Wednesday, July 25, 2012 | Yash Sutariya, Saturn Electronics Corporation/Saturn Flex Systems
Editor's Note: This article originally appeared in the June 2012 issue of SMT Magazine.
"Life can be much broader once you discover one simple fact: Everything around you that you call life was made up by people that were no smarter than you and you can change it." – Steve Jobs
Like the rest of the industry, I was swept up by the high-powered marketing campaigns promoting the performance benefits of cutting-edge dielectrics for LED PCBs. Not to mention I thought it was kind of cool making a PCB from a sheet of metal. Appealing to total cost of ownership, the wave informed us that the dielectric’s reliability performance justified the higher (purchase) cost. The wave had seemingly short-circuited that part of my brain responsible for basic physics. As a result, when the current bragged about a thermal conductivity of 2-3 W/m K, I was inhibited from realizing that this was less than 1/100 that of copper’s thermal conductivity (400 W/m K).
In 2009, I consulted a thermal management guru who began teaching me the ways of the (thermal) force. Now, like Sid the Science Kid, I just have to know: Are brand-name thermal dielectrics on metal core printed circuit boards (MCPCBs) more effective than traditional FR-4 PCBs with Cu-plated vias?
Figure 1: MCPCBs for LEDs.
PCBs for LED Thermal Management: The Basic Mechanism
The mechanism by which a thermally conductive PCB material works is fairly simple. The base of the LED component is soldered to a center pad of the component footprint. This center pad is not electrically connected to any of the other features. Its sole purpose is to provide a conduit for heat to be drawn away from the LED, increasing the light output as well as life of the product. MCPCBs in their simplest form consist of a circuit layer, a thermally conductive dielectric layer, and a metal substrate (most commonly aluminum). Once the PCB is assembled it is typically mounted to a heatsink with a thermal interface material (TIM).
PCBs for LED Thermal Management: The Basic Problems
MCPCB materials have numerous issues associated with them. First and foremost is the lack of an industry specification. As our past webinars have discussed, this results in a wide array of potential issues to the designer--primarily incorrect specifications that leave the end customer open to failures. Further, the MCPCB material can run up to 10 times the cost of standard FR-4, eroding the full potential savings of moving from incandescent to LED lighting.