Embedded component technology can benefit oems.
By Michael Fitts
Different types of materials, increased automation and advanced team design processes are just some of the ways companies can lower costs and maintain high standards. Add to that the desire of consumers to have smaller and lighter products, and the challenge that OEMs face today is clearly recognized.
This push for miniaturization and cost savings of electronic systems has increased the viability of using embedded component technology (ECT). By using embedded components, OEMs can realize a number of other benefits, including:
- System cost and weight reduction
- Assembly cost reduction
- Board surface area preservation
- Performance increases
- Reliability improvements
- Design density, functionality and profitability increases
The majority of these technologies have been deployed and are in use in critical systems today. It could be argued that the push for profitability is the leading catalyst in today's economy for the growing adoption of ECT in today's designs.
This article provides a basic understanding of ECT and includes a more in-depth discussion of one particular embedded technology, embedded passive resistors. Before embarking down the path of achieving an in-depth technical understanding of any or all embedded component technologies and bringing them “in-house” to increase the value of a company's system, remember that people have made careers out of researching the myriad of embedded component technologies in an effort to find the proper fit for their systems.
ECT is the art of embedding passive or active components within a substrate. This embedding can take place on a single layer of material, a combination of material layers or even can be achieved by placing a component within a cavity in a substrate. The substrate can be one used for a multi-chip module (MCM), printed circuit board, flex circuit or even one within an IC. Having benefits in almost all applications, ECT has even proven itself to be a valuable technology for harsh environment systems.
The value that can be achieved by integrating this technology within a system includes knowing what types of components can be embedded — including which technologies can be “mixed” together — and what impact they would have on the entire system as one starts to look at manufacturability, reliability, testability, etc.
 Figure 1. One substrate filled with a myriad of ECTs. |
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The process of performing trade-off studies to determine the point where ECT use should take place can be tedious. Quick estimates can give an idea as to the viability of ECT in a system. However, software programs are available to help make this less of an effort. The most accurate software trade-off, or determination, programs available today require the input of all of the parameters and cost factors required in the ECT assembly and manufacturing process. This can be extremely impractical for the novice ECT implementer.
Embedded Component Types
The myriad of ECTs that are in use or in development today is quite impressive. Types of ECTs include:
- Vertical (plugged hole) resistors
- Discrete resistors
- Mezzanine capacitor (embedded discrete)
- Planar capacitance layers
- Inter-digitated capacitors
- Parallel-plate capacitors
- Planar inductors
- Spiral inductors
- Parallel-plate inductors/transformers
- Folded flex substrate
- Stacked components
- Embedded active integrated circuits
- Passive resistors
Some of these referred to by other names. Unfortunately, an industry-standard naming convention does not exist. An IPC Committee for Embedded Components will take on this task.
Probably the most common of the embedded technologies for a company to deploy today, embedded resistors have a multitude of types, materials, value ranges, manufacturing processes, reliability and costs that make their selection for a first-time user a challenge. Chosen in most cases to reduce the large number of discrete resistors needed for today's designs, the decision to use this technology can dramatically reduce assembly cost, reduce form factor, increase active component density and improve system reliability (reduction of solder joints). For high-speed systems, embedded passives — specifically embedded resistors — can shorten signal paths, reduce series inductance, and reduce electromagnetic interference (EMI) and crosstalk.
 Figure 2. A mixture of inter-digitated and multi-layer capacitors and inductors. |
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Implementing Embedded Resistor Technology
Once the particular technology, vendor, material, process and manufacturer are selected, the crucial part of the design process begins. Technology implementation depends on having the proper tools to determine the actual size, shape, value and tolerance of embedded resistors and successfully adding them to the design. The embedded resistor shape added to the design is inherent to understanding all of the manufacturing parameters and tolerances that exist to ensure the creation of a high-yield, low-cost, process-repeatable shape. Material manufacturers and computer-aided design (CAD) companies have teamed up to help make this happen.
Some CAD companies have parametric embedded resistor capability. This means that embedded resistors and their properties (including value range, tolerance, power rating, voltage rating, trim allowance, minimum size, etc.) can be synthesized automatically from a schematic into an actual substrate design. From there, the resistor(s) can be dynamically updated as all necessary shapes/features (masks, resist areas, etc.) are optimized when properties are modified. Taking this to the next level, several CAD companies have teamed with the embedded component material vendors to provide modules specific to their technology, eliminating the need of the user to understand all of the manufacturing and material parameters needed to create a proper shape for a given resistor value.
A pre-planning model gives one the ability to see the component value distribution of a design, identify the resistors that are candidates for embedding and change these to embedded resistors within a design.
Resistor Trimming
When resistors are embedded within a substrate, they can end up 10 to 20 percent off the target resistance due to the screening process and material inconsistencies, which is known as process tolerance. With design tolerances typically less than 5 percent, something must be done to bring the resistor into range. Borrowing a technology common to hybrids, MCMs and discrete resistors, manufacturers employ laser-trimming techniques to accomplish this task. This process adds manufacturing steps, time and cost, and introduces design challenges.
Resistors typically are designed 15 to 25 percent below target value to account for the manufacturing process tolerance, and because the trimming process can only increase resistance. For example, a 100 Ω resistor would be designed at 80 Ω to account for a 20 percent process tolerance. A resistor's value is largely defined by its aspect ratio (length/width) and material resistivity. This means a 5th:10th resistor has the same value as a 10th:20th resistor, assuming the same material is used for both. However, with a typical laser diameter of 2th, the trimming accuracy on the two resistors will be drastically different. Resistor dimensions as small as 10th are trimmable, but 20th is recommended. Small resistors are good for space conservation, but they should not be too small. Using resistive materials on top of traditional FR4/copper structures, trimming has been proven to be accurate within 1 percent of target resistance.
Conclusion
While not necessarily a new technology, ECT can help lower costs, improve reliability, increase performance and decrease size. This is especially true in the use of embedded resistors where the ability to dramatically reduce the number of discrete resistors can see an increase in speed and reliability, while decreasing the cost and form factor of the boards being manufactured.
To effectively implement ECT, a partnership between manufacturers, designers, and EDA technology vendors is necessary.
MICHAEL FITTS, product marketing manager, Layout Marketing, may be contacted at Mentor Graphics Corp., 1811 Pike Rd., Building 2, Suite F, Longmont, CO 80501; E-mail: [email protected].