Laminates Conductive materials

We should not think that heat is lost only from the copper side. The usual laminate (board material) used for SMT (surface mount technology) applications is epoxy-glass FR4, which is a fairly good conductor of heat. So some of the heat from the side on which the device is mounted does get across to the other side, where it contacts the air and helps reduce the thermal resistance. Therefore, just putting a copper plane on the other side also helps, but only by about 10 to 20%. Note that this opposite copper plane need not even be electrically the same point it could for example just be the usual ground plane. A much greater reduction of thermal resistance (by about 50 to 70%) can be produced if a cluster of small vias (thermal vias) are employed to conduct the heat from the component side to the opposite side of the PCB. 

For thermoplastic laminates the material obviously needs to be heated before entering the roller region. Induction (450 kHz.) was selected as the means for doing this. The basis for the selection was its noncontact nature and its ability to heat through the thickness quickly. Use of induction was also predicated on the fact that most components of interest utilized graphite fibers, which had the required electrical conductivity. A great deal was learned about the... 

As mentioned above, the main application of the epoxide /dicyanate systems are copper clad laminates. Other important uses are conductive materials with silver... 

In heat transfer analysis, a material is normally assumed to be isotropic that is, to have unifonn properties in ail directions. This assumption is realistic for most materials, except those that exhibit different structural characteristics in different directions, such as laminated composite materials and wood. The thennal conductivity of wood across the grain, for example, is different than that parallel to the grain. 

Fillers provide films with conductive properties, influence their surface properties, affect their permeability, mechanical and optical properties, and affect their durability against environmental exposure. Various technologies are used to produce conductive films. These include lamination to metal foils (in-plant, using pressure sensitive adhesives), surface coating, and addition of conductive materials. Conductive films are widely used in packaging to limit static electricity. 

Blistering A localized swelling and separation between any of the layers of a laminated base material or between a base material and a conductive foil or protective coating, blistering is a form of delamination. 

Ziac foil coated with a conductive, pressure-sensitive adhesive is used for repair of other ziac coatings or for imparting corrosion resistance at field sites. The 0.08-mm ziac tape or sheet has a 0.025-mm coaductive adhesive. The laminate is cut to size and pressed tightly to activate the adhesive. Conductive tape can be wrapped around pipe, especially around welds or connections. The corrosion resistance of this material is iatermediate between galvanized or thermally sprayed coatings and zinc-filled paints (21,50). 

Transient Heat Conduction. Our next simulation might be used to model the transient temperature history in a slab of material placed suddenly in a heated press, as is frequently done in lamination processing. This is a classical problem with a well known closed solution it is governed by the much-studied differential equation (3T/3x) - q(3 T/3x ), where here a - (k/pc) is the thermal diffuslvity. This analysis is also identical to transient species diffusion or flow near a suddenly accelerated flat plate, if q is suitably interpreted (6). 

Typically items with a thickness of less than about 1 mm can be treated as thermally thin. This constitutes single sheets of paper, fabrics, plastic films, etc. It does not apply to thin coatings or their laminates on noninsulating substances, as the conduction effects of the substrate could make the laminate act as a thick material. The paper covering on fiberglass insulation batting would be thin pages in a closed book would not. 

Composites. See also Composite materials Composites. See also Laminates aluminum-filled, 10 15-28 carbon fiber, 26 745 ceramic-filled polymer, 10 15-16 ceramic-matrix, 5 551-581 conducting, 7 524 from cotton, 8 31 ferroelectric ceramic-polymer,... 

According to filler theory, connectivity can be achieved at lower values when the filler form is plates rather than spheres. Depending on the proportions of the plates and whether or not an inactive phase is included in the blend, connectivity can be achieved at 8 to 16% (v/v) filler (4). The starch-plastic blends developed by Otey (2) have a laminate structure when the starch content is under 30% by volume (Figure 1) and the threshold for microbial attack on these materials is under 13% starch by volume (Figure 2). This low threshold value can be explained by considering the LDPE as a non-conductive (enzyme-impermeable) phase combined with a conductive phase of starch-EAA complex. 

A multicomponent solid material has many more degrees of freedom in arrangement than an isotropic and homogeneous fluid. The thermal conductivity of a composite material, formed by the lamination of sheets of two components with different thermal conductivities, is a well-analyzed system. When heat is flowing parallel to the sheet surfaces, the composite thermal conductivity is given by linear additivity of conductivities... 

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