1. Home
  2. Electronics Design
  3. For the ultimate heatsinking...
  4. Page 2

For the ultimate heatsinking...

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

Reply to
legg
Loading thread data ...

h*

YOUR ANUS IS A GOOD HEATSNK

OH NO IT IS JUST A GOOD SHRINKHOLE

I AM PROTEUS

Reply to
Proteus IIV

Good grief, they are insane. Not to mention dishonest and dangerous.

John

Reply to
John Larkin

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.

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

Reply to
Rich Grise

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

Reply to
legg

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.

Reply to
Hammy

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.

Reply to
Mycelium

h

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.

-- Cheers, James Arthur

Reply to
dagmargoodboat

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.

Reply to
Mycelium

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.