Query Regarding Via-on-Pad Strategy for 0.5mm pitch BGA device STM32MP157FAC1

[PS_115]

Hello,

We are designing a custom board using the STM32MP157FAC1 device (361 balls with 0.5 mm pitch).

As per AN5031 (Page 50), laser vias with a 100 µm (~4 mil) drill hole diameter and 250 µm (~10 mil) outer pad diameter are recommended for BGA balls located within the 0.5 mm pitch matrix. A snapshot of the relevant section is attached for the reference.

We would like to clarify whether a Via-On-Pad strategy can be used instead of laser vias for the BGA balls within the 0.5 mm pitch matrix of STM32MP157FAC1 device.

Specifically, can we use a via of 200 µm (~8 mil) drill hole diameter and 400 µm (~16 mil) outer pad diameter as via-on-pad on the STM32MP157FAC1 BGA pads instead of the recommended laser vias ? 

Kindly confirm whether this approach is acceptable from the CAD layout perspective and whether it can be used in the CAD layout of our design.

Regards,
PS
 

 

[Erwan SZYMANSKI]

Hello ​@PS_115 ,
With a 0.5mm pitch, it is not forbidden but we do not recommend to do this and prefer to promote laser vias.
With your method, the PCB cost will be higher and you will not be able to route some signals between the balls. 

Kind regards,
Erwan.