need QFP leads bent the other way

Hello,

We had an ASIC made through MOSIS, and they were supposed to make it die down, but they have made it die UP by mistake. The only real problem is the gull-wing bending of the leads goes the wrong way. Does anyone know if there are tools to bend the leads after they have been sheared from the leadframe? I assume the normal way is they break the corners of the leadframe, but keep the edge strips on when forming the gull-wings. Now that the edge strips are sheared off, it would be a lot harder to keep the leads straight.

This chip is a 128-pin LQFP with 0.4mm lead pitch, if that helps any.

Thanks much in advance for any ideas.

(Yes, we are going to have MOSIS re-make the chip, but that is going to take months, for sure.)

Jon

Reply to
Jon Elson
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Skilled hand labor with attention to detail will get it done on a small scale. If the material is not so brittle it won't take backbending, I'm pretty sure I could pull this off with a pair of pliers, a strong light, and my fussy-work glasses. Lord knows I've done it with DIPs often enough to salvage boards other people built. I've raised pins (and soldered jumper wires on) on SSOPs for rework, but not QFPs that I recall, but assuming similar material/process they are probably backbendable.

If there were moderate volume, I'd probably go find a set of wide flat pliers to make it more efficient. If you need a large volume done cheaply, I could see a die set to backflip the leads en masse, but there has to be enough volume to justify the tooling cost and fuss. If you get fussy enough machining, you can even put guide grooves in those, but if you handle leads nicely (and uniformly) they don't generally cross.

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Reply to
Ecnerwal

Am 11.05.2011 00:34, schrieb Jon Elson:

Why not just change the PCB?

Jan

Reply to
Jan Lucas

Well, we have 85 chips or so in this condition. I think you misunderstand the difficulty of working with leads of 0.4mm pitch, they are REALLY tiny. It is very easy to pull the leads off the body, and just looking at them funny will kink the leads sideways.

Jon

Reply to
Jon Elson

If the board is populated only one side, just move the pattern to the other side of the board without changing anything, and mount the chip on the bottom.

Cheers

Phil Hobbs

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ElectroOptical Innovations
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Reply to
Phil Hobbs

Well, we just made a test fixture with a $700 socket to test these chips. The "foot" that mounts to the PCB is not likely to be re-usable. MOSIS will have to re-do the chips for us, as they goofed. So, it won't cost us anything but delay.

If I were to redo the board, it would take some time. The board is pretty tight spacing, and 6 layers, and they cost us about $1000 to make a small quantity. Then, I'd have to make a new test fixture to test the chips before putting them on the boards. So, it would be a BIG hassle and some expense to fix somebody ELSE's mistake.

Jon

Reply to
Jon Elson

I'd be happy to give ruining one a try. Under NDA if it makes you happy, not that I'd blab or snoop without one. Or you could send me a dummy if you prefer. And if I fail to ruin it I'd be happy to quote you on the other 84. While I have not tried this exact procedure on those exact parts, I do understand what pitch you are talking about.

And here's an amusing (though not cheap) tool that might help - if a bit fancier than I was thinking of going. Sort of one half of the die set I made reference to.

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Reply to
Ecnerwal

Holy COW!!! That's phenomenal! Thanks for digging that item up. I'm not sure we could really do this lead bending on 86 chips, that's eleven THOUSAND leads to bend manually. Also, we'd need to make up some kind of frame to go around the chip body to perform the bend with the right radius, and relieve stress at the package. But, I appreciate knowing this device exists.

Jon

Reply to
Jon Elson

Yes, that is a definite possibility. There are a bunch of caps on the back side, I could flip the caps to the front and put the chips on the back. Of course, one of the issues is the boards are already assembled on the back side, but that is just $25 worth of caps and such, not too big a deal. We'd probably have to make a test fixture for the reversed chips, too, that's a pain.

Thanks for the suggestion, although I had pretty much already thought of that.

Jon

Reply to
Jon Elson

You're welcome. There are a few other types you can find.

Well, this might illuminate part of your problem approaching the problem. It's not 11,000 leads to bend. Bending them one at a time is crazy, and not the good kind of crazy. It's 344 sets of 32 (assuming you have a square pack - or 172 sets of X and 172 sets of Y where X+Y = 64 for a rectangle) The tool above would be of some use in making sure that any minor issues with the mass bends got sorted out, but all the way back to DIPs, the way to bend chip leads is en masse. Grab one whole side in smooth flat jaws, flattening the lower bend and grabbing at the point of the upper bend, and back bend the upper - then slide out and do the lower bend. You can make the radius purely by hand, or you could dress the jaws to help with it. 8 bends per chip, plus clean-up.

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Cats, coffee, chocolate...vices to live by
Reply to
Ecnerwal

Yup, I tried bending them with the handle end of an X-acto blade, and was able to easily bend 15 leads or so at a time, under the microscope. It worked way better that I ever would have imagined. This allowed the chips to be placed in the test socket on our test fixture. The BAD news: After testing 3 chips, it is looking like the latest minor revision screwed something up, and one pair of output pins of the chip are stuck at the rails. These chips might still be usable in some systems, but probably most users will want that feature that is not working.

Thanks for the ideas!

Jon

Reply to
Jon Elson

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