I have a design using the bq24765 charge controller. My question is related to the use of the thermal pad. I used the recommended four layer board with a large number of small feedthroughs to all layers under the thermal pad. It works fine but I am concerned with the reliability of the soldering at the pad. I read the ap note relating to the pad and it states that you should ex ray your board to make sure you have at least 50% coverage at the pad to the board. That does not seem practical to me.
It would seem like if I used 2 or 3 large plated through holes rather than 12 small ones at the thermal pad area, after assembly, I could simply turn the board over and fill those holes with solder thus ensuring a 50% + coverage. Even more extreme, I could put a plated through rectangle opening a little smaller than the thermal pad under the part and fill that with solder. I know the thermal properties of copper are better than solder but it would seem I would be offsetting that by eliminating the even worse thermal properties of the circuit board material.
What is wrong with this theory?
dpk
