Concur with Ed ; one of pretin's main function is washing out as much gold
as possible .
If I could recoment one of the DIP rework solder fountains (sometimes called
miniwaves):
keeps dross out ;
washes in continuous stream .
Don't make a mistake of mixing that solder ever to your main solder wave ;
or use it for anything else but washing or desoldering (soldering would give
you seriously contaminated joints).

Paul Klasek
ResMed

-----Original Message-----
From: Edward Hare, <SEM Lab, Inc.> [mailto:[log in to unmask]]
Sent: Wednesday, 1 September 1999 0:30
To: [log in to unmask]
Subject: Re: [TN] Pre-tinning gold leads


Nick,

In my opinion pretinning of gold plated leads is important to (1) prevent
gold
embrittlement of the solder joint and (2) determine if the leads are
solderable prior
to assembly (i.e. gold can be plated over oxidized nickel).  I've seen
several
instances of gold imbrittlement associated with soldering to gold plated
leads and gold
thick film pads.  The volume fraction of brittle AuSn4 intermetallics tend
to be high
due to the 4:1 ration of Sn to Au in the intermetallic compound.  You might
want to
check into John Lau's book,  "Solder Joint Reliability", Van Nostrand
Reinhold, pp. 205
- 212.

Regards,
Ed Hare
SEM Lab, Inc.
[log in to unmask]

Nick D'Onofrio wrote:

>   We are pre-tinning the gold leads prior to assembly on our military
> products. I'm looking for some constructive data or argument to decide if
we
> should continue this practice.
>   My concern would be gold embrittlement in the solder joint and any
latent
> failures attributed to this.
>   Any comments or guidance in this matter would appreciated.
>
> Regards,
> Nick D.
>
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