Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Craig Holloway

#12358

Thermal Interface Materials | 10 March, 1999

Looking for advice/products on ways to get heat out of a package and into an internal thermal plane. Will have electrically isolated thermal pads (going to an internal thermal plane) under the part.

Need a way to get good thermal contact between part bottom of part an these thermal pads. Have considered thermally conductive epoxies but have not found any with decent conductivity (all are ~<1.2W/mK). It is not clear on how a thermally conductive elastomer pad could be used in conjuction with assembly for vapor phase (what elastomer thickness would you use to avoid having the leads lift - and how do you maintain compression to assure good conductivity during soldering)?

Thanks,

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P.L. Sorenson - Technical Consultant

#12359

Re: Thermal Interface Materials | 11 March, 1999

| Looking for advice/products on ways to get heat out of a package and into an internal thermal plane. Will have electrically isolated thermal pads (going to an internal thermal plane) under the part. | | Need a way to get good thermal contact between part bottom of part an these thermal pads. Have considered thermally conductive epoxies but have not found any with decent conductivity (all are ~<1.2W/mK). It is not clear on how a thermally conductive elastomer pad could be used in conjuction with assembly for vapor phase (what elastomer thickness would you use to avoid having the leads lift - and how do you maintain compression to assure good conductivity during soldering)? | | Thanks, | I have used aluminum core PWBs for power supply applications. These boards were designed and procured with the board materials under the power components machined away. Thermally conductive epoxy was used under the parts. Although these materials are relatively poor conductors compared to metal, they are excellent conductors compared to air. The main purpose of the epoxy is to fill in the air gaps under the part. The film thickness of the epoxy is small and therefore the thermal resistance is small for the composit path.

Pete Sorenson

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