Bondable Substrates

Cyanoacrylate adhesives will bond most substrates to themselves and to each other. The few adherends which do not bond well with standard adhesives are polyethylene, polypropylene, EPDM rubber, plasticized PVC, teflon, and acidic surfaces. A few manufacturers sell modified adhesives which will bond some of these materials, such as EPDM and flexible PVC. Adhesion to low surface energy plastics like polyolefins and Teflon can be improved by an etching or oxidizing treatment. 

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Although acrylics are slightly less versatile with respect to bondable substrates than are modified acrylics, they are more versatile than anaerobic adhesives, which are usually limited to the assembly of cleaned or prepared, closely mating metal, glass, and ceramic parts (3). 

Bondable substrates for aerobic and second-generation acrylics include clean as well as oily or "as received" metal polyurethanes, filled polycarbonates, filled nylon, phenolics, thermosets, wood, concrete, ceramics, glass, and other common materials of manufacture. Some thermoplastic materials are bonded better by using a second-generation acrylic adhesive. Examples are unfilled nylon, ABS, and rubber. 

Although there is considerable evidence that chemical surface treatments improve the substrate bondability of stainless steels, there is no general agreement on which is the best. One etchant commonly used with stainless steels is an HNO3-HF mixture [128-131] others are chromic acid and ferric chloride/hydrochloric... 

TF1V has a unique combination of properties that include relatively low processing temperatures, bondability (to itself and other substrates), high flexibility, excellent clarity, low refractive index, and efficient electron-beam cross-linking.91 It also exhibits properties associated with fluoroplastics, namely, very good chemical resistance, weatherability, low friction, and low flammability. Typical properties of the dry grades are summarized in Table 3.9 and those of THV in aqueous dispersion form in Table 3.10. 

Different methods have been devised to test the bondability of the treated plastic. The specimen can be joined in different ways butt joint, disk joint, and lap shear. An adhesive layer or film is applied to the treated surface, which is then placed against the substrate and heated in a press or oven. The substrate could be a duplicate of the plastic itself. Table... 

Surface Roughening - In adhesive bonding, a commonly used surface preparation technique in which the substrate surface is mechanically abraded. The roughened surface increases bondability by dramatically increasing the number of sites available for mechanical interlocking. 

Hydroxybenzamines of the general formula have been claimed to improve the adhesion of a wide range of coatings to zinc and cadmium and other metallic substrates when used as either pretreatment primers or additives [63]. Ethylenically unsaturated hydroxy-functional amines have been claimed to improve the adhesion of water-based systems [64], and amines have been examined as adhesion promoters for aromatic isocyanate cured adhesives on glass and other substrates [65]. Primary aliphatic amines are claimed to improve the bondability of polyolefines [66] and an oxyethylated polyethylene... 

In the future the various families of acrylic adhesives are expected to grow as more and more design engineers specify bonded parts and as specialty substrates continue to emerge that are bondable only with acrylic adhesives. The development of formulations with lower overall odor, 1-part systems, and hybrid types will also have a positive effect on overall growth. 

Features Flexible transparent hydrophobic coprocessable with oletinic plastics, hydrocarbon elastomers processes at relatively low temps. exc. chem. resist. bondable to itself and other substrates Properties Pellets or agglomerate melt flow index 15 (265 C, 5 kg) sp.gr. 

In summary, preliminary studies indicate that plasma spray coatings show great potential for improving the bondability of steel. Potential drawbacks include the requirement for relatively expensive plasma spray equipment and the necessity to keep the substrate temperature below that which would lead to undesirable metallurgical changes. 

As a second example of a weak surface layer it is easy to plasma treat a vraxy or oily surface and make it completely wettable and bondable by adhesives. However, these bonds will show almost no strength because the adhesive is not bonded to the substrate, only with the surface contamination layer. This is the ultimate example of a weak boundary layer. It is also the primary danger of using a wetting test as a quality control test for plasma treatment. The apparent surface of the part may be completely wettable but still give very poor bonding because that surface is really a layer of cross-linked contaminant. 

Thick-film materials for AIN substrates have been in use for over a decade. Earlier, considerable effort was made on treating the surface of AIN to make it more bondable to thick-film materials. Recently, more attention has concentrated on making conductor materials more compatible with AIN substrates and overcoming difficulties with conventional thick-film materials that work well on alumina substrates but either blister or adhere poorly to AIN substrates. This development was also driven by enviroiunental concern for the use of high-thermal-conductivity beryllium oxide (BeO) ceramic, where many manufacturers felt compelled to switch to alternative substrates. Typical data for popular substrates used in high-dissipation applications are tabulated in Table 2.6. 

For substrates metallized with thick-film copper that will see subsequent soldering, manufacturers typically plate them with nickel and optionally with a top layer of gold. Some manufacturers will solder dip their copper thick-film subsfrafes after nickel plating. The resulting metallization has toe same solderability and wire bondability characteristics as DEC and plated copper. 

Test Pattern. The basic conductor properties can be measured using a single test pattern, as illustrated in Fig. 8.15. These include resistivity, print definition and film thickness, film density, solder leach resistance, wettability, adhesion, and wire bondability. Each property will be discussed individually with reference to Fig. 8.15. Many applications require functional use tests which usually require specific test patterns and even multilayer construction processes. Similarly, numerous applications require standard conductor tests on thick-fihn dielectrics instead of the bare substrate. 

To achieve successful coating adhesions, coating formulations must have chemistries which are covalently bondable to the chemical surface properties of the plastic adherend to be coated. In order to meet this objective it is necessary to determine the substrate s receptivity to thermal or non-thermal pretreatment, as well... 

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]... 

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