A Permanent ESD-Safe Coating With Clear Benefits

 ESD-Safe Coating

EMS and PCB repair facilities that work with static sensitive equipment are very familiar with ANSI/ESD-S20.20 and the challenge of maintaining compliance. You buy all the right benches, mats, straps, bags, and more, sometimes at a steep premium. Then in comes a stray plastic bin, cart, or tool that puts the whole program into question during a customer audit.

That’s where Licron Crystal can save the day.

Techspray Licron Crystal Permanent ESD-safe Coating is a versatile, transparent urethane coating that adheres to metal, plastic, and most other surfaces. It is ideal for converting standard bumpers, bins, tools, and surfaces to ESD­safe, saving expensive replacement cost. The end result is compliant with ANSI/ESD­S20.20, which prevents static damage to sensitive electronic components.

Licron Crystal operates from 0-100% humidity, unlike other temporary coatings that relies on absorbed moisture from the air. The cured coating is durable, will not chip and maintains 107-109 ohms resistivity. Licron Crystal can be sprayed as an aerosol or using a standard spray gun or paint system. As long as the coat is thin, smooth, and even, the finish will be transparent. A grounding wire can then be attached (i.e. by conductive adhesive) similar to an ESD floor.

So to summarize the benefits and properties of Licron Crystal:

  • Rugged static dissipative coating
  • Superior adhesion to a variety of surfaces: glass, plastic, etc.
  • Surface Resistivity of 106 To 109 ohms
  • Humidity independent
  • Transparent finish (if applied thinly and evenly)
  • Operating temperature range up to 302°F (155°C)

 

Why should I use Licron Crystal?

Techspray Licron Crystal can help maintain tools and work surfaces within the ANSI/ESDS20.20 standards set by the ESD Association. Electrostatic Discharge (ESD) occurs when the charges of two dissimilar surfaces with a large electronic potential (difference) equalize instantaneously. The resulting discharge or spark can cause catastrophic or latent damage to electronic components.

Electrostatic discharge happens all the time, especially in dry climates and in the winter season, when there isn’t moisture in the air to help bleed the excess electrons (water is conductive, so allows the electrons to flow more easily). Normally it is nothing more than an irritation, but with sensitive electronics, it can lead to PCB failures.

Without the appropriate equipment and supplies, a worker can generate thousands of volts. SMOS logic devices can be damaged with 250-3000 volts, EPROM devices down to 100 volts, and microprocessor chips as low as 10 volts. Damage can shut down functions or create intermittent problems, and it can either be catastrophic (immediate) or latent (later as in “field failure”). (source: Phil Storrs PC Hardware Book)

 

How does Licron Crystal work?

Licron Crystal is a urethane-based coating that forms a static dissipative matrix over a surface. When it is applied over an insulative surface, such as rubber grips on shear lead cutters, it prevents the surface from generating a triboelectric charge when the tool is handled. In addition, if the operator is grounded, like with a wrist or heel strap, it will allow any excess charge to bleed off in a controlled way. This is because the coating is 106 To 109 ohms resistivity range.

Charge dissipation to ground 

Charge dissipation to ground

 

What surfaces can Licron Crystal coat?

Licron Crystal is able to adhere to a wide variety of smooth and textured materials, including metal, plastic, rubber, and even cardboard. It is ideal for converting standard bumpers, bins, tools, and surfaces to ESD­safe. Like any coating, you need to ensure the surface is clean and oil-free before the coating process. Textured surfaces will generally provide the best adhesion and durability, but it can be applied to smoother surfaces as well.

 

What are the best applications for Licron Crystal?

Licron Crystal can be applied to a wide variety of smooth and textured materials, including metal, plastic, rubber, and even cardboard. Good examples of Licron Crystal applications include:

  • Bins and packaging
  • Work stations and carts
  • Tools and equipment
  • Enclosures and work surfaces

Keep in mind Licron Crystal is not particularly rugged and chemically resistant. It is not intended to replace ESD-safe mats, flooring, or act as a rubberized dip for tools. It is best for areas with light wear.

 

Licron Crystal applied to Plexiglas enclosure

 

Can Licron Crystal be used on the rapid prototype, 3D printed parts?

Coating 3D printed parts in a rapid prototyping process is a popular application for Licron Crystal. 3D printing wire or filament is used in 3D printers to build prototype or short-run parts without the use of a mold. Starting from the bottom and working up layer-by-layer, the filament is melted according to a 3D computer model.

3D wire comes in a wide variety of materials and colors, but choices are limited for static dissipative materials. Engineers needing to produce ESD-safe rapid prototyped parts can 3D print using standard insulative filament, and then coat with Licron Crystal to add a dissipative surface.

 

How do I apply and cure Licron Crystal?

Licron Crystal can be sprayed from an aerosol or using a standard spray gun or paint system. As long as the coat is thin, smooth, and even, the finish will be transparent. Keep in mind that full coverage, like a coat of paint, isn’t required to achieve the desired static dissipative matrix. A light “dusting” is all that is needed.

With the aerosol spray, hold the can 8 to 10 inches from the surface and make one to two light passes. Shake the can vigorously prior to spraying and reshake occasionally during extended applications. When using a spray gun or dispensing system, there should be a moderate air mix and the best nozzle to produce an evenly atomized spray pattern.

The surface to be coated should be dry and free of dirt, grease, and oils. The aerosol can, coating material (if in a dispensing pot) and surface should be at room temperature. Heavy application or spraying when humidity is over 50% RH may result in a hazy coat. Allow drying 24 hours at room temperature (i.e. 70°F/21°C) for full cure, when final resistivity and hardness will be achieved. Coated parts can generally be handled within an hour. Accelerate cure by placing the coated part in an oven at 120°-150°F (49°- 66°C) for 1-2 hours.

 

How much Licron Crystal do I need to apply?

Keep in mind that full coverage, like a coat of paint, isn’t required to achieve the desired static dissipative matrix. A light “dusting” is all that is needed. A heavier coating may allow for longer wear time, stretching the time between applications, but will not generally change the final resistivity.

 

How do I get a transparent coating with Licron Crystal?

Licron Crystal can be used on Plexiglas, Lexan, and other surfaces where you need a clear coat, but that can take practice and a very controlled spraying process. Heavy or inconsistent coverage can create a bluish, hazy coat.

Keep in mind that full coverage, like a coat of paint, isn’t required to achieve the desired static dissipative matrix. A light “dusting” is all that is needed.  The goal is to apply as thin and even a coat as possible. 2 thin coats, allowing a few minutes curing between coats, is better than one heavy coat. Licron Crystal has very low viscosity, similar to isopropyl alcohol, so will tend to drip if too much is applied. Those drips will cure into a hazy light blue color.

 

Will Licron Crystal damage plastic surfaces?

Licron Crystal is compatible with a wide variety of plastics including ABS, nylon, polycarbonate, polyethylene, polypropylene, and PVC. Licron is isopropyl alcohol (IPA) based, so if you are able to clean a surface with IPA, it should be ok for Licron Crystal. Avoid using Licron on polyoxymethylene (POM), polystyrene, and polytetrafluoroethylene (PTFE or Teflon). To ensure material compatibility, test on an inconspicuous area before general use.

 

How permanent/durable is Licron Crystal?

How often do I have to reapply Licron Crystal?

The coating material itself is urethane (although thin) and is not meant to be as robust as a conformal coating or paint.  It is simply a matrix to hold the dissipative component together and adhere to the substrate.  That said, we’ve found that how long it lasts before a reapplication is required depends on the surface and how much wear and tear it receives – such as banging the tools down on a table, tossing them around, dropping them, etc. 

Any damage (scratches, gouges) will lessen the performance over the surface.  In development testing, we applied Licron to 3 work tables for assembling electrical equipment.  In the areas where the hand tools were used and the equipment was dragged across the table, the surface resistivity remained fairly constant over a 3-month period before reapplication was required.  Each of the 16 test points on the tables were checked daily and then weekly with a SOAR resistivity meter to make that determination.

 

In a real-world example, we have a customer that coats battery pack casings made of textured plastic, which are handled almost continuously 24/7.  After extensive testing, they felt it was more than adequate to prevent static in explosion-proof areas (Class 1, Div 1).  They even “drop tested” the coated units for abrasion resistance by skipping and throwing the cases around a parking lot!  The parts remained firmly in the dissipative range for two main reasons:

  1. For a surface to maintain good anti-static dissipative properties, there needs to be enough coating intact for electrical continuity. In other words, there can be gouges and scuffs as long as the open areas aren’t large enough to become isolated from the remaining coated areas.
  2. The textured surface of the plastic makes this application much more forgiving. Because Licron Crystal has low viscosity and surface tension, it settles into the fine crannies of a texture. While the coating on the peaks of the texture may become worn, continuity can be maintained in the valleys.

So the surface texture can make a big difference in the durability of Licron Crystal. Here are a few examples and how to adjust your testing protocol:

  • Hard textured plastic – Licron will last a long time in the crevices, so they should be ok to check annually.
  • Untextured plastic – If used regularly, check after a month to see how it is holding out, and adjust your testing protocol from there.
  • Rubber grip material – Since there is more friction with a rubber surface, the coating is more likely to rub off. We suggest testing after 2-weeks and then stretching it out depending on the results.

 

Simple monitoring over a period of time will give you a general trend on when Licron Crystal should be re-applied to various surface materials.

 

For more information on Licron Crystal, or if you need technical advice about your ANSI/ESD-S20.20 program, go to www.techspray.com or call 800-858-4043.

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