Best way to stick a sensor to the top of an IC

Question

I've been looking around for the right search terms to use to find out how to stick a thermistor to the top of a 6mmx8mm chip (approx).

I have plenty of Kapton tape so I could use that, but I'd have to stretch it across multiple parts to get it to stick - I know it's non-conductive but still. And frankly, it's not that sticky really either - I don't want to be opening a case to keep re-applying tape. Is there some useful cement or sticky stuff that I could use - maybe something that I could remove the sensor without damaging anything if I wanted to but was secure enough to last. At the moment I have it held in place with some blu-tack at the edge of the board but it's not really resting properly on the IC.

Gough Lui · Accepted Answer

Try Thermally Conductive Adhesives category - e.g. in element14 Australia: https://au.element14.com/c/chemicals-adhesives/adhesives-glues/thermally-conductive-adhesives/prl/results

Jan Cumps · Answer

thermal (conducting) cement like used to fix a heatsink?

jw0752 · Answer

This is just an idea. Perhaps you can tack a flattened copper wire to the chips ground terminal and loop it over the top to retain the thermistor. I would also use some heat sink compound to make a better heat channel between the IC and the thermistor.

John

michaelkellett · Answer

The heatsink will give you precious little idea of the actual chip temperature. The plastic of the package has a big thermal resistance from chip to surface - when you stick a heatsink to that several things happen, the chip is cooled (so your measurement technique has changed things) but the heat flow though the chip package to the surface is increased so the difference in temperature is increased. I've found the best way is to glue the sensor to the chip, normally I use quick set epoxy - it's much cheaper than thermally conductive and easier to use. If the sensor is small compared with the chip you are measuring the normal stuff works fine. If the sensor is big (like yours in the picture) it will affect the chip temperature. You can get smaller thermistors or you could use a thermocouple (cheap and tiny but you need something that can use it.) You can also get very small platinum resistance sensors which can be read with a DMM - the chip like ones are easy to glue to things. Farnell have 2775588 (about 2mm square)which is about £2.12 but US stock only (so a £15 surcharge if you are in the wrong place !) MK

Andrew J · Answer

The idea is a clever one John, but I think the springiness of the thermistor's wire would require quite a chunky piece of copper. Also, and you wouldn't know this of course, that pin labelled ground is actually a 'Gate' - the chip is a Mosfet, so no ground! I was hoping that there was a special substance that could do this acting as heat sink compound but I don't know what it might be called to search for. What I have found, is that if I were to use normal heat sink compound on anything, Kapton tape and tack won't stick at all.

jw0752 · Answer

In the old days they used to use a contact glue much like that used to glue linoleum to the floor to secure thermistors to output transistors in amplifiers. This was a long time ago and I would hope the technology has improved. Now days I suspect they design a thermistor right into the IC if one is needed. Also if there is no ground pad on the IC perhaps there is one nearby on the circuit that can be used.

John

msebok · Answer

what about mounting a small cooler to the chip and wedging the thermister between the fins? (the PI comes with small coolers that have sticky stuff on them, and my cooler has not come off yet?)

Best way to stick a sensor to the top of an IC

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