Acid Gases in the Fabrication of Microelectronics

If Sentry Air’s chemical engineer, Ben, were to make a one-off printed circuit board (PCB) for his latest project at the local hack lab, he’d likely have to handle some hazardous chemicals.

To make sure his board is clean enough to have conductive pathways etched into it, he might use a solvent such as acetone. To do the actual etching, Ben might use ferric chloride (iron chloride) or an acid.

Toxic Exhaust Gases

Both one-off and large-scale manufacturing of microelectronic components have similar requirements for solvents and etching acids. And both solvents and etching acids have the potential to produce toxic exhaust gases.

OSHA says toxic exhaust gases “can be irritating and corrosive to the eyes, skin, and mucous membranes. Exposure to high concentrations can cause laryngitis, bronchitis, and pulmonary edema.”

We’ve frequently blogged on the respiratory hazards of solvents. This post discusses acid etching, one of many processes that may be used in the fabrication of microelectronic devices.

Acid Etching

Each material to be etched (e.g., silicon, titanium, chromium) may require a particular recipe of chemical etchants.

The following table lists some (but not all) commonly used chemical etchant ingredients with links to agency health and safety resources for each chemical.

Chemical Name
 Links to agency resources
hydrofluoric acid (HF)
nitric acid (HNO3)
hydrochloric acid (HCI)
CDC: Toxic Substances Portal – Hydrogen Chloride
phosphoric acid (H3PO4)
ferric chloride (FeCl2)

All the above agency resources list appropriate ventilation strategies that detail how to ensure the respiratory safety of workers who handle and use hazardous acids.

Respiratory Safety

The fumes produced by etching acids use the human respiratory system as a pathway into the body, where they can cause harm.

Sentry Air’s Ductless Fume Hoods and other fume extractors utilize specifically designed filters consisting of high-grade, activated carbon media that has been impregnated with proprietary reagents for the removal of airborne acid gases. These “acid gas” filters in combination with negative pressure airflow help protect workers by drawing toxic acid vapors away from the workers’ breathing zone and into the filters where they are absorbed.

40″ Wide Ductless Fume Hood, Model # SS-340-DCH,
is large enough to accommodate instruments and
tools within the hood.
Small operations may be well served by our
Portable Floor Sentry, Model # SS-300-PFS, which 
can house multiple filter types for applications that
emit both particulates and vapors.

Acid Gas Filters

Using a Sentry Air Ductless Fume Hood with our Acid Gas Filter reduces the health risk associated with acid etching. As noted in an earlier post on acid gas filters, a typical activated carbon filter doesn’t adsorb acid gas, but our Acid Gas Filter reduces the airborne concentration of acid gas by more than 99%.

Sentry Air Application Specialists

For information on acid gas filtration options for your acid etching process, give us a call at 1.800.799.4609, email us at, or fill out form below to have a Sentry Air Systems Applications Specialist contact you.


Additional Resources

Device Fabrication

Toxic gases