Pad design - Standard IPC 20 pitch QFP
Thermal pad design - Layout the thermal pad 0mm to 0.15mm larger per side (0mm to 0.30mm larger overall) than the exposed die pad on the package. �Larger than�, as opposed to the same size, is preferred. Obviously any increase in the in thermal pad should not comprimise signal connections.
Thermal via design - A grid of 1.0mm to 1.2mm pitch thermal vias that connect to a copper plane. The vias should be about 0.3mm to 0.33mm in diameter, with the barrel plated to about 1.0 ounce copper.
Stencil design for pads - Select apertures for the pads to be 50 to 80 perecent of the size of the lead pad on the board. Here's an example: Part Type||Pitch||Aperture Width ||Aperture Length||Thickness range||Aspect Ratio Range||Area Ratio Range QFP||0.50mm (20thou)||0.22-0.25mm (9-10thou)||1.2mm (47.2thou)||0.125-0.15mm (4.92-5.91thou)||1.7-2.0||0.69-0.83
Stencil design for thermal pads - Use multiple small stencil openings [maybe 15 thou square], where total area approximately 50% of total thermal pad on the board.
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