Multilayer Resin systems

A modified BMI-epoxy resin system has been introduced by Shell Chemical Company. The system is a highly reactive blend of a bismaleimide, COM-PIMIDE 1206 (55-60% by weight solution of BMI in DMF), and EPON Resin 1151, a polyfunctional epoxy resin (60). In contrast to many polyimide resins on the market, no free MDA is present in the product. This is an important feature, since MDA has been identified as an animal carcinogen and possibly a human carcinogen. This resin system has been fully evaluated for use in multilayer PCB boards (61). 2-Methylimidazole is recommended as a catalyst. However, if required, the processing window can be widened by using 2-phenylimidazole... 

The thin inner shell of the core-shell polymers contained less than 20% rubber by weight, with 60% by weight of a plastic core in the particles. It is unusual to enhance the toughness of the normally brittle epoxy-resin system at such a low level of rubber content. We believe that the unique design, the use of a multilayer toughener with a thin, elastomeric inner layer, and the large plastic core together produced behavior like that of solid rubber particles and, hence, enhanced crack resistance. 

As a material is heated to higher temperatures, a point is reached where the resin system will begin to decompose. The chemical bonds within the resin system will begin to break down and volatile components will be driven off, reducing the mass of the sample. The decomposition temperature, Td, is a property which describes the point at which this process occnrs. The traditional definition of Td is the point where 5 percent of the original mass is lost to decomposition. However, 5 percent is a very large number when multilayer PCB reliability is considered, and temperatures where lower levels of decomposition occur are very important to understand, particularly with respect to lead-free assembly. To illustrate this, consider Fig. 6.4. 

In controlling z-axis expansion, the key factors to consider are the choice of resin system, the resin system Tg, and the resin content of the base materials. Fillers in the resin system, in addition to the fiberglass cloth, can also be used to lower the CTE of the material. Table 8.1 compares the thermal expansion of several commercially available base materials. These values can vary significantly based on the exact resin content of the material or PCB tested. In multilayer PCBs, the amount of copper in the sample will also have a significant impact as the z-axis expansion of copper is very low compared to the resin system. 

As the fundamental building block for printed circuits, base materials must meet the needs of the printed circuit board (PCB) manufacturer, the circuit assembler, and the original equipment manufacturer (OEM). A balance of properties must be achieved that satisfies each member of the supply chain. In some cases, the desires of one member of the supply chain conflict with another. For example, the need for improved electrical performance by the OEM, or improved thermal performance by the assembler, may necessitate the use of resin systems that require longer multilayer press cycles or less productive drilling processes, or both. 

In addition, although seldom done in practice, using a resin system in the prepreg materials that can be cured below the Tg of the resin system in the laminate can avoid the softening of the laminate resin system and therefore prevent much of the movement that takes place. The resistance to the use of this technique is usually driven by a desire to keep the resin system same throughout the multilayer PCB. 

A low dielectric constant is particularly desirable for two-sided or multilayer boards used for high-speed computer circuits or other high-speed applications where distributed capacitance is important. For the glass fabric resin systems such as FR4 this can be reduced by increasing the resin-to-glass ratio since the E-glass used has a dielectric constant of 6-1 compared with approximately 3 5 for a typical epoxy resin. Figure 9.6 shows the effect of resin content on dielectric constant. 

Two newer resin systems have been developed and have found apphcations in widely diverse areas. The cyanate ester resins, marketed by Ciba-Geigy, have shown superior dielectric properties and much lower moisture absorption than any other structural resin for composites. The dielectric properties have enabled their use as adhesives in multilayer mi-... 

Printed circuit boards manufacture is aided by the use of KMnO. Alkaline permanganate solution is used to remove resin smeared on the interior hole wall of multilayered printed circuit boards. Additionally the hole wall is etched, resulting in a surface with excellent adhesion characteristics, for electrodeless copper (250). The alkaline permanganate etchback system containing >60 g/L KMnO and 40-80 g/L NaOH at 70—80°C, is effective for difunctional, tetrafiinctional, and polyimide resin substrates, where the level of etchback is direcdy proportional to the immersion time (10—20 min) (251). 

As with trapping, the delivery mechanisms for the pheromones are important. They must be able to provide a nominated dose over an extended period, often under adverse weather conditions. Thus, various slow-release methods have been devised for field use and incorporated into the delivery systems. These have involved the use of hollow fibres as reservoirs which can be applied aerially on to the canopy of plants twisted rope formulations consisting of wire-based sealed polyethylene tubes filled with disruptant that are twisted around the base of plants other polyethylene or rubber tube or polymeric ampullae dispensers, multilayered laminates of acrylic polymer flakes, resin-treated filter paper and micro-encapsulated formulations. 

Nicotine polacrilex contains nicotine bound to an ion exchange resin in a chewing-gum base. The nicotine transdermal system is a multilayered unit containing nicotine as the active agent that provides systemic delivery of nicotine for 24 honrs following its application to intact skin. 

Reiser asserts that in some resist fomulations, the DNQ is directly attached to the phenolic resin, as is the case in the methacrylamide derivative shown in structure (V). This resist has found application in multilayer systems where the diffusion of the inhibitor into adjacent resist layers cannot he tolerated. However, this resist has poor thermal stahility. 

Each type of resin is melted in an individual extruder, and the melts are carefully brought together prior to or in the die, in a manner that keeps them in homogeneous layers, without mixing. The process used to combine the polymers is usually different in the cast and blown film processes. In cast processes, as illustrated in Fig. 7.12, the polymers are typically combined in an adapter, called a feed block, before they enter the coat hanger die. This permits a simpler design for the die itself. Multimanifold dies are used when plastics with widely different flow properties are to be combined, as such systems provide a shorter multilayer flow path before solidification, and thus minimize distortion of the interface. 

Heating oil storage premises must be equipped with a collection trap so that any heating oil leaking from the tank cannot contaminate the soil. The interior of these premises must be painted with an officially approved coating material that is not dissolved or penetrated by heating oil. The coating must also cover cracks in the substrate. Multilayer systems based on waterborne acrylic resin dispersions are suitable for this purpose. 

For the co-extrusion of multilayer actuators, Yoon at. al. used a binder system consisting of ethylene ethyl acrylate, acrylic resin, mineral oil, polyethylene glycol and stearic acid. After sintering the resulting multilayer actuator was composed of 40 active PZN-PZT and PZN-PZT/Ag layers. The thicknesses of the PZN-PZT and the PZN-PZT/ Ag layers were 200 and 70 pm, respectively. 

In this chapter, the characteristics of air explosions are briefly described and various blast protection paradigms are discussed. The blast behaviour of plain composites and multilayered structures are then discussed. Plain composites typically comprise polymeric resins with a fibre reinforcement, such as carbon fibre-reinforced epoxy resins. Multilayered systems include composite sandwich stmctures and hybrid composite-metal structures, known as fibre-metal laminates (FMLs). 

Various systems are now available to quickly and automatically identify plastics by resin type—or at least to distinguish between desired and undesired materials. Many of these rely on differences between resins in absorption or bransmission of various wavelengths of electromagnetic radiation. Many can also separate plastics by color or color family in addition to sorting by resin type. Most of these systems work well with whole containers but are not effective in separating chipped plastics or multilayer materials. 

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