Copper Plugged Vias

This Gold Phoenix PCB Knowledge Center article explains copper-plugged vias, their filling process, benefits, application considerations, and conductive-epoxy alternatives.

Printed circuit boards would not function without vias, the conduits that transfer signals between PCB layers. During PCB production, the manufacturer adds a layer of copper to the board substrate. This copper layer not only makes the traces conductive but also connects each PCB layer between the holes drilled into the board. The manufacturer can then leave the vias as-is and use the copper plating on its own to transfer signals.

However, for added capacity, they can also fill the plated through holes with another conductive material.

To create a copper-filled via, the manufacturer fills the through holes with epoxy resin and copper. The extra materials add cost to board production, but copper-filled vias make a PCB more suitable for certain applications. Copper-filled vias also provide properties that can be useful in applications requiring enhanced thermal or electrical conductivity. This guide explains the primary purposes of copper-filled vias and how they can enhance PCB design.

Via Filling Process

When filling a through hole with copper, the manufacturer must pay attention to creating an even layer of copper in the via without creating too thick an outer layer. Without using the proper techniques, an overabundance of copper can increase PCB weight or add too much copper to the traces. This can result in a failure to meet specifications, defects, or increased costs. With via holes becoming smaller than ever, observing these requirements becomes vital to meeting tight design specifications.

Classic copper via filling methods involve using pure copper to fill the hole. However, this approach often results in the formation of voids, in which contaminants become trapped in the middle of the copper. This void can release gas when heated during future production steps, creating holes that disrupt the connections between the PCB’s copper layer.

Current strategies to counteract this issue include leaving a recess at the top of the blind via filling and creating an “X” patterned connection in through holes.

Benefits of Copper Filled Vias

PCBs featuring copper-filled vias have the following advantages over boards that only have copper-plated vias:

• Thermal conductivity: Filling a via with copper increases its thermal conductivity. In applications involving high heat, keeping the heat away from the board can help manage thermal conditions and reduce the risk of defects. Copper provides a thermal path through the via from one side of the board to the other.

• Electrical conductivity: Copper-filled vias also suit applications that require strong currents to travel from one side of the board to the other. The copper’s conductivity allows large currents to cross to deeper layers. Because of this capacity, designers may request copper-filled vias for PCBs that will experience high voltage levels.

Filled Via vs. Plated Through Hole Applications

While PCBs that feature copper-filled vias have added capacity, they also cost more to produce than PCBs with plated through holes. Some situations require the added reliability associated with copper-filled vias. However, a PCB can also serve certain applications with a via that has only the copper plating applied alongside the copper traces.

When you decide on your PCB’s vias, you must consider the intensity of the application’s heat and voltage. In low-stress applications, a properly manufactured PCB with plated through holes can function without defects. Meanwhile, PCBs with copper-filled vias can be used in high-power, radio frequency, microwave, and LED applications.

The high-power integrated circuits used in these types of PCBs may require the current-carrying capacity of a copper-filled via rather than a plated through hole.

Copper vs. Silver Conductive Epoxy

In addition to filling the PCB’s vias with copper, a manufacturer also has the option of using a silver conductive epoxy resin. Compared with silver conductive epoxy, copper provides:

• Higher thermal conductivity

• Higher electrical conductivity

• Suitability for high-power applications

• Longer service life in the applications described