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Thermal Interface Materials 101

June 20, 2019

 

Thermal management of electronics has become increasingly important. Heat is created when an electronic device is in use, and left unmanaged can result in damaging the device. That’s why keeping devices cool is crucial in the overall performance of a device. To help pull the heat away, thermally conductive interface material can be used. A thermally conductive interface material is placed between an electrical component and a heat spreader and/or heat sink to dissipate the heat generated away from the unit.

When choosing what thermal interface material to work with you can choose from thermally conductive tapes, interface pads, epoxies, or greases. What product you choose is dependent on the application. We’ll take a deeper dive into the different thermal management materials and applications where they work best.

Start with asking the right questions.

  1. How hot will the device get?
  2. What EMI challenges are we facing?
  3. Can I combine different solutions in this application?

Other considerations: 

  • Thermal conductivity and resistance
  • Viscosity
  • Ease of application
  • Mechanical properties of the material
  • Long term performance

Characteristics of Thermal Interface Materials

Thermal interface resistance occurs when there isn’t close contact between substrates. Starting with a smooth and clean substrate is an ideal way to begin. One way to combat resistance is by using a highly conformable material to help displace air once applied. Working with a thinner material can help combat resistance issues that may occur. A thicker material may work better if the material wets out, which leads to less air becoming trapped. Thermal interface material may include an adhesive on one, both, or neither sides. It can be made of either silicone or acrylic material and die cut or laser cut. When determining the correct thermal interface material, it’s important that what is chosen provides a thermal path, so the device can cool properly.

Thermal management materials help to protect electronic devices from the heat that is generated when in use. They help with:

Thermal conductivity– A material’s ability to conduct heat.

Conformability– Flexible material that can be used in most applications.

Dielectric strength– High performance materials combine efficient heat transfer with electrical isolation properties.

Versatility– Thermal pathway analysis leads to material selection and component configuration.

Efficiency– Incorporate effective assembly line component delivery methods.

Cost Effectiveness– Produced with sophisticated dispersion chemistry, these materials help our customers control production costs and improve uniformity, with important performance and durability benefits.

3M Thermally Conductive Interface Pads– Silicone and Acrylic: The materials are usually soft and squishy with the ability to conform to rough or uneven surfaces eliminating air gaps and limiting the amount of areas heat can accumulate.

Silicone Pads
Applications:

  • Integrated chip (IC) packaging heat conduction
  • Heat sink interface
  • Chip on film (COF) heat conduction
  • LED board thermal interface material (TIM)
  • HDTV integrated chip (IC)
  • General gap filling electronic device

Acrylic Pads
Applications:

  • Gap filling parts in electronic components
  • IC packaging heat conduction
  • Heat sink bonding
  • Chip head conduction
  • LED board TIM
  • HD TV address IC Chip and Scan Module Board
  • Non-silicone requirement

3M Thermally Conductive Greases– The grease has a low viscosity and is applied in thin layers to help with the transfer of thermal energy from heat source to heat sink. Ideal in applications that are flat and smooth.

Applications:

  • Thermal interface material for CPU
  • Thermal Interface material between heat sink and heat spreader for LED lighting

3M Thermally Conductive Interface Tapes-Are good for quick and easy applications.  Pressure sensitive adhesive (PSA) is used to bond it to a substrate. These tapes have good dielectric strength which makes them an excellent choice for heat sinks, heat spreaders and other cooling/heating devices. When choosing what tape would perform best it’s important to consider the following: substrate surface, the environment, contact resistance, material thickness and strength and assembly process.

Applications:

  • General heat sink bonding
  • IC chip packaging heat conduction
  • Printed circuit board
  • LED module/board bonding
  • Flat panel display assembly (e. g. LCD and PDP devices)
  • COF chip heat conduction
  • Mechanical fastening such as a clamp, bracket or screw can be used in parallel with this tape

3M Thermally Conductive Epoxies — Dispenses evenly and easily for a thin bond line. For a more secure bond, put a “fillet” at the ends. A fillet is extra product squeezed at the ends that adds to creating a more secure bond. The softer consistency of the epoxies makes it a messier application.

Applications:

  • LED Assembly
  • Thermal fixing battery cell and thermal management for EV/HEV battery
  • Potting applications
  • General gap filling

 

Technology Thermal

Conductivity vs. Air*

Pros Cons
Grease 20-185x Thin bond lines

Low cost

Good wetting

Messy

No adhesion (needs mechanical attachment)

Liquids 20-125x Thin bond line

High bond strength

Good wetting

Messy

Pot life of epoxy

Needs cure time

Phase Change 20-125x Good wet-out

Less messy than grease

Thin= Low Impedance

No adhesion (needs mechanical attach)

Needs initial heat cycle

Tapes 20-40x Good wet-out,

No mechanical fasteners

Ease of use

Typically, <10-15W applications
Pads 35-500x Greater thicknesses

Very soft/Conformable

Gap filling

Light adhesion

Need mechanical fastener

Cost

Solder/Liquid Metal 500-1000x Thin bond lines

High conductivity

Gap filling

Difficult to apply,

Low viscosity when melted, CTE , Cost

The Importance of Thermal Management for Electronics

Heat is the enemy of electronic components. It can compromise performance and cause premature failure. Severe thermal management problems arise when ever-greater speed and processing power is squeezed into smaller devices. High performance materials combine efficient heat transfer with electrical isolation properties. Produced with sophisticated dispersion chemistry, these materials help our customers control production costs and improve uniformity, with important performance and durability benefits.