Printed circuit boards reinforcement materials

The markets for polyetherimides arise to an extent from stricter regulations concerning flammability and smoke evolution coupled with such features as high strength, toughness and heat resistance. Application areas include car under-the-bonnet uses, microwave equipment, printed circuit boards and aerospace (including carbon-fibre-reinforced laminated materials). The polymer is also of interest in flim, fibre and wire insulation form. 

Some electrical properties of reinforcing fibers, composite resins, and the resulting composites are given in Tables 6.12, 6.13, and 6.14, respectively. These values should be taken as approximate only, especially for the composites, since fiber orientation, content, and field strengfh have an enormous impacf on fhe dielecfric properties of these materials. Some of the most widespread electrical applications for glass-fiber-reinforced epoxy systems are in printed circuit boards and electrical housing such as junction boxes. 

Reinforced epoxy resins are the basis of printed circuit boards, tanks, pipes, and aerospace materials. Cast epoxies are very useful in electrical potting and encapsulation of transistors, switches, coils, integrated circuits, transformers, and switchgears. 

Bismaleimide resins are extensively used in multilayer printed circuit boards. They can also be used in insulation fibres for protective clothing. Due to their ability to adhere and retain adhesive strength at high temperature, bismaleimides are widely used as a base material for flexible printed circuit boards in the electrical and electronics industries. Bismaleimides are often linked with rubber chains for use as flexible linking molecules to reinforce the rubber compound for tyre applications. The double bond of bismaleimides readily reacts with all hydroxy or thiol groups found on the matrix to form a stable carbon-sulfur, carbon-nitrogen or carbon-carbon bond. 

Major Applications Display device,3 semiconductors,. optical flbers, antireflection fllms, pho-toimaging process, printed circuit board, inks,io i2 toners,i3.i4 paints, . adhesives, . packing materials, molding materials for fiber-reinforced plastics, building materials, prediction of deterioration of resins, materials for treating animal manure ... 

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. 

One of the most critical requirements for electronic surface-mount components is the CTE. In this respect, LCPs are unique in that their thermal expansion properties can be tailored by the judicious incorporation of reinforcements (such as short glass fibres and chopped carbon fibres) and fillers (such as talc, silica and calcium carbonate). Figure 7.9 illustrates the thermal expansion of LCPs and how they compare with other engineering materials. The CTE can be adjusted within the wide limits to practical requirements by varying the processing conditions, and can approach that of FR4 epoxy/glass fibre - one of the most widely used substrates for printed circuit boards. Other application-related examples are discussed in section 7.5. 

The main engineering applications of phenolic resins are laminates, foundry and friction materials. In the electrical laminating field, phenolic resins are used to impregnate kraft paper for the production of insulation boards, printed circuits and transformer bushings. The resin used in this case is usually based on cresol or a substituted phenol and used in a water/alcohol solution. The properties obtained would be a function of the reinforcement and the characteristics of resin used, eg high or low molecular weight. 

The thermoplastics used for MID are neither as rigid nor as strong as the glass-reinforced themosets routinely used for printed-circuit boards. The layer of metal deposited on the substrate is typically hard and compensates for the poor wirebonding properties of the soft substrate material. This is why bondability is largely independent of the polymer used. It is important to bear in mind, however, that there is a minimum thickness specification for plating (Table 5.7). The thicker the metallization, the more dependable the wire-bonding process becomes. [182]... 

The major applications of LCP films in electronics are multilayer boards and multichip modules, and flexible printed circuits. Current materials used in the.se applications include polyimide film, high performance thermoplastic film such as polyphenylene sulfide and polyetherether ketone, and fiber reinforced composites such as quartz fiber-polyimide. The price of these materials for electronic packaging is in the range of. 50 to. l(K)/lb, so LCPs can compete very effectively at their current prices. Based on a two to three times increase in price... 

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