The size to cost ratio describes how large or complex a PCB component can be without becoming cost-prohibitive.
Different industries and applications have different acceptable size-to-cost ratios depending on their audience and the available materials.
Cost-effectiveness analysis involves analyzing many types of data to determine the best way to build an electronic component.
Complex, but tiny, PCBs with an acceptable size-to-cost ratio.
The design of electronic components is a delicate balancing act. The more complex a component is, the larger it becomes, and that also makes it more expensive. There comes a point where a component is too large or too complex to be manufactured in a cost-effective way, and designers must know where that inflection point is before beginning the fabrication process. The component size-to-cost ratio gives designers an easy metric to determine if their designs will run over budget because they are too large or too complex.
What is the Component Size-to-Cost Ratio?
The component size-to-cost ratio measures the viability of an electronics project based on how much it will cost given the resources needed to build it. Productivity and profit must be carefully balanced so enough components can be made while still generating a profit for the manufacturer. The more complex a component is, the less likely it can be built at a low cost. High complexity in a single component can also require costly modifications to the rest of an electronics project. For example, high voltages traveling through a component may require adding a heat sink to the entire project, while lower voltages may not require as much heat dissipation. It is important to consider safety as well, however, designers should never remove safety precautions just to save money.
As the size of PCB components decreases, the mechanical constraints needed to ensure functionality in smaller spaces has affected their size-to-cost ratio. The high density of individual components on PCBs increases the risk of failure due to high voltages and current levels, requiring mitigation such as heat sinks and specific types of circuits or transistors. As the number of components on a PCB increases, the fabrication cost and size increases.
To prevent costs from ballooning, many manufacturers have maximum size limits on PCBs. The number of components on a PCB does not itself create an unsustainable size-to-cost ratio. The difference between an unsustainable and sustainable size-to-cost ratio lies in the method by which a PCB is assembled within its mechanical constraints. Different soldering methods, for example, can change the structural integrity and surface area of a PCB, thereby changing how components can be laid out.
Why Can Component Size-to-Cost Ratios Vary?
Creating an optimized PCB design is an iterative process, requiring design changes, testing, and data analysis. A valid, verified STEP file is a reliable starting point, but the optimization of the final design may change the size-to-cost ratio dramatically from the initial plan. Size and shape requirements, combined with mechanical constraints, may cause components with similar functions to have different size-to-cost ratios. Further variation can come from whether a manufacturer uses ECAD (electronic computer-aided design), MCAD (mechanical computer-aided design), or a combination of the two. The most reliable method of optimization is a combination of the two since they each address different requirements in the PCB fabrication process.
Different industries may also have different acceptable size-to-cost ratios, depending on the types of products they produce. For example, Internet of Things (IoT) machines must be able to make complex calculations and communicate with each other, requiring some of the most complex fabrication in modern machines. This includes PCBs with multiple layers and strict standards for best practices, some of which are essential for successful wireless connectivity. These PCBs tend to be quite small since IoT components such as smart sensors rely on them. IoT PCBs also rely on a newer type of PCB, called flex PCB, which has fewer stress points, but can be more expensive than traditional PCBs. Complex components like these often require high production costs, but the advantages these components confer over older variants are seen as acceptable tradeoffs.
This is a good example of how the component size-to-cost ratio is a useful metric, but not the end-all for PCB fabrication. Some complex projects and applications require component size-to-cost ratios that would be unacceptable for simpler projects.
An amplifier with a potentially unacceptable size-to-cost ratio.
What Types of Analysis Are Useful With Size-to-Cost Ratios?
Cost-effectiveness analysis takes into account all parts of the PCB manufacturing and testing process, creating a cumulative estimate of fabrication and testing costs for each unit before production begins. The analysis involves finding any errors or inconsistencies in the project’s bill of materials, checking component clearance and positioning, adjusting footprint land pattern sizes, testing solder quality, and making sure a complete battery of tests has been done. It’s possible for all of these things to pass minimum requirements for operational viability, but to not be optimized for a PCB’s required applications. In that case, a cost-effectiveness analysis can reveal areas that can benefit from small changes to make a component better. Eliminating errors through cost-effectiveness analysis reduces the chance of manufacturing delays and additional costs incurred from faulty fabrication.
Critical area analysis is a form of risk assessment designed to show if a component has any physical vulnerabilities before fabrication. Eliminating these vulnerabilities is essential to keeping the component cost-to-size ratio down, since reworkings due to fabrication defects are part of the ratio. Critical area analysis examines a component’s performance, compliance with regulatory standards, and resistance to damage from electrostatic discharge, among other factors. Circuit analysis is also important, not only to make sure the PCB functions properly but to make sure it doesn’t overheat or fail, requiring costly repairs.
Determine the best way to build a component through cost-effectiveness analysis
The PCB Design and Analysis overview page at Cadence Design Systems provides tools ideal for optimizing your component size-to-cost ratio, including the OrCAD PCB Designer. Learn what’s new in OrCAD to keep your PCB design processes efficient in both time and cost. If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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