Inspection Method
Microscopic inspection methods utilize electron beams to capture high resolution images of the internal structures and grain boundaries of a circuit board. Technicians use microsection sem analysis to inspect the quality of the plating inside small vias and the integrity of the solder to pad interface. This technique provides much higher magnification and depth of field than a standard optical microscope.
Sample Preparation
Sample preparation begins by cutting a small piece of the board and mounting it in a resin puck. After grinding and polishing the surface to expose the cross section, the sample is coated with a thin layer of gold or carbon to make it conductive. Microsection sem analysis then reveals the metallic structure, including the intermetallic layers formed during soldering.
Measuring the thickness of these layers helps predict the reliability of the joint over time. The scanning electron microscope also detects the presence of contaminants or voids that are too small for optical detection.
Root Cause
When a board fails a pull test or an electrical test, this analysis identifies the exact location of the fracture. It distinguishes between a brittle failure at the interface and a ductile failure within the bulk solder.
