Spatial analysis of underfill flow in flip-chip encapsulation

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Fei Chong Ng ◽  
Mohd Hafiz Zawawi ◽  
Mohamad Aizat Abas
Keyword(s):  
Spatial Analysis ◽  
Formation Mechanism ◽  
Flip Chip ◽  
Void Formation ◽  
Past Research ◽  
Air Entrapment ◽  
Time Model ◽  
Content Type ◽  
Filling Time ◽  
Underfill Flow

Purpose The purpose of the study is to investigate the spatial aspects of underfill flow during the flip-chip encapsulation process, for instance, meniscus evolution and contact line jump (CLJ). Furthermore, a spatial-based void formation mechanism during the underfill flow was formulated. Design/methodology/approach The meniscus evolution of underfill fluid subtended between the bump array and the CLJ phenomenon were visualized numerically using the micro-mesh unit cell approach. Additionally, the meniscus evolution and CLJ phenomenon were modelled analytically based on the formulation of capillary physics. Meanwhile, the mechanism of void formation was explained numerically and analytically. Findings Both the proposed analytical and current numerical findings achieved great consensus and were well-validated experimentally. The variation effects of bump pitch on the spatial aspects were analyzed and found that the meniscus arc radius and filling distance increase with the pitch, while the subtended angle of meniscus arc is invariant with the pitch size. For larger pitch, the jump occurs further away from the bump entrance and takes longer time to attain the equilibrium meniscus. This inferred that the concavity of meniscus arc was influenced by the bump pitch. On the voiding mechanism, air void was formed from the air entrapment because of the fluid-bump interaction. Smaller voids tend to merge into a bigger void through necking and, subsequently, propagate along the underfill flow. Practical implications The microscopic spatial analysis of underfill flow would explain fundamentally how the bump design will affect the macroscopic filling time. This not only provides alternative visualization tool to analyze flow pattern in the industry but also enables the development of accurate analytical filling time model. Moreover, the void formation mechanism gave substantial insights to understand the root causes of void defects and allow possible solutions to be formulated to tackle this issue. Additionally, the microfluidics sector could also benefit from these spatial analysis insights. Originality/value Spatial analysis on underfill flow is scarcely conducted, as the past research studies mainly emphasized on the temporal aspects. Additionally, this work presented a new mechanism on the void formation based on the fluid-bump interaction, in which the formation and propagation of micro-voids were numerically visualized for the first time. The findings from current work provided fundamental information on the flow interaction between underfill fluid and solder bump to the package designers for optimization work and process enhancement.

Analytical and numerical analyses of filling progression and void formation in flip-chip underfill encapsulation process

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Fei Chong Ng ◽  
Aizat Abas ◽  
Muhammad Naqib Nashrudin ◽  
M. Yusuf Tura Ali
Keyword(s):  
Flip Chip ◽  
Volume Fraction ◽  
Void Formation ◽  
Content Type ◽  
The Past ◽  
Flip Chips ◽  
Incomplete Filling ◽  
Filling Time ◽  
Underfill Flow ◽  
Encapsulation Process

Purpose This paper aims to study the filling progression of underfill flow and void formation during the flip-chip encapsulation process. Design/methodology/approach A new parameter of filling progression that relates volume fraction filled to filling displacement was formulated analytically. Another indicative parameter of filling efficiency was also introduced to quantify the voiding fraction in filling progression. Additionally, the underfill process on different flip-chips based on the past experiments was numerically simulated. Findings All findings were well-validated with reference to the past experimental results, in terms of quantitative filling progression and qualitative flow profiles. The volume fraction filled increases monotonically with the filling displacement and thus the filling time. As the underfill fluid advances, the size of the void decreases while the filling efficiency increases. Furthermore, the void formed during the underfilling flow stage was caused by the accelerated contact line jump at the bump entrance. Practical implications The filling progression enabled manufacturers to forecast the underfill flow front, as it advances through the flip-chip. Moreover, filling progression and filling efficiency could provide quantitative insights for the determination of void formations at any filling stages. The voiding formation mechanism enables the prompt formulation of countermeasures. Originality/value Both the filling progression and filling efficiency are new indicative parameters in quantifying the performance of the filling process while considering the reliability defects such as incomplete filling and voiding.

Surface energetic-based analytical filling time model for flip-chip underfill process

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Fei Chong Ng ◽  
Mohamad Aizat Abas
Keyword(s):  
Analytical Model ◽  
Flip Chip ◽  
Current Model ◽  
Analytical Models ◽  
Time Model ◽  
Content Type ◽  
Package Design ◽  
The Past ◽  
Filling Time ◽  
Underfill Flow

Purpose This paper aims to present new analytical model for the filling times prediction in flip-chip underfill encapsulation process that is based on the surface energetic for post-bump flow. Design/methodology/approach The current model was formulated based on the modified regional segregation approach that consists of bump and post-bump regions. Both the expansion flow and the subsequent bumpless flow as integrated in the post-bump region were modelled considering the surface energy–work balance. Findings Upon validated with the past underfill experiment, the current model has the lowest root mean square deviation of 4.94 s and maximum individual deviation of 26.07%, upon compared to the six other past analytical models. Additionally, the current analytically predicted flow isolines at post-bump region are in line with the experimental observation. Furthermore, the current analytical filling times in post-bump region are in better consensus with the experimental times as compared to the previous model. Therefore, this model is regarded as an improvised version of the past filling time models. Practical implications The proposed analytical model enables the filling time determination for flip-chip underfill process at higher accuracy, while providing more precise and realistic post-bump flow visualization. This model could benefit the future underfill process enhancement and package design optimization works, to resolve the productivity issue of prolonged filling process. Originality/value The analytical underfill studies are scarce, with only seven independent analytical filling time models being developed to date. In particular, the expansion flow of detachment jump was being considered in only two previous works. Nonetheless, to the best of the authors’ knowledge, there is no analytical model that considered the surface energies during the underfill flow or based on its energy–work balance. Instead, the previous modelling on post-bump flow was based on either kinematic or geometrical that is coupled with major assumptions.

Regional Segregation With Spatial Considerations-Based Analytical Filling Time Model for Non-Newtonian Power-Law Underfill Fluid in Flip-Chip Encapsulation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Fei Chong Ng ◽  
Aizat Abas ◽  
M. Z. Abdullah
Keyword(s):  
Power Law ◽  
Flip Chip ◽  
Current Model ◽  
Process Time ◽  
Time Model ◽  
Package Design ◽  
Absolute Value ◽  
Filling Time ◽  
Underfill Flow ◽  
Encapsulation Process

Abstract This paper presents a new analytical filling time model to predict the flow of non-Newtonian underfill fluid during flip-chip encapsulation process. The current model is formulated based on the regional segregation approach, instead of the conventional porous media approximation. In this approach, the filling times were computed separately at different filling stages, before being summed up till the required filling distance. The non-Newtonian property of underfill fluid is modeled using the conventional power-law constitutive equation. Additionally, the spatial aspects of the underfill flow were incorporated into the present analysis. For instance, the evolution of underfill menisci from convex to concave was analytically developed and the contact line jump (CLJ) criterion was improved using minimal flow assumption. Upon validated with three distinct past underfill experiments, the current analytical model is found to have the best performance as it predicted the filling times with the least discrepancy among other existing filling time models. Quantitatively, the discrepancies were averagely reduced by an absolute value of at least 8.68% and 4.90%, respectively, for the first two set of validation studies. Generally, this model is particularly useful in manufacturing lines to estimate the process time of flip-chip underfill, as well as for the optimizations of process and package design.

Filling efficiency of flip-chip underfill encapsulation process

2019 ◽  
Vol 32 (1) ◽  
pp. 10-18 ◽  
Author(s):  
Fei Chong Ng ◽  
Mohamad Aizat Abas ◽  
Mohd Zulkifly Abdullah
Keyword(s):  
Numerical Simulation ◽  
Flip Chip ◽  
Scaling Limit ◽  
Scaling Factor ◽  
Dimensionless Number ◽  
Time Model ◽  
Content Type ◽  
The Past ◽  
Filling Time ◽  
Encapsulation Process

Purpose This paper aims to introduce a new indicative parameter of filling efficiency to quantify the performance and productivity of the flip-chip underfill encapsulation process. Additionally, the variation effect of the bump pitch of flip-chip on the filling efficiency was demonstrated to provide insight for flip-chip design optimization. Design/methodology/approach The filling efficiency was formulated analytically based on the conceptual spatial and temporal perspectives. Subsequently, the effect of bump pitch on filling efficiency was studied based on the past actual-scaled and current scaled-up underfill experiments. The latter scaled-up experiment was validated with both the finite volume method-based numerical simulation and analytical filling time model. Moreover, the scaling validity of scaled-up experiment was justified based on the similarity analysis of dimensionless number. Findings Through the scaling analysis, the current scaled-up experimental system is justified to be valid since the adopted scaling factor 40 is less than the theoretical scaling limit of 270. Furthermore, the current experiment was qualitatively well validated with the numerical simulation and analytical filling time model. It is found that the filling efficiency increases with the bump pitch, such that doubling the bump pitch would triple the efficiency. Practical implications The new performance indicative index of filling efficiency enables the package designers to justify the variation effect of underfill parameter on the overall underfill process. Moreover, the upper limit of scaling factor for scaled-up package was derived to serve as the guideline for future scaled-up underfill experiments. Originality/value The performance of underfill process as highlighted in this paper was never being quantified before in the past literatures. Similarly, the scaling limit that is associated to the scaled-up underfill experiment was never being reported elsewhere too.

Effects of nano-copper particles on the properties of Sn58Bi composite solder pastes

2017 ◽  
Vol 34 (1) ◽  
pp. 40-44 ◽  
Author(s):  
Hao Zhang ◽  
Yang Liu ◽  
Fenglian Sun ◽  
Gaofang Ban ◽  
Jiajie Fan
Keyword(s):  
Formation Mechanism ◽  
Composite Solder ◽  
Defect Formation ◽  
Void Formation ◽  
Experimental Results ◽  
Solder Paste ◽  
Content Type ◽  
Weight Percentage ◽  
Copper Particles ◽  
Solder Pastes

Purpose This paper aimed to investigate the effects of nano-copper particles on the melting behaviors, wettability and defect formation mechanism of the Sn58Bi composite solder pastes. Design/methodology/approach In this paper, the mechanical stirring method was used to get the nano-composite solder pastes. Findings Experimental results indicated that the addition of 3 wt.% (weight percentage) 50 nm copper particles showed limited effects on the melting behaviors of the Sn58Bi composite solder paste. The spreading rate of the Sn58Bi composite solder paste showed a decreasing trend with the increase of the weight percentage of 50 nm copper particles from 0 to 3 wt.%. With the addition of copper particles of diameters 50 nm, 500 nm or 6.5 μm into the Sn58Bi solder paste, the porosities of the three types of solder pastes showed a similar trend. The porosity increased with the increase of the weight percentage of copper particles. Based on the experimental results, a model of the void formation mechanism was proposed. During reflow, the copper particles reacted with Sn in the matrix and formed intermetallic compounds, which gathered around the voids produced by the volatilization of flux. The exclusion of the voids was suppressed and eventually led to the formation of defects. Originality/value This study provides an optimized material for the second and third level packaging. A model of the void formation mechanism was proposed.

A Model for Underfill Viscous Flow Considering the Resistance Induced by Solder Bumps

2004 ◽  
Vol 126 (2) ◽  
pp. 186-194 ◽  
Author(s):  
Chyi-Lang Lai ◽  
Wen-Bin Young
Keyword(s):  
Flip Chip ◽  
External Pressure ◽  
Good Prediction ◽  
Parallel Plates ◽  
Rectangular Array ◽  
Chip Technology ◽  
Solder Bumps ◽  
Proposed Model ◽  
Filling Time ◽  
Underfill Flow

During the underfill process, polymers driven by either capillary force or external pressure are filled at a low speed between the chip and substrate. Current methods treated the flow in the chip cavity as a laminar flow between parallel plates, which ignored the resistance induced by the solder bumps or other obstructions. In this study, the filling flow between solder bumps was simulated by a flow through a porous media. By using the superposition of flows through parallel plates and series of rectangular ducts, permeability of the underfill flow was fully characterized by the geometric arrangement of solder bumps and flat chips. The flow resistances caused by adjacent bumps were represented in its permeability. The model proposed in this study could provide a numerical approach to approximate and simulate the undefill process for flip-chip technology. Although the proposed model is applicable for any geometric arrangement of solder bumps, rectangular-array of solder bumps layout was used first for comparison with experimental results of other article. Comparisons of the flow-front shapes and filling time with the experimental data indicated that the flow simulation obtained from the proposed model gave a good prediction for the underfill flow.

Effect of hourglass shape solder joints on underfill encapsulation process: numerical and experimental studies

2020 ◽  
Vol 32 (3) ◽  
pp. 147-156
Author(s):  
Muhammad Naqib Nashrudin ◽  
Zhong Li Gan ◽  
Aizat Abas ◽  
M.H.H. Ishak ◽  
M. Yusuf Tura Ali
Keyword(s):  
Solder Joint ◽  
Numerical Method ◽  
Flip Chip ◽  
Solder Joints ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Cross Sectional ◽  
Content Type ◽  
Filling Time ◽  
Encapsulation Process

Purpose In line with the recent development of flip-chip reliability and underfill process, this paper aims to comprehensively investigate the effect of different hourglass shape solder joint on underfill encapsulation process by mean of experimental and numerical method. Design/methodology/approach Lattice Boltzmann method (LBM) numerical was used for the three-dimensional simulation of underfill process. The effects of ball grid arrays (BGA) encapsulation process in terms of filling time of the fluid were investigated. Experiments were then carried out to validate the simulation results. Findings Hourglass shape solder joint has shown the shortest filling time for underfill process compared to truncated sphere. The underfill flow obtained from both simulation and experimental results are found to be in good agreement for the BGA model studied. The findings have also shown that the filling time of Hourglass 2 with parabolic shape gives faster filling time compared to the Hourglass 1 with hemisphere angle due to bigger cross-sectional area of void between the solder joints. Practical implications This paper provides reliable insights to the effect of hourglass shape BGA on the encapsulation process that will benefit future development of BGA packages. Originality/value LBM numerical method was implemented in this research to study the flow behaviour of an encapsulation process in term of filling time of hourglass shape BGA. To date, no research has been found to simulate the hourglass shape BGA using LBM.

Underfill Flow in Flip-Chip Encapsulation Process: A Review

2021 ◽  
Author(s):  
Fei Chong Ng ◽  
Mohamad Aizat Abas
Keyword(s):  
Flip Chip ◽  
Parametric Design ◽  
Microscopic Analysis ◽  
Technological Advancement ◽  
Filling Time ◽  
Underfill Flow ◽  
Encapsulation Process ◽  
Time Determination ◽  
Reliability Issue ◽  
Analytic Skills

Abstract The scope of review of this paper focused on the pre-curing underfilling flow stage of encapsulation process. A total of 80 related works has been reviewed and being classified into process type, method employed, and objective attained. Statistically showed that the conventional capillary is the most studied underfill process, while the numerical simulation was mainly adopted. Generally, the analyses on the flow dynamic and distribution of underfill fluids in the bump array aimed for the filling time determination as well as the predictions of void occurrence. Parametric design optimization was subsequently conducted to resolve the productivity issue of long filling time and reliability issue of void occurrence. The bump pitch was found to the most investigated parameter, consistent to the miniaturization demand. To enrich the design versatility and flow visualization aspects, experimental test vehicle was innovated using imitated chip and replacement fluid, or even being scaled-up. Nonetheless, the analytical filling time models became more accurate and sophiscasted over the years, despite still being scarce in number. With the technological advancement on analysis tools and further development of analytic skills, it was believed that the future researches on underfill flow will become more comprehensive, thereby leading to the production of better packages in terms of manufacturing feasibility, performances, and reliability. Lastly, few potential future works were recommended, for instance, microscopic analysis on the bump-fluid interaction, consideration of filler particles and incorporation of artificial intelligence.

Effect of different temperature distribution on multi-stack BGA package

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Lun Hao Tung ◽  
Fei Chong Ng ◽  
Aizat Abas ◽  
M.Z. Abdullah ◽  
Zambri Samsudin ◽  
...  
Keyword(s):  
Capillary Flow ◽  
Correlation Study ◽  
Statistical Correlation ◽  
Effect Of Temperature ◽  
Content Type ◽  
Filling Time ◽  
Underfill Flow ◽  
Bga Package ◽  
Simple Implementation ◽  
Volume Method

Purpose This paper aims to determine the optimum set of temperatures through correlation study to attain the most effective capillary flow of underfill in a multi-stack ball grid array (BGA) chip device. Design/methodology/approach Finite volume method is implemented in the simulation. A three-layer multi-stack BGA is modeled to simulate the underfill flow. The simulated models were well validated with the previous experimental work on underfill process. Findings The completion filling time shows high regression R-squared value of up to 0.9918, which indicates a substantial acceleration on the underfill process because of incorporation of thermal delta. An introduction of 11 °C thermal delta to the multi-stacks BGA managed to reduce the filling time by up to 16.4%. Practical implications Temperature-induced capillary flow is a relatively new type of driven underfill designed specifically for package on package BGA components. Its simple implementation can further improve the productivity of existing underfill process in the industry that is desirable in reducing the process lead time. Originality/value The effect of temperature-induced capillary flow in underfill encapsulation on multi-stacks BGA by means of statistical correlation study is a relatively new topic, which has never been reported in any other research according to the authors’ knowledge.

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