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BQ51025: BQ51025EVM

Errol Leon6
Expert 5830 points
Part Number: BQ51025

Hello,

My customer has two questions relating to the BQ51025. The EVM design includes a 6mil hole/10mil pad, via-in-pad from top layer to bottom layer through a 4-layer .062 board. These cannot be reliably filled in a mass production environment, air gaps will be left in the vias. So the questions are: 

1) Is there a specific reason why the board is designed this way?

2) Is there a specific reason why blind vias that drill down only one layer cannot be used?

Thank you,

Errol Leon

Texas Instruments

Field Applications Engineer

  • 0
    TI__Guru 65866 points

    Hello
    1) Is there a specific reason why the board is designed this way?----Bill J -- This design have been used on all the receiver design and has worked well for us.

    2) Is there a specific reason why blind vias that drill down only one layer cannot be used?----Bill J -- This should work. But the device will heat up and does need a thermal path to ground plane for cooling.

  • 0 in reply to Bill Johns
    Prodigy 120 points
    Thanks Bill, concern about the thermal performance is exactly why I asked.

    The questions that follow your answer to #1 above would have to do with production quantities, yield rates and failures in the field. "works well" covers a lot of ground. We've only been able to reliably fill the holes by drilling each hole 3 times. First and second with a 4 mil laser drill from each side to create a pilot hole to the inner layers and then with a 6 mil mechanical drill. through the inner layers. At that size even a copper fill is hard to guarantee and these are expensive, added process steps.

    I'll take a very close look at the thermal performance using blind vias.