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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.

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Purpose The aim of this study was to evaluate the feasibility of pad printing for producing electrical conductors and to define the factors affecting the print quality of polymeric silver ink conductors. Design/methodology/approach Polyethylene terephthalate (PET) film and polyphenylene oxide (PPO) compound film were used as substrate materials. Three different polymeric silver inks, marked A, B and C, were used and tested. Findings The results indicated that the important factors in the pad printing of silver ink conductors are the printing parameters and characteristics of the ink, pad, cliché and substrate. The interactions of these factors should be considered on a case-by-case basis. The sheet resistances of triple-pressed ink conductors varied between 20 and 110 mΩ/sq for 5.7- to 8.5-μm-thick conductors. Ink (B) had a higher sheet resistance than Ink (A) because of its lower silver particle content but also because of the shorter curing time and lower curing temperature. Ink (A) showed excellent adhesion on PET, and Ink (B) had moderate adhesion on PET without corona or plasma pre-treatments, but both inks adhered weakly on PPO compound. Both corona and plasma treatments raised adhesion of these two inks on all test substrates to the highest classification value, 5B. Originality/value This paper contains a survey and preliminary testing of the pad printing of polymeric silver ink conductors on flexible thermoplastic foils. Finally, the paper introduces the advantages and drawbacks of the technique.

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