Optodic bonding of optoelectronic components in transparent polymer substrates-based flexible circuit systems

Abstract

In the field of modern information technology, optoelectronics are being widely used, and play an increasingly important role. Meanwhile, the demand for more flexible circuit carriers is rapidly growing, since flexibility facilitates the realization of diverse functions and applications. As a potential candidate, transparent polymer substrates with a thickness of about a hundred micrometers by virtue of their low cost and sufficient flexibility are getting more attention. Thus, accomplishing an integration of optoelectronic components into polymer based flexible circuit systems increasingly is becoming an attractive research topic, which is of great significance for future information transmission and processing. We are committed to developing a new microchip bonding process to realize it. Taking into account the fact that most economical transparent polymer substrates can only be processed with restricted thermal loading, we designed a so-called optode instead of a widely adopted thermode. We employ UV-curing adhesives as bonding materials; accordingly, the optode is equipped with a UV irradiation source. An investigation of commercial optoelectronic components is conducted, in which their dimensions and structures are studied. While selecting appropriate transparent polymer substrates, we take their characteristics such as UV transmission degree, glass transition temperature, etc. as key criterions, and choose polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) as carrier materials. Besides bonding achieved through the use of adhesives cured by the optode, underfill is accordingly employed to enhance the reliability of the integration. We deposit electrical interconnects onto the polymeric substrate to be able to bring the optoelectronic components into electrical operation. In order to enlarge the optical coupling zone from component to substrate within the proximity of the adhesive or underfill, we employ transparent interconnects made of indium-tin-oxide. We present the results of the performance tests, including the contact resistances, mechanical tests and environmental tests.

Fine-pitch chip-on-flex packaging of optoelectronic devices using low temperature optodic bonding

“…In contrast to the thermode using thermal energy, ultraviolet light is utilized as the driving energy in the optode to activate the bonding materials and further completing the bonding process. As introduced, two types of optodes, the sideway optode and the optode from the bottom, were designed and implemented by utilizing the transparency of the polymer foils [11,12]. In consideration of the required integration compactness of the optode into a die bonding assembly system, we prefer the optode from the bottom since no extra unit for fixing or adjusting the UV source is necessary in this variation and the UV source is already integrated in the designed unterplate of the optode [12].…”

“…However, this low temperature is still not low enough for processing those aforementioned cost-effective transparent polymer foils because of their fairly low glass transition temperature, abbreviated as Tg. Therefore, in order to eliminate the thermal loading, we proposed to adopt ultraviolet (UV) curable adhesives as bonding materials to conform to this requirement and accordingly developed a novel bonding process, the so-called optodic bonding, which was firstly introduced in [10] and has been further developed in terms of the types of optode [11,12]. Based on the previous work, we use the optode from the bottom in this work and make essential improvements on the layout design of the nontransparent electrical interconnects to achieve a higher bonding efficiency.…”

Optical coupling of bare optoelectronic components and flexographically printed polymer waveguides in planar optronic systems

“…However, we have to consider its low glass transition temperature (Tg) of 105 °C, which poses a big challenge of controlling the thermal loading while being processed. In order to comply with this, we developed a low temperature bonding technology, the so-called optodic bonding [4] [5]. The key solution here is the utilization of the UV-irradiation as driving energy instead of the thermal effect to complete the bonding process.…”