Parylene Coating Blog by Diamond-MT

3 Key Properties of Acrylic Conformal Coating

Posted by Sean Horn on Fri, Aug 04, 2017 @ 07:39 AM

Conformal coatings made of acrylic resin (AR) are very popular, because of their distinctive beneficial properties. They protect printed circuit boards (PCBs) and similar electronics from corrosion, dirt, dust, fungus, moisture, and thermal shocks. Exceptionally user-friendly, liquid AR can be simply applied by brush, dip, or manual/robotic spray, generally resulting in the fastest turnaround-time of all conformal coatings. Ease of application and rework generates low cost for both manufacturer and client. AR’s moisture protection is also very highly rated, adding to its utility for a wide range of coating uses.

Ease of Application/Rework

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Acrylic conformal coatings are very easily applied by standard wet methods. As one‐part systems, there are similarly few obstacles to their rework or removal. Liquid methods for acrylic conformal coatings most prominently encompass brush, dip, spray or robotic techniques. Method selection varies according to the:

  • product requiring coating,
  • it’s substrate’s surface complexity,
  • difficulty of masking requirements
  • quantity of items being coated,
  • performance requirements of the AR-coating during operation,
  • assignment throughput requirements.
  • operators’ skill level.

In accordance with IPC-610, film thickness varies between .002” and .005” inches.

Application methods involve:

  • Brushing’s slower coating process is suitable for low-volume application, finishing and repair. Larger-volume brushing results in often inferior surface finish, with defects like film-bubbles commonplace. Skilled operators are suggested for film-application to assure quality outcomes of appropriate (and limited) thickness.
  • Dipping’s very repeatable processing can generate the highest-volume production, but requires expert masking to assure assignment quality, since components are submerged, assuring complete AR-penetration while immersed. The potential leakage-factor limits dipping-application for many assignments.
  • Suitable for low and medium volume processing, dedicated spray booth coating uses a spray aerosol or gun for application. If the PCB is appropriately clean and the coating has no adhesion issues, processing with a skilled operator can generate finish superior to all other methods.
  • Fast and accurate robotic atomized spraying is the best method for high-volume applications, providing components excellent coating coverage as well. Applicator technologies program material flow rates and viscosity, moving above PCBs, dispensing AR to precise, selected substrate regions.

AR curing seldom exceeds 30 minutes, making it an excellent option when a short turnaround time is necessary to meet production scheduling. AR coatings are easily repaired by solvent-application to the region requiring attention. They also have the capacity to be soldered through if solvent application is unsuccessful. The fact that solvent-removal of acrylic coatings is possible with even weak solvents like isopropyl alcohol or xylene, renders AR unsuitable for many coating purposes.

Low Cost

AR’s lower costs are directly connected to straightforward application and/or rework procedures. Very simply, AR application requires less time to complete than coating with other conformal film materials, whether liquid epoxy, silicone or urethane, or vapor-deposited parylene. The manufacturing costs of liquid conformal coating application are invariably driven by labor and the complexity of the process. In this case, AR’s ease of application emerges as the clear winner, lowering production expense considerably; also, by limiting the amount of touch time involved, costs similarly decline.

Moisture Protection

AR offers superior moisture protection, conformally-coating PCBs, which can be subjected to harsh operating conditions. It generates dependable, long-term defense from environmental developments that present obstacles to appropriate functioning, including:

  • rain and salt seawater,
  • moisture condensation,
  • water spray and
  • similar liquidized threats to component performance.

Quick-drying AR is recommended; it withstands humidity during component operation, resisting moisture-development within the assembly,

Conclusion

Acrylic resin is the most commonly used compound in the conformal coating industry, for coating PCBs and similar electronics. Despite lower abrasive/chemical and solvent resistance, AR coatings nevertheless provide good acid and base protection. Acrylic conformal films are invariably applied, cleaned, reworked and removed easily. These factors combine with low production costs and superior moisture protection to enhance acrylics’ popularity for many simpler conformal coating processes.

In addition to the properties mentioned above, acrylic conformal coatings provide fair surface elasticity and overall component protection. Other advantages include dielectric properties capable of withstanding most static/voltage discharge, and quick-drying to a clear, salt/fungus-resistant conformal finish, achieving maximal physical properties in minutes. AR conformal films also:

· do not shrink during operation,

· display low glass-transition temperatures,

· provide considerable post-application flexibility, and

· fluoresce under UV light for simplified inspection.

These benefits recommend AR films for a wide range of less complex conformal coating assignments.

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Tags: acrylic conformal coating, conformal coating, conformal coating properties