Indium metal has long been used for a variety of applications including low-temperature solder, cryogenic sealing, coatings for touch screens, and in fusible alloys. Most recently it has found its niche in thermal management, as a thermal interface material in electronic and other devices.
As components need more relief from the heat they generate, more people are discovering the versatility of indium in dissipating that energy.
I have recently taken on the responsibility of managing Indium's Heat-Spring® product line; and navigating a pretty significant learning curve. I want to share with you what I am learning along the way in my conversations with two of the Heat-Spring designers, Bob Jarrett and Jordan Ross.
To start with I needed to understand the origin of the product. Bob was able to help me. I found out that, like most of our projects, customer need was the initial driving force.
According to Bob, "The Heat-Spring concept came out of a joint program with one of our customers to develop a high-performance thermal interface material (TIM). Conventional polymer TIMs have inherent issues due to the low conductivity of the polymers and the thermal mismatch between the polymer and conductive fillers. The polymer TIM faces degradation due to pump-out, where the planarity of the interface changes during cycling - which squeezes the TIM material out of the space where it is needed. Also, migration of the polymer results in failure when the TIM dries out to the point where it is no longer pliable."
Great, now that we know the problem, how is this unique indium foil a solution?
Bob continued, "Indium foil offers a simple solution to these problems because it is highly conductive and highly conforming to the interface surfaces. Since it is a metal, it conducts heat (and electricity) with its electrons, so the thermal mismatch is not an issue. Polymers, semiconductors, and the ceramic filler of the polymer TIMs rely on lattice vibrations to conduct heat. If the vibration frequencies don't match up, heat transfer is interrupted at each interface within the TIM. Using a conductive metal (like indium) avoids that issue altogether."
Bob concluded, "The indium foil eliminates pump-out since it is solid. However, it doesn't flow between the mating surfaces like a liquid or gel does. To overcome this conformability issue, we came up with several options - with the most exciting one being a patterned foil ... and the Heat-Spring was born. The Heat-Spring patterning consists of an array of deformed material that is thicker than the average in some places and thinner in others. The thicker spots make intimate contact between the two interface surfaces. Plastic deformation is essentially the same as a solder joint. These points of contact draw heat through the bulk of the metal foil, which also serves as a local heat spreader as a bonus! This approach was so unique that Craig Merritt (an Indium Manufacturing Engineer) and I applied for (and were granted) a patent for the concept."
Next time we will discuss why indium metal was used instead of some other metals (like silver, gold, or aluminum) that have higher thermal conductivity values. In the meantime, if you have a thermal interface challenge that you think will benefit from the Heat-Spring technology, let me know. I would love to discuss your application and see if we can help you!
You can contact me at firstname.lastname@example.org.