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I'm going to install a heatsink on a KBU810 bridge rectifier. As the picture shows, the leads are closer the face with markings on it.

KBU810

I wonder if one of the two faces is the preferred site for installing heatsink, maybe because the semiconductor inside the package is closer to it. I wasn't able to find any related information in the datasheet.

Update:

Pictures from front and rear sides:

front side

rear side

JRE
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apadana
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    Writing side up would be normal. –  Sep 06 '21 at 18:25
  • Some heat-sink arrangements provide a thermal path to both sides. If it is not explicitly stated in the data sheet or obvious from exposed metal (less likely on a bridge rectifier) it might be possible to test. Glue an identical thermal mass to both sides and then run a reasonable current through the device and measure the temperature of the thermal masses and see which one increases in temperature faster. – KalleMP Sep 08 '21 at 07:13

4 Answers4

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If one side seems to be metallic, I would mount the heatsink on that. Otherwise, I would mount it on the side that does not have lead markings etc.

Leave this side uncovered and put the heatsink on the opposite side.

enter image description here

12

I doubt there will be any significant difference. Maybe I should measure this.... Text side is also not guaranteed to be same side between the brands making these types of diodes.
Just do a google image search.

But here you can see a leadframe photo, which suggests the thick plastic side is the side with the metal since the leads come up a bit.

enter image description here

Jeroen3
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Normally you’d want a minimum thickness of plastic between the lead frame and the heat sink. I'd suggest that the markings should be against the heat sink, based on this illustration from a Vishay datasheet for a 25A bridge in a similar GBU package.

enter image description here

In general, when dealing with second-sourced products, or copies of copies, it’s sometimes useful to look up the original datasheets for information that may be omitted from cloned datasheets. Of course you can’t depend on anything that isn’t in the manufacturer’s datasheet (and sometimes not even that) but it can still be valuable. The congruence of original and clone manufacturer’s specs is a kind of twilight zone.

user371366
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Spehro Pefhany
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  • Are the letters not slightly raised, therefore (potentially) creating an air gap between heatsink and case? Unless your thermal pad is thick and soft enough to bridge it. – Michael Sep 07 '21 at 06:01
  • @Michael aren't the letters usually etched with a laser? I would assume they would generally be sunk down, not raised. maybe packages with dyed markings are slightly raised but i imagine that would be thin enough to be dwarfed by other irregularities – user371366 Sep 07 '21 at 06:20
  • I don’t think that is significant- run your fingernail along a chip and see if you can feel anything. Anyway, you would not likely use a silicone thermal pad, they are pretty terrible thermally (but cheap, and provide insulation), you’d just use a bit of thermal grease to fill the inevitable gaps from roughnesses and differences in flatness between the two parts. – Spehro Pefhany Sep 07 '21 at 06:27
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    @SpehroPefhany . Congratulations on achieving 300000 reputation. Always accurate. Always helpful. – Marla Sep 07 '21 at 19:03
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I wasn't able to find any related information in the datasheet.

This is on page 2 of the data sheet: -

enter image description here

It's telling you to options. The first option is use big solder copper pads and the 2nd option is to mount a heatsink and, as Charles as pointed out that will be on the non-written side of the device.

And this is on page 1 of the data sheet: -

enter image description here

This information allows you to calculate how big a heatsink you need for such and such a power dissipation.

Andy aka
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    Yes, I had seen this information. I decided to mount a heatsink, but didn't know which side is better. – apadana Sep 07 '21 at 08:04
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    This does not answer OP's question, which is not asking about how to determine the size of the required heatsink, but is rather *which side of the device to install it on*. – J... Sep 08 '21 at 10:29