Details of test chip designs: pad pitch, layout, materials, and opening.

PCB design in the shape and size of the pad design standards - Andwin Circuits

Introduction of Plastic Ball Grid Array (PBGA) - FS PCBA

Working With BGAs: Design And Layout

Design guide - Mandalon EN

PCB Pads - MorePCB

Understanding Wafer Bumping Packaging Technology - AnySilicon

Fine Pitch Flip Chip with Cu Pillar

Understanding the Importance of Prerequisites in the VLSI Physical Design Stage

Is It Printed or a Component? All About PCB Test Points

What is a Pad in PCB Design and Development