PCB Microsection Analysis and Failure Detection Guide
How cross-section analysis verifies PCB manufacturing quality and diagnoses failure mechanisms.
What Is PCB Microsection Analysis?
Microsection analysis — also called cross-sectioning or metallographic analysis — is a destructive testing method that cuts through a PCB to expose its internal layers for microscopic examination. It is the only way to directly observe the quality of plated through-hole walls, the integrity of inner layer bonds, and the microstructure of solder joints.
A microsection sample is cut from a specific area of the PCB, then encapsulated in epoxy resin, ground, and polished to a mirror finish. The polished surface is examined under an optical microscope at magnifications of 50× to 1,000×. Measurements of copper thickness, hole wall quality, and intermetallic compound formation are taken and compared against IPC standards.
Microsection analysis is performed on every new production lot as part of first article inspection, and periodically throughout production as a process control check.
What Microsection Analysis Reveals
Copper plating thickness is the most basic measurement. IPC-6012 specifies minimum average copper thickness in plated through-holes: 20µm for Class 2 boards, 25µm for Class 3. Thinner plating reduces current-carrying capacity and mechanical strength.
Hole wall quality is assessed by looking for: resin smear, glass fiber protrusion, plating voids, and cracks in the plating. Any of these defects can cause intermittent or permanent open circuits.
Inner layer bond integrity is checked by examining the interface between copper foil and prepreg. Delamination — separation between layers — appears as a dark line or gap, caused by contamination, insufficient prepreg flow, or thermal stress. Microsection analysis after thermal stress testing (288°C solder float, 10 seconds) reveals latent delamination risks.
For solder joints, microsection reveals: intermetallic compound (IMC) thickness, voiding, and cracks caused by thermal or mechanical stress.
The Process: From Sample to Report
A proper microsection analysis follows a defined process: select area of interest → cut sample with precision diamond saw → mount in epoxy under vacuum → grind with progressively finer abrasives → polish to mirror finish → etch to reveal grain structure → examine under microscope → capture images and measurements → prepare report. The entire process takes 2–4 hours.
Common Failure Modes Detected by Microsection
| Failure Mode | Description | Root Cause |
| Corner Cracking | Cracks at knee of hole where wall meets pad | CTE mismatch thermal cycling |
| Plating Voids | Gaps where copper did not deposit | Poor electroless copper coverage |
| Inner Layer Separation | Copper foil separates from prepreg | Inadequate oxide treatment, moisture |
| IMC Overgrowth | IMC layer >4µm at solder-copper interface | Excessive reflow temperature |
| Wicking | Inner layer copper drawn up hole wall | Plating process parameter issue |
Why Customers Should Request Microsection Reports
A microsection report is the most definitive proof of PCB manufacturing quality. Unlike electrical testing — which tells you whether the board passes or fails — microsection analysis tells you why it passed or failed, and whether it will continue to perform reliably over its intended lifetime.
For high-reliability applications — medical devices, aerospace electronics, automotive safety systems, and military equipment — microsection analysis should be a standard part of the first article inspection package.
Send your PCB design files to pcba@superb-tech.com for a free quotation including quality assurance documentation.
