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Due to the ongoing component miniaturization and integration in the electronics industry, there is a need for asymmetric lay-ups for printed circuit boards (PCBs), especially in the case of complex boards that house both analog and digital circuits. This paper focuses on the contribution of the constituent layers that make up the PCB to the board's macroscopic multilayer properties in terms of stiffness and coefficient of thermal expansion (CTE). The thermoelastic material properties for constituents, like cured prepreg and laminate layers, have been determined. Using classical laminate theory, individual layer properties are assembled to the macroscopic level and compared to fabricated multilayer boards. Following this approach, the contribution of various copper features on constituent layers can de deduced. The experiments show that properties of cured prepreg, taking z-direction expansion into account, and laminate layers are dependent on the type of fiberglass reinforcement and the fiber volume fraction. Depending on these properties, the Young's modulus and CTE varies from 11 to 31 GPa and from 10 to 28 ppm/K, respectively. Datasheet values deviate significantly from these results as they do not take the fiber volume fraction into account. By alternating the measurement directions, the experiments have also shown that the fiberglass reinforcement plays a dominant role in determining macroscopic multilayer board properties. The multilayer board follows iso-strain conditions. Therefore, the material properties depend linearly on the copper volume fraction and follow the rule of mixtures independent of the type of copper patterning. Overall, the presented model and method to determine material properties increase the accuracy for predicting multilayer board behavior and offers the possibility to design and predict bow and twist behavior of PCBs with asymmetric lay-ups.
Abstract.The synthesis and characterization of the copper tetrafluoroborate compound containing the bidentate N,S ligand 5-methyl-4-(ethylthiomethyl)imidazole (memi), [Cu(memi), (BF,),], is described. The activities of this compound and of [Cu(memi),(H,O),] (NO,), as oxidation catalysts have been determined in the reaction of 2,6-dimethylphenol with molecular dioxygen to give polyphenylene oxide (PPO) and diphenoquinone (DPQ). For optimum catalysis, an additional base is required in order to dehydronate the phenol. Triethylamine proved to be most useful as a base. Initial reaction rates encountered are between 1 x and 6 x 10-'M O,/s and ca. 50% of the phenol was converted after a reaction time of one hour. Less than 10% phenol was converted into DPQ. Both compounds have comparable reactivities. A single crystal of [Cu(memi),( BF4),] was used in an X-ray structure determination: monoclinic space group C2/c, a = 13.844(4)A, b = 11.251(1)A, c = 15.753(4)A, p = 111.39(2)", Z = 4 and T = 293 K. The structure was solved using heavy-atom techniques and refined by least-squares methods to a residual R value of 0.050. The copper ion is in a centrosymmetric distorted octahedral environment with all chemically identical donor atoms in trans positions. The tetrafluoroborate anions are coordinated to the copper ion with relatively short distances, i.e. 2.55 A; Cu-N and Cu-S distances are 1.93 and 2.41 A.
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