Ceramic films adhesion

In assembling hybrid microcircuits or multichip modules, ceramic interconnect substrates fabricated using thin-film or thick-film processes are attached to the inside base of a ceramic or metal package. Generally, film adhesives that have been cut to size are used to attach large substrates (greater than 1-inch square) while either paste or film adhesives may be used for smaller substrates. Substrates may be alumina, beryllia, aluminum nitride, or silicon. 

The surface layers are mainly characterised by the formation of mono- and diboride arrays[2,5]. As found [8], the boron depleated composites have the tendency to form ceramic films of high density and avoid crack formation by prevailing compressive residual stress. Therefore the surface films show excellent adhesion enhancing the resistance against abrasion[8,12]. 

To make use of the excellent thermal and electrical properties of plated copper, an adhesion layer is required between tire ceramic and the copper. One technique for doing this is to apply a tiiick-film adhesion layer on the ceramic. 

Copper can be electroplated onto the substrate in two techniques. In the first process, as shown in Figure 8.25a, an adhesion or seed layer is deposited on the ceramic. This adhesion layer can be thin film, either sputtered or evaporated, thick film, or refractory metallization. A sputtered or evaporated gold layer is deposited on top of the seed layer for thin-film metallization. Copper is then electroplated to the required thickness. This is followed by electroplated nickel and an optional gold electroplate. Figure 8.26 shows the buildup of plated copper metallization. 

Once a polymer dispersion or adhesive has been used in a formulated product, microbial growth can still take place either in the liquid phase, e.g. in paints and inks or, especially in high moisture environments, on dried materials after application, e.g. ceramic tile adhesives and paint films. To prevent this, biocides need to also be used in such end products, i.e. wet-state preservatives in liquid formulations and dry-film fungicides/algicides in products susceptible to such attack or infection (Ludwig, L.E., 1974 Springle, W.R., 1990 Paulus, W., 1992 ... 

Bullett and Prosser ° have reviewed, critically, various methods for measuring paint film adhesion. An empirical method was developed to determine metal-ceramic and metal-glass bonds. The adhesion of gold-underlayer film combinations to glasshas also been investi-... 

Figure 15 depicts schematically a process for depositing a TiN film using dynamic mixing, carried out by a simultaneous operation of Ti evaporation and nitrogen ion implantation. The ceramic film deposited by dynamic mixing shows excellent adhesion because of the presence of a mixed layer formed between the film and substrate. Ceramic films such as TiN, ZrN, AIN, (Ti, Al) N, cBN, and TiC are prepared by this method. 

Poly(vinyl acetate) homopolymers adhere well to porous or ceUulosic surfaces, eg, wood, paper, cloth, leather (qv), and ceramics (qv). Homopolymer films tend to creep less than copolymer or terpolymer films. They are especially suitable in adhesives for high speed packaging operations. 

Adhesives. Poly(vinyl alcohol) is used as a component in a wide variety of general-purpose adhesives to bond ceUulosic materials, such as paper and paperboard, wood textiles, some metal foils, and porous ceramic surfaces, to each other. It is also an effective binder for pigments and other finely divided powders. Both fully and partially hydrolyzed grades are used. Sensitivity to water increases with decreasing degree of hydrolysis and the addition of plasticizer. Poly(vinyl alcohol) in many appHcations is employed as an additive to other polymer systems to improve the cohesive strength, film flexibiUty, moisture resistance, and other properties. It is incorporated into a wide variety of adhesives through its use as a protective coUoid in emulsion p olymerization. 

Ceramics are joined to metals by metal eoating and brazing, and by the use of adhesives. In metal coating, the mating face of the ceramic part is coated in a thin film of a refractory metal such as molybdenum (usually applied as a powder and then heated). 

The metal film is then electroplated with copper, and the metal part brazed to the copper plating. Adhesives, usually epoxy resins, are used to join parts at low temperatures. Finally, ceramic parts can be clamped together, provided the clamps avoid stress concentrations, and are provided with soft (e.g. rubber) packing to avoid contact stresses. 

XPS has been used in almost every area in which the properties of surfaces are important. The most prominent areas can be deduced from conferences on surface analysis, especially from ECASIA, which is held every two years. These areas are adhesion, biomaterials, catalysis, ceramics and glasses, corrosion, environmental problems, magnetic materials, metals, micro- and optoelectronics, nanomaterials, polymers and composite materials, superconductors, thin films and coatings, and tribology and wear. The contributions to these conferences are also representative of actual surface-analytical problems and studies [2.33 a,b]. A few examples from the areas mentioned above are given below more comprehensive discussions of the applications of XPS are given elsewhere [1.1,1.3-1.9, 2.34—2.39]. 

Conversely, cling film (plasticised PVC/PVDC, (poly(vinyl chloride)/poly (vinylidene chloride), copolymer, which has very high gas-barrier properties) on peeling from a roll generates static electricity thus promoting adhesion to a surface, e.g., ceramics, but not metallic surfaces which conduct the static electricity away... 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

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