Simulative Investigations of the Mechanical Reliability of the Flexible Optoelectronic Packaging Using Optodic Bonding
With the constant innovation and development of the advanced materials and technologies in the field of optoelectronics, a variety of applications adopting the benefits of optoelectronics is increasingly penetrating into our daily routines. The way of packaging has a huge impact on the performance of optoelectronics in mechanical, electrical as well as optical properties. Particularly, flexible packaging is becoming a trend thanks to its compatibility to any irregular surfaces in diverse applications. By employing transparent polymer foils, such as polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET), as carrier substrates for optoelectronic packaging, a greater mechanical flexibility can be achieved. Their transparency expands the range of application, for instance in optical sensing areas. In addition, they are mostly cost-effective, which enables an economical roll-to-roll manufacturing process. However, the challenge of using them is their low glass transition temperatures. In previous works, a novel optodic bonding process employing UV curable adhesives for processing these thermally sensitive polymer foils was introduced and verified as a promising technology for flexible optoelectronic packaging. In this work, we conduct further investigations of its mechanical reliability with the focus on the aspect of flexibility. FEM-based simulations for emulating various mechanical loadings including shear, bending and tensile stresses are implemented. We perform analyses of the influencing factors, particularly their degree of efficiency on the mechanical stability, e.g. the material properties of the optoelectronic components, the employed polymers as well as the bonding adhesives. These comprehensive investigations establish a constructive guideline for choosing materials for flexible optoelectronic packaging. In addition to this, we attain a convincing statement for the reliable feasibility of the optodic bonded packages with respect to a sufficient mechanical flexibility and stability.
Development of chip-on-flex using SBB flip-chip technology
Abstract A bare LSI chip mounted onto a flexible substrate is called chip-on-flex (COF). Companies and universities are desperately developing COF. In this paper, the development of COF using stud bump bonding (SBB) flip-chip technology will be introduced. So far, SBB technology has been adopted when ceramic or glass-epoxy is used as a substrate material for chip size packages (CSPs) and multi-chip modules (MCMs). Recently there is a great demand for developing SBB technology toward a flexible substrate. SBB technology needs to keep a flexible substrate flat during the assembly process. A flexible substrate was adhered to a flat carrier using a thermal release sheet in order to keep it flat. Since this thermal release sheet loses its adhesive strength by applying heat beyond 160°C, it is easy to peel off accomplished specimens from the flat carrier after assembling. SBB specimens were prepared using liquid crystal polymer (LCP) and polyimide (PI) as a flexible substrate. Reliability tests, such as pressure cooker test (PCT), thermal shock test (TST) and reflow soldering after moisture storage test, were carried out for these specimens. In PCT, both LCP and PI specimens passed as a result of using proper underfill for each substrate. In TST, both specimens also passed using the underfill selected in PCT. In reflow soldering after moisture storage test, LCP specimens passed, on the other hand PI specimens needed to be baked after moisture storage in order to pass the reflow.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.