From IPC Standards to Practical DFM

Estimated reading time: 4 minutes

Design for manufacturability (DFM) seems like common sense: If we know the rules a PCB must meet, why not check the design against them before it ever reaches the factory? In practice, of course, it’s not quite that simple. I caught up with Susan Kayesar, product manager at Siemens and longtime contributor to Global Electronics Association standards activities, to talk about an ongoing effort between Siemens and the Association to translate IPC requirements into practical, software-based DFM checks. Susan explains where standards lend themselves to automation, where the gray areas begin, and why checking for IPC compliance is an important starting point, but not a substitute for understanding the capabilities and limitations of the fabricator who will actually build the board.

Marcy LaRont: Susan, what does your work involve at Siemens, and how are you engaged with the Global Electronics Association?

Susan Kayesar: I'm a product manager at Siemens. I've been active in the electronics industry for over 20 years, mostly supporting the Valor and Mentor, and later Siemens’ line of products, doing design verification and, specifically, DFM analysis. That's my niche skill.

LaRont: Is DFM a big part of your engagement with the Association?

Kayesar: Yes. I've been involved in IPC standards for a long time, both in reviewing them and contributing to them. The crossover is in understanding the demand in the industry for standardization, what manufacturability means, and interpreting that into software that can test for manufacturability. That is my expertise.

LaRont: What else holds your interest in this space?

Kayesar: My personal side quest is sustainability, and what that means to the electronics industry, which is historically problematic when it comes to sustainability. As well, I am honored to sit on the Design Leadership Council, a group with a lot of experience and valuable input. We look at the world of electronic design, and how to approach that going forward, and how the Association can serve as a linchpin or as a collaboration space for ideas and knowledge. How can we engage the rest of the industry in fruitful discussions about issues that affect them now and in the future? Maybe we can preempt some of those issues, but there’s also value in just gathering and disseminating that information.

LaRont: Tell me about your partnership with Siemens and the Association to create a DFM tool.

Kayesar: We started a pilot project about two years ago, just to see if there was any willingness on all sides to create and use a set of DFM rules that might assist our users, or any users, in determining compliance with IPC standards.

On the one hand, it's like chasing a unicorn because everybody says, "That sounds good, but can you just put that into my tool so that I can check?"

It’s common sense that if we have rules to follow, we should be able to translate those rules into a check you can run while you're designing your board to make sure that it's compliant with those rules before your design is done.

LaRont: How is that normally done? Is it separate once the design is finished, or do you just have to have it all in your brain?

Kayesar: There are a few levels of complexity here. First, a DFM analysis is sometimes considered a nice-to-have. I have never understood why, because it is such a valuable tool to achieve not only better design but often huge cost-savings.  But the biggest hurdle to adopting DFM as your best practice is that it appears difficult to set up correctly.

In reality, the setup process is not that challenging, but when you don't have the assistance or tools to set things up properly, you can easily get sidetracked. You start with, “What kind of internal compliance do I need?” Then you say, "What is my manufacturer actually doing? What are the limitations of that factory?" Now, some of the IPC standards lend themselves very well to this because they are all “shall” statements: “The tolerance of a pad to a component lead shall be X. Annular ring must be calculated with a specific formula for specific circumstances.  Those are some good examples of when a value is explicitly laid out in IPC standards.

Some standards do not lay things out quite as explicitly. They do not necessarily have “shall” statements. Sometimes you need to cross-reference multiple standards. Sometimes there are “should” statements, and there are some gray areas. Some of the standards are actually acceptance tests, which cannot be accommodated in DFM analysis at all.

LaRont: How has your team addressed this?

Kayesar: Our team has extracted practical information from the IPC standards about issues that can be identified at the design stage, issues that we know will make the board that you're designing non-compliant with an IPC standard, or if you will need a special manufacturer to achieve the build.

It gets tricky when manufacturers build products that are well beyond the IPC Class 3 standard, very tiny boards or those used in aerospace, defense, or medical applications with very strict reliability requirements. When employing these checking tools, one really needs to understand that there's a fine line. There's compliance, and then there's the manufacturing environment. You need to test for IPC compliance, and then it's a really good idea to also test against your actual manufacturer's limitations. They're supplementary, but they're not necessarily the same, and I don't want to give that impression.

We want to get the message out there that this is a really good starting point. It's not the end, but it's definitely the start.

LaRont: Well said, thank you.