Impelementatoin of a viscoelastic model for the temperature dependent material behavior of underfill encapsulants

Chhanda, Nusrat J.; Suhling, Jeffrey C.; Lall, Pradeep

doi:10.1109/itherm.2012.6231440

Cited by 8 publications

(4 citation statements)

References 25 publications

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“…After the Prony coefficients were determined, the master curve at a reference temperature was shifted to the various temperatures for comparison with experimental data. Chhanda, et al [24][25] have also used a Prony series viscoelastic model to represent the time dependent mechanical behavior of underfill encapsulants. They showed the model could accurately represent creep and stress-strain for a variety of temperatures.…”

Section: Figure 1 -Flip Chip Cbga Assemblymentioning

confidence: 99%

“…Free standing underfill samples for mechanical testing were prepared using a novel procedure described in previous work of the authors [13][14][24][25][26][27][28]. A stacked assembly view of the "mold assembly" utilized in this investigation is pictured in Figure 2a, and Figure 2b shows example uniaxial specimens after curing.…”

Section: Test Specimen Preparationmentioning

confidence: 99%

“…shear modulus vs. time and bulk modulus vs. time data, curve fitting can be used to get the Prony coefficients and two methods have been implemented [23][24][25]. In the first method, the temperature shift factor for each temperature can be determined by constructing a master curve, where the shear moduli or bulk moduli at all temperatures are shifted to the curve for a selected reference temperature.…”

Section: Mechanical Test Systemmentioning

confidence: 99%

“…The glass transition region for T > +100 C is clearly evident. In our prior work [24][25]32], we have found that an empirical four-parameter hyperbolic tangent model can be used to accurately model the observed nonlinear stress-strain data at any temperature. The general representation of this relation is…”

Section: Experimental Data For Underfillmentioning

confidence: 99%

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Effects of moisture exposure on the mechanical behavior of flip chip underfills in microelectronic packaging

Chhanda

Suhling

Lall

2014

Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)

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Reliable, consistent, and comprehensive material property data are needed for microelectronics encapsulants for the purpose of mechanical design, reliability assessment, and process optimization of electronic packages. Since the vast majority of contemporary underfills are epoxy based, they have the propensity to absorb moisture, which can lead to undesirable changes in their mechanical and adhesion behaviors. In this study, the effects of moisture adsorption on the stress-strain behavior of an underfill encapsulant were evaluated experimentally and theoretically.A novel specimen preparation procedure has been used to manufacture 60 x 3 mm uniaxial tension test samples, with a specified thickness of 0.5 mm. The test specimens were dispensed and cured with production equipment using the same conditions as those used in actual flip chip assembly, and no release agent was required to extract them from the mold. The fabricated uniaxial test specimens were then exposed in an adjustable thermal and humidity chamber to combined hygrothermal exposures at 85 C and 85% RH for various durations.After moisture preconditioning, a microscale tension-torsion testing machine was used to evaluate the complete stress-strain behavior of the material at several temperatures (T = 25, 50, 75, 100 and 125 C). The viscoelastic mechanical response of the underfill encapsulant has also been characterized via creep testing for a large range of applied stress levels and temperatures before moisture exposure.From the recorded results, it was found that the moisture exposures strongly affected the mechanical properties of the tested underfill including the initial elastic modulus and ultimate tensile stress. With the obtained mechanical property data, a three-dimensional linear viscoelastic model based on Prony series response functions has been applied to fit the stress-strain and creep data, and excellent correlation had been obtained for samples with and without moisture exposure. The effects of moisture were built into the model using the observed changes in the glass transition temperature within the WLF Shift Function.

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Section: Figure 1 -Flip Chip Cbga Assemblymentioning

confidence: 99%