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Printed Electronics Circuits: Get on the Bandwagon
November 19, 2009 |Estimated reading time: 5 minutes
Printed electronics and nano technology are revolutionizing the product identification and inventory management industry. RFID tags provide a multitude of information to manage the inventories of giants retailers like Wal-Mart. Of course, these devices needed to get to a certain price point, especially for the big W.
Tags today are being manufactured and sold by the millions and at a profit because their manufacturing process has been streamlined. Roll-to-roll, direct deposition of conductor traces (DDCT) utilizing nano particle conductive ink and ink jet printing methods have made this possible.
Lately, many companies have introduced - or will soon introduce - a number of innovative conductive inks, largely as a result of R&D efforts fostered onward by the energy crisis. Some of these firms are large players who see the potential market: Inks used to cover areas larger than football fields in the quest of harnessing solar power.
PEC and our Industry
The PCB industry produces millions of square feet of boards every year, yet we are overlooked by these same companies because we are considered a commodity that generates no profits.
Ironically, without the PCB there would be no electronics industry.
Ever since the demise of the large captive PCB producers, we have as an industry lost most of our R&D efforts. The formation of giant EMS firms also did little to push PCB innovation. These companies are too busy with moving the technology to Asia, making carbon copies of the US plants they once occupied.
Equipment manufacturers with little resources today are satisfied with simply fine-tuning existing equipment to meet performance demands. Personally, I wonder why the plug hasn't been pulled on the large publically-owned consumables suppliers with divisions that cater to our industry.
PEC can and will change the way that "printed" circuits are made. It is inevitable. The questions remain: Will our PCB industry grab hold of this opportunity or will we simply disappear and be an anecdote in Wikipedia? Will the printed electronics industry become the PCB manufacturers of tomorrow?
PEC Technology
PEC is a technology that can provide existing PCB shops the required R&D products to form tomorrow's interconnect manufacturing process with little investment. The technique itself is relatively simple, and thanks to nano technology, the proper ink formulations needed to produce the PEC are now available.
PEC, as opposed to inkjet deposition, can create ultra-fine-line conductors with a cross-sectional value, reducing the conductor's resistance. Using a base unclad laminate, the first component of PEC is applied using silk screening equipment. This specially formulated LPI dielectric ink is deposited at about 1-1.2 mils thickness, depending on screen mesh selections. Extra layers of the dielectric, if desired, will provide for thicker conductor lines.
Tack-cured (up to four layers, so far) and then exposed using ordinary UV exposure units, the LPI is spray-developed on typical developing equipment and chemistry. What remains is a coating on the substrate with trenches and pad openings. See Figure 1.
Figure 1. PEC developed LPI dielectric
PEC's second component is a nano technology silver conductive ink which is applied onto the surface of the LPI. Filling of the trenches and pads is accomplished and the conductive ink is cured. The ink fuses into a solid mass with a slight deposit on the surface of the LPI, which is easily removed.
The next step is a repeat of the first, except that this interconnection layer will be a via formation layer only. Coat, tack, expose, develop and silver fill.
Because the LPI is never stripped off and the entrenched silver conductive ink is level with the top of the LPI, everything conductive is flush to the dielectric. (Figure 2)
Figure 2. PEC 4 mil lines/space flush silver
The same process is repeated for the second conductive layer.
The result is that the interconnect "vias" are buried and there is a 100% metal connection to the first layer. In the end, anything similar reliabilitywise to a PCB PTH interconnect has been eliminated.
Figure 3. PEC .004" flush silver conductors
The process is repeated for as many layers as is required by the design. The last top layer's pads are left exposed for component mounting. All circuitry and interconnections are buried.
Figure 4. PEC dielectric on FR-4/copper/silver-filled
An interesting aspect about this technology is that every layer constructed can be reworked after an electrical test is performed. Thus, traditional scrap rates are tremendously reduced and profitability increases.
Nowhere in this process description were the following mentioned:
- Inner layer fab
- AOI
- Oxide
- Multilayer pressing, post lamination tooling
- Drilling
- Deburr, HP, ultrasonics
- desmear, etch-back
- Metalizing (electroless or other)
- Metal finishing (Cu, Sn)
- Strip, etch, strip
- Waste water treatment
- DI water generation
As a result, PEC requires no wastewater treatment. It is overall an environmentally friendly process.
Should a NEW manufacturer decide to start building PECs, the capital equipment outlay is minimal, because many of the old process steps are eliminated. In parallel is the reduced footprint of the factory floor, again contributing to major savings in manufacturing costs.
Power, water and compressed air consumption - often overlooked in the actual cost of manufacturing PCBs - are reduced to just a small percentage.
Existing PCB manufacturers can easily incorporate PECs into their product portfolios. They also have an opportunity to experiment with packaging options.
PEC can be created at all levels, including university research, hobbyist and small enterprise. There is no need to get into chemistry to make even the simplest boards for prototyping. PEC can be introduced into even low-tech shops with no multilayer capabilities and allow the facility to create HDI multilayer product.
PEC inks are available in "eval" kits to enable current PCB producers to R&D and evaluate - at minimal cost - the potential of this technology. With its obvious manufacturing benefits comes an opportunity for an existing firm to open up an R&D file on the project and claim government funding based on technology, education, green manufacturing or business development/marketing angle.
As Ray Rasmussen said in the title of his column on printed electronics, "This One Will Come Back to Bite Us." With that said, a question arises: Will there be a need for the PCB quickturn and prototype fab shop in a few years if a reliable PEC be built in nothing more than a small corner of a plant with a screen printer, exposure, developer, oven and a drill/router?
Best to get on the PEC bandwagon before the rug is pulled out from under us.
Mike DuBois is an industry veteran who dates back to military PCB manufacturing using shoe eyelets for interconnection of layers. As materials manager for value engineering and corporate projects manager for Circo-Craft (Viasystems), Mike played a leading role in the company's introduction of SMOBC, LPI, multilayer manufacturing and thick-film ceramic hybrid manufacturing. Independently designing equipment, processes and consulting, he later joined DAPC with the scope to purpose design and build their high tech PCB facilities. Joining the ranks of a growing distribution firm, Mike is involved in diversification efforts and searching for alternative PCB processing methods. He can be reached at mdubois@caledoncontrols.com.