Printed wiring

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Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

Ch oline in the form of choline base (hydroxide) is a strong organic base with a pH of approximately 14. This product can have industrial apphcations where it is important to replace inorganic bases with organic materials. Ch oline base is currently used in the formulation of photoresist stripping products for use in the printed wire board industry. Dilute aqueous solutions (5%) of ch oline base that have very low concentrations of metallic ions have been utilized for apphcations in the semiconductor industry. 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

The next step is to connect the individual unit operations in a block diagram, creating a process flow sheet. Figure 1 is an example of a simplified process flow diagram for a pattem-etch process for a printed wiring-board operation. There are... 

Figure 12.4. Left—Scanning electron microscope image of the input/output pads of a silicon IC bumped with eutectic lead/tin solder after solder reflow. Right—Photograph of printed wiring board interconnect pads that have been printed with lead/tin solder prior to reflow.

Electronic Materials. Applications of photopolymer technology to electronic products is probably one of the largest imaging categories in terms of sales and total number of patents and publications. A wide variety of products have been developed for the production of printed wiring boards (PWB) and the manufacture of integrated circuits (IC). 

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

This technology is currently commercially available. Polylonix Separation Technologies, Inc., offers polymer filtration for the treatment of metal-contaminated wastewaters from the electroplating and printed wire board industries. 

Printed wiring boards electronic coatings for pLECTRONICS, COATINGS] (Vol 9)... 

The most important application of parylenes is as a conformal coating for printed wiring assemblies. These coatings provide excellent chemical resistance, and resistance to fungal attack, hi addition, they exhibit stable dielectric properties over a wide range of temperatures. 

Numerous protective conformal coatings are also used in the hybrid circuit industry. Most of the criteria that pertain to use in printed wiring also apply here (4). 

Many of the fabrication processes for integrated circuits are similar or conceptually related to those used in the manufacture of printed wiring boards. However, because of the extremely fine device features, fabrication must be carried out in clean rooms having strictly controlled environments. Particulate and chemical contamination are minimized, and temperature, humidity, and even vibration are carefully controlled. 

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