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Etching a Printed Circuit Board Using the Immersion Process

A printed circuit board should be etched first before electronics parts can be attached to it. There are various processes you can use to etch a PCB. This article will discuss the simplest of them all: the immersion process.

The immersion process is a chemical etching technique. It is the widely-used method for etching a printed circuit board. It is commonly used by hobbyists. Together with add-on techniques, this method is also used for small-scale production. A PCB is just dropped to a non-metallic basin that contains the etching solution. The quantity of the solution must be large enough for the surface of the PCB to be completely submerged.

printed circuit boardThe standard product used for small-scale PCB etching is ferric chloride. This acid is also the one you will use in creating the etching solution. The steps for the immersion are as follows:

1. Created first a masked printed circuit board. Without the mask, all of the board’s copper surface will be eaten away by the etching solution.

2. Just pour the solution into a non-metallic container or basin. The combination of the basin, or container, and the solution is called the etchant bath. You can either use of the following forms of the chemical:

a. the liquid solution – use this solution undiluted

b. the solid pellet type – a suggested ratio is 250 grams of pellets for every 500mL of water

3. Drop the masked board to the etchant bath. The solution’s quantity must be sufficient enough to completely submerge the solution.

4. Agitate the container to speed up the etching process. You can also use heat to increase the etching rate. You can heat the solution to at most 135 degrees Fahrenheit, or 55 degrees Centigrade.

5. You can also use additional techniques to speed up the rate even more:

a. spray etching – the etchant solution is sprayed on the printed circuit board. The solution that settles to the bottom of the catch basin are then sucked in, and re-sprayed by pumps.

b. bubble etching – high-pressured air is passed through the bath

c. splash etching – uses a paddle to splash the boards with the solution. The splash paddle is driven mechanically by a motor.

6. Observe the unmasked portion of the board. Remove the PCB from the bath once all the exposed copper has been eaten away.

7. Take note of the etchant’s color, if another PCB is to be etched. The solution may be already saturated with copper. Replace the solution immediately. A saturated solution may look mossy-green due to the copper byproducts. These byproducts can make your solution less effective.

8. Carefully dispose of the solution. This solution is toxic and corrosive, due to its copper and iron content. It is illegal in some countries to pour the solution down the drain. You can either do one of the following:

a. You must contact your waste disposal utility company to learn the proper procedures in disposing these chemicals.

b. You can add sodium hydroxide or sodium bicarbonate (or baking soda) to neutralize the acidic content of the solution. You can test its pH level if you have a litmus test paper. Stop when the pH level goes neutral between 7.0 and 8.0. The copper will settle down the container as sludge. Wait for the sludge to settle completely, and pour off the liquid to another container. Collect the sludge and dispose of it completely. Pour additional water to the liquid to dilute the chemicals further. Pour the diluted water to the drain.

Take note that ferric chloride is a hazardous chemical. It can generate odors which are very unpleasant. Its vapors are a health risk. Its liquid can also cause stains, and even mild burns. This chemical must kept out of reach of children. The standard immersion process for the printed circuit board will always contain this chemical. It is, therefore, important to first establish a better understanding of it before etching your PCB.

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