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DirectFET®; MOSFET: Thermal Engineer

System Thermal Anatomy


DirectFET MOSFET v. PowerPack & SO-8
Top & Bottom Side Thermal Resistance

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DirectFET MOSFET vs. SO-8
(Rth-ja)

Thermal Interface Material (TIM)

Interface Materials Features Thermal Conductivity
W/m-K
Thickness (mil) Imax (amp)
GPA3000 Highly conductive gap filler
polymer laminate
3 20 105.9
15 104.9
SPA2000 Sil-Pad, thermally conductive
silicon elastomer
3.5 15 96.9
GPVO, Ultra Soft Highly conformable
used for uneven surface
1 20 97.9
40 95.9
Bond Ply 100 Double sided tapewith bond strength 0.8 8 92.9



Heat Sink Mounting


Temp Cycle Performance

Material Class Description
Benefits Drawbacks
Grease These are the traditional TIMs filled with conductive particles of Al2O3, BeO, Al, Ag, etc.
Can achieve very thin bondlines <0.0005" Difficult to apply to pre-apply to assemblies
Messy
Typically pumps out, effecting long-term reliability
Requires controlled dispensing
No electrical isolation
Gel Grease replacement that cross-links during cure to form a gel-like substance.
Can achieve very thin bondlines <0.005”
Does not pump out
Cannot be preapplied to assemblies
Requires cure which can be from burn-in
Messy
Requires controlled dispensing
Adhesive Heat cured adhesives filled with conductive particles similar to grease.
Can achieve very thin bondlines <0.005”
Mechanical and thermal attach
Cannot be preapplied
Typically requires process oven curing
Messy
Requires controlled dispensing
Typically no electrical isolation
Tape Usually pressure sensitive adhesive filled with conductive particles on a fiberglass or plastic carrier.
Mechanical and thermal attach
Can be die cut and preapplied
Clean, simple processing
Typically electrical isolating
Typically thick bondlines with low thermal conductivity
Phase Change A waxy type material that changes to a gel at approximately 50 C allowing it to conform to surface irregularities. Can be preapplied or supplied on a carrier.
Can achieve very thin bondlines <0.005” when preapplied
Fairly clean process
With carrier has electrical isolation
Typically low thermal conductivity
The phase change material itself is usually very thin and does not conform to large irregularities
Pads Typically thick materials 0.010”-0.250” thick. Some are very compliant with a low K and others are not very compliant with a reasonably high K.
Simple to use
Can typically be re-used
Can be die cut and preapplied
Clean process
Typically requires moderate to high pressures to achieve reasonable performance - can be tricky to use effectively
Typically do not conform well to small surface irregularities
Thick bondlines

Material Class Bulk K Surface Wetting Surface Conforming Vendors
Grease 0.3-2W/mK Al Filled 6+ Very Good Very Good Hi-K Grease
Shinetsu
Bergquist
Gel 0.3-2W/mK Very Good Very Good Thermoset-Lord MG Series
Adhesive 0.3-1.3W/mK Very Good Very Good Dow Corning
3M
Tape 0.7-1.5W/mK Moderate Poor Bergquist
3M
Dow Corning
Phase Change 0.8-1.5W/mK Very Good Very Good for irregularities <0.002"
Very Poor for large irregularities or bowing
Bergquist
3M
Dow Corning
Pads 0.8-4W/mK Poor Very Good for large irregularities
Very Poor for small irregularities
Bergquist
3M
Dow Corning


IR’s proprietary DirectFET®; technology is covered by US Patent 6,624,522 and other US and foreign pending patent applications.

 
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