PCB007 Magazine

PCB-Dec2017

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34 The PCB Magazine • December 2017 In this article we will take a brief look at each method available (Figure 1). Typical heat mitigation techniques include: • Materials • Copper thickness • Thermal vias • External heatsink • Internal heatsink • Coin technologies Materials One of the simplest and most common ways that is often overlooked as a function of removing heat from components, is to care- fully choose the right materials. When design- ing bare PC boards at the CAD level, we tend to think of material choice as more of a dielec- tric, impedance or signal speed requirement, neglecting the need for heat movement. Often when a PCB is going to see high temperature in its environment or operation, we tend to think polyimide. Polyimide is a great heat-sustaining material that possesses a higher heat transfer rate than that of FR-4; however, there are others that can do more. There are many material choices today which can gain one both the signal speed and the thermal conductivity needed, as referenced in Figures 2 and 3. As you can see by these charts, thermal conductivity greatly improves when considering alternative materials. The is- sue here is to balance all the needs of the design together: electrical, environmental and perfor- mance. Copper Thickness Copper thickness is another common way of controlling and/or moving temperature into the PCB and away from the component for add- ed performance. It is not unusual to see cop- per thickness for internal plane layers to be any- where from two ounces upwards of four ounc- es or even higher. The problems start to oc- cur when a designer wants to run smaller trace widths on the same plane as the heavy copper weights; if this can be avoided and these small- er traces can be placed on other layers, it is al- ways advised. One example of a simple copper weight im- provement relates to a design of a former cus- tomer. The product was a high-speed camera for ultra-slow-motion detection (8-layer rigid-flex design). There were many components gener- ating tremendous heat on both sides of the de- sign. As a fix we simply added two additional THERMAL MANAGEMENT CONSIDERATIONS AT THE BARE BOARD LEVEL Figure 1: Comparison chart for choosing heat mitigation method.

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