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132 QFN footprint

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132 QFN footprint | 25 July, 2007

Our board layout folks are currently designing a PWB using a 132 QFN. The component is .5mm pitch with .35mm square pads. The component manufacturer recommends the following footprint:

.4mm square land .3mm square solder resist

1.why do they spec the solder resist to overlap the pad by .05mm on all sides? prevent solder shorts?

2.Does anyone disagree with the footprint recommendation and why.

3. Suggestions for stencil aperture size/shape.

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132 QFN footprint | 26 July, 2007

And they're using a stencil that is how thick?

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132 QFN footprint | 16 August, 2007

This could be the reason for the mask defined pad.

ERROR in docs! This happens a lot. I believe this to be case honestly, I would not use mask defined pads for these. If you get a registration shift in mask which is likely you will run into trouble. I would reverse the specs.

Does this part have the center pad? if so make sure you reduce the stencil aperture by about 50% or it will cause part to lift.

You could use up to a 6 mil stencil and a square pad with radiused corners.


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132 QFN footprint | 3 September, 2007

A suggestion for your stencil which works is as follows. Cut your stencil aperatures beyond your pads to a length of 0.1mm , this then allows the paste to pull back into the pad creating a blob of solder which can be inspected by AOI.Best length and width of pads for a QFN 56 and 64 is 0.8mm by 0.28mm.

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