Chao-Ming Lin

Analysis of new anisotropic conductive film (ACF)

This paper designs a new multilayered particle anisotropic conductive film (ACF) compound. Using the particle-reinforced composite model and probability theory, the novel ACF compound is compared with three traditional ACFs having the same particle volume fraction. The particle-reinforced model applies the concept of bonded and debonded structures in the interfaces between the adhesive resin and the particles. The elastic modulus of the particle-reinforced ACF is a function of the particle volume fraction and the bonded condition. In the failure model, probability theory is used to calculate the probability of opening and bridging. The volume fraction of the conductive particles plays an important role in determining the optimal ACF design. The current results indicate that the flip chip packaging performed using the novel multilayered particle ACF compound (particles distributed in the top/bottom surface layers) exhibits superior particle-reinforcement properties and a lower failure probability than traditional ACFs. The improved understanding of reinforcement mechanisms and failure probability developed by this study facilitates the enhanced design of novel ACF compounds.

The prediction of failure probability in anisotropic conductive adhesive (ACA)

This paper develops a model for predicting the failure probability of flip chip packaging using anisotropic conductive adhesive (ACA). The proposed approach modifies the box model to improve the accuracy of the bridging probability estimation by considering bridging in all directions. In the current failure analysis, probability theory is applied to calculate the probability of both opening and bridging failure. The Poisson distribution is used to calculate the probability of opening in the vertical gap between the pads, while the modified box model is used to estimate the probability of bridging between the pads. The results indicate that the modified box model provides an effective means of accurately estimating the probability of failure. The failure analysis takes the volume fraction of the conductive particles as the major variable in defining the optimal ACA design condition. A V-shaped curve model can be employed to establish an appropriate value of the volume fraction as a function of conductive particle radius, pitch, and pad dimensions such that the overall probability of failure is minimized.

Reliability analysis of the fine pitch connection using anisotropic conductive film (ACF)

A novel method (the V-shaped curve) is presented to predict the failure probability of anisotropic conductive film (ACF) in IC/substrate assemblies. The Poisson function is used to calculate the probability of opening failure in the vertical gap between the pads, while the box and modified box models are used to estimate the probability of bridging failure between the pads in the pitch direction. The opening and bridging probabilities are combined using probability theory to establish four different failure prediction models. The results reveal that the model combining the Poisson function for fewer than six particles per pad with the modified box model provides the most accurate predictions of the failure probability of ACF in IC/substrate assemblies.

Flip-Chip Underfill Packaging Considering Capillary Force, Pressure Difference, and Inertia Effects

This study aims to enhance the flow rate and reduce the filling time in flip-chip underfill packaging by combining capillary force, pressure difference, and inertia effects. In the designed underfill apparatus, the capillary force effect is developed by surface tension, the pressure difference between the inlet and the outlet is established using a pump or a vacuum, and the inertia force is achieved via circular rotation. The governing equations containing the three analyzed effects are derived and solved using a dimensionless technique. The analytical results indicate that for the general gap height of approximately 10-1000 μm, the pressure difference and inertia effects dominate the driving force and provide a significant reduction in the filling time. However for a gap height of less than 1 μm, the driving force is dominated by the capillary effect. The present results confirm that the productivity of the flip-chip underfill packaging process can be enhanced through the appropriate control of the capillary force, pressure difference, and inertia effects.

Thermally induced viscoelastic stresses in multilayer thin films

This paper presents a viscoelastic analysis of the thermal stress in multilayer thin-film structures. In this analysis the viscoelastic field was calculated utilizing the Laplace transform. The thermal stress equation in the Laplace transform space can be numerically inverted to obtain the time domain. In the case of a single-layer film the stress of the thin film at any time can be obtained analytically. In a bilayer system, the normalized viscoelastic stress of the thin film is affected by the relaxation times, the biaxial moduli ratio, and the ratio of thickness between the film layer and the substrate. The effects of different ratio values of thickness on the normalized viscoelastic stress were analyzed. Viscoelastic stress can also be calculated if the elastic behavior in either the film or the substrate is considered. Furthermore, when both the substrate and film’s relaxation times approach infinity, they begin to exhibit elastic behavior, and then the residual stress in the film can be determined. ...

CYCLIC NANOINDENTATION OF SEMICONDUCTOR AND METAL THIN FILMS

The nanoindentation technique was used to measure the hardness and Youngs modulus of semiconductor and metal thin films on a Si(100) substrate under cyclic loading. The results showed that in all instances and at a constant cyclic load that the loading curves overlapped the previous unloading curve and had a small displacement after each cyclic nanoindentation. It was observed that the plastic energies of metal materials from the first loading–unloading cycle were much larger than that observed in semiconductor materials. Furthermore, the hardness and Youngs modulus of the thin films decreased when the number of cyclic nanoindentations was increased. The effect of the cyclic loading on the hardness and Youngs modulus of semiconductor material was much larger than that of the metal material. Youngs modulus, the hardness and the contact stiffness of thin films conform to the relationship that Youngs modulus was proportional to the contact stiffness and the square root of the thin films hardness.

Failure Analysis of Anisotropic Conductive Film Packages With Misalignment Offsets

This paper utilizes the V-shaped curve method to analyze the failure probability of anisotropic conductive film (ACF) packages with various degrees of IC/substrate misalignment. In evaluating the failure probability of the ACF package, the probability of an opening failure in the vertical gap between the pads is determined in accordance with a Poisson function, while the probability of a bridging failure between the pads in the pitch direction is computed using a bridging model. In computing the opening and bridging probabilities, the Poisson function and bridging model are modified to take account of the effects of package misalignments on the effective conductive area between opposing pads and the bridging-path length between neighboring pairs of opposing pads, respectively. The opening and bridging probabilities are then combined using probability theory to establish an overall failure prediction model for the IC/substrate assembly. It is shown that, for any given value of the IC/substrate misalignment, the modified V-shaped curve method enables not only the failure probability of the ACF package to be reliably predicted but also an estimate to be made of the optimal ACF volume fraction. The results show that the semilogarithmic failure probability increases approximately linearly with the volume fraction for both uni- and bidirectional misalignments of the ACF package. The optimal volume fractions for ACF packages with misalignments not considered in this paper can be derived from the current results via a process of interpolation.

Failure Probability Estimation of Anisotropic Conductive Film Packages With Asymmetric Upper-to-Lower Pad Size and Misalignment Offsets

Anisotropic conductive films (ACFs) are widely used in the packaging of flat panel displays and liquid crystal displays and for attaching bare chips to both flexible and rigid substrates. This paper utilizes the V-shaped curve method to analyze the failure probability of ACF packages with an asymmetric upper/lower pad size and misalignment offsets. In the proposed method, the probability of opening failures is modeled using a Poisson function, modified to take into account the effects of the pad-width difference and misalignment offset on the effective conductive area between opposing pads. Meanwhile, the probability of bridging failures is evaluated using an enhanced bridging model based on the distance between the neighboring pad pairs in the array. The failure probability of the pad array is evaluated as a function of both the difference in width of the upper and lower pads and the degree of misalignment between the opposing pads in the array. The results show that the V-shaped curve method provides the means to predict the ACF volume fraction which minimizes the failure probability of the ACF assembly given a knowledge of the pad-width difference and the misalignment offset. In addition, it is shown that when the misalignment offset is greater than the pad-width difference, the minimum failure probability reduces as the pad-width difference increases due to the corresponding increase in the effective conductive area between opposing pads. Conversely, when the misalignment offset is less than the pad-width difference, the minimum failure probability increases with an increasing pad-width difference due to the corresponding reduction in the effective conductive area between the pads.