Effects of package and mold cavity structures on the wire sweep behavior during package array transfer molding
In order to maximize product throughput, an increasing number of electronic packages, such as Small Outline Transistor (SOT) package, are manufactured in a package array mold. Due to the complicated structure design of the package and mold cavity, wire sweep is becoming an increasingly severe problem. In this study, the numerical model which had been validated by experimental work was used for wire sweep analysis. Firstly, the leadframe structure was studied. Given the thin thickness of leadframe and the relative position to the bond wire loop, the leadframe structure has very limited influence on the wire sweep value. Besides, for fixed width and length of the die, the wire sweep behavior was simulated to examine the influence of the die height (thickness). The results show that the thinner the die, the smaller the wire sweep. Furthermore, the effect of cavity height on wire sweep value was also estimated. Based on the previous simulation and analyses, the ratio of the die height to that of the cavity was introduced as an index to optimize the flow pattern of epoxy molding compound (EMC) in order to find a guideline for package and cavity design to avoid the wire sweep issue. In addition, the influence of injection velocity and viscosity of EMC on wire sweep during transfer molding process were inspected and discussed according to the simulation results as well. It can be further concluded that the velocity plays the key role in resulting in the severe wire sweep in package array mold during transfer molding process.
Optimization of process conditions for the transfer molding of electronic packages
Abstract Transfer molding is used extensively in electronic packaging. To achieve a high production rate and high molding quality, it is necessary to have strict control on the epoxy resin characteristics as well as identify the optimal process conditions of the transfer molding. In this paper, process simulations of transfer molding for electronic packages were conducted according to Taguchi experiments. The simulation results were then used to derive quality indexes by using TOPSIS (techniques for order preference by similarity of ideal solution) algorithm. Through the analysis of the quality indexes, optimal process conditions can be identified. Two verification tests were carried out and results of the tests are found very close to the predictions. This project has demonstrated that numerical simulation combining with Taguchi method and TOPSIS can be a useful tool for optimization of process conditions for transfer molding of electronic packages.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.