Routine questions & their easy answers...

This page contains answers to common routine questions handled or faced by me in electronics, along with some tips and tricks
that I have found useful during my long experience and presented here as questions...

1) How do I make a PCB of the given circuit?

2) What is the step-by-step process of making a PCB?

3) What is the toner translation method?

4) What is the toner translation method?

5) How to expose the artwork?

6) What is plating, tin plating in particular?

7) How should I drill holes (actually such small holes) in the hard copper clad?

How do I make a PCB of the given circuit?

The designing of PCB is an art. But anyone of you can perform this artistic task. The task consists of following important steps. You will need some material ready for this task. Its list is given below.

First of all collect the components required for your circuit. Then note down the REAL SIZES AND DIMENSIONS of the components to be used, like transistors, diodes, ICs, electrolytic capacitors, 1/2W, 1/4W resistors etc.
For a general purpose transistor like BC 548 or SL100 or so, its takes 3-holes in triangle of the veroboard like ...
For a 14-pin IC like the TTL IC used in digital circuits like .  .
The leads distance between the terminals of a 1/4 Watt resistor  .    .
For an electrolytic capacitor of 1000mfd to 5000mfd  .  .
Else you can always test the sizes of different components just by inserting them in the appropriate holes of a veroboard. So that you will get the exact size of the particular component. Have a look at one example of PCB and observe how the components are arranged on it.

What is the step-by-step process of making a PCB?

Now using these dimensions and the structure of the circuit given on paper, first draw two lines which will indicate the connection of supply lines i.e. +ve and -ve terminals of the battery. Also the list of material required for making PCB is as follows -
Permanent marker pen (black or red color only).
Copper clad, on which the PCB is to be drawn.
Ferric chloride (FeCl3 preferably in anhydrous form).
Handheld drilling machine. A 0.5mm drilling bit (this bit is very delicate, handle it very carefully).
A 10mm drilling bit for making holes at the corners of PCB for screw fitting.
One small veroboard without any components mounted on it.
Sharp and small needle.
One plastic tray with flat bed.
Some lukewarm water. The total list and relevant details are also given here.
Now using permanent marker pen draw the layout of PCB as per the given circuit. While drawing a track, if you want to bend it, then the angle between its two edges must be an obtuse angle.
Now arrange the other components accordingly and follow the procedure given in the article of designing the PCB.

What is the toner translation method?

Second method is by using an electric iron (toner transformation method). For this you need the mirror image of the circuit layout. Then print this mirror image using a laser printer (set the toner deposit to high i.e. Image will look dark). Place the image on the surface of clad board upside down. Heat the electric iron and place the iron on the paper having image which is now on the surface of the clad board. Keep the iron for some seconds. Do not heat excessively. Then the toners on the image get transferred to the clad board. After this put the clad board along with the sticky paper on hot water and kept for a long time. The paper becomes lousy. Now remove the paper from the clad board carefully. Do not remove the sticked toner. Now you will get the layout on the clad board. The next step is the process of removing copper which are not covered by the layout.

How the etching of the PCB is done? Which solution should I use?

For etching process we need ferric chloride (Fe Cl2) solution. About 100 ml of tap water should be heated to 85 degree Celsius and 30-50 grams of ferric chloride added to it. The mixture should be thoroughly stirred, and a few drops of hydrochloric acid (HCl) may be added optionally to speed up the process.

The board with its copper side facing upwards, should be placed in a flat bottomed plastic tray and the aqueous solution of ferric chloride poured in. The etching process will take25-60 minutes to complete, depending upon the size of the PCB. After etching the board should be clearly visible. If not allow it to stand in the solution for some more time. The paint (toner, OHP marking) should be removed with the help of alcohol or petrol. The etching solution may be preserved for later use until its color turns green.

After the etching is complete, holes of suitable diameter should be drilled using a power or hand drill. 1mm bit should be used for IC holes, 1.25mm for resistors and 105mm for diodes, 3mm or 5mm for mounting nuts and 8mm for potentiometers, switches, etc.

Now the PCB should be scribbled clean until a shiny finish is obtained. The PCB may be tin-plated using an ordinary 35W soldering rod along with solder core.

How to expose the artwork?

The photo resist board needs to be exposed to UV light through the artwork, using a UV exposure box. UV exposure units can easily be made using standard fluorescent lamp ballasts and UV tubes. For small PCBs, two or four 8-watt, 30.5cm tubes will be adequate. For larger (A3) units, four 38cm tubes are ideal. To determine the tube-to-glass spacing, place a sheet of tracing paper on the glass and adjust the distance to get the most even light level over the surface of the paper.
Even illumination is a lot easier to obtain with 4-tube units. The UV tubes you need are sold as replacements for UV exposure units, ‘black light’ tubes for disco lighting, etc. These look white, occasionally black/blue when off, and light up with a light purple. Do not use shortwave UV lamps like EPROM eraser tubes and germicidal lamps that have clear glass, because these emit shortwave UV which can cause eye and skin damage. A timer that switches off the UV lamps automatically is essential, and should allow exposure times from 2 to 10 minutes in 15- to 30-second increments. It is useful if the timer has an audible indication when the timing period has completed. A timer from a scrap microwave
oven would be ideal.

What is plating, tin plating in particular?

Tin-plating a PCB makes it a lot easier to solder, and is pretty much essential for surface mount boards. Unless you have access to a roller tinning machine, chemical tinning is the only option. Unfortunately, tin-plating chemicals are expensive but the results are usually worth it.
If you don’t tin-plate the board, either leave the photo resist coating on (most resists are intended to act as soldering fluxes) or spray the board with rework flux to prevent the copper from oxidizing. Room-temperature tin-plating crystals produce a good finish in a few minutes. There are other tinning chemicals available, some of which require mixing with acid or high-temperature use. For more information read the guide.

How should I drill holes (actually such small holes) in the hard copper clad?

If you have fibreglass (FR4) board, you must use tungsten carbide drill bits. Fibreglass eats normal high-speed steel (HSS) bits very rapidly, although HSS drills are alright for odd larger sizes (>2 mm). Carbide drill bits are expensive and the thin ones snap very easily. When using carbide drill bits below 1 mm, you must use a good vertical drill stand—you will break drill very quickly without one.
Carbide drill bits are available as straight-shank or thick (sometimes called ‘turbo’) shank. In straight shank, the whole bit is the diameter of the hole, and in thick shank, a standard-size (typically about 3.5 mm) shank tapers down to the hole size. The straight-shank drills are usually preferred because they break less easily and are usually cheaper.
Small drills for PCB use usually come with either a set of collets of various sizes or a 3-jaw chuck. Sometimes the 3-jaw chuck is an optional extra and is worth getting for the time it saves on changing collets. For accuracy, however, 3-jaw chucks aren’t brilliant, and small drill sizes below 1 mm quickly form grooves in the jaws, preventing good grip. Below 1 mm, you should use collets, and buy a few extra of the smallest ones, keeping one collet per drill size, as using a larger drill in a collet will open it out and it no longer grips smaller drills well.

More questions and their relevant answers to follow. If you want to discuss a topic in particular,
please give me your feedback on my email address: dsvakola@hotmail.com