Gap-filling Capability

One of the benefits of adhesives is that they will fill gaps between poorly fitting parts or parts with large manufacturing tolerances. The cure of epoxies is not affected by the gap between the parts but cyanoacrylates are very much driven by this gap and are limited to gaps of less than 0.2 mm. The gap therefore has an important bearing on the family of adhesives that will be best suited for the application. 

If the gap between two cylindrical parts is very small ( 0.05 mm) then it is unlikely that an epoxy will be suitable as it will probably be too high in viscosity and will be pushed out of the joint as the parts are assembled, resulting in joint starvation. In this case a low-viscosity cyanoacrylate or UV adhesive that will capillary down into the interstitial spaces may be better suited. 

The optimum gap for most adhesive applications for engineering plastics is between 0.05 mm and 0.2 mm but sometimes a thicker joint with a flexible adhesive is the best solution, especially if there are high peel loads or the adhesive is acting primarily as a sealant and not as an adhesive (see Section 1.5). 

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The development of low-dielectric-constant materials as ILDs is crucial to achieve low power consumption, reduce signal delay, and minimize interconnect cross-talk for high-performance VLSI devices. In one of the multilevel interconnect process routes, metal lines (e.g., A1—Cu or Cu) are patterned through reactive ion etching, and then dielectric films are filled in the trenches formed between these lines. These trenches can have widths in the sub-0.5 pm range and aspect ratios greater than 3. Therefore, small gap-filling capability is also required for such dielectrics. 

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabilities, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

The gap filling capability of the bath was also tested throughout the experiment. Test wafer used for this study is 0.3 um trenches with aspect ratio of S.S. Fig. 6 contains three SEM pictures of the sample deposited in the fresh bath, 5-turnover, and 10 turnover with the same process recipe. All three samples have seamless filling of copper film. These results indicate that the gap filling capability of the bath remains good as bath ages. 

As mentioned previously, neat pMDI does not have gap filling capability for wood bonding because of its low viscosity and propensity for deep penetration. Consequently, neat pMDI is not used for applications such as plywood, laminated veneer lumber, etc. However, gap filling properties may be achieved by modifying pMDI with a wide variety of difunctional or polyfunctional polyols. Viscosity and NCO content are easily tailored to meet many application requirements. 

Good gap filling capabilities and weathering Excellent flexibility even shear strengths... 

The second is a two-component adhesive " component A is a m-aminophenol modified novolac at a pH of 5 (about 63% solids) and component is a formaldehyde donor used as hardener. The adhesive has gap-filling capability, impact resistance, and is thixotropic. A phenol-resorcinol laminating resin can be used as a primer, with good results. 

The selection of a particular adhesive type is for reasons other than modulus and associated stress distrihution. This might be for example, specific adhesion, chemical resistance, setting speed, gap fill capability, durability, heat resistance, fire performance, electrical properties, thermal conductivity, colour, toxicity or price. Low modulus adhesives are used very successfully in low stress applications to accommodate differential thermal expansion in applications like bonding glass to aluminium in double glazing assembly. 

The fact that the polymerisation of anaerobics is initiated from the surface of the substrates being bonded gives them a deficiency in common with cyanoacrylates (see Section 2.7) namely a very limited gap-filling capability. Primers must be used to improve this situation, thus negating the one-component benefit of the adhesives. 

Ideal for SMC and GRP Beige, fight handling 1.5 h, good water and impact resistance, flexible, excellent gap filling capability, for primer less SMC bonding... 

Advantages They require no solvents (100% solids), exhibit fast bond formation, gap-filling capability, barrier properties, and wide deformability range. 

Epoxy High strength Good solvent resistance Good gap-filling capabilities Good heat resistance Wide range of formulations Relatively low cost Exothermic reaction Exact proportions needed for optimum properties Short pot life... 

Epoxies, poljmrethanes, two-part acrylics and the adhesive/sealant products (silicones, and modified silanes) all have excellent gap-filling capabilities and some of these products will offer excellent resistance to impact loading and peel loads. 

Viscosity is a product property associated with all engineering adhesives and with most sealants. The rheology of an adhesive is the key to determining its potential field of application (gap-filling capability, strength before curing, penetrability, orientation... 

Check for distortion correct or discard distorted components. If distorted components must be used, try adhesive with better gap-filling capability... 

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