TO-220 Failures due to lead bending?

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On 1 Jun 2006 11:37:04 -0700, "Yzordderrex" Gave us:

Production management as well as QA should be rode out of town on a rail for this behavior then.

One must NEVER bend a lead AT the package!

It stressed the lead frame internally in the device, and can lead to welded lead connection failures internally, as well as package fracturing.

ALL mechanical stress placed on a lead MUST be captured externally. There is ALSO a minimum lead bend radius to consider as sharply bent copper leads tend to "work harden" and micro-crystalline fractures WILL occur making the lead current carrying capacity less than half what it was.

So, even the engineer that designed it should be reamed for not designing this thing such that proper lead forming practices could be maintained.

One is not even supposed to bend a resistor lead at the body, much less more advanced components.

The interesting thing is the environmental circumstances you gave. It sounds like more is going on than the customer has disclosed.

On Fri, 02 Jun 2006 18:46:18 +1200, Terry Given Gave us:

Bends on copper leads should also be done S L O W L Y as copper "work hardens" and subsequently fractures in a heartbeat. This is particularly true is the bend radius is sharp, or at a high degree, as in the 90 degree bends mentioned in the thread.

On Fri, 2 Jun 2006 00:34:37 -0500, "Brian" Gave us:

Said the most retarded f*****ad in all of Usenet.

On Sat, 3 Jun 2006 01:46:29 -0500, "Brian" Gave us:

Do you have ANY humor that is funny or not 100% retarded?

On Sat, 3 Jun 2006 01:47:21 -0500, "Brian" Gave us:

Will your LAME ass ever grow the f*ck up?

I would point you to the post I made to the other Usenet retard of late in abse... the frogtard.

The Gubna has a message for your retarded ass as well.

On Sun, 4 Jun 2006 03:00:44 -0500, "Brian" Gave us:

I find it funny that you seem to claim to know the activities of so many people in these groups.

I think you are an utter f****ng retard. That is aside from the troll thing, f*****ad.

On Sun, 04 Jun 2006 08:04:30 -0700, John Larkin Gave us:

Good one! I actually laughed at that FACT!

On Sun, 4 Jun 2006 14:08:13 -0500, "Brian" Gave us:

Is there any post that you make that doesn't accuse others of being what you seemingly are?

On Sun, 4 Jun 2006 14:06:02 -0500, "Brian" Gave us:

You are full of s*it, little boy.

Sure you do.

Do you ever make ANY sense? Technical or otherwise? Where is your technical and correct response to the OP?

Grow the f*ck up, retard boy. Until then, shut the f*ck up.

On Mon, 5 Jun 2006 02:41:15 -0500, "Brian" Gave us:

I think that you are a goddamned liar, boy.

On Mon, 5 Jun 2006 02:41:15 -0500, "Brian" Gave us:

The funny part is that YOU are NOT one of those "other people".

On Mon, 5 Jun 2006 02:41:15 -0500, "Brian" Gave us:

You mean like you were trying to do with us, and your lies about what you have done and do in life?

Why do I keep thinking that we will see you on Dateline NBC being caught up in a child solicitation sting?

On Mon, 05 Jun 2006 06:48:00 -0400, Spehro Pefhany Gave us:

However, a SINGLE stamped (read coined or swaged) bend is nowhere near as stressful as a full 90 degree bend in open air with a small bend radius. Note that THEIR bends are all at an appropriate radius for the medium being bent. Also, copper CAN be formed ONE time pretty reliably. It is successive, subsequent motion that causes the failure modes.

A simple 90 degree bend of a bare solid 14Ga wire will show cracks at the large radius side of the bend upon close inspection. Those are stretch stress cracks. Others form inside the wire as copper is very crystalline in nature. Bend the wire back, and bend it down again, and the cracks become readily apparent. The bond between the molecules tear as the medium is not tightly bonded together. Bend it till it breaks and inspect the break point to find that it is a very grainy medium.

It is a fairly loosely bound metal.

How slowly do you reckon they bend the leads on a leadframe after the molding process? These guys

Best regards, Spehro Pefhany

True. Although I think the bend of a lead on a TO-220 package is quite likely to be the first bend (and hopefully the last) it ever sees.

I suspect the dies for leadframe bending effectively support (and create a controlled radius, as you say) the lead being bent.

Anyone who has ever run flexible copper tubing knows about the work hardening. It gets a lot more inflexible after a bend or two.

Best regards, Spehro Pefhany

I learned that lesson the hard way. the very hard way. but with an SOIC8.

It was after discovering the effect of Zout on a gatedrive (or in other words, if I keep driving bigger and bigger IGBTs wiht the same cheap little circuit, what happens?) late in the development phase of a small box of tricks (0.5kW - 5kW). My colleague and I had sorted out why the small ones all worked and the big ones all died, and we designed a new circuit to fix the problems (although we kept making the old circuit for the smaller units, half of the product range).

time being short, and us being in a hurry, our layout guy made a silly mistake that nobody picked up, and swapped the pins on a comparator. Our GM interfered behind our backs, and changed our very fast turnaround prototype order of 10PCBs into 1,500 PCBs (this we discovered when they turned up). Within a day we had the gatedrive up and running, and found the swapped leads. doh.

With a bit of butchery we got the damned thing going, and it performed very well. So off on soak test. 2 hours later, kaboom. Ah f*ck, back to where we first started.

repeat many times.

After about a week of looking very, very closely at the gatedrive, I'd concluded it was, in theory, fine. My colleague then managed to show the comparator output changing state when heated up sufficiently; cool it down and it changed back. scope measurements confirmed the physical pins themselves werent changing, but the output was. We attributed this to bending the leads of the SOIC8 having damaged the bond wire. when it heated up, the bond wire went open circuit, and BANG.

some units lasted longer than others; depending, we presumed, on the degree of damage done to the bond wire, it would survive one or more thermal cycles before expiring.

We swapped the two pins, did another super-fast re-spin, only bought 10 pcbs this time, and it worked beautifully, first time. So we built a few hundred thousand of them.

To add insult to injury, the GM attacked us at a budget meeting a few months later, for "wasting so much money on prototype PCBs". Our spineless leader didnt have the balls to point out the GM was the idiot that ordered the extra 1,490 PCBs.

Cheers Terry

No, I'm a circuit designer who likes to discuss circuit design and peripherals topics, with other circuit designers, on a circuit design newsgroup, and I don't understand your public masturbatory fantasies.

John

Yeah, he should show us a link.

John