Printed Circuit Design & Fab Online Magazine - Current Issue

Roughly Speaking

New entrants into the PCB industry are bringing their own skills to the table.

Transferable skills are bringing in new designers to the PCB industry because there aren't clear paths into it from the outside. Looking around and speaking with attendees at PCB West 2023, a significant number either identified themselves as an electrical engineer or an engineer of some type.

As a quick aside, as someone who studied electrical engineering, a certain amount of pride comes in identifying oneself as an electrical engineer, because it is known as one of the more challenging disciplines. A growing number of engineering programs are also dedicated to focusing electrical engineers toward signal integrity and power integrity, like Dr. Eric Bogatin's program at the University of Colorado Boulder.

So, it wasn't entirely a surprise that at PCB West, roughly 18% of attendees identified themselves as an electrical engineer, up from previous years. Several of the designers that I spoke with indicated they were seeing increased time allocations from their management to focus on designing printed circuit boards, which is something I always chuckle about because my first inquiries into printed circuit board design was met with a quick rebuff.

Read more: Pivoting to PCB Design

A tech conference presentation spurs study of an exciting material option.

I like to ask designers about interesting projects or technologies they have worked on, and I heard from two designers, whom I met through my local PCEA chapter, about some very interesting and complex boards they designed using sintered copper. Both had used sintered Ormet Transient Liquid Phase Sintering Paste (TLPS) to design boards that would not have been possible otherwise. (There are a couple different vendors for sintered copper for vias, but I looked further into Ormet materials, as that was the material used in both the boards they told me about.) These boards were complex, with a lot of parts, limited space, RF signals with antennas and sensitive digital components, and I was told these boards would have been impossible to design without the sintered copper to create any-layer vias connections.

The Ormet paste provided a path forward to route, but this wasn't the first time I encountered this material. I first heard about it in 2014 from a fabricator that wanted to be able to document these types of vias in their stackup. In the past two years, however, I heard more and more requests for it from both designers and fabricators. What is it, and why has it taken so long to get traction in the PCB industry? This prompted me to put on my investigation cap and pursue some answers.

Read more: Sintered Copper Can Handle the Pressure

Models can reveal what design rules "forgot."

A picture is worth a thousand words, and that is especially true when evaluating the impact of changing trace dimensions in your printed circuit board.

The capabilities today of visualizing, in a matter of seconds, the complexity of the electromagnetic fields in one's printed circuit board are astounding. Twenty years ago, software tools to help designers make informed decisions were limited to numerical outputs or very rudimentary images. Often one required a significant level of understanding of the physics involved as well as a solid imagination to properly visualize the electromagnetic field lines and their significance. Even then, most visualizations were representations, not actually calculated fields displayed over the actual board and components. Many tools today provide unprecedented insights through such visualizations, equipping and enabling quick and intelligent decision making by designers on an unprecedented level.

I recall – and I hope you had a similar experience – a science class that used iron shavings and a magnet to make visible the once invisible magnetic fields as in FIGURE 1.

Read more: Changing PCB Trace Dimensions

Numbers on a data sheet are a good start, but confirm them with your own testing.

"Trust, but verify." While some readers will recall hearing this in the context of nuclear disarmament, I have it most notably drilled into my conscience by my first engineering manager while working in software quality assurance. And for good reason too! It was literally my role to verify the fixes that the engineers claimed they had implemented and to find the issues that were still open. While most of the time their fixes resolved the issue, sometimes it was only partially dispositioned.

So how do we successfully trust, but verify when it comes to information in data sheets for not just copper roughness, but other values significant for modeling signal integrity in printed circuit boards?

In a previous column, I discussed copper roughness and a partial story of the lifecycle of the copper as it moves along in the process of becoming part of a printed circuit board. In that article, I mentioned the dielectric constant/permittivity (Dk) and the dissipation factor/loss tangent (Df) of the resin/filler/glass combination. The data sheets used to be very secretive, with material suppliers concerned about corporate espionage regarding chemistries if the Dk and Df information was made publicly available. Depending on the material supplier and the materials in question, many times one can also find the construction data – glass weave style and quantity, resin content, and shelf thickness.

Read more: Models Can Be Deceiving: Trust, but Verify