I'm not sure how you would secure the heatsink and thermal pad without using screws anyway. Some thermal pads are sticky, but your surface area is going to be irregular so I don't think it will hold on its own.
Drilling holes: you would have to first confirm that it's only a two-layer board. Hold it up to the light and look through it, see if its opaque (multilayer with ground planes) or semi-transparent (2 layer). After confirming there are no hidden secrets inside the layers: choose a convenient spot on the pads near the end of each resistor and very gently drill (you don't want to risk removing the pad or damaging the resistors).
It might be easier/better to solder heatsinks on.
EDIT: After some thought: your issue is with the caps nearby, not the resistors themselves? In that case adding heatsinks probably won't help, you likely need airflow.
I previously modified a old warm audio amplifier that I wanted to last longer by adding a 120mm fan and running it on a lower voltage (so it was silent). Any passively cooled amp will run dramatically cooler if you do this, even a tiny amount of forced airflow is much bigger than passive convection in a small case.
Is this the material you're talking about?
https://www.digikey.com/en/products/detail/cui-devices/SF100-202005/9805509
Is this the material you're talking about?
https://www.digikey.com/en/products/detail/cui-devices/SF100-202005/9805509
No, that's just a thin insulator pad for mounting transistors and such. The stuff I'm talking about is much thicker, 5mm or more in some cases.
Thanks, I ended up purchasing these instead:
https://www.digikey.com/en/products/detail/t-global-technology/TG-A6200-30-30-1-5/11617042
The resistors are 3x7mm, with the leads less than 0.5mm above the resistor body. Isn't 5mm at this scale too thick?
It's for a one off modification. I'm trying to add some life to my amplifier. Accessing the other side of the PCB is a last resort. Can you tell me more about drilling holes and using fasteners as the heatsinks? I haven't drilled through a PCB before. Are you implying the thermal pad and heatsink combo are ineffective? The heat sink volume is 8x8x8mm^3. I'm guessing worst case scenario is the heatsinks and thermal pad are easy enough to remove.
If there is no airflow: I don't think replacing the resistors with through-hole axials or adding heatsinks will make the nearby capacitors any cooler. The heat has to go somewhere, and without airflow it will just diffuse into nearby objects just the same regardless of what heatsink you use.
If there is no airflow: I don't think replacing the resistors with through-hole axials or adding heatsinks will make the nearby capacitors any cooler. The heat has to go somewhere, and without airflow it will just diffuse into nearby objects just the same regardless of what heatsink you use.
You need to take the heat away from the local area where the capacitors are. Forced airflow works, as would a very long heatsink/heatpipe that takes it somewhere else (eg all the way to the metal chassis).
If there is no airflow: I don't think replacing the resistors with through-hole axials or adding heatsinks will make the nearby capacitors any cooler. The heat has to go somewhere, and without airflow it will just diffuse into nearby objects just the same regardless of what heatsink you use.
You need to take the heat away from the local area where the capacitors are. Forced airflow works, as would a very long heatsink/heatpipe that takes it somewhere else (eg all the way to the metal chassis).
If there is no airflow: I don't think replacing the resistors with through-hole axials or adding heatsinks will make the nearby capacitors any cooler. The heat has to go somewhere, and without airflow it will just diffuse into nearby objects just the same regardless of what heatsink you use.
You need to take the heat away from the local area where the capacitors are. Forced airflow works, as would a very long heatsink/heatpipe that takes it somewhere else (eg all the way to the metal chassis).There is always airflow even if the case is totally enclosed there will still be internal convective currents carrying the heat away from the hotter components to distribute it throughout the case before that heat is lost through the sides of the case. The overall average temperature within the case will be the same as there is still the same amount of heat generated but the hot-spots will not be quite as severe adjacent to the sensitive components.
The advantage of using THT components in this case is that more of the heat is carried away by convection and less through the leads and into the PCB. Having less heat transferred through the leads means that there is less heat conducted through the tracks and laminate to adjacent heat sensitive components such as the electrolytics.
There is always airflow even if the case is totally enclosed there will still be internal convective currents carrying the heat away from the hotter components to distribute it throughout the case before that heat is lost through the sides of the case. The overall average temperature within the case will be the same as there is still the same amount of heat generated but the hot-spots will not be quite as severe adjacent to the sensitive components.
The advantage of using THT components in this case is that more of the heat is carried away by convection and less through the leads and into the PCB. Having less heat transferred through the leads means that there is less heat conducted through the tracks and laminate to adjacent heat sensitive components such as the electrolytics.
Also if the caps are in low-ripple bus i.e. they don't self-heat much and all the heat is from resistors, you can try shielding the caps. You could try a small piece of reflective aluminum tape just on the resistor side of the caps, but not on the opposite side. Remember that the aluminum tape will prevent both absorbing (incoming) thermal radiation but also prevent radiative cooling, this is why you use it only on the hot side, and it's no good if the capacitor itself runs hot because then it will reduce the cooling.
Aluminum tape will almost completely drop the radiation component to zero, of course doing nothing to thermal conduction by air. But if the resistors are running very hot, say like 100degC surface temperature, radiative part can be pretty large.