Experimental Characterization of Underfill Materials Exposed to Moisture Including Preconditioning

2015 ◽  
Author(s):  
Promod R. Chowdhury ◽  
Nusrat J. Chhanda ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Room Temperature ◽  
Flip Chip ◽  
Mechanical Response ◽  
Testing Machine ◽  
Ultimate Tensile Stress ◽  
Production Equipment ◽  
Material Behavior ◽  
Tensile Creep ◽  
Uniaxial Test ◽  
Humidity Chamber

Microelectronic encapsulants exhibit evolving properties that change significantly with environmental exposures such as isothermal aging and high humidity conditions. In this work, the material behavior changes occurring in underfill materials subjected to moisture exposures in an humidity chamber have been characterized using 60 × 3 × 0.5 mm uniaxial test specimens which were cured with production equipment using the same conditions as those used in actual flip chip assembly. After curing, the samples were divided into two groups and subjected to different preconditioning: (1) no preconditioning, (2) prebaking at 85 C for 24 hours. The fabricated and preconditioned 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 (0, 1, 3, 10, 30, 60 days). After the moisture exposures, a microscale tension-torsion testing machine was used to evaluate the complete stress-strain behavior of the material at room temperature (25 C). In addition, the viscoelastic mechanical response of the underfill encapsulant has also been characterized via creep testing at room temperature for several applied stress levels after the moisture exposures. From the recorded results, it was found that the moisture exposures strongly degrade the mechanical properties of the tested underfill including the initial elastic modulus, ultimate tensile stress, and tensile creep rate. Prebaking was found to increase the initial material properties, but the degradations due to subsequent moisture exposures occurred in a similar manner.

Experimental Characterization and Viscoplastic Modeling of the Temperature Dependent Material Behavior of Underfill Encapsulants

2011 ◽  
Author(s):  
Nusrat J. Chhanda ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Flip Chip ◽  
Mechanical Response ◽  
Testing Machine ◽  
Production Equipment ◽  
Material Behavior ◽  
Specimen Preparation ◽  
Viscoplastic Material ◽  
Stress Strain ◽  
Release Agent ◽  
Stress Levels

In this work, the viscoplastic mechanical response of a typical underfill encapsulant has been characterized via rate dependent stress-strain testing over a wide temperature range, and creep testing for a large range of applied stress levels and temperatures. A specimen preparation procedure has been developed to manufacture 80 × 5 mm uniaxial tension test samples with a specified thickness of .5 mm. The test specimens are dispensed and cured with production equipment using the same conditions as those used in actual flip chip assembly, and no release agent is required to extract them from the mold. Using the manufactured test specimens, a microscale tension-torsion testing machine has been used to evaluate stress-strain and creep behavior of the underfill material as a function of temperature. Stress-strain curves have been measured at 5 temperatures (25, 50, 75, 100 and 125 C), and strain rates spanning over 5 orders of magnitude. In addition, creep curves have been evaluated for the same 5 temperatures and several stress levels. With the obtained mechanical property data, several viscoelastic and viscoplastic material models have been fit to the data, and optimum constitutive models for subsequent use in finite element simulations have been determined.

Effects of Moisture Exposure on the Mechanical Behavior of Polymer Encapsulants in Microelectronic Packaging

2013 ◽  
Author(s):  
Nusrat J. Chhanda ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Testing Machine ◽  
Adsorbed Water ◽  
Ultimate Tensile Stress ◽  
Stress Strain ◽  
Uniaxial Test ◽  
Organic Structure ◽  
Strain Behavior ◽  
Humidity Chamber

Polymer encapsulants exhibit evolving properties that change significantly with environmental exposures such as moisture uptake, isothermal aging and thermal cycling. In this study, the effects of moisture adsorption on the stress-strain behavior of a polymer encapsulant were evaluated experimentally. The uniaxial test specimens were exposed in an adjustable thermal and humidity chamber to combined hygrothermal exposures at 85 °C/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. It was found that moisture exposure caused plasticization and strongly reduced the mechanical properties of the encapsulant including the initial elastic modulus and ultimate tensile stress. Reversibility tests were also conducted to evaluate whether the degradations in the mechanical properties were recoverable. Upon fully redrying, the polymer was found to recover most but not all of its original mechanical properties. As revealed by FTIR, some of the adsorbed water had been hydrolyzed in the organic structure of the epoxy-based adhesive, causing permanent changes to the mechanical behavior.

Measurement of the Constitutive Behavior of Underfill Encapsulants

2003 ◽  
Author(s):  
M. Saiful Islam ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Flip Chip ◽  
Mechanical Response ◽  
Capillary Flow ◽  
Mechanical Test ◽  
Testing Machine ◽  
Production Equipment ◽  
Uniaxial Tensile ◽  
Stress Strain ◽  
Strain Behavior ◽  
Nonlinear Stress

Reliable, consistent, and comprehensive material property data are needed for microelectronic encapsulants for the purpose of mechanical design, reliability assessment, and process optimization of electronic packages. In our research efforts, the mechanical responses of several different capillary flow snap cure underfill encapsulants are being characterized. A microscale tension-torsion testing machine has been used to evaluate the uniaxial tensile stress-strain behavior of underfill materials as a function of temperature, strain rate, specimen dimensions, humidity, thermal cycling exposure, etc. A critical step to achieving accurate experimental results has been the development of a sample preparation procedure that produces mechanical test specimens that reflect the properties of true underfill encapsulant layers. In the developed method, 75–125 μm (3–5 mil) thick underfill uniaxial tension specimens are dispensed and cured using production equipment and the same processing conditions as those used with actual flip chip assemblies. Although several underfills have been examined, this work features results for the mechanical response of a single typical capillary flow snap cure underfill. A three parameter hyperbolic tangent empirical model has been shown to provide accurate fits to the observed underfill nonlinear stress-strain behavior over a range of temperatures and strain rates. In addition, typical creep data are presented.

Mechanical Properties of Winding Conductors Affected by Cyclic Thermal Overloads

2006 ◽  
Vol 113 ◽  
pp. 541-544 ◽  
Author(s):  
N. Višniakov ◽  
J. Novickij ◽  
D. Ščekaturovienė ◽  
M. Šukšta
Keyword(s):  
Mechanical Properties ◽  
Metal Matrix ◽  
Room Temperature ◽  
Pure Copper ◽  
Testing Machine ◽  
Liquid Nitrogen Temperature ◽  
Ultimate Tensile Stress ◽  
Climatic Chamber ◽  
Fast Heating ◽  
Before And After

The influence of thermal cyclic overloads on mechanical properties of winding conductors was investigated. Copper-niobium microcomposite, soft and hard pure copper wires were conditioned at temperatures range from 77 K to 500 K. The treatment was done during 100 cycles of fast conductor cooling to liquid nitrogen temperature and further fast heating in a climatic chamber. The ultimate tensile stress limit and the elongation at failure of metal-matrix copper-niobium microcomposite, soft and hard copper wires were measured before and after thermal treatment with a testing machine at room temperature.

Die Stress Variation During Thermal Cycling Reliability Tests

2007 ◽  
Author(s):  
M. Kaysar Rahim ◽  
Jordan Roberts ◽  
Jeffrey C. Suhling ◽  
Richard C. Jaeger ◽  
Pradeep Lall
Keyword(s):  
Thermal Cycling ◽  
Electronic Packaging ◽  
Room Temperature ◽  
Flip Chip ◽  
Constitutive Relations ◽  
Temperature Cycling ◽  
Material Behavior ◽  
Aging Effects ◽  
Test Chips

Thermal cycling accelerated life testing is an established technique for thermo-mechanical evaluation and qualification of electronic packages. Finite element life predictions for thermal cycling configurations are challenging due to several reasons including the complicated temperature/time dependent constitutive relations and failure criteria needed for solders, encapsulants and their interfaces; aging/evolving material behavior for the packaging materials (e.g. solders); difficulties in modeling plating finishes; the complicated geometries of typical electronic assemblies; etc. In addition, in-situ measurements of stresses and strains in assemblies subjected to temperature cycling are difficult because of the extreme environmental conditions and the fact that the primary materials/interfaces of interest (e.g. solder joints, die device surface, wire bonds, etc.) are embedded within the assembly (not at the surface). For these reasons, little is known about the evolution of the stresses, strains, and deformations occurring within sophisticated electronic packaging geometries during thermal cycling. In this work, we have used test chips containing piezoresistive stress sensors to characterize the in-situ die surface stress during long-term thermal cycling of electronic packaging assemblies. Using (111) silicon test chips, the complete three-dimensional stress state (all 6 stress components) was measured at each rosette site by monitoring the resistance changes occurring in the sensors. The packaging configuration studied in this work was flip chip on laminate where 5 × 5 mm perimeter bumped die were assembled on FR-406 substrates. Three different thermal cycling temperature profiles were considered. In each case, the die stresses were initially measured at room temperature after packaging. The packaged assemblies were then subjected to thermal cycling and measurements were made either incrementally or continuously during the environmental exposures. In the incremental measurements, the packages were removed from the chamber after various durations of thermal cycling (e.g. 250, 500, 750, 1000 cycles, etc.), and the sensor resistances were measured at room temperature. In the continuous measurements, the sensor resistances at critical locations on the die device surface (e.g. die center and die corners) were recorded continuously during the thermal cycling exposure. From the resistance data, the stresses at each site were calculated and plotted versus time. The experimental observations show cycle-to-cycle evolution in the stress magnitudes due to material aging effects, stress relaxation and creep phenomena, and development of interfacial damage.

Evolution of Lead Free Solder Material Behavior During Isothermal Aging

2006 ◽  
Author(s):  
Hongtao Ma ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall ◽  
Michael J. Bozack
Keyword(s):  
Isothermal Aging ◽  
Room Temperature ◽  
Material Behavior ◽  
Lead Free ◽  
Aging Effects ◽  
Uniaxial Test ◽  
Room Temperature Aging ◽  
Free Solder ◽  
Lead Free Solders ◽  
Temperature Aging

Solder materials demonstrate evolving microstructure and mechanical behavior that changes significantly with environmental exposures such as isothermal aging and thermal cycling. These aging effects are greatly exacerbated at higher temperatures typical of thermal cycling qualification tests for harsh environment electronic packaging. In the current study, mechanical measurements of thermal aging effects and material behavior evolution of lead free solders have been performed. Extreme care has been taken so that the fabricated solder uniaxial test specimens accurately reflect the solder materials present in actual lead free solder joints. A novel specimen preparation procedure has been developed where the solder uniaxial test specimens are formed in high precision rectangular cross-section glass tubes using a vacuum suction process. The tubes are then sent through a SMT reflow to re-melt the solder in the tubes and subject them to any desired temperature profile (i.e. same as actual solder joints). Using specimens fabricated with the developed procedure, isothermal aging effects and viscoplastic material behavior evolution have been characterized for 95.5Sn4.0Ag-0.5Cu (SAC405) and 96.5Sn-3.0Ag-0.5Cu (SAC305) lead free solders, which are commonly used as the solder ball alloy in lead free BGAs and other components. Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. In our total experimental program, samples have been solidified with both reflowed and water quenching temperature profiles, and isothermal aging has been performed at room temperature (25 °C) and elevated temperatures (100 °C, 125 °C and 150 °C). In this paper, we have concentrated on reporting the results of the room temperature aging experiments. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of room temperature aging time. Microstructural changes during. room temperature aging have also been recorded for the solder alloys and correlated with the observed mechanical behavior changes.

Impact of Environmental Preconditioning and Composition Parameters on Constitutive Behavior of Underfills

2003 ◽  
Author(s):  
Saiful Islam ◽  
Pradeep Lall ◽  
Jeffrey C. Suhling ◽  
R. Wayne Johnson
Keyword(s):  
Thermal Cycling ◽  
Flip Chip ◽  
Testing Machine ◽  
Sample Thickness ◽  
Constitutive Behavior ◽  
Fatigue Reliability ◽  
Uniaxial Test ◽  
Creep And Stress Relaxation ◽  
Thermal Cycling Fatigue ◽  
Underfill Material

The use of underfills in electronic applications is becoming more prevelant with the decrease in package pitch to 0.5 mm and the increase in I/Os. Underfill encapsulation is typically used in flip chip on laminate assemblies to more evenly distribute and minimize the solder joint strains, thus improving thermal cycling fatigue life. The material constitutive and damage behavior of underfills is however poorly understood. Typical underfill material data sheets often do not provide the parameters required for development of accurate predictive models. In this paper a new methodology for preparation of thin uniaxial test samples for mechanical testing of underfills has been used to better understand the non-linear constitutive behavior of underfills. Bulk underfill samples exhibit different behavior because of non-uniform curing and the effect of sample thickness on the response of underfill layers. A microscale tension-torsion testing machine has been used to measure stress-strain, creep, and stress relaxation behavior if several underfills as a function of temperature. Thermal-fatigue reliability response of various permutation of underfill materials have been analyzed using statistical models. The effect of thermal aging, thermal cycling, and moisture preconditioning on the constitutive behavior of materials have been analyzed. Models have been developed to represent the underfill behavior in an operating range of −40 to 125C.

Comparison of Substructures Between Uniaxial and Biaxial Deformation in 1100-0 Aluminum

1981 ◽  
Vol 39 ◽  
pp. 52-53
Author(s):  
D. L. Rohr ◽  
S. S. Hecker
Keyword(s):  
Plastic Strain ◽  
Cell Walls ◽  
Room Temperature ◽  
Mechanical Response ◽  
Biaxial Tension ◽  
Initial Deformation ◽  
Uniaxial Deformation ◽  
Biaxial Deformation ◽  
Stress States ◽  
Comprehensive Study

As part of a comprehensive study of microstructural and mechanical response of metals to uniaxial and biaxial deformations, the development of substructure in 1100 A1 has been studied over a range of plastic strain for two stress states.Specimens of 1100 aluminum annealed at 350 C were tested in uniaxial (UT) and balanced biaxial tension (BBT) at room temperature to different strain levels. The biaxial specimens were produced by the in-plane punch stretching technique. Areas of known strain levels were prepared for TEM by lapping followed by jet electropolishing. All specimens were examined in a JEOL 200B run at 150 and 200 kV within 24 to 36 hours after testing.The development of the substructure with deformation is shown in Fig. 1 for both stress states. Initial deformation produces dislocation tangles, which form cell walls by 10% uniaxial deformation, and start to recover to form subgrains by 25%. The results of several hundred measurements of cell/subgrain sizes by a linear intercept technique are presented in Table I.

Dynamic and Quasi-Static Compressive Deformation Behaviour of Polyimide Foam at Various Elevated Temperature

2014 ◽  
Vol 566 ◽  
pp. 158-163 ◽  
Author(s):  
A. Yosimoto ◽  
Hidetoshi Kobayashi ◽  
Keitaro Horikawa ◽  
Keiko Watanabe ◽  
Kinya Ogawa
Keyword(s):  
Compressive Strength ◽  
Room Temperature ◽  
Deformation Behaviour ◽  
Testing Machine ◽  
Negative Temperature ◽  
Strain Rates ◽  
Compression Tests ◽  
Hopkinson Pressure Bar ◽  
Universal Testing ◽  
Pressure Bar

In order to clarify the effect of strain rate and test temperature on the compressive strength and energy absorption of polyimide foam, a series of compression tests for the polyimide foam with two different densities were carried out. By using three testing devices, i.e. universal testing machine, dropping weight machine and sprit Hopkinson pressure bar apparatus, we performed a series of compression tests at various strain rates (10-3~103s-1) and at several test temperatures in the range of room temperature to 280 ̊C. At over 100 s-1, the remarkable increase of flow stress was observed. The negative temperature dependence of strength was also observed.

Uncertainty Quantification in Predicting Behaviour of Rubber-Like Materials in Uni-Axial Loading

2020 ◽  
Author(s):  
Aref Ghaderi ◽  
Vahid Morovati ◽  
Pouyan Nasiri ◽  
Roozbeh Dargazany
Keyword(s):  
Uncertainty Quantification ◽  
Mechanical Response ◽  
Pure Shear ◽  
Constitutive Models ◽  
Material Behavior ◽  
Elastic Behavior ◽  
Deterministic Models ◽  
Data Set ◽  
Material Parameters ◽  
Axial Extension

Abstract Material parameters related to deterministic models can have different values due to variation of experiments outcome. From a mathematical point of view, probabilistic modeling can improve this problem. It means that material parameters of constitutive models can be characterized as random variables with a probability distribution. To this end, we propose a constitutive models of rubber-like materials based on uncertainty quantification (UQ) approach. UQ reduces uncertainties in both computational and real-world applications. Constitutive models in elastomers play a crucial role in both science and industry due to their unique hyper-elastic behavior under different loading conditions (uni-axial extension, biaxial, or pure shear). Here our goal is to model the uncertainty in constitutive models of elastomers, and accordingly, identify sensitive parameters that we highly contribute to model uncertainty and error. Modern UQ models can be implemented to use the physics of the problem compared to black-box machine learning approaches that uses data only. In this research, we propagate uncertainty through the model, characterize sensitivity of material behavior to show the importance of each parameter for uncertainty reduction. To this end, we utilized Bayesian rules to develop a model considering uncertainty in the mechanical response of elastomers. As an important assumption, we believe that our measurements are around the model prediction, but it is contaminated by Gaussian noise. We can make the noise by maximizing the posterior. The uni-axial extension experimental data set is used to calibrate the model and propagate uncertainty in this research.

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