Low-dielectric substrate

A substrate is a robust element that provides mechanical support for the die. It can be mounted with more than one die such packages are called multichip modules. Because parasitic capacitance effects are directiy proportional to the dielectric constant, substrate material should have a low dielectric constant. 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

The partial racemization of isolated 2-octanol suggests that the hydrolysis may proceed via ionization of optically active substrates as in the Sjjl hydrolysis in homogeneous solution. The hydrolysis via ionization may be suppressed in media with low dielectric constant like micelles (Okamoto and Kinoshita, 1972), resulting in net retention. The ineffectiveness of the stereochemical influence of the CTAB micelle may be interpreted as a consequence of the mutual repulsion of the positively charged head groups of [46] and CTAB, so there is need for molecules of solvent to be incorporated between surfactant head groups (Sukenik et al., 1975). An appreciable increase in retention was also observed in a reversed micellar system (Kinoshita and Okamoto, 1977). 

The situation is different for solvolysis reactions in most other solvents, where the intermolecular interactions between ions at an ion pair are stronger than the compensating interactions with solvent that develop when the ion pair separates to free ions. This favors the observation of racemization during solvolysis. There are numerous reports from studies on solvolysis in solvents with relatively low dielectric constant such as acetic acid, of polarimetric rate constants (fe , s ) for racemization of chiral substrates that greatly exceed the titrimetric rate constant (fet, s ) for formation of acid from the solvolysis reaction. ... 

For some enzymatic reactions a transition state will be favored by a medium of very low dielectric constant and a correctly constructed active site can provide just such a surrounding.1893 Hydrophobic groups may be packed around a site where an ion pair or other ionic interaction between enzyme and substrate occurs increasing the strength of that interaction. Conformational changes may enhance such effects. 

Foams have a large variety of applications. Solid foams are widely used as insulating materials. Due to the presence of air bubbles they have a low thermal conductivity. Polyurethane foams and Styrofoam are examples. Styrofoam is also used as a packing material. The light weight of polymer foams makes them attractive as filling materials to stabilize otherwise hollow structures. A natural solid foam is pumice stone. Metal foams are used in the automotive and aerospace industry as light and stable materials [567], Ceramic foams are developed for electronic applications as piezoelectric transducers and low dielectric constant substrates [568],... 

Another interface that needs to be mentioned in the context of polarized interfaces is the interface between the insulator and the electrolyte. It has been proposed as a means for realization of adsorption-based potentiometric sensors using Teflon, polyethylene, and other hydrophobic polymers of low dielectric constant Z>2, which can serve as the substrates for immobilized charged biomolecules. This type of interface happens also to be the largest area interface on this planet the interface between air (insulator) and sea water (electrolyte). This interface behaves differently from the one found in a typical metal-electrolyte electrode. When an ion approaches such an interface from an aqueous solution (dielectric constant Di) an image charge is formed in the insulator. In other words, the interface acts as an electrostatic mirror. The two charges repel each other, due to the low dielectric constant (Williams, 1975). This repulsion is called the Born repulsion H, and it is given by (5.10). 

In order to treat the combined effects of added salt and dielectric boundaries on a manageable level, we use screened Debye-Hiickel (DH) interactions between all charges. In the presence of a dielectric interface, the Green s function can in general not be calculated in closed form [114] except for (i) a metallic substrate (with a substrate dielectric constant e =oo) and (ii) for e =0 (which is a fairly accurate approximation for a substrate with a low dielectric constant). For two unit charges at positions r and r one obtains for the total electrostatic interaction including screening and dielectric boundary effects... 

Most steatite ceramics are either dry mixed and pressed, or wet-mixed, spray-dried and pressed, but they can also be wet-mixed and extruded. Typical firing temperatures lie close to 1300 °C. Many small parts are made for the electronics components industry where low dielectric losses are required, for example for tie-bars and other parts for ganged capacitors, small trimmer capacitors, high-power capacitors (see Section 5.6.3), coil formers, lead-throughs and substrates for... 

---