TO-220 Heatsinks & Potential Mounting Pin Issues

Thread Starter

jwilli

Joined Apr 21, 2009
42
Is there a real reason to solder heatsink pins onto your PCB other than stability? As the heatsink heats up, would this potentially heat up a small area on the PCB surrounding the soldered heatsink pins?

I've been using a small heatsink on a TO-220 device that I just use a 4-40 screw and nut, but I will be using a larger heatsink now that comes in 2 models- one with solderable pins and one without.

I'm trying to figure out if there is a reason why I should choose the model with the solderable pins.
 

bertus

Joined Apr 5, 2008
19,944
Hello,

I see you have a second thread open:
http://forum.allaboutcircuits.com/showthread.php?t=26210

The mounting pins are mainly for mechanical stability.
Often the mounting pins are twisted or bend through the PCB for more fixing stability.
The weight of the heatsink can be spead over the mounting pins and the transistor-pins.
Without the mounting pins the transistor-pins will carry the load.

Greetings,
Bertus
 

Thread Starter

jwilli

Joined Apr 21, 2009
42
Yes, I found a different heatsink that I am thinking of using. 55 deg c @ 6w. My main concern about the pins is when the heatsink gets hot, does a lot of heat transfer through the pins directly in/onto the PCB?...
 

bertus

Joined Apr 5, 2008
19,944
Hello,

There are different approaches on the use of the mounting pins.
Some people just make a couple of small lands for soldering the pins in ( the PCB will thermally isolate the heatsink from the rest ).
Some people make holes in the grounding area for soldering the mounting pins ( in the hope some heat will spread in the grounding copper ).

The type of PCB used is also of influency on the durability.
A PCB made of pertinax ( a kind of pressed paper ) will turn black after some time it has been exposed to heat.
A PCB made of glassfiber will stand the heat a much longer time ( it will turn brown afther some time ).

Here is some general information on the use of heatsinks from ESP.
http://sound.westhost.com/heatsinks.htm

Greetings,
Bertus
 
Last edited:

jj_alukkas

Joined Jan 8, 2009
753
If you are using the heatsink on a device that dissipates a lot of heat, (like those which burn your finger when you touch it), it is better to use a heatsink which doesn't touch the PCB as almost all PCB's turn black or brown after a few cycles of usage and then breaks of the PCB with a bit pressure. Cooler devices are safe to be soldered but it is recommended as a quality standard to avoid devices having heatsinks soldered. Increases the reliability a lot.
One main issue with soldering is that after the PCB gets heated up after quite a while, the tracks come off the board and ruin the whole board.
 

Thread Starter

jwilli

Joined Apr 21, 2009
42
If you are using the heatsink on a device that dissipates a lot of heat, (like those which burn your finger when you touch it), it is better to use a heatsink which doesn't touch the PCB as almost all PCB's turn black or brown after a few cycles of usage and then breaks of the PCB with a bit pressure. Cooler devices are safe to be soldered but it is recommended as a quality standard to avoid devices having heatsinks soldered. Increases the reliability a lot.
One main issue with soldering is that after the PCB gets heated up after quite a while, the tracks come off the board and ruin the whole board.
That's exactly my concern... thanks for pointing that out.

The TO-220 is definately hot to the touch so the heatsink will be dissipating a lot of heat. I wonder if there is any other way to increase the stability of the heatsink and take some of the pressure off of the TO-220 legs without having to solder heatsink pins down on the board...
 

Thread Starter

jwilli

Joined Apr 21, 2009
42
Hello,

To keep the themperature lower, you could take a larger heatsink.
This is an example of a larger one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HS380-ND

The material is much heavier then the one you named in the other thread.

Greetings,
Bertus
Well, that was an example of a heatsink that I might be able to turn backwards so the protrusion is facing the opposite direction. I updated my circuit board layout and made room for this heatsink:

http://mouser.com/Search/ProductDetail.aspx?R=637-20ABPvirtualkey56720000virtualkey567-637-20ABP

It is more fitting for my application, only I was curious whether or not to solder the pins onto my PCB.
 

jj_alukkas

Joined Jan 8, 2009
753
There are many options. You can use a larger heatsink or if you have a metal case, you can screw the chip to the body instead of using a heatsink or if you want the best of both, use whatever heatsink you need and screw it to the PCB with good heat insulators like bakelite or ceramics.
 
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