Via Plating
A continuous deposit of electroplated metal that extends from the inner barrel of a filled via hole onto the outer surface of the printed circuit board ensures electrical continuity. This continuous layer, termed copper wrap, is a requirement for high-reliability electronics where filled vias sit directly under surface mount component pads. The plating process establishes a durable joint that prevents the plated copper from separating from the foil during thermal stress.
Fabricators must maintain a minimum wrap thickness specified by industry standards such as IPC-6012.
Thermal Stress
Mechanical stresses generated during assembly reflow can split the outer copper layer from the via barrel if the transition is too thin. As the resin substrate expands along the vertical axis, it exerts an upward force on the outer pads. A durable copper wrap acts as a reinforcing collar that absorbs these stresses and prevents open circuits.
Failures typically occur at the knee of the via where the plating bends from the vertical hole to the horizontal surface. Thus, ensuring adequate metal thickness at this transition zone is critical for long-term field reliability.
Process Control
Electroplating parameters, chemical baths, and agitation rates are carefully monitored to produce a uniform wrap layer. Inconsistent chemistry or current density variations can cause thin plating on the board surface while leaving the via barrel over-plated. Fabricators verify wrap compliance by cross-sectioning test coupons and measuring the metal thickness under a microscope.
