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Dry-Film Solder Mask for Flexible Printed Wiring Board

June 4, 2001

Showa Denko K.K. (SDK) has developed Topflex (trademark pending) dry-film solder mask for flexible printed wiring boards. This is a joint development with Nippon Polytech Corporation, a venture-capital company specializing in the photoresist ink business and is now a subsidiary of SDK.

Topflex can be put, without any gap, on a flexible circuit, using conventional dry film laminators. The new product can be used in a general photoresist process (UV exposure; development; heating) and equipment. Because of the formation of a high-precision, photographic flexible solder mask, Topflex will contribute to higher production efficiency on the part of flexible printed wiring board manufacturers. The product has clear advantages of high crease resistance and high precision covering (up to 30 micron-m of line/space width).

Currently, a coverlay film is heated and pressed on flexible printed wiring boards for coverage. In this process, adhesive is applied to the coverlay film having mechanically provided apertures. After strict alignment on a flexible printed wiring board, the film is heated and pressed. This process involves several problems: relatively low precision of coverage; machining cost for creating apertures; bleeding of adhesive; failure in alignment; and time/complexity of heating/pressing steps. As more and more elements are directly mounted on flexible printed wiring boards to increase the circuit density, higher precision is required for forming the cover.

The newly developed dry-film solder mask will solve these major problems for flexible printed wiring board manufacturers.

Nippon Polytech Corporation is a manufacturer of liquid photo solder mask, which is highly valued by customers for use as covering material of high-precision flexible circuits relating to hard disk drive, liquid crystal terminal, and T-BGA/COF semiconductors.

SDK and its Group of companies possess technologies to fabricate a wide variety of films. Topflex is a fruit of the fusion of know-how and production technologies of Nippon Polytech and SDK.

Marketing of the new product will start soon, after the performances are confirmed in field tests being conducted by Nippon Polytech. Annual sales of the product are expected to amount to ¥2 billion in three years' time. The product will be presented at the JPCA Show scheduled for inauguration on June 6 at Tokyo Big Site.

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Terminology

Flexible printed wiring boards (flexible circuits)

Printed wiring boards with flexibility, whose base material is made of polyimide film, etc. Circuits made of copper foil are formed on a film.

Dry-film solder mask

A three-layered photosensitive material used to cover a flexible circuit. It consists of a photoresist layer containing photosensitive resin composition (solder mask) sandwiched by a base film and a cover film.

Liquid crystal terminal

A tape-form flexible printed wiring board used in the surface-mounting of liquid crystal displays. It connects electrodes on the TFT board side (screen side) with electrodes on the driving LSI side.

T-BGA (Tape carrier ball grid array)

A high-density surface-mounting system that mounts semiconductors on a tape-form flexible wiring board, using a grid array.

COF (Chip on film)

A surface-mounting system that places semiconductor chips directly on a flexible circuit.

Outline of Nippon Polytech Corp

Address 358-2, Nibukata-machi, Hachioji City, Tokyo
President Atsushi Kabe
Established In July 1989
Capital ¥10 million
Ownership Showa Denko K.K. 60%; Atsushi Kabe 40%
Business Development, production and sale of photoresist for the manufacture of printed circuit boards
Annual sales ¥589 million (for fiscal 2000 ended June 30)
Telephone number 042-652-0216