COSHH Information on Ferric Chloride

Uses/Processes

To produce, by etching away unwanted copper, an electronic circuit board designed to meet a specific requirement. 

The prepared board is immersed in ferric chloride (iron (III) chloride) solution or sodium peroxodisulfate (persulfate) solution to etch away the copper.  The board is sometimes cleaned with a solvent before or after soldering, formerly mainly 1,1, 1 – trichloroethane, now propan-2-ol (isopropanol) or other alcohols (e.g. ethanol).

Assessment

Sodium peroxodisulfate (OES of 2 mg/m3 – 15 min ref period) and ferric chloride are harmful if swallowed and steps should be taken to minimise the risk of ingestion.   Mist produced makes it less suitable for use in a bubble-etch tank.  When used with a small manual developing tray, little mist will be produced.

If the two etchants are mixed, toxic chlorine gas is produced.

Propan-2-ol has an OES of 500 ppm (15 min ref period).  Ethanol OES is 3000 ppm (15 min ref period).  If applied by a brush (not a spray) these concentrations will not be approached in a school electronics area.

Iron salts have an OES of 2 mg/m3 (15 min ref period).  If the solution is prepared with gentle agitation and used in a tank with a lid, the mist produced will be minimised.

Solid etchants and the etching solution can be irritant to the skin or respiratory system.

Controls

Eye protection and protective gloves must be worn when preparing solutions and emptying tanks.  If the processes are carried out in bubble tanks, the lids must be fitted to contain any mist.

Ferric chloride and sodium peroxodisulfate should not be available together in one workplace to eliminate the possibility of mixing.  See over for changing etchants.

Users with cuts or sensitive skin must wear disposable plastic gloves.  The wet boards must always be handled with plastic tongs.

Ignition sources should be removed from the area when using highly flammable solvents and natural ventilation is required to keep the minimise the level of vapour.

If a single bubble-etch tank is used, it is recommended that a base board is used to improve stability.  The tank can be held in an aluminum U-channel with sides at least 100 mm high and screwed to the board.

Storage

Both substances should be stored in a secure, well-ventilated area.  Ferric chloride should not be stored in the vicinity of metals.

Disposal

Solid waste of both etchants should be placed in appropriate containers and passed to an authorised waste disposal contractor.  Used ferric chloride solution should be neutralised with sodium carbonate and flushed away.  Emptying the tank requires  care and a siphon pump is recommended.

If changing from ferric chloride to sodium peroxodisulfate (or vice versa), the tank must be washed out thoroughly before filling with the new etchant.

Solutions of sodium peroxodisulfate should not be stored in sealed containers but may be re-used until they are a deep copper-sulfate blue when they can be well diluted and flushed away.

Immediate Remedial Measures

If swallowed: Wash out mouth thoroughly with water and give plenty of water to drink.  Obtain medical attention.

If mist is inhaled: Remove from exposure.  Keep warm and at rest.  In severe cases, obtain medical attention.

If in the eyes: Irrigate immediately with water for at least ten minutes, holding eyelids apart.  Obtain medical attention.

If spilt in workshop:  Dilute with copious quantities of water and swill away.