Surface Morphology of Electroless Copper Deposits Using Different Reducing Agents

Electroless copper plating has been used in the printed circuit industry for plating from bare laminate and plating through hole. Common commercial plating solutions consist of formaldehyde as the reducing agent. However, due to its hazardous nature, many alternatives were brought out to reduce the potential risk in electroless copper plating process, among which glyoxylic acid is highly competitive. The aim of this research is to examine the surface evolution process and the surface morphology of the electroless copper deposits plated under different conditions with either formaldehyde or glyoxylic acid as the reducing agent.

Electroless copper deposits were plated on the epoxy board in solutions with either formaldehyde or glyoxylic acid as the reducing agent with different chemical concentrations at 60°C or 45°C. Four substrates were used for each plating, each of which was taken out of the plating solution after being plated for 5, 15, 60 and 120 minutes, respectively. The surface morphology of all the samples was characterized using scanning electron microscopy (SEM).

The SEM image of the epoxy substrate before plating shows an eroded‐like rough surface where many dimples can be observed. The images of the plating sequence indicate that copper was plated almost evenly on both inside and outside of the dimples in the formaldehyde solutions and the final surface tended to be still rough or even hollow, while in the glyoxylic acid solutions, copper was plated more on the inside of the dimples and the final surface tended to be smoother. Lowering temperature resulted in much smoother surfaces from both formaldehyde and glyoxylic acid solutions. The research reveals that glyoxylic acid has promising prospect as an alternative to formaldehyde in electroless copper plating. Under certain conditions, glyoxylic acid can be very effective for smooth plating on rough surfaces.

Keywords:

• electroless copper
• glyoxylic acid
• surface morphology
• surface residual stress

The authors would like to acknowledge Huchinson Wampoa and the EPSRC for the financial support of the PhD project.