Used around the world, the VAETEC® Thin Film Deposition Process is a UL-approved technology for coating the insides of intricately shaped plastic casings with a thin, uniform layer of aluminum to provide the shielding characteristics of a metal enclosure without adding weight to the component.
VAETEC® Thin Film Coating is demonstrably superior to conductive spray-painting in virtually all respects, including adhesion, conductivity, and uniformity. As well, the process ensures precise repeatability from part-to-part to ensure that each precisely meets your specs.
- How is VAETEC® Thin Film Metalization different from other “plating” processes?
- How exactly are your plastic parts treated?
- What are the steps in VAETEC® Thin Film Deposition?
- Why thin film coating instead of conductive spray painting?
How is VAETEC Thin Film Deposition different from other “plating” processes?
There are many ways to “plate” a flat plastic surface with metal. But today’s electronic casings are intricate and demand a high degree of repeatable precision for their metal coatings.
If the metal fails to entirely penetrate the interior of the plastic case, then it will remain vulnerable to both electromagnetic and radio-frequency emission or absorption—especially at the extremely high clock-frequencies typical of today’s digital circuitry. As well, its protection against ESD will be compromised.
Precision must be repeatable.
Since it is typical for component or device cases to be uniquely shaped and proprietary, each requires custom tooling for it to be metalized. The centerpiece of this tooling is the vacuum metalizing mask. As the name suggests, its job is to ensure that precise heights and widths of vaporized metal are deposited onto the “mask lines” of the case interior while simultaneously isolating the rest of it from metal deposits.
This process is repeatable and ensures that every plastic case is protected against EMI, RFI, and ESD—no matter how large the run. Over the course of the last two decades, we have designed some of the most complex vacuum metalizing masks to meet our customer needs in the field of medical, defense, and aerospace manufacturers.
How exactly are your plastic parts treated?
Plastic parts are placed in a vacuum deposition metalizing chamber wherein aluminum is vaporized. The vaporized aluminum adheres as a uniform layer onto the plastic—less than 15 microns thick. This provides robust shielding against high-frequency EMI/RFI absorption or emission that is comparable to a totally metallic enclosure. It also allows plastic enclosures to be grounded against ESD just like metal ones. Back to top.
The shielding characteristics of aluminum are surpassed only by silver, copper, gold, and chromium respectively—but only marginally. Silver, gold, and chromium are, of course, prohibitively expensive.
Copper is usually top-of-mind as a conductor. But copper’s DC resistance to current is .0167Ω/in2 compared to .0266 Ω/in2 for aluminum: a difference of only .0099 Ω/in2. Clearly aluminum is the best choice. Back to top.
Steps in the VAETEC® Thin Film Coating Process
- Plastic parts that you ship to us for vacuum metalization are unpacked and carefully inspected upon arrival and inventoried. This allows you and us to keep precise track of your inventory as it moves through our processes, and it also ensures that you receive as many pieces as you send.
- Your packaging is set aside in special storage areas and will be used to return your products to you. This means that you will purchase and use half as much packaging as you would otherwise, and you can re-use that packaging for any future lots you send us, which is expeditious, cost effective, and eco-friendly for both you and us.
- Any pieces we deem too flawed for processing—either by your standards or our own—are bought to your attention by digital photography and email. We can proceed with these pieces if you believe they nonetheless meet your quality standards. Otherwise we can return them to you for refinement to specs, or we can discard them as you direct.
- Depending on your unique product requirements, each plastic enclosure is carefully cleaned in one of two ways to remove contaminants and create bonding sites, thus insuring a uniform bond with the aluminum: (1) manually washed in a chemical bath and then cleaned to a microscopic level in our Plasma Prep chamber, or (2) manually etched via bead blasting with plastic media.
- Your parts are masked using one-of-a-kind tooling, including a vacuum metalizing mask, custom designed for the unique shape and dimensions of your enclosure. Each is then carefully positioned onto a specially-designed rack inside one our state-of-the-art vacuum deposition metalizing chambers, either static or rotating depending on your precise specifications and the dimensional complexity of your enclosure.
- Based on our internal QC sampling plan, before shipping your processed parts back to you, each undergoes a regimented QC examination using sophisticated equipment to assure that adhesion, uniformity, and conductivity meet or exceed your precise specifications. Back to top.
Why not use conductive spray painting?
Prior to Thin Film Coating, conductive spray painting was the most common method of providing metallic shielding to plastic electronic casings. Conductive paints are composed of copper, silver, nickel, or graphite particles suspended in water or a solvent-based matrix. Like common paints, they are sprayed onto plastic surfaces using an air atomizer or airless spray equipment. But there are QC issues with spraying conductive paints onto plastic that can severely compromise shielding effectiveness.
Along with flaking, peeling, and bubbling, spray painting can create inconsistent coating thicknesses, which can adversely affect part-to-part geometric fit. Also, paint buildup within threaded inserts can interfere with screw engagement. Any of these conditions—especially in combination—can allow seaming gaps that not only pass high-frequency radiated energy, but also increase measured emissions by collimating that energy and causing hot spots.
There is also the matter of esthetics—particularly for consumer products. Overspray onto visible or cosmetic surfaces is an inherent problem with spray painting, in no small part because masking techniques for spray painting are generally not as sophisticated as they necessarily are for Thin Film Metalization. It is not uncommon for tape to be used, which can result in blurred, uneven, and/or inconsistent masking lines.