At the printed circuit board (PCB) level, the heat flux is the highest in the system. While it is advantageous to dissipate heat as close to the source as possible, this can be difficult, while simultaneously satisfying the electrical isolation requirements. Unfortunately in many cases electrical isolation is only achieved using materials that are thermally insulating, such as with FR4 boards. Recent work at ACT has explored adding heat pipes to the structure of Metal Core Printed Circuit boards to help spread heat right at the source. If the ratio of the heat source to circuit board area is sufficient, this can be an effective way to improve heat spreading at the board level while requiring minimal design impacts to the lighting system.
Figure 1 shows an example of heat pipes embedded into a Metal Core Printed Circuit Board (MCPCB). Heat pipes are seen on the left, while the circuit side is seen on the right. In Figure 2, a 3 LED structure is shown on the right, while a thermal image of that structure is seen on its left. Measurements have shown that the embedded heat pipes can reduce the heat spreading resistance by 45% over the standard aluminum MCPCB and even 15% over a copper MCPCB. This is a valuable improvement, particularly so close the heat source.
Figure 1. Photograph of metal core printed circuit board with heat pipes soldered into the metal core of the circuit board.
Figure 2. IR images and photographs of heat pipe embedded circuit board during LED operation. The scale (58°C to 68°C) has been set to emphasize the thermal spreading in the circuit board. The heat spreading resistance is reduced by 45% over the standard aluminum MCPCB.
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