What Is Overlap in PCB?
Overlap or Overlapping in printed circuit boards (PCBs) refers to some features cover some other features partly by going over their edge. Some common overlapping include pad overlap, carbon overlap and solder mask overlap.
- Pad Overlap: The pad overlap means hole overlap, it leads to hole damage in drilling process because one hole will be drilled more than once. If two holes overlapped in multi layers PCB, the overlapped connecting pad will be treated as isolation pad after negative film is painted, then must throw away.
- Carbon Overlap: in conductive carbon ink printed PCB, the carbon features should connect solder mask features and copper pattern features. Thus, there are carbon overlapping requirements on carbon on copper and carbon on solder mask.
- Solder Mask Overlap: in some BGA areas, there are solder mask defined (SMD) design, which requires solder mask overlapping a little bit BGA pads. In some standard boards, solder mask overlapping is also common.
Besides, there are copper overlap, plane overlap and etc.
Overlap Application in Flexible PCB
The transition areas where rigid and flex circuits, or stiffener and coverlay come together are stress-relief areas, where require overlap of material and special spacing for holes and conductive materials to avoid or eliminate stress points, which can reduce the chance of rigid-flex PCB delamination.