September, 2017
www.us-tech.com
Smarter, Faster, and Leaner: The Democratization of DFM
By Patrick McGoff, Valor Product Manager, Mentor — A Siemens Business D
esign for manufacturing (DFM) software for printed circuit boards has been around since the mid-1990s. It began with bare- board fabricators who wanted to make sure that they fully understood the design they received, in order to avoid any manufacturing issues. When PCB designers got frustrated receiving DFM reports from their fab- ricators, they began implementing their own DFM systems. With DFM tools in the design department, they could identify and resolve the manu- facturing issues before they sent the data to the fabricator. It was a big step in the right direction.
The first challenge many design companies faced was to find a resource that understood manufac- turing enough to set up the DFM sys- tem. OEMs no longer fabricated their bare boards, and fewer were assem- bling their PCBs in-house. The man- ufacturing domain knowledge of their workers was no longer a given. Secondly, like many technologi- cal solutions, the early adopters of DFM were the largest and richest corporations. They had the greatest number and complexity of designs. These are the same companies that were first to implement PCB layout software decades ago or more recent- ly simulation and thermal analysis tools. The benefits of in-house DFM would more than offset the burden required to staff, set up and operate the software.
A company new to DFM could take a couple of months to set up a new tool, and even then it would be left to a subject matter expert to run. That person’s expertise was as much about navigating the tool and dis- cerning the real DFM issues from the false calls as it was about manufac- turing knowledge.
Adding to the support burden of legacy DFM approaches was the need to maintain the rule sets. As board technology and suppliers’ manufac- turing capabilities evolve, DFM rules must be kept current. Otherwise, DFM results will be filled with thou- sands of issues flagged falsely, and the time needed for reviewing will soar.
Lengthy, Complicated Process
The legacy approach to DFM rules management required exten- sive effort to set up. The process was complex. First, categories of PCB technology had to be defined and DFM rules were created and main- tained for each. It then had to be determined which DFM would be applied to board technology (out of roughly 1,000 choices).
Next, the numbers to use for severity thresholds had to be set for red, yellow and green levels. Finally, DFM checklists had to be made that could be applied to a given product, based on the combination of board classifications and manufacturing processes used. It is easy to see how this entire process could take months. Performing DFM analysis was not much easier. First the CAD data had to be entered into the system. Then the PCB technology class had to be determined. Then the manufac- turing processes involved and the manufacturing supplier had to be decided. The appropriate DFM rule
Legacy DFM flows heavily depended on DFM subject matter experts, and often required circling back to a layout stage to resolve issues.
set then needed to be applied. After that, DFM analysis was run. The most time-consuming part was filtering through DFM results for real issues. The real issues needed to be reviewed. Decisions could then be made about the requested changes. Finally, that information was sent back to the PCB designer to adjust the board. This process left the bulk of the work to the DFM expert, while the design modification steps were han- dled by the PCB designer.
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