Archive for December 5th, 2016

Mica Compression Capacitor: Unsolderable Pins

The mica compression capacitors have a finish on the pins that turned out to be completely un-solderable:

Mica compression capacitor - solder vs pin

Mica compression capacitor – solder vs pin

Some casual searching suggests this is a problem with sulfur contamination of the tin-lead solder layer. I can’t vouch for any of that, as the flat areas forming the capacitor seem to be silver-plated, but …

After some flailing around, I completely disassembled the capacitor, applied 800 grit sandpaper to remove all of the solder / flux / corrosion / tarnish / surface plating from the pins, dabbed on some RMA flux, then applied a thin layer of solder to both sides. Fortunately, the capacitor could be disassembled; they don’t make ’em like that any more.

The solder layers must be thin, because the slots in the ceramic base must pass two or three pins apiece: four or six solder layers add too much thickness. Solder-wick is my friend!

For reference, the 700 pF side looks like this:

Mica compression capacitor - 700 pF disassembled

Mica compression capacitor – 700 pF disassembled

The steel washer does not have a mica washer underneath (as does the washer on the 400 pF right side). The two grayish steel plates go on the top.

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