This technical information has been contributed by
Plastic-Metals Technologies

Thin-film Metallization Protects Electronic Circuitry from Harmful Noise Interference

EMI RFI Shielding

A job shop situated near Portland, Oregon is one of the few companies in the country that perform thin-film metallization, a specialized type of work that only a handful of companies accomplish mostly for decorative or cosmetic applications. Few companies, however, focus primarily on shielding for electromagnetic interference (EMI), radio frequency interference (RFI), and electrostatic discharge (ESD).

As all engineers know, electronic circuits make what is known as noise. Because noise can interfere with other electronic devices, product manufacturers need to make sure that their devices aren't susceptible to outside interference, or that their products don't give off noise. For medical parts, it's imperative that the parts don't receive any outside signals that will throw off their operation in critical situations. And for cell phones, it's necessary to keep them from emitting too much microwave energy that could be harmful to end users.

Plastic-Metals Technologies Inc. is the Tigard, Oregon job shop—one of only about five companies in the country—that applies thin films of metal to plastic parts for electronic noise shielding. The ultra-thin coating is less than one micron, a millionth of a meter. Keeping in mind that it takes 10,000 angstroms to produce one micron, a primary copper coating will often be 6,000 to 7,000 angstroms, and a second metal could be 3,000 to 4,000 angstroms.

This esoteric methodology, which is basically a vacuum deposition (evaporation) process, has been used in the automotive industry for many years to decorate parts. But in the past decade, more emphasis has been put on giving electronic devices electromagnetic compatibility (EMC), an industry standard for the negation of incoming and outgoing static interference.

"What sets us apart from the few companies that do this work is the fact that most only use one metal," says Richard Allen, a co-owner and president of Plastic-Metals Technologies (P-MT). "With our process, we can apply two metals all in one process, putting them down one at a time in layers. We start with copper and then add nickel, aluminum, stainless steel, or other metals."

Two-metal Process Proves More Effective

Copper is the most effective shielding material in thin-film metallization. "The thing that separates us the most from about five other companies is we are one of only a few that uses copper," Allen affirms. "Most of them use only one metal, although it does not shield as effectively as our two-metal process. I think our process is fairly unique because we can apply two metals with excellent adhesion and still keep down the cost."

Plastic-Metals Technologies was founded in 2002, and now has a 14,000-sq-ft facility operating with 15 full-time and four part-time employees. In 1993, at a firm known as Strategic Finishing, P-MT initiated the process that it uses today. Most of P-MT's present staff members have been with the company from the beginning. The company started on its own path in 2002, and then purchased the other firm in 2004. The metallizing company has been ISO 9000-certified almost three years, and its process has several Underwriters Laboratories certifications for adhesion with different plastic substrates. A UL certificate tells a customer that every process that goes into the making of the final product is certified by virtue of the testing and QC that is actuated.

P-MT's primary markets are electronic devices, many hand-held. About 75% are used for the consumer and trade electronics and medical fields. The company processes parts for resuscitation units and other EMT devices, intensive-care monitoring equipment, and other medical devices used in hospitals and doctors' offices. Plastic-Metals Technologies works on black boxes for helicopters, enclosures for test and measurement equipment, a support frame that goes in an airplane cockpit, cases for hand-held GPS systems, and cell phone enclosures and battery cases.

Inside the vacuum chamber, thin-film metallization is achieved by activating a solid piece of metal that is inserted into a tungsten filament. The shielding metal is evaporated into microscopic molecules that bond with the plastic material. Because the process is handled in a vacuum, no heat is transferred to the parts.

"We have three sizes of chambers, 30-inch diameter, 48 inches, and 72 inches. Sensors are inside each chamber that measure the thickness of the metal being applied," Allen explains. "If we are applying two metals, the control processor in conjunction with the sensors will turn off the first metal filament and then turn on the filament for the second one automatically. When the process is finished, each metal will have less than a one-micron coating, which is enough to shield 99% of the products on the market. Because of our testing, we know that there is no necessity to put on a thicker coating."

Since conductive painting is the process frequently used for electronic shielding, most design engineers are not familiar with the metallization process. Many of the engineers that P-MT talks to are of the belief that thin thicknesses are not enough to crowd out interference. The in-house testing that P-MT performs usually alleviates an engineer's wariness about the microscopic coatings.

P-MT contends that the way its vacuum chambers are set up gives them so much latitude and efficiency with metallization. The company uses the same type of Stokes vacuum chambers—which have been around for about 30 years—as those used elsewhere, but the similarity stops there.

"We build our own vacuum chamber by first finding a machine that is out of production," says Allen. "We'll completely rebuild the machine to fit our process. Our competitors have vacuum chambers that are similar to ours, but our machines have a more sophisticated control panel that makes them fully automated. With our equipment, we can make the process very consistent and repeatable. And we can also maintain the tolerances and thicknesses of the metals much more efficiently."

Metallization Process Maintained by Exacting Control Panel

Metallization starts when parts are washed in an automated wash line. Once they are washed, they go to a staging area for masking to delineate the affected area or prep work to prepare the part for the chamber. The next step is a loading process, whereby the parts are loaded into a carriage that is slid into the machine. The parts then rotate inside the machine very slowly, and are controlled and monitored by exacting control-panel instructions.

The most prevalent shielding process available covers a part with conductive paints, but painting is expensive and paints are hard to apply in a consistent, repeatable manner.

"It's very easy to apply too little or too much paint, or to coat the surface unevenly," Allen insists. "And in order to get a good conductive coating with paint, it may be necessary to coat the part with a mil (0.001-inch) and a half thickness, which is significantly thicker than one micron. Also, the paint can chip, peel, outgas, and put debris on top of the circuit board. We get a lot of customers who come to us because they are fearful of these possibilities."

Whenever possible, P-MT strives to give an OEM a part ready for final assembly. Subassembly processes like painting, silk screening, fastener hardware insertion, hole drilling, and ultrasonic welding are usually completed by P-MT before metallization takes place. The company can also install lenses and lights into plastic enclosures or cases after parts have been metallized.

The only tooling required for the process is the building of fixtures. Laser-cut stainless steel fixturing is necessary to attach parts to a carriage for loading inside the vacuum chamber. The one-time, up-front charge to build fixtures is anywhere from about $200, up to $3,000 for one fixture setup. Depending on the size of the chamber, the carriage that goes in with the parts will have four sides, six sides, or nine sides. Each side of the carriage is a flat piece of stainless steel. A fixture has to be built for each group of parts to attach the parts to the carriage. The number of parts to be processed and their size determines how many fixtures will be necessary to hold them.

One innovative system that P-MT has created is a high-detergent, non-chemical, aqueous part washing system. It's a conveyorized system, allowing every part that comes into the plant to be thoroughly washed for good product quality and metal adhesion. "I know for a fact that very few companies are washing their parts as thoroughly as we are, which helps us create a high level of quality," says Allen.

Test Data Prove That Coatings Meet Existing Industry Standards

Another one-of-a-kind approach initiated by P-MT is the hiring of outside testing agencies to research how its coatings fare against harmful interference. With the test data, the company is able to prove to existing and prospective clients that its metallization coatings meet or exceed shielding standards. In addition, test data tell them which particular metal or combination of metals will work best for the OEM's application. In an effort to offer as many value-added services as possible, engineering assistance and consultation are always available. Allen says that P-MT tries to spend as much time with a customer's engineers as it does with purchasing people. And while most of the consulting that the company offers is for better manufacturability, P-MT's engineers are willing to perform testing on different metal combinations for maximum shielding.

"We have engineers and a chemist on staff to assist customers," Allen affirms. "Sometimes a client will design a part and have it molded or die cast before they come to us. Then they'll have an EMI issue that could have been solved during the design stage. Clients who have done a lot of work with us usually get us involved early on when new products come on line. Quite often, we'll have plastic injection molders or die casters come to us to help their client with EMI shielding. We can help them design the parts more effectively for shielding."

Metallization Company Welcomes Complex Manufacturing Challenges

P-MT is always willing to formulate solutions for a customer's manufacturing challenges. One instance was a top cover for an emergency resuscitation device that needed to have several different subassembly procedures completed before metallization, including pad printing and painting for labeling and decoration, hole drilling, and ultra-sonic welding for hardware inserting. The secondary work was being handled by several different vendors, causing turnaround time for the subassembly and metallization to total twelve weeks.

"We were able to bring the part into our shop and handle all of the subassembly work and the metallization in about four weeks," Allen recalls proudly. "So we were able to speed up the final output by 66%, saving the client time and money, and getting their product to market quicker. The total cost savings was about 25% to 30% per part."

Right now P-MT is working with the engineers of a company that produce a precision hand-held GPS device. They come to P-MT's plant periodically to monitor the testing of different metals to see which combination will be the best for their parts.

"We can save the time and money it would cost them if they had to go to outside testing agencies multiple times, since there aren't any additional costs for our testing," says Allen. "And we can help them find the metals that will work best for their specific product using our metallization process, instead of them just getting a bunch of tests done and then bringing the raw data to us to sort out. A standard test at these outside agencies can cost anywhere from $2000 to $5000. So with several tests, it would have cost them in the tens of thousands of dollars. We saved them from this high startup cost and saved them time getting to market with their product. Besides cost savings and high quality, it's obvious that we have a lot of value-added services to offer our clients," Allen summarized.

This technical information has been contributed by
Plastic-Metals Technologies

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