Cure-induced Shrinkage Research Articles

A Precise Prediction of the Chemical and Thermal Shrinkage during Curing of an Epoxy Resin.

A precise prediction of the cure-induced shrinkage of an epoxy resin is performed using a finite element simulation procedure for the material behaviour. A series of experiments investigating the cure shrinkage of the resin system has shown a variation in the measured cure-induced strains. The observed variation results from the thermal history during the pre-cure. A proposed complex thermal expansion model and a conventional chemical shrinkage model are utilised to predict the cure shrinkage observed with finite element simulations. The thermal expansion model is fitted to measured data and considers material effects such as the glass transition temperature and the evolution of the expansion with the degree of cure. The simulations accurately capture the exothermal heat release from the resin and the cure-induced strains across various temperature profiles. The simulations follow the experimentally observed behaviour. The simulation predictions achieve good accuracy with 2-6% discrepancy compared with the experimentally measured shrinkage over a wide range of cure profiles. Demonstrating that the proposed complex thermal expansion model affects the potential to minimise the shrinkage of the studied epoxy resin. A recommendation of material parameters necessary to accurately determine cure shrinkage is listed. These parameters are required to predict cure shrinkage, allow for possible minimisation, and optimise cure profiles for the investigated resin system. Furthermore, in a study where the resin movement is restrained and therefore able to build up residual stresses, these parameters can describe the cure contribution of the residual stresses in a component.

Universal Cure-Induced Shrinkage Model Applied to an Epoxy Amine as a Method to Optimize Composite Processing Time, Shrinkage, and Residual Stress

Universal Cure-Induced Shrinkage Model Applied to an Epoxy Amine as a Method to Optimize Composite Processing Time, Shrinkage, and Residual Stress

In situ characterization of direction-dependent cure-induced shrinkage in thermoset composite laminates with fiber-optic sensors embedded in through-thickness and in-plane directions

This study develops a fiber-optic-based technique for in situ characterization of direction-dependent cure-induced shrinkage in thermoset fiber-reinforced composites. A procedure is established to embed fiber Bragg grating (FBG) sensors in composite out-of-plane directions and to measure key through-thickness chemical cure shrinkage directly under practical curing conditions. First, sensitivity of the proposed method is evaluated through comparison with a standard technique (i.e. thermo-mechanical analysis (TMA)), and the effect of sensor tail length on measurement sensitivity is discussed considering shear-lag effect. Next, combined with double-sided vacuum bagging and demolding during curing, FBG sensors embedded in through-thickness and in-plane directions clarify direction-dependent cure-induced shrinkage in autoclaved unidirectional carbon/epoxy. Finally, the feasibility of characterizing through-thickness shear strain, which is important in complex-shaped parts but cannot be measured using conventional techniques, is confirmed. The developed technique will be a powerful tool for evaluating cure shrinkage in complex-shaped parts and for validating process-simulation tools based on internal strain.

Warpage Prediction and Experiments of Fan-Out Waferlevel Package During Encapsulation Process

A wafer level package (WLP) that has a flip chip form and uses thin-film redistribution with solder bumps to connect the package to the printed wiring board directly is discussed in this paper. A liquid molding compound is used for the encapsulation process. Since the thickness of the fan-out WLP is smaller than that in a traditional integrated circuit (IC) package, the fan-out WLP induces more serious warpage. Warpage plays an important role during the IC encapsulation process, and too large a warpage would not let the package proceed to the next manufacturing process. This paper uses an approach that considers both cure- and thermal-induced shrinkages during the encapsulation process to predict the amount of warpage. Cure-induced shrinkage is described by the pressure-volume-temperature-cure (PVTC) equation of the liquid compound. The thermally induced shrinkage is described by the coefficients of thermal expansion of the component materials. The liquid compound properties are obtained by various techniques, such as cure kinetics by differential scanning calorimetry- and cure-induced shrinkage by a PVTC testing machine. These experimental data are used to formulate the PVTC equation. A fan-out WLP is first simulated, and the simulation results are verified with experiments. It is shown that an approach that considers both thermal and cure/compressibility effects can better predict the amount of warpage for the fan-out WLP. The PVTC equation is successfully implemented, and it is verified that warpage is governed by both thermal and cure shrinkages. The amount of warpage after molding could be accurately predicted with this methodology. Simulation results show that cure shrinkage of the liquid compound is the dominant factor responsible for package warpage after encapsulation.

Simulations of Process-Induced Warpage During IC Encapsulation Process

Warpage during integrated circuit encapsulation process is a serious problem. Previous researchers had focused on warpage analysis with thermal-induced shrinkage and the cure-induced shrinkage was neglected. A new approach considering both cure- and thermal-induced shrinkage during encapsulation process was presented to predict the amount of warpage. The cure-induced shrinkage was described by the pressure-volume-temperature-cure (P-V-T-C) equation of epoxy. The thermal-induced shrinkage was described by the coefficients of thermal expansion of the component materials. The thin small outline package (TSOP) DBS-27P and low-profile quad flat package (LQFP) LQFP-64, which were manufactured by Philips Semiconductor located in Taiwan and Siliconware Precision Industries Corporation, respectively, were chosen to be the simulation models. By comparing the amount of predicted warpage with the experimental results, it showed that the approach could better predict the amount of warpage than that considering only thermal-induced shrinkage. It was also found that the sign of cure-induced warpage could be opposite to the thermal-induced warpage. Appropriate design of a package to make cure- and thermal-induced shrinkage to be of opposite sign could minimize the warpage of a package.