Ed

Why an indium solder alloy? A tin solder would seem to do the job,
unless the Kovar post is aged to the extent that the nickel underplating
is oxidised. If this happens, then pretinning with a water-soluble flux
and a wash before assembly should do the trick. Sn60/Pb40 tins Pt well,
but Sn62/Pb36/Ag2 would be better to reduce fast dissolution of Pt.
Cheaper, too!

You may also consider wire bonding.

Brian

"Noble, Ed" wrote:
>
> Hello Fellow Netters,
>
>         Here's a recipe for a soldering nightmare.  We're developing a
> process that involves the following materials, but not having very good
> success with attaining an 'acceptable' solder joint.
>
>         Lap soldering a .4 mil dia platinum wire to the top of a .040" dia
> kovar post using indium solder (60% indium/40% lead).  Additional info:  the
> kovar post has a nickel coat 200 micro inches, then 30 micro inches of hard
> gold plating.
>
>         One issue:  indium solder does not wet to tip of iron and platinum
> wire (tip temp is at 670F)
>         Second issue: If we use zinc chloride as a fluxing agent, the end
> solder is better, but we would rather stay away from using this flux (too
> corrosive).
>
>         Does this challenge anyone out there?  We'd appreciate any and all
> feedback.
>
> Process Control Supervisor
> [log in to unmask]
> Industrial Scientific Corp.
> www.indsci.com
> voice  412.490.1884
>
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