To ensure compatibility in creating stencils for BGA/LGA umodules, follow the fabrication instructions in the Design Files included on the umodule's evaluation kit.
As example in finding a fabrication instruction for LTM8042.
Navigate to the product page of LTM8042.
Scroll down to reach the evaluation kits section
Expand an evaluation kit section and find the link "-Design Files"
On the zip file navigate to the "-PDF.ZIP" and find the document that has a suffix "-FAB.pdf"
"-FAB.pdf" should contain the stencil used in creating the evaluation board.
In cases that a reference design or eval board is not available follow the guidelines presented on the following linked documents