Printed circuits, first developed

Typical of the temporary or manufacturing aid coating systems is the RISTON dry film photoresist for printed circuit (PC) board fabrication. This was the first of these systems developed. The RISTON product stmcture and the basic steps in its use are shown in Figure 2. It consists of a photopolymer sheet laminated between a Mylar cover sheet and a polyolefin separation sheet. It is manufactured as a continuous web (see Coating PROCESSES, survey), and is suppHed in roUs of varying width and photopolymer composition. 

To measure the current distribution in a hydrogen PEFC, Brown et al. ° and Cleghorn et al. ° employed the printed circuit board approach using a segmented current collector, anode catalyst, and anode GDL. This approach was further refined by Bender et al. ° to improve ease of use and quality of information measured. Weiser et al. ° developed a technique utilizing a magnetic loop array embedded in the current collector plate and showed that cell compression can drastically affect the local current density. Stumper et al."° demonstrated three methods for the determination of current density distribution of a hydrogen PEFC. First, the partial membrane elec-... 

Transistors have had an immense impact on the technology of electronic devices for which signal amplification is needed, such as communications equipment and computers. Before the invention of the transistor at Bell Laboratories in 1947, amplification was provided exclusively by vacuum tubes, which were both bulky and unreliable. The first electronic digital computer, ENIAC, built at the University of Pennsylvania, had 19,000 vacuum tubes and consumed 150,000 W of electricity. Because of the discovery and development of the transistor and the printed circuit, a hand-held calculator run by a small battery has the same computing power as ENIAC. 

The first major dry film resist was introduced in 1970 hy the Dupont Corporation and was marketed under the trade name Riston. It has undergone many updates since then and remains fairly competitive to this day. Other dry film resists have been developed since the invention of Riston, and have found applications in printed circuit board (PCB) and printed wiring board (PWB) manufacturing. ... 

The first system, introduced as Kodak KPR resist in 1956, was based on poly(vinyl cinnamate) derivatives as resins and organic solvents like cellosolve acetate UV exposure brings about crosslinking, after which the unexposed parts can be developed with the original solvent of the resist. A second system, which was introduced for printed circuits in 1960, was based on derivatives of polyfisoprene) rubber as a resin and a bis-azide sensitizer. Upon UV exposure, crosslinking occurs and Nj is evolved. 

Once the proper performance of the circuit has been verified, it is convenient to build a more definitive system. There are two alternatives on the one hand it can be made by a photographic system, on the other hand with the milling machine. The first requires fewer tools, while the second does not require chemicals. In both cases an image of the printed circuit to be developed is needed. There are different ways of obtaining it. However, we will focus on the most comfortable one, based on the use of commercially available software. 

One obvious method to increase printed circuit functionality is to put more circuitry per unit area of the circuit. Printed circuit densification has driven several improvements in copper foil technology. One of the first developments was high temperature elongation (HTE) foils. Other advances include low- and very-low-profile foils, thin foils, and foils for high-performance resin systems. 

This type of printed circuits actually started in 1980, when researchers started investigating ways to reduce the size of vias. The first innovator is not known, but some of the earliest pioneers include Larry Burgess of MicroPak Laboratories (developer of LaserVia), Dr. Charles Bauer at Tektronixs (who produced photodielectric vias), and Dr. Walter Schmidt at Contraves (who developed plasma-etched vias). Laser-drilled vias were used in mainframe computer multilayers in the late 1970s. These were not as small as the laser-drilled vias today and were produced only in FR-4 with great difficulty and at great cost. 

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