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Processes & Skills : Precision lapping and polishing of substrates

Substrates made of technical ceramics – alumina, aluminium nitride, beryllium oxide – quartz or sapphire find their main applications in the manufacturing of microelectronics circuits. Depending upon the standards for material, roughness, thickness or geometry called by the customer, it is necessary to machine the as-fired substrate by a lapping and/or polishing process which allows the substrate to acquire a very high level of finish.

Principle

Lapping is a process utilized to control the thickness, parallelism and flatness of substrates, as well as their surface finish. The process is different depending upon the type of material and the physical dimensions required. Lapping allows to achieve :

  • minimum thickness of 0.076 mm
  • tolerances as tight as 1.2 µm for thickness, 0.33 µm for flatness, 0.25 µm for parallelism
  • roughness ranging from 0.127 µm to 1 µm depending upon the material.

Polishing, combined with lapping, is a processed utilized to assure the surface finish of substrates, as well as guaranteeing a tight tolerance of the thickness and camber.
Typically, polishing allows to achieve :

  • roughness < 0.025 µm with 99,6 % alumina, < 0.05 µm with aluminium nitride, < 0.0025 µm with fused silica
  • thickness tolerance of about 2 µm
  • camber of 0.01 mm / 25 mm

Equipment

Microcertec has the relevant equipment to implement those processes. But in view of the specificity of these machining techniques Microcertec is also relying on the capabilities of specialized companies in this field. 

Benefits

Surface finish by polishing is particularly required for the manufacturing of circuits with thin-film metallizing and photolithography process. Thickness uniformity enables a better control of impedance and a good camber allows the optimal transfer of photo mask – allowing lines and spaces in the 5 µm range. A very smooth surface finish leads to a good definition of patterns and high yields.

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