Conductive vs. Non-Conductive Via Fill PCB

When it comes to your PCB via fill, you have two choices. You can opt for a conductive fill or a non-conductive fill. What are the benefits and disadvantages of each option? Why would you choose one over the other?

Conductive Via Fill

If you choose to fill your vias with conductive epoxy, your main choice is usually between the silver-coated copper particle epoxy matrices of the Tatsuto AE3030 epoxy fill or the DuPont CB100. Both offer thermal and electrical conductivity when cured. The DuPont fill has a larger particulate size and a higher finished co-efficient of thermal expansion (CTE), as well as a longstanding reputation for being a highly effective conductive epoxy fill.

Non-Conductive Via Fill

If you are choosing a non-conductive epoxy for your via fill, you will often choose the Peters PP2795 epoxy. However, a popular alternative over the last few years has been the San-Ei Kagaku PHP-900 epoxy. Both should be able to meet your basic needs when it comes to a non-conductive via fill epoxy.

Choosing Your PCB Via Fill

So how will you choose your PCB via fill? For general via filling, you will most often choose a non-conductive epoxy. This is because non-conductive epoxies usually provide a better CTE match with the laminate material that surrounds it. This means the structure will expand or contract cooperatively with the laminate material as the board heats and cools, reducing the chance of stress fractures and board failure.

So why would you ever use a conductive via fill? You would want a conductive epoxy when conductivity is of paramount importance, particularly if you are filling a thermal via whose primary purpose is to dissipate heat. A via filled with conductive epoxy is more effective at transferring thermal energy, so it works well with thermal vias to quickly and effectively transport heat away from the board.

You may also find conducive epoxy via fills in older PCB designs simply because that is the type of fill that board has always used — since 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 always. It does not transmit through the epoxy, but neither does the epoxy interfere with the transmission.