Thermal Interface Materials -Thermal Greases/ Thermal Gap Fillers

Thermal Interface Materials for Power LED heatsink

Thermal Greases is a traditional TIM material:

 Silicone-based paste format with a variety of fillers
 Typically applied in manual application or semi-automated process
 High-volume screen printing applications
• Typically viewed as lowest-cost TIM material of any kind.
• Referred to generally as “thermal paste”, “thermal compound”, “thermal grease”.
• User costing typically does not account for waste, clean-up, labor cost for
Application:
 Low material cost does not accurately describe total applied cost.
 Makes accurate cost comparisons to alternative TIM materials difficult.
 Bond line thickness generally predominates in thermal impedance performance, not filler material conductivity.
 Filler particle size is generally more critical than filler conductivity.
 High thermal conductivity fillers may result in higher thermal impedance, not lower.
 Development of a material with greatest ease of application may outweigh thermal impedance performance as the primary development target for many TIM2 applications.

Thermal Gap Fillers General statements: 

 Purpose of these materials is to fill a large air gap between a heat source and a convenient metal surface
 Relative high thickness precludes high performance relative to phase-change, thermal greases, LMAs, PSHs:
• Many materials available with modest thermal performance.
• Compressibility is an important determinant in material selection for a given
application
• Surfaces of gap-fillers may be tacky, to reduce interfacial resistance.
• Protection of surfaces with release liners prior to application is important to prevent dust, particulate accumulation.
• Application requirements are specific to individual material types.
• Very common for power LED applications:
 Luminaire lighting fixtures: heat transfer from LED baseplate to luminaire “can” for heat transfer to ambient air
 Very commonly used as TIM2 for projector light sources and other power LED
applications.

Compressibility is a key characteristic of Thermal gap-filler:

 Ability to deflect at low pressures
 Minimum pressure is important
 Relative high thermal conductivity is important because of the relatively thick nature
of a gap-filler
 Young’s Modulus of material is strongly affected by use of a high percentage of the high
thermal conductivity filler constituent.