Some of the many benefits of polished substrates are the thickness uniformity and extremely smooth surface consistency from piece to piece. Thickness control of the substrate is important because many circuit line widths are designed for optimal impedance and impedance is also dependent on the control of substrate thickness. Controlling the camber of the substrate to less than .0005'' allows the optimal transfer of photo mask features allowing lines and spaces in the .0002” range. For tighter tolerances call Accumet Engineering. The surface finish as well as consistency from piece to piece allows better yields and increased performance in higher frequency applications as well as Infrared/Visible/UV light applications.
The polishing process is employed when a secondary step after lapping is needed to provide an even greater level of surface smoothness and evenness. The surface finish tolerance limit with polishing is dependent upon the structure of the material used. This is why certain materials lend themselves to different applications, dependent on surface roughness of the raw, or as-fired material. For example, low-density 96% alumina can be lapped to 20 micro-inches and polished to less than 5 micro-inches, nominally. High-density 99.6% alumina can be lapped to 10 micro-inches and polished to less than 1 micro-inch, nominally.
When necessary, thickness tolerances with polished substrates can be brought down to ± .0005'' or even lower for demanding applications. Material defects, such as pits, can typically be lessened to a minimum diameter of 0.0125'' for 99.6% alumina and even lower for other materials. Accumet's micro-fine polishing process can further reduce a pit diameter down to 0.0'' for 99.6% alumina, and further for other material. Thickness tolerances as tight as .00005'' and surface finishes ranging from one tenth of a micro inch (.0000001”) to 5 micro-inches (.000005'') can be achieved, even at production rate volumes.
|Material||Surface Finish (u-inches)||Thickness Tolerance (Typ)||Applications|
|Polished 99.6% Alumina||Less than 1u-in||±0.0005"||Used for low to medium power RF & Microwave circuits|
|Polished 99.5% Beryllium Oxide||Less than 4u-in||±0.0005"||Used for high-power DC/RF/Microwave circuits|
|Polished Aluminum Nitride||Less than 2u-in||±0.0005"||Used for high-power DC/RF/Microwave circuits|
|Polished Fused Silica||Less than 1u-in (60/40 optical)||±0.0005"||Used for high frequency circuits requiring extremely low loss of performance|
|Polished Sapphire||Less than 1u-in (60/40 optical)||±0.0005"|
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