Drivers and material sets: in the first of a regular column, we take a look at the embedded materials landscape.

THIS IS THE first in a series of monthly columns on embedded passives, embedding discrete passive components and functions (primarily resistors and capacitors) directly into the PCB structure. I want to introduce myself, let you know what stimulated my interest in embedded passives and leave you with an understanding of where I'm headed with the column. Given time, my path may change, as the technology matures and market needs clarify.

My background is simple: I build circuit boards. Although my academic credentials are in biology, the need for a job resulted in the earlier years of my professional career being spent developing applications of organic materials for launch vehicle and spacecraft structures. I later migrated into aerospace electronics, applying the same science on a smaller scale. Ultimately this led me into printed circuit boards, which for 28 years have been my passion. Most of my work has been in the military and aerospace sector. Today, the need for high-reliability products is not limited to missiles, airplanes and spacecraft.

I was aware of embedded passive technology (although we didn't call it that) and had dabbled in OhmegaPly since its inception in the Mica Corp. days (the mid 1970s for you younger readers). Recently, I became friends with Greg Lucas, one of the inventors of ZBC2000, an embedded capacitance material, through our common roots in Colorado. Coretec, my employer, is licensed for BC2000. Despite this early exposure, my interest in embedded passives really fired up in April 2000. I attended an IMAPS conference on integrated passives. I went out of curiosity, clearly influenced by the fact that the conference was on a Saturday, at a local venue and the price of admission was only $60. Among the many interesting papers was one from Dr. John Felton of DuPont on ceramic thick-film resistors embedded in organic PCB structures. John's presentation was fascinating. He commented about being part of a government-funded research consortium and that he was having difficulty getting PCB fabrication support. During a break, I introduced myself and told him his fabrication problems were solved, as I would like to work with him.

Initially we contracted directly with DuPont to develop processes and provide test vehicles. Within a few months we went through the challenging process of joining the consortium--challenging because of the government paperwork. My work initially was with the ceramic thick-film processes--resistors and capacitors. That quickly expanded to include new planar capacitance and thin-film resistor materials. As manufacturers, for several years we regularly processed the benchmark material sets, i.e., BC2000 and OhmegaPly. Through our customer educational initiatives at Coretec, I have been speaking to numerous groups, private and public, on the topic, and in the past year have interacted with well over 1,500 designers from 500 organizations in North America.

My hope is that this column will be an ongoing series of discussions of topics that will help stimulate the adoption of embedded passives technology and provide a collection of useful reference materials for future adopters.

Enough for background, let's get on with embedded passives. Here we present an overview of the drivers and material sets. Subsequent articles will flesh out the details.

3 Drivers

There are three primary drivers, all of which are interrelated: performance, miniaturization and cost. The drive for cost-reduction is virtually universal. PCB buyers, however, think in terms of unit price of PCBs. Embedded passives will not necessarily reduce the cost of bare PCBs. Buyers must think of cost in terms of systems, not individual parts. Cost per function may be lowered by increasing the functionality per unit area. Costs per unit may be lowered by decreasing the size of parts. This is particularly true with PCBs, where the cost per panel is relatively constant, and more parts per panel reduces the unit cost proportionately. Similarly, performance may increase due to smaller size and shorter signal paths. These factors are all extremely interactive.

The table summarizes the resistor and capacitor materials commercially available (or almost available). It is noteworthy that a couple of years ago this list boasted only two or three materials.

These materials are available in a wide range of values and properties (TCR, TCC, temperature and moisture resistance, etc.) and no single material covers the entire range. They also are integrated into the circuit board by different manufacturing processes. Some of these are very easy and inexpensive for the board manufacturer to install, and others require significant process development and capital investment. Resistors may require trimming depending on the design requirements. Untrimmed tolerances may be as high as +/-40%. Laser trimming equipment is available but is expensive, and trimming costs may be expensive and is design/layout-dependent.

Infrastructure such as CAD tools, test tools, cost models, performance models and a base of interconnect manufacturing services firms are slowly developing. IPC, among other organizations, is working to facilitate and accelerate EP adoption and infrastructure development.

RICHARD SNOGREN is a member of the technical staff at Coretec Inc. (coretec-inc.com). He has a bachelor's in chemistry and biology from Western Michigan University. Snogren spent 25 years in the aerospace and defense sectors of the PCB industry, including 15 years as an aerospace materials engineer. He was co-founder of SAS Circuits (now Coretec Denver). Snogren can be reached at [e-mail].