Dx Blame MKIII-Hx - Builder's thread

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AndrewT

R.I.P.
Joined 2004
The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.
 
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A

AndrewT

R.I.P.
Joined 2004
MagicBox said:
What a space, what an opportunity to spread the transistors physically!.................a better buffer for thermal transients.
Click to expand...
The PCB is done. It fixes the devices in a tight group.
Looks like it is designed for blown tunnel cooling. At the maximum power expected they are more like PA amplifier PCBs, where blown cooling is the norm.
 
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M

MagicBox

Member
Joined 2011
AndrewT said:
the PCB is done. It fixes the devices in a tight group.
Looks like it is designed for blown tunnel cooling. At the maximum power expected they are more like PA amplifier PCBs, where blown cooling is the norm.
Click to expand...

Ah, with active cooling it's less of a concern yes :) I just didn't get that from the chosen heatsink - if it would have been these high-density fin designs I'd have assumed active cooling.
 
meanman1964

meanman1964

Member
Joined 2006
AndrewT said:
The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.
Click to expand...

Yes Andrew it is coated with a compound on both sides.I do use them very often.
 
meanman1964

meanman1964

Member
Joined 2006
AndrewT said:
Your concern is valid.
The PCB is designed for tunnel cooling, if high power must be dissipated.
That tall heatsink is quite unsuited to obtaining good heat dissipation efficiency with the PCB.
Click to expand...

I will use this sink
 

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J

Junie

Member
Joined 2010
AndrewT said:
The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.
Click to expand...

Andrew it's not a Kapton it's a Sil-pads, here's what it says:

Sil-pads come in a few different varieties. The most common is a silicone rubber material reinforced with fiberglass. A different version has 2 thin silicone rubber layers sandwiching a layer of polyimide film. Many manufacturers use sil pads because they don't require grease to perform to spec (which makes assembly quicker and easier).
 
a.wayne

a.wayne

Member
Joined 2008
meanman1964 said:
I will use this sink
Click to expand...

Nice setup for fans, fans will not work for me due to the noise, i will have a fan to cool the case if temps escalate , but only for those brief moments. Also i do not like the heat concentration such a setup creates ....

Junie said:
Andrew it's not a Kapton it's a Sil-pads, here's what it says:

Sil-pads come in a few different varieties. The most common is a silicone rubber material reinforced with fiberglass. A different version has 2 thin silicone rubber layers sandwiching a layer of polyimide film. Many manufacturers use sil pads because they don't require grease to perform to spec (which makes assembly quicker and easier).
Click to expand...

Thanks for that tid bit junie ....
 
a.wayne

a.wayne

Member
Joined 2008
Meanman,

I don't believe that setup at low speed with such a small sink will cool the outputs at such a load, well from past experience. Anyway such a setup was not an option for me , i needed a tall case and did not want a fan running constantly.


Why not the big sinks, it's not unprecedented ..?


regards,
 
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M

MagicBox

Member
Joined 2011
They're nice heatsinks. I plan to passively cool my amp as well, they'll be reasonably big at approximately 0.0135 K/W. They will form the sides of the case and the PCB will be designed to be mounted to the back of the heatink. All TO220 semis along with the outputs will be cooled by it.
 
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