Friday, June 29, 2012 7:41 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Embrittlement Calculator

For that THICK layer of Au it does. Honestly, I don't remember seeing any
component with that thick Au plating.

One should also keep in mind that bulk percentage of Au in a solder joint
may be "deceptive". All it takes is to have enough Au in a narrow band to
form Au-Sn intermetallics and cause Au embrittlement.
Regards,

Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

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