- Buyers Guide
PCBs: Making the Impossible Possible
When Subtracting Doesn’t Add up
Unlike other areas of advancing technology, PCB manufacturing isn’t very “sexy.” It doesn’t begin to compare with the innovation-per-minute, adrenaline pumping pace that semiconductor companies keep. PCB processes are fairly static. Outside of incremental advances in chemistry, photolithography or the advent of things like laser drilling, we pretty much rely on well-founded, albeit old, technology. What progress we have made, has enabled us to barely keep-up with the driving forces of miniaturization and speed. PCB technology has not enjoyed any fundamental, game-changing innovation for decades. In other words, we have risen to meet industry demands by improving the existing subtractive (print-and-etch) processes that is unfortunately fraught with inherent limitations—especially for high performance boards.
For the past several years (at least in North America) the technology of semiconductors and components has definitively outstripped our ability to consistently and reliably keep stride. We are now pressed hard against the limits of print-and-etch technology itself—but it’s the only tool we have. Within the past 30 years or so, a couple of bright stars have arisen promising us the hope of an additive technology that would allow us to apply metals to PCB substrates, instead of etching (or subtracting) them away. Unfortunately, they quickly faded, leaving behind a crusty cynicism towards the viability of additive technologies which lingers to this day.
So, what if there was a truly viable additive solution available? What if we could cut a dozen or so processes out of the equation (saving our customers money and getting far better yields)? What if, we could consistently and reliably offer conductor widths down to 2 mil lines and spaces? What if over and under-etching was a thing of the past and we could offer pristine conductor geometries to RF/Microwave engineers aiding in signal integrity? What if we could do all of this with a water-soluble chemistry that can be washed down city drains and be environmentally conscious without giving up performance and or costing us a fortune (even in California!)? What possibilities would open up if we could metalize 3D surfaces of all shapes and sizes? What if we had an additive process that offered better peel strength than off-the-shelf laminated copper clad substrates? To PCB manufacturers and engineers alike this technology sounds like a fantasy of science fiction proportions. Yet, despite prevailing wisdom and cynicism, it appears that just such a technology has arrived!
A Print-and-Etch Primer
For those of you not thoroughly familiar with the steps of print-and-etch technology, let me give you a brief overview of the subtractive process, before I jump ahead to the newly available additive (or “embedded) alternative.
Print and Etch Steps (Click here for photos of this process)
(For Inner Layers or a single or double sided board):
1. Start with copper-clad substrate
2. Coat panel with dry film photo resist
3. Place photo tool in photo printer
4. Overlay coated panel onto photo tool
5. Vacuum in frame and remove all air bubbles
6. Expose photo image onto coated panel surface
7. Put panel through developer (Sodium Ash-Water rinse-Air dry) Unexposed areas are washed away.
8. Visually inspect for registration
9. Etch panels with chemical etchants
10. Remove remaining photo resist
11. Wash and Dry
(From this point, if it is a multilayer board, the layers would be laminated together, then drilled and the thru-holes would be plated. Afterwards, the outer layers would go through the print and etch cycle process a second time)
Pretty straight forward stuff—as long as you have nice healthy conductor widths and reasonable holes and pad sizes. However, if you have tiny features or need consistent conductor geometries to keep your signal integrity in check, it gets a bit tricky. When your design features shrink to 4 mil pitch or below, or your speed/frequency increases dramatically—there are dozens of ways we can screw up your boards at this point! It’s not because we don’t know what we’re doing, it’s because while we etch batches of boards, the chemistry is changing slightly with each lot. Among other chemical dynamics, the bath is getting loaded with spent copper. Of course we monitor these levels and change the chemistry as needed, but it is not a constant, static chemical balance—it is kept in a “range” suited for optimal etching. Also, etchants don’t only etch vertically; they also etch horizontally meaning that your conductors often have slightly curved sidewalls and are not perfectly vertical. Furthermore, they are not all exactly the same which may play havoc on the performance you simulated vs. what you get in reality. I’ve had more than one RF/Microwave engineer tell me—“we can deal with the conductor variation as long as it is consistent on all the boards.” Trouble is that no matter how hard we try, consistency (on a micro-level) is not achievable with the subtractive process. So we tweak, and do tricks and pull all the black magic out of our hats to do the very best we can. Unfortunately, we have a process that was never intended to achieve the things we are asking it to do today. Oftentimes, if the boards are particularly challenging, we just run many additional panels, knowing our yield will be low. Unfortunately, that cost must be passed on to our customers.
The Impossible becomes Possible
Earlier this year an additive (embedded) technology was introduced at the IPC Apex show in Las Vegas. While IPC does not support or endorse any particular supplier or process, two executives from IPC gave interviews expressing (cautious) optimism regarding the discovery of a viable additive process. eSurface made a memorable splash surprising a whole cadre of “old guys” in our industry. So what is eSurface? eSurface is a patented covalent bond discovered and developed by Dr. William E. Wismann, D.SC TECH. It represents a fundamental shift in the way we will make PCBs in the future. It appears to be a truly viable additive technology that will enable much untapped innovation in the electronics industry and beyond. eSurface uses equipment that already exists in most board shops, with the exception of a 2 retrofit machines which are available from Chemcut and Austin American Tech.
Here are the steps for eSurface:
1. Start with any unclad substrate
2. Apply eSurface covaler bond
3. Photo Image/water rinse/dry
4. Electroless copper plate (up to ½ oz)
Now, I realize I am speaking to mostly RF/MW engineers and layout professionals here. But to people like me who have been in the PCB industry since the 80’s—watching the eSurface process is akin to watching Jesus walk on water. Pick any buzzword: “Disruptive”, “Game-Changing”, “Breakthrough”, none of these are nearly sufficient to express the possibilities that may be afforded by eSurface.
Additive or Embedded?
eSurface is so unique that it almost needs its own category. It is not simply applying metal to the surface of the substrate; it is fusing the metal to the substrate at an atomic level. This defies our typical understanding of the additive process. (See covalent bond definition) The chemistry is partially absorbed into the pores of the substrate and acts as a catalyst to draw metal into that space effectively embedding the metal into the substrate.
So What’s next?
eSurface is based in Carlsbad, California and has a small lab there for demo purposes. They are talking with dozens of OEMs and PCB manufacturers currently. They are licensing the technology to PCB manufacturers and have installed a line in one facility in Silicon Valley to date. They are working with another dozen or so manufacturers in California, with interest growing across the country. I am happy to report that we at Transline Technology are one of these companies. We are in the process of a full technical evaluation, as well as assessing cost and feasibility for our facility. I will be sure to keep you posted on our progress. Meanwhile, you can visit the eSurface website and contact them directly for more information.
The Devil’s Advocate
It is always wise to evaluate new technology with some level of skepticism, and quite honestly I have been trying to “shoot holes” in the claims of eSurface for weeks now with no success. I am collaborating with their technical team now to make evaluation boards, running side-by-side samples using traditional subtractive processes and eSurface. We will then measure performance and mechanical properties from each sample lot. (If you have a board design you want to volunteer, let me know!) Once I have this information, I will be sure to share it with you! Meanwhile, I remain cautiously optimistic that we may indeed be on the threshold of unleashing a new technology that may revolutionize the PCB industry and give us new tools to meet the demands of cutting edge technologies. So buckle your seatbelts and stay tuned!