Replace thermal grease by solder paste

  • Again and again, i had problems to remove the fragile heatbreak out of the cold end heat sink because the thermal grease was old and glued everything together.

    To overcome this annoying problem, a couple of months ago i started to replace the thermal grease by solder paste.

    The advantages are:

    • it doesn´t matter how old it is, when heated, the metal (solder) will melt;)

    • the thermal heat transfer can only be better

    • nearby as easy to use as thermal grease

    • can be stored for a very long time

    For the cold end, i use a Sn42/Bi58 solder paste with a melting point of 138 °C, so it is no problem to apply it with a heat gun.

    Because the cold end worked fine, the next step was clear, the hot end. At the hot end my experience is, that it is just a matter of time (number of heat up and cool down cycles) until a hot end starts to leak - and yes, i know how to mount a nozzle….

    I started with normal Sn63/Pb37 or 60/40 which melts at about 180-200 °C. In principle, it worked. But because the metal melts < 250 °C, i could squeeze it out, when (for testing) i did lose the nozzle to make a gap between the heatbreak and the nozzle. Because there are other solder pastes available, i tried Sn97Cu3, which melts at about 227-310 °C. It is not needed to heat everything up to 310 °C, 270-280 should be enough to apply it. There are also other solder pastes available which melt around 220-230 °C, which i did not try.

    I print at < 250 °C, so Sn97Cu3 is rock solid and not oozing even with a gap between nozzle and heatbreak. Beside this, the thermal heat transfer is for sure also not worse - but this won´t be significant.

    If somebody wants to try also, it is easy, buy a solder paste, apply it with gloves as it would be a thermal grease, take care not to put it somewhere it should not be (like for normal thermal grease), screw everything together in place (you don´t need to care if the paste is squeezed out), heat it up with your hot end or hot air gun, wait until the flux cooks and the “smoke” is gone and wipe or shake (protect your eyes) too much solder just away. Even Sn97Cu3 is not toxic, the flux of the paste is, so always avoid any skin contact and so on.
    At the very 1st time applying the solder paste one might want to do it twice because the 1st time the solder might not “wet” the surface good enough.

    This process has nothing to do with real “soldering”, it is just gap filling with metal, but it does what it should !

    Solder pastes (especially for this purpose) can be stored in the fridge or even being frozen, to keep them working over a long time - i didn't try that with thermal grease, but i have a bunch of unusable old thermal grease tubes….

  • Interesting idea. I use copper grease and find this helps with conduction and dismantling. Smokes a bit when it's first heated up but it's safe up to 1200 deg C.

  • administrators

    Perhaps you just haven't found the right thermal grease? I use Arctic Silver on the cold end because I happen to have some left over, and I have never had a problem removing the heat break from the heatsink. I don't use anything on the heater block end, but if I did then I would choose copper grease.

  • @DjDemonD:

    Interesting idea. I use copper grease

    Thats a damn good idea; I just spent quite a bit of money on a very small tube of thermal paste; while there is a half-used tub of copperslip in my toolbox. Humm.

  • Just don't use it between heatbreak and heater block. I use it on nozzles heater cartridges, and thermistors/pt100s. There's a guy on ebay who sells little pots of it which are very handy and you barely use any at all.

  • @dc42: thanks for the advice. i have used several "aliexpress" and similar whatever it is thermal grease, they are for sure not the best ones. But also whenever i had to dismantle CPUs and so on the same story… the thermal grease is hard and glued everything together.

    @DjDemonD: that is also very interesting, how much temperature does this copper grease need to melt ? I think it cannot melt (cu melts at about 1100 °C) or is there something else, it will just separate the parts or ? In my case i had solder pastes in stock, so i just tried it...

  • administrators

    The copper isn't supposed to melt.

  • It burns off the solvent base on first heating up, so you'll see some smoke, probably best not to have naked flames around for the first few seconds. After that the copper sits in the joint providing I suspect some thermal conductivity advantage, but mainly enabling the part to be unscrewed later without excessive force being required.

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