In order to enhance the adhesion strength of copper metal lm to a polyimide (PI) lm substrate, a method combining surface microroughness formation and imide ring cleavage was investigated. The results showed that imide rings were cleaved with a KOH treatment while carboxyl and amide groups were formed on the surface of the PI lm. The surface micro-roughness did not change with the KOH treatment, and the adhesion strength of the copper metal lm to the PI lm was slightly improved to 30 g/ mm, which could be attributed to the interaction of both carboxyl and amide groups with the copper atoms. When the PI lms were successively treated with an alkaline permanganate and a KOH solution, many recesses were formed on the surface in an alkaline Z. Wang et al.permanganate solution, and the size and depth of the recesses increased with alkaline permanganate treatment time. The results of the AFM measurements showed that the average roughness .R/ increased from 3.54 to 10.23 nm after combined treatment with alkaline permanganate and KOH solutions. The adhesion strength of the copper metal lm to the PI lm reached 150 g/ mm, which was ve times greater than that achieved with the KOH treatment only.
A copper plating process for printed wiring boards operating in the GHz frequency range has been developed that improves the adhesion strength between the copper interconnects and the resin substrate by using an imidazole compound to form coordinate bonds. The coordinate bonds are prepared by impregnating the resin substrate with an aqueous solution of amino-group-containing imidazole (AI). The adhesion strength is measured by a tensile test with various concentrations of AI solution and different treatment times of impregnation. As a result, the highest adhesion strength of 4.2–5.1 N·cm-1 can be obtained on the entire surface of a 340×340 mm2 substrate, where the flatness is down to 58.7 nm. This result is due to the optimization of the impregnating condition for AI and of the removal condition for weak boundary layers. The signal transmission characteristics of the interconnects on the substrates fabricated by this processes are compared with the conventional process by S 21 parameter extraction in the GHz frequency range. The transmission characteristics of this process are markedly improved compared with those of conventional processes.
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