This paper describes the design, simulation, fabrication and characterization of micro checkvalves suitable for integration into polymeric microfluidic devices such as micropumps or test cartridges for biomedical analysis. The valves are fabricated by a polymeric surface micromachining process, which utilizes SU-8 as the functional material. The devices are assembled with the lamination technique. A micro checkvalve consists of 3 layers: an inlet layer, a valve layer and an outlet layer. The valve is a disc of 1-mm diameter. The disc is suspended on folded beams, which act as valve springs. Both valve disc and springs are fabricated in a 100-µm SU-8 layer. The valves prove a clear flow rectification function. Relatively low pressure is required for opening the valve. The valves were tested and characterized with water. One of the valves are successfully integrated into a polymeric micropump. These valves prove the facile and reliable lamination technology for fabrication complex polymeric microfluidic devices for biomedical analysis.

In this study, the interfacial behavior of a flip chip structure under thermal testing was investigated using high sensitivity moire interferometry. The real-time moire interferometry was used to monitor and measure the deformation of the specimen during the test. Two kinds of specimen were prepared: 1) specimen without crack and 2) specimen with horizontal crack at the silicon-epoxy interface. The results show that the maximum shear strain occurs ,at the silicon-epoxy interface. The shear strain variation increases significantly along the interface, with the maximum shear concentration occurring at the edge of the specimen. The creep effect is more dominant in the FR4-epoxy interface. In order to characterize the behavior of the interfacial crack, stress intensity factors KI and Kn, and the strain energy release rate in the vicinity of the crack tip were used to conduct a qualitative study. It was observed that a sharp strain gradient occurred at the crack tip. The stress intensity factors KI and Kn were dependent on temperature.The strain energy release rate with respect to temperature was dominated by KI for the interfacial crack in the specimen. IntroductionThe model package used in this study was a sandwich structure consisting of a silicon chip, epoxy underfill and FR4 substrate. The behaviour of underfillhbstrate and underfillkhip interfaces of the specimen under certain thermal loadings was examined. The thermal deformations of the specimen under thermal cycling tests were obtained by laser moire interferometry and the interfacial behaviour was assessed through analysis of the moire fringe patterns. The main interest of this study was to apply a real-time moire interferometry technique to investigate the variation of thermal strains experienced at the interfaces of the specimen. Upon application of thermal loading to the specimen, the specimen grating deformed along with the specimen, and the resulting interference with the reference grating produced fringes. Based on the fringe patterns captured by a CCD camera, information on the displacements and strains experienced by the specimen was obtained and analyses were carried out.

Abstract-In this paper, the interfacial behavior of a flip-chip structure under thermal testing was investigated using high sensitivity, real-time Moiré interferometry. The model package studied was a sandwich structure consisting of a silicon chip, epoxy underfill and FR4 substrate. The behavior of FR4-underfill and silicon-underfill interfaces of the specimen under certain thermal loading was examined. The results show that the shear strain variation increases significantly along the interfaces, with the maximum shear strain concentration occurring at the edge of the specimen. At the edge, the maximum shear strain occurs at the silicon-underfill interface, and the FR4-underfill interface experiences a slightly lower shear strain. The creep effect is more dominant in the FR4-underfill interface when the specimen is heated for 2 h at 100 C. Upon cooling to 20 C, both the interfaces of the specimen experience partial strain recovery.

Deformations of a Si-epoxy-FR4 (simplified flip chip) structure under thermal testing were inspected with a real-time Moiré technique. Specimens without cracks and specimens with a crack at the silicon-epoxy interface were prepared. The measurement results showed that the maximum deformation appeared at the edge. When the specimen was cooled to 20 • C, there was residual plastic deformation in the specimen. The creep effect was more dominant in the FR4-epoxy interface. Upon cooling to 20 • C, the specimen experienced partial strain recovery. To characterize the behavior of the interfacial crack, stress intensity factors K I and K II , and the strain energy release rate G in the vicinity of the crack tip were calculated using the measured deformations to conduct a quantitative study. It was observed that a sharp strain gradient occurred at the crack tip. K I and K II were dependent on temperature, and G was dominated by K I for the interfacial crack in the specimen.

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