Circuit substrates

Properties desired in cable insulation and flexible circuit substrate materials include mechanical flexibiUty, fatigue endurance, and resistance to chemicals, water absorption, and abrasion. Both thermoplasts and thermosets are used as cable-insulating materials. Thermoplastic materials possess excellent electrical characteristics and are available at relatively low cost. 

Other sohd-state apphcations of sihcon carbide include its use as an electroluminescent diode for use in sound recording equipment and photomultipliers and controllers. It has been studied as a reflective surface for lasers. By combining its excellent thermal conductivity and high electrical resistance, sihcon carbide has also found apphcation as an insulating material for integrated circuit substrates. 

Integrated circuit substrates Insulation, heat resistance Alumina, magnesia... 

The past introduction of TP materials into the area of printed circuit substrates has led to a broader type of application for the circuits. The products can be injection molded and the circuit applied to a molded part which will have a molded-in connector structure used to interconnect the device to the rest of the system. By combining the connector and substrate functions, it is possible to make very compact printed circuit units. 

Metal ohmic contact pads 55 are formed on the n-type islands and the detector is bonded to a multiplexer integrated circuit substrate 53 via indium columns 54. 

Alumina ceramics are widely used for thick-film circuit substrates and for integrated circuit packaging. This aspect is discussed in Section 5.5.5. 

Polymeric substrate materials in use include highly filled phenolic and epoxy resins for rigid printed circuit boards, polyimides and polyesters for circuit substrates as well as for more general applications, special foamed poly(tetrafluoroethylene) polymers and copolymers, foamed composite materials of the latter, special epoxy fiberglass composites, and polyimide support layers for TAB. In addition, epoxies and silicone polymers are used increasingly in applications as encapsulants, as humidity and environmental barriers within packages, and as packaging materials themselves. 

PBZT and PBO are ordered polymers which form long rigid-rod molecules which give rise to a microfibrillar network structure in biaxially oriented films (Figure 1). Such biaxial films have been used in combination with low dielectric constant resins, such as cyanate ester resins, to make circuit substrates for use in MLBs... 

Circuit substrates are products that are totally dependent on the electronics industry for their existence and future. They are the basic raw materials that the PCB and hybrid industries convert into carriers which mechanically support active and passive devices, and which contain the customised interconnection patterns to link the devices together in an assembly. Any changes in these products have to arise from the changes in equipment design, improvements in the electronic devices themselves, and modifications to the packages that contain the devices ... 

Although metals are good heat conductors, they obviously must have some electrically insulating layer added to make them into a useful circuit substrate. However, as seen from Table I, good electrical insulators are also good thermal insulators. Even a thin layer of insulation greatly reduces the conductivity of the composite structure. 

Another important low-permittivity, low-loss ceramic is alumina. Alumina has such an excellent combination of good mechanical properties, high thermal conductivity, and ease of metallization that it is widely used today for thick-film circuit substrates and integrated electronic packaging. 

The dielectric constant of LCP films is typically 2.7 to 3.0, making them attractive for high speed electronic circuit substrates. Tlie dielectric strength of over 7,000V per mil combined with very low moisture absorption (less than 0.2 percent by weight) meets requirements for electric wire and cable insulation. 

TLCPs have many outstanding properties that uniquely qualify them for these high performance multilayer boards (12). Table 7 compares the applicability of LCPs with other state-of-the-art materials for electronic packaging. They can be made into very thin, self-supporting films (<50 J.m) with a controllable CTE. By processing LCP films as described above, circuit substrates can be manufactured with a CTE around 7 ppm/°C and thermal stability over 250°C. TLCPs do not require secondary resins for fabrication into MLBs, they can be thermally bonded to themselves and to copper foil. Control of molecular orientation has been shown to result in a substrate with the desired CTE of 6 to 7 ppm/°C for matching alumina, or 16 ppm/°C for matching copper. 

Polyetherimide is used in a variety of applications. Electrical applications include printed circuit substrates and bum-in sockets. In the automotive industry, PEI is used for under-the-hood temperature sensors and lamp sockets. PEI sheet has also been used to form an aircraft cargo vent. The dimensional stability of this polymer allows its use for large flat parts such in hard disks for computers. 

The polysulfones are used for manufacturing of printed-circuit substrates, moving parts of relays, coils, clamps, switches, pipes socles, potentiometers details, bodies of tools, alkaline storage and solar batteries, cable and capacitor insulation, sets of television and stereo-apparatuses, radomes. The details under bonnet, the head lights mirrors, the flasks of hydraulic lifting mechanisms of cars are produced from polysulfones. 

In order to ensure safety, electronic circuit substrates are required to use flame-retardant materials (5). A cured film formed by an inkjet ink containing a compound of a special structure can achieve a high flame retardancy. In particular, poI Tneric derivatives based on oxaphosphorin, cf. Figure 5.3, are used. 

Integrated circuit substrate, package, wiring substrate, resistor substrate, electronics interconnection substrate Ceramic capacitor... 

Chip on board (COB)—the die is mounted directly on the printed circuit substrate (or board). See also tape automated bonding (TAB) and tape carrier packages (TCB). 

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