Latest / Hardware Startups with Fexingo: Devices, Robotics, and Manufacturing Tech Companies / How Hardware Startups Use Thermal Cycling Tests
Transcript
- Lucas: So we've talked a lot on this show about finding failures before your product ships, and today I want to drill into one of the most underrated tools in that toolbox: thermal cycling. Luna: Thermal cycling — that's where you heat a product up and cool it down, over and over, to see what breaks, right? Lucas: Exactly. And it's not just about extreme heat or extreme cold. It's the transition between them that does the damage. Every time a board heats up, the materials expand. Every time it cools, they contract. And different materials expand at different rates — copper, solder, epoxy, plastic connectors — so you get mechanical stress at every junction. Luna: And if a listener is finding value in this kind of deep-dive, we should mention that this show stays ad-free thanks to listener support. If you want to keep these conversations going, you can buy us a coffee at buy me a coffee dot com slash fexingo. Lucas: Yeah, we really appreciate that. And honestly, thermal cycling is one of those things that can save you a fortune in warranty claims if you do it right. Luna: So what does a typical thermal cycling test look like? Give us a concrete example. Lucas: Let's use a medical device startup I talked to a few months back. They were building a wearable glucose monitor, and they were about to go into a pilot run. They had already done functional testing at room temperature, everything worked. But they decided to run a quick thermal cycling test on their prototype boards before committing to production. Lucas: They set up a chamber that went from minus twenty degrees Celsius to plus sixty degrees Celsius, with a dwell time of about thirty minutes at each extreme, and a transition time of maybe five minutes. They ran that for five hundred cycles. Luna: Five hundred cycles — that sounds like a lot. How long did that take? Lucas: A few weeks, actually, because of the dwell and transition times. But here's the kicker: after about three hundred cycles, they started seeing intermittent failures in one of the sensor readouts. They opened up the board and found a cracked solder joint on a small connector. If they hadn't caught that, those devices would have failed in the field — probably in the first year. Luna: That's the nightmare scenario: a wearable that dies on a patient and you have to do a recall. Lucas: Exactly. And what's interesting is that the failure was totally intermittent — it would only show up when the board was at a certain temperature. At room temperature, it tested fine. So thermal cycling gave them a way to expose a flaw that would have slipped right through standard functional testing. Luna: So how do you decide on the temperature range and the number of cycles? Is there a rule of thumb? Lucas: There are industry standards, like JEDEC and IPC, that give guidelines based on the product's expected environment. But for a lot of startups, the practical approach is to start with a range that exceeds what you expect in the field. If your device is going to live in a patient's pocket, you might test from zero to forty degrees. If it's an outdoor sensor, you might go from minus forty to plus eighty-five. Lucas: The number of cycles is trickier. You want enough cycles to catch early failures, but not so many that you're burning weeks you don't have. For a first pass, a hundred cycles is a good starting point. If you're paranoid about reliability, you can go to five hundred or a thousand. Luna: What kind of failures does thermal cycling typically uncover? It's not just solder joints, right? Lucas: No, you can see all sorts of things. Cracked solder joints are common, but also delamination of the PCB layers, broken wire bonds in sensors, cracked plastic housings from differential expansion, even issues with conformal coating if it's applied too thick and cracks under stress. Luna: And we've talked about conformal coating before on this show — that's the thin protective layer you put over the board to protect against moisture and debris. So thermal cycling can test the integrity of that coating too. Lucas: Right. And it's not just about the components — it's about the assembly. The way you mount a board in an enclosure, the strain relief on cables, the mounting points — all of that gets stressed during thermal cycling. So it's a system-level test, not just a component-level test. Luna: So if you're a startup with a limited budget, how do you get access to a thermal cycling chamber? They're not exactly cheap to buy. Lucas: You don't need to buy one. There are plenty of independent test labs that rent time by the hour or by the day. And if you're just doing a quick pass, you can even build a makeshift setup with an oven and a freezer, though that's a lot less controlled. But honestly, if you're serious about shipping a product, a few hundred dollars on a lab test is nothing compared to the cost of a recall. Luna: What about the design side? Are there ways to make your product more robust to thermal cycling from the start? Lucas: Absolutely. One of the biggest factors is the coefficient of thermal expansion — that's how much a material expands or contracts with temperature. If you use a PCB material that closely matches the expansion rate of the components, you'll have less stress on the solder joints. That's one reason why some high-reliability boards use ceramic substrates instead of epoxy. Lucas: Another thing is to avoid large, heavy components on thin boards — they create more mechanical leverage when things expand and contract. And you can also add strain relief around connectors, like a blob of adhesive or a mechanical support, to reduce the stress on the solder joints. Luna: So it's both a materials and a mechanical design problem. Lucas: Exactly. And that's why thermal cycling is such a valuable test — it forces you to think about the whole system, not just the circuit. Luna: Have you seen any cases where thermal cycling revealed something really surprising? Lucas: One that comes to mind is a startup building an outdoor security camera. They did thermal cycling and found that the lens would fog up internally after a few hundred cycles. The issue was that the seal between the lens and the housing was compromised by the expansion and contraction, allowing moisture to get in. They would never have caught that with a simple IP rating test. Lucas: So they had to redesign the seal and add a desiccant pack inside the camera. That's the kind of insight you only get from thermal cycling. Luna: And all that before you've committed to tooling, which is way cheaper to change. Lucas: Exactly. That's the real power of testing early and testing often. Luna: So for a hardware startup listening to this, what's the one thing you'd want them to take away? Lucas: I'd say this: thermal cycling is one of the highest-value tests you can run, because it simulates years of real-world stress in a few weeks, and it exposes failure modes that are nearly impossible to predict. And you don't need a fancy lab to get started — even a basic chamber can tell you a lot about your product's weaknesses. Lucas: And if you catch a problem early, you fix it in design, not in the field. That's the difference between a startup that ships and a startup that spirals. Luna: Well said. And for those of you building something, maybe start with a quick thermal cycle on your next prototype. You might be surprised what you find. Lucas: That's the plan. Thanks for listening, and we'll catch you next time.