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Old   December 22, 2010, 08:23
Default QFN & thermal capacitance
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Has anyone have thermal capacitance and resistance model for the QFN and TSSOP package (QFN, 4x4, 7x7 and 9x9 with exposed pad) and similar size for TSSOP with exposed pad.

I actually have thermal resistance, derived from IC website but they do not have thermal capacitance, I need this to estimate heat flow from IC (ie 3W) into PCB.

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Old   December 22, 2010, 10:16
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Robin Bornoff
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Some package vendors will publish transient impedence curves from which you could derive the thermal capacitance but mainly only for power packages.

The only advice I can give would be to get a geometrically detailed 3D numerical model, solve it in a transient CFD model (in an operating environment close to the intended one) then get C (J/s) from the resulting T vs t curve.

I work for Mentor Graphics and so would of course advise use of our tools to achieve this.

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