Conductive vs. Non-Conductive Via Fill PCB

This Gold Phoenix PCB Knowledge Center article explains conductive and non-conductive PCB via fill options and their thermal, mechanical, and electrical considerations.

When it comes to PCB via fill, there are two choices: a conductive fill or a non-conductive fill. Each option has different benefits and disadvantages, depending on the application requirements.

Conductive Via Fill

If you choose to fill your vias with conductive epoxy, conductive epoxy matrices may use silver-coated copper particles and provide thermal and electrical conductivity when cured. Different conductive epoxy formulations can vary in particulate size and finished coefficient of thermal expansion (CTE).

Non-Conductive Via Fill

If you are choosing a non-conductive epoxy for your via fill, different non-conductive epoxy formulations can be used. Such formulations should be selected according to the requirements of the PCB design and via-fill process.

Choosing Your PCB Via Fill

For general via filling, a non-conductive epoxy will often be selected. This is because non-conductive epoxies usually provide a better CTE match with the surrounding laminate material. This allows the structure to expand or contract cooperatively with the laminate as the board heats and cools, reducing the chance of stress fractures and board failure.

A conductive via fill is useful when conductivity is of paramount importance, particularly for a thermal via whose primary purpose is to dissipate heat. A via filled with conductive epoxy is more effective at transferring thermal energy, making it suitable for thermal vias that transport heat away from the board.

You may also find conductive epoxy via fills in older PCB designs simply because that is the type of fill that board has always used, from before the benefits of non-conductive epoxies were fully appreciated.

Because of its name, some people may be under the misconception that a via filled with non-conductive epoxy cannot transmit an electrical signal to the other side of the board. This would defeat the purpose of a plated via if it were true. In a non-conductive epoxy-filled, copper-plated via, the electrical signal transmits through the copper as usual. It does not transmit through the epoxy, but the epoxy does not interfere with the transmission.