Microsection, also called Micro-section or Specimen, is a small rectangular area punched out of the printed circuit board (PCB) in order to inspect the quality of plated through holes (PTH) or vias, and copper plating. It allows for a look at the inner layers of the board to verify the overall PCB manufacturing process. As this is destructive analysis rather than an actual printed circuit, test coupons are normally used from the same board.
Although a destructive specimen testing procedure, the PCB fabrication industry widely uses Microsectioning Analysis, as it allows them to see inside the PCB by exposing a cross-sectional view of microstructure, and make precise measurements to check the production processes for confirming the quality of the finished PCBs. Microsectioning, also known as Cross-sectioning or Metallographic Preparation, is the art of taking a two dimensional slice out of a sample in order to uncover an important feature.
A specific coupon design has been introduced by IPC, IPC-9241 Guidelines for Microsection Preparation, which can be included on each panel so that the coupon will experience the same process, as well as being representative of the remaining board. It is possible to remove this coupon for cross sectioning at any stage of production.
Typically, Microsectioning Analysis can help to check the quality of:
- The base material of the PCB
- Build checking in multi-layer boards
- Hole-wall plating thickness in a plated through hole
- Thickness of external and internal conductors
- Registration of external and internal pads
- Connection between layers
- Thickness of Surface Finish
- Thickness of Soldermask or Coverlay
PCB manufacturers perform the Cross-Sectional Analysis at different stages of PCB manufacturing such as:
- After drilling, they look for internal registration and hole quality
- After plating, they look for barrel and wrap thickness
- During final quality analysis, they look for overall thickness, final registration, plating requirements, and defects.