Dynamic constitutive relation of EMC over a broad range of temperatures and strain rates
In this paper, dynamic properties of EMC were studied sat different temperatures and different strain rates. Firstly EMC was investigated by quasi-static tests. Secondly a series of dynamic compressive experiments of EMC were conducted using the Split Hopkinson Pressure Bar (SHPB) at high strain rates. Corresponding measurements were conducted at temperatures ranging from 20°C to 200°C. The results indicate that the yield strength and flow stress of EMC increase remarkably with the increase of strain rate. However, the yield strength of EMC is almost unchanged with the increase of temperature which is ranging from 20°C to 200°C.
EMC characterization and process study for electronics packaging
Transfer molding process has been used in the packaging industry for decades for the encapsulation of all kinds of plastic packages. In the transfer-molding process, the solid but reactive epoxy molding compounds (EMCs) in the preformed pellet form are injected into the preheated mold that contains the substrate and the attached chip. The EMCs are thermally cured and then ejected with encapsulated parts. For microelectronics encapsulation, EMC selection and molding conditions can strongly affect the final quality of the encapsulated parts, such as warpage, wire sweep, microvoid formation and reliabilities. In this study, the curing behavior of two epoxy molding compounds from different sources was evaluated. The activation energies for curing reactions were estimated using Kissinger and Ozawa methods. These two EMCs were also subjected to process study through transfer molding. The warpage values of the encapsulated substrates with a dummy die were measured and the molded parts were inspected using an acoustic microscope. The processing conditions of these two EMCs were optimized. The determining factors for warpage control and void formation were evaluated through the design of experiments.
Shape and surface texture of molten droplets deposited on cold surfaces
When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.