The problem is not the deposition of gold, but rather how much of the
deposited gold is leached off into the resultant connection.  Typical
depositon thickness values run from 30 to 100 micro inches.  Old Mil-Spec
requirements were from 50 to 100 u-in. of gold and they required the parts
to be tinned prior to use (they also admonished contractors to double-tin
the parts if deposition thickness exceeded 100).  Anyway, the problem of
course is the percent of gold that is wicked from the component termination
into the connection.  That is a variable which is controlled by process
parameters such as: deposition thickness, flux activity, solder volume,
duration of solder in liquidus state, etc.  The second and perhaps more
important question is, how important is the elasticity of the solder
connection.  Are you assembling Class 3 (Hi-Rel) equipment with a
component/pwb Tce differential of greater than 6-8 ppm/Deg C, if so you have
a need for "good" connections (e.g. gold < 2%), or are you assembling Class
1 (consumer electronics) with a Tce differential of greater than 8 ppm/Deg.
C.  Re a study, the Tin Institute (Branch in Ohio I think) has studied this
problem in the distant past (in addressing the effect of various
contaminates in solder connections) and probably has a report available, but
I don't have their address readily available.   Regards, Jim Moffitt    



t 07:31 AM 8/15/96 PDT, you wrote:
>
>     This question has come up again.  What are the adverse affects of gold 
>plated terminations on SMT components?
>     We have been seeing a number of new sample components with gold 
>terminations, and to date, have disqualified  them based on gold 
>embrittlement. .  Many of the vendors reps say that this issue is new to 
>them and that they sell these parts all over with no questions/problems.  Is 
>this still an issue?  If so, why are these vendors supplying parts, 
>especially taped/reeled parts, with gold on them?  Tinning these would be 
>expensive and hardly practical.
>     Is there a spec/study/whatever that shows the maximum deposition of 
>gold before it becomes a problem?
>
>***************************************************************************
>* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
>***************************************************************************
>* To unsubscribe from this list at any time, send a message to:           *
>* [log in to unmask] with <subject: unsubscribe> and no text.        *
>***************************************************************************
>
>

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************