Melissa Mitchell:  Hi, John. How are you?

John:  Good. Melissa, what is Tough‑Seal potting compound, and why should customers try or use the Tough‑Seal potting compounds?

Tough Seal Potting Compound Properties

Melissa:  Tough‑Seal is a really unique, high‑elongation epoxy potting compound. What’s really great about it is that it doesn’t exotherm. Typically epoxies, when they are curing, will exotherm, get hot, can damage the components of your PCB or other components on your electronic board, and Tough‑Seal does not exotherm. It doesn’t crack. It doesn’t pull back from your housing.

Typically when potting compounds contract as they’re cooling after exotherm, they crack — leave places for moisture to get into your components and cause damage to the boards.

John:  Could they even pull things apart on the board and make them actually break?

Melissa:  Exactly. Some people have embedment stress happen during potting, and that doesn’t happen with Tough‑Seal, either, because it doesn’t exotherm, and it doesn’t shrink while it’s curing. Definitely a positive if you’re potting and see that as a problem when you’re manufacturing.

Potting Compound Adhesion to Aluminum

John:  Right. What are some other properties of Tough‑Seal?

Melissa:  Tough‑Seal is absolutely known for its excellent adhesion to aluminum. We’ve had customers buying Tough‑Seal for over ten years, and they are all very happy with the aggressive adhesion to aluminum; and the thermal cycling stability of Tough‑Seal is definitely critical. Tough‑Seal can thermal cycle from ‑40C up to 150C.

John:  Explain thermal cycling a little bit.

Melissa:  Yes, it’s when you expose the part that contains the Tough‑Seal and the other components, to temperatures that go down to ‑40C. They’re usually held at that temperature for a while, brought back up to 150C, at that temperature for a while, and they keep altering the temperature and cycling through from the ‑40 to the 150.

John:  Right, so getting cold, and then getting hot again, and then getting cold, etc.

Melissa:  Exactly. Yes, so Tough‑Seal has very good thermal cycling stability. It doesn’t crack. It doesn’t degrade in any way or decompose in any way. It stays strong, thus giving it the name Tough‑Seal.

Customer Satisfaction

John:  Right. How long have people been using Tough‑Seal, and what is it that customers like most about it?

Melissa:  They’ve been buying Tough‑Seal for, I would say, over 10 years. They are very happy with the aggressive aluminum adhesion, the thermal cycling stability, and then the fact, again, that it doesn’t exotherm and cause damage to the components on their board is pretty critical, for sure.

John:  Tell me about the different formulations of the Tough‑Seal potting compound. I know it comes in a number of different varieties.

Tough Seal Formulations and Viscosity

Melissa:  Sure. Tough‑Seal comes in eight different formulations. We have different viscosities, ranging from low viscosity, self‑leveling viscosities of maybe like maple syrup, up to very high viscosities, like maybe toothpaste consistency.

John:  This is when I have a housing, and I have an electronic component that’s in the housing, and I pour the Tough‑Seal potting compound into it, the viscosity is how well it’s going to flow out and surround the component.

Melissa:  Correct, and if there’s a lot of components on the board, someone wants to make sure that it’s a lower‑viscosity material so it can actually self‑level nicely around all the components. Lower viscosity allows any air bubbles that might be trapped underneath some of these components to rise to the surface. Viscosity’s definitely important.

For other customers that don’t have housings, and they need to somehow pot the board, but don’t know how to contain it because they don’t want to move forward with a housing, we have the high toothpaste‑consistency Tough‑Seal, which is definitely a higher viscosity. You could actually dam around the board itself with Tough‑Seal 23 or 24, and from that standpoint, you’d be able to contain a lower viscosity Tough‑Seal, like our Tough‑Seal 21 or 31, or 22 and 32.

John:  You could actually combine different types of Tough‑Seal and use a lower viscosity Tough‑Seal around the edges to create a housing, in a way, and then use a higher viscosity component in the middle?

Melissa:  Actually, flip that around.

John:  OK.

Melissa:  You put the higher viscosity around the edge to create a dam, and then you’d pot in the middle with a lower viscosity where it could self‑level out around all the components.

John:  I see.

Potting Compound Gel Times

Melissa:  Then, not only do we have different viscosities, but we also have different gel times. We have things with a working time of 10 minutes, and then we have other products, other potting compounds, that have a working time of 60 minutes. Depending on your application, depending on your production process, there’s a little longer working time.

All of our products, all of our Tough‑Seal potting compounds can be heat‑cured. You can typically heat‑cure our products for, I’d say, an hour at 80C, and that’s going to get your product to about 94 percent of its full hardness. The products all have a gel time or a working time of 10 to 60 minutes, and then they have to sit overnight for them to reach a de-moldable cure. Typically that’s about 94 percent of the full hardness with overnight.

You could either do overnight cure, or you can do a heat‑cure with Tough‑Seal, which is really great. Depending on your production process, if you need to speed things up, you can have it pass through a conveying oven, and your parts can be ready within an hour.

Picking the Right Potting Compound for You

John:  Great. How do you know what Tough‑Seal to choose? You have all of these different formulations, as you said. How do I know what’s right for me?

Melissa:  Typically we recommend that our customers call. I’m the product manager, and I work very closely with all of my customers, with all of their different applications, to help them select exactly what would be the best fit for what they’re trying to do.

We do offer an evaluation kit. We would tailor what product would fit the application, and then we would recommend the evaluation kit. The evaluation kit comes with three 50-milliliter cartridges, a dispenser, static mixers, a cured sample of the Tough‑Seal, so that you can see the final hardness of the material, and the final product before you even use it.

The kit is great because — I would say with the kit you could cover about nine cubic inches of material. Volumetrically, each cartridge covers three cubic inches. You get three cartridges; you can cover nine cubic inches. You can calculate exactly how much material you need to do your testing.

It’s great because we can customize the kit, too. If there’s one or two or three products that you’re unsure would be a better fit for you, we can customize the kit and give you samples of all, and you can do your evaluation.

We also work closely with customers for difficult new applications. We have a full testing laboratory. We can run a variety of adhesion testing internally to help customers determine which product might be a better fit for their applications.

John:  You’ll actually, in that case, have a customer send you some samples of their products so that you can do some testing in‑house.

Melissa:  Exactly. Yes, we work really closely with customers, especially if it’s a new application that we haven’t been exposed to, or that the customer is at a dead end with other products they’ve tried in the past. We work really closely with them to try to make sure that we can find a good fit for them.

John:  Great. Well, thanks for that information, Melissa. I appreciate you speaking with me today.

Melissa:  Great, thanks for having me.

John:  For more information, you can visit the Key Polymer website at, or call 978‑683‑9411. That’s 978‑683‑9411.