PurposeThis paper investigates the influence of moisture absorption on the mechanical properties of carbon/epoxy composites.Design/methodology/approachThree types of specimens are prepared, which are for longitudinal, transverse and shear tests. Specimens are immersed in distilled water at 70°C for 1, 3 and 9 months. These correspond to the moisture content of 2.2, 3.8 and 5.3%.FindingsCompared to the values at dry condition, the longitudinal modulus, shear modulus and Poisson's ratio are invariant with the moisture content. However, the transverse modulus, transverse strength and shear strength are sensitive to moisture attack. The maximum degradation is 33%, 76 and 33% for the three properties, respectively. It is also worth to note that the longitudinal tensile strength is stable at 1 and 9 months of immersion. However, at 3-months ageing period, there is only 67% of the longitudinal tensile strength retained.Originality/valueThe experimental results are fitted with a residual property model. Results show comparatively good fit, with a difference within 16% except the longitudinal tensile strength at 9-months immersion. This highlights that the model is not suitable to fit the experimental data with a fluctuated trend.

Rate-dependent deformation and failure process of adhesive joints are investigated in this study. For this purpose, acrylic foam pressure sensitive adhesive (PSA) was employed with aluminum adherents. Tensile and shear loading of the adhesive joint was applied at displacement rates ranging from 5 to 500 mm/min. Results show that the failure process under tensile loadings start with initiation of cavities, hardening through fibrillation process and final fracture of the fibrils. For shear loading the failure process is a combination of fibrillation processes, shear flow, and by interfacial sliding. Both modulus and strain energy density at fracture reach maximum value at a displacement rate of 100 mm/min under tension, while continuously increase with displacement rate under shear loading. Adhesive failure dominates at low loading rate (below 10 mm/min.), while mixed-mode and cohesive failure are common at faster loading rates above 250 mm/min. Finite element employing Yeoh constitutive model adequately predicts viscous shear deformation of the PSA joints.

The lead-free Sn-0.4Ag-0.5Cu (SAC405) solder arrays provides an interconnection between the electronic package and printed circuit board (PCB) of the assembly. The ball grid array (BGA) test assembly was exposed to thermo-mechanical loading during solder reflow cooling and subsequent reliability temperature cycles. This could contribute to the solder/IMC interface damage and cracking. Finite element (FE) analysis was utilized to model the BGA assembly under the prescribed temperature loading profile. The unified constitutive (Anand) model was used to describe the temperature- and strain rate-dependent response, and solder/IMC interface damage of the SAC405 solder interconnects. Solder reflow cooling begins from the assumed stress-free reflow temperature of 220 °C to 25 °C at 1.3 °C/s. This was followed by temperature cycling between 125 and -40 °C with 15 minutes dwell time at upper and lower peak temperature levels. The temperature ramp rate of 11 °C/min was used. Results show that the most critically stressed solder joint was the one located underneath the edge of the silicon die. The solder/IMC interface crack initiated at the interface near the package side of the assembly. Catastrophic fracture of the BGA assembly was predicted during the first temperature cycle due to the relatively low input strength and toughness of the brittle-like solder/IMC interface properties. The solder/IMC failure prediction could not be inferred solely from inelastic strain in the bulk  solder joint but should also consider the damage of the interface. This study shall benefit the newly designed BGA packages through rapid generation of reliability data and by providing insight into the reliability aspects of the BGA assembly with interface fracture issues.

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Solder joint reliability has become an increasingly important factor in electronic industries to obtain sustainable and reliable electronic packages. The simulation study of 3D finite elements on BGA test assembly models with geometries of SMD-NSMD and NSMD-NSMD is conducted through ABAQUS software and is applied with Anand model equation. The applied loading onto the test assembly is set with reflow cooling temperature of 220 °C to 25 °C. The purpose of this research is to obtain the package warpage, stress, and inelastic equivalent strain throughout the package and solder joints and to develop a predictive finite element model for mechanics and deformation of solder joint in BGA package under reflow cooling. The results obtained showed that solder joints with NSMD-NSMD pad geometry has a greater inelastic equivalent strain and has a greater potential in failing than SMD-NSMD pad geometry. Therefore, it can be concluded that SMD-NSMD pad geometry is more preferable for obtaining a more reliable solder joint.