Reworkable anisotropic conductive adhesives (ACAs) are of interest when the material is used for assembling electronic modules with high value, such as in medical devices. Adhesive matrices comprising a blend of a thermosetting epoxy and a thermoplastic polymer are selected because it has shown potential to ensure good electrical and mechanical integrity whilst still allowing reworkability for ACA assemblies. Our previous work demonstrated the feasibility of using blends of an epoxy and a thermoplastic polysulfone as an adhesive matrix for the reworkable ACAs. The rework temperature, however, is relatively high (190°C) which causes disadvantages for the rework process and safety of sensitive electronic components nearby. ACA material with lower rework temperature is thus of interest. This paper presents the findings of favorable mixing ratio between an epoxy compatible with ACA applications and a thermoplastic polymer that offers good mechanical strength combined with reworkability at a temperature as low as 100°C. The results show that the adhesive blends with a high concentration of thermoplastic polymer (35–65 wt%) exhibit satisfactory die shear strength at temperatures relevant for production/storage (23°C) and operation of medical devices (50°C). Furthermore, successful rework at temperature as low as 100°C is confirmed for such adhesive blends.
Thermal performance of an epoxy resin reinforced by carbon fibers is studied by numerical simulation method. Various carbon fiber structures are taken into consideration and the effective thermal conductivity of the composite carbon fiber waved structure is obtained. The influences of the number, size, shape, spacing and arrangement of the carbon fibers on the thermal conduction of the composites are analyzed. The deformation of the composite under mechanical loading and the corresponding the thermal conductivity of the carbon fiber-reinforced epoxy resin are also investigated.
Corrosion occurs on metallic materials in the presence of moisture and reactive gases, such as H2 S, SO2 or NO2 and is enhanced by different substances like e.g. chlorides. Particularly electronic materials and components are affected, because they are exposed to increasingly harsh environmental conditions, resulting in damage to corrosive media (e.g. off-shore systems, electronic components in engine compartment of automobiles). Especially for the materials and contacts of micro-and power electronic components, corrosion induced processes are significant reliability limiting. Additionally, depending on process parameters, corrosion can also be induced during manufacturing (e.g. nickel corrosion in pad metallization). We developed an innovative method, based on electrochemical measurements by a local measuring cell that allows corrosion sensitivity analyses of typical metallization systems for substrates and electrical contacts in a very short time. In this paper, we present and discuss the results for electrochemical corrosion testing by the new method in correlation to standard reliability tests, like mixed flow gas testing (MFG) and neutral salt spray testing as well as standardized electrochemical testing for metallization systems pf printed circuit boards. High resolution microstructural analyses after standard testing as well as after miniaturized cyclovoltammetric testing are giving evidence for the running corrosion mechanism. The investigations carried out in this study show the application potential of the new local electrochemical test method and the usability for quality inspection of PCBs.
In recent years, laser-reduced graphene oxide (LRGO) has received widespread interest, however, the thermal properties of graphene films obtained by laser reduction of GO are rarely reported. In this paper, a pulsed laser was used to reduce the prepared GO films. The obtained LRGO films were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS). The thermal diffusivity of the LRGO was measured as 7.3 mm 2 /s, higher than that of GO measured as 5.9 mm 2 /s. The heating performance of LRGO was performed under different DC voltages and the results show that the temperature can reach up to 91 °C with a response time of 14 s under the voltage of 18 V. The excellent electrothermal performance of LRGO films indicate that the LRGO films are promising as heating elements for various application such as defoggers.
In this work, laser-induced graphene (LIG)/ polyimide (PI) films with good thermal properties were prepared by directly inducing graphene on the bare PI substrates by a computer numerical control (CNC) laser engraving machine. The obtained samples were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results showed that the laser energy density has a significant impact on the microstructures of the samples. Moreover, the thermal diffusivity of LIG/PI was increased from 0.5 mm2/s to 1.6 mm2/s, which is 3 times higher than bare PI. Finally, the electrothermal properties of the LIG films were investigated and the results showed that under a 12 V power supply, the equilibrium temperature of LIG films increases from 45°C to 74°C with the increase of laser energy density from 1.8 J/mm2 to 2.4 J/mm2. Our results indicate that this time-saving, low-cost, and environment-friendly method is promising for fabricating excellent graphene-based materials.
