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DRV8704: Thermal pad connection issue

David Yang
Intellectual 720 points
Part Number: DRV8704

Hi,

Thermal pad solder issue. When the steel plate thickness is 0.12mm, the opening size is 2.9*4.7mm.

The height will be due to the large opening area, and the solder paste in the middle will be about 107um lower than the thickness of the steel plate.

The volume will be about 85% due to height. Do you have any suggestions on how much required volume should be achieved?

The gap between EPAD and pin is 0.05mm~0.15mm. Is there a normal distribution diagram?

Follow recommend of TI spec , tin beads will appear after production. Are there any other good suggestions?

Thanks & best regards,

  • 0
    TI__Mastermind 23401 points

    Hey David,

    I understand your concerns on the specs, but all very few customers have had any manufacturing issues with these packages of devices.  See these two apps notes on the PowerPad packages:
    PowerPAD Thermally Enhanced Package  <-- I think this is the best one for you to look through, it details the solder mask, pin land size, and other fine details.  
    PowerPad Made Easy

    David Yang said:
    The gap between EPAD and pin is 0.05mm~0.15mm. Is there a normal distribution diagram?

    The wide tolerances are due to the way the Mold Flash adheres to the leadframe of the device package.  Mold Flash is the black outside plastic you see on an IC.  Depending on how much this mold flash creeps onto the thermal pad, the size of the pad can differ by a little bit.  

    In practice, the customer should set the size of the thermal pad cutout to be the largest dimension of the thermal pad in the drawing.  This way there will be solder paste completely covering the thermal pad no matter where the pad dimensions land within the tolerance.  The Texas Instruments SMT guidelines today are 0.4mm of underhang or less is low-risk, which is the case here  Therefore it is safe to assume this should also be low risk

    This tolerance is a very standard amount among all IC manufacturers.  It has been specced this way for many years without issue. Also, when the pick and place machine places the device onto the PCB it will gently press the device into the solder.  Once the solder melts it will become a liquid and surface tension will cause it to grab onto the device above it when the solder balls up.  

    Hopefully the above points give you confidence on this moving forward. You shouldn't run into manufacturing issues here.  

    Best,

    Jacob