Mechanical lock design for LED silicone lens with silicon substrate

In this paper, a mechanical lock is first proposed and designed for LED silicone lens mounting. Since LED has many new applications in areas such as automobile headlight, micro-projector and local network optical communication, a potential serious issue must be solved. Due to the poor adhension between silicone and mostly materials including silicon, silicone lens may drop off from the silicon substrate during the usage, especially when LED is used in those harsh environments with thermal shock, mechanical shock, such as in automobile headlight application which is also needed in accelerated testing. The mechanical locks are holes fabricated on the silicon substrate by wet etching. These through holes have smaller cross sectional area on the front side and bigger cross sectional area on the back side. In the silicone lens fabrication process, silicone has been injected into those holes. Then the substrate will be placed into a vacuum chamber, therefore, the air bubbles can be removed from the silicone. Next, substrate will be placed on a hotplate for silicone curing. Then the lock is realized. This mechanical lock structure increases the contact area between substrate and silicone lens. And the silicone at the bigger end of the through holes becomes the anchor point of the lens. The lock manufacture process is compatible with the existing manufacture process of the silicon substrate. No additional step has been added to the existing manufacture process of the silicon substrate. Therefore, the cost of the package virtually will not rise. And the performance of the mechanical lock has been investigated by pull test and shear test of silicone lens simplified test vehicles. Results of comparison experiments show that the adhension strength between silicone lens and silicon substrate has been greatly enhanced. Furthermore, the size of mechanical lock also influences the adhension strength. The mechanical lock can work better when its size is larger.