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Opening cm300's

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Marko

Thu Feb 03 2011, 12:14AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys,

I just underwent opening one of those current limited CM 300's, to disable the limiter as well as try to fix a dead kelvin emitter that I didn't even notice before...
I had a lot of trouble getting those copper flanges bent back properly to remove the lid - and after finally getting it done, I'm puzzled what to do with the alien looking JELLO inside the igbt? I've heard of some igbt's possesing this inside, but I expected something more like paste that could easily be scooped up and returned later. This has really unusual consistency though and an eerie sticky skin which I was afraid to puncture... It also seemed that any dust or dirt that comes into contact with the jello remained permanently stuck to it's surface... at that point I closed the igbt realized I would need more help on this.

I also couldn't find any pictures or guides regarding this on the forum, which I remember some people have posted. I remember pictures too, where igbt looked plain dry inside and the job looked like straightforward cutting of wires.

I'm afraid that draining out the jello through whatever means might compromise the voltage clearances inside the igbt, as well as leave the dies exposed to air? Do they have other protection apart from it?

I'd appreciate all advice on how to get past this 'biological' part of this 'biomech' igbt without messing something up.

PS. After a prolonged search I found the thread I was looking for...

Apparently the igbt that I thought was gooless just had translucent goo, and I'm the unlucky one because my goo is grey... Anyone had a similar case and yet still managed to perform sucessful surgeries on the modules?

I'm thinking of picking up the gel with a clear syringe and then putting it back, now I'm unsure whether that will ruin it's shape and it won't spill around the case anymore, or it will just take some time?

It seems pretty dense and doesn't flow at all when the module is turned on side or upside down. I also suspect heat won't soften it since it shouldn't leak out when the module gets hot.

Apart from that, though not on the main topic - I managed to probe with a multimeter through the goo, and apparently the kelvin emitter 2 is connected to the bonding wire inside.. which just disappears in the goo, but probes open to C1E2... that's worrying me because I didn't expect this problem to be so internal, I thought the external terminal has cracked under bending or something like that.

Marko

Goodchild

Fri Feb 04 2011, 03:08AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Hey Marko,

Yeah that jello inside is horrible, the photo that I posed "looks" dry inside but infarct it has clear jello.
This was the only IGBT that had this clear stuff in it, so I didn't have to go scooping it all out first.
I just stuck the cutters right in and cut the wires without removing the stuff.

With the other IGBTs that had the stuff you can't see threw I just had to carefully "peal" back a section that was generally in the area of interest, clip the wires and put the jello back in place.

You can reheat the jello to make it liquid again and get it to reform to the inside of the IGBT, but be warned the stuff is kinda flammable. If you get it to hot it burns until there is nothing left.

Have fun

Marko

Sat Feb 05 2011, 04:01AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi goodchild,

Well, yeah, that's just what I did, I peeled the goo carefully over the limiter boards - not even all of it, just enough that I can see my work and there's still a protective layer left. I tried putting what I scooped back but realized it's a bad idea since it can easily push the cut wires back into contact together (or with something else!) when the lid is closed, so I better left it out. It could also even rip the aluminum bonding wires since they are really flimsy.

The kelvin emitter connection problem was exactly that, the long wire leading from the main terminal has simply snapped, apparently due to vibration in some point of the module's hard life... one might at first thing that goo is there to dampen the vibration and shocks, but I think it makes it worse to the wires since it adds a lot of mass around them and they can't move freely in it as if in oil... I repaired the problem by the way by removing the damaged wire and soldering my own in it's place.

Regarding heating the jello - have you tried it and do you have some idea of what temperature would it take for that? I wouldn't risk damaging the modules if it's too high, but if it's like boiling point of water I'd try it.

Marko

Goodchild

Sat Feb 05 2011, 08:24AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I have not tried heating it my self, but you could try heating a small amount and see how much heat it takes to get it to turn to liquid.

Dr. Dark Current

Sat Feb 05 2011, 10:11AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I would say the jello will not turn liquid at a safe temperature for the module, otherwise it could turn liquid during normal operation of the module and that would be bad...

Goodchild

Sat Feb 05 2011, 04:24PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

What I'm thinking is that is you heat the jello outside the module and then pore it in it shouldn't damage the module.

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