AN-1035 Datasheet, PDF (8/42 Pages) International Rectifier – Application Note

Type
Grease
Gel
Adhesive
Tape
Phase
change
Pads
Description
Traditional form, filled with conductive
particles of Al2O3, BeO, Al or Ag
Thermal conductivity: 0.3–2.0 W/(m·K)
(up to 6 W/(m·K) for Al)
Vendors: Shinetsu, Bergquist
Grease replacement, cross-links in
curing to form a gel-like substance
Thermal conductivity: 0.3–2.0 W/(m·K)
Vendors: Thermoset (Lord MG series)
Advantages
Good surface conformance
Good surface wetting
Thin bonds (<0.005")
Good surface conformance
Good surface wetting
Thin bonds (<0.005")
Does not leak out over time
Heat-cured and filled with conductive
particles similar to grease
Thermal conductivity: 0.3–1.3 W/(m·K)
Vendors: Dow Corning, 3M
Good surface conformance
Good surface wetting
Thin bonds (<0.005")
Mechanical attachment
Pressure-sensitive and adhesive-filled, Moderate surface wetting
with conductive particles on a fibreglass Mechanical attachment
or plastic carrier
Can be die-cut and pre-applied
Thermal conductivity: 0.7–1.5 W/(m·K) _{Clean and simple processing}
Vendors: Bergquist, Dow Corning, 3M _{Electrical isolation}
Waxy material, changes to a gel at
Good surface conformance for
about 50°C
irregularities < 0.002"
Thermal conductivity: 0.8–1.5 W/(m·K) Good surface wetting
Vendors: Bergquist, Dow Corning, 3M Clean processing
Can be pre-applied or on a carrier
Thin bonds (<0.005") (if pre-applied)
Electrical isolation (if on carrier)
Thickness: 0.010–0.250"
Thermal conductivity: 0.8–4.0 W/(m·K)
Vendors: Bergquist, Dow Corning, 3M
Good surface conformance for large
irregularities
Simple to use
Can be reused
Can be die-cut and pre-applied
Clean processing
Disadvantages
Difficult to pre-apply
Messy processing
Can leak out over time
Needs controlled dispensation
No electrical isolation
Cannot be pre-applied
Needs curing (can be from burn-in)
Messy processing
Needs controlled dispensation
No electrical isolation
Cannot be pre-applied
Needs curing (can be from burn-in)
Messy processing
Needs controlled dispensation
No electrical isolation
Poor surface conformance
Thick bonds
Poor surface conformance for large
irregularities and bowing
Poor surface conformance for small
irregularities
Poor wetting
Thick bonds
Pressure required to fit pads can make
them difficult to use effectively
If excess TIM is applied, this can flow under the
DirectFET device. Thermal expansion can then break
the device-substrate joints. In Figure 15, a heatsink
has been removed with floss to show that excess
heatsink adhesive has spread across the substrate. It
has covered the devices and sealed their sides.
In Figure 16, a cross-section reveals that the adhesive
has flowed under the DirectFET devices. It has filled
the gap between substrate, die and device body.
Figure 16 Heatsink adhesive under devices
Figure 15 Excess heatsink adhesive covering devices
DirectFET^® Technology
www.irf.com
AN-1035
Version 28 (revision history), April 2016
Board Mounting Application Note
Page 8 of 42