One of the perennial problems of the amplifier builder is keeping those power semiconductors cool. All the heat goes out the flat face of the power device to the heatsink., and it is a bottleneck that if it isn't performing properly then all the heatsink in the world isn't going to help you. I myself am a believer of directly connecting the power semi to heatsink wherever possible, and running live heatsinks as a consequence. This gets rid of the insulating washer and improves things quite a bit. Another must is to have a flat heatsink surface so the heatsink paste can be squeezed into the thinnest layer possible. Then just today I was looking at the back of some TO-247 shape devices and some were shiny and some were matte finish. I thought the shiny ones would be almost perfectly flat, but when I looked in the reflection they were far from it. I couldn't really tell with the matte ones.
Then I got this idea: I got some 1200 grade wet and dry sandpaper - really fine stuff - and laid it on a good flat surface and then ran water from a tap continually across it. Then I got one of my trusty hexfets and rubbed the rear surface across the sandpaper. Straight away I could see just how un-flat it's surface was; the high and low spots were obvious. I continued for about a minute and then used somewhat less pressure and it really began to smooth out and felt like it was gliding across oil. Important to have plenty of water flowing. Maybe underwater would be a good method. Anyway, pulled the fet out and had a look and it had an almost perfect mirror finish! Copper colour too. Really cool it looked, it did.
I did a similar thing with the copper block that the fet is going to go onto and now the pair have a noticeable suction between them when you draw them apart. Any thermal paste I now put between them will be squished into the thinnest layer imagineable and therefore offer the least thermal resistance.
That's the good thing about diy - there are almost endless tweaks to do that commercial manufacturers for the most part don't bother with because they only want to satisfy the masses.
GP.
Then I got this idea: I got some 1200 grade wet and dry sandpaper - really fine stuff - and laid it on a good flat surface and then ran water from a tap continually across it. Then I got one of my trusty hexfets and rubbed the rear surface across the sandpaper. Straight away I could see just how un-flat it's surface was; the high and low spots were obvious. I continued for about a minute and then used somewhat less pressure and it really began to smooth out and felt like it was gliding across oil. Important to have plenty of water flowing. Maybe underwater would be a good method. Anyway, pulled the fet out and had a look and it had an almost perfect mirror finish! Copper colour too. Really cool it looked, it did.
I did a similar thing with the copper block that the fet is going to go onto and now the pair have a noticeable suction between them when you draw them apart. Any thermal paste I now put between them will be squished into the thinnest layer imagineable and therefore offer the least thermal resistance.
That's the good thing about diy - there are almost endless tweaks to do that commercial manufacturers for the most part don't bother with because they only want to satisfy the masses.
GP.