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Tool path generation is an interesting and challenging task in free-form surface machining. Iso-planar tool path generation is one of the common approaches to dealing with this task. However, it suffers from an inherent drawback that intersecting intervals of the iso-planar method are limited to surface geometric features. This results in poor machining efficiency in flat regions due to redundant machining paths. For this problem, a new tool path generation method for triangular meshes is proposed based on the least-squares conformal map (LSCM). After LSCM parameterisation with minimal stretching energy, the triangular meshes are unfolded on a plane, where the principal component analysis (PCA) technique is employed to determine a suitable drive line for calculating cutter contact paths by the iso-planar strategy. Therefore, the tool paths are generated in a plane and the unevenness of the traditional iso-planar method is improved. The feasibility and effectiveness of the developed method is demonstrated through a test experiment. [ABSTRACT FROM AUTHOR]

Nondestructively and efficiently peeling thin chip from the adhesive tape is still one of the crucial techniques in IC packaging technology. In order to improve the process efficiency, a novel approach with the inverted ejecting mechanism and spring buffer head is proposed, where, however, the ejecting and spring forces applied at the chip for generating the interfacial crack are also more likely to resulting in the damage of chip. In view of this, an effective theoretical and finite element models are established considering the tape–adhesive–chip structure with ejecting and spring forces, and in the frame of fracture mechanics, the energy release rate is calculated and introduced to reveal effects of the spring buffer on the interfacial crack growth and chip breaking stresses. It is showed that the spring buffer is able to reduce the stress concentration on chip. Furthermore, according to the competing fracture behavior between the interfacial delamination and the chip cracking, the process window of thin chip peeling is suggested for selecting an appropriate spring coefficient and ejecting needle force. [ABSTRACT FROM AUTHOR]

The reliable picking-up of thin chip using the vacuum sorption determines the success rate of flip chip assemblies from donor tape to receptor substrate. An analytical solution to model the chip–adhesive–tape structure with vacuum loads is introduced to understand the fracture mechanism of chip picking-up. The critical process parameters (the length of bonded region, vacuum strength, and pick-up displacement, etc.) are investigated. Theoretical predictions are used in combination with virtual crack-closure-based finite-element technique to reveal the detaching behavior between the chip and the adhesive tape. The results show that the length of the bonded region should be controlled less than 40% of chip length to eliminate the effects of chip thickness, and the higher vacuum strength acting on the adhesive tape is able to accelerate the detachment of the chip from the adhesive tape. In particular, a process window is proposed to enhance the reliability and efficiency of picking-up for a thin chip. [ABSTRACT FROM AUTHOR]

A mechano-electrospinning method is presented to direct-write oriented nanofiber with high deposition accuracy in continuously tunable manner. This method uses a large nozzle to deposit high-resolution fiber-arrays by near-field localization. Due to the existence of mechanical drawing force, a higher resolution pattern can be direct-written by a lower voltage, which just keeps the Taylor cone stable. Then the fiber is stretched through a moving substrate, by which the deposited fiber can be continuously tuned from 400 nm to 200 nm in a linear relationship. The effects of the speed on the diameter and morphology of fibers are studied, and the analysis of the mechanism of the fiber alignment is given. The positionability and controllability make mechano-electrospinning very different from the traditional electrospinning, which only collects the fibers in the form of nonwoven fabric. In addition, the fibers fabricated by this method can directly deposit over a large flat area in the form of arrays and complex patterns with high precision. [ABSTRACT FROM AUTHOR]