Thermal vias

Intramolecular nitrone cycloadditions often require higher temperatures as nitrones react more sluggishly with alkenes than do nitrile oxides and the products contain a substituent on nitrogen which may not be desirable. Conspicuously absent among various nitrones employed earlier have been NH nitrones, which are tautomers of the more stable oximes. However, Grigg et al. [58 a] and Padwa and Norman [58b] have demonstrated that under certain conditions oximes can undergo addition to electron deficient olefins as Michael acceptors, followed by cycloadditions to multiple bonds. We found that intramolecular oxime-olefin cycloaddition (lOOC) can occur thermally via an H-nitrone and lead to stereospecific introduction of two or more stereocenters. This is an excellent procedure for the stereoselective introduction of amino alcohol functionality via N-0 bond cleavage. 

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. 

Eox-----1.5 V versus SCE) - reacts thermally via electron transfer with a... 

Many of the unique properties of cyclopropanes, and to a lesser extent, cyclobutanes, are derived from the formation of bent bonds. They may act in a fashion similar to 7r-bonds in interacting with electron-deficient centers, and are more easily cleaved thermally via electrophilic attack than are ordinary C-C bonds. The strain energy associated with bond angle deformation is also an important quantity, especially when considering thermal reactions. 

Much less information is available about [2 + 2]-cycloadditions. These allow the formation of cyclobutane derivatives in the reaction between two alkenes, or that of cyclobutenes from alkenes and alkynes. The reaction can be achieved thermally via biradical intermediates,543 by photoreaction,544 and there are also examples for transition-metal-catalyzed transformations. An excellent example is a ruthenium-catalyzed reaction between norbomenes and alkynes to form cyclobutenes with exo structure ... 

Figure 16. Cross section of thin-film multilayer interconnections on a pinned cofired ceramic substrate, with face-up tape-automated-bonded chip and thermal vias. (Reproduced with permission from reference 79. Copyright 1988 Materials Research Society.)...

The addition of thiols to olefins (thiolene reaction), to form thioethers, is a well-known reaction. The process can occur by either free-radical or ionic mechanisms. The free-radical reaction can be initiated thermally via a peroxide or by UV irradiation with benzophenone. The initiation step involves the formation of a thiyl radical by hydrogen atom abstraction. Both of these species are capable of starting polymer chains (Table 2.30). 

One other system shows potential for the production of ammonia and amines from dinitrogen. It was shown several years ago (155) that [(T 5-C5H5)2TiPh2] decomposes thermally via a benzyne intermediate formulated as 42. Such species fix nitrogen. The benzyne complex generated by thermal decomposition as above, or from the reaction of 43 with dinitrogen to form a species formulated as 44. A diphenylacety-... 

The de-excitation path available to conjugated organic molecules is controlled by quantum-mechanical rules which are complex. Some molecules will relax spontaneously, other will not (within a reasonable time) without assistance from another material/mechanism. The presence of Oxygen is a special case. Resonant conjugated molecules with two Oxygen atoms will not fluoresce and there only means of de-excitation is by means of a direct transition that is not allowed because of the presence of the triplet state. The nonresonant conjugates normally de-excite thermally via a two-step process. 

The electrocyclic reactions of phenyl fulgides and l,8a-DHNs can be photo-induced by a conrotatory process. The electrocyclic ring-opening reaction of cyclohexadiene systems (l,8a-DHNs) can also be induced thermally via a disrota-tory process. 

Goplen B, Sapatnekar S. Thermal via placement in 3D ICs. In Proceedings of the American Computing Machinery International S5unposium on Physical Design 2005. p 167-174. 

The earliest examples of diene ligands. Reaction of Isomers of 2,4-hexadiene with dodecacarbonyl triruthenium gave two isomers of [RuiH(CO)9 Mr C6H9)], 98(a) and 98(b) (Scheme 27) (53,a,b). Isomer 98(a) readily transforms to 98(b) thermally via a facile 1,2-hydrogen shift. The structure of 98(b), which has been known since 1972, contains a 1,3-dimetalloallyl hydrocarbon ligand. Its isomeric counterpart was the first allenyl cluster to be structurally characterized. Gervasio and co-workers (53c) showed... 

Alkynes containing methylene (—CHi—) functionalities a to the triple bond readily undergo thermal C-H activation under conditions necessary to initiate reaction with group VIII metal carbonyls (54). The allenyl clusters obtained isomerize thermally via a 1,2-hydrogen atom shift to afford the thermodynamically more favorable 1,3-dimetalloallyl clusters (Table 1) (49,55). A similar chemistry has been recognized for osmium clusters, albeit under more severe conditions. 

Depending on the employed boundary condition, a distinction is made between the so-called surface and volume models. The difference between them is schematically illustrated in Fig. 10. In the surface model(s), the position of the receding interface is specified by the attainment of a specific temperature, whereas in the volume models, the interface is specified by the condition that the surface concentration of broken bonds reaches a specific/ critical value. Bonds are assumed to be broken thermally via simple uni-molecular reaction. 

The photoaddition reactions (Scheme 1) of benzo[b]thiophenes with alkynes (R3C=CR4) have been extensively studied. In some cases, the unrearranged adducts 22 (R1 = R2 = H, R3 = R4 = Ph167 R1 = H, R2 = Me, R3 and R4 = Ph or C02Me168) are obtained in very low yield. Generally, only the rearranged cyclobutenes 23 are isolated these may then decompose thermally via 24 to the naphthalenes 25. With unsymmetrical alkynes,... 

Treatment of dibenzothiophene with potassium metal generates the radical anion (154). This dissociates thermally via S- bond cleavage to the radical anion (155). The latter reacts with another molecule of (154) to form the dianion (156) and dibenzothiophene. Flash photolysis of (156) in the presence of excess dibenzothiophene leads to (154) (Equation (13)) <82JCS(P2)lll3>. 

Essential driving factor Photon promoted Thermal via self assembly... 

The crude-oil market demands that water in crudes from all these processes must be removed to a level of less than 0.5% BS W (bottoms, solids, and water) (2,3). In order to remain competitive, emulsions must be resolved economically. The available treatment options are mechanical, thermal, via electrotrea-tors (electrocoalescers), chemical, or a combination of physical and chemical methods. Chemical demulsifica-tion is one of the most economical means of dehydrating oil. 

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