Electroless copper plating and surface characterization of thermoplastic PPO based printed circuit boards

Abstract

Purpose -The adhesion between electroless copper and a substrate is one of the most important factors in the reliability of thermoplastic printed circuit boards. The purpose of this paper is to investigate the effects of mechanical grinding and acid etching of thermoplastic substrate materials on the adhesion of copper deposited by an electroless copper plating process. The base material of the test substrates was a new high temperature thermoplastic polyphenylene oxide (PPO) compound. Design/methodology/approach -The effects of pre-treatment on plastic surfaces are analyzed by the following methods: Fourier transform infrared (FTIR), SEM, the Dyne surface energy test and the surface roughness test. The adhesion between electroless copper and thermoplastic substrate is measured with a peel strength test. Findings -The results showed that mechanical grinding of the substrates significantly increased adhesion but the highest adhesion is gained by using an acid etch treatment before electroless plating. These results indicated that adhesion between copper and the substrates was not directly proportional to the roughness and surface energy values. Originality/value -The conventional sweller/desmear treatment used in a printed circuit board factory for pre-treating epoxy based laminates prior to electroless plating is not suitable for these PPO compound boards. The copper adhesion is adequate when the substrates are etched with sulphuric acid/ chromate solution. In that case the bonding between the metal layer and the plastic surface is stronger than the bondings between the polymer chains of the thermoplastic material. The adhesion mechanism of electroless copper in these mechanically abraded samples is mechanical interlocking of metal particles.

Enhancing peel strength between liquid crystal polymer and copper with plasma treatment, surface oxidation, and silane coating

“…Finally, plasma‐treated LCP and oxidized copper coated with functionalized agent were laminated at 180°C to obtain the final sample. The peel test results showed that the peeling strength of the sample reached 8.92 N cm −1 , which met the standard for industrial application 28,29 …”

“…The peel test results showed that the peeling strength of the sample reached 8.92 N cm À1 , which met the standard for industrial application. 28,29 F I G U R E…”

A critical review of copper electroless deposition on glass substrates for microsystems packaging applications

“…Uniform surface is due to improved surface chemical activity resulting in higher catalyst adsorption during electroless deposition. However, no noticeable improvement in the adhesion strength was seen as the surface morphology of the substrate did not change considerably [118]. Laine-Ma et al [119] studied the effect of acid etching and mechanical grinding on the thermoplastic polyphenylene oxide compound substrate.…”

“…Hong et al [118] demonstrated an air plasma treatment for improving the adhesion of copper films on the epoxy resin substrates. Substrates were cleaned and heated for 30 min in an oven maintained at 60°C.…”

“…Uniform surface is due to improved surface chemical activity resulting in higher catalyst adsorption during electroless deposition. However, no noticeable improvement in the adhesion strength was seen as the surface morphology of the substrate did not change considerably [118].

Figure 8 Optical images of the copper surface (left), tape surface (middle), and SEM image (right): tape test performed on (a) unmodified substrate and (b) modified substrate [118].

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