Inside the Challenges Working with DFM Guidelines for Flex and Rigid-Flex PCBs Ebook, we’ll be discussing Design for Manufacturing (DFM) guidelines and the various challenges a designer may face when trying to follow them. We will also be discussing just how to make sense of and navigate the various aspects of DFM guidelines, how to identify the aspects of the guideline and how they interact with one another, and when the guideline should be followed and when it should be broken.
DFM guidelines make up a critical junction of the process of designing and building a flex or rigid-flex circuit board. In many instances, a DFM guideline is used to detail what can and cannot be done for a design, from simple things such as line widths and spacing to more complicated items such as via placements in and among the board.
As is, considering and following every word of a DFM guideline can be challenging. Not every word in the guideline may apply to a design, and even worse still, sometimes the guideline can mislead in how it is applied or worded. Because of this, DFM guidelines can end up hurting more than helping when trying to design a circuit board. This isn’t even considering that some guidelines may be too numerous to be able to thoroughly apply to a design effectively, such as how IPC-2223, the standard for flex and rigid-flex designs, totals over 40 pages. Trying to work 40+ pages into every design can be tedious and frustrating.
The complexities intensify when considering that each design parameter is not isolated but interrelated with others, complicating the decision-making process. Changing one variable, such as copper weight, has a domino effect impacting line widths, coverlay adhesives, and even dielectric thicknesses if impedance is involved. This highlights the importance of consulting your board manufacturer, particularly for those one-in-twenty or even rarer designs that challenge DFM conventions. In such special cases, a manufacturer’s input is invaluable for determining when it’s advisable to deviate from standard guidelines and when doing so could lead to unintended negative consequences.
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