Issue link: https://iconnect007.uberflip.com/i/1069358
JANUARY 2019 I PCB007 MAGAZINE 61 possible. The challenge is how to make a very thin layer and keep the electrical strength from the functional copper to the heat sink whether it's made out of copper or aluminium. Johnson: Specific to the application of headlights, do you see that being a challenge for automotive design and electronics in general? Benmayor: Yes, it's a big challenge because everybody is trying to apply more power, but they have limitations. Don't forget that for the thermal stress of all the headlights, the automotive industry applies a big temperature on the whole set of the components, so they usually get the whole headlight and enter it into a chamber of 125°C, and the LED needs to operate inside that temperature. So, it's not only the temperature generated by the LED component, but it's also the ambient where they test the whole set of the headlight. It's very challenging for them to dissipate as much temperature as they can to guarantee the output of the light coming out of the headlight. It's very challenging today. Johnson: Those temperature extremes are commonplace throughout all of the automotive electronics as well, I would think. Benmayor: Not only for the headlights. Now, there is a trend in the market going to the battery and the electric cars. Electric cars need power modules and battery chargers, which also generate a big amount of heat. Then, the heat needs to be dissipated from the charger to guarantee that the operation remains stable in the long term. Time power modules also require high current, which means thick copper on the circuitry. Releasing temperature on many parts of the electronics inside the car is a big issue today. Johnson: And your recent product development is providing solutions for that? Benmayor: We try to keep developing and figure out how to produce a thinner layer with lower thermal impedance. This is a never- ending development. We do this by doing a lot of R&D on the resin technology and mineral content to be capable of increasing the thermal conductivity of the layer and dissipating from one side of the copper layer—the functional copper layer—down to the heat sink. Many aspects are influenced there, not only the thermal stress on the dielectric layer. You must also consider the maximum operational temperature (MOT) values and how long you can operate a substrate at a higher temperature without losing its initial properties. Don't forget that a dielectric layer is an organic layer, and because of this, higher temperatures over a long time will deteriorate its properties. So, MOT value is always a figure to pay attention to. Further, what are the coefficient of thermal expansion values (CTE) of the laminate? The minimum CTE, the better because on thermal boards, there is a big fluctuation on the temperature. An LED or power board can go from very low temperatures to high temperatures many times per day, and this affects the interconnects among others. CTE values are very important for high-end PCB producers and OEMs to keep the interconnects in between layers after temperature cycle testing. Figure 3: An example design of an LED automotive headlamp using Aismalibar's Cobritherm Ultrathin HTC materials.