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OhmegaPly® Embedded Resistor Technology
Introduction
The demand for high speed/high density printed circuit board (PCB) packaging compels the use of advanced packaging technologies, including embedded passives, in new circuit designs. OhmegaPly® has become the technology of choice in many critical circuit applications. It is used globally as a high volume, cost effective alternative to discrete SMT resistors.
There are numerous benefits in using OhmegaPly® including reduced surface EMI (Electrical Magnetic Interference), reduced inductive reactance, improved signal integrity of high speed, high frequency circuits and greater reliability resulting from the elimination of solder joints required for surface mounted resistors. More routing area is made available with elimination of the discrete SMT resistors and their interconnecting traces and vias.
Description
OhmegaPly resistors are thin film planar resistive elements that are part of the printed and etched circuitry on a standard PCB layer. OhmegaPly RCM® (Resistive Conductive Material) is comprised of a copper-conducting layer (copper foil) and a thin-film resistive alloy layer that has been deposited onto the “tooth” or matte side of the copper foil. The copper foils are single and double treat copper and are available in 1/2 oz (17 micron) and 1 oz (35 micron) weights.
The OhmegaPly RCM® is available in a number of standard sheet resistivities expressed in ohms per square (OPS): 10 OPS, 25 OPS, 40 OPS, 50 OPS, 100 OPS, 250 OPS and 377 OPS.
Based on original equipment manufacturers (OEM) and PCB requirements, the OhmegaPly RCM® is laminated by independent laminators or PCB manufacturers to specific dielectric materials. It can be bonded to virtually any dielectric material and thickness currently being used by the Industry.
Design
Design of a specific resistor value follows thin film resistor design criteria – see the Ohmega Toolbox for more information. Sheet resistivity is the resistance in ohms per square and is a dimensionless number. The value of any specific resistor is determined by the ratio of the length of the resistor to its width multiplied by the sheet resistivity used. A simple example would be a 68 ohm value resistor that uses 25 ohm per square OhmegaPly. The total number of squares required would be 68 ohms divided by 25 ohms per square, or 2.72 squares. If the resistor width is designed to be 10 mils (0.010″) then the length of the resistor must be 10 mils x 2.72 squares or 27.2 mils (0.027″).
The OhmegaPly® laminate is processed by the PCB manufacturers the same way as other PCB laminates by a subtractive print and etch process. As with normal processing procedures, the board shop uses artwork or laser direct imaging to define geometric patterns that are imaged and etched to create individual resistors on either existing inner layers of a multilayer board or on the surface of a printed circuit board.
Reliability
OhmegaPly® embedded resistor technology has been used in numerous applications since the early 1970′s. Over the decades it has exhibited excellent long-term stability and reliability and has become the technology of choice in many critical circuit applications. In the millions of printed circuit boards, and trillions of component hours of use, OhmegaPly® has demonstrated absolute reliability. OhmegaPly® resistors in new designs are an application of a mature, well proven, technology.
Processing
Any PCB shop can process OhmegaPly®. No license or other fee is required. Since standard equipment, chemistries and process consumables are used there is minimal capital investment required by the board shop to process OhmegaPly®. Most electrical test equipment can be used with a software upgrade to enable resistor testing – see the Ohmega Toolbox for more information.
Cost/Benefit Analysis
The cost of using OhmegaPly® is dependent on the material price as supplied by Ohmega Technologies, Inc., the conversion cost that is applied to a printed circuit board by the board shop and any reduction in the overall board cost due to design enhancements. In addition to eliminating discrete surface mount resistors (SMT) and their assembly costs, PCB cost reduction is achieved by smaller board form factors, reduced layer counts, and the use of conventional PCB technologies rather than more expensive build-up and/or high density interconnect (HDI) technologies. In general, OhmegaPly® becomes economical to use as a replacement for chip resistors when the resistor density is approximately 5 to 6 resistors per square inch of board area.
Applications
OhmegaPly® is used in all areas of the electronics industry: military/aerospace, computer, telecommunications, consumer and medical electronics. Some of the applications include supercomputers, servers, graphic enhancement cards, workstations, application specific integrated circuit simulators (ASIC), automated test rquipment (ATE), active electronically scanned array radar systems (AESA), resistive cards (r-cards), probe cards, telecommunications switching cards, burn-in boards, heater elements, antennas, base stations, and cellular telephone modules. OhmegaPly® resistors are used as a direct replacement for discrete resistors. Some examples are as potentiometers, line terminators, pull-up/pull-down resistors, series and parallel terminating resistors, isolation resistors and as heater elements.
Please contact us with any questions you may have and we’ll be delighted to assist you.
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