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TO-220 leadbend failure - Update

The thread was hijacked and by the time we got to post number 153 it had morphed into something else which had nothing to do with my post - Heheh - So I figured to start fresh. I placed OP at the bottom for reference.

We stuck a couple of controls in the environmental chamber and brought them down to 20 below. Took them out and walked them downstairs to the high power lab and plugged in in - Boom. Blew up 2 out of 4. Looks like the moisture getting into the drive was enough to kill the power supply. Drive looks clean as a whistle when the moisture gone.

I had mentioned to the group that I had thought contamination was killing units. One of the other (young & green) engineers would offer up the fact that units would come back clean in an effort to shoot down contamination as a cause. So now we will have a meeting on Monday and I have all the ammo I'm going to need. Clean up the packaging and if failures continue we will take another look.

Boss is having a leadbend fixture made as well. Thanks for all the comments that apply I'll sort them out and send them up the chain.

regards, Bob

I have a small 480v 5w flyback power supply that has had a large number

of field failures. In general the failure rate is about 0.4%, one out of 250 units. This I can live with. One particular customer in Northern California has had a 25% failure rate. Most of the units come

back filthy so that there may be an environmental aspect to the problem

as well. I think units are in an air stream which may be blown in from

a rooftop intake. We have beat the crap out of the power supplies here

at the factory and have not been able to kill them. Heated transistors to 150c, put 1500v dc on the supply, etc and they keep on running. I am begining to think there may be a stress related problem with the lead bend. Production is bending a complete 90degree at the drain lead

of the mosfet directly at the package. It looks like the package ruptures and sends plasma out and destroys the clamp diodes and control

chip and so forth. Destruction is very complete here.

So question is then - has anybody ever heard of failures related to this type of handling? I will contact mosfet vendor after discussing here.

thanks, Bob

Reply to
Yzordderrex
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Once upon a time you could get 'hermetic TO-220' IIRC. Look into it. Otherwise redesign for TO-3.

Graham

Reply to
Pooh Bear

did you mention something about a rooftop intake?

have you considered lightning?

Mark

Reply to
Mark

You'd checked normal operation at -20(C?) first?

I think most operating environments specify non-condensing RH.... so a spritzer might have been just as informative.

RL

Reply to
legg

Good Idea.

I'll mention it when we meet again. The sales and service groups seem to have come around to accepting the fact that it is contamination causing probs.

We are about to offer an IP64 (NEMA 4 type) so that maybe there is an opportunity to use this particular installation as a beta test site.

regards, Bob

legg wrote:

Reply to
Yzordderrex

One dead drive I looked at came from a milk powder factory. the heatsink was an inserted-fin type, 4mm fin-fin spacing. The *entire* heatsink was one solid block of Al and rock-hard milk powder. moist environment made milk powder stick, heat baked it. repeat until no airflow at all. customer eventually sent the drive for service as it kept tripping.

The service guys couldnt get the milk powder out, it was like concrete. So they replaced the entire heatsink. Other than that, the drive worked fine.

Cheers Terry

Reply to
Terry Given

Otherwise

TO-3? Who has that kind of real estate nowdays? TO-66 maybe.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller
Reply to
joseph2k

I doubt that many devices even exist in TO-66 any more actually.

Graham

Reply to
Pooh Bear

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