Heat sink + a shunt copper tape. Why shunt copper not equal to heat sink temp?

[zhiling0229]

Hi everyone,

I'm working on a project where the processor is attached to a copper tape about 8cm long where it sticks from 1 end of the processor case to the other while remaining length was insulated with a cardboard. the other end was slightly exposed for temperature measurement

The exposed copper tape on the processor is connected to a heatsink. (i.e processor case -> copper tape -> heat sink)

The strange thing is the copper tape is at ambient temperature when i force the heat sink fan to stop running but the heat sink itself is heating up.

I have done:

1. applied thermal grease on the copper tape and heat sink
2. remove any sticker residue on the tape so is only pure copper.

Is this a normal phenomena, if yes could you advice how does this relates to the theory of conductivity?

Thank you in advance

 

[Mech_Engineer]

The exposed copper tape on the processor is connected to a heatsink. (i.e processor case -> copper tape -> heat sink)

The strange thing is the copper tape is at ambient temperature when i force the heat sink fan to stop running but the heat sink itself is heating up.

Sounds to me like there was an error in your data collection, because unless the hetasink is generating heat on its own, it has to be conducting through your intermediate component.

I'd suggest taking your temperature data again, making sure your data collection equipment is properly calibrated and attached.

 

[MRFMengineer]

How close to the heatsink are your measuring the tape temperature?

 

[zhiling0229]

Thanks for the response. I think there is something wrong too and rechecking my setup and calibration.

The length of the copper tape is approximately 8cm I have insulated the exposed area with cardboard. Can it be due to the heat loss when it travel across the 8cm length?

 

[MRFMengineer]

Well, you could test your hypothesis with a temperature measurement at the start and at the end of the tape.

 

[Mech_Engineer]

Heat flows from hot to cold- so if your heatsink is hotter than the copper strip this means the heatsink is actually being cooled by the tape rather than visa-versa.

Check your setup first, and make sure your data collection is set up properly.

 

[Unrest]

The strange thing is the copper tape is at ambient temperature when i force the heat sink fan to stop running but the heat sink itself is heating up.

The tape will be losing heat all over its surface, despite insulation. This small heat loss can cause a large temperature gradient along its length because it has a high thermal resistance (very thin).

Use a thicker or shorter "tape" so that its thermal conductance is large compared to the heat loss from its surface.

 

[Mech_Engineer]

The tape will be losing heat all over its surface, despite insulation. This small heat loss can cause a large temperature gradient along its length because it has a high thermal resistance (very thin).

Use a thicker or shorter "tape" so that its thermal conductance is large compared to the heat loss from its surface.

None of this addresses the fact that his heatsink is apparently hotter than the tape going to it...

 

[Unrest]

None of this addresses the fact that his heatsink is apparently hotter than the tape going to it...

The OP was a bit unclear (can you clarify, Zhiling?). But it sounds like the tape is sandwiched between the heatsink and the processor, with an extra length hanging off the end, connected to a temperature sensor. In that case it's reasonable for the heatsink to be hotter than the free end of the tape.