At the conclusion of our webinar, Navigating UL and CSA Standards for Flexible Heaters Used in Industrial Equipment, we had several questions submitted to our presenter, Steven J. Goodman, Product Manager of User Interfaces and Cable Assemblies at Epec. We have compiled these questions into a readable format on our blog.
Q&A From Our Live Webinar
Quick Links:
- How are polyimide heaters laminated to aluminum surfaces?
- Do you have any knowledge of heaters for flexible textiles? Machine washable standards?
- For what specific applications would you consider to use conductive ink-based heaters (silver and carbon inks screen printed)? Do you manufacture screen-printed heaters?
- Do you support Kapton flexible heaters?
- You mentioned that Hi-Pot is performed on 100% of production parts. Why not the other tests you mentioned?
- Can you discuss more about the surface-mounted thermistors and thermostats?
- What happens if UL testing fails, and what's the impact on certification?
- Do we use Intertek and SGS?
- Any work with positive temperature coefficient heater materials?
- I didn't see any information on cartridge or thick film heaters. Do they follow the same path?
Watch the Recording Below:
Question: How are polyimide heaters laminated to aluminum surfaces?
Answer: Two typical situations for this: 1) one is that we design the aluminum plate or heat sink, manufacture the metal, and then perform the lamination process ourselves, attaching the heater directly, or, 2) we provide just the heater to our customers so they can then laminate and attach our custom heater directly to their aluminum substrate or mating part. For either situation, we must include an acrylic adhesive in sheet form that we attach directly to our heater. 3M467 and 3M468 are our most common types of pressure-sensitive adhesives, aka PSA. There are dozens of types of PSAs to choose from, but these varieties are readily available, low-cost, and have the 3M branding that we stand behind.
To actually laminate the heater with PSA onto a plate is very simple. First, we suggest cleaning and preparing the mating surface per 3M's instructions; usually, a wipe of isopropyl alcohol is sufficient. Then peel off the brown paper adhesive liner, exposing the acrylic adhesive. Then marry up the parts using a locating fixture (if needed) and apply pressure. You can refer to 3M's guidelines for the exact steps, but usually this is nothing more than a quick press by hand or roller and can be accomplished with basic benchtop assembly tools.
Question: Do you have any knowledge of heaters for flexible textiles? Machine washable standards?
Answer: Yes, on a personal level, I do. This stemmed from a project many years ago where I was involved with a washable shirt that was built with conductive threads and accelerometers to characterize the motion of athletes. For this to be a heater, you would just need to modify the design from a conductive thread to another thread. We do not have any current designs geared towards these types of textiles. We do, however, use our waterproof flexible silicone heaters in various clothing applications, but they are geared towards therapeutic devices that are not designed to be machine washable.
Question: For what specific applications would you consider to use conductive ink-based heaters (silver and carbon inks screen printed)? Do you manufacture screen-printed heaters?
Answer: Yes, we do make these screen-printed types of heaters that use conductive inks. Typically, they are inexpensive and more suited for low-cost consumer products and ultra-high volumes. The screen-printed type is labeled as a general-purpose heater and can only support “low” power consumption applications. We can absolutely make these, but when a customer is looking to build with one of our heaters, we usually suggest the polyimide and silicone variety due to their extremely high reliability and robust circuit elements, as well as their ability to operate at higher temperatures.
Question: Do you support Kapton flexible heaters?
Answer: That is a great question. Kapton is just a brand name for polyimide. We typically do not use the brand name Kapton. It's wildly expensive. And what we have is form-fit function equivalent, and we have a UL rating for our own house brand polyimide. So, we can support it, but typically, we do not. My response to this question would ultimately be, if you need brand name Kapton, I'd like to work with you and your team to understand why, but we certainly could build with it.
Question: You mentioned that Hi-Pot is performed on 100% of production parts. Why not the other tests you mentioned?
Answer: The answer, at least, I have, would be that UL dictates that Hi-Pot is performed on 100% of production parts because it's a screening test to make sure that there's no manufacturing defect. Whereas a lot of the other tests are more looking at the bill of materials, the actual raw materials used. So, as long as your build plan doesn't deviate in the raw materials that you're using, if you pass flammability testing day one and you're using the exact same silicone or the exact same polyimide, you should get the same results in perpetuity.
Question: Can you discuss more about the surface-mounted thermistors and thermostats?
Answer: Our most common applications use surface-mounted thermistors and in-line thermostats wired in series with the power leads. Depending on the application, we may have to use a specific brand-name component, or in others, we can use one of our form, fit, function equivalent temp sensors or control devices that are readily available for us in Southeast Asia. Either way, we can help recommend components if you do not have one in mind or use your brand-name component if that’s required. We always provide a data sheet and/or samples for any of our equivalent components if that’s the route you would go.
Question: What happens if UL testing fails, and what's the impact on certification?
Answer: It would depend on what specifically fails. A lot of what we see is clarifications of the design intent, or how it's assembled, or how it's grounded. So, I wouldn't call those failures as much as just part of the back and forth that is inherent with bringing any UL-approved heater to market. These third-party entities will go through the design and application and completely investigate every one of these situations.
If there's an actual failure, that's another issue altogether. If the failure is related to a flammability test, in our experience, it may be due to sampling or a change in the flame retardant that's needed for a given material. Or if there's an electrical failure, it could be a mechanical or electrical design flaw that UL or CSA's testing has actually ferreted out. So, depending on the actual issue, there are any number of actions that either Epic or our customer would need to take to remedy the situation.
Question: Do we use Intertek and SGS?
Answer: Yes, we do, absolutely. The follow-up is: "If so, what do they need to quote UL certification?" So, if you're unfamiliar, Intertek and SGS are the actual third parties who do a lot of this testing and will actually issue the certification and do the site audits. And in our experience, they don't need a lot to quote, but they need what the spec is you're trying to adhere to. They'll need a complete set of drawings for the design, information on the application, and a complete bill of materials. If they actually go through and do the testing, they will need all that information formalized, and actually, a whole bunch of samples that they're going to take apart.
Question: Any work with positive temperature coefficient heater materials?
Answer: Yes, absolutely. These are not as common for us as the silicone and polyimide type, but we do offer a complete suite of automatic temperature regulation/PTC style heaters. We use them for safety-critical applications since the material's resistance increases significantly with temperature. And these do not have a snap disc like a conventional thermostat, so we see their benefit for applications with extended service lives or where you do not want to hear the click of a thermostat. We do have UL-approved PTC-style heaters if that is of interest to you.
Question: I didn't see any information on cartridge or thick film heaters. Do they follow the same path?
Answer: So, while we do support some cartridge and thick film designs, that is not, at least today, a core competency of ours. We do some of them. And, yes, they absolutely would follow a similar path, almost an identical path.
Key Takeaways
- UL and CSA certification for flexible heaters requires detailed design documentation, including drawings, bill of materials, and application details, along with physical samples for testing.
- Not all testing is performed on every unit, Hi-Pot testing is required on 100% of production parts to catch manufacturing defects, while other tests validate materials and design consistency over time.
- Polyimide and silicone heaters are typically preferred over screen-printed conductive ink heaters due to their higher reliability, durability, and ability to operate at elevated temperatures.
- Adhesives and proper surface preparation play a critical role in heater performance, with pressure-sensitive adhesives like 3M467 and 3M468 commonly used for secure and repeatable lamination.
- Certification failures are often part of the normal review process, but true failures can reveal design, material, or electrical issues that must be corrected before approval, making early planning and collaboration essential.
