Preparation of Translucent Al2O3 Ceramic Substrates for LED Filament Bulb

As the most possible substitutes for traditional incandescent bulbs, LED filament bulbs are becoming a research hotspot all over the world in recent years. The LED filament bulb has many advantages, including its similar appearance to incandescent bulbs, 360° lighting angle, high brightness, and low energy consumption. However, its price is so expensive that it cannot occupy the lighting market completely. So a big challenge of LED filament bulbs is how to reduce the cost of production. For the actual low-cost application requirements of a LED filament bulbs manufacturer, who is our customer, a translucent Al2O3 ceramic substrate has been prepared by tape casting and sintering process. We optimize the formulation of tape casting and technological process of preparation continually, in order to satisfy the needs of the customer as well as reduce the cost, finally 2# formula (1.2wt.%Ca-3wt.%Si-0.8wt.%Mg sintering additives with 95wt.% α-Al2O3 powder) is selected and used for preparing the ceramic substrate. The substrate can dramatically reduce the cost of LED filament bulbs from two aspects: materials and process. In terms of materials, the ceramic substrate is sintered by low-cost α-Al2O3 green tape at 1600°C in the air furnace, and the performance fully reaches the targets of the customer: the flexure strength is 470MPa, the light transmittance is 22%, and the fluctuation of shrinking percentage is ±0.14%. From the aspect of process, the ceramic substrate is divided into strips efficiently and conveniently, through scribing before sintering with hot knives on the flexible green tape substrate and breaking after sintering with automatic machines on the ceramic substrate. The dimensional precision of ceramic strips is very high, so the customer can employ automatic equipment for fabricating LED filament strips, not only reducing the process cost, but also increasing the production efficiency.