Mark,
        this is something that I had looked into closely over the years. We
have posted previously about this on the PEDA group so you may be able to
search the PEDA Yahoo archives and find more but here are my comments from a
previous thread on this issue.

"April 23 2002,
Re: [PEDA] Gold is not evil, it just has a mischievous side to it .
Linden,
here is the study that I have found to be the best available for
quantifying the gold embrittlement issue. According to the findings of this
study, if you gold is less then 30 micro inches thick then there should not
be any solder joint embrittlement using only regular Lead-Tin solder. This
equates to the gold being less then 3% by weight of the solder joint, if
this volume is not exceeded then there should be no embrittlement problem.

The article was titled "Effect of AU on the Reliability of
Fine Pitch Surface Mount Solder Joints" by Judith Glazer, HP, Palo Alto,
California. It was published in "Proceedings, Surface Mount International
Conference, Aug 25 - 29 (1991), San Jose, CA." It was republished in Circuit
World 18, pg 41-46 1992 and Surface Mount Technology 4, pgs 15 - 28 (1992).

There are also several books by John Lau which deal with this issue,
sorry can't recall the titles but the issue is dealt with just as an issue
within various books of his.
I got my copy of the HP article directly from HP, possibly if you
ask real nice you can find someone at HP who will also find it for you."

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com

Check out our fall promotion at www.norsat.com. Limited quantities. Sale
ends December 24, 2002.
Contact your Account Manager or call 1-800-NII-4LNB or email
[EMAIL PROTECTED]



> -----Original Message-----
> From: Mark witherite [mailto:[EMAIL PROTECTED]]
> Sent: Friday, November 22, 2002 3:56 AM
> To: Protel EDA Forum
> Subject: [PEDA] Gold embrittlement in solder joints
> 
> 
> 
> 
> Hi Everyone,
>          Does anyone know the maximum recommended plating 
> thickness you can 
> use for gold with out causing gold embrittlement  in the 
> solder joint.  My 
> application is for BGAs.   I attended a class and PCB east a 
> few years ago 
> and was introduced to a new term "Sacrificial Gold platting" .  I 
> interpreted it to mean the minimum  thickness required to 
> prevent oxidation 
> and not cause embrittlement of the solder joint.   So does 
> anyone know what 
> thickness I should speck for my boards?
> Thanks
> Mark

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