Author Topic: MOSFET/Rectifier thermal pads  (Read 475 times)

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Offline raybies

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MOSFET/Rectifier thermal pads
« on: July 17, 2018, 09:38:28 pm »
Howdy.

I received some MOSFETs (IRFP250N) and a rectifier (D25XB60). I was expecting some thermal pads to put on the heatsink block but I received these:

And I'm not totally sure what to do. They're plastic w/ a protector film on each side.
Do I need to get some pads too?
Do I need paste?
Do I just use the plastic?





Thanks.
« Last Edit: July 17, 2018, 09:40:12 pm by raybies »
 

Offline senso

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Re: MOSFET/Rectifier thermal pads
« Reply #1 on: July 17, 2018, 11:41:48 pm »
Thats mica, you should put a tiny dab of thermal paste on it, because neither the mica nor the mosfet/bridge is perfectly flat, so thermal paste to help conduct the heat out of them.
 

Online T3sl4co1l

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Re: MOSFET/Rectifier thermal pads
« Reply #2 on: July 17, 2018, 11:48:09 pm »
On the upside, thermal doesn't matter much. Those are some shitty counterfeits, hoo whee!

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Online DerekG

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Re: MOSFET/Rectifier thermal pads
« Reply #3 on: July 18, 2018, 10:23:33 am »
Put some thermal paste on both sides of the mica washer.

I have not checked on-line, but it looks like both your devices have their heatsinks fully encapsulated. If this is true, you don't need to use the mica washers at all. Just place some thermal paste between your devices & the heatsink.

To be safe, check the insulation specs of each device to ensure the device voltage insulation is satisfactory for your application. You might need to use a plastic sleeve for the screw & the nut. As always, check the manufacturer's datasheets.
I also sat between Elvis & Bigfoot on the UFO.
 

Online blueskull

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Re: MOSFET/Rectifier thermal pads
« Reply #4 on: July 18, 2018, 10:29:03 am »
On the upside, thermal doesn't matter much. Those are some shitty counterfeits, hoo whee!

The IR logo doesn't even seem to be etched by a Q-switched laser. It seems someone used a CW laser to scorch the plastic...
The bridge has good printing, though.
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Offline wraper

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Re: MOSFET/Rectifier thermal pads
« Reply #5 on: July 18, 2018, 10:38:36 am »
Both MOSFETS and rectifiers are salvaged used crap, likely with fake markings, especially mosfets. Terminals were cut off close to the package and then new terminals welded on top. It can be clearly seen on pictures. BTW mica + thermal paste have much better heat transfer than silicone pads.
 

Offline raybies

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Re: MOSFET/Rectifier thermal pads
« Reply #6 on: July 18, 2018, 04:46:29 pm »
Thanks for the mica info, I had no idea.
Chinese mofo assured me all components were 100% authentic and original.
 

Offline TERRA Operative

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Re: MOSFET/Rectifier thermal pads
« Reply #7 on: July 18, 2018, 04:53:27 pm »
Thanks for the mica info, I had no idea.
Chinese mofo assured me all components were 100% authentic and original.


HAHAHA! :P Yeah, that's a hard nope if it's not from a real supplier. Power transistors would have to be the most counterfeited electronics part out there.

If it's from ebay etc, get a refund for sure.
 

Offline wraper

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Re: MOSFET/Rectifier thermal pads
« Reply #8 on: July 18, 2018, 06:05:17 pm »
Chinese mofo assured me all components were 100% authentic and original.
Just as any other counterfeit crap on ebay  :-DD.
 

Offline Whales

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Re: MOSFET/Rectifier thermal pads
« Reply #9 on: July 18, 2018, 07:07:08 pm »
Something to note: you only need to use those clear bits of plastic if you need to insulate the chips from their heatsinks.  If your heatsinks are seperate or if your circuit doesn't mind them sharing electrically then it's not needed.

Eg I can't see exposed metal on that bridge rectifier (I could be wrong).
 

Offline Halcyon

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Re: MOSFET/Rectifier thermal pads
« Reply #10 on: July 19, 2018, 02:05:33 pm »
Thanks for the mica info, I had no idea.
Chinese mofo assured me all components were 100% authentic and original.

100% authentic and original fakes. ;-)
 

Offline Red Squirrel

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Re: MOSFET/Rectifier thermal pads
« Reply #11 on: July 20, 2018, 01:13:51 pm »
Sorta off topic here, but when it comes to these fakes, do they still more or less operate the same as the real ones and just more likely to fail or are their specs completely off, ex: are they fine to play with as a hobbyist to get the result you expect or will they completely throw you off?  Also if you order from places like Digikey are you guaranteed to get the real thing or is it possible for fakes to somehow land in their supply chain?

I tend to order from Digikey but every now and then I'll buy misc components off Amazon to pad an order for free shipping.  I tend to assume anything from Amazon to probably be a Chinese fake.
 

Online blueskull

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Re: MOSFET/Rectifier thermal pads
« Reply #12 on: July 20, 2018, 01:17:57 pm »
Sorta off topic here, but when it comes to these fakes, do they still more or less operate the same as the real ones and just more likely to fail or are their specs completely off, ex: are they fine to play with as a hobbyist to get the result you expect or will they completely throw you off?  Also if you order from places like Digikey are you guaranteed to get the real thing or is it possible for fakes to somehow land in their supply chain?

I tend to order from Digikey but every now and then I'll buy misc components off Amazon to pad an order for free shipping.  I tend to assume anything from Amazon to probably be a Chinese fake.

It depends. Certain parts from China are certainly fake, such as HiFi caps, trannies, OPAMPs.
Some more DIY oriented products, such as MCU/CNC/power/sensor modules, are mostly at least operational, and lots of are actually genuine.

In other words, it depends on target. If the intended audience are going to find the fake, they tend not to scam you.
If the intended audience only wants psychological placebo, then chances are you will get fake.

Again, if scamming doesn't make money, why bother?
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Offline Circlotron

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Re: MOSFET/Rectifier thermal pads
« Reply #13 on: July 20, 2018, 01:42:55 pm »
Sorta off topic here, but when it comes to these fakes, do they still more or less operate the same as the real ones and just more likely to fail or are their specs completely off, ex: are they fine to play with as a hobbyist to get the result you expect or will they completely throw you off?
I have bought in the last 15 years about 5000 pcs of 8 Mbit eprom ST M27C801 and Infineon mosfet SPW47N60C3 both from the same supplier in China. The EPROMs are definitely not ST. You can scrape off some of the black coating and there is some other markings and Chinese writing. They supposedly have 100nS access time but I only run them with about 3-4uS access time so I don’t make big demands of them. They may or may not run at full speed. They do take about 2 hours to erase though. Real ones take 10-15 minutes. About 1 in 25 approx fail to program properly. I have had other M27C2001 EPROMs that took maybe 10uS to read!

The SPW47N60C3 mosfets I’m sure are not genuine either. The metal surface is all scratchy and dull. Real ones are shiny. Also if you bend the leads at 90 deg sometimes they will crack and break. Real ones bend very nicely. About 1 in every 100 doesn’t work at all, either very high off state leakage current e.g. 0.5 amps @ 15 volts, or simply not responsive to gate drive. Quite reliable though. Not switching them very fast so don’t know about speed. They’re not perfect but adequate for my purpose.

I did once buy several tubes of TO-247 IGBTs and they had way to high voltage drop. Cracked open some of them and the die was only 40% the size of a good one.
« Last Edit: July 20, 2018, 01:48:39 pm by Circlotron »
 
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