Adhesive bond appropriate process

The reliability of electronic systems depends on extensive testing, inspection, and evaluation of all parts of the design and manufacturing process, including the adhesives used in the systems. Test methods for adhesives and adhesive-bonded assemblies may be generally classified as physical, electrical, environmental, thermal, mechanical or thermomechanical, and chemical (Table 7.1). This chapter summarizes most of the methods used to test and evaluate adhesives used in electronics. It is not intended to provide detailed instructions, but to lead the reader to the appropriate government or industry specifications, documents that are available from the various organizations listed in Table 7.2. 

Successful bonding of parts requires an appropriate process. The adhesive must not only be applied to the surfaces of the adherends but the bond should also be subjected to the proper temperature, pressure, and hold time. The liquid or film adhesive, once applied, must be capable of being... 

Thermoplastics and paint systems that behave Uke thermoplastics are quite often soluble in organic solvents. Many adhesives contain small amounts of such solvents or plasticisers. The diffusion of these products towards the boundary layer can lead to a softening of this layer at the adhesive interface. If the joint is then subjected to stress, the adhesive bond may fail. Since the diffusion process takes place very slowly, months may elapse before the damage manifests itself. Additionally, the user should seek the adhesive manufacturer s advice on an appropriate method of surface preparation. 

Having explained the phenomena governing the behavior of adhesively bonded joints, it is appropriate to conclude this chapter with an outline of the steps involved in the typical Joint-design process. 

As a rule, manufacturers are required to inform customers of the adhesive shelf life under the recommended conditions in the product information. Within this period, the specified adhesive properties should he guaranteed for dehvery as well as for the final bond performance after appropriate processing steps. The manufacturing date, shelf life, and suitable storage temperature of the adhesive should also be indicated on the packaging. While many products can be stored at room temperature, some may require low temperatures for a prolonged shelf hfe. The aspect of storage at low temperatures will be addressed separately. 

The quality control of adhesively bonded joints in fabrication lines includes control of adhesion processes, appropriate design of joints to ease the process control, and education and direction for works to conduct the manufacturing. Many efforts have been made to improve the quality stabilities (Petrie 2007 Espie 1995 Roberts 1990 DeFrayne 1983 Bandaruk 1962). Due to the invention of new types of adhesives such as acrylics whose strengths are less sensitive to processing conditions than those of conventional adhesives, the quahty control can he done more easily and precisely in these days than the previous as shown by Haraga et al (2009). 

A highlight of the reactive compatibilisation of extremely incompatible polymers is the chemical bonding between the anti-adhesive PTFE and the polar polyamides. It had been assumed for a long time that a chemical bonding between PTFE and polyamide is impossible because there was no appropriate reaction mechanism. PTFE is a highly crystalline polymer which could only be processed by using special equipment. The utilisation in tribological systems is a well-known... 

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