Why Polish Substrates?

While many customers will be satisfied with an as-fired surface for their applications, others may require a smoother, more parallel surface finish. The reasons for this are varied, but generally fall under the following requirements:

Finer Line Geometries

An as-fired surface finish is generally adequate for lines as thin as 1 mil in thin-film applications and 5 mils in thick film applications. Forming finer lines than these on as-fired surfaces will exhibit poor pattern definition resulting in increased conductor resistance, which inhibits current flow and reduces circuit performance. Poor pattern definition can also contribute to performance anomalies in RF and microwave circuits.

Polishing the substrate material makes it possible to pattern much finer lines. This has several benefits including the following:

• The capability to create tighter, denser circuit designs
• The ability to incorporate tightly integrated RF and Microwave circuit features such as Lange Couplers, Wilkinson power dividers, circulators, and bandpass filters
• The ability to utilize more intricate serpentine resistor patterns to create high value resistors.
• The ability to pattern fine pitch spiral inductors
• The ability to pattern fine pitch, high density interconnections

Thinner Metallization Layers

Polishing reduces the amplitude of peaks and valleys on the surface enabling the use of significantly thinner metalization layers. Thinner resistor layers increase the sheet resistance of the material thereby allowing the formation of higher value resistors when using thin-film technology - especially when serpentine patterns are used.

Better Top and Bottom Surface Parallelism

Lapping and polishing the substrate results in improved parallelism between the top and bottom surfaces. The benefit is tighter control over substrate capacitance and inductance when the substrate is metalized and patterned. Since capacitance and inductance are the major factors that determine impedance, the improved parallelism results in better RF and Microwave circuit predictability and performance.

Controlling the camber (flatness) also greatly improves the transfer of the photo mask patterns to the substrate surface thus allowing finer lines and spaces.

Better Optical Performance

The very nature of fabricated optical devices demands surface smoothness and flatness beyond that typically required by microelectronics. Generally, light must be precisely moved around, bent, reflected, split, sent through fibers, and used in ways that were not intended by nature. All of this has to be accomplished with as little loss of light as possible. In most cases, the colors can’t be altered or shifted within the spectrum. Polishing and super polishing are the only means that can achieve highly reflective or transmissive surfaces. The surface must be polished and flattened to a small fraction of a wavelength for optimum performance.

Centerline Technologies takes great pride in producing a superior product consistently and repeatedly. To find out more about our Polishing Services please contact us.