Wafer Level Packaging With Nano Metal Paste Interconnects For UV-C LEDs

Wafer Level Packaging With Nano Metal Paste Interconnects For UV-C LEDs

Harsha Achanta, S.

Zhang, K. (mentor)
Kolahdouz Esfahani, Z. (mentor)

Electrical Engineering, Mathematics and Computer Science

Electronic Components, Technology and Materials

2016-12-14

: Light emitting diodes (LEDs) have made remarkable progress since their invention and today they can be found in a wide range of applications such as TV remotes, automotive headlamps, general lighting, traffic signals, camera flashes, display and screens. LEDs that emit light in the ultraviolet-C (UV-C) range are used in applications such as air/water purification and sterilization. Cost per chip of these LEDs is relatively higher than the blue LEDs due to the expensive manufacturing process and low demand. But, the market for these LEDs in applications such as water purification is expected to grow in the coming years into a multimillion dollar market resulting in high volume manufacturing and low cost of chips. Consequently there will be a need for high volume and cost effective packaging solution with excellent thermal and optical performance. Existing packaging technologies like ceramic and lead frame packaging are expensive, less productive, and offer limited processing options. Meanwhile, wafer level packaging is a highly productive and cost-effective solution. Today, Silicon is the most common substrate of the integrated circuits. Moreover, its close coefficient of thermal expansion (CTE) with the LED base materials such as GaN and AlGaN, and the high thermal conductivity make it a good choice as a substrate of UV-C wafer level package. In this study we developed a silicon wafer level packaging approach combining advanced processes such as through silicon via (TSV) technology and chip to wafer (C2W) bonding for flip chip UV-C LEDs. We have integrated Si reflector cups for redirecting light from the sidewalls of UV-C LEDs using suitable material such as Aluminum. Complexities of a monolithic flow and the advantages of a dual wafer flow will be discussed. A new method to establish the interconnection in TSVs with metal nano pastes (MNPs) is introduced. The current vs voltage characteristics, optical performances, merits of reflectors, and improvements in spectral distributions of each package are measured and characterized. Different ways of bonding the chips to the submount and the thermal resistances of each package are studied. In conclusion we demonstrate the fabrication of a wafer level package for UV-C LEDs with a new cost effective TSV interconnection method using MNPs. We also show that sidewall emission of the LEDs is redirected with almost no loss in light which will be suitable for applications like water purification and protein analysis where the target doesn’t encapsulate the LED.

wafer level packaging
UV-C light
LED
Nano metal paste
Through silicon vias
3D wafer lithography
3D wafer processing

http://resolver.tudelft.nl/uuid:133e2ab3-185f-43fe-a2e7-e54a823d91e8

2018-12-14

Student theses

master thesis

(c) 2016 Harsha Achanta, S.