PCB Capabilities
Capped & Filled Vias
Epoxy-filled, copper-capped vias for via-in-pad and fine-pitch BGA designs.
Capped vias — also called filled and plated-over vias — are through-hole or blind vias that are filled with epoxy or conductive paste, then plated with copper to create a flat, solderable surface. This process enables via-in-pad designs where vias are placed directly under surface-mount component pads without causing solder wicking, voiding or tombstoning during assembly. Capped vias are essential for fine-pitch BGA, QFN and LGA components where escape routing cannot avoid placing vias directly beneath solder pads.
Why capping is necessary
An open via under a solder pad creates three assembly problems. First, molten solder wicks down through the via during reflow, starving the pad-to-component joint of solder and potentially creating an open or weak connection. Second, flux and solder paste volatile gases become trapped in the via, creating voids in the solder joint that reduce mechanical strength and thermal conductivity. Third, the uneven pad surface caused by an open via hole can cause component misalignment during placement. Capping the via eliminates all three problems by filling the hole and providing a flat copper surface for the solder pad.
Capping process
The standard capping process fills the via with non-conductive epoxy (typically IPC-4761 Type VII), cures the epoxy, then plates copper over the filled via to close the surface. The copper cap is polished or planarized to ensure a flat surface suitable for solder paste printing. The result is a via location that is electrically indistinguishable from a solid copper pad on the board surface — the solder paste prints evenly, the component sits flat, and the solder joint forms without wicking or voiding.
Conductive fill (IPC-4761 Type VI) uses a silver or copper-filled epoxy that provides both structural filling and a thermal/electrical path through the via. Conductive fill is specified when the via must also serve as a thermal conduit — for example, a thermal via array beneath a power component ground pad that must conduct heat from the component to an internal ground plane.
When to specify capped vias
Fine-pitch BGA components with ball pitch below 0.8 mm almost always require via-in-pad with capped vias, because the pad pitch is too tight to route vias between pads (dog-bone pattern). QFN and LGA packages with exposed thermal pads require capped vias in the thermal pad area to prevent solder wicking during reflow. High-density designs where routing space is at a premium use via-in-pad to eliminate the fan-out area that dog-bone routing requires.
Design guidelines
Specify via fill type in the fabrication notes: non-conductive fill (standard) or conductive fill (for thermal vias). Minimum via diameter for reliable filling is typically 0.2 mm (8 mil) for mechanical drilled vias. Laser-drilled microvias (0.1 mm) are filled during the standard HDI process. Ensure that the fabrication drawing clearly identifies which vias require filling and capping — not all vias on the board may need this treatment, and selectively specifying filled vias controls cost.
Request a quote with capped vias
Upload your design files with via fill requirements noted. The engineering team will confirm the fill process and include it in the fabrication quotation.