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Old 4th February 2006, 03:42 PM   #101
anatech is offline anatech  Canada
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That's true enough. I don't know how you can fault the package for that. This would seem to be an intentional way of destroying the part if you ask me.

I have bent a few leads and carefully straightened them back up with no ill effects.

-Chris
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Old 4th February 2006, 04:50 PM   #102
K-amps is offline K-amps  United States
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Same here... had no issues, but I can see them rotating if not straightened correctly.
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Old 4th February 2006, 11:35 PM   #103
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I'm not faulting the package.

Just comparing that it's harder to do this to a TO220.

If you look up the properties of glass you'll see it's not as resistent to stress as epoxy.

My only point was that some care is required in handling the TO3.

You dont have to take that advice; you are free to abuse it as you wish.
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Old 5th February 2006, 12:48 AM   #104
clem_o is offline clem_o  Philippines
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Quote:
Originally posted by vectorplane

Question for anyone who has cracked open flat packs (TO220, 247, 264):
Is the top face of the die in direct contact with the epoxy molding material, or is there a small space of air above it?

Hi vectorplane - I'm late into the discussion - again. Why the question anyway? You looking at extra capacitance due to the epoxy?

One of the problems with epoxy is actually bending of the gold wires, causing shorts. This is caused by the plastic not quite being liquid enough as it is injected and molded. So, the stuff definitely gets into contact with the silicon and would be out-of-norm to have voids...

Cheers!

Clem
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Old 5th February 2006, 12:51 AM   #105
anatech is offline anatech  Canada
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Hi Vectorplane,
I don't think epoxy would survive that test either in the same mechanical configuration. Epoxy packages have their own issues, so I think you simply have to be aware of the issues with whatever package you are using.

This is a bit O.T. anyway.

-Chris
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Old 5th February 2006, 02:15 PM   #106
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Clem:
Do you still need to pursue a uC solution?
Or are you ok with using a capacitince meter.

The question about epoxy voids was to determine if an additional heatsink placed on TOP of the flatpack could in some cases be implemented for enhanced heat removal from the die.
(ie. sandwich the flatpack between 2 heatsinks)

Andy
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Old 5th February 2006, 03:09 PM   #107
anatech is offline anatech  Canada
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Hi Andy,
There would be problems with the leads that attach to the die. They are attached from the top "flying" as it were. When you crack a transistor apart, these normally leave with the top encapsulation.

-Chris
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Old 5th February 2006, 11:15 PM   #108
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Default OT: encapsulation voids

Quote:
Originally posted by anatech
Hi Andy,
There would be problems with the leads that attach to the die. They are attached from the top "flying" as it were. When you crack a transistor apart, these normally leave with the top encapsulation.

-Chris


Chris, I'm not sure which question you're addrssing.

If there are no voids in the epoxy, it means that both sides of the flatpack can be used to conduct heat away.

For any given heat sink arrangement, anytime you want to add an additional 5 square inches of heat sink, it's better to add it close to the device, than at the extremity of an existing heat sink.

But if there is a void inside the epoxy, than removing heat through the top face becomes less attractive.

The above might be relevant only if you need to minimize thermal resistance(case-to-ambient) in a space-constrained application.

Again, sorry for the OT.

Andy
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Old 5th February 2006, 11:20 PM   #109
anatech is offline anatech  Canada
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Hi Andy,
Sorry for being ambiguous. I was answering
Quote:
The question about epoxy voids was to determine if an additional heatsink placed on TOP of the flatpack could in some cases be implemented for enhanced heat removal from the die.
Although not very clearly.

You would be further ahead to contact the heatsink around the device and provide more surface area on the top side too. That is sometimes seen.

-Chris
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Old 5th February 2006, 11:41 PM   #110
clem_o is offline clem_o  Philippines
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Quote:
Originally posted by vectorplane

Do you still need to pursue a uC solution?
Or are you ok with using a capacitince meter.

The question about epoxy voids was to determine if an additional heatsink placed on TOP of the flatpack could in some cases be implemented for enhanced heat removal from the die.
(ie. sandwich the flatpack between 2 heatsinks)

Hi Andy - I'm certainly fine with using a capacitance meter - but I do have to check if my unit is up to it (many things seem to have gotten in the way this weekend)...

re: additional heatsink on top of a flatpack - I don't remember the specs from sumitomo plastics, but had the impression that the thermal resistance wasn't that good. The only reason the top gets hot "faster" than the rear is the low thermal mass, so it will probably help only a little...

Cheers!

Clem
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