Hygrothermal Effect on MWCNT-Filled Epoxy Electrically Conductive Adhesives

To-date, limited studies are found in the literature on the reliability performance of electrically conductive adhesive (ECA) using multiwalled carbon nanotube (MWCNT) fillers. Hence, this study aims to provide an understanding on the performance of the ECA with the objectives (i) to study the electrical conductivity and (ii) joint strength of ECA with varying conductive filler’s aspect ratio and environmental conditions. Here, epoxy with MWCNT aspect ratio of 55.5 and 1666.5 were subjected to 85°C and 85% RH for up to 96 hours. The test specimens were prepared in accordance with ASTM F390-11 using a four-point probe for electrical conductivity measurement while the lap shear test was conducted with reference to ASTM D1002-10 using a universal testing machine. For the thermal aging study, the ECA samples were conditioned in a humidity chamber at 85 °C and 85 % of relative humidity to assess the reliability performance of the ECA. Overall, it was found that ECA filled with higher aspect ratio of MWCNT exhibit better electrical and mechanical stability when subjected to hygrothermal aging. Moreover, the presence of moisture attack has yield in an increase in the electrical conductivity of the ECA with thermal aging period. Meanwhile, lap shear test results revealed a contradicting trend. Regardless of the amount of MWCNT filler loading, voids are created in the epoxy matrix of the ECA, which results in a decrease in the shear strength of the ECA, when the samples were subjected to thermal aging

Buckling Of Imperfect Cylinder-Cone-Cylinder Transition Under Axial Compression

This paper presents the numerical investigation results focusing on the buckling behavior of geometrically imperfect cylinder-cone-cylinder transition subjected to axial compression. The models are assumed to be made from unalloyed mild steel. Several initial geometric imperfections techniques such as (i) Eigenmode imperfection approach, (ii) Axisymmetric outward bulge and (iii) Single Perturbation Load Analysis (SPLA) imperfections were superimposed on the perfect cylinder-cone-cylinder shell. Reduction of the buckling strength was then quantified numerically. As expected, the buckling strength of cylinder-cone-cylinder shells was strongly affected by initial geometric imperfection and the reduction in buckling strength was seen to be strongly dependent on the approach and the location of imperfection. Eigenmode imperfection is seen to produce the lowest knockdown factor, followed by axisymmetric outward bulge and SPLA imperfections, respectively. Finally, the lower bound knockdown factors that can be implemented for design purposes has been proposed for the worst initial geometric imperfection case, i.e., Eigenmode, imperfections

The Evolutions Of Microstructure In Pressureless Sintered Silver Die Attach Material

Sintered silver (Ag) is one of the most promising interconnect materials for high temperature electronics applications due to its potential to withstand harsh and extreme environments. This paper investigates the microstructure evolutions of Ag particles under pressureless sintering in a polymeric adhesive binder at 200 °C, 250 °C, 275 °C, and 300 °C for a duration of 2 hours. The grains, particles, and neck growth observed via two-dimensional Focused Ion Beam (FIB) cuts on the samples at different sintering temperatures were associated with the atomic motions and reduction of surface energy that is the driving force for sintering. In this study, the pressureless sintering process in a polymeric adhesive binder successfully transformed the scattered Ag particles into a compact and dense Ag joining at 300 °C. The electrical conductivity value obtained at 300 °C was 5.2E+05 S/cm, which was the highest among the evaluation samples

Perforation Behaviour Of Composites Sandwich Structures On Low-Velocity Impact At Oblique Angles

This paper presents the perforation behaviour of polyethylene terephthalate (PET) foam cored sandwich structures when subjected to quasi-static and dynamic loading at normal (0°) and oblique angles of 10° and 20°. An instrumented drop-weight hammer rig was used with fully-clamped conditions for the low-velocity impact test with impact energy of 40 J and velocity of 3.78 m/s. Meanwhile, the quasi-static indentation test was carried out using a universal testing machine via an Instron 4505, at crosshead displacement rate of 1 mm/min, with boundary conditions similar to those of the dynamic test. Results obtained showed that the normal impact generated the highest peak force for both the first and second peaks, which are associated with the damage to the top and bottom skins of the sandwich structures. Moreover, regardless of whether the test was done on the normal or inclined angles, it was observed that the dynamic loading produced higher force magnitude in comparison to those of the quasi-static response, due to the enhanced strength and stiffness of the components because of the strain rate and inertia effects. However, in terms of the damage profiles, it is evident that the maximum damage area increased with the increase inclination angle as supported by simple geometric analysis. For the oblique impact cases, the damage was due to the combined effect of tensile, compression, and shear for impact at 10°. The damage occurred as a result of pure shearing for the 20° impact case. In conclusion, the perforation behaviour at inclined angles allowed more area to be perforated in comparison to those of the normal cases

Diffusion Mechanism Of Silver Particles In Polymer Binder For Die Attach Interconnect Technology

Sintered Ag has gained strong interest as an important alternative material for interconnect technology in wide bandgap (WBG) semiconductor industries specifically for high thermal dissipations and high-speed applications. This material typically consists of metallic particles bounded by polymer binder expected to diffuse at the temperature much lower than its melting temperature. This paper studies the diffusion mechanism between Ag particles and its microstructural change over different heat treatment temperature that leads to the understanding on the formation of bonding particles into a predominantly solid Ag network as a conducting path for the interconnect systems. The surface diffusion initiated between Ag particles as they come into intimate contact through the formation of necking. Further atomic movement and diffusion between the particles neck resulting in volume expansion, necking growth as well as the transformation of the particle shape from spherical into an elongated structure. This results in the formation of a long chain of connecting particles, which transform the Ag particles into a solid Ag network

Effect of water absorption on the mechanical properties of cross-ply hybrid pseudo- stem banana/glass fibre reinforced polypropylene composite

The initiative to reduce the consumption of non-renewable resources increases the awareness of being green in composites. The synthetic fibres are currently substituted by natural fibres applicable in various industries such as automotive and building. In this study, the effects of water absorption on the tensile and flexural properties of cross-ply hybrid pseudo-stem banana/glass fibre reinforced polypropylene composites are investigated. The hybrid banana (B)/glass(G) polypropylene composites and the reference specimens of the non-hybrid composites of the plain banana and glass fibres termed the BBB and GGG specimens were fabricated using hot compression moulding method. Water absorption test was conducted according to ASTM D570 until the specimens reached saturation. Tensile (ASTM D3039) and flexural (ASTM D790)test were carried out on the dry specimens as well as the wetted specimens. It can be observed that non-hybrid GGG has the best water absorption properties and hybrid specimen with glass as outermost skin shows a comparable result. However, water absorption reduced the mechanical properties of the composites. The incorporation of glass fibre in the composites improved overall properties of the composites. The hybrid GBG dry specimen tensile strength and wet specimen flexural strength is 136.28 and 73.86 MPa respectively. The hybrid composite GBG shows comparable flexural properties to GGG composit

Low Velocity Impact Behaviour Of Pineapple Leaf Fibre Reinforced Polylactic Acid Biocomposites

In this study, impact performance of biocomposites fabricated from pineapple leaf fiber reinforced polylactic acid subjected to low-velocity impact loading is presented. The biocomposites were fabricated using compression moulding technique, in which two grades of the polylactic acid matrix materials were considered. Following these, the biocomposites were subjected to dropweight impact testing as per ASTM 3767. In general, it was found that the maximum impact force and total energy absorbed increased linearly with an increase in the impact velocity. Moreover, at velocity of 3 m/s, the PLA 6100D based biocomposites exhibit slightly higher energy absorbed in comparison to those of the PLA 3251D biocomposites, with a value of 16.25 J and 15.74 J, respectively. In addition, more severe damages are observed for the 3251D PLA based biocomposites due to brittle nature of the material, leading to weaker impact properties in comparison to those of the PLA 6100D based biocomposites, as evident in the images of the front and back impact surface

Fatigue characteristic and Weibull analysis of sustainable rubberwood flour/recycled polypropylene composites

Although there is a perpetual interest in natural fibre composite, the fatigue data and their durability behaviour is still lacking, thus limiting their potential use in high-end applications. In this study, wood polymer composite made from rubberwood flour and recycled polypropylene was subjected to a tension-tension fatigue test in order to investigate their fatigue characteristic. Hysteresis loop was captured in order to establish their stress to number of failure (S-N) curve. The fatigue strength of the composite strongly depends on the stress amplitude. At the lowest stress level, the fatigue life of the composite exceeds the 1.5 million cycles limit, suggesting that the endurance limit for composite materials to be 11.06 MPa. The residual modulus and energy dissipated are plotted as a function of number of fatigue cycles. As the cycles progress, the residual modulus fall and dissipated energy increase indicated the cyclic damage in the composite structure. Two parameters Weibull probability were used to statically analyse the fatigue life and reliability of the rubberwood/recycled polypropylene composite. The S-N curve was plotted at different reliability index (RI = 0.1, 0.368, 0.5, 0.9, 0.99) using Weibull data. This data is used to identify the first failure time and design limits of the materials

The Effect Of Aspect Ratio On Multi-Walled Carbon Nanotubes Filled Epoxy Composite As Electrically Conductive Adhesive

Multi-walled carbon nanotubes (MWCNTs) filled epoxy resin is a type of Electrically Conductive Adhesive (ECA) that is used as interconnect materials in electronics application. Carbon-based conductive adhesive usually has inferior electrical conductivity to silver but mechanically superior in terms of its bonding integrity. The aim of this paper is to study the effect of aspect ratio on the electrical and mechanical properties of the composite adhesive. The aspect ratio of the two types of MWCNT fillers are of 55.5 and 1666.5. The filler loading for both MWCNTs varies from 5wt.% to 12.7wt.%. From the experimental study, the sheet resistance for the ECA with higher aspect ratio is approximately 4.42kΩ/□ in comparison to only 44.86kΩ/□ for the ECA with lower MWCNT aspect ratio. Morphological analysis of the ECA showed evidence of MWCNT distribution in the ECA with different diameter size. Nonetheless, the MWCNTs filled epoxy with lower aspect ratio exhibit higher shear strength with a maximum value of 8.08MPa, in comparison to only 4.68MPa to that of the ECA with higher MWCNTs aspect ratio, possibly due to the tendency in forming agglomeration of the MWCNT with smaller tube diameter, resulting in weaker interfacial strengt