# Transistors



## Slochteren (Jul 5, 2015)

Hi,

I had 20 different transistors wich i pulled from different boards. They had al goldplated legs, some had a gold plated ring on the base and some had a fully plated base. I put them in Nitric to dislove the base metals and filter the foils.
3 transistors didn't dislove at all and from the other ones the base didn't dissolve. After washing in water i was able to peal off the most off the gold plating (about 80%).
The remainings (except the 3 that didn't dissolve at all in Nitric) i put in AR on a hotplate, now all metal is dissolved including the base and the remaining gold plating.
If i test with stannous it tests possitive for palladium (start with light green and then to green). 
Where did the palladium come from? Are the base off those transistors made off palladium, and the other three the cap also?

Picture undisolved tranisitors.


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## johnny309 (Jul 5, 2015)

I do not think is Pd.....may be Ni....from the transistor case(KOVAR material).....the transistors didn't dissolve in nitric due to enviroment in which they work( o thin layer of insulating varnish on the case) or due to the fact that the case is Al ....so .....


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## patnor1011 (Jul 5, 2015)

I would not think that is positive for Pd. 
Test with DMG.


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## Slochteren (Jul 6, 2015)

Thx for the answers, i don't think its PD either but am confused by the Stanous test. I have another 500 gr off these sort of transistors/ics and this was just a test to see what happens. Till now i'm not confinced this was the best way to do it.
What would be the best way to get the gold out/from them? Wenn i sell them on Ebay i might get more for them but less fun and no learning..
I don't have dmg, but i see you (patnor) sell it,.. will pm you

Paul


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## solar_plasma (Jul 6, 2015)

I have tried HCl as well as dill. HNO3, both were slow, HNO3 produced a lot of iron oxides. Has anyone tried to do them by straight AR and recover from dirty solution?


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## Barren Realms 007 (Jul 6, 2015)

solar_plasma said:


> I have tried HCl as well as dill. HNO3, both were slow, HNO3 produced a lot of iron oxides. Has anyone tried to do them by straight AR and recover from dirty solution?



Yes I have run them in poor mans AR with no problem and dropped the gold with copperas.


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## johnny309 (Jul 7, 2015)

In this case the best way is AR....because you aim to a complete dissolving the case....more gold is in the solder where the die(silicon waffer is attached)...and the bonding wires (solid Au 99.99%)....
So....in short ....AR...but for a faster reaction....crush the case with pliers (also that give a indication if some thermal paste appears that the transistor is germanium type and you should separate it from the rest ).


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## lanfear (Jul 7, 2015)

I think I have read somewhere that the thermal paste in these can consist of berylium oxide.
I don't remember where, but it was on this forum. And after that I decided to only run them in cell and discard the rest. I could be wrong of course, but just wanted to trow that out there..

...................
My bad. This was in the TO3-transistor.

Jon


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## johnny309 (Jul 11, 2015)

If you run them in a cell ....you will be missing the large amount of gold( bonding wires...solid gold,solder for die attach...90-98 gold)....
Thermal paste is an indicator that your transistor is germanium type....silicon do not need thermal transfer to the case.
Most of thermal paste that i know have a lot of Ag in composition.


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## macfixer01 (Jul 11, 2015)

johnny309 said:


> If you run them in a cell ....you will be missing the large amount of gold( bonding wires...solid gold,solder for die attach...90-98 gold)....
> Thermal paste is an indicator that your transistor is germanium type....silicon do not need thermal transfer to the case.
> Most of thermal paste that i know have a lot of Ag in composition.




I was surprised to read in your earlier reply and again today, that the transistors with thermal compound inside are Germanium types? I never knew that was the distinction. I had asked here once before about how to process those, and if I recall correctly someone recommended crushing or removing the cases then boiling them in water to remove the grease before processing? I ended up just setting them aside for now. In my experience most I've come across have a grayish-translucent silicone grease. A lesser number have had a thick white grease which looks like the old Dow Corning 340 heat sink compound that GC and a Radio Shack used to sell in the small tubes for mounting heat-sensitive components. That's basically again just a silicone grease but it also contains white zinc oxide. A lot of thermal compounds made in recent years specifically for mounting processors to heatsinks do contain silver. However I can't imagine that would ever be used inside a transistor due to having some electrical conductivity? Plus the fact that Germanium transistors are generally old technology, and have mostly been replaced by silicon except perhaps for use in vintage sounding guitar amplifiers.


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## eastky (Jul 11, 2015)

johnny309 said:


> In this case the best way is AR....because you aim to a complete dissolving the case....more gold is in the solder where the die(silicon waffer is attached)...and the bonding wires (solid Au 99.99%)....
> So....in short ....AR...but for a faster reaction....crush the case with pliers (also that give a indication if some thermal paste appears that the transistor is germanium type and you should separate it from the rest ).



johnny309 in your opinion are you saying to separate because of the grease? I have quite a few germanium transistors. I did some reading on them and if I remember correctly. Some have indium bonding wires and are soldered with tin solder.

Would you recommend AR for these type or no AR because of the tin involved?


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## Slochteren (Jul 12, 2015)

I have also 300 pcs of these transistors
labeled ON408 G8402 and ON408 H8402.
They have labels on it not to dismantle because off berillyum oxide.
Beter keep them closed then i guess.
Can i run them safely thru sulfiric cel?
The legs are crimped (don't know if this good english) as you can see on the picture. This means it where holow pins, if it is gold plated on the outside it will be gold plated insode also. I was wondering if it was/is possible to goldplate hollow pins on the inside?
















Paul


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## Synom (Jul 16, 2015)

As for Beryllium Oxide, it was used a lot on the exact same type of transistor OP shows too!
I have a lot of different transistors from the golden age and many of them include BeO but it is very hard to tell what kind of ceramics it really is as most are not labeled for BeO and they have no color codes while there are dozens of different colors used :evil:

"White wet paste" is most likely not dangerous, but no guarantee given :roll:


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## machiavelli976 (Jul 16, 2015)

Those look like RF final or pre-final stage emitting amplifier transistors . Could worth more like that than the gold of them .


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## johnny309 (Jul 22, 2015)

eastky said:


> johnny309 said:
> 
> 
> > In this case the best way is AR....because you aim to a complete dissolving the case....more gold is in the solder where the die(silicon waffer is attached)...and the bonding wires (solid Au 99.99%)....
> ...




In a germanium transistor is indium,mostly because of the PN junctions(PNP and NPN types of transistor).
Separate them because of the different types of materials they are build.
Indium and thermal grease have more value than the gold used for plated legs( in the hand of an refiner)

EDIT:

http://www.learnabout-electronics.org/bipolar_junction_transistors_02.php


This is why thry need thermal grease inside the capsule and the reason that they contain indium.


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