Estimated reading time: 6 minutes

Tim’s Takeaways: Conquering Layers of Challenges in PCB Stackups

There is an expression, “You can’t have your cake and eat it too,” which is another way of saying that for those things in life that are either one way or the other, you can’t have both. That’s really a shame in my opinion. Oh, not about wanting something both ways. I think that we all know from past experiences that trying to accomplish something by going about it in what is obviously the wrong way never ends up the way we really want or expect it to. For instance: trying to get into shape without exercising; wanting to improve yourself without being willing to learn; or trying to fly a remote-control airplane without extending the antenna on the control box. (Even though it’s been many years, I’m still kind of bitter about that last one.)

I think it’s a shame, literally—not being able to have a cake and eat it too. Can you imagine? There are very few things on a plate that I like better than a slice of good, rich, moist, multi-layer chocolate cake. Your mouth is starting to water now, too, isn’t it? Just imagine having all of that chocolate goodness in a cake like that right in front of you, and then not being able to eat it. That would be sheer torture, and I think that is one of the reasons why I’m not the biggest fan of cooking shows. I can’t stand to watch them create something incredibly delicious and not be able to grab a fork and plunge in. But as we all know, there is a price to be paid for over-indulgence, whether it is in multiple layers of chocolate cake, or even multiple layers in a circuit board.

When I first started laying out printed circuit boards many years ago, I was working for a computer systems manufacturer whose PCB designs were all multilayer boards. While there were a great many things that I learned there, it also fostered one bad habit: I became accustomed to relying on being able to use multiple layers for routing instead of planning a more efficient layout.

“Can’t get this bus routed in? No problem; we’ll just throw in another couple of layers for you to work with.”

It probably wasn’t quite that easy, as memories like that tend to be a bit untrustworthy. It is true, though, that they were very generous with the amount of board layers that you had to work with, and critical board configuration decisions like layer stackups were created for me by others. This proved to be quite an inconvenience later in my career when my next employers didn’t give me the same flexibility in board layers that I was used to in order to work myself out of a jam. Instead, not only was I expected to work with what I had, but I was also supposed to reduce the layer count to improve on it whenever possible. This meant dealing with a whole new set of design rules and considerations related to board layer stackups that I had never had to work with before.

As we all know, it takes a herculean balancing act to create a circuit board that will deliver the maximum amount of performance for the least amount of manufacturing expense. Trying to sort out all the different pieces of the circuit board puzzle to achieve this balancing act can end up being a real brain teaser for new designers. Just for starters, you need to consider the following as you configure the board layer stackup that you will be working with:

• Signal integrity
• Power integrity
• Placability
• Routability
• Manufacturability
• Profitability

There are enough “itys” in that list to sink a ship, and we haven’t gotten to testability or designer confusability yet.

Thankfully, I worked with some great people who helped me to relearn some of the basics of PCB layout. They taught me how to work correctly with circuit board layer stackups, and why there was a whole lot more to multilayer boards than just providing more room to route on. It took some time, but after a while I came to a better understanding of the relationship between the different board materials and thicknesses, and how they should all be configured to design the board correctly.

I was very fortunate to have co-workers who helped me understand and refine the art of printed circuit board layout. I wonder, though, who will help today’s new designers work through problems like these. Company cultures are changing, experienced designers are retiring, and more is being expected of PCB layout personnel with less time to make it happen. How are today’s puppies going to learn some of these more advanced skills, such as how to correctly configure their board layer stackup? Here are some of my ideas on how this can happen:

• Circuit board manufacturers: I have talked to different manufacturers, and one of the more common themes I’ve have heard is that they want to engage with their customers more before the board is designed. They typically have years and years of experience building circuit boards under their belts, and they understand the challenges that designers face better than most. They also are very aware of the capabilities and limitations of their own manufacturing processes, and the PCB materials being used. They want to help designers come up with the best layer stackup configurations possible because their customer’s success will ultimately translate to their own success. New designers can gain a wealth of information simply by working with their manufacturers.
• Professional resources: There is more technical training available out there than you probably realize. It not only covers PCB layer stackups, but many other aspects of PCB design. You can easily find a variety of seminars and classes from various organizations and groups within the design industry. There are design conferences that feature instructional sessions from some of the brightest minds in our industry, along with product demos and information on new design methods and technologies. In addition, you can also find a plethora of online videos, white papers, and design-related publications that can help.
• New technology: One of the more exciting things happening in our industry is the creation of new tools intended to help PCB design and manufacturing work better together. One of those tools is the IPC-2581 data exchange format. Many manufacturers now can take your board information directly from your CAD system and create a layer configuration that will best fit its needs. Then, using the same data format, they send that layer configuration right back to your CAD system for inclusion in your design.
• You: One of the best resources to pass along some of these advanced PCB design skills can often be found by looking in a mirror. Yes, I mean you. If you’ve been laying out circuit boards for any length of time, chances are good that you already have a lot of knowledge that can be extremely valuable to those who are laying out their first designs. Don’t be afraid to reach out a helping hand to those who still have a lot to learn.

Along with the variety of online resources, I want to mention this edition of Design007 Magazine you are currently reading. As you already know, this month’s issue is focused on PCB layer stackups, and it is chock full of information and data from those who know what they are talking about. If you know someone looking for a little help with determining the most optimum PCB layer stackup for their design, be sure to point them this way.

The good news is that with all of the help available from manufacturers, professional resources, new technologies, co-workers and peers, you have the ability to create the perfect layer stackup for your PCB design. The more I think about it, the more I realize that I was wrong about my first statement. I guess that this is one way that you can have your cake and eat it too. Parden me while I grab a fork.

In the meantime, keep on designing, everyone.

This column originally appeared in the January 2021 issue of Design007 Magazine.