Quality control of microelectronic wire bonds

Report evaluates ultrasonic bonding of small-diameter aluminum wire joined to ceramic substrates metalized with thin-film and thick-film gold. Quick testing technique for nondestructive location of poor wire bonds is also presented

High reliability bond program using small diameter aluminum wire

The program was undertaken to characterize the performance of small diameter aluminum wire ultrasonically bonded to conductors commonly encountered in hybrid assemblies, and to recommend guidelines for improving this performance. Wire, 25.4, 38.1 and 50.8 um (1, 1.5 and 2 mil), was used with bonding metallization consisting of thick film gold, thin film gold and aluminum as well as conventional aluminum pads on semiconductor chips. The chief tool for evaluating the performance was the double bond pull test in conjunction with a 72 hour - 150 C heat soak and -65 C to +150 C thermal cycling. In practice the thermal cycling was found to have relatively little effect compared to the heat soak. Pull strength will decrease after heat soak as a result of annealing of the aluminum wire; when bonded to thick film gold, the pull strength decreased by about 50% (weakening of the bond interface was the major cause of the reduction). Bonds to thin film gold lost about 30 - 40% of their initial pull strenth; weakening of the wire itself at the bond heel was the predominant cause. Bonds to aluminum substrate metallization lost only about 22%. Bonds between thick and thin film gold substrate metallization and semiconductor chips substantiated the previous conclusions but also showed that in about 20 to 25% of the cases, bond interface failure occurred at the semiconductor chip

Cross Recurrence Plot Based Synchronization of Time Series

The method of recurrence plots is extended to the cross recurrence plots (CRP), which among others enables the study of synchronization or time differences in two time series. This is emphasized in a distorted main diagonal in the cross recurrence plot, the line of synchronization (LOS). A non-parametrical fit of this LOS can be used to rescale the time axis of the two data series (whereby one of it is e.g. compressed or stretched) so that they are synchronized. An application of this method to geophysical sediment core data illustrates its suitability for real data. The rock magnetic data of two different sediment cores from the Makarov Basin can be adjusted to each other by using this method, so that they are comparable.Comment: Nonlinear Processes in Geophysics, 9, 2002, in pres

Humic substances-based polymer system

A system for use in forming polymer compositions, including as a replacement for phenolic based resin systems, for instance, in preparing foundry molds. In a preferred embodiment, the system includes the use of a) a polyermizable hydroxyl-containing component comprising a humic substance (as can be provided by lignite), b) an isocyanate component, and c) a catalyst, and preferably amine catalyst, component adapted to catalyze the polymerization of a) and b). The system is optionally used as binder system in the presence of a filler, such as, in combination with a foundry aggregate such as sand. A polymer system of this invention can be substantially free of formaldehyde or phenol, and preferably contains little or no aromatic solvents

Network Mutual Information and Synchronization under Time Transformations

We investigate the effect of general time transformations on the phase synchronization (PS) phenomenon and the mutual information rate (MIR) between pairs of nodes in dynamical networks. We demonstrate two important results concerning the invariance of both PS and the MIR. Under time transformations PS can neither be introduced nor destroyed and the MIR cannot be raised from zero. On the other hand, for proper time transformations the timing between the cycles of the coupled oscillators can be largely improved. Finally, we discuss the relevance of our findings for communication in dynamical networks.Comment: 15 p

Convergence in the QM-only and QM/MM modeling of enzymatic reactions: A case study for acetylene hydratase

We report systematic quantum mechanics-only (QM-only) and QM/molecular mechanics (MM) calculations on an enzyme-catalyzed reaction to assess the convergence behavior of QM-only and QM/MM energies with respect to the size of the chosen QM region. The QM and MM parts are described by density functional theory (typically B3LYP/def2-SVP) and the CHARMM force field, respectively. Extending our previous work on acetylene hydratase with QM regions up to 157 atoms (Liao and Thiel, J. Chem. Theory Comput. 2012, 8, 3793), we performed QM/MM geometry optimizations with a QM region M4 composed of 408 atoms, as well as further QM/MM single-point calculations with even larger QM regions up to 657 atoms. A charge deletion analysis was conducted for the previously used QM/MM model (M3a, with a QM region of 157 atoms) to identify all MM residues with strong electrostatic contributions to the reaction energetics (typically more than 2 kcal/mol), which were then included in M4. QM/MM calculations with this large QM region M4 lead to the same overall mechanism as the previous QM/MM calculations with M3a, but there are some variations in the relative energies of the stationary points, with a mean absolute deviation (MAD) of 2.7 kcal/mol. The energies of the two relevant transition states are close to each other at all levels applied (typically within 2 kcal/mol), with the first (second) one being rate-limiting in the QM/MM calculations with M3a (M4). QM-only gas-phase calculations give a very similar energy profile for QM region M4 (MAD of 1.7 kcal/mol), contrary to the situation for M3a where we had previously found significant discrepancies between the QM-only and QM/MM results (MAD of 7.9 kcal/mol). Extension of the QM region beyond M4 up to M7 (657 atoms) leads to only rather small variations in the relative energies from single-point QM-only and QM/MM calculations (MAD typically about 1–2 kcal/mol). In the case of acetylene hydratase, a model with 408 QM atoms thus seems sufficient to achieve convergence in the computed relative energies to within 1–2 kcal/mol

On the Effect of Varying Constraints in the Quantum Mechanics Only Modeling of Enzymatic Reactions: The Case of Acetylene Hydratase

Quantum mechanics only (QM-only) studies of enzymatic reactions employ a coordinate-locking scheme, in which certain key atoms at the periphery of the chosen cluster model are fixed to their crystal structure positions. We report a case study on acetylene hydratase to assess the uncertainties introduced by this scheme. Random displacements of 0.1, 0.15, and 0.2 Å were applied at the ten terminal atoms fixed in the chosen 116-atom cluster model to generate sets of ten distorted structures for each given displacement. The relevant stationary points were reoptimized under these modified constraints to determine the variations of the computed energies and geometries induced by the displacements of the fixed atoms. Displacements of 0.1 Å cause a relatively minor perturbation that can be accommodated during geometry optimization, resulting in rather small changes in key bond distances and relative energies (typically of the order of 0.01 Å and 1 kcal/mol), whereas displacements of 0.2 Å lead to larger fluctuations (typically twice as high) and may sometimes even cause convergence to different local minima during geometry optimization. A literature survey indicates that protein crystal structures with a resolution higher than 2.0 Å are normally associated with a coordinate error of less than 0.1 Å for the backbone atoms. Judging from the present results for acetylene hydratase, such uncertainties seem tolerable in the design of QM-only models with more than 100 atoms, which are flexible enough to adapt during geometry optimization and thus keep the associate uncertainties in the computed energies and bond distances at tolerable levels (around 1 kcal/mol and 0.01 Å, respectively). On the other hand, crystal structures with significantly lower resolution should be used with great caution when setting up QM-only models because the resulting uncertainties in the computational results may become larger than acceptable. The present conclusions are mostly based on systematic DFT(B3LYP) calculations with a medium-size basis set. Test calculations on selected structures confirm that similar results are obtained for larger basis sets, different functionals (ωB97X, BMK, M06), and upon including solvation and zero-point corrections, even though the fluctuations in the computed relative energies become somewhat larger in some cases