potentiometer case soldering (cadmium difficulties)

[J M Fahey]

Agree that tinned pot cases would be easier to solder with tin-lead.

That said, 2 problems:

1) tin is more expensive than zinc .
Yes, amount used is minimum, but 1 cent a piece in 10000000 pots soon adds up.

2) the *real* problem: tin is way less corrosion resistant than zinc, soon (from months to years) a grey/silver surface develops which is hard to solder, if sulfur+humidity are present in the air a black surface appears which eventually grows so thick that it forms *scales* (ugh).

I have caches of old transistors and ICs which I keep "just in case" , think LM391 , NE571 , old RC4558, TI58 Fets, which simply can't be soldered so are wasted.

I had mixed success wiping them bright with dry wet or dry 200 grit emery paper and soldering them *now* , not tomorrow, or swabbing them with diluted clorhidric acid, tinning with a dedicated soldering ikron (its tip dies quickly) and then washing them thoroughly, while zinc plated oarts, worst case lose brightness and if in a very humid atmosphere, turn white and even develop a (very toxic) "white dust" on their surface.
Yet in general it can still be soldered with a hot iron and good solder/flux.

That's why pot cases are still zinc plated.

Of course, gold is better

Silver also gets attacked by sulfur and humidity.

Cadmium used to be very good, but very toxic and an environment nightmare, I guess it's still used for Military equipment .
No contradiction, Military equipment in general is used to delve Death, so .......

[hewo]

1st Surface Metallurgy and Soldering

Agree that tinned pot cases would be easier to solder with tin-lead.

That said, 2 problems:

1) tin is more expensive than zinc .
Yes, amount used is minimum, but 1 cent a piece in 10000000 pots soon adds up.

2) the *real* problem: tin is way less corrosion resistant than zinc, soon (from months to years) a grey/silver surface develops which is hard to solder, if sulfur+humidity are present in the air a black surface appears which eventually grows so thick that it forms *scales* (ugh).

I have caches of old transistors and ICs which I keep "just in case" , think LM391 , NE571 , old RC4558, TI58 Fets, which simply can't be soldered so are wasted.

I had mixed success wiping them bright with dry wet or dry 200 grit emery paper and soldering them *now* , not tomorrow, or swabbing them with diluted clorhidric acid, tinning with a dedicated soldering ikron (its tip dies quickly) and then washing them thoroughly, while zinc plated oarts, worst case lose brightness and if in a very humid atmosphere, turn white and even develop a (very toxic) "white dust" on their surface.
Yet in general it can still be soldered with a hot iron and good solder/flux.

That's why pot cases are still zinc plated.

Of course, gold is better

Silver also gets attacked by sulfur and humidity.

Cadmium used to be very good, but very toxic and an environment nightmare, I guess it's still used for Military equipment .
No contradiction, Military equipment in general is used to delve Death, so .......

Understood and experienced, esp old guitar electrical metal parts.
Visually observed plating on old gibson and old rickenbacker electric guitar electrical metal parts sprouting dendritic whiskers as if "feeling the atmosphere". At 1st I thought biological life form, mold, etc. But now that you clarify such whiskers are passification dealt by the dissimilar metallurgy in conjunction with atmospheric constituents such as vapor and sulfur and oxygen and charge.