Accumet was the first in the RF and Microwave industry to create surface preparation standards for ceramics back in 1970, and the who, what, why, where, when, and how of it all is still part of our core. You can tap into that tribal knowledge right now by reviewing our most frequently asked questions and then sending us your own application engineering questions. Our combined material science expertise and microelectronics substrate processing knowledge is at your disposal any time you need help from an expert consultant. Whether it’s an alumina surface preparation or silicon carbide or BeO tolerance question, a material choice question, or best practice question on lapping vs. polishing, Accumet technical consultants are here to provide the consulting, advice, and insight you need to improve your ceramic and metal substrate processing steps, and optimize your RF and microwave integrated circuits (ICs).
Polishing a substrate enables much finer line geometries, tighter tolerances, and greater consistency from piece to piece. An as-fired surface finish can be adequate for thick-film applications with link thickness down to 5 mils and thin-film applications with line thickness down to 1 mil. However, for tighter tolerances and smaller dimensional lines, lapping, and for even greater refinement, polishing, are used to condition a substrate to allow for higher performing films. Learn more in our Tech Brief "A Pre-metallization Guide to Lapping and Polishing Ceramic Substrates"
Typical Polishing Benefits Include:
Enables thinner resistor layers for increased sheet resistance and higher value resistors in smaller areas
Allows for much denser circuit designs with tighter tolerances and greater consistency
Facilitates the development of RF/Microwave circuit features that require tight tolerances and a high degree of integration, such as bandpass filters, circulators, Lange couplers, and Wilkinson power dividers.
Grants the ability to develop more intricate metallization patterns with finer pitch and thinner metal layers, which may be required to build high-performance spiral inductors, high density interconnect, and intricate serpentine resistor patterns.
Many applications can benefit from lapping and polishing, as these processes can improve yields, increase consistency from batch-to-batch, simplify the design process, and enable performance and tolerances for thin-film and thick-film applications otherwise unreachable. Typically, higher performance applications with demands for reliability, yield, and consistency, such as with high power semiconductors, RF and Microwave devices/components, and with optical devices
Lapping and polishing are similar processes that both use mechanical action and abrasives to remove unwanted material from a substrate in order to deliver a result with better parallelism, flatness, and surface finish. Lapping uses a rolling abrasive against a hard lapping surface to remove moderate amounts of substrate material. Polishing on the other hand, uses comparably much finer abrasives with a soft polishing surface and removes very little material. Lapping is often used to control parallelism, flatness, and surface finish (from 5 micro-inches to 60 micro-inches) for certain materials whose properties don’t allow for finer surface finishes. Polishing is purely for refining a surface finish to tolerances far tighter than what can be achieved with lapping (as low as 1 micro-inch depending upon the material used). Learn more by reading our blog which further explains the differences >>
Depending upon the substrate, the surface finish, flatness/camber, and parallelism of an as-fired substrate can vary widely. For applications that require a consistent substrate would only be able to achieve that through lapping and polishing if a more refined surface finish is necessary. For example, with a thin-film application that requires the use of a photo-resist, the waves, bumps, grooves, and camber of an unprocessed substrate could lead to inconsistent thickness of the photoresist, as well as light diffraction from voids and bumps during development. In this application example, device performance and yields may be greatly impacted by the poor condition of an as-fired substrate.
The most common materials that are lapped and polished are ceramic substrates, such as varying grades of Alumina, Beryllium Oxide, Aluminum Nitride, Fused Silica, and Sapphire. However, certain applications also require lapping and polishing of metals, carbides, and other industrial materials like Cordierite, Graphite, Corning Macor, Mullite, Corning Pyrex, Quartz, Silicon, Silicon Carbide, Silicon Nitride, Steatite, Boron Nitride, Zirconia, and other .