Electrical printed wiring board

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. 

The electrical properties of polymers are important in many applications [1]. The most widespread electrical application of polymers is the insulation of cables. In recent years, high-performance polymers have become important in the electronics industry as encapsulants for electronic components, as interlayer dielectrics, and as printed wiring board materials. The dielectric constant (or permittivity) and the dissipation factor (or power factor or electrical loss tangent) tan 8, which are dimensionless quantities, are the key electrical properties. 

Electrochemistry is a central theme in the interconnection of chips and other microelectronic components. The manufacture of printed wiring boards, such as single-layer, multilayer, or flexible boards, involves electroplating of the conductor that forms the electrical paths. The corrosion of these paths and the interfacial stability of the conductor-polymer composites that determine the reliability of these interconnections are electrochemical problems. 

Adhesives may substitute for wire or solder in forming electrical connections for example, in connecting capacitors, resistors, or semiconductor devices to a printed-wiring board or to a thin-film or thick-film hybrid microcircuit. The best and most... 

Besides this prime role of attachment, electrically conductive adhesives are widely used to form electrical contacts between components and the printed-wiring board or other interconnect substrate, such as thin-film or thick-film ceramic substrates or flexible cable. For this function, adhesives serve as low-cost alternates to wire, solder, and other metallurgical connections. 

In this section we discuss three applications of electrically conductive adhesives die attach adhesives, anisotropically conductive adhesives for liquid crystal display (LCD) assembly, and conductive adhesives for surface-mounted assembly of packaged components on printed wiring boards (PWBs). These applications were selected based on overall... 

Furthermore, the human health section of the EU Risk Assessment has concluded that the fire retardant additive TBPBA carries no risks, and the EU Scientific Committee on Health and Environmental Risks (SCHER) has confirmed the EU (Risk Assessment) conclusions that TBPBA presents no human health risk. TBPBA is a brominated flame retardant (used in electrical equipment including computers, televisions, and in printed wiring boards (PWB), and so on [21],... 

Kraft paper is widely used as a reinforcement. When saturated with phenolics, it is made into a common printed wiring board. When combined with melamine, it becomes a decorative high-pressure laminate used in furniture, countertops, and wall panels. Paper reinforcement is inexpensive and easy to machine, drill, and pxmch. It imparts good electrical properties, but it is sensitive to moisture and cannot withstand high temperatures. 

Polymer adhesives have found their place in numerous electronics applications. Major uses include eommercial/consumer products computers and military, space, automotive, medical, and wireless communications. Some adhesives may be used aeross several applications while others have been formulated to meet applieation-specific requirements. For example, reworkability is not a consideration for high-production, low-cost consumer products such as cell phones or calculators, but is important for high-value, high-density printed-wiring boards (PWBs) used in military and spaee electronics. Further, thermal stability at high temperatures is required for near-engine electronics in automobiles, aircraft, and for deep-well sensors, but not for office computers. The major applications for polymer adhesives are to attach and electrically insulate or to electrically connect components, devices, connectors, cables, and heat sinks to printed-circuit boards or to thin- or thick-film hybrid microcircuits. In addition, over the last several decades, new uses for adhesives have emerged for optoelectronic (OE) assemblies, microelectromechanical systems (MEMS), and flat-panel displays. 

UL746 A B C D E Underwriters Laboratories. Pol5mieric materials Short term property evaluations Long term property evaluations Use in electrical equipment evaluations Fabricated parts Industrial laminates, filament wound tubing, vulcanised fibre, and materials used in printed wiring boards... 

Among all electrical and electronic products, computer, TV and similar housings account for 59% of brominated FR sales, and printed wiring boards for 30%. Connectors and relays are responsible for 9% of sales, while wire and cable insulation and sheathing use only 2%. Epoxy and phenolic PCBs represent high volume sales. 

NEMA standards include many variations for reinforcements, resins, and applications. Reinforcements include paper, fabrics, and glass mats. Resins include phenolic, melamine, silicone, epoxy, and polyester. Copper-clad laminates are covered with copper foil for use in printed wiring boards, whereas unclad laminates do not have a foil. Unclad laminates are used in many industrial applications, but NEMA s primary concern is when they are used as electrical insulation. 

Electrical Laminates. Printed wiring boards (PWB) or printed circuit boards (PCB) are used in all types of electronic equipment. In noncritical applications such as inexpensive consnmer electronics, these components are made from paper-reinforced phenolic, melamine, or polyester resins. For more critical applications such as high end consnmer electronics, computers, complex telecommunication equipment, etc, higher performance materials are required and epoxy resin based glass fiber laminates fnlfill the requirements at reasonable costs. This application constitntes the single largest volume of epoxies used in structural composites. In 2000, an estimated 200,000 MT of epoxy resins were used globally to manufacture PCB laminates. 

Amoco [7] reported several polyaryl ether-sulfones to be miscible with each other. The miscible blend comprises a 1,4-arylene unit separated by ether oxygen and another resin 1,4 arylene separated by an SO2 radical. The miscible blends showed a single glass transition temperature in between the constituent values. The blend was transparent. These can be used for printing wiring board structures, electrical connectors, and other fabricated articles that require high heat and chemical resistance and good dimensional and hydrolytic stability. 

In addition to providing circuit interconnection, a multilayer printed wiring board (ML-PWB) provides the electrical and mechanical platform for the system. This means that the electrical and thermal properties of the ML-PWB material are very important for the proper functioning of the system. Among the properties of importance are dielectric constant, Du (also known as Er) dielectric loss, Df (or tan 8) glass transition temperature, Tg time to delamination,Txxx thermal decomposition temperature.Ta coefficient of thermal expansion, CTE and moisture absorption. The following sections discuss the importance of these properties to an ML-PWB snbstrate. 

RoHS Compliance. Most PCB fabricators now insist that any solder mask products they use be compliant with Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment, the RoHS directive, and Directive 2003/11/EC, the 24th amendment to Council Directive 76/769/EEC. This directive places requirements on specific materials and amounts of each that may be included in a formulation. Meeting this criterion is essential for most printed wiring board (PWB) fabricators. 

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