On a recent episode of I-Connect007’s On the Line With… podcast, we discussed electroless copper deposition—depositing a thin copper layer into the through-holes and vias of what will eventually become a printed circuit board. Specifically, it is a chemically catalyzed deposition of copper, mainly to the epoxy inside the holes (as well as on the entire surface of the board). Electroless differs from electrolytic in that electrolytic deposition relies on electricity.

Without proper electroless copper deposition, boards can wind up with voided copper holes, usually identified later in the manufacturing process. This preparatory step is critical, and it is important for the manufacturer to get it right. When done correctly, it creates a very fine layer of copper that makes the connection from the top to the bottom of the through-hole. Since this thin layer of copper is conductive, it allows a later electrolytic process to deposit a thicker, more substantial layer of copper.

When designing for manufacturing (DFM) ultra-high-density interconnect (UHDI) PCBs, the choices you make regarding electroless copper plating help ensure mechanical reliability. They also reduce the risk of issues with electrical and signal integrity. Designers should consider manufacturability, material properties, and their manufacturing partner’s process controls to maximize yield and ensure the board performs to specs.