Re: Another scope 7854

Bruce Griffiths
 

The older heavily gold plated HP boards used to develop distinctive dark gold tin intermetallics between the solder and the board after a few years. The forrmation of such intermetallics is why a solder pot is used to remove gold from the solder pockets on connectors for high reliability wiring harnesses. Indium solder is another approach but its more susceptible to corrosion

Bruce

On 05 May 2017 at 17:55 "David @DWH [TekScopes]" <TekScopes@...> wrote:



I originally thought that but when I ran across the problem, removing
the solder revealed that the entire solder to gold interface was a
purple-brown color. I suspect this was a long term effect of whatever
flux Tektronix used during assembly.

On Fri, 5 May 2017 17:23:04 +1200 (NZST), you wrote:

>No its just the usual formation of gold-tin intermetallics:
>
>http://www.semlab.com/papers/goldembrittlementofsolderjoints.pdf
>
>http://www.semlab.com/papers/intermetallicsinsolderjoints.pdf
>
>However bonding of aluminium wires to gold pads can result in Aluminium gold intermetallics
>
>One of these intermetallics (AuAl2) is purple (hence the name purple plague) and another (Au5Al2) is white in color.
>
>Bruce






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