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70 SMT007 MAGAZINE I MARCH 2018 Article by Ken Horky PETERSON MANUFACTURING Electronic assembly thermal management has always been an issue but has become more significant as we pack more power and func- tion into a smaller form factor. In recent years, the growing use of LEDs for illumination on a large scale has presented additional ther- mal demands. EMI control also benefits from generous copper use. The first inclination for a designer is to add copper in the form of planes and flood- ing. How this copper is added with respect to the component footprint's pads can alter the termination quality. Calculating the area for each pad: Cu-D = 63.0(L1), 11.8(W1) Oval Pad = ((63-11.8) *11.8)+(PI() *(11.8/2)^2) = 714 + Partial Rectangular Trace = 5.0*3.0 = 14.5, 14.5+714 = 729 Msk-D = 73.0(L2), 16.5(W2) Unmasked Rectangular Copper Area = 73.0*16.5 = 1205 Where: Cu-D = Non-solder mask defined or copper defined pads • Pad features are created by the copper etching process in fabrication. Msk-D = Solder mask defined pads • Pad features are created by the respective solder mask pattern applied over copper, post etching in fabrication. The Msk-D pad is 65% larger than the Cu-D pad.

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