Do transistors deteriorate?

[serengetiplains]

Does transistor functioning deteriorate (change from spec?) over time and use? I have some 30 year old solid state electronics for which I'm wondering if changing some of the transistors might offer improved or closer to spec performance.

A related question concerns whether current production of said transistors might operate better (closer or more consistently closer to spec?) than the 30 year old dudes. TIA.

[Netlist]

Old Germanium sure did; they started leaking.
Pure theoretically, Silicium are there for many, many decades without deterioration. At least this is what I learned. Operating them near SOA might perhaps give some parameter changes over the years.

/Hugo

[janneman]

Originally posted by serengetiplains
Does transistor functioning deteriorate (change from spec?) over time and use? I have some 30 year old solid state electronics for which I'm wondering if changing some of the transistors might offer improved or closer to spec performance.

A related question concerns whether current production of said transistors might operate better (closer or more consistently closer to spec?) than the 30 year old dudes. TIA.

Tom,

Transistors do deteriorate but I think the rate is so slow that 30 years are unnoticable. It may be different if you take your stuff through the Allen belt on a trip to Mars .

Anyway, I really don't have a clue on the rate of deterioration, but if the equipment is designed well it will be insensitive to parameter shifts in the components. For the same reason, 'modern' parts shouldn't make a lot of difference. You should be OK for another 30 years, at least.

Jan Didden

[SY]

p-type semiconductors run out of holes over time and must be refreshed. There are quite a few online vendors for hole replacement kits.

FWIW, my two transistor amps are 22 and 30 years old, have had heavy use, and spec fine. No deterioration in performance that I can measure or hear (though I've replaced all the electrolytics and a few of the film caps as preventive maintenance).

[Netlist]

Originally posted by SY
p-type semiconductors run out of holes

I should add that n-types need periodic demagnetizing. (Roughly ten years) This is best done by taking them out of circuit as the p-types suffer heavily from the nearby magnetic field that is obviously opposite to the general flow of electrons through the given device.

/Hugo

[john_ellis]

HI all

of course trannys can deteriorate!

classical problem was thermal cycling. After a (large) number of thermal cycles, the silicon chip may crack. Good old TO-3's used to do 100,000 cycles no problems, but plastic used to be worse. I have not seen any thermal cycling data for recent plastic devices. Thinner chips might help.
But as a general rule, the cooler the chip runs the more cycles it will do.

another classical problem was ionic contamination. Once again TO-3 metal cans prevented e.g. sodium getting into the chip. Plastic may be more porous, but the manufacturers should have used a better passivation on their chips too to stop that, so may be recent plastic devices are OK. If sodium gets in the most likely problem is that the leakage currents start increasing.

Another problem is electrical overstress. If any device is runs in a circuit which overstresses it, perhaps an inverter without a snubber, the junctions may be suffering. If any point in the device gets very hot, it may cause a change in characteristics. This is up to the designer to make sure his circuit isn't a destroyer.

Otherwise, the transistor might only show a gain change over a period of maybe a millenium or two if all else is equal. 30 years is nothing!

So if you want your trannys to last a long time, design within spec., and keep them as cool as possible!. Most diy-ers on these pages seem to like big sinks. For good reason. Cray, the supercomputer people, didn't want any junction to run over 55 C. That's not a bad guideline, actually. But difficult to achieve in a hot amp!

Another less well publicised effect but already hinted at is deterioration from space borne-radiation. Don't take your hifi on too many airplane trips or the silicon may deteriorate from cosmic ray events. But at maybe one or two atoms knocked out of place per trip, it will still work for many years.

cheers
John

[CBS240]

I always use flyback diodes keep the outputs from reverse biasing, even if it is for tiny amount of time, do to reactive loading. This is not a good situation for a transistor at any time.

[QSerraTico_Tico]

Originally posted by serengetiplains
Does transistor functioning deteriorate (change from spec?) over time and use? I have some 30 year old solid state electronics for which I'm wondering if changing some of the transistors might offer improved or closer to spec performance.

A related question concerns whether current production of said transistors might operate better (closer or more consistently closer to spec?) than the 30 year old dudes. TIA.

Heat kills semiconductors. The amplifier too hot to touch won't live long.

[mjraudio]

Originally posted by QSerraTico_Tico



Heat kills semiconductors. The amplifier too hot to touch won't live long.

The 150W Sanyo Predriver Transistors (two on the input stage) in a TO-220 package have been operating in my GFA-565 for 20 years at temperature at and above 70 degrees Celsius and they are still strong and running fine. I have considered replacing them though...

Meanwhile the Darlington transistors on the output stage (averaging 40 degrees Celsius operation under load for +1 hours) are metal-encased Toshiba units which have slight oxidation on the casings...I too have considered the plausibility of replacing or even upgrading them to a newer (if possible, better) design. What are your guys' thoughts on this? Sometimes it is not smart to modify an amplifier if the circuitry is particularly complicated....

From my understanding though, when replacing transistors, they must be matched with very strict tolerances to have a stably functioning amplifier. Can anyone confirm this with me?

[MikeBettinger]

Originally posted by john_ellis
of course trannys can deteriorate!

classical problem was thermal cycling. After a (large) number of thermal cycles, the silicon chip may crack. Good old TO-3's used to do 100,000 cycles no problems, but plastic used to be worse. I have not seen any thermal cycling data for recent plastic devices. Thinner chips might help.
But as a general rule, the cooler the chip runs the more cycles it will do.

During fabrication semiconductors can be subjected to temperature exceeding 400C. The chips don't deteriorate due to temperature and would not normally crack.

What is affected is the intermetallics that are formed when bonding the gold wire to the aluminum bondpads on the chip during assembly. As part of the bonding process part of the aluminum bond pad is consumed by the gold ball bond, creating the intermetallics that form the welded connection. this consuming of the pad continues even after the part is packaged and put into service. This intermetallic formation (pad consumption) is accelerated by elevated temperatures and eventually the aluminum is completely consumed and the connection to the die is broken.

This was a common heat related failure in older devices. For more recent devices the mechanism is well understood and the wirebonding processes and equipment are far superior to their counterparts of even 10 years ago.

It's facinating technology that blew me away the first time I was exposed to it; still does.

Regards, Mike.