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Publication Date: 07/1/2007
Archive >  July 2007 Issue >  Partnering > 
Partnering to Combine Embedded Passives

Resistance and capacitance core.

Embedding passive components within PC boards is not a new science; at Ohmega, we've been doing it for 35 years. But the technology has evolved dramatically in that time period, and today's inside-the-board possibilities are more diverse than ever. Ohmega Technologies, Inc. manufactures OhmegaPly®, the U.S. Industry standard for thin film embedded resistive materials for printed circuit boards. Oak-Mitsui, Inc. manufactures FaradFlex®, an embedded capacitive material for printed circuit boards. There have been serious collaborative (partnering) efforts by both companies to develop a recently patented combined embeddable resistor/capacitor layer called Ohmega/Faradflex.

Separate Layers
Many designs using OhmegaPly embedded resistors also use separate capacitive layers. The elimination of both resistors and capacitors from the board surface frees up board surface area for additional active devices or to allow for greater board density and/or size reduction. Overall board thickness is also an issue and the need to make thinner circuits is counterbalanced by the increasing circuit layers required in complex designs. Embedded resistors and capacitors on the same core and not just the same board would therefore be welcome by the circuit designer.

Ohmega Technologies' expertise is in the deposition of thin film resistive materials onto copper foil. Over the past 35 years, refinements in the deposition process and alloy composition resulted in an embedded resistor technology noted for its reliability and is extensively used in microwave, military/aerospace and other extreme and demanding applications. Faced with the development of new technologies for embedded capacitors in conjunction with embedded resistors, the company had to decide on the best strategy to develop and implement such a combined material.

Burden of Development
In the past, many new interconnect technologies were developed by OEMs either in collaboration with, or through, captive printed circuit facilities and their suppliers. Over the years, cutbacks in R&D funding by OEMs and the elimination of captive printed circuit facilities has shifted the burden of new interconnect development onto the shoulders of the merchant PCB shops. Greater collaboration between complementary material suppliers is therefore very attractive, especially in light of the significant material and financial requirements necessary to bring to market new interconnect technologies. With this in mind, Ohmega Technologies reviewed the available capacitive technologies and decided that Oak Mitsui and their FaradFlex product was the best fit as a potential complement to the OhmegaPly product.

Communication and a clear understanding of goals are important for any successful project. That is even more critical when two companies are working together to develop a new product. Numerous meetings and conferences between Ohmega Technologies and Oak Mitsui personnel reviewed and defined both the developmental tasks required to create the new product as well as all aspects of production, sales and marketing.

With a clear vision of the steps necessary to develop the joint product and measurable goals and timelines defined, both companies began the developmental efforts of combining their respective technologies into one product. We discovered that the low-profile, low-loss copper used for OhmegaPly was perfect for thin dielectric capacitance applications. After numerous refinements, a final product was successfully developed and tested. The results of the testing demonstrated both the viability and reliability of a subtractively processed, embeddable, resistor/capacitor core material. The properties of the combined product meet the requirements of the printed circuit designer and the printed circuit processor.
OhmegaPly resistors on flex circuit.

Of particular note are the synergistic effects of the combined product. Increased power dissipation can be expected as the dielectric becomes thinner and heat transfer from the resistor element to copper becomes more effective. As tested, the power rating of resistors on the FaradFlex core increased by a factor of 3 from 0.15mW/mil2 to 0.45 mW/mil2 of resistive area when compared to a standard FR4 substrate. What was not expected was the significant improvement in the RTC characteristic of the resistive element. RTC, or Resistor Temperature Coefficient, is the measurement of the change in ohmic value of a resistor with a change in temperature. This is expressed in parts per million of ohmic value per degree C (PPM/°C) and is normally tested from -65 to +125°C. The OhmegaPly thin film resistive material already exhibited excellent RTC stability on FR4, Polyimide and other traditional dielectric materials (typically about 50 PPM/°C). When the Combined Product was tested, the RTC of the resistive material was only -6 PPM/°C. Clearly the stability of the resistive material vs. temperature had improved by an order of magnitude.

There has also been unexpected and welcome demand for OhmegaPly on the thin FaradFlex dielectric for flexible circuit applications. Interest in the resistive material on flexible dielectrics has grown over the years. OhmegaPly has been successfully used on a number of flexible materials as heater elements, electronic shielding, termination resistors, power dividers, etc. in consumer, medical, aerospace and other electronic applications. Recent requirements for OhmegaPly on very thin flexible dielectrics (less than 1 mil, or 24µ) has led to applications that use the Faradflex BC12 (12µ or 0.5 mil thick) and thinner dielectric as the flexible substrate for the OhmegaPly resistors.

Successful partnering by material suppliers can result in the development of new and innovative products. With clear and focused goals and expectations, and leveraging off of the strengths and expertise of each partner, the challenges of today's electronic packaging can be faced and met.

For more information, contact: Ohmega Technologies, Inc., 4031 Elenda St., Culver City, CA 90232 310-559-4400 fax: 310-837-5268 E-mail: Web: or Oak-Mitsui, 80 1st Street, Hoosick Falls, NY 12090 518-686-4961 fax: 518-686-8080 E-mail: Web:

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