Copper-filled Vias

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 feature capabilities that other conductive fillings do not provide. This guide explains the primary purposes of copper-filled vias and how they can enhance your 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, they can create an overabundance of copper that increases PCB weight or adds too much copper to the traces. This results 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 specs.
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 will increase its lifespan and prevent defects. Copper's high thermal conductivity attracts this heat, keeping it away from critical areas of the PCB. Instead of traveling to different parts of the board, the heat instead moves through the copper 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 without overloading the PCB. Because of this capacity, designers often 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 that have copper-filled vias will stand up to the conditions presented by high power, radio frequency, microwave and LED applications. The high-power integrated circuits that run these types of PCBs use currents that a copper-filled via can withstand, but not 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. While a silver conductive epoxy resin may seem like the logical choice for filling vias because of its higher value, copper works more effectively. Compared to silver epoxy, copper has:
•    Higher thermal conductivity
•    Higher electrical conductivity
•    A more cost-effective price
•    A longer lifespan
•    More reliability
•    Better capacity for high-power applications
At a more economical price, copper-filled vias exceed the capabilities of silver epoxy vias. Their higher levels of thermal and electrical conductivity allow them to redirect excess heat more effectively. Copper vias also handle higher voltage levels without overloading.