What is DFM, Really?

Reading time ( words)

Okay, so what is DFM, really? The term "design for manufacturability" has been used for many years now, but does everyone really understand this concept?

For instance, do you design for 10%? Do you design for a specific manufacturer’s capabilities, therefore making you less likely to seek alternative fabricators? How are your drawings worded?

In this article, I will be discussing the reality of DFM and what benefits you, the end-user, by embracing these practices.

Why Design For Manufacturability at All?

Good question. Even if you only buy your boards from a single source--if you have qualified the company already and feel you can expect certain press parameters and dielectric constants based on what they have provided you--it is STILL a good idea to at least design with some latitude. If your design is .1 mm lines and spaces there is not a whole lot of room to either expand or decrease the traces to achieve certain impedances. Clearly, when you have to ingress and egress out of tight-pitch components and your design takes you down to .003”/.003” there is NO ROOM at all for an etch compensation, so you are typically quoted by manufacturers as quarter-ounce foil start. This foil is so thin that we need not compensate for a loss at the etcher like the other copper weights.

Again, as I have mentioned before in my columns, the general rule of thumb is that for every half-ounce of starting copper, you give all the metal features an etch compensation of half a mil. Asking for 1 oz. starting copper, for instance, with 0.003”/0.003” will normally be a no-bid as fabricators would be hard-pressed to be able to run with .002” spaces at Image prior to etch. (Attempting to compensate the 0.003” traces for 1 oz. copper with 1 mil will result in 0.002” spaces at Image prior to etch.) So, 0.003”/0.003” is usually the limit.

Read the full article here.

Editor's Note: This article originally appeared in the May 2014 issue of The PCB Design Magazine.


Suggested Items

Electronics vs. Physics: Why Vias Don’t Get Hot

12/06/2022 | Douglas Brooks, Consultant, and Johannes Adam, ADAM Research
Most of are aware that when we pass an electrical current through a trace (conductor), the trace will heat up. This temperature increase is caused by the I2R power loss dissipated in the resistance of the trace. The resistance of a copper trace is mostly determined by its geometry (cross-sectional area), and there are lots of studies trying to look at the relationship between the current down a trace (of known size) and the resulting temperature of the trace. But the situation is much more complicated than this. There are physical properties that exist that result in helping to cool the trace. These properties are usually a combination of conduction of the heat away from the trace through the material, convection of the heat away from the trace through the air, and radiation of the heat away from the trace.

My Experience With Maxwell

11/23/2022 | Happy Holden, I-Connect007
I was first introduced to James Maxwell in 1967 as a college student. I had to decide whether I would take the Maxwell fields course or the switching and coding course. Being a chemical engineering major with a co-major in control theory, I had heard about the trials and tribulations of the infamous Maxwell fields course.

Sunstone’s Matt Stevenson Shares Insights From New PCB Design Book

10/27/2022 | Nolan Johnson, I-Connect007
There’s designing the “perfect” circuit board and then there’s designing a board that is “perfect for manufacturing.” While seasoned designers and design engineers understand many of the nuances, PCB fabricator Sunstone Circuits has just published a new book specifically for new designers who have the knowledge of design but are still learning what it means to get the board manufactured. Sunstone’s Matt Stevenson takes the reader through a series of situations that should help clarify what’s happening in the fabrication process and how to adjust a board design to be better suited for manufacturing.

Copyright © 2022 I-Connect007 | IPC Publishing Group Inc. All rights reserved.