The importance of material selection for flip chip on board assemblies

O’Malley, Grace; Giesler, J.; Machuga, S.

doi:10.1109/96.311770

Cited by 41 publications

(11 citation statements)

References 3 publications

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“…The total number of elements in this case is 7601 and the number of nodes is 4439. In the dispensing simulation, the contact angle at the melt front has been assumed to be either constant or else dynamic as given by (5). Curvature in theplane has been neglected (that is, only the curvature in the thickness direction has been considered).…”

Section: Comparison Of Experimental and Analysis Resultsmentioning

confidence: 99%

“…However, Schonhorn et al, [10] measured the contact angle versus time using several polymers on various substrates and found that the contact angle starts from some initial angle (typically close to 90 ) and slowly develops toward an equilibrium value. In particular, Newman [11] suggested the following equation to describe the time dependence of contact angle (5) where (6) (7) in which is the contact angle at time , is the initial contact angle, is the equilibrium contact angle, and is a constant which depends on the surfaces in contact with the encapsulant. Using this time-dependent contact angle, the fill time can be calculated by (8) which has to be solved iteratively due to the nonlinear dependence on .…”

Section: A Analytical Solutionsmentioning

confidence: 99%

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Analysis of the flow of encapsulant during underfill encapsulation of flip-chips

Han

Wang

1997

IEEE Trans. Comp., Packag., Manufact. Technol. B

141

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In this paper, the flow of encapsulant during the underfill encapsulation of flip-chips has been studied. Analytical as well as numerical methods have been developed to analyze the flow. For capillary-driven encapsulation (by dispensing), the capillary force at the melt-front has been calculated based on a model for the melt-front shape. A model has also been developed for the analysis of forced-injection encapsulation. The numerical analysis uses a finite-element method based on a generalized Hele-Shaw method for solving the flow field.Experiments have been performed to investigate the flow behavior using actual chips and encapsulants. Short-shot runs have been performed to observe the melt-front advancement at different flow times. In addition, measurements have been made of the material properties of the encapsulant, namely its viscosity, curing kinetics and surface-tension coefficient. The experimental and simulation results have been compared in terms of the flow-front shapes and times at different fill fractions. Such comparisons indicate that the model developed in this study is adequate to approximately simulate the flow during encapsulation of flip chips.

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Section: Comparison Of Experimental and Analysis Resultsmentioning

confidence: 99%

Section: A Analytical Solutionsmentioning

confidence: 99%

Analysis of the flow of encapsulant during underfill encapsulation of flip-chips

Han

Wang

1997

IEEE Trans. Comp., Packag., Manufact. Technol. B

141

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“…In addition, to get the sufficient process time for filling the space, the cure rate of underfill is relatively slow and requires additional oven curing process for several hours, which need lots of addition process cost and cycle time [3]. The other problems related with reliability, process and quality issues such as, moisture resistance, fillet coverage, adhesion strength between die and substrate interfaces problem all been reported in previous studies [3,4,5,6]. , is able to provide a better solution by utilizing conventional transfer molding technology .…”

Section: Introductionmentioning

confidence: 99%

A study on the rheological characterization and flow modeling of molded underfill (MUF) for optimized void elimination design

Lee¹,

Jung²,

Sohn³

et al. 2008

2008 58th Electronic Components and Technology Conference

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The molded underfill (MUF) process has a lot of advantages compared with capillary underfill process in view of reduction of process, cycle time of process, material and equipment cost since this application utilizes the conventional mold materials and equipment systems. But the extremely narrow gap at the underfill area for flip-chip bonding make it difficult to get stable MUF material set and appropriate processing conditions because of the severe void trapping problem. In this paper, the MUF process of flip-chip package on package (POP) is investigated. The rheological and curekinetic parameters of commercial MUF compound are acquired using parallel plate rheometer and dynamic DSC (differential scanning caloriemeter) analysis. The experimental results showed severe void at the underfill area for both top-left and bottom-right pin type gate locations. The modeling results by full 3D mold filling simulation show good agreement with the actual void occurring area investigated by the SAT pictures. Applying the benchmarked constitutive relations and finite elements model, seven kinds of different gate types and locations are tried, but the void trapping is not completely removed. To resolve void trapping phenomena of current flip-chip structure, we devised a proprietary mold design. From the modeling results, the void trapping zone under the large die are effectively removed through the optimized design. From this study, we can conclude that the optimized mold design will be very effective on the elimination of void in the underfill area for flip-chip MUF processing.

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“…3) Encapsulant: Development of materials suitable for flipchip encapsulation is difficult. Currently, most encapsulants are epoxy-based thermosets which are heavily loaded with solid fillers [10]. The encapsulant needs to have good fluidity, wettability, matching thermalexpansion coefficient with the solder and appropriate curing kinetics.…”

Section: Introductionmentioning

confidence: 99%

“…10. A view of the encapsulation layer for the pressurized case when IBM chip is encapsulated with encapsulants (a) "A" and (b) "B.…”

mentioning

confidence: 99%

Study on the pressurized underfill encapsulation of flip chips

Han

Wang

1997

IEEE Trans. Comp., Packag., Manufact. Technol. B

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Flip-chip technology generally requires encapsulation of the solder joints to reduce the loads on such joints during thermal excursions. At present, the encapsulation process by dispensing constitutes the primary obstacle to widespread acceptance and implementation of flip-chip technology because of the long process times involved and the subsequent reliability and reparability problem. A new process to encapsulate flip-chips has been developed. This process uses a special mold to surround the chip to be encapsulated and injects the encapsulation material at elevated pressure. The experimental results show that the pressurized encapsulation process reduces the fill time (by as much as a factor of 1000), is able to perform the encapsulation at room temperature, fills the cavity completely without any voids and increases the capability of handling highly viscous encapsulants (1000 times more viscous than current commercial encapsulants) relative to the customary dispensing process for the particular case used in the current experiment.

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The importance of material selection for flip chip on board assemblies

Cited by 41 publications

References 3 publications

Analysis of the flow of encapsulant during underfill encapsulation of flip-chips

Analysis of the flow of encapsulant during underfill encapsulation of flip-chips

A study on the rheological characterization and flow modeling of molded underfill (MUF) for optimized void elimination design

Study on the pressurized underfill encapsulation of flip chips

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