There are a variety of thermal pads and gap fillers to choose from -- so many choices that it can become so overwhelming. How can you decide what's best for your application? And how does quality come into play? Read on, we answer these questions and much more.
Back to the basics: what are thermal gap fillers?
Thermal interface materials are used to improve performance and reliability of electronic devices by dissipating heat from a heat source to a heat sink. Both the semiconductor component and the mating heat spreader inherently have uneven surfaces.
The contact area can consist of more than 90% air voids, representing a significant resistance to heat flow. Thermally conductive gap fillers are used to eliminate these air gaps by conforming to the rough and uneven mating surfaces of both the heat sink and the semiconductor.
THERM-A-GAPTM gap fillers are a family of soft, thermally conductive silicone elastomers for applications where heat must be conducted over a large and/or variant gap, always between a semiconductor component and a heat dissipating surface. Gap fillers are supplied either in pad-form which can cover a wide range of thickness (0.25mm to 5mm), or as fully cured dispensable gels.
How to identify quality thermal gap fillers in four steps (summary):
- Thermal performance
- Low mechanical stress
- Assembly
- Reliability
Now, let's review each step in more detail.
Step 1: Identify thermal performance
First, it's a good idea to Identify the amount of heat [Watts] that you need to dissipate to determine the thermal conductivity performance of a gap filler. This is usually displayed in Watts per meter Kelvin, or W/m-K. The higher the number, the more heat the material can theoretically dissipate. Gap filler materials offer a high tack surface which reduces contact resistance.
Step 2: Choose low mechanical stress
Generally speaking, the softer the gap filler, the better it is at filling voids and surface irregularities under low pressure. You can tell the hardness of the gap filler as it's usually measured in Shore A or Shore 00. The lower the hardness rating, the softer the material. Gap pads and gels are also good at absorbing shock and vibration to help with reliability.
Step 3: What's my assembly?
Gap filler pads are offered on a variety of carriers for ease of assembly and end-use. They include:
- Aluminum foil – includes high strength pressure sensitive adhesive (PSA) for permanent attachment
- Fiberglass carrier – ease of rework, allows for the pad to be removed
- Polyimide carrier – ideal for sliding across substrate
Thermal gap filling gels are single-component products that require no mixing or refrigeration, and can be dispensed directly on to parts.
Step 4: Make sure there's reliability data
THERM-A-GAPTM products have been examined for physical and thermal reliability after being subjected to multiple environmental stress tests (elevated temperature, random vibration, heat and humidity, etc.) with varying gap thickness. The results have indicated superior long-term physical integrity and thermal reliability. Discover these test reports for THERM-A-GAP G579 and THERM-A-GAP GEL30 now.
This blog was contributed by Callie King, applications engineer, Parker Chomerics Division.
Related content:
The Benefits of Thermally Conductive, Fully Cured Dispensable Gel
The Difference Between Thermal Conductivity and Thermal Impedance
Selecting a Thermal Management System Supplier for Aerospace and Defense Applications