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Breaking down the pillars of dfm

We all recognize design for manufacture (DFM) as a method for optimizing your PCB designs. The aim is to reduce costs, increase yield, and improve manufacturability. Many of us designing PCBs do so as a secondary professional discipline. We are makers, engineers, and product managers who also design circuit boards.

Piled atop our other responsibilities, keeping up with new design requirements and product innovations can be a challenge. The changes to design requirements will just keep coming and, as electronic devices increasingly need smaller and higher-density components, adherence to DFM best practices will be more important than ever.

This article will explore best practices for ensuring manufacturability of your design with a focus on tools, process, and partners.

Evaluating Design Tools for DFM

Design for manufacturability is not the practice of making two isolated processes work together well. Rather, DFM is a design process that looks forward to the manufacturing process, considering yield and other manufacturing issues that affect cost and quality. DFM integrates the design and manufacturing processes so that manufacturing requirements and capabilities can be accurately reflected in the design work.

There are multiple design tool types for creating DFM-optimized designs:

  • Standalone DFM clients
  • Web-based DFM clients
  • Interactive DFM tools

Standalone and web-based DFM clients can be generally referred to as back-end DFM tools. While these tools often have the best performance and most extensive ability to find DFM rule-set violations, they can also be a bottleneck in the design process. The cost of fixing design flaws tends to increase in geometric proportion to how late in the design cycle the designer identifies the flaw.

Finding errors earlier makes them cheaper to fix.

Interactive DFM tools offer inherent efficiency. Because back-end DFM tools require a round-trip between the design tool and the DFM tool, their usage inevitably interrupts the design process. Interactive DFM tools demonstrate how design choices will impact the yield or manufacturability of their design while you are working in the design tool. This helps you make more robust design decisions.

When you can see a violation in process, you can fix it quicker—saving time and money while improving the design process moving forward.

Examining Elements of Sound Process

How you approach designing PCBs is an often-overlooked contributor to the ultimate quality and manufacturability of the boards. If you are juggling PCB design with other job functions, it is common to overlook the simple ways in which you can optimize your design process. And if there is one thing experience tells us, it is that a good design process trumps heroics every time.

Team Communication

Communicate with your manufacturing partner at the beginning of, and regularly throughout, the design process. Your manufacturing partner has valuable insight into how design decisions can impact manufacturability, yield, and quality of the boards you are designing. Don’t wait until the design handoff time to start the conversation.

If your manufacturer has response telephone or email support, you can use their expertise to help you grow your knowledge base.

When starting a new project, verify that you, your manufacturer, and your fabricator are all using consistent DFM rule sets and component footprint files—and do not forget about your supplier(s).

Even though the typical designer may have to manage a library of about 10,000 parts, not all of them are on the shelf all the time. When possible, choose parts that are readily available; especially when time is of the essence. You do not want a great design sailing through the fabrication process just to sit and wait for hard-to-find parts.

As your board manufacturer’s capabilities and process requirements have a large impact on the manufacturability of your design, the accuracy of the footprint files you use on your board also affect the design’s success. Don’t be shy; like with your manufacturer, keep an open line of communication with your supplier(s) to help guarantee that you are using up-to-date footprint files throughout the design process.

Simulations

PCB design is the interface between the perfect world of the schematic and the real world of the manufacturing facility. Particularly with high-speed board designs, you cannot optimize only for yield or other physical characteristics. This is because the electrical characteristics of the board can interfere with correct signal transmission. To avoid costly re-designs, use a simulation tool to balance the electrical performance of your design against other desirable physical characteristics, like size and yield.

Manufacturer Specifics

If you are using a rapid prototyping service for your PCB manufacturing, be aware of any capabilities that may be specific to your manufacturer’s service. For example, your board outlines or via diameters may need to fit within specifications that are unique to that manufacturer’s rapid prototyping service.

As PCB manufacturers know very well, highly manufacturable designs exist within a range of specifications. Good manufacturers can help you tweak your design to make the best use of range or wiggle room. If your DFM rule sets seem to be constraining a goal for your design, reach out to your manufacturer to see if there is some flexibility in their DFM requirements. This kind of designer-manufacturer communication about DFM can help save time, reduce costs, and even improve the functionality of your board.

Evaluating Manufacturing Partners

When selecting a PCB manufacturing partner, there are several specific manufacturer capabilities that will help you get your designs produced more quickly, for less money, and with fewer manufacturing turns.

We recommend evaluating three key areas when choosing a manufacturing partner.

Manufacturer-sourced DFM Rule Sets

Not every manufacturer prioritizes making DFM rule sets for popular design tools available, cost effective, and up to date. Working with a manufacturer who does will save time and money in the end.

Front-end Expertise

Carefully evaluate the process through which the manufacturer moves a design from CAD file to completion. In particular:

  • What kind of DFM checks happen after they receive a file?
  • How robust are their DFM and quality assurance (QA) processes?
  • If they receive a design that has manufacturability problems, how will they work with you to resolve the problem?
  • What is their scrap rate? A manufacturer’s scrap rate is a single metric that serves as a good proxy for other important efficiency and quality-related metrics. A low scrap rate tends to indicate that a manufacturer has good internal DFM and QA processes.

Answers to these questions will help you identify manufacturers with a robust DFM process that can help compensate for any gaps in your own DFM expertise.

Quick Access to Support Staff at the Manufacturer

Choosing a manufacturing partner with readily available support staff can help you solve manufacturability puzzles during the design process, rather than after submission.

  • Do they make it easy to get competent technical support?
  • How quickly will they respond to your needs?
  • How can you get support for time-sensitive issues other than by email?
  • Are they available around the clock?
  • What is their escalation policy for difficult support requests?
  • Is support free or is it pay-per-incident?

Probing questions like these are important, and best asked before you settle on a manufacturing partner for your projects.

Conclusions

The real key to optimizing the manufacturability of your PCB designs is to choose tools, processes, and a manufacturing partner that meet your needs. Treat your parts suppliers, PCB manufacturer, and PCB fabricator as members of your design team—prioritizing open and persistent collaboration with each.

This along with adherence to your own DFM-focused process will have a significant effect on your product’s cost and quality.

 

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