Sheng-Jye Hwang

Temperature prediction of rolling tires by computer simulation

A numerical procedure has been applied for investigating the temperature distribution in a smooth tread bias tire of a light truck, operated under different speeds, pneumatic pressures, and loading conditions. Prior to simulation by the finite element analysis, two separate sets of testing, namely dynamic mechanical testing and material testing, have been conducted in relation to the evaluation of hysteresis (H) and total strain energy (Used), respectively. Hysteresis loss energy is given as (H × Used) and considered to relate directly to heat generation rate. Temperature rise is assumed to be due to the energy dissipation from periodic deformation. This dissipation of energy may be equated to be the primary heat generation source. Hysteresis energy loss is used as a bridge to link the strain energy density to the heat source in rolling tires; temperature distribution of rolling tires may be obtained by the steady-state thermal analysis. The above procedure has been shown to facilitate the simulation of the temperature distribution in the rolling tire.An efficient computational process is being introduced to decrease the time for coupled 3D dynamic rolling simulation of tire. Temperature rise under different conditions is discussed with reference to the results of other published studies.

Three-dimensional modeling of mold filling in microelectronics encapsulation process

In this paper, a fully three-dimensional (3-D) numerical model is developed to simulate the mold-filling behavior in the plastic encapsulation of microelectronics. The conventional Hele-Shaw approximation is inadequate to analyze such a complex process owing to the 3-D nature inherent in the molding compound flow between leadframe and mold cavity. The developed methodology combines the efficiency of SIMPLE-based finite volume method (FVM) and the robustness of VOF volume-tracking method to solve the two-phase flow field in complex mold geometry. An efficient method for automatic generation of prismatic mesh for plastic packages is also presented. The molding process of a TSOP II 54L LOC package is studied. Short-shot experiments are conducted to investigate the filling patterns at several different flow times. The close agreements between experimental data and simulated results demonstrate the applicability of the present computational model for practical plastic encapsulation simulations.

Static analysis of the die picking process

A numerical procedure was applied to simulate the pickup process for a die bonder to study the breakage of GaAs dice. Parameters such as needle ejecting speed, vacuum pressure, and radius of needle were investigated by the Taguchi method to obtain the manufacture process working-window in order to shorten the tuning time. It was found that the ejecting speed of the needle and the downward pressing force of the pickup collet are the major factors for die breakage. This procedure could also be applied to inspecting the effects of other factors or analyzing different types of pickup machines.

Prediction of paddle shift via 3-D TSOP modeling

This study develops a methodology to simulate the molding process of thin small outline packages (TSOPs) and to predict the paddle shift caused by pressure difference and viscous stress during molding through the help of a true three-dimensional (3-D) Computational Fluid Dynamics (CFD) software.

Design and fabrication of an IC encapsulation mold adhesion force tester

In integrated circuit (IC) packaging, when epoxy molding compound (EMC) is filling the mold cavity and cured in the mold, adhesion occurs in the interface between EMC and mold surface. Too large an adhesion force can damage an IC and lower the yield rate. However, there was no report showing how to measure the mold adhesion force. This paper described the design and fabrication of an automatic EMC adhesion force test instrument that will measure adhesion force between mold surface and EMC. By measuring the adhesion force, one can judge how much does a specific type of surface treatment help in reducing the amount of mold adhesion force. One can also use this instrument to determine what parameters are important for reducing the magnitude of adhesion force between EMC and mold surface.

Computer-Aided Design of a TSOP II LOC Package Using Taguchi’s Parameter Design Method to Optimize Mold-Flow Balance

This paper presents a methodology for TSOP II LOC packaging design. The design objectives are: 1) to optimize mold-flow balance, which in turn minimizes air traps, and 2) to minimize manufacturing variability, which implies optimal quality. A mold-flow simulation tool called C-MOLD is used to evaluate various design configurations. Taguchi’s robust design method is used for manufacturing variability considerations. The simulated results are verified with experimental flow patterns produced by means of ‘‘short shots.’’ In the nomenclature of the Taguchi method, mold-flow balance was chosen as quality characteristics and select a set of design parameters called control factors. The objectives are to find the levels of the control factors, which optimize the flow balance, and, at the same time, minimize the sensitivity of the variations of the control factors. @DOI: 10.1115/1.1569957#

Simulation of warpage considering both thermal and cure induced shrinkage during molding in IC packaging

O C C U ~ owing to differences in shrinkage among constituent materials. Thermal shrinkage is usually considered as the main cause for warpage in an IC. However, cure induced warpage is also important during molding. Analysis without considering c u e induced shrinkage can not he accurate. This paper used the P-V-T-C relation and CTE of an encapsulation material to predict the amount of warpage and experimentally verifying the results. Comparing the simulation and experiment results of an EMC-copper composite shows that warpage predictions with P-V-T-C relation and CTE can better predict the amount of warpage of an IC package after molding. For an EMC-copper composite, the amount of warpage is proportional to the cure pressure and inversely proportional to the mold temperature. Besides the P-V-T-C relation and CTE, elastic modulus is found to play an important roll on the amount of warpage in simulation. With this study, the simulation shows that this approach can well predict the amount of warpage for an EMC composite after molding without too much computation effort.

The Development of Paddle Shift Analysis for IC Packaging Processing

During IC packaging processes, defects such as warpage, paddle shift and wire sweep etc, may happen. There was little literature about paddle shift and wire sweep analyses while most research in the past were focusing on warpage phenomenon in package outline. Excessive paddle shift reduces the encapsulation protection for the components, and may result in failure due to excessive wire sweep and stress, then cause the signal breakdown or a short circuit. Computer-aided analysis is one of the feasible tools for simulating and predicting the occurrence of such defects in molding process, even prior to the commencement of mass production of a package. Because of several analyses, such as mold filling analysis, wire sweep analysis, paddle shift analysis, warpage analysis, and stress strain analysis need to be assembled in one simulation series, more than one mesh models are needed for the analysis during the overall IC packaging analysis. The number of elements of those mesh model are often more than 600,000. For such large mesh model, a high quality methodology of mesh generation would be used. Unbalance pressure between top and bottom cavities was used as the loading for the analysis. In this study, a thin small outline package TSOP-I 48L produced by ChipMOS Technologies Ltd., was used for paddle shift simulation. In the simulation results, the lead shift phenomenon agreed very well with the experiments. This example demonstrated the feasibility and usefulness of this approach.

Mold Adhesion Force Measurement

During the encapsulation process of IC packages, when epoxy molding compound (EMC) is filling the mold cavity and cured in the mold, adhesion effects occur in the interface between EMC and mold surface. Adhesion effects can cause many problems. For example, too large an adhesion force may damage an IC during ejection and cause the package to fail and thus lower the yield rate and reliability. To get rid of the mold adhesion problems, improving the mold design and applying suitable surface treatments such as mold surface coating are the common approaches. Applying suitable surface coating is a more popular and practical approach. How to evaluate the mold adhesion force and use the data to improve products yield rate are the main issues for packaging. This paper uses a semi-automatic EMC adhesion force test instrument that had been developed and fabricated to measure normal and shear adhesion forces between the mold surface and EMC. By measuring the adhesion force, one can judge how much does a specific type of surface treatment help in reducing the amount of mold adhesion force. Nine kinds of various mold surface coating were tested with this instrument to measure the magnitude of adhesion force between EMC to determine the effectiveness of mold coating. The measured data showed that with different coatings on mold surface, the mold adhesion force can be very different. This paper also discussed the issue of successive normal force test. Engineers would use the most effective mold coating material to execute the continuous normal adhesion experiment. The variation of normal force during successive molding test could be used to predict the time for mold cleaning. By counting the total number of shots when the normal force begins to rise, engineers can accurately predict the number of shots for a specific kind of mold surface coating to be cleaned. This paper also described the effects of defrosting period on mold adhesion force of EMC. Defrosting is a process to increase the frozen EMC temperature to room temperature and stay at room temperature for some time before molding. It was found by molding engineers that increased defrosting time period would increase the frequency of mold cleaning. But there had been no quantitative description on how much mold adhesion force increase during the defrosting process. A semi-automatic EMC adhesion force test instrument was used to evaluate the effects of defrosting period on mold adhesion force of EMC. It was found that increase the defrosting time will increase the amount of adhesion force between EMC and mold surface. The higher is the relative humidity during defrosting on the adhesion force, the higher is the increase of adhesion force.Copyright