Emerging trend for LED wafer level packaging

Currently most light emitting diode （LED） components are made with individual chip packaging technology. The main manufacturing processes follow conventional chip-based IC packaging. In the past several years, there has been an uprising trend in the IC industry to migrate from chip-based packaging to wafer level packaging （WLP）. Therefore, there is a need for LEDs to catch up. This paper introduces advanced LED WLP technologies. The contents cover key enabling processes such as preparation of silicon sub-mount wafer, implementation of interconnection, deposition of phosphor, wafer level encapsulation, and their integration. The emphasis is placed on how to achieve high throughput, low cost manufacturing through WLE

Spacing optimization of high power LED arrays for solid state lighting

This paper provides an analytical approach to determine the optimum pitch by utilizing a thermal resistance network, under the assumption of constant luminous efficiency. This work allows an LED array design which is mounted on a printed circuit board （PCB） attached with a heat sink subject to the natural convection cooling. Being validated by finite element （FE） models, the current approach can be shown as an effective method for the determination of optimal component spacing in an LED array assembly for SSL.

Phosphor-free microLEDs with ultrafast and broadband features for visible light communications

Modulation bandwidth and the emission region are essential features for the widespread use of visible light communications(VLC).This paper addresses the contradictory requirements to achieve broadband and proposes ultrafast,asymmetric pyramids grown on adjacent deep concave holes via lateral overgrowth.Multicolor emission with an emission region between 420 nm and 600 nm is obtained by controlling the growth rate at different positions on the same face,which also can provide multiple subcarrier frequency points for the employment of wavelength division multiplexing technology.The spontaneous emission rate distinction is narrowed by lowering the number of the crystal plane,ensuring a high modulation bandwidth over broadband.More importantly,the residual stress and dislocation density were minimized by employing a patterned substrate,and lateral overgrowth resulted in a further enhancement of the recombination rate.Finally,the total modulation bandwidth of multiple subcarriers of the asymmetric pyramids is beyond GHz.These ultrafast,multicolor microLEDs are viable for application in VLC systems and may also enable applications for intelligent lighting and display.

Mechanical system and dynamic control in photolithography for nanoscale fabrication: A critical review

As one of the most advanced and precise equipment in the world,a photo-lithography scanner is able to fabricate nanometer‐scale devices on a chip.To realize such a small dimension,the optical system is the fundamental,but the me-chanical system often becomes the bottleneck.In the photolithography,the ex-posure is a dynamic process.The accuracy and precision of the movement are determined by the mechanical system,which is even more difficult to control compared with the optical system.In the mechanical system,there are four crucial components:the reticle and wafer stages,the linear motor,the metrology system,and the control system.They work together to secure the reticle and substrate locating at the correct position,which determines the overlay and alignment per-formance in the lithography.In this paper,the principles of these components are reviewed,and the development history of the mechanical system is introduced.