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UFBGA Paste Stencil Recommendation

billymit
Associate

‎2025-09-03 2:32 PM - last edited on ‎2025-09-05 2:05 AM by

Hello,

 

I'd like to use the STM32WLE5 in an upcoming design. Looking at the datasheet, I noticed the recommendation for the BGA package is to have the stencil opening larger than the pad diameter, instead matching the ball diameter . To me this seems counterintuitive, as I would typically reduce the paste for balls <0.4mm in diameter. Can anyone help me understand this recommendation?

Thanks,

Billy

 

billymit_0-1756934944815.png

 

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STTwo-32
ST Employee

‎2025-09-26 9:26 AM

Hello @billymit 

A stencil opening larger than the pad diameter ensures that an adequate amount of solder paste is deposited and helps in achieving proper wetting of the solder ball to the pad. This is essential for the mechanical and electrical reliability of the joint. 

Best Regards.

STTwo-32

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