[Tim Williams]

Would you consider soldering TO-220s directly to a heat spreader?

I wonder what happens to the die after all that heating and warping...

I'm considering using "powIRtab" devices in a project. 150A diodes are
nice, but they're claiming 150W in a TO-220 package, which makes me uneasy.
And how are you supposed to grease them? Something conductive
(silver-filled) I suppose...

Tim

 

[Jim Yanik]

Would you consider soldering TO-220s directly to a heat spreader?

I've seen TO-220's soldered to PCBs.Commercial products.

I wonder what happens to the die after all that heating and warping...

I'm considering using "powIRtab" devices in a project. 150A diodes
are nice, but they're claiming 150W in a TO-220 package, which makes
me uneasy. And how are you supposed to grease them? Something
conductive (silver-filled) I suppose...

Tim

Arctic Silver.

 

[Tim Williams]

Why solder? TO-220s are designed to mount on heat sink with a screw.

Indeed. And if it's not quite flat on that heatsink, thermal resistance
goes way up. So you put heatsink goo inbetween, maybe with a pad of some
sort (not sil-pads, but maybe mica for this). Now you depend on the screw
for electrical connection, and thermal resistance is higher than polished,
greased surfaces should be.

If you haven't looked at what a powIRtab is, this might be confusing.

For 150W, you might want to try a copper heat sink with fan. They are
much better and smaller than aluminium, at leasr for CPUs.

I'm not concerned about moving the heat. Ten of these things, along with
ten IGBTs, will be mounted on water cooled heat spreaders. I'm concerned
with removing the heat from the die as efficiently as possible

Tim

 

[Tim Williams]

IR keeps publishing specs that are unbelievable, like TO220s at 350
amps. Sometimes they add some stars ** that point to tiny text
footnotes like "package limited"

Yeah, but these are neither package or current limited. I just wonder about
over 100W from that size device, and how best to deal with it. Since I need
a mechanical and electrical connection to the tab, I'm thinking soldering is
a good idea.

Be very careful here. I'd prefer to use more/bigger parts and spread
the heat out.

Well, I'm already intent on using 7 in parallel to handle the reaction of a
big stinking buck converter: 120V supply, 1kA max. output (it's a constant
current feedback loop). Figure 1kA and 40V as a worst-case scenario. If
that's 1kA at up to 66% duty cycle for the diodes, it's 667A / 7 per diode,
or a bit under 100A average, and about as many watts per diode (Vf ~= 1V).

IR shows the powirtab parts as "divested."

They show up as "cheap" at Mouser. About a quarter the price of a
comparable module-style device (e.g. HFA135NH40).

Seriously, what idiots make, and buy, those things? Parallel is way
cheaper. I haven't seen, say, a 600V 100A dual IGBT module that's less than
four times the price of 4 x TO-247 IGBTs, either. Is all the silicone goo
they fill them with really worth that much?

But anyway, if they'll dissipate the power, that's good enough for me.

Tim

 

[Tim Williams]

if you can stay within the soldering profile I guess you could, is
there really much difference between a to220 and a d2pak other than
the missing tap and pin?

Even better, the powIRtab thing has a *solid* leadframe. So, like, you
could bend the lead end down in a zig-zag so it's level with the backside
and tack it to a board. It would look like a D2PAK with a whole ribbon lead
(and extra tab..).

I guess you could use some lowtemperature solder, something the melts
at the upper end of the allowed operating range

I don't think they make anything like that? Bismuth solder (pricey!) melts
at some really low temperature, like 120C. Ordinary 60-40 isn't too bad.
Just don't use lead free shit, eh?

Tim

 

[AtTheEndofMyRope]

I'm not concerned about moving the heat. Ten of these things, along with
ten IGBTs, will be mounted on water cooled heat spreaders. I'm concerned
with removing the heat from the die as efficiently as possible

Silver filled chip die epoxy. No, not a suggestion for die attachment,
a suggestion for attaching each device you place on that spreader.

If isolation is an issue, you need a thin, electrically insulative film
or "layer". Hopefully one that has good thermal characteristics as well.

The epoxy takes up all the gaps, just like the old cream (paste) used
to do.

Still, that is what the industry uses for die-to-carrier and
die-to-heatsink attachment, so it has a lot of research behind it.

Have to bake at 180° F for four hours to cure. Very good numbers after
that.

 

[Adrian Tuddenham]

Would you consider soldering TO-220s directly to a heat spreader?

I wonder what happens to the die after all that heating and warping...

I'm considering using "powIRtab" devices in a project. 150A diodes are
nice, but they're claiming 150W in a TO-220 package, which makes me uneasy.
And how are you supposed to grease them? Something conductive
(silver-filled) I suppose...

Not the answer you want, but is there any way to use a few more devices
and run them at reduced ratings? If the cost of the individual devices
is not high, this might be the most pragmatic answer - and it might give
you a good reputation for bomb-proof designs.

(I presume that proving you can use devices right on their limits is not
the real object of the project)

 

[Jasen Betts]

Would you consider soldering TO-220s directly to a heat spreader?

I wonder what happens to the die after all that heating and warping...

the surface mount version of TO220 seems to handle it OK.

 

[Jim Yanik]

-=*GACK*=- !!!

to which Arctic product are you referring?
the epxoy adhesives or the thermal compound(s)?

And why?

I note neither is meant to be electrically conductive.(I was referring to
the "grease" comment.)

 

[DarkMatter]

to which Arctic product are you referring?
the epxoy adhesives or the thermal compound(s)?

And why?

I note neither is meant to be electrically conductive.(I was referring to
the "grease" comment.)

The gak comment is retarded.

Both the silver filled thermal compound, used widely by the PC builder
folks (AND SUCCESSFULLY), and the silver filled epoxy, used universally
by the chip fab industry, are the best on the market. One does not see
"copper filled" pastes. So let the science boys come up with it and then
USE it. If you are a skeptic, you are likely too stupid to be working in
this industry, because you are a STUPID skeptic, whereas a smart engineer
is an intelligent skeptic.

 

[Nemo]

Tim Williams writes

Would you consider soldering TO-220s directly to a heat spreader?

Not sure whether 'heat spreader' refers to something specific? I'd
consider mounting them on a heat pipe, those are ridiculously cheap
these days:

http://uk.farnell.com/cci/00c93390101/heat-pipe-100mm-5mm-dia/dp/1373301

 

[Hammy]

IR keeps publishing specs that are unbelievable, like TO220s at 350
amps. Sometimes they add some stars ** that point to tiny text
footnotes like "package limited"

Be very careful here. I'd prefer to use more/bigger parts and spread
the heat out.

IR shows the powirtab parts as "divested."

John

Yes I've been noticing amperage ratings in the 100's when searching
Newark,Digikey.

Here is there testing procedure from an-1140

"IR defines what can be called the "ultimate current" for power
packages on discrete products. This ultimate current represents the
largest current any given package can withstand under the most
FORGIVEING of setups for heat management.

The BENCH SETUP used in measuring the ultimate current at
International Rectifier is full immersion of parts in a
nucleated-boiling inert fluid."

The approach adopted here is more than adequate to SHOWCASE the
ability of new Silicon platforms. The key word in this approach is
SHOWCASE.

To actually utilize our parts in an application that targeted
currents at the level of the ultimate current would likely be costly
and impractical." Gee no shit!

Full pdf - Continuous dc Current Ratings of International Rectifier's
Large Semiconductor Packages

http://www.irf.com/technical-info/appnotes/an-1140.pdf

 

[Archimedes' Lever]

Tim Williams writes

Not sure whether 'heat spreader' refers to something specific? I'd
consider mounting them on a heat pipe, those are ridiculously cheap
these days:

IDIOT! The heat gets from the generation point to the pipe *through*
the SPREADER! A "pipe" only has a single, thin line of tangency
otherwise.

 

[legg]

Would you consider soldering TO-220s directly to a heat spreader?

I wonder what happens to the die after all that heating and warping...

I'm considering using "powIRtab" devices in a project. 150A diodes are
nice, but they're claiming 150W in a TO-220 package, which makes me uneasy.
And how are you supposed to grease them? Something conductive
(silver-filled) I suppose...

Tim

Due to it's single offset mounting screw, TO220 is a notoriously poor
package, if a predictable mechanical or electrical interface to the
entire mounting surface area is required. Clamps are usually required
to distribute mounting forces equally across the mounting surface.

For direct soldering, you should follow the recommended reflow
soldering profile provided by the mfr. If a large heatsink is
involved, maintaining this profile will require extreme controller
energy inputs due to the specific heat of the heatsink material's
mass.

Soldering the devices to smaller intermediate structures that DO offer
reliable mating to a heatsink is usually more practical, as is
demonstrated in most higher-powered commercial semiconductor modules.

Without soldering, both thermal and electrical contact to aluminium or
other hard copper can be improved marginally by introducing soft
copper foil stock. Alternately an intermediate soft copper sheet can
be introduced for direct electrical pick-off. Passivation of the
surface of the copper is required to reduce oxidation in service.

This will not overcome the physical problems of TO220.

RL

 

[Rich Grise]

Would you consider soldering TO-220s directly to a heat spreader?

I wonder what happens to the die after all that heating and warping...

I can't speak directly at this, but considering that there are surface
mount components which are _intended_ to be soldered down by the heat
pad, and that people can do reflow at home in a toaster oven, I'd say
go for it - at least once - but be careful that the heating is even
so that there are no drastic delta-T's in the assembly, and just reflow
them. Presumably silicon doesn't significantly degrade at the temp. of,
say, 63/37 eutectic solder.

I'm considering using "powIRtab" devices in a project. 150A diodes are
nice, but they're claiming 150W in a TO-220 package, which makes me
uneasy. And how are you supposed to grease them? Something conductive
(silver-filled) I suppose...

Well, if they're soldered to the spreader, you don't need grease there;
from the spreader to the heat sink, I've always had impeccable results
with DC-340, which is basically silicone grease with some thermally
conductive oxide embedded in it. It looks like that zinc oxide stuff that
lifeguards smear on their nose, and it's about as tenacious as Vaseline.

Good Luck!
Rich

 

[legg]

Here is there testing procedure from an-1140

"IR defines what can be called the "ultimate current" for power
packages on discrete products. This ultimate current represents the
largest current any given package can withstand under the most
FORGIVEING of setups for heat management.

The BENCH SETUP used in measuring the ultimate current at
International Rectifier is full immersion of parts in a
nucleated-boiling inert fluid."

The approach adopted here is more than adequate to SHOWCASE the
ability of new Silicon platforms. The key word in this approach is
SHOWCASE.

To actually utilize our parts in an application that targeted
currents at the level of the ultimate current would likely be costly
and impractical." Gee no shit!

The basis for rating a semiconductor has to start from somewhere -
historically this assumes an 'infinite' heatsink maintaining case
temperatures at 25degC. How this is achieved in a test site is
irrelevant. IR simply suggests a method using conventionally available
hardware and materials that assist to overcome the increasing
difficulty of making real measurements under the theoretical
condition.

This is only attempted to investigate the increasing influence of
internal bond-wire limitations at higher currents - the effects of
which will not follow behavior of previous data that assumed all
losses were in the die.

RL

 

[Hammy]

The basis for rating a semiconductor has to start from somewhere -
historically this assumes an 'infinite' heatsink maintaining case
temperatures at 25degC. How this is achieved in a test site is
irrelevant. IR simply suggests a method using conventionally available
hardware and materials that assist to overcome the increasing
difficulty of making real measurements under the theoretical
condition.

This is only attempted to investigate the increasing influence of
internal bond-wire limitations at higher currents - the effects of
which will not follow behavior of previous data that assumed all
losses were in the die.

RL

You are right they do have to have a standard baseline comparison.

It's really no different then claiming a FET can dissipate 200W;
obviously not practical unless your immersing it in a
"nucleated-boiling inert fluid" (I had to say it "nucleated-boiling
inert fluid") to maintain a case temp of 25C.

I've just been noticing higher and higher current ratings.

 

[Mycelium]

It goes beyond that. You want ZERO internal contact, so even though
there is no dust, if you cut your finger, you do not want one of these
pads making contact with your internals.

In fact, if you cut your finger WITH a pad, it is dangerous as well.
ANY internal contact is bad... VERY bad.

So NO, dipshit, it is NOT just the dust that is a danger.

 

[Mycelium]

I did some reading on this, and then more back when I gave John Larkin
an old '486 for use as an X-acto blade sharpener (works really well!).

The danger is berylliosis, it's an allergic reaction, and comes from
getting the stuff in your lungs. Something like 5% of the population
is susceptible.

If you're allergic, dust trapped in your lungs inflames the hell out
of them, they scar up, and it's nasty. Otherwise, no problem.

Beryllium, its salts, and many of its compounds are dangerous
carcinogens.

The metal itself is fairly safe, when fresh and new. I would not want
to even be around ANY of its oxides though.

So, the "danger" of the DUST is Berylliosis. The dangers of other
Beryllium based mediums is as bad, if not worse than Berylliosis.

Just because you were aware of THAT particular affliction does not mean
that it is the only affliction associated with the compound.