Coefficient Of Moisture Expansion Research Articles

Hygroscopic strain measurement by fibre Bragg gratings sensors in organic matrix composites – Application to monitoring of a composite structure

This study is devoted to the identification of the moisture expansion coefficients of composite materials by means of a novel measurement technique. This method is based on the insertion of Fibre Bragg Grating (FBG) sensors between composite layers. The sensor enables to measure the hygroscopic strain induced by moisture diffusion in the plane of the laminated composite. Experimental results from immersed samples, varying both the direction of measurement and the fibre volume fraction are given according to the water uptake, and leading to the characterisation of moisture expansion coefficient.

Study of Voids in the Flexible RFID Tag Inlays Packaged by Anisotropic Conductive Adhesive

RFID is recognized one of the most potential information technologies. The RFID tag is a small tag containing an integrated circuit chip and an antenna. Voids can very often be detected in the non-metalized area of the RFID tags, they generated with unpredictable size and located randomly in the tag. The formation of the voids is the combined action of material properties and bonding parameters. In this work, the formation of the material related voids in the tags was investigated by thermogravimetric analysis. All specimens showed continuous loss of mass to varying degrees during the heating process. The air and moisture entrapped in the polymer matrix in the fabrication process and the process of use are the mainly reason. The loss mass of the etched antenna substrate primarily came from the lamination adhesive has not cured completely. With the simultaneous reaction of thermal stresses and internal vapor/volatile gas pressure drives both pre-existing and newly nucleated voids to grow. In addition, the voids growth under the high temperature (85°C) and high humidity (85%RH) conditions was investigated. The characteristic size of voids increases gradually with the increasing aging time because of the combined effects of the residual stress and the different coefficients of thermal expansion and moisture expansion.

J046032 高面精度フォームコアCFRPサンドイッチパネルの作製および表面形状の評価(〔J046-03〕高分子基複合材料の加工と評価(3))

As a new material suitable for the primary mirror of space telescopes, we focused on foam core CFRP sandwich panels which satisfy lower surface roughness than the conventional honeycomb core sandwich panels. However, large deformations appeared at edge of the ROHACELL (polymethacrylimide based foam) core sandwich panels surface. In order to improve the surface accuracy, we analytically investigated the influence of core thickness and of using the GRAFOAM core (carbon-based foam) having a low coefficient of thermal expansion. Then, ROHACELL core sandwich panels with two different core thickness and GRAFOAM core sandwich panels were manufactured and the surface accuracy of those panels were experimentally measured. Analytical and experimental results showed that edge effect decreased on ROHACELL core sandwich panels with thinner core thickness, and that the edge effect was suppressed by using the GRAFOAM core. In addition, because of lower CME(coefficient of moisture expansion), deformation due to moisture absorption is small.

Experimental and numerical investigation of the static response of environmentally aged adhesively bonded joints

The aim of this research is to investigate the effect of moisture on the static response of adhesively bonded monolithic single lap joints and laminated doublers loaded in bending. All joints were made of aluminium alloy Al 2024-T3 bonded using epoxy film adhesive FM 73M OST. The joints were aged in deionised water at a temperature of 50°C for up to 2 years exposure. The use of different widths of specimen (5mm for monolithic single lap joints and 15mm for laminated doublers) allowed both full and partial saturation of the adhesive layer. The bulk adhesive has been characterised to obtain the coefficient of moisture diffusion, the coefficient of thermal and moisture expansion and the moisture dependent mechanical properties. The testing results showed that the mechanical properties degraded in a linear way with the moisture content. The residual strength after exposure decreased with increasing moisture content (exposure time) and tended to level off towards saturation. The damage evolution and failure of the joint has been successfully monitored using the backface strain technique and in-situ video microscopy. Progressive damage finite element modelling using a moisture dependent, bilinear traction-separation law has been undertaken to predict the residual strength. Residual stresses due to thermal and swelling strains in the adhesive layer have been included; however their effect on the predicted static strength was not significant. Good agreement was found between the predicted residual strength and the experimental result.

An experimental–numerical study of moisture absorption in an epoxy

It is well known that moisture absorption impairs the mechanical and physical properties of polymers. Conventionally, the material’s hygric strains are described as the product of a constant coefficient of moisture expansion (CME) and moisture concentration. This hypothesis, however, has not been thoroughly examined experimentally. In this paper, the hygro-mechanical response of a DGBA based epoxy is reported as a function of moisture uptake. Cylindrical specimens are made of epoxy with an axially located optical fiber that contains a 23mm Bragg grating sensor (FBG). Strain data from the sensor and from a micrometer are combined with experimental absorption curves to determine the resin’s CME. The data indicate that diffusion and CME depend on moisture. Analysis of the experiments is carried out by numerical simulations of heat transfer, moisture diffusion and elastic stress analysis of the single fiber composite. The simulated results correlate well with the experimental data.

Shrinkage-based die design for drying ceramic parts

Drying of ceramic parts with complex geometry has been studied with emphasis on the effects of shrinkage on their final dimensions. The first step was to understand the processes governing moisture loss from a porous medium through experimental measurements yielding the coefficient of moisture expansion. As a result, non-homogeneous dimensional changes (shrinkage) occur in three-dimensional artefacts with varying cross-section. The moisture diffusion problem governed by Fick’s laws was solved numerically by analogy to the heat conduction problem. To this end the correspondence was established between physical parameters, variables and boundary conditions of heat flow and diffusion, characteristically the coefficient of moisture expansion being analogous to the coefficient of thermal expansion. The numerical model established and solved using finite element analysis predicted moisture distribution inside the part as well as the resulting change in its shape. Validation of numerical predictions was first ensured in two dimensions by modelling a simple slab and comparing with experimental measurements. Validation for a fully three-dimensional shape required use of the well-established iterative closest point algorithm for surface point matching and subsequently the creation of an error map. The reverse of this numerical model was used to predict the appropriate die geometry starting with the shape of the desired part by taking into account the variable drying shrinkage allowance, and the relevant steps are outlined.

Hygroscopic and thermal micro deformations of plastic substrates for flexible electronics using digital image correlation

Thin polymer substrates are promising materials for flexible electronics with many advantages. However, the dimensional stability of polymer substrates is low. Nowadays, this is overcome by laminating polymer substrates onto a rigid carrier. Nevertheless, carrier-less processing will be a foreseen next step for future manufacturing of plastic electronic devices, which will intensify the interest in dimensional stability of the plastic substrates. This paper describes a measurement method to characterise the in-plane hygroscopic and thermal properties of thin polymeric substrates using a Digital Image Correlation (DIC) based method. The precision and accuracy of the method is addressed, and the method was validated using copper, aluminium and silicon test samples. The hygroscopic and thermal properties of semi-crystalline Polyethylene Naphthalate (PEN) and amorphous Polyether Sulphone (PES) substrates, both attractive for flexible electronics, were characterized. The coefficients of thermal and moisture expansion were measured. Furthermore, the anisotropy in thermal and hygroscopic expansion was quantified using the full in-plane deformation measurement data.

Hygro-Thermo-Mechanical Reliability Assessment of a Thermal Interface Material for a Ball Grid Array Package Assembly

The thermal efficacy of thermal interface material (TIM) is highly dependent on its ability to adhere to the surfaces of interest. Any delamination of the TIM from the die or the lid will increase the local thermal resistance and, thus, will reduce the overall effectiveness of the TIM. Although significant amount of work has been done on understanding the thermal and moisture effects of various polymer materials used in microelectronic package assemblies, very limited work has been done to study the effect of temperature and moisture on TIM delamination. In this paper, a sequential hygro-thermal-mechanical finite-element model has been developed to mimic the loadsteps associated with package assembly as well as moisture soaking under 85°C/85RH over 500 h. The predictions from the models have been validated with a wide range of experimental data including laser Moiré data for thermomechanical loading and digital image correlation data for hygro-thermo-mechanical loading. Weight gain and coordinate-measurement machine have been used to characterize moisture diffusivity and moisture expansion coefficient of various polymer materials in the package assembly. The developed models show the evolution of normal strain in TIM during various loadsteps and provide important insight into the potential for TIM delamination under package assembly process and moisture soaking. Thus, the models can be used for developing various designs and process steps for reducing the chances for TIM delamination.

Hygro-thermo-mechanical effects on FGM plates resting on elastic foundations

A hygrothermal bending analysis is presented for a functionally graded material (FGM) plate resting on elastic foundations. The elastic coefficients, thermal coefficient and moisture expansion coefficient of the plate are assumed to be graded in the thickness direction. The equilibrium equations are given and a number of examples are solved to illustrate bending response of Titanium/Zirconia plates subjected to hygro-thermo-mechanical effects and resting on elastic foundations. The influences played by many parameters are investigated.

Interface delamination analysis of TQFP package during solder reflow

Interface delamination during solder reflow is a critical reliability problem for the plastic IC packages. The main objective of this study is to apply modified virtual crack closure method (MVCCM) for the analysis of interface delamination between the leadframe pad and the encapsulant during a lead-free solder reflow after the level 1 moisture preconditioning. In this study, the moisture diffusion parameters and the coefficient of moisture expansion (CME) of two different epoxy molding compounds (EMC) are characterized for moisture diffusion analysis and the deformation analysis due to hygroscopic swelling. At the same time, the entire thermal and moisture history of Thin Quad Flat Pack (TQFP) package is simulated from the start of level 1 moisture preconditioning (85 °C/85%RH for 168 h) to subsequent exposure to a lead-free solder reflow process. Finally, the transient development of the stress intensity factors due to thermal stress only K t , hygrostress only K h , vapor pressure only K p and combined energy release rate G tot are computed and studied by using MVCCM. Based on the calculated stress intensity factors and energy release rates, it seems that for the EMC, the Young’s modulus, moisture diffusion coefficient, CME and adhesion strength with leadframe at high temperature appear to be the most significant variables for the MSL performance of TQFP package and this matches well with the experimental finding.

A Study of Hygrothermal Behavior of ACF Flip Chip Packages With Moiré Interferometry

A primary factor of anisotropic conductive film (ACF) package failure is delamination between the chip and the adhesive at the edge of the chip. This delamination is mainly affected by the thermal shear strain at the edge of the chip. This shear strain was measured on various electronic ACF package specimens by micro-Moire interferometry with a phase shifting method. In order to find the effect of moisture, the reliability performance of an adhesive flip-chip in the moisture environment was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different geometric size specimens in terms of interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between the adhesive and other components in the package, which induces hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated by using the Moire interferometry. From Moire measurement results, we could also obtain the stress intensity factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> . Through an analysis of deformations induced by thermal and moisture environments, a damage model for an adhesive flip-chip package is proposed.

Study of joining of carbon/carbon composites for ultra stable structures

The aim of this work is to study joining materials and innovative bonding technologies for ultra stable joints of carbon/carbon composite (C/C) sandwich panels for the manufacturing of next generation space instruments. The proposed solutions have low coefficient of thermal expansion (CTE) and coefficient of moisture expansion (CME), and a good mechanical strength, in order to guarantee the dimensional stability and mechanical reliability of the joined C/C panels.

Comprehensive Hygro-Thermo-Vapor Pressure Model for CMOS Image Sensor

A combined effect of moisture diffusion, heat transfer, and hygro-thermo-vapor pressure modeling for pre-mold QFN CMOS Image Sensor (CIS) package has been developed in this study. Hygroscopic swelling properties such as saturation, coefficient of moisture expansion (CME) and activation energy can be extracted through TMA (Thermal Mechanical Analysis) and TGA (Thermal Gravitational Analysis) instruments. Fick’s second law of transient diffusion is solved by using finite element analysis (FEA) to evaluate the overall moisture distributions. With obtained experimental data, a three-dimensional FEA CIS model using the “thermal-wetness” technique is developed to predict the moisture absorption, moisture desorption, temperature distributions, hygro-thermo-vapor pressure mechanical coupled effect and the residual stress distributions at JEDEC pre-conditioning standard JESD22-A120.

Characterization of Hygroscopic Swelling and Thermo-Hygro-Mechanical Design on Electronic Package

AbstractThis paper discusses a successful experimental procedure to determine the hygroscopic swelling property of polymeric materials used in electronic packaging. Saturated moisture concentration and moisture diffusivity were determined by measuring the weight gain during moisture absorption. Hygromechanical properties, such as the coefficientof moisture expansion (CME), were determined through Thermo-Mechanical Analyzer (TMA) and Thermo-Gravimetric Analyzer (TGA) techniques. Fick's law of transient diffusion is solved by using finite element (FE) analysis to evaluate the overall moisture distributions. Both two-dimensional and three-dimensional models based on the FE software ANSYS were developed to predict the thermal-induced strain, hygroscopic swelling deformation, and residual thermohygro-mechanicalstress distributions. Reliability analysis at three JEDEC preconditioning standards 60°C60%RH, 85°C60%RH and 85°C85%RH was carried out. A series of comprehensive parametric studies were conducted in this research.

Analysis of time-dependent deformation of a CFRP mirror under hot and humid conditions

The long-term micro-dimensional stability of a carbon fiber reinforced plastic (CFRP) mirror was investigated in terms of creep deformation, moisture swelling and self-shrinkage. A 4-point bending creep test was carried out using specimens made from pitch-based high-modulus CFRP laminates to obtain a creep constant based on linear viscoelasticity, and we then investigated the weight change and geometrical change during a moisture absorption test using a CFRP specimen. The anisotropic diffusivities and coefficients of moisture expansion (CMEs) in CFRP laminates were obtained by fitting analytical data into the experimental data. Finally, the shrinkage behavior caused by physical aging of the polymeric material was examined using a fiber Bragg grating (FBG) sensor embedded in the neat resin specimen. Applying these results, we analyzed the geometrical changes in a CFRP mirror that resulted from time-dependent deformation by the mirror’s weight, moisture absorption and physical aging, respectively. We discuss which factor is dominant in the deformation of CFRP mirrors under various conditions.

Underfill selection methodology for fine pitch Cu/low-k FCBGA packages

A systematic underfill selection approach has been presented to characterize and identify suitable underfill encapsulants for large size flip chip ball grid array (FCBGA) packages. In the selection scheme, a total of six evaluation factors such as fracture toughness, coefficient of moisture expansion, flowability, delamination performance and filler settlement were considered. Driving stresses for package failure were also included as a factor of consideration, which clearly depends on the package size and geometry. Based on the approach adopted, underfill material that is suitable for 35 × 35 mm 2 packages with 15 mm die size and 45 × 45 mm 2 packages with 21 mm die size was selected. Target value for underfill properties has also been revised.

Monitoring of hygrothermal ageing effects in an epoxy resin using FBG sensor: A methodological study

This study demonstrates the feasibility of using fibre Bragg grating (FBG) sensors to monitor the effects of hygrothermal ageing on the axial strains in a cylindrical epoxy specimen with a centrally located optical glass fibre. A 24 mm long FBG, inscribed on the fibre, is used to monitor the moisture absorption in the epoxy, immersed in distilled water at 50 °C for 2330 h. Hygromechanical simulations support the experimental strain data when the first part of the absorption process is neglected or when a variable coefficient of moisture expansion is used. Also, the effects of using average moisture or when it is distributed according to Fick’s law are negligible. The FBG response also indicates the appearance of progressive debonding after sufficient exposure to moisture.

Thermo-Hygro-Mechanical Design and Reliability Analysis for CMOS Image Sensor

In this paper, the characteristics of polymeric packaging materials for Pre-mold QFN type CMOS Image Sensor (CIS) have been carefully investigated. Hygro-mechanical property, the coefficient of moisture expansion (CME) for different materials was measured through Thermal Mechanical Analysis (TMA) and Thermal Gravitational analysis (TGA) at given humidity and temperature. Moisture absorption/desorption diffusivity were determined under Arrhenius behavior. The transient moisture diffusion analysis described by Fick's equation is performed to evaluate the overall moisture distribution. In accordance with the JEDEC pre-conditioning standard JESD22-A120, reliability and thermal design were carried out due to mismatch of the coefficient of thermal expansion (CTE) and CME for multi-material package of CIS. A three-dimensional solid model of CIS based on finite element ANSYS software is developed to predict the thermal-induced strain, hygroscopic swelling deformation and the residual thermo-hygro-mechanical stress distributions. A series of comprehensive parametric studies were conducted in this research.

Analysis of Time-Dependent Deformation of CFRP Considering the Anisotropy of Moisture Diffusion

The moisture absorption behavior of carbon fiber-reinforced plastic (CFRP) and its effect on dimensional stability were examined. Moisture diffusivity in CFRP was determined by measuring a specimen's weight during the moisture absorption test. Three types of CFRP specimens were prepared: a unidirectionally reinforced laminate, a quasi-isotropic laminate and woven fabric. Each CFRP was processed into two geometries — a thin plate for determination of diffusivity and a rod with a square cross-section for the discussion of two-dimensional diffusion behavior. By solving Fick's law expanded to 3 dimensions, the diffusivities in the three orthogonal directions were obtained and analyzed in terms of the anisotropy of CFRP moisture diffusion. Coefficients of moisture expansion (CMEs) were also obtained from specimen deformation caused by moisture absorption. During moisture absorption, the specimen surfaces showed larger deformation near the edges due to the distribution of moisture contents. This deformation was reasonably predicted by the finite element analysis using experimentally determined diffusivities and CMEs. For unidirectional CFRP, the effect of the fiber alignment on CME was analyzed by micromechanical finite element analysis (FEA) and discussed.

ＣＦＲＰの吸湿濃度を考慮した微視的寸法変化の調査

Moisture absorption behavior of CFRP and its effect on dimensional stability was examined. Moisture diffusivity in CFRP was determined by measuring specimen weight during the moisture absorption test. Three types of CFRP specimens, unidirectionally reinforced, quasi-isotropically laminated and cloth-laminated composites were prepared. Each CFRP was processed into two geometries; a thin plate for determination of diffusion constants and a rod with square cross-section for the discussion of two-dimensional diffusion behavior. Coefficient of moisture expansion (CME) was also obtained from specimen deformation involving moisture absorption. During moisture absorption, the specimen surfaces strongly deformed especially near the edges because of three-dimensional moisture concentration distribution. This deformation was reasonably predicted by the finite element analysis using diffusion constants and CME, which have been experimentally determined. For unidirectional CFRP, an effect of fiber location distribution on CME is discussed by a micromechanical FEA.