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

Visit us at Booth 2G2-09 at CommunicAsia 2002 in Singapore June 18-21.


> -----Original Message-----
> From: Linden Doyle [mailto:[EMAIL PROTECTED]]
> Sent: Monday, April 22, 2002 6:35 PM
> To: PEDA
> Subject: [PEDA] Gold - good or evil?
> 
> 
> Greetings all,
> 
>     I have been following the recent thread dealing with gold 
> plating (WANTED: PCB Expert) where the subject of 
> embrittlement was raised. The original focus of this thread - 
> PCB warping - is not a problem for us. The comment made by 
> Brad Verlander got me thinking and a little worried:
>  (In the extreme cases I have been told of boards having 
> significant numbers of their components drop off the boards 
> when the board is manually flexed.)
> 
>     This has raised some issues with a couple of the boards 
> we make here at Zener. The story goes like this...
> 
> We have a number of PCBs designed to accept terminations made 
> via spring loaded contacts. We have had reliability problems 
> with straight tinned copper for these terminations, mainly 
> due to surface irregularities of the solder film. A decision 
> was made to try gold plating to alleviate the problems. This 
> has proved successful but the PCB manufacturer has gold 
> plated the entire PCB not selectively in the areas of 
> concern. After reading the above mentioned thread enquiries 
> were made regarding the nature of the gold plating, the reply 
> being Au (2 microinches) over Ni (100 microinches). 
> 
>     Is this good, bad or indifferent? Do these figures 
> indicate possible embrittlement problems in the future?
> 
>     Can anyone point me towards further reading on this topic 
> - books, articles, web sites etc.?
> 
>     Thanks in advance for any input.
> 
> 
> Best Regards,
> 
> LINDEN DOYLE
> Product Development Engineer
> Zener Electric Pty Ltd
> 

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