Germanium diodes

[jkenned5]

I was wondering if these are worth removing from the boards or not. When I say "worth" I refer to stacking the metal, not for profit.

 

[Alondro]

You mean the black cylindrical Schottky diodes? Or the larger rectifying diodes, also called Shottky transistors, with their big copper heat sink with the hole on top? I do take them all off and save them, because they're so easy to remove.

I store each of the two main classes seperately.

Or, are you referring to LEDs, which is the main use of germanium in electronics today. I also save those, because each LED has a tiny gold nanowire inside, and the plating of the 'cup' is usually rhenium or even rhodium (mainly those on the older boards).

The only germanium found in other diodes (and rectifiers and transistors) would be those made between the 1950's and 1970's. After that, high-purity silicon took its place in those applications, because of the much lower cost compared to the relatively rare germanium.

Now, in the Shottky diodes it's not merely the primary electrode metal that's of interest (which in the largest cylindrical diodes is frequently gold-plated, I've found!); the junction with the n-type silicon semiconductor wafer can often be palladium silicide or platinum silicide! This is due to the need for a fairly high forward voltage, which cannot be maintained with more refractory silicides such as titanium silicide, even though those types can withstand much higher temperatures; they have too much reverse leakage to be useful for Shottky diodes.

Other metals that can be found are molybdenum, chromium, tungsten, and germanium-silver alloy.

It's tough to judge which type of metal is used just based on the appearance of the diode, as the composition changes based not just on year and company of manufacture, but also by application and voltage requirements of the circuit pathway the diode rests in.

The big Shottky transistors have so much copper relative to anything else that it may not be feasible to separate out the other metals unless you're quite skilled with chemistry and have the equipment. That's why I'm just saving them all up for now. If I do process them, it's most logical to do them all at once. I've got about a pound of the cylindrical diodes, and 5 pounds of the Shottky transistors.

 

[orvi]

Be specific, best with pictures. There are many many types of Ge diodes.

Considering precious metals content - the old glass tubular ones have often gold bonding wire inside, fairly thick. I am speaking of high end Soviet and eastern block components. Otherwise, diodes are pretty much free of any considerable precious metals - most of the times, and modern stuff even less likely to contain any appreciable PMs.

Places where leads connect to the waifer (this apply both to Ge and Si types) can be brazed or plated with gold. And typically, bigger the waifer, bigger the plated area = bigger currents = better possibility of thick plate.
Aside of the possibility that there is gold bonding wire bonded to the wafer from one side.

 

[jkenned5]

I will get a picture, those little Schottky diode (glass diode); I keep seeing them so that's why the question. Thanks for the replies

 

[Alondro]

I will get a picture, those little Schottky diode (glass diode); I keep seeing them so that's why the question. Thanks for the replies

The glass diodes are a VERY mixed bag. There are so many types, unless you have a lot from the same era it'll be difficult to deal with them.

 

[jkenned5]

The glass orange/black sometimes I find them painted blue

 

[eaglekeeper]

Not sure about the Diodes, but these (circled) generally have a tiny gold bonding wire/wires inside. I doubt it's cost effective to recover gold from these at todays spot price.....I save them anyways, maybe one day they'll be worth the expense. Or whenever you're already processing IC chips you can throw a hand full of these in the mix.

 

[Alondro]

Not sure about the Diodes, but these (circled) generally have a tiny gold bonding wire/wires inside. I doubt it's cost effective to recover gold from these at todays spot price.....I save them anyways, maybe one day they'll be worth the expense. Or whenever you're already processing IC chips you can throw a hand full of these in the mix.

Ah, the little IC transistors. I have about a pound of those. They shouldn't be hard to process by the incineration method used for small chips. Perhaps actually easier, since the legs tend to be tin-plated copper instead of kovar, meaning the simple HCl-CuCl2 process after the plastic's burned away will easily dissolve them, leaving the tiny chip and gold bond wires behind. Rarely, I've even come across some with gold-plated legs. But barely 1 out of 100 are like that.

 

[madscientistatlarge]

Actually it's unlikely those are germanium. Most likely silicon zener diodes or silicon switching diodes, possibly small silicon rectifier diodes or tuning diodes (varactors, usually silicon). Germanium is rarely used because besides the other reasons, germanium semiconducters are very sensitive to soldering heat etc. and hence have reliability problems. The low grade board says "consumer electronics", modern assembly techniques make galium very rare and it has few if any advantages over silicon and other more rugged semi materials. Nice to hear about the gold (etc.) in shottkys, I've got stacks of those!

 

[jkenned5]

Not sure about the Diodes, but these (circled) generally have a tiny gold bonding wire/wires inside. I doubt it's cost effective to recover gold from these at todays spot price.....I save them anyways, maybe one day they'll be worth the expense. Or whenever you're already processing IC chips you can throw a hand full of these in the mix.

View attachment 54310

I've been saving those circled little transistors as well. I have almost a pound of them, when I have more experience I plan to toss them in for that negligible increase.

 

[jkenned5]

Ah, the little IC transistors. I have about a pound of those. They shouldn't be hard to process by the incineration method used for small chips. Perhaps actually easier, since the legs tend to be tin-plated copper instead of kovar, meaning the simple HCl-CuCl2 process after the plastic's burned away will easily dissolve them, leaving the tiny chip and gold bond wires behind. Rarely, I've even come across some with gold-plated legs. But barely 1 out of 100 are like that.

I found about 100 with gold legs with an older style wide cylinder with a dome cap. I broke my ankle before I was able to depopulate the boards.

 

[jkenned5]

Figured someone would want to see what I was talking about, also I'm pretty sure these sprague resistors are worth saving. I save ceramic capacitors as well and I think the bigger components in the picture are electrolytic capacitors (maybe wrong).

 

[Alondro]

Figured someone would want to see what I was talking about, also I'm pretty sure these sprague resistors are worth saving. I save ceramic capacitors as well and I think the bigger components in the picture are electrolytic capacitors (maybe wrong).

Just pop one of those red 'sausages' open. If foils' inside, it's trash. If it's a block of black compressed powder, it's tantalum and worth saving.

The Sprague resistors look like those I've gotten from an old organ I'm dismantling. I cracked one open and it certainly looks like there's PM plating the semiconductor. It's very bright and silvery, but I haven't done tests on it yet. I'm sure others here have already tested them thoroughly and know what the metal actually is.