Controlling Hazardous Dust from PCB & Electronic Abrasive Blasting

Abrasive blasting is commonly used to remove a thin layer of conformal coating from electrical components or printed circuit boards (PCB).

Conformal coatings protect such components against a variety of environmental, mechanical, electrical and chemical problems.

However, when a PCB needs changes or repairs, the conformal coating surrounding the work area must be removed.

The type of conformal coating used dictates which method of removal would be most effective.

Conformal Coating Spot Removal Methods
Epoxy Mechanical, Abrasive
Acrylic Thermal, Mechanical, Abrasive
Urethane Chemical, Abrasive
Silicone Thermal, Mechanical, Chemical, Abrasive
Parylene Thermal, Mechanical, Abrasive
Ultraviolet-cured materials Thermal, Mechanical, Chemical, Abrasive

Examples of abrasive cutting media include aluminum oxide, biological medias, sodium bicarbonate and other plastic cutting medias.

The basic process of abrasive blasting is introducing a cutting media into a compressed air stream which is ejected through a hand held nozzle.

The air stream is directed at a component on the PCB that has a conformal coating applied to it that you wish to remove.

Respirable hazards of cutting media

In their standards on ventilation, the Occupational Health and Safety Administration (OSHA) says abrasives and the surface coatings on the materials blasted are shattered and pulverized during blasting operations and the dust formed will contain particles of respirable size.

The below chart outlines common cutting media and their respective effects:

Cutting Media OSHA Exposure Limits Side Effects Engineering Controls
Aluminum Oxide PEL: 5 mg/m3TWA: 15 mg/m3 Material is irritating to mucous membranes and upper respiratory tract. May cause lung injury. Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommendedexposure limits. If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants

below the exposure limit.

Sodium Bicarbonate TWA: 5 mg/m3 May cause respiratory tract irritation. Repeated or prolongedinhalation of large amounts may cause metabolic abnormalities. May affect the blood, kidneys, respiration, and cardiovascular system. Severe toxicity may also affect behavior/central nervous system. Same as above
Silicon Carbide TWA: 5 mg/m3 May cause respiratory tract irritation with coughing, and shortness of breath. Same as above
Acrylic Plastic Abrasive None Gross overexposure to nuisance particles, regardless of how generated, may cause irritation of the respiratory tract. Provide sufficient ventilation in volume and pattern to keep airborne levels of methyl methacrylate below 100ppm and dust levels below 10mg/m3.

Dust containment and ventilation

In order to reduce the amount of respirable dust entering the operator’s breathing zone, consider a ductless containment hood with HEPA and Carbon filtration.

Our Ductless Containment Hoods, also known as Ductless Fume Hoods, are self-contained workstations that utilize a powerful fan to pull harmful dust and particulate away from the operator.

These systems require no exterior ductwork and their lightweight, modular design makes them easily portable around a room.

Clear, anti-static vinyl curtains are available that attach to the face opening of the hood, offering greater dust containment while still allowing the operator access to the interior of the hood.

We also offer custom hoods for applications requiring a unique configuration.

Contact Sentry Air

For more information about conformal coating removal or to receive a free quote, contact Sentry Air Systems at 800.799.4609, sales@sentryair.com, visit www.sentryair.comor fill out the feedback form below.

Resources

OSHA Standards on Ventilation

Conformal Coating Removal Techniques – Hal Horrocks, NEPCON West