Parameter Optimization for Unstable Pin Bonding

Plastic frame power modules with press-fitted or molded pins create challenging bonding conditions. Pin stability variations, from relatively stable to unstable within a single power module, makes it difficult to find process parameters that fit to all pins equally well. Also, tight space, full utilization of the pin surface for bonding and a large number of pins per module makes clamping solutions difficult or impractical. Therefore, we used process optimization to find optimal process parameters for the unstable pin bonds and active process control feature to reduce deformation variance in bonding. The study revealed the importance of the cleaning phase optimization for both sides of the pin stability variations. We found that ensuring a good cleaning phase, typically within first 10ms of the process on the unstable pins, significantly improved the quality of the bonds. Unstable pins tended to lift after bonding with traditional parameters, but demonstrated good shear strength with optimized parameters. Active process control ensured that all bonds reached optimal deformation, regardless of the pin stability. Generally, the best approach to reach good bond quality is to ensure an optimal bonding environment, including clean and stable bond pads. However, when it is not possible or practical to stabilize the bond pad, this study shows that carefully executed process optimization combined with the active process control can lead to robust bonding on unstable pins.

Paper-Supported High-Throughput 3D Culturing, Trapping, and Monitoring of Caenorhabditis Elegans

We developed an innovative paper-based platform for high-throughput culturing, trapping, and monitoring of C. elegans. A 96-well array was readily fabricated by placing a nutrient-replenished paper substrate on a micromachined 96-well plastic frame, providing high-throughput 3D culturing environments and in situ analysis of the worms. The paper allows C. elegans to pass through the porous and aquatic paper matrix until the worms grow and reach the next developmental stages with the increased body size comparable to the paper pores. When the diameter of C. elegans becomes larger than the pore size of the paper substrate, the worms are trapped and immobilized for further high-throughput imaging and analysis. This work will offer a simple yet powerful technique for high-throughput sorting and monitoring of C. elegans at a different larval stage by controlling and choosing different pore sizes of paper. Furthermore, we developed another type of 3D culturing system by using paper-like transparent polycarbonate substrates for higher resolution imaging. The device used the multi-laminate structure of the polycarbonate layers as a scaffold to mimic the worm’s 3D natural habitats. Since the substrate is thin, mechanically strong, and largely porous, the layered structure allowed C. elegans to move and behave freely in 3D and promoted the efficient growth of both C. elegans and their primary food, E. coli. The transparency of the structure facilitated visualization of the worms under a microscope. Development, fertility, and dynamic behavior of C. elegans in the 3D culture platform outperformed those of the standard 2D cultivation technique.

Nonlinear Analysis of Flat Steel Frame Semi rigid Connection Subjected to Dynamic Loads

The paper aims to analyze the plastic frame elasticity with a beam-column joint which is a nonlinear semi-rigid linkage, an ideal plastic elastic material model; set up the elastic elastic equation, using the Newmark method to solve the differential equations of oscillating equations with Newton-Raphson iterative method of improvement and programming to determine the internal force and the movement of the frame by the programming language MATLAB program; limit the scope of research on structural problems subject to earthquake load described by acceleration diagram.

Ultrasonic Bonding on Unstable Pin

In power electronics modules, ultrasonic wire bonding is a common method to make electronic connections between the connector pins and the IGBTs. In these modules the connector pins are often residing on top of the plastic frame. Due to the pins being in positions which are hard to reach, clamping of these pins is either suboptimal or not used. This poor or absent clamping combined with the plastic frame's elasticity (softness) means that the pin has more freedom to move compared to the bonding on a metal substrate or IC. In our experiments we measured the pin and the plastic frame displacement with a laser Doppler vibrometer during the ultrasonic heavy wire (400 um in diameter Al wire) bonding process. We measured that the press fitted pin can move laterally along the ultrasonic excitation axis (2.0 ± 0.2) um whereas the frame under the pin moved (0.3 ± 0.1) um. This indicates that the pin slips over the frame while bonding. The slipping of the pin is also visible on the ultrasonic frequency waveforms of the transducer. While molded pins in general are thought to be more stable compared to the press fitted pins, similar behavior is seen in heavy wire bonding where high ultrasonic power is needed. We measured molded frame displacement (0.6 ± 0.2) um while bonding on the pin. In this paper we show how to use process traces and visual inspection to detect unstable pins and how to improve bondability on unstable pins by selecting process parameters that are optimized for the unstable pins rather than stable surfaces.

Electrochemical Bubbling Transfer of Graphene Using a Polymer Support with Encapsulated Air Gap as Permeation Stopping Layer

Electrochemical bubbling transfer of graphene is a technique with high industrial potential due to its scalability, time- and cost-effectiveness, and ecofriendliness. However, the graphene is often damaged due to the turbulence and the trapped bubbles formed by the direct H2O and H+permeation through the supporting polymer. We invent a graphene mechanical support of polyethylene terephthalate foil/plastic frame/poly(methyl methacrylate) sandwich, with an encapsulated air gap as the permeation stopping layer. The graphene damage is drastically reduced, as confirmed by the morphology and structural and electrical characterization, ultimately improving the controllability/reproducibility of the bubbling transfer of graphene and other two-dimensional materials.

Analysis of Elasto-Plastic Frames

This chapter, as well as Chapter 4, deals with the algorithms for the analysis of frames; specifically, it shows how the models for elasto-plastic elements presented in Chapter 7 can be used in a structural analysis. In the first section, a particularly efficient algorithm is presented: the hinge-by-hinge method; in this case, the analysis of an elasto-plastic frame can be treated as a sequence of linear problems; this analysis also allows for an estimation of the ultimate resistance forces of the structure; on the other hand, the hinge-by-hinge procedure can only be used in very particular cases. A general procedure for the analysis of any kind of elasto-plastic frames under quasi-static forces is presented in Sections 8.2 and 8.3; this method is based on an algorithm called elastic predictor-plastic corrector that is a key concept for most of the inelastic structural analyses, even for the damage and fracture models that are described in the next chapters. The same algorithm can also be used for the dynamic analysis of elasto-plastic frames as discussed in Section 8.3.4.

Flow Control of a Bluff Body Wake by Means of Self-Adaptive Flaps

The performance of two self-adaptive flaps designed with a biomimetic approach is investigated. Each flap comprised a rigid plastic frame covered with a porous material (characterized by its solidity, σ) and is installed on the side of a square cylinder. In order to investigate the effect of the flap dynamics, the flaps are either positioned at a given angle (passive control) or hinged on their leading edges and left free to adapt to the flow changes (self-adaptive control). For the optimum position of 20° and σ=100%, a significant drag reduction of 30% is obtained over a large range of Reynolds numbers (Re 20,000 to 60,000). The investigation of the flow in the close wake of the model for both fixed and moving flaps reveals a modification of the flow topology and a possible change in the mode of vortex formation.