Electrodeposited Copper Additive Dynamics in Printed Circuit Board Fabrication
Controlled additive balance between suppressors, accelerators, and levelers drives bottom-up microvia filling, requiring strict CVS control to avoid scrap.
Interfacial Corner Cracking
Meaning
Thermal and mechanical stresses in multi-layer electronic assemblies frequently concentrate at the junctions where dissimilar materials or structural geometries meet. The term interfacial corner cracking refers to the microstructural separation that occurs at the high-stress junction between the copper plating of a via hole and the internal copper land or knee of the via.
Stress Distribution
Differential thermal expansion between the fiberglass-reinforced epoxy resin and the copper via barrel drives localized deformation. This strain profile promotes interfacial corner cracking during thermal cycling or solder reflow processes. The highest concentration of stress resides at the sharp ninety-degree turn where the copper barrel connects to the surface pad.
Failure Mechanism
Microscopic examinations of failed circuit boards reveal structural voids that initiate at the inner knee of the via. When interfacial corner cracking develops, the electrical resistance of the circuit path increases or becomes intermittent. This deterioration leads to system failures under operational loads.
Prevention Strategy
Increasing the plating thickness in the via barrel provides greater resistance to thermal expansion forces. Avoiding interfacial corner cracking also requires optimization of the chemical desmear process to ensure a robust mechanical bond between the electroless copper and the inner-layer copper foils. Process engineers verify these bonding surfaces through mechanical pull tests during routine audits.
The structural integrity is confirmed when microsections show a continuous metallic structure without any micro-voiding or separation at the joint.