Potting Compounds And Thermally Conductive Adhesives

Interview conducted by G.P. ThomasJul 24 2013

Rohit Ramnath, Technical Sales Representative for Master Bond Inc., introduces the concept of thermally conductive adhesives, how these can be utilised, and practical considerations that need to be taken into account.

Could you please give a brief overview of thermal adhesives and potting Compounds and their typical applications?

A wide range of thermally conductive adhesives and related potting compounds, including epoxy and silicone compounds are available on the market. In addition, thermally conductive epoxy films that address certain application issues are also available.

Thermally conductive systems offer a number of advantages owing to their range of capabilities. These systems can be employed in a wide range of applications, such as bonding, sealing, coating and encapsulation. They help improve heat transfer and some of them have excellent strength properties. Certain systems are also resistant to vibrations, mechanical shocks, thermal cycling and high temperatures.

What are some of the beneficial properties that thermally conductive products can provide?

Thermally conductive products provide a range of physical and mechanical properties, such as resistance to low and high temperatures, moisture and chemicals. Certain grades are available that are optimized for thermal cycling applications as well as for shock and vibration resistance. In addition, these products are available with different viscosities and cure rates as well as with different moduli that range from flexible to rigid.

Thermally conductive products are also developed as electrical insulators, which are essential when bonding or potting different types of electronic parts. In certain applications that require electrical and thermal conductivity, uniquely formulated adhesives are available that conduct both electric current and heat. Master Bond prepares certain grades of products that comply with NASA’s low outgassing specifications and/or USP Class VI biocompatibility standards.

How do you compensate for the fact that polymeric materials in their natural state have a low thermal conductivity?

Aluminum has around 200 W/mK of thermal conductivity when compared to unfilled epoxy, which has just 0.14 W/mK. However, formulators can increase the baseline thermal conductivity values of adhesives by a factor of 10 or more.

This can be done by adding different types of ceramic, metallic, or nano fillers. Although the resulting products may not have the conductivity of metals, they conduct sufficient heat to become an essential part of a thermal management system. In addition, thermal adhesives and potting compounds remove the thermally insulating air gaps that are present between heat transfer surfaces.

What range of thermal conductivity values do Master Bond products have generally possess?

Thermally conductive adhesives and related potting compounds offered by Master Bond have conductivity values between 1.5 and 3 W/mK. This range covers a large number of bonding and potting applications in commercial electronics.

In special cases, however, we are constantly researching the possibility of developing systems with thermal conductivity values 4 W/mK and above without significantly compromising the mechanical performance of the adhesive.

What is the relationship between thermal conductivity and bond strength?

When compared to a filled version of the same epoxy, the unfilled one might exhibit higher bond strength. This is because products that are highly filled tend to have less epoxy for bonding. The same logic applies to silicone products. However, this trade-off between thermal conductivity and bond strength is not a major issue in certain electronics applications. Silicones and epoxies, even when filled with thermally conductive additives, have sufficient bond strength to resist the forces seen by power dissipating components.

For instance, potted components endure some level of stress and strain during the production process, but they do not encounter the high forces that distinguish a true structural adhesive bond.

In certain applications, adhesive plays a structural and thermal management role. In such situations, engineers must check the aspect of strength/thermal conductivity trade-off and should take appropriate steps to design around it.

Could you provide examples of products that Master Bond formulates that can meet design application specifications for thermal management?

Master Bond offers the following products that have been tested and certified to meet NASA low outgassing standards:

• SUP10AOHT-LO: One component heat curing toughened epoxy is resistant to extreme temperatures. It is cryogenically serviceable
• FLM36-LO: B-staged heat curing film adhesive with exceptional thermal cycling resistance
• EP30AN-1: Two component room temperature curing epoxy with high thermal conductivity
• EP21TCHT-1: Two component room temperature curing epoxy is resistant to extreme temperatures. It is cryogenically serviceable

Some of the other thermally conductive products include:

• EP3HTSMED: One component heat curing silver filled epoxy is USP Class VI tested and has good thermal and electrical conductivity
• MS705TC: One component moisture curing silicone with outstanding flexibility
• Super Gel 9AO: Two component epoxy-urethane offers excellent flexibility
• MS151AO: Two component room temperature curing silicone with high temperature resistance

Master Bond offers thermally conductive adhesives and potting compounds that are used in a range of electronics applications. Master Bond is also exploring the possibility of making systems that have thermal conductivity values of 4 W/mK and above without affecting the adhesive’s mechanical performance.

About Rohit Ramnath

Rohit Ramnath is a Technical Sales Representative for Master Bond Inc., a custom formulated adhesives manufacturer. He analyzes application oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical and oil/chemical industries.

He graduated from Carnegie Mellon University with a masters degree in chemical engineering, where he wrote his thesis on analyzing drilling fluid emulsions for enhanced oil recovery.

His internships (with BASF and Rohm & Haas) and undergraduate experience (UDCT in India) have also been in the fields closely related to surface and interfacial science.