Dielectric adhesives

FIGURE 15.7 A schematic of the wafer-level dielectric adhesive bonding via-last approach to 3D demonstrated by Lu et al. (from Ref. 46-50). 

Pozder et al. have employed this approaeh to demonstrate paekaging compatibility of dielectric adhesive 3D with active electrical structures [50]. 

Layer pairs are prepared using conventional processes of etching, plating, drilling, and so on, or by conductive paste processes. The layer pairs are laminated together using B-stage resin systems or some other form of dielectric adhesive into which conductive paste vias have been placed. 

Aiming at the CSP application market, Merix Corporation and Auburn University collaborated to develop anisotropic conductive adhesives called Area Bonding Conductive (ABC) adhesives. ABC adhesives are two-region thermoset adhesives with electrically conductive adhesive pads surrounded by a continuous oxide-filled dielectrical adhesive to form a total area bond. Both regions are solvent-free, B-staged, nontacky epoxies supplied on a Mylar carrier release film. In contrast to conventional ACAs, conductive areas of ABC adhesives are located only at bond pad locations. The assembly process for using ABC adhesives is shown in Fig. 9. The ABC adhesives... 

Particle Contamination. In assembling large, high voltage equipment such as coaxial lines, contamination by metal particles may occur which may decrease the dielectric strength under various conditions by 5 to 10-fold (44—45). Metal needles are the worst contaminants and electrostatic traps or adhesive areas have been designed to cope with them (46). 

In the electronics industry. Pis find wide appHcations as a dielectric material for semiconductors due to thermal stabiHty (up to 400°C) and low dielectric constant. Pis are being considered for use in bearings, gears, seals, and prosthetic human joints. The intended part can be machined or molded from the PI, or a film of PI can be appHed to a metallic part. Because of their superior adhesion, dielectric integrity, processing compatibUity, and lack of biological system impact. Pis have been used in many biological appHcations with particular success as body implants. 

Sihcones (qv) have an advantage over organic resias ia their superior thermal stabiUty and low dielectric constants. Polyurethanes, when cured, are tough and possess outstanding abrasion and thermal shock resistance. They also have favorable electrical properties and good adhesion to most surfaces. However, polyurethanes are extremely sensitive to and can degrade after prolonged contact with moisture as a result, they are not as commonly used as epoxies and sihcones (see Urethane polymers). 

In some cases it is possible to form bridges of metal using air as the dielectric (150). However, if more than two levels of wiring are required then dielectric spacing is necessary. The ideal dielectric film has excellent adhesion and alow dielectric constant to minimize parasitic capacitances. The most common films include siUcon oxide, siUcon nitride, and a number of spin-on dielectrics (216). 

The exceUent adhesion to primed films of polyester combined with good dielectric properties and good surface properties makes the vinyhdene chloride copolymers very suitable as binders for iron oxide pigmented coatings for magnetic tapes (168—170). They perform very weU in audio, video, and computer tapes. 

W. R. Grace Co. dielectric and conductive adhesives, encapsulants, heat dissipating materials, manufacturing aid coatings... 

Unilver Table 1. Worldwide 1992 Electronics Industry Value/ x 10 adhesives, dielectric coatings, protective coatings, dielectric interlayers, electronic functional coatings... 

Because there are many other properties that also are important, coatings cannot be selected only on this basis. The mechanical and chemical properties of the coating, change of properties with temperature, dielectric and adhesion properties, and particulady the cost of fabrication are all important parameters. Coatings can also be used to transport heat created away from a component and keep the component functioning as designed, or to protect a component from temperature variations in the environment. 

PSA coated tapes are used for a variety of applications in the electrical industry, but they have to meet additional requirements to be accepted in this industiy The adhesive are typically expected to be non-corrosive, they need to have good dielectric properties, they need to hold out moisture, and they need to show good flame retardaney. Espeeially for eleetronic applieations, little or no outgassing is aeceptable, and the adhesive should not introduce migratory contaminants resulting from exposure to release coatings or the presence of additives. 

In situations in which piping protrudes partitions or bulkheads of dissimilar metals, proper precautions should be taken against galvanic corrosion. Possible solutions include the use of dielectric gaskets or sleeves and the use of plastic adhesive tapes. Examples are illustrated in Figure 2.6. 

Thin polymeric films have important industrial apphcations (e.g., as protective coatings, lubricants, adhesives, dielectric or nonlinear optic devices, etc.) and pose many fundamental problems of film stability [1,2,4]. An important question, therefore, is whether these films break up and spontaneously dewett the substrate, resulting in the formation of droplets. The... 

Material Thickness of film plus adhesive (mm) Tensile strength (kg/cm width) Elongation at break (%) Moisture absorp- tion (%) Moisture- vapour transmission rate (g/m per 24 h Dielectric strength (V)... 

Adhesive Dielectric Induction Mechanical Solvent Spin Thermal Ultrasonic... 

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