Chelator plays an important role in Cu electroless deposition (ELD) solution. It has the function to maintain the stability and to regulate the deposition rate of the ELD solution. Industry uses Cu ELD process to deposit Cu layer on non-conductive substrate, such as a printed circuit board (PCB). This process relies on the traditional Sn/Pd colloid as the catalyst to initiate the Cu ELD. However, Sn/Pd colloid has disadvantages, such as Pd is very expensive and the residual Pd has to be removed after the photolithography process for preventing the short between two copper lines in the semi-additive process (SAP). As a result, we employ copper nanoparticle (CuNP) as catalyst to overcome these issues. In this work, we select two chelators to study their effect on the Cu ELD by using CuNP and formaldehyde as the catalyst and the reducing agent, respectively. The surface roughness of deposited copper layer was measured by atomic force microscopy (AFM). The amount of ELD Cu was measured by atomic absorption spectrometry (AA). The morphology of the ELD Cu deposited layer on the sidewall a of through hole of a PCB was imaged by scanning electron microscope (SEM) and optical microscope (OM) to evaluate the influence of the two chelators on the Cu ELD, whose catalyst is CuNP rather than Pd.

Keywords:

Chelator, Cu electroless deposition, Copper nanoparticle, Printed circuit board

Reference:

• M. Lin, S.C. Yen, Applied Surface Science,116-126, 178 (2001)