TO-220 Heatsinks & Potential Mounting Pin Issues

Discussion in 'The Projects Forum' started by jwilli, Aug 1, 2009.

  1. jwilli

    Thread Starter Active Member

    Apr 21, 2009
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    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.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    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
     
  3. jwilli

    Thread Starter Active Member

    Apr 21, 2009
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    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?...
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,645
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    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: Aug 1, 2009
  5. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    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.
     
  6. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    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...
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. jwilli

    Thread Starter Active Member

    Apr 21, 2009
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    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.
     
  9. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    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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