Basic patent granted for Hitachi Chemical's new copper surface treatment technology

Tokyo-based Hitachi Chemical Co, Ltd has acquired a basic patent for a new copper surface treatment technology that can be applied to high density multi-layer PWBs designed for the next generation of electronic devices.

In the production of multilayer wiring boards, copper surface treatment technology is widely used. This technology makes microscopic roughness on the surface of copper wiring to ensure firm adhesion between the insulation layer and the copper wiring. With electronic devices becoming increasingly compact and lightweight, there is a growing need to form finer wiring patterns and reduce transmission loss for high-speed signals.

However, when forming microscopic roughness with conventional technology, there is substantial etching of copper during surface treatment; the finer wiring patterns are, the more difficult it becomes to maintain their precision. Moreover, the formation of microscopic roughness causes transmission loss in high-speed signals due to the skin effect where the current flows near the surface of wires. For this reason, the challenge has been to ensure good adhesion between the insulation layer and the wiring, while accommodating finer wiring patterns and minimising transmission loss.

New treatment has been developed and patented by Hitachi Chemical. This technology is based on the "oxidation and reduction method", one of several conventional treatment technologies. Hitachi chemical has a high level of expertise in this method that it has built up over many years. New treatment can form microscopic roughness (Rz) with an asperity of 20-40 nm, less than one tenth the size of that formed with the basic technology. In addition to ensuring a satisfactory level of adhesion and minimizing transmission loss, New treatment technology involves minimal etching of copper during surface treatment, can form ultrafine wiring with a line / space (wiring width and space) of 5 µm / 5 µm, and hence is expected to be integral to the production of high density multi-layer PWBs.

Hitachi Chemical acquired a basic patent for this new treatment technology and is now establishing a global patent network, including acquisition of international patent rights. At the same time, efforts are underway to commercialise a surface treatment agent for this technology, with samples for circuit boards with maximum dimensions of 500 mm x 400 mm being distributed for evaluation purposes.

Moreover, the substrate surface can be treated at relatively lower temperatures and shorter times. One of its possible applications is as a horizontal conveyor system that can accommodate mass production of thin circuit boards, a process that is not possible with conventional oxidation and reduction treatment. There is also a plan to combine this technology with the company's expertise in next-generation build-up and solder resist materials to further improve its performance, with applications in the treatment of the adhesive surface of copper foils for copper-clad laminates and high-resolution copper etching in mind. Meeting the needs of the market and customers, Hitachi Chemical is stepping up efforts to commercialise this innovative technology.

The research on the technology was commissioned by New Energy and Industrial Technology Development Organization, Board Technology Research Promotion Business Private Technology Research Support Scheme.