Edward K L Chan

Investigation of moisture diffusion in electronic packages by molecular dynamics simulation

Moisture-related failure is one of the main concerns in the integrated circuit (IC) package design. To minimize such failure in multi-layered electronic assemblies and packages, it is important to develop a better understanding of the reliability at a molecular level. In this paper, molecular dynamics (MD) simulations were conducted to investigate the respective moisture diffusion into the epoxy molding compound (EMC) and at the EMC/Cu interface. Moisture diffusion coefficients into the bulk EMC material and at the EMC/Cu interface can be derived from the mean-squared displacements calculated from MD simulations. The MD results showed that the seepage along the EMC/Cu interface is more prevalent when compared to moisture diffusion into the bulk EMC and, thus, rendering it a dominant mechanism causing moisture induced interfacial delamination in plastic packages.

Molecular dynamics simulation of thermal cycling test in electronic packaging

Interfacial failure under thermal cycling conditions is one of the main concerns in package design. To minimize such failure in multi-layered electronic assemblies and packages, it is important to develop a better understanding of the reliability at a molecular level. In this paper, molecular dynamics (MD) simulations were conducted to investigate the interfacial energy of the epoxy molding compound (EMC) cuprous oxide system during the thermal cycling test. In order to investigate the effect of the cuprous oxide content in the copper substrate on the interfacial adhesion, two kinds of MD models were examined in this study. The results revealed that the cuprous oxide content in the copper substrate had a large effect on the interfacial adhesion between the EMC and copper which is consistent with the experimental observation.

Study of Interfacial Moisture Diffusion at Cu/Epoxy Interface by FTIR-MIR Technique

The delamination at the copper lead frame and the epoxy interface adversely affects the reliability of IC packages and this is a common failure mode during the qualification process. One of the factors governing the interfacial delamination is the moisture content at the interface. This study further developed the experimental measurement of interfacial moisture diffusion by Fourier Transform Infrared Spectroscopy -multiple internal reflection (FTIR-MIR) with new calibration method. In this study, interfacial moisture detection was conducted on isothermal gloptop epoxy system at different positions of sample with constant humidity level 85% relative humidity at 85 degree Celsius by FTIR-MIR. By comparing the FTIR results on the epoxy samples with different pre-conditioning time, the interfacial moisture content at different position in epoxy sample was obtained and comparison was made. Mechanism of interfacial moisture diffusion was then characterized. This study has demonstrated the seepage mechanism along the copper/epoxy is the major driver for interfacial delamination under moisture pre-condition. It is likely that is the prevailing mechanism as compared to the established bulk diffusion mechanism in the epoxy molding compound.

Effect of Interfacial Adhesion of Copper/Epoxy under Different Moisture Level

Understanding interfacial adhesion subjected to different levels of moisture content and temperature elevation is of significant interest to the electronic packaging industry. The conventional study has focused primary on moisture diffusion into the encapsulated molding compound (EMC) of plastic packages. This paper looks at the alternative path of interfacial seepage into the EMC and copper interface of the IC package. In this study, the effect of moisture on interfacial bonding energy was calculated by running a molecular dynamics simulation. A series of MD models consisting of a network of epoxy macromolecules and copper atoms with different amount of water molecules at its interface were built with the Discover module. The mass ratio of water molecules to epoxy varied from 1% to 6% while the surrounding temperature kept at 85degC in order to simulate a similar environment condition in MSL-1 qualification test. Calculations were carried out at different humidity level with a prescribed moisture concentration value, using the NVT ensembles. From the simulation results, it is observed that the interfacial bonding energy decreases with the increase of mass ratio of water molecule to the epoxy due to locking of water molecules at the nanopores at the epoxy/Cu interface. Interfacial bonding energy between the epoxy and copper substrate weakens when water molecules increasingly accumulate at the interface. To verify the simulation results, epoxy was molded on pre-cleaned copper substrate and undergone MSL-1 test. Adhesion strength of the sample set was evaluated by button shear test at different times. They show a strong qualitative correlation between the MSL-1 test data and the MD simulation results. It is concluded that the interfacial moisture diffusion is also an important factor contributing to delamination in plastic packages

Study of Interfacial Moisture Diffusion at Epoxy/Cu Interface

The delamination at the epoxy/copper interface adversely affects the reliability of IC packages and this is a common failure mode during the qualification process. One of the factors governing the interfacial delamination is the moisture content at the interface. This study has developed an experimental measurement procedure for interfacial moisture diffusion using the Fourier Transform Infrared–Multiple Internal Reflection (FT-IR–MIR) technique with a new calibration method. In this study, interfacial moisture was detected by FT-IR–MIR on an isothermal gloptop epoxy system at selected locations on the epoxy/copper interface of samples which went through 1000 h of 85% relative humidity at 85°C pre-conditioning. By comparing the FT-IR–MIR results for epoxy samples with different pre-conditioning times, the interfacial moisture contents at different positions in the epoxy sample were obtained and a comparison was made. This study has demonstrated that the seepage mechanism along the epoxy/copper interface is the major driver for interfacial delamination under moisture pre-conditioning. It is the prevailing mechanism as compared to the established bulk diffusion mechanism in the epoxy molding compound. Surface analyses conducted on fracture surfaces of button shear test specimens show that interfacial moisture diffusion affects the cuprous oxide content in the epoxy/copper interfacial region and this leads to adhesion degradation.

Interfacial Moisture Diffusion: Molecular Dynamics Simulation and Experimental Evaluation

To minimize moisture-related failure in electronic packages, it is important to develop a better understanding of reliability study at a fundamental level. Molecular dynamics simulations were conducted and the MD results showed that the moisture seepage along the EMC/Cu interface is more prevalent when compared to bulk moisture diffusion. This diffusion path is believed to be a dominant mechanism causing moisture-induced interfacial delamination in plastic packages. Experimental investigation by FTIR–MIR measurements with the new calibration method also confirmed higher interfacial moisture content than that at the exposed surface. On the other hand, the effect of interfacial moisture diffusion on adhesion was also investigated by both MD simulation and analysis of the fracture surface in button shear tests using XPS surface analysis.

Reliability study of RFID flip chip assembly by isotropic conductive adhesive through computer simulation

Radio Frequency Identification (RFID) is quickly gaining a foothold in the identification and security industry. However, one major roadblock that prevents companies in adopting RFID technologies is its high manufacturing cost, particularly assembly cost. One approach to reduce the assembly cost is using surface mount technology. Currently anisotropic conductive adhesives (ACA) tape, isotropic conductive adhesives (ICA) and non-conductive adhesives (NCA) are being used for RFID flip chip assembly. Typically the ACA tape and NCA provide the necessary height control in the assembly. However, few literatures discuss about the possibility of using ICA as flip chip connection for different RFID product. In this work, we have developed techniques based on finite-element method. We use the full wave analysis approach that combines full wave simulator HFSS (High Frequency Structure Simulator) with circuit simulator ADS (Advanced Design System) to simulate the different packaging approach and the electromagnetic effects on the transponder strap. From the results, design guideline by using low cost ICA as RFID flip chip interconnect can be obtained. The result is helpful in height control for the batch printing process for different RFID products.

UV-activated surface modification of photo-cleavage polymer for contact printing applications

Polymer electronics is an emerging technology for the last decade. For cost-efficient mass production and for thin, flexible polymer electronic systems, large area patterning processes may be an interesting option as an economic production method and will potentially play an important role in polymer electronics manufacturing. High resolution patterning methods for defining the separation between electrodes in electronic devices are important in manufacturing. The control of surface wettability during contact printing is an interesting approach because of its wide variety of applications. Stimuli-responsive surfaces make it possible to control the wettability of the surface and have been demonstrated by various methods, including UV light-irradiation. Herein, a new strategy was demonstrated using free radical initiator to induce mold release between PDMS mold and the resins under UV irradiation. For example, by applying a thin layer of benzoyl peroxide (BPO) on PDMS surface, an increase of contact angle is achieved after UV irradiation. This method can be used as a transfer mechanism from mold to substrate. It was noticed that sufficient time of BPO deposition for the PDMS mold surface treatment is required for this strategy. Optimum concentration of BPO and suitable solvent system are concerns in the effectiveness of surface treatment. From this study, some preliminary insight in studying the controlling factors for the UV activation of free radicals on PDMS surface was shown. It can be shown that the molecular structure, polarity of materials, UV sensitivity of the free radical initiators, and solvent used, have direct effect on the efficiency of the wettability change under the UV irradiation. By knowing the controlling factors of UV assisted stimuli responses, printing can be improved and be applied in many other cases.

A Study of Interfacial Moisture Diffusion at Metal/Epoxy Interface by FTIR Technique

The delamination at the copper lead frame and the epoxy interface adversely affects the reliability of IC packages and this is a common failure mode during the qualification process. One of the factors governing the interfacial delamination is the moisture content at the interface. This study developed the experimental measurement of interfacial moisture diffusion by Fourier transform infrared spectroscopy - multiple internal reflection (MIR-FTIR). In this study, MIR-FTIR measurement was conducted on isothermal gloptop epoxy system at different positions of sample with constant humidity level 85% relative humidity at 85 degree Celsius. By comparing the FTIR results on the epoxy samples with different pre-conditioning time, the interfacial moisture content at different position in epoxy sample was obtained and diffusion coefficient was calculated to compare with the bulk diffusion results. Mechanism of interfacial moisture diffusion was then characterized. This study has demonstrated the seepage mechanism along the copper/epoxy is the major driver for interfacial delamination under moisture pre-condition. It is likely that is the prevailing mechanism as compared to the established bulk diffusion mechanism in the epoxy molding compound.

Using polymer and ionic liquid as liquid droplet study in single-plate electrowetting system

In this study, several printing inks were used as liquid medium in single-plate electrowetting system. The goal is to study the feasibility of contact angle change of different liquid on single-plate electrowetting device under low voltage (<;40V). Results showed large ionic molecules inside the aqueous solution can prevent undesired electrolysis with appropriate selection of electrical bias. Addition of ionic surfactants and inorganic salts inside the aqueous solution to decrease interfacial surface condition is another common method used to decrease the electrowetting onset voltage but its concentration needs to be carefully controlled. It was shown that dielectric failure is strongly dependent on the size of the polar liquid molecules themselves. In addition, polymer with appropriate chain length or size and low enough viscosity can improve electrowetting behavior. Throughout this work, an initial guidance to electrowetting practitioners is provided.