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Heat Sink for QFP

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Heat Sink for QFP | 24 March, 2006

Hi. We are designing in a 128 pin LQFP that has a heat sink in the center of the package. The size of this is 7.44 by 7.55 mm.

Can anyone recommend what pad size should be on the board for this? How about stencil aperture/pattern?

Thanks, Mike.

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Heat Sink for QFP | 28 March, 2006

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. ´┐ŻLarger than´┐Ż, 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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