PLANSEE ultra-smooth tungsten crucibles yield more sapphire wafers for LED fab

June 20, 2012 — PLANSEE has developed a pressed-sintered tungsten crucible with an ultra-smooth surface to avoid sapphire ingot or crucible damage in the Kyropoulos method.

When the sapphire crystal is extracted from the crucible, surface adherence can result in cracks or faults in the crystal, as well as damage to the crucible walls. Easier extraction results in higher-quality, higher-yield sapphire ingots for light-emitting diode (LED) wafers. It also enables longer crucible lifetimes.

PLANSEE developed the fully automated crucible manufacturing process with precise control over the material properties of refractory metals. The pressed-sintered tungsten crucible has surface roughness of less than 0.8┬Ám. The smooth surface is less susceptible to corrosion caused by the aggressive melted sapphire, in addition to preventing sapphire cracks and damage.

The tungsten crucible from PLANSEE is high-density, 93%, to retain its shape in high temperatures and rapid temperature changes. PLANSEE tunes the sintering process for the crucibles at very high temperatures and under a uniform temperature distribution to increase density with an extremely homogeneous density distribution.

The crucibles are manufactured in ultra-clean environments and materials supplied in-house to prevent contaminants — iron, titanium, chromium, etc — that can transfer to the sapphire wafers. Purity is in excess of 99.97 %.

Crucibles can be made for 35 to 100kg sapphire ingots, and PLANSEE is process-ready for 200kg sapphire production.

Plansee provides molybdenum, tungsten, tantalum, niobium and chromium products for electronics manufacturing. Learn more at

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