SMD Package Selection and Board Land Pattern Tolerances
Calculated land pattern dimensions matching IPC-7351 guidelines balance solder fillet volume and placement tolerance to prevent joint stress and yield loss.
Microsectioning
Analytical Procedure
Destructive physical analysis of printed circuit boards allows for the direct inspection of internal copper layers and plating. This analytical process, known as microsectioning, involves cutting a specimen from the board and mounting it in a plastic resin. The sample is then ground and polished to expose the cross-section of interest.
Sample Preparation
Preparation of the specimen must be done with high precision to avoid introducing artifacts like copper smearing or glass-fibre cracking. The technician cuts a small coupon containing the vias or solder joints to be analyzed. Next, the coupon is cast in an epoxy resin and allowed to cure completely.
Once cured, the resin block is polished using progressively finer abrasive papers and diamond pastes.
Defect Detection
Examination under a metallurgical microscope reveals the internal structure of the vias, copper plating thickness, and solder joint integrity. Microsectioning exposes hidden faults such as internal voids, micro-cracks, and resin recession that are invisible to surface scanners. These defects indicate failures in the plating or laminating processes.
Quality Audit
Reliability specifications require regular sample testing of production lots to audit the assembly line. Each test coupon undergoes microsectioning to verify that the internal board quality meets industry standards.