PCB Etching Instructions

["Keith Doxey" <keith.doxey@xxxxxxx>]

Hi All,

As asked for by others, here are the instructions that came with my UV
Lightbox that I use for making PCB's

---------------------------------

INSTRUCTIONS FOR PROCESSING P.C.B's


I.	Electrical connections to the U. V. Exposure Unit Ref. XRIOL


Fit a suitable 3 pin fused plug to the 2 core cable extending from the rear
of the U. V. Unit. The brown lead should be connected to the live (L)
terminal and the blue to the neutral (N) terminal according to the
international colour code. I.e. with the plug cover removed, the (L)
terminal screw is on the right and the (N) is on the left.
No earth is required; therefore the third terminal is not used. Before
replacing the plug cover, fit a 2amp fuse in the fuse holder across the (L)
terminal and ensure that the cable clamp securely holds the cable.

2.	Preparation

Prepare artwork by applying transfers (see Maplin catalogue Page 97) to a
sheet of transparent film Maplin Ref. BW 20W.
The 1/10" grid sheet supplied with the film sheets may be used as an
underlay and as a guide when positioning pads and tracks.  In most cases,
P.C.B's are designed on a 1/10" pitch system as most components are
manufactured with 1/10" pitch mounting pins.
As this is a "positive" working resist system, the artwork may be
used as a
direct 1:1 photo master without the need to produce photo negatives.  That
is to say that when processed, copper will remain in the areas covered by
the black transfers and that the background copper will be etched away
after
"exposure" to Ultra Violet light and "development" in
sodium hydroxide.

3
Developer Solution

Make up a solution of developer by adding 6 grams (1 level teaspoon) of
Sodium hydroxide * to 1/2 litre (a-little under 1 pint) of tap water in a
plastic tray.  Always add the crystals to the water and not the water to
the
crystals.
Cold tap water may be used, but it is preferable to raise to room
temperature
I.e.	approximately 20C.
The quantity will be sufficient to develop 0.2 square metres.  Do not mix
more than you require for each session, as the mixture cannot be stored for
re-use.
Note *	Sodium hydroxide (commonly called caustic soda) is available from
most High Street chemists including Boots.  The specification required is
98
to 100% pearl.
See notes below regarding handling of chemicals.

4.	Etchant

Make up a solution of etchant according to the instructions supplied with
dry etching materials.

5.	Washing

In addition to the trays of developer and etchant, it is desirable to have
2
trays of water for washing after each process unless a running water supply
is available.

6.	Exposure to Ultra Violet light

Remove a presensitised copper board (Ref. BW20V) from its light protective
black plastic bag and observe the copper surface. Unclip the lid of UV
Exposure unit, place the artwork on the glass plate (transfer side down)
and
then place the copper board (copper side down) on top of the artwork sheet,
ensuring that it is correctly aligned and approximately in the centre of
the
available exposure area of the machine. Carefully close the lid so as not
to
disturb the work piece and fasten clips, thus applying pressure to the work
piece and ensuring that good contact is made between the artwork and the
copper board.
Switch on the lamps by operating the switch on the front of the box and
check that the neon indicator is illuminated.  Also check the time and
allow
8 minutes for Ultra Violet light to give suitable exposure.  Longer
exposures of a few minutes are not likely to be detrimental.

WARNING	Due to the low power and long wave Ultra Violet emission from this
unit, the radiation is not harmful.  However it is advisable not to look at
the lamps directly as this may cause some discomfort to the eyes.

NOTE	The pre-sensitised panels may be handled in normal room lighting for
short periods but must not be exposed to direct sunlight or other forms of
strong Ultra Violet light.

7.	Developing

Immerse the exposed board face side (exposed side) upwards in the developer
solution for I to 2 minutes until the background is fully dissolved away
leaving the circuit pattern. Due to the dark blue/green colour of the photo
resist it is a simple matter to see when full development is complete.
Agitation by gently rocking the tray will help to develop the board
uniformly and speed up the process. Continuous agitation is unnecessary.
When development is complete immerse the board in the tray of fresh water
to
remove the developer solution. Keep the water clean by changing after
developing 2 or 3 boards.

8.	Etching

Place the developed board in the tray of etching solution until the
background copper is removed.  Once again this process will be accelerated
by agitation but may take up to 20 minutes or longer.
When etching is complete, immerse the board in a tray of clean water to
remove the etching solution.  Once again keep the water clean by changing
frequently.  After drying, the photo resist may be removed by adding 12
grams of sodium hydroxide to the developer solution, thus increasing its
strength, and immersing the etched board.  Naturally this would be done
after developing and processing a batch of boards and before discarding the
used developer solution.
Alternatively stripping of the resist can be done with normal strength
developer by exposing the etched pattern to ultra violet and developing 'in
the normal way.

WARNING - Handling of chemicals.

The developer and etching solutions may be harmful if not handled with
care.
Always use rubber gloves when handling chemicals and solutions.  Also keep
away from the eyes and face generally.  If chemicals accidentally contact
the skin, wash immediately with fresh running water.

-----------------------------------

DISCLAIMER.

As I have said before..... the chemicals involved are hazardous and it is
up
to YOU to ensure proper safety precautions are taken.

Keith

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