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TPA3251 Heasink design

Other Parts Discussed in Thread: TPA3251EVM, TPA3251


I had wrote following Post on Dec. 2015, but I had no answer yet.

My customer pushes me about this, so I change hte subject name  and change my question.


Customer want to use  the Thermal interface silicone soft pad rather than grease of Shin-etsu..

The reason is to manage the height mechanically  between heatsink and top of DDV package Power Pad  is easy if customer use silicone soft pad.

( soft pad  absorbs the tolerance.)


However, TPA3251EVM recommend grease .

( Also, customer is concerned about overheat if silicone soft pad used.)


In the EVM design,

Heat sink height is 1.0mm and DDV package height is 1.2mm.   please see attached.

Customer is concrened about the mechanical stress for IC package also.



Abut the meaning of 1.0mm of heatsink drawing.  ... see attached.

Is the mechanical height of heatsink  1.0mm  is MINIMUM value, and 1.2mm MAX value?

Or, 1.0mm  is TYP value?



Don't you have no concen( do you?)  about mechanical stress  even if heatsink height is 1.0mm (typ) and DDV is 1.2mm max?

Please let us know about the your heatsink design guideline in regard to TPA3251 .

We already have your advise that 95N to power pad top is no problem.


Best Regards






Would you please let me know the guideline for designing the heat sink in case soft pad?

( guideline means the mechanical



  • Hi Shibatani-san,

    The heat sink has to be design for the min DDV package height to ensure good contact between the DDV package thermal pad and the heat sink. The heat sink should be designed for 1.0mm height.

    The mechanical stress can be controlled by the tightening of the heat sink screw to apply 95N, even if the DDV package height is 1.2mm and the heat sink is 1.0mm.

    Our data and datasheet guaranteed parameters are based on using thermal grease. If the customer wants to deviate from that and use silicone soft pad, they can but they will have to manage the risk of the thermal performance based on the material property used between the thermal pad and heat sink of TPA3251D2.

  • Hi Damian-san
    Thank you for your quick answer.