Fabricating Printed Circuit Boards

by Daniel Wee, 9V1ZV, 7 Dec 1994 Introduction

Since the beginning of my electronics construction hobby, I've just about built circuits in every possible way I could think of. I still remember my early days when I actually had germanium transistors screwed down on a block of wood. That was before I acquired my first soldering iron. I then progressed to the well- known "ugly" construction technique where component leads were simply soldered together. Other methods I remember include, breadboards, matrix boards which were quite popular at one time, wire-wrapping, board-excavation and printed circuit boards. Of all these, I have found the printed circuit board method to be one of the most satisfying and aesthetically pleasing, so far. This does not mean that it was an easy method, in fact, I had avoided circuits requiring printed circuit boards until I had tried everything else, and there was a good reason for this. There are also limits to what you can produce yourself, for example, you will not have the facility to fabricate through-plated boards or multi-layer boards. For these, if you ever need them, its best to go to the PCB manufacturer to have them made for you.

Like many, I had supposed, rightly, that the fabrication of printed circuit boards was a tedious process, requiring a lot of basic tools and equipment which I did not possess. As such, the whole process of fabricating a printed circuit board had remained pretty much a mystery to me until I entered the field of radio electronics. I discovered then that the parasitic capacitance and electrical properties of other construction methods were simply unsatisfactory for circuits operating in the RF regions. Thus began my quest for the printed circuit board. The purpose of this article is to briefly outline the various methods and steps of producing a usable printed circuit board.

Basic Theory

The whole idea of making a printed circuit board is really a chemical process of removing copper from the circuit board at the right places, in order to leave behind tracks suitable for carrying current as required by the circuit in question. Boards can be bought which come with copper clading one or both surfaces, used for making single or double sided PCBs respectively. A visual survey of the board reveals an uninteresting copper surface with no holes or tracks. The constructor must find some way of removing the copper in order to obtain a circuit pattern which can be used. One way to do this is by "excavating" the board with a sharp cutting tool to remove the copper. This proves to be an extremely tedious method and can only be used for the simplest circuit patterns. It is sometimes useful for making quick and dirty modifications to an existing pattern.

The standard way of creating a pattern, however, is by means of a method known as "etching". Etching is a chemical process whereby the unwanted copper is removed by a process of reduction, a chemical reaction, which "corrodes" away the copper. This is often achieved by immersing the copper clad board into a solution of Ferric Chloride or Sodium Persulphate (I think). Upon contact, a reaction occurs which reduces the copper on the PCB to copper chloride which comes off the board. Ferric Chloride has now become a controlled substance in some places because of its toxic and environmentally unfriendly nature and this makes it difficult to obtain from the usual sources. Sodium Persulphate is the substitute for Ferric Chloride but has not arrived at the shops here yet. Either of the etchtants can be obtained in liquid or in crystallized form. Nowadays, they are rarely found in liquid form because of the high rate of oxidation which renders the chemical useless. More often than not, they come in the form of dehydrated crystals which we mix with water to produce the etching solution. This solution is then used to etch the boards.

If you have been asking yourself how the chemical can be prevented from removing all of the copper, then you have asked an appropriate question. There are a number of methods by which this can be done. The whole principle lies is preventing the etching solution from coming into contact with the copper you wish preserved on the board. This can be by means of a water-proof tape on the board, rub-on transfers, marker ink, etch-resist ink, toner ink, plotter ink or photo-resist. In short, any method that can protect the board from the chemical solution is usable. Some methods are easier than others, of course, and the method to use depends on a number of factors, such as complexity of the pattern you want to produce, the density of the tracks, the boards available etc.

Once you have, for example, drawn a pattern onto the clean copper clad board with etch-resist ink, you may immerse the board into a properly prepared etching solution for the etching process. This can take from 5 to 30 minutes or more, depending on the concentration of the etching solution. After that, the board is removed from the solution, revealing a board where the unmarked portions of the board has no copper on it, the board material beneath being now visible, and the marked parts of the board still having the ink in it. Once the ink is removed either by sanding of by the use of solvents, the copper will become visible. The one last remaining step is to drill the holes for component leads in the right places and the board is ready for use.

That is generally what happens in the process of fabricating a PCB. Time does not permit me to cover all the methods that you can use so I will highlight some of the major steps in the following text.

The Copper Clad Board

Boards suitable for etching can easily be obtained from parts suppliers and come in a number of varieties. Typically, there are two major types of board materials that are used for the base board, fibre-glass (glass-epoxy) and phenolic paper. Fibre-glass boards tend to be tougher, look better and probably has slightly lower surface capacitance properties, as well as being the more expensive of the two. Phenolic paper, on the other hand, is easier to cut and drill though it tends to crack or fragment as it is more brittle, and cheaper. Both types can be used for homebrew construction projects as the mentioned RF properties are quite insignificant until VHF frequencies and above.

You will find single-sided copper clad boards as well as double sided ones and you choose the type of board appropriate for the circuit board you wish to fabricate. Double sided boards are normally used for RF related circuits because it offers a stable one- point ground-plane which helps stability and prevents unwanted oscillations or ground loops. However, producing double-sided PCBs requires high precision tools and I will only briefly mention some of the methods for producing simple ground-plane double sided boards later. This should be sufficient for a start.

You will also come across boards which are "pre- sensitized" or "photo-sensitized" which are used to produce photo- resist patterns. These boards are typically much more expensive than the plain boards because of the photo-resist film that has been pre-deposited over the surface. Such boards often come in light- proof wrapping with an additional layer of opaque plastic on the board surface which will not be removed until ready for exposure. I will detail this technique below.

Before you get started with the boards however, you will need to cut the board down to the size you need. Normally boards are sold in several sizes so you may pick either a large sized board and cut it up as you need, or select a size that is closely matched with your required size to minimize the cutting. The boards can be difficult or easy to cut, depending on the material of the board and its thickness. Average boards are about 2 mm thick and are quite tough and difficult to cut. Some boards come in 1 mm thickness and can be cut using a heavy-duty cutter. This type of board is usually quite flexible and thus the bending will not damage it. The thicker types on the other hand, will tolerate little bending before fracturing or fragmenting. Cutting can be achieved using a hobby saw with a fine-serrated blade. Thick saw blades are not suitable for this. Sawing should be done slowly and gradually in order not to damage the board. Saw perpendicularly to the board, which should be clamped down to the work-bench firmly using a G- clamp or a similar device. Alternatively, you can use a heavy-duty Exacto knife to engrave the border lines of the appropriate size. When using this method, it is not necessary to completely cut through the board. Once about 3/4 of the thickness has been cut, you can usually snap the board along the engraved lines. It is important to engrave BOTH sides of the board, otherwise you will not get a clean break. This method is very tedious, time consuming and tends to destroy your blade, especially when cutting fibre-glass boards. It can be used when a hobby saw is not available. Try not to scratch or damage the copper surface when doing this. After the board has been cut down to size, use a medium sized file to smooth out the edges for a nice finish.

The Etching Process

The next most important component you require is the etching solution. As of now, very few shops will sell Ferric Chloride crystals to unlicensed buyers and Sodium Persulphate is not publicly available. There is a good reason for this but it means a lot of inconvenience for the home constructor. There are means of obtaining the chemicals which will not be detailed here.

Ferric Chloride is most commonly available as dehydrated crystals and sold in plastic containers. It is very important to keep these crystals in a dehumidified environment as it tends to combine with moisture in the atmosphere and turn into a really messy and staining liquid. Be forewarned that this substance stains permanently on clothes and even some plastics or ceramics, is highly corrosive, carcinogenic and toxic. As such it should be kept out of reach from children and water. For the same reasons, it should not be discarded into the public drainage system before diluting it with large amounts of water.

Sodium Persulphate is a white crystal and though it is environmentally more friendly that Ferric Chloride is, similar precautions should be taken and care exercised when dealing with concentrated chemicals of any type. This substance is considerably safer however. For one, it is endothermic when dissolved in water and the resultant solution is a clear and non-staining solution. It is also slower acting than Ferric Chloride and probably needs more agitation and perhaps a little warming up. A good way to speed up the reaction may be to dissolve the Sodium Persulphate crystals in boiling water. Take all necessary precautions to avoid scalding.

The way to prepare the solution is to mix the crystals into some water, usually 1 part crystals to 5 parts water. This is just a guide and once you understand the process you can easily produce higher concentrations to etch boards more quickly. You should also be aware that the process of hydrating these crystals is a highly exothermic one so do not be surprised if the water starts to boil. As such, one should NEVER throw any substantial amount of crystals into the water. Similarly, one should NEVER add water to crystals, always crystals to water.

Normally, a plastic tray suitable for immersing the circuit board is filled with about 2 cm of water. The crystals are then added to the water BEFORE putting in the board, using a plastic spatula or any other suitable instrument. The instrument MUST be dry before applying to the crystals. Never leave the crystals exposed to atmospheric air for long. As soon as you have taken out enough crystals, wipe dry the rim of the crystal container and re- seal it in its air-tight container and store in a dry place out of reach of children. Do not get the crystals or solution on to your skin or eyes, and if you do, rinse under cold running water to remove it. See a doctor immediately in the event of ingestion. As you add the crystals to the water, the water will change color, to dark brown if using Ferric Chloride, and you should notice some heat being produced. Do not be too worried by the heat as it is useful for the etching process. Do not inhale any fumes produced during the entire process, these are poisonous and though in very small amounts, may cause asphyxiation (Chlorine). All this should be done after you have readied the board for etching. All instruments coming into contact with the solution should be non-metallic. Stir the solution until all the crystals have dissolved to produce an evenly colored solution. Now the solution is ready for use. Try to use it while it is hot so this step should always be done after your board is ready.

Put your resist-masked board into the solution slowly so as not to cause a splash. Remember that the solution is very hot sometimes. Once the board is completely immersed, regularly agitate the tray and pay attention to the exposed copper. After sometime, the exposed surface will appear dull, not necessarily evenly. The after more agitation you will see patches of circuit board becoming exposed. Do this until ALL the unwanted exposed copper surface has been removed and the board material is visible beneath it. This may not be easy initially as the etching solution may obscure your view of the board. It is therefore good to have a deeper tray which allows you to tilt the tray to expose the board. Normally, surfaces with less exposed copper tend to etch faster that surfaces with more copper, and once you are more experienced, you may want to use a stronger concentration for surfaces which require a lot of etching. The copper corrosion normally starts from the edge of the board and works its way to the center. Be sure to keep on agitating the board so that the resultant copper chloride (a powdery precipitate black in color) will get swept off the surface. This will speed up the etching process.

While it is important to make sure every part of the board is sufficiently etched, DO NOT keep the board in the solution longer than absolutely necessary. This is because extended exposure will allow the etchtant to get under the resist and affect the fringe of your tracks, resulting in ugly patterns. Experience will soon tell you how long to leave it in for the concentration you use. Normally everything should be done in 25 minutes but it may be less, depending on the size of the board, exposed surface, and the concentration of the solution. Proper timing is especially important when very thin running tracks are involved.

If you are doing double sided boards, you should at some point, turn the board over. In this case, unless you have special holders, you should not over agitate the tray as the copper chloride precipitate which sinks to the bottom of the tray is rather abrasive and may scratch off some of the resist on the bottom side. Other than that, the procedure remains the same.

Some of the shops sell special etching tanks which stand vertically and has a little electric motor to automatically agitate the tray. This is not suitable for small scale productions as the tank normally requires large amounts of etching solution to fill up, and cost quite a lot to buy. For me, the above method is more than sufficient.

Drilling of Holes

The drilling of holes is typically the last stage of the PCB fabrication process so this may seem a little anachronistic. Nevertheless, this is the last common step of the various methods of PCB fabrication so I thought it'd be good to cover it now.

Clearly, you will need to drill the holes yourself if you intend to put components on the board. In some surface-mounted designs, especially common with microwave and UHF circuits, this may not be necessary. Unfortunately, you cannot use your trusty Black & Decker power drill for this purpose because of the excessive speed of the drill and the oversized drill bit. A hobby or hand-drill is suitable and cheap ones, both battery powered and mains powered, can easily be found in Singapore for under S$50. You will need to get a few common small sized drill bits for PCB use. The most useful by far is the 0.8 mm drill bit. The 1 mm and 2 mm drill bits also come in handy when drilling larger holes on the PCB. Generally drilling PCBs do not require a lot of effort because the PCB material is relatively soft and easy to drill. Be sure to get spare bits because the bits tend to break easily and are rather brittle due to their small cross-sectional area.

You should position the drill bit perpendicularly to the PCB for drilling any holes, and always maintain a steady and firm grip of the drill. If necessary, you may want to use a sharp instrument to slightly indent the spot you want to drill, as a guide as sometimes the drill bit tends to spin away from the point and scar the rest of the copper surface. Usually though, properly made boards should have these guides etched in. Do not apply undue force as this might cause the bit to break or the board to crack. Apply a steady force on the drill until you feel the penetration of the PCB. It is also advisable to have a piece of unwanted even wood surface beneath the board so that you won't destroy your workbench or your drill bit. Soft-wood is best but other soft material will also do, eg. old hard cover books.

Normally the drilling process produces a substantial amount of debris which will obscure your drilling template. Thus you will want to drill holes systematically so as not to miss any holes inadvertently, and to drill a section at a time, clearing away the debris as they accumulate. Do not have the fan blowing while you are doing this or your XYL will be all over you for messing up the place! Once you have drilled all the holes, inspect the board for undrilled or partially-drilled holes. Also be on the lookout for tracks that may have come off as a result of the drilling. This may sometimes be the case when drilling large holes on a small pad. Remove burrs from the holes and then your board is ready.

Masking the PCB

As was mentioned in the basic theory section, there must be a way of controlling which parts get etched and which parts of the board don't. I also briefly mentioned a number of methods. Here I will highlight two of the methods most relevant to us homebrewers. Direct penning onto the board using etch resist pens and photo-resist.

Using Etch-Resist Pens

You can actually draw the desired tracks or patterns onto the copper clad board with etch resist ink. Get a normal copper clad board that has been cut down to size, washed and dried completely. Do not soak the board in the water for too long or the water may damage the board. Be certain to make sure that there is not grease on the board or oxidized surface. If necessary clean the board with some mild abrasive to obtain a shiny surface. Avoid touching this surface with you fingers or dirtying it. This will ensure a more even etching later on. There is no need to specially buy etch-resist pens for this purpose though you could do so. For simple purposes, permanent markers or Indian ink seems sufficient for the job. There are advantages and disadvantages of using such a method. On the plus side, this is a very convenient method for producing one-off, not too intricate or complex patterns, and can be done rather quickly. However, you cannot obtain high resolutions tracks or any degree of evenness with this method. The results tend to look amateurish. Just as a reminder, the tip of the etch-resist pen tends to dry up quite quickly so the pen should be re-capped tightly when not in use. Have a pice of paper near by to get the ink flow even before tryin to mark the PCB with the pen.

Sometimes you can buy rub-on transfers for tracks or pads which you can incorporate as part of your pattern to make it look neater. On the whole, however, this method is reserved mostly for experimentation or very simple circuits with broadly spaced tracks. Alternatively, you can also use special tracking adhesives to paste out your tracks. Either way, the end result is rather coarse and difficult to reproduce.

Recently, there are available in the United States, special transparencies which you can laser print or photostat your track onto, and then iron-off the pattern from the transparency onto the board. Below is an excerpt which says something of this method:-

From: gary%ke4zv.UUCP@mathcs.emory.edu (Gary Coffman)

There is a special transparency film called Tec 200 marketed for this purpose, but I've found that Avery overhead transparency film works just as well, and is available at most larger computer or office supply stores. You just print your board layout to the transparency with your CAD package laser driver, remember you want a mirror image, and then iron it onto the copper. The copper needs to be clean, just as it would be for any resist application. You need a fairly hot clothes iron to fuse the toner to the copper. I use a regular home iron set for "cotton" and use an old Tee shirt between the iron and the film. After it cools, you can peel the transparency film off the circuit board and the toner will remain behind as the resist pattern. There may be a few pinholes or gaps where the toner didn't transfer well. You can patch them up by hand with an ordinary resist pen.

Note you can also use Avery film in ordinary copiers to generate a transfer from magazine artwork or hand drawn paper layouts. Of course when laser printing the film, you need to adjust your CAD driver so that the laser printer gives a properly dimensioned copy, and when using a copier, one with infinitely adjustable "zoom" feature is handy for the same purpose. If the artwork is "normal", you can first make a copy to a transparency, flip it over, and use that as your master for making the transfer transparency.

Works good, costs little.

Another method I have come across of directly masking the PCB is through the use of flatbed plotters. Apparently, the ink used in these plotters are etch-resistant and if you can design the board using CAD software, you should be able to plot the mask directly onto the board using the plotter. I have not tried this myself but a friend of mine has and reports good success.

Photo Resist Masking

This is probably the best way I know for making nice looking PCBs. Unfortunately, the technology behind it is rather obscure for many people entering the hobby and remains a mystery for others. Thus I will try to demystify the process here, with some luck. Contrary to the belief of many, the photo-resist method does NOT produce tracks on the PCB, it only produces a mask or pattern of etch-resist material, after which the board still needs to be etched like in all the other methods.

In this method, you need to get your pattern or mask onto a piece of clear transparency. This is usually done by laser printing direct on to the transparency, or photostating on to it. This means that anything that can be photostated, eg. patterns from magazines or from the ARRL handbook, or even texts and pictures, can be etched. This adds a number of advantages. For one, it is much easier to draw patterns on normal paper than on the copper surface. There is no need to use special etch resist ink for this purpose. You can also draw lines with higher density and definition as well as accuracy than you can using the direct method. You can use PCB layout software to print out computer generated patterns as well as including printed texts as part of the pattern. The possibilities are numerous. It should be noted that all the patterns must be black and white, no grays, and that the transparency must be clear, clean and colorless. Transparencies used for OHP presentations are suitable for this purpose. As an additional hint, you should try to get the transparency prepared such that the side with the toner is also the side that will be in contact with the PCB during exposure. This yields slightly better defined lines as there is then only one clear edge. It does not matter that the print is not completely opaque when you look at it against the light, usually normal photostat contrast is sufficient. You may want to cut the transparency to the size of the PCB for easier handling. Do not scratch the transparency as the toner may come off. If you notice missing tracks, you can still fix it by drawing on the missing tracks using an opaque black marker pen. If you notice excess tracks, slowly scrape off the toner/ink gently using a paper cutting blade. One advantage is that once you have produced one mask, you can use the same mask to produce a number of identical boards. When producing the mask, you should try to get it so that the emulsion side (the print side) is the side that contacts the PCB. This way when you expose the board, there is a minimum of shadow and fringe effect at the edges of the tracks and results in higher definition tracks.

The copper clad board must be specially prepared or sensitized by spraying a film of photo-sensitive masking material on to it. This spray is normally available in a canister and leaves a coat of clear green color (usually) when applied to the board. Spraying must be even and a sufficiently thick film must be deposited and dried before commencing exposure. All this should be done in low light/UV conditions as the spray is photo-sensitive. Alternatively, and more conveniently, boards that have been presensitized can be purchased quite easily from the shops. In any case, the spray is very expensive and not easy to use. These pre- sensitized boards come in light-proof wrapping which you may remove. The boards have a second protective plastic film over the surface so you need not worry about accidentally exposing the boards. The rate of reaction is way slower than that of the camera film so you need not be overly concerned of over exposure. Just be sure that you are not doing this under intense fluorescent or sun- light. The second protective layer is an opaque adhesive plastic layer which is stuck to the board surface. This is usually white in color. Do not peel off this layer until you are ready to expose the board. If you do accidentally peel it off pre-maturely, store the board in a dark place until you are ready. In any case, these boards need to be stored in the dark and in a cool environment.

Once your transparency is ready and you have cut the board to size (without removing the protective layer), prepare yourself a clear piece of flat glass such as that found in picture frame. Be sure that the glass surface is clear and clean, and that its size exceeds the size of the PCB. This glass is used to hold the transparency to the PCB during exposure. Put the PCB on a flat surface and align the transparency over it, making sure that when you look at the transparency, you see the exact image of the track/pattern that you want, NOT the mirror image NOR the negative. Be sure your UV source is NOT active. Once you are ready and have double-checked every detail, slowly peel off the protective layer from the pre-sensitized PCB and replace it on the flat surface. Under the protective coating you should see a hard and dry, green film over the copper. Place the transparency correctly over the PCB and align it. Then, place the piece of glass over the transparency to press it firmly to the PCB surface. Once again check your alignment and then expose the board to the UV source.

The UV source can be a table top fluorescent lamp, or the sun, or special UV lamps. In all cases the UV content is not the same, thus exposure time varies. In my case, I use a table top lamp with an 11-watt fluorescent tube and place it about 2 to 3 inches above the board for 6 minutes to give me a properly exposed board. Under the afternoon sun on a clear day, it takes about 8 to 15 minutes to get sufficient exposure. Under UV lamps, the period may be as short as 30 to 90 seconds depending on the intensity of your source. Experimentation is the key to knowing how long to get the right exposure. Excessive exposure will damage the board and under-exposure will be equally disastrous. Once you have determined the correct exposure time, however, it is the same every time when using the same type of board, so be prepared to experiment a little with your first few boards. NEVER move or adjust the board once you have started exposure. Once you get good at it, you can even expose a number of boards simultaneously. Some types of board will exhibit a slight color change on the exposed parts once they are done but do not count of this method to determine when to end because the change is barely perceptible. Note that if you are using a UV lamp, be careful not to look at the light direct as it may damage the eyes because the iris of the eyes do not respond too well to UV and may result in retinal- burn.

During the few minutes of exposure, get the developing solution ready. This solution is normally sold in the same shops where you purchased the PCB in the first place. They sometimes come under the name of POSITIV 20 or something similar and consists of an alkaline solution. Have this ready when you finish exposing. If you observe the board carefully, you may notice that the exposed portions are a little lighter green in color than the masked portions. This allows you to actually see a faint trace of your masking pattern on the exposed board. Rinse the exposed board in the developer solution and if properly exposed, you will see the exposed parts of the green photo-sensitive film dissolve in the developer solution. Once the unwanted parts have been completed dissolved and washed away, rinse the board under cold running water to remove any remaining developer solution. You should now see a very clearly defined, green, image of your original pattern on the PCB now. Dry the board carefully, making sure that you do not accidentally scratch off the resist/film. At this point you can still make corrections to the pattern using etch-resist pens or by scraping off resist/film from excess sections. Once everything has been confirmed, put the board aside and prepare for etching as outlined above.

Making your own PCB layout masks

There are a number of ways you can use to produce your own photo-exposure masks and layouts. Typically you want to draft out the layout on paper first before committing it to the final mask. Be sure to take into consideration RF paths and good grounding. There are a lot of considerations that need to be taken into account of in the design of a good PCB layout. Once you have drafted out the layout you can use hand-drawn masks, or combine hand-drawing with the use of Decal-Dry or rub-on transfers. These methods are suitable only for low density/complexity designs. The easiest way however is by the use of CAD software. There are some easy to use but fairly competent PCB CAD shareware available and if you intend to produce PCB designs of your own, you should be familiar with such software. Describing how they work is outside the scope of this article but among the features of such software, are their flexibility, multiple printer support, multiple layer support, silk-screening support, automatic drill guides on pads, auto-routing, easy editing, free/shareware, standard component templates and the list goes on and on.

Summary

In summary, let me outline the steps and tools involved in the direct PCB fabrication method. First, the tools and materials:-


	 a)   Ferric Chloride or Sodium Persulphate crystals (or
	      solution).
	 b)   A plastic tray big enough to immerse the board fully.
	 c)   The single or double sided copper clad board.
	 d)   Etch resist pen and/or transfers.
	 e)   A small medium speed drill with 0.8 mm bits.
	 f)   Hobby saw or Exacto knife to cut the PCB down to size.
	 g)   File to give the board a good finish.
	 h)   Mild abrasive for removing the resist from the PCB after
	      etching.

	      The steps involved are as follows:-

	 a)   Prepare a draft of the desired layout.
	 b)   Cut out the required size of the copper clad board.
	 c)   File the edges of the cut down board for a smooth finish.
	 d)   Transfer the layout to the copper clad board by drawing
	      it on with the etch resist pen or transfers.
	 e)   Double check for errors.
	 f)   Prepare the etching solution as by adding 1 part crystals
	      to 4 or 5 parts water. Refer to section on etching.
	 g)   Immerse the masked board into the tray with the etching
	      solution.
	 h)   Agitate the tray slightly for about 15 to 25 minutes,
	      paying attention to the extent of the etch.
	 i)   Remove board from tray when completely etched.
	 j)   Rinse board under cold running water from the tap.
	 k)   Dilute used etching solution with lots of water before
	      disposal.
	 l)   Use the mild abrasive to remove the etch-resist from the
	      board.
	 m)   Use the drill to drill the appropriate holes for the
	      components.
	 n)   Remove burrs from the holes.


	      For the photo-resist method, the tools required are the
	 following:-

	 a)   Ferric Chloride or Sodium Persulphate crystals (or
	      solution).
	 b)   A plastic tray big enough to immerse the board fully.
	 c)   Pre-sensitized copper-clad board.
	 d)   Transparency suitable for photostating.
	 e)   UV light source.
	 f)   Developer solution.
	 g)   A piece of clear glass to hold mask in place.
	 h)   Marker pen or transfers.
	 i)   A small medium speed drill with 0.8 mm bits.
	 j)   Hobby saw or Exacto knife to cut the PCB down to size.
	 k)   File to give the board a good finish.
	 l)   Mild abrasive for removing the resist from the PCB after
	      etching.

	      The steps involved in the photo-resist method are as
	 follows:-

	 a)   Prepare the masking pattern on a piece of white paper.
	 b)   Transfer pattern to the transparency by photostating.
	 c)   Cut the pre-sensitized board down to size.
	 d)   File the edges to remove unevenness.
	 e)   Place transparency on the board to check alignment.
	 f)   Peel of protective layer from board.
	 g)   Align the transparency on the board.
	 h)   Place glass over the transparency to hold it firmly in place.
	 i)   Place the UV source over the board and glass.
	 j)   Activate the source and expose board for a suitable period. Read above.
	 k)   Rinse the exposed board with the developer solution to
	      dissolve unwanted resist.
	 l)   Double check for errors.
	 m)   Prepare the etching solution as by adding 1 part crystals
	      to 4 or 5 parts water. Refer to section on etching.
	 n)   Immerse the masked board into the tray with the etching
	      solution.
	 o)   Agitate the tray slightly for about 15 to 25 minutes, paying
	      attention to the extent of the etch.
	 p)   Remove board from tray when completely etched.
	 q)   Rinse board under cold running water from the tap.
	 r)   Dilute used etching solution with lots of water before disposal.
	 s)   Use the mild abrasive to remove the etch-resist from the board.
	 t)   Use the drill to drill the appropriate holes for the components.
	 u)   Remove burrs from the holes.

Conclusion

The real key to learning to make PCBs is to do it yourself. In this article I have tried to provide a general idea of the process of fabricating your own PCBs and have purposely included a number of cautionary and warning notes so that the reader will be aware of the hazards involved. On the other hand I have been making my own PCBs for about 8 years now and have not suffered any side-effects or harm. Hopefully, this article will open new doors and possibilities for the homebrewer and that through homebrewing, one very significant aspect of the original spirit of Amateur Radio may be restored. If there should be further inquiries, I will be more than glad to help out.

73, Daniel Wee

Newsgroups: sci.electronics
	 From: pvr@wang.com ()
	 Subject: PC board manufacture: my technique
	 Date: Tue, 3 Nov 1992 18:41:34 GMT

	         I have followed the past thread on making pc boards and
	 have tried all of them except for plotting with ink on copper
	 directly.   I don't have a suitable plotter.   I have tried
	 transparency film and release paper with only mediocre results.

	         The best luck that I am having now uses ordinary copier
	 paper.   I print on the paper at normal density.   I am using a
	 "super black" toner cartridge from Black Lightning.   I don't think
	 that this is necessary because I tried the output from another
	 printer with an ordinary cartridge and got equivalent results.
	 All of the following technique is with the super black toner.

	         I prepare the copper surface by sanding it with number 320
	 wet sanding sand paper.   I do the sanding dry (don't know if this
	 matters).   I sand in small circles so the scratches go in all
	 directions so the adhesion will not have a perfered axis.
	 I iron the paper onto the copper with the iron at 170 degrees C,
	 that is the highest temperature on my iron.   The fuser
	 in my laser printers (LaserJet II and III) runs at 160 degrees C.
	 I iron for about 30 seconds on my counter top with a paper
	 towel between the board and counter top.   This provides
	 insulation and a slight springiness to the board as I iron.
	 I iron enough to insure that every part of the paper is heavly
	 pressed onto the board.

	         Immediately after ironing I place a wet (dripping)
	 paper towel on the ironed on paper and press the iron onto
	 the wet towel.   This drives steam into the paper.   Without
	 this step the paper will shrink and pull the toner off the
	 copper.   The steam causes the paper to swell up and relieve
	 the strain.   The iron should be placed on the towel for
	 a split second or the paper will dry out.   I then soak
	 the paper with dripping water and let it sit for about 5
	 minutes.

	         The paper should be completely soaked and swelling
	 between traces.   I then rub the paper with my fingers under
	 running water.   The paper will begin to ball up and come off
	 in layers.   I rub it until I get as much off as I can.   At
	 this point the traces should be well attached to the copper and
	 not at risk at coming off.

	         You will find that all the toner has a paper fibers
	 imbeded into its surface.   This is not a problem in most cases.
	 The problen arises when the fibers bridge the gap between
	 traces or pads.   To solve this I scrub the board with a brass
	 brush.   This brush is like a tooth brush with bristles made
	 of fine brass wire.   The brush will break the fibers that
	 bridge gaps between toner areas.   Do this while the board
	 is wet.   Let the board dry and inspect all the toner
	 for fibers that would prevent proper etching.   Pick any
	 remaining fibers away with an exacto knife.

	         While I etch the board, I periodically scrub the surface
	 with a real tooth brush to insure that the fibers are not blocking
	 etchant access to any portion of the exposed copper.   Do not use
	 the brass brush in the etchant as it will be desolved itself.

	         I have made a number of small boards up to 2 by 4.5 inches
	 using this process and some with very fine traces and spacings.
	 I complete the etching of one side before I apply the toner
	 to the other side.   I don't know it this process will scale up to
	 larger sizes well.   It seems to me that the steam step is
	 particularly important.   Before I did this traces would pull off at
	 the edges of the board as the board cooled.

	         Good luck


	 --
	 >>>>>>>>>>>> Peter Reilley ..... pvr@wiis.wang.com ..... KA1LAT <<<<<<<<<<<<<
	                      Well, that about says it.


	 ehare@arrl.org (Ed Hare - KA1CV) writes:

	 >> If anyone knows of any other suppliers of inexpensive custom prototype
	 > printed-circuit boards or small-quantity printed-circuit board supplies,
	 > please send the information by postal mail to:
	 >
	 >

	 The best deal in DOUBLE SIDED that I know of is
	 AP Circuits
	 #14-3650 19 St NE
	 Calgary, Alberta
	 Canada T2E 6V2
	 (403)250-3406

	 But they require that you have a GERBER file and drill tape, and you have
	 to buy two boards.  I have not tried them so I cannot speak to the quality.
	 The price is something like $92 for two 5x6in boards.  Same price for
	 single sided.  I've seed their add in Nuts and Volts.

	 The best deal that I know of in SINGLE SIDED prototypes, and the most
	 exciting thing to come around in a long time is
	 First Proto
	 1355 W. Palmetto Park Rd.  Suite 158
	 Boca Raton, FL 33486
	 (407)392-8677

	 Get this, $25 for any 4x8in board or smaller.  And they will do ONE
	 for that price.  They will also put smaller boards onto that 4x8in area
	 if you meet certain criteria like total number of holes and cutting them
	 apart yourself.  They do NOT require GERBER files nor drill tapes.
	 They take HPGL plot files, PCX bitmaps, laserjet PCL files, and
	 Postscript files.  If all that is not enough,  they also scan artwork you
	 send them from magazines or books, or that you drew by hand,  and the
	 scanning is included in the price.  They also have a alternate pricing scheme
	 which is beneficial for very small boards;  $4 per square inch with a ten
	 dollar minimum. I've seen their classified in Nuts and Volts, Popular
	 Electronics and occasionally in 73 Amateur Radio Today.

	 Disclaimer: I have no affiliation with either of these two companies
	 other than my wife works at the latter company.  I have used the
	 latter service and can speak for the quality.

	 ========================================================================
	 Charlie Bustamante     ... In balmy Boca Raton, Fl USA

	                            internet email: charlieb@cybernet.cse.fau.edu


	 Newsgroups: rec.radio.amateur.homebrew
	 From: alanb@sr.hp.com (Alan Bloom)
	 Subject: Re: Directly plotting etch-resist on PC boards?
	 Date: Wed, 13 Apr 1994 19:36:37 GMT

	 David DiCarlo (r14793@waccvm.sps.mot.com) wrote:

	 : Well, I tried it this weekend by photocopying on to a sheet of
	 : transparency and ironing that onto the copper.  ...

	 I'm surprised nobody mentioned the ready-made kit you can buy
	 specifically intended for this application.  It uses a
	 specially-coated paper so that after you iron it onto the PC board
	 the paper soaks off in a pan of water, leaving the toner behind as
	 resist.  You then etch the board in the normal way.

	 The pattern can be laid down on the paper using a photocopier
	 or laser printer.

	 The only tricky part is that the board must be completely clean and
	 scoured with fine steel wool.  The steel wool seems to roughen the
	 copper so the toner sticks better.  Another trick is to soak the
	 board with the paper side down.  Otherwise, the paper can pull off
	 some toner as the paper floats up.

	 : My question is, what iron temperature was used and was the transparency
	 : peeled off hot or cold?  I used 1 sheet of paper between the iron and the
	 : transparency.

	 Seems like the hotter the better.  I haven't had any trouble with
	 toner smearing or widening of the traces.

	 I bought my kit (with 5 sheets of 8-1/2 x 11" paper) for $12.95 from:

	      DC Electronics
	      POB 3203
	      Scottsdale, AZ 85257
	      800-467-7736
	      800-423-0070

	 AL N1AL