Design And Manufacturing Of Integrated Multi-chip Light-emitting Diodes Packages

With the development of solid state lighting, light-emitting diodes (LEDs) are becominga mature technology at present. The brightness and the luminous density are still the keybarriers, which impedes the penetration of such light sources to general markets. Multi-chipintegrated LED package are now attracting more and more attentions because of their smallvolumes, high luminous flux and uniformity of light-output. In conventional packagingmethod，LED chips are mounted on the flat specular reflective leadframe substrate. In suchpackage configuration, a large amount of light will be totally internally reflected from theencapsulant-air interface, which will propagate up and down before finally absorbed bymaterials. This means the light extraction efficiency is relatively low. Meanwhile, theconventional integrated LED package is usually phosphor-coated by using free-dispensingmethod. As a result, the phosphor coating layer can not be precisely controlled, leading to thepoor light quality. In addition, the integrated LED package belongs to extended sources, eventhree-dimensional sources. It is difficult to obtain uniform illumination on a specific planar byusing the conventional light distribution design methods which is derived for point sources.Finally, as the integration of LED devices increases, the package is facing an unprecedentedthermal management challenge, especially the three-dimensional sources, in which the heatflux has exceeded the heat transfer limits of aluminum and copper.This paper aimes at solving the above key problems during the design and manufacturingof Multi-chip integrated LED packages. LED sources including flat-integrated devices andthree-dimensional-integrated devices are studied. A patterned leadframe substrate (PLS)configuration is developed for light extraction enhancement. The pulse-sprayed conformalphosphor coating is applied to improve the light quality of LED devices. More importantly, anovel light distribution design methods named―energy feedback freeform lens （EFFL）design methods‖has been proposed to realize uniform illumination on a specific planar. Asfor the thermal management problems, phase-change package configurations are developedtheoretically and experimentally in order to decrease the junction temperature of LED chips.The main research contents are as follow:(1) Multi-chip integrated LED package configuration design Based on the introduction of Multi-chip integrated LED package manufacturingprocedure:1) This paper has further studied the shortcomings of the conventional packageconfiguration in terms of light extraction efficiency, and developed a PLS configuration toimprove the light-out of LED devices. The light propagation dynamic of PLS method hasbeen discussed, and the optimal patterning structure parameters has been derivedmathematically. Monte Carlo ray tracing simulations confirm our design before the PLSintegrated LED package configuratin was fabricated by micro-drilling. Experiments provedthat the PLS methods has greatly improved the light extraction efficiency of LEDs.2) Thispaper has detailedly investigated the white-light LED technology for integrated packagedevices by using pause sprayed conformal phosphor coatings.3) Finally, a novelthree-dimensional-integrated packaging configuration has been developed and discussed. Thelight-out properties of such kind of devices were measured experimentally.(2) Light distribution design for multi-chip integrated LED packageAfter the requirements of illumination systems and the common light distribution designmethods was presented:1) An freeform lens illumination model for point sources wasestablished first, and the algorithm for solving the profile of the lens was derived andcalculated. By comparing the illumination qualities between point sources and extend lightsources, the original algorithm was improved and evolved to EFFL algorithm.2) A specificlight distribution requirement for general lightings was set as an example to present the detailsof EFFL algorithm. And the multi-chip integrated LED package with an optimal freeform lenswas fabricated and tested.3) The EFFL algorithm was then extended to the light distributiondesign problems for three-dimensional-integrated LEDs, and a freeform reflector wasdeveloped to realize a uniform illumination.(3) Phase-change thermal management for Multi-chip integrated LED packagesAccording to the analysis of heat conduction bottleneck in the integrated LED packages:1) This paper has developed the thermal conduction network models of phase-changeleadframes (heat slugs) for plane-integrated devices and three-dimensional-integrated devices,studied the influence of several key parameters on the chip operation temperature, andobtained the optimal structures.2) Thermal simulations have been implemented for LEDpackage phase-change thermal management in system level and package level, and the heat transfer barriers were discussed.3) At last, phase-change leadframes were fabricated andmeasured.(4) Applications of multi-chip integrated LED package in lighting systemsThis paper finally studied the applications of multi-chip integrated LED package in highpower lighting systems, including:1) Applications of multi-chip integrated LED package inhigh bay lighting systems;2) Applications of multi-chip integrated LED package inautomobile headlight systems.