Additive Electronics Conference Set for October 2019 Debut
Kelly Dack and Tara Dunn talk about the upcoming conference "Additive Electronics: PCB Scale to IC Scale" on October 24, 2019, hosted by SMTA in San Jose, California, and why it’s an important event for people to attend—especially those involved in the design process.
Kelly Dack: I’ve heard a lot recently about additive electronics, and I’m familiar with the subject only from the standpoint of 3D printers layering up different materials, including conductive materials. But a couple of weeks ago, I reconnected with Tara Dunn who talked to me about the Additive Electronics Conference that’s coming up, which will cover a very different realm. My perception was that this particular context of additive electronics is more of a micro-scale take on finished copper. We discussed seeing copper on a very small scale, which can build circuitry in the range of three-thousandths of an inch all the way down to five microns. I am excited and want to know more about it. Tara, can you tell us what this conference is about?
Tara Dunn: We’re looking for different options to attack the market segment that is sub-75-micron trace and space all the way down to the 5-micron trace-and-space range. This is that gap area between PCB manufacturing and IC fabrication.
Dack: That’s sounds very interesting. Would this be considered cutting-edge or uncharted territory for most PCB designers and engineers?
Dunn: Definitely. People being introduced to the technology will often ask, “What are the design rules?” The blunt answer is there are really aren’t design rules just yet; everything is still developing quickly, and the designs tend to be much more collaborative than we’re used to with traditional PCB design rules. For instance, somebody may come to us and say, “I have this idea, I need this type of material, and I’m trying to accomplish this. How can we go about it?” Tt becomes a brainstorming session. How can we use the technology that we have today in different ways to figure out how to solve the problem?
One of the things we’re hoping to do at the conference is spark a lot of ideas. We want to provide a lot of opportunities for people to let their imagination kick into gear and think, “This person is using this technology this way; how might I be able to apply that?” We want it to be very interactive.
Dack: This is a really good subject for designers. As a designer myself, and having designed lots and lots of flex circuitry, I have learned what you can’t do by making mistakes—especially with copper. Over the years, a designer learns that there are types of processed copper. The copper thickness and grain structure must be considered along with conductor layer topology. Trace or conductor widths are critical not only in considering electrical performance but also in manufacturability. That criticality has to do with the subtractive process of the way we etch copper circuitry onto flex material or any other type of material.
With a subtractive or chemical etching process, there’s a trace structure that based on the height or thickness of the copper foil and relative to the trace width. If a designer isn’t properly considering conductor height to width formulas, the nominal design data—if not addressed by a supplier in CAM—could etch away the base of the copper conductor because of the unique way conductors etch in the tank.
Now, with the additive process, my understanding is that there’s no etch factor. Therefore, the limitations are only in how thin the copper can be printed. At the point that seed copper is printed or imaged onto a surface, the conductors can be grown from that copper, and the cross-section of the conductor doesn’t take on this strange trapezoidal shape as it does during a print and etch cycle; instead, it forms a rectangular shape or thereabouts. Is that true?
Dunn: Yes. There are a couple of different technologies that have received a lot of publicity within the last couple of years, which were triggered by the news that many of the current smartphones are using the modified semi-additive process in very high volume, offshore. Now, we’re looking at having similar technology to mSAP or a semi-additive process here domestically with low-volume and development-type work.
The basic idea behind these two processes is that you start with a very thin seed layer of copper, and that’s usually the key: the thinness of that copper, whether you’re using a very thin copper foil or putting a seed layer of copper down chemically. Then, it becomes an imaging process. You apply your resist, do your imaging, and then use electrolytic copper to plate the traces up to the desired width that you’re looking for. And you’re right, Kelly; because we’re not subtractively etching the trace will straight up and down, there will be no trapezoidal effects. There are RF benefits, in addition to the advantages of space, weight, and packaging. From that point on, these processes are run through PCB fabrication with the same processes used for subtractive etch today.
Dack: From a design standpoint, can we expect to get answers for the application of these circuits and what to watch out for? As a designer, I’m very familiar with the rolled annealed copper that’s commonly used in flexible circuits. But I have a feeling that additive copper is not going to end up as rolled annealed and instead will be a crystalline structure. Are there mechanical ramifications to this? Will the conductive paths be more brittle and delicate?
Dunn: The keynote presentation by Rich Brooks, senior engineering manager at Jabil Circuit Inc., will include some of the additive applications that they have been involved with over the recent years.
Dack: At first, additive processing was often perceived as something mainly for HDI and the super high-tech end. But it sounds like it’s being used for all sorts of applications—not just for the cutting edge.
Dunn: It definitely has a role with HDI technology. It can help solve a couple of things, such as working with a 12-layered design with three lamination cycles; that’s expensive because each of those lamination cycles comes with yield loss at extra costs. And it also hurts the lead time when you need to expedite product, so that’s a challenge and a constraint. Instead, if you can bring in this additive process, or a semi-additive process, and replace specific layers in a stackup, it doesn’t have to be the entire circuit done that way; you can have some layers be with the additive process, with some being etched when they have larger features, and then you can integrate those together.
In one customer application, we went from 12 layers to eight layers, which cut the lamination cycles from three to one; that’s a significant change in the way that we look at designs and how we can process things. Beyond HDI, I also see single-sided or double-sided circuit applications benefiting from these very fine feature sizes. If you think of something like a neuro-probe application or something that’s going to be bonded to the tip of a catheter, you’ll realize that additive has new applications on its own and independent of HDI.
Dack: You mentioned semi-additive a couple of times. What’s the difference between additive and semi-additive? Is it combining a couple of processes? What do you mean by semi-additive?
Dunn: That’s a good question, and I probably use those interchangeably when I shouldn’t. In general, we’re looking at additive electronics: the additive, semi-additive process, and modified semi-additive processes all fall under that umbrella term. The additive process would be just fully additive in that you’re not starting with the seed layer of copper. You may start with a seed layer of a catalyst, image the catalyst, and then build the copper up from there; that can be a little limited in terms of how tall and wide your circuitry can be with that, but it certainly has its place. Down in the five-micron range is where we would see that technology come into play.
When we have slightly larger traces—such as 17, 25, or 50 microns—then either the semi-additive or modified semi-additive processes come into play, which both start with that seed layer of copper. Semi-additive tends to start with it as chemically applied, and modified semi-additive typically starts as copper-film based laminate, and it’s slightly thicker in the electroless seed layer.
Dack: It took me by surprise when you mentioned additive because I thought it required a seed layer of copper.
Dunn: There are a lot of options, which is exciting, and that’s one of the things that we’re looking forward to hearing about at the conference. We are going to kick off the conference with a keynote speaker from Jabil who we’re very excited to hear from, as I mentioned earlier. Then, we’re going to hear from different people who currently have a need for this technology, including NextFlex, Crane, and Lockheed Martin. They will explain the need that they see in the market. We’ll also have presenters who talk about different options that are going to be available to help fill the gap.
After we take a break, we’ll move on to some of the practical applications. How are these technologies being applied in low- to medium-volume production domestically right now? And what is planned for the future? One piece that is going to be very interesting for me is our very interactive panel discussion. All of our presenters and users of the technology will come up and sit on the panel, and we’re going to have case studies. Then, we’re going to take a bunch of questions from the audience. You will have a full range of technologies represented that, as an attendee, you can ask questions about.
Dack: That sounds really comprehensive. And since it’s in San Jose, it’s easy to fly in, fly out, and get all of the information one would need.
Dunn: And for those who are interested, it is being held in the same location as the International Wafer-Level Packaging Conference, which is taking place the three days before our event.
Dack: I see Lenora Clark from MacDermid Alpha Electronics Solutions is also involved with this conference. Tell me about that.
Dunn: I was talking with Tanya Martin from SMTA about new technologies out in the market. There was a lot of interest and questions being asked at the SMTA level, and I was being asked similar questions as someone working in the PCB industry. We both said, “I think there could be a need here for a conference and some new information for people to start looking at.” At that point, she introduced me to Lenora, who had been fielding similar questions and we’ve been working on the conference together ever since.
Dack: This is going to be interesting. I think the industry is really looking forward to hearing about the ideas discussed and the outcome of this event. Thank you for sharing.
Dunn: You’re welcome. This will be fun because I work with one part of the semi-additive process, but I’m excited to hear about all of the other options too.