Is Building the Printed Circuit Board - PCB. It is Sometimes Possible to Use Strip Board or Some Other Pre-fabricated

8/9/2019 Is Building the Printed Circuit Board - PCB. It is Sometimes Possible to Use Strip Board or Some Other Pre-fabricated

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How to Make PCB'sOne of the most discouraging things about making a hardware project (apartfrom obtaining all of the components) is building the printed circuit board -PCB. It is sometimes possible to use strip board or some other pre-fabricatedboard but more often than not the circuit complexity and performance requiresa proper PCB to be made. The good news is that due to improvements in

printing and processing technologies it is now relatively easy to makeinexpensive high quality PCB's at home.

WARNING: Making PCB's requires the use of Ferric Chloride (FeCI3) which iscorrosive so avoid skin and eye contact. Remember safety first use glasses,gloves and protective overalls. Ferric Chloride is also very good at distortingcloths weeks after you think you have washed it off. If you do get any on yourskin then wash it off immediately with lots of water and soap.

The Shopping List

This is the minimum things you will heed,

1. Access to a PC with a Laser printer eg: HP Laser Jet2. Cloths iron3. Kettle4. Water bucket5. A one litre glash jar with plastic screw top (biscuit jar)

6. PCB hand drill with 0.8mm and 1mm drill bits - FR84F, QY64U7. Copper-Clad fiberglass board - WF40T8. Press-n-Peel PCB transfer system - AB15R9. Ferric Chloride Copper etching fluid 250ml - WF10L10. Two plastic etching trays (ideally different sizes) - CH38R11. PCB cleaning rubber - HX04E12. PCB solvent cleaner - LL59P13. Safety glasses, latex gloves, old clothes/overalls - KE83E, YJ84C

All part numbers are from the Maplin Electronics catalogue.

The Artwork

Until recently the artwork had been an area of DIY PCB manufacture whichcaused the biggest problems. But now by combining high quality laser printingwith the Press-n-Peel PCB transfer system these problems have been solved.The first stage is to transfer the circuit layout from the PC to the special Press-n-Peel film. You will find that my projects provide Laser print files (.prn) for

printing the circuit layout direct onto this film,1. I cut the Press-n-Peel film in half for small boards so it lasts longer2. Put the film in the laser printer so that the print will appear on matt blue


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side3. At a DOS command prompt type: copy filename.prn lpt1 to print onto thefilm

This will produce a contact print where the black image will end up as Copper

on the final PCB. Now to transfer the artwork to the Copper board by followingthe instructions with the Press-n-Peel film,

1. Clean the Copper board very well with the PCB cleaning rubber2. Heat the cloths iron to 300 deg.F (Acrylic to Polyester setting)3. Hold the film with the print in contact to the Copper and smoothly iron thefilm

down until the print appears black through the film (about 1min)4. Allow 5mins to cool down (or speed this up with water) then peel the film off

This should produce a clean black print onto the Copper. If you let the filmmove or overheat then you will find that the tracks and writing will be smearedand out of focus also the film may be wrinkled up. If you don't use enoughheat or heat unevenly then the film may not stick or be dark enough. In eithercase clean off the PCB and try again, you should get it right after a couple ofgoes.

The Etching

Now for the messy bit, etching the PCB to remove the unwanted Copper.Please read the warning at the top of the page as it is important to takeappropriate precautions before handling the etch chemicals. I recommend youdo this outside or in a shed and you must ware glasses and gloves. Keepingthe etch chemicals warm (45deg C) is essential as it reduces the etch timefrom over an hour to about 15mins.

1. Dilute the concentrated Ferric Chloride fluid with water (1:1) and pourinto the

one letre glass jar and screw the top on

3. Place a sheet of news paper on a flat surface and put the trays on this2. Fill the kettle with water and boil3. Heat the Ferric Chloride jar in a bucket of hot water. Caution don't spill any

drops and keep away from food

1. Pour 1cm of boiling water into the bottom tray then place the othertray on top2. Put the PCB copper side up on the top tray and pour all the Ferric Chlorideon top3. Gently rock the top tray to keep the etch fluid moving avoiding spillage

4. After about 15mins all of the unwanted Copper should have disappeared5. Remove the board and drop it into a bucket of cold water to clean off


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Usefull tip: For small boards just drill a 1mm hole in the corner of the boardand tie 2ft of strong cotton to this. Now put the board straight into the FerricChloride jar with the end of the cotton outside and put the top on the jar. Keepthe jar hot by heating in a tray of boiling water and gently rock to keep theetch fluid moving. Every 5mins use the cotton to lift the board out and check

progress. This method is much less messy as the Ferric Chloride is always leftin the glass jar.

Drilling

Drilling with 0.8mm drill bits can be a bit tricky as it's easy to break the drillbits. Always hold the drill straight and do not bend it when the hole hasstarted. Putting a soft block of wood under the PCB provides a good base to

drill into. Once you have become experienced at drilling I would recommendusing Tungsten Carbide drills (FE49D) which easily break but last much longer,

1. Dry off the board and clean away the blue etch resist with PCB solventcleaner2. Using a 0.8mm PCB drill bit drill out all of the component holes3. Some 1mm holes may need to be made for connectors, 3mm for cornerfixings4. Finally use a PCB rubber to clean the copper ready for soldering

So now your PCB's finished and you can start soldering the components in. Youshould do this soon after you have cleaned the PCB (within 1 hour) as thecopper soon oxidises and becomes hard to solder onto.

Links

Maplin Electronics home pageFrontier Engineering the U.S. Distributor for Maplin ElectronicsUK based low cost Press-n-Peel sheets

EAGLE PCB softwareOlimex PCB manufacture

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Is Building the Printed Circuit Board - PCB. It is Sometimes Possible to Use Strip Board or Some Other Pre-fabricated