Making the Best of Miniature Circuits

June 22, 2016
For circuits with miniature dimensions, this firm provides the expertise and equipment to fabricate micron-sized features on both rigid and flexible substrate materials.

Miniaturization is the key to many successful applications, including pocket-sized radios and medical electronic solutions. While small components like planar antennas and inductive coils enable many small-scale electronic products to operate, making circuit structures and components with micron-sized features is (pardon the pun) no small feat.

Fortunately, Metrigraphics has been doing just that for five decades. The company houses both the equipment and the expertise to fabricate micron-scale components and circuit structures with dimensions of 5 μm or less on hard and software substrate materials.

Micron-sized circuit features are usually associated with semiconductor devices, but Metrigraphics has been fabricating micron-scale circuit features for passive components, including induction coils and optical components. Miniature induction coils enable such applications as pill-sized ingestible medical biosensors, where the inductors provide an energy source for the sensors without need for a much larger battery.

Miniature circuit dimensions can be achieved on both rigid and flexible, bendable circuits such as this.

The general trend of making components smaller will continue for all forms of sensors, particularly in Internet of Things (IoT) security sensors where devices should remain as unobtrusive as possible. Expansion of such applications will fuel a growing need for miniature coils and other passive circuit elements. Luckily, Metrigraphics has the equipment and processes to manufacture fine-featured components in prototype as well as production quantities.

The firm works with thin-film and flexible substrate materials, employing a blend of standard and proprietary processes to achieve fine feature resolution with high repeatability. Multilayer flexible circuits can be fabricated with as many as seven metallized layers and up to six substrate layers. Metallization processes include photolithography, plated metal deposition, and sputtered thin-film techniques.

Metal (conductor) layers for flexible circuits include gold, nickel, copper, and aluminum sputtered onto substrates in a thickness range of 0.1 to 1.0 μm. Viaholes with conductive metal are formed to connect the different circuit layers as needed.

Diving into Dimensions

Thin-film circuits are based on polished and as-fired ceramic substrates, in addition to polished sapphire and quartz glass substrates, in a range of thicknesses. The dielectric constants of these substrates range from 3.8 to 10.0 at 10 MHz with low loss tangents. For example, the loss tangent for a quartz glass substrate with dielectric constant of 3.8 at 10 MHz is just 0.000015 at 1 MHz. Conductor lines and spacing on thin-film substrates can be formed with precision of 0.050 mm and tolerance as good as ±0.005 mm.

Conductor widths can be maintained to a tolerance of ±0.005 mm. Conductors can be places within 0.200 mm of the edge of a substrate, allowing for the formation of extremely high-density, miniature circuits. For multilayer circuits, viaholes can also be tightly spaced, as close as ±0.05 mm from the center of one viahole to the center of another viahole, depending upon the diameters of the holes.

Drawing on a staff with years of practical experience, and some of the industry’s finest fabrication equipment—including several ion-beam milling machines, sputtering systems, mask aligners, and dedicated equipment and clean rooms for prototyping and production—Metrigraphics has fabricated a wide array of planar and three-dimensional (3D) circuits and circuit structures for RF, medical, and optical applications.

As an example, the firm has fabricated over 160 different induction coils for various applications, including biomedical use. These are single-layer or multiple-layer structures (see figure) in round and square configurations with different metallizations and substrate materials.

Coil traces as fine as 3 μm have been formed repeatably on some of these coils, as a demonstration of fabrication capabilities that extend from the prototype stage to full production. Visitors to the company’s website can learn more about the various dielectric and metallization combinations and dimensional tolerances for different structures and circuit configurations.

Metrigraphics, 1001 Pawtucket Blvd., Lowell, MA 01854; (800) 261-2557

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About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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