Formulation film adhesives

Films of PATE were cast on copper plated circuit boards. Typical solutions contain from 8% to 17% PATTE solids and 0.02% Flourad FC 135 surfactant. No other additives, such as adhesion promoters, sensitizers, viscosity modifiers or stabilizers, were employed in the formulations. Films of 0.001 to 0.008 inches wet film thickness were cast on abrasively cleaned circuit boards and then oven dried for 5 minutes at 105 °C. Thus, in each case the... 

Epoxy adhesives can be manufactured into a film form. This is most conveniently done with solid epoxy resins in solution. Epoxy film adhesives can be thermoplastic (e.g., linear ultrahigh molecular weight phenoxy resin) hot melts, but more commonly they are formulated, thermosetting materials. 

Heat curing epoxy systems may consist of one or two components. The nomenclature is similar to that employed with the room temperature curing adhesives (e.g., resin component, curing agent component, 2Ksystem, etc.). Many heat curing epoxy adhesives systems are liquids or pastes. However, heat curing systems also can be processed into solid adhesive forms (e.g., powders and films). This chapter describes the paste and liquid formulations solid adhesive forms are considered separately in Chap. 13. 

A significant advantage of tape and film adhesives is the greater toughness that is available compared to other adhesive types. This is primarily due to the ease with which resinous modifiers can be added to the formulation via solvent solution. Thus, hybrid epoxy adhesives such as epoxy-nylon, epoxy-phenolic, etc., are often found in tape or film form. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

The final thickness of epoxy tape or film adhesives is on the order of 5 to 15 mils. These adhesives may be soft and tacky, or stiff and dry, depending on their formulation. The soft and tacky products are valuable in products requiring application to contoured or vertical surfaces. If the product is especially tacky, a release liner (e.g., polyethylene film, coated paper) is generally used to keep the film from blocking. The stiff and dry products are generally used for flat surfaces where speed and ease of application are required. 

TABLE 13.2 Common Epoxy Hybrid Resins Used in the Formulation of Tape and Film Adhesives... 

Starting formulations for epoxy tape and film adhesives... 

As may be expected, many factors affect polyurethane properties which are important in practical apphcations. For example, films, adhesives, and foamed resins can be obtained by suitable formulation, particularly by variation in the nature of the polyol (72). 

Epoxies are not the only resins used in aerospace bonding. A common formulation is a nitrile/phenolic film adhesive. A typical formulation may consist of the following (pbw) ... 

As previously mentioned in this chapter, carboxyl-reactive nitrile liquids appear to be the preferred modifiers for latent epoxy structural film adhesives. One of the major components used in formulating these adhesives is a solid epoxy resin of similar molecular weight (1000). This limited coatings study suggests that similar elastomer-modified epoxy resins are equally impressive in solution epoxy coatings. In addition. Table XI/Recipe 3 features a high impact coating modified with both liquid and solid carboxylated nitrile elastomers. 

Electrically conductive film adhesives, if filled with silver particles, are also highly thermally conductive. Thermal conductivities range from 0.9 to 7 W/m K, depending on the formulation. Aluminum-to-aluminum lap shear strengths range from 2200 psi to 5100 psi. Films are commercially available in thicknesses from 2 to 6 mils. 

A third approach to underfilling involves applying an insulative thermoplastic preform (film) prior to attaching the device. Under pressure and heat, the preform softens and flows around the solder bumps, then solidifies quickly on cooUng. The devices may then be solder reflowed to make the connections or the preform may be formulated to flow and encapsulate the solder during solder reflow. Table 5.6 lists some commercially available preforms used as underfills. Anisotropic film adhesives have also been used as underfill preforms, in which case z-direction conductive paths are formed beneath the solder bumps at the same time that the rest of the insulating film flows and cures around the bumps. Anisotropic paste adhesives can be similarly used (Figure 5.11). 

The thickness of the adhesive applied to the substrate should be considered in the early stages of formulation. The required thickness is a function of the geometry of the substrate and device to be interconnected. If a film adhesive is used, the film thickness must be sufficient to fill the gap between substrate and device to prevent void formation, as illustrated in Fig. 6a. The film thickness cannot be arbitrarily large, however, as the bonding temperatures, pressure, and time must be sufficient to displace the excess... 

Fahs, A. Brogly, M. Bistac, S. Schmitt, M. Hydroxypropyl methylceUulose (HPMC) formulated films Relevance to adhesion and friction surface properties. Carbohydr. Polym. 2010, 80 (1), 105-114. 

Uses Epoxy for film adhesives, fiberglass-reinforced plastics, chem. resist. pipe, elec, dip coatings, varnishes, solv.-free formulations, fiber finishes, industrial textile applies. 

Storage Store in cool, dry place keep tightly closed Uses Intermediate for polymer formulations for specialty coatings such as low VOC coatings, high strength fibers and films, adhesives, elec, chems., and engineering resins Manuf./Distrib. ABCR Acros Org. TCI Am. 

Figure 3.22. Manufacturing steps in formulating film/preform adhesives.

Most textile adhesive formulations are available in a waterborne liquid or solid (film or powder) form. When supplied as a film, the adhesive is unsupported, reinforced with fabric or nonwoven, or coated on both sides of a carrier material. These film adhesives are made flowable by heating to a melt and then gain strength on cooling back to a sohd form. Film adhesives offer convenience, since no coating operation is required by the user, energy (drying costs) is minimized, and waste is eliminated ... 

Franich and co-workers [5] described two simple methods using internal standards for the quantitative analysis of 2,6-di- er -butyl-4-methylphenol (butylated hydroxy toluene, BHT) antioxidant in samples of solvent-formulated liquid adhesive and in cured polychloroprene adhesive films. Because only very small samples of cured adhesive could be taken from articles or components without substantially detracting from the product, the methods were developed to use minimal quantities of cured adhesive. The Py-GC method required... 

Sauer, R.A., Mergel, J.C., 2014. A geometrically exact finite beam element formulation for thin film adhesion and debonding. Finite Elem. Anal. Des. 86, 120—135. 

COMA polymers (Fig. 17), synthesized by conventional radical polymerization, have a 1 1 alternating structure, a consequence of the preference for each radical to react exclusively with the other monomer. As a rnle, the products are high Tg materials for example poly(norbornene-co-maleic anhydride) has a Tg > 300°C. The polymerization allows the incorporation of small amoimts of other vinyl monomers (e.g. acrylic acid) without disruption of the alternating structure (117). Substituted norbornenes can be included in the pol5mierization mixture to incorporate acid-labile functionality, to modify polymer polarity, and to improve film adhesion (118). Cholate dissolution inhibitors can be added in the formulated resist to further modify functional properties (119). 

A 121"C cure toughened cyanate ester film adhesive formulated for use in specific applications where low moisture absorption and/or low dielectric constant/low loss are of utmost importance. The system s strength and toughness when bonding solid, honeycomb or foam core structures, is a>mparable and often greater than high performance epoxy adhesives, particularly at elevated temperatures. 

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