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Wiring part 5 : Printed Circuit boards


Step 1 :  Slide.

This slide is made ​​from Cadsoft Eagle, a CAD software for electronic circuits.
There is a free version (freeware) of this software
(see Links page).
You can also use the slides presented in various magazines, websites, etc.. . .

This Slide is printed on a simple printer HP Inkjet 840C using a transparent film.
Here I use "HP Premium Transparency Film. "

Caution, this film has a smooth face and a grainy face, observe good sense!
To print the slide, I set the printer to 'Black and White "and" Best printing quality"
Last advice: do the first print on normal paper, check the sizes of the print and if OK, print the slide.
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Step 2 : Ultraviolet processing.

We are now going to  transfer the design of the slide on a  ultraviolet sensitive circuit board.
Either you buy the pre-sensitized board, or you do it with a special varnish spray.

You can easily make this ultraviolet processor device with plywood and glass. You will find the ultraviolets tubes from RS Components (see Links page).

Exposure time: 1 to 2 minutes according to quality of the ultraviolets tubes and of the photo sensitive varnish. (test it)

Caution: Despite its pre-sensitization to ultraviolet, the varnish is sensitive to light, avoid exposure to the  light rich in ultraviolet (sun, fluorescent tubes)
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Here are the various products and accessories needed for the realization of printed circuits.

Left to right:

Developer (2 kinds)
Safety gloves and safety glasses
Ferric chloride (2 kinds)
Containers and essential accessories.
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Here are the baths ready for use.

Left to right:

Developer bath

Rinse bath

Ferric chloride bath

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Step 3 : Developer

Here we use a specific PCB developer.

You see 2 different packages according to their origin:

VELLEMAN dose for 1L  or RS Components 500 gr pot.

I prefer to use the 2nd because it's cheaper, 50 grams are enough for a 1L bath.
I go to my chemist with small plastic bags and I ask him to weigh portions of 50 grams!

Preparation: 1L warm water for 50 gr developer, stir to melt the crystals. . . it is ready.


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Here is a circuit under developing, you see clearly appearing the traces on the circuit.

Gently shake the circuit during soaking to quick, but be careful not to scratch the surface of the circuit, the varnish coating is mechanically fragile.

Soaking time: 2 to 5 min according to bath quality, visually, the developing is ready when traces are properly visible and have a good contrast with the rest of the circuit.
If the contrast is low after 4-5 minutes, it is missed!
Varnish is of poor quality or too old UV tubes or inactive developer bath.
After 2 or 3 circuits of 160 x 100 mm, the developer bath must be changed, do not keep it to use another day!

After developing, the circuit must be rinsed properly, be careful not to damage the varnish with your fingers, do not rub or wipe!
Simply rince it in a bath of cold water or under the tap.
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Step 4 : Chemical process.

The etching is done using a corrosive to the copper. The most frequently used is ferric chloride.

Preparation: 1 L hot water (40 to 50 C) for 1 kg of ferric chloride, stir to melt the pellets. . . it is ready.

Warning: ferric chloride is a corrosive, wear safety glasses and gloves while using it. It is also a  clothes destroyer, a stain. . . your clothe is lost. . . must know!

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Here the circuit during the etching, I use a plastic spoon to "stir" the circuit during this operation.

You can also use a tank specially designed for this purpose, with air bubble pump and heating resistor (the type used in aquariums). Everything depends on the number of printed circuit boards that you will achieve. In my case, their numbers do not justify such an investment. . .
Up to you!
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After etching, the circuit must be properly rinsed with water.

After this rinse, clean the working surface with isopropanol (isopropyl alcohol) to remove the remains of photo-sensitive varnish.

Here the circuit after the rinsing and cleaning.
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Step 5 : Cutting.

When you put several circuits on a single board, they must now be cut.

You can do this either by sawing or by cutting into the circuit with a cutter, several passes with the cutter and then fold the circuit at the location of this cut.
I prefer the second option because it avoids losing the width of the blade. Up to you.

A little bit of sanding paper on the edges . . this is it !
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Step 6 : Drilling.

For the components wires, drill 0.8 or 0.9 mm.

Drill 1.2 mm for soldering lugs.

A Dremel in a stand is very convenient for this operation.

Caution: Do not drill too big, the bigger the holes will be, the smaller the copper pads will be.
Use a speed of rotation as large as possible, otherwise the epoxy that makes your PCB will break your bit !
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Another view of the drilling operation.
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Step 7 : Wiring and tests.

After drilling, you have to solder the components on the circuit and you must also test its proper functioning.
Indeed, it will be much harder to do these tests when the circuit will be installed on the layout.

In addition, you'll never be sure to identify the problem, circuit, wiring, power supply ? ? ?

Here is the test of a current sensor, note the small resistor of 10 K ohms which short-circuits the rails, it determines the minimum value of current detection.

And now, your circuit is ready to be installed on the layout, you are sure it works !
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