Pat Diamond asked:
>This is my second attempt to get any suggestions on my
>solderability query, someone please answer me as I am
>getting lonely!
>
>My query is as follows:
>
>I want to solder to a firewall hermetic connector that has
>#24/20 solderwells that are plated with 5 microns of Gold
>over both Alumel and Chromel using 5S HMP solder, cored
>with 2% "no clean" flux.
>
>The environment they will be used in will typically see
>temperatures in the range of -55 to +270 degrees C.
YIKES, a 325°C range, your are talking thermal shock, now!
>If I do not remove the Gold prior to soldering will this cause
>me embrittlement problems?
Keep in mind that gold is highly soluble in tin based solder alloys (of
course you have me totally baffled with the 5S HMP alloy, this may be a
non-sequiter).
In general, you do not solder "to" gold, you dissolve the gold into the new
solder joint, and wet the base metal.
Five microns is about 200 micro-inches, a very thick gold plating typically
used for electrical contacts. I'd be curious, why is that gold so thick?
You must be talking about a type K thermocouple (chromel-alumel)?
My thoughts are, do you really want to connect that wire with another
metal, will this cause you to have another junction on a thermocouple loop?
Even if this is OK, I would suggest that those base metals (chromel and
alumel) probably have abysmal solderability. I'll bet that gold is a
cladding. You could likely get a good connection with a lug (compression)
terminal, or by welding - this is how most thermocouples are connected -
and I'd therefore want to explore other methods than low temp soldering to
make such connections, even on terra firma.
I hope you find reading the above passage to be a cure. Just the very
thought of gold, chromel-alumel, and solder is enough to generate thermal
voltage here, even with a cold solder iron.
regards,
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
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