Etch Your Own Crossover Printed Circuit Boards

A tutorial on etching printed circuit boards.


With the proliferation of DIY speakers, building professional looking crossovers is becoming more important to many builders. Numerous ways to assemble crossovers exist, but many are difficult to implement, or duplicate. Printed circuit boards solve most of the problems, making it simple to build professional looking and easily duplicated crossovers.

There are several vendors where printed circuit supplies can be purchased. Parts Express is a sponsor of AudioKarma, and sells presensitized PC boards, and developer using the “positive” system. Other vendors have supplies for both “positive” and “negative” systems, as well as developers, etchants, and equipment to make the job easier. Many vendors have “Do-It-Yourself” tutorials on how to etch their PC boards, but they all want to sell you all the equipment they feel is “necessary” to make the job easy. Since the average DIY’er is going to be making only one or two pairs of boards, investing hundreds of dollars in special lights, holders, and etching tanks with their assorted heaters and bubblers doesn’t really make financial sense.

Positive systems mean that where light can get through the artwork, copper will be removed from the printed circuit board. Negative systems means that where light gets through the artwork, copper will be retained. A photo positive is required to expose artwork in the “positive” system, and a photo negative is required in the “negative system. The presensitized boards and developer from PE are "positive" system components. They are slightly more expensive, but eliminate several steps. The “negative” systems all use raw PCB’s and allow you to spray on sensitizer before exposing them. If a mistake is made, you can then clean the boards, and start over. With the “positive” system you only get one chance to expose and develop the board properly. The “negative” system also adds cost of sensitizer, so the overall cost of building boards is roughly the same.

Etching your own circuit boards doesn’t have to be a costly process. Who needs special lights to expose his layout, when we all have the sun. A special holder is not needed to hold the board during exposure, as long as a little care is used. And an etching tank with heater and bubbler would be great if we were going into production, but for just a pair or two of PCB’s, they are not necessary, but not using them may add 10 minutes of time to the process.

This tutorial will detail the way I make PC boards, and it will not call for any special equipment. It is done on the “cheap”. The equipment I use is as follows:

Pyrex pan for developing and etching.
Piece of glass for holding artwork and board during exposure.
Book to support the artwork and board during exposure.
Presensitized PC board of correct size.
Artwork or photo positive.
Etchant solution.
Developer solution.
Measuring device for preparing developer solution.
Folded blue cloth towel.
Drill and bits to drill holes in PCB.
Piece of steel wool to remove photo resist from etched PCB.
Double Stick Scotch tape.
PCB material for guides (or any thin stock).
Popsicle stick or wooden pencil.
Rubber Gloves if you are sensitive skinned.


The Pyrex pan I use is roughly 8 inches by 12 inches and 2 inches deep. I stole it from mama’s kitchen years ago. You probably can steal one from your own kitchen or pantry.

The glass for holding the artwork and board should be about one or two inches larger per side than the PCB you plan to make. Larger is OK, but more difficult to keep in place during transport. I bought a new piece at the local glass shop which is 6” by 8” and ¼ inch thick. I used to use a big piece of seeded glass, but felt the tutorial would be better with a reasonable sized piece of clear glass. The bubbles in the seeded glass did not affect the exposure. The new piece of plate glass cost $2.50.

Virtually any book larger than the PCB will do, since it is just to provide support for the board, artwork, and glass during transport and exposure.

The folded cloth towel is simply one removed from a roll of shop towels that can be bought at any hardware store. The ones I use are blue in color. Yours may vary. It is used to provide some support for the board during exposure.

The presensitized PC boards, developer and etchant can all be bought in many places. This tutorial will use PCB’s and developer from Parts Express, and etchant (ferric chloride) bought from Capital Electronics in Phoenix, Arizona.

Picture 1 shows all of the supplies needed to etch your own PC boards, except for the drill and bits, and rubber gloves. Picture 2 shows a closeup of the etchant and developer.

Preparation of Artwork

A photo positive of the desired layout is required for the PC boards used here. The actual layout can also be used, but the layers of overlapping tape to build the desired patterns will add thickness to the artwork. I will use a photo positive for my last crossover layout, which can be used to build the EconoWave crossover. The artwork for this crossover was scanned and stored by a local printer, who then made photo positives for me, with the emulsion on the back side (against the PCB). This will help prevent light undercutting the desired exposure area.

The artwork or positive needs to be aligned exactly with the presensitized pc board when exposed to light. Once the protective layer is peeled away from the PCB, the board needs to be protected from any strong light hitting it, since it is light sensitive. Aligning the positive on the PCB can be done without any guides, but that takes manual dexterity and some time to get done correctly. By adding two guides to the positive, alignment can be accomplished very rapidly by sliding the PCB against both stops of the positive. Then any accidental exposure to light will not expose areas which should not be exposed.

The guides should be attached to the positive with Double Stick Scotch tape. I use a piece of PC material cut from an old board. Virtually any material will do, but it should not be thicker than the PC board itself, or it will lift the positive from the board being exposed, which will allow light to get under the positive and expose areas where copper should be protected.

Use a straight edge to span the corner marks on the artwork. Apply Double Stick Scotch tape just outside of the PC area, and apply one guide to this area up against the straight edge. Picture 1 shows the artwork after application of the guide on the long side. The straight edge used here is the back of an old PC artwork that was made years ago. The second picture shows both guides taped onto the positive. Note that the guides go on the back side of the positive, so that the nomenclature will be readable when the board is exposed. It is now ready to use, and will make the alignment to the PCB quick and accurate.

Preparation of developer.

Once the exposure to light is accomplished, the PCB should be developed as soon as possible, since the PCB is still light sensitive. Any areas protected by the positive during exposure can still be affected by strong light hitting them when the PCB is removed from the positive. Therefore the developer solution should be mixed and ready to go before exposing any PCB’s to the sun.

Mix the developer according to the directions on the product. The PE developer used here recommends a mixture of 1 part developer concentrate to 10 parts of water. It should be mixed in the Pyrex or glass tray, and placed near a sink where the developed PCB can be rinsed after developing.

The measure used by me is a 2 TBSP coffee measure, again stolen from mama’s kitchen years ago. One measure of concentrate and 10 measures of water are added to the pan. This makes an adequate amount of developer for use in the large pan. The developer only needs to cover the PCB in the pan.

The first picture shows the developer in the pan awaiting use. It probably doesn’t show up yet, since it is clear, but it is really in there. After developing five PCB’s it becomes blue, as shown in the second picture.

Exposure of the PCB to the light source

With the developer mixed and waiting, the PCB is ready to be exposed to the light source, in this case, the sun. I wait till the sun is high in the sky (about noon) and the skies are not cloudy. That requirement is easy in Arizona, but may delay your etching of PCB’s is some areas. Slightly cloudy skies may just require a little longer exposure time, but extremely cloudy skies should probably delay the exposure until another day. If all else fails, you can buy a light source from one of the PC supplies vendors, but that will add cost to the project. Read this entire step and understand it before attempting to expose the PCB. The “positive” system only gives you one chance to get it right. It is really quite simple, but there are several ways to screw it up.

Place the book on a surface in a reasonably dark area. My office in the garage becomes relatively dark with the lights turned off, and the blinds closed. There is still enough light to see what I am doing, and as long as I don’t dally, the light is not strong enough to affect the sensitized board. Place a folded cloth towel on the center of the book, and then place the sensitized PCB on the towel, sensitized side up, so that it’s edges are just within the towel about ¼ inch or so. The protective cover of the sensitized side of the PCB should be removed to expose the PCB. The first picture shows the towel and PCB laying in proper position, but for photography, the protective cover has not been removed yet.

Place the positive w/guides on top of the PCB and slide the positive to align the PCB with the added guides. The towel gives the back of the PCB support, so that it is cushioned in case the book is not perfectly flat. This is shown in the second picture. Note how the corner marks of the artwork align themselves with the actual corners of the PCB. If yours do not align correctly, rework the guides before proceeding.

Place the piece of glass over the positive, being careful not to slide the positive out of alignment. This is shown in picture 3. The glass provides a bit of pressure to push the artwork against the PCB and hold it so light cannot infiltrate between the artwork and PCB.

A few trials of building this exposure “assembly” should be done with the protective cover still on the PCB to develop your skills at getting it done right. Then, remove the protective cover and go for it.

Pick up the book, artwork and glass assembly by each end, and hold them tightly aligned while moving to the exposure area. Place the assembly on some stable platform with the glass facing the sun. I place mine on the air conditioner unit, which is just outside the back door of the garage. It is tilted on top, so I can almost always set the artwork with its face directly to the sun. This is shown in picture 4.

As long as the artwork is dark enough to completely block the sun, exposure time is not too critical. The five PCB’s that I made today for this tutorial were exposed for intervals of 2, 3, 4, 5, and 6 minutes, just to show that it isn’t all that critical. With bright sun. an exposure time of around 3-4 minutes should be adequate. In semi cloudy skies an exposure time of 6-10 minutes would probably work OK. In extremely cloudy skies, wait for a better day.

Bring the assembly into a semi dark area and remove the PCB. It can then be dropped into the developer. The last picture shows what the exposed PCB looks like before developing. The exposed areas are now almost blue, while the protected areas are still green.

Developing the exposed PCB

Drop the exposed PCB into the developer, exposed side up. The developer will remove the exposed sensitizer from the PCB. It will take a few minutes.

Alternately lift the edges of the pan to move the developer solution back and forth across the face of the PCB. The exposed areas will begin to lose the sensitizer from the PCB. The first three pictures show the PCB in the developer at the start, midpoint, and almost finished.

When all of the sensitizer in the exposed areas has been removed by the developer, and bare copper can be seen where it was exposed, remove the PCB from the developer, and rinse it with lukewarm water. Movement during the developing process is important, since the movement of the developer helps wash off the sensitizer that was exposed. Lukewarm rinse water allows a bit of additional development if there are places that need more removal of the exposed sensitizer. Cold rinse water “sets” the PCB so no further development is possible. Rinsing is shown in picture 4.

Shake the water off the PCB and allow it to dry completely before the next step. If you have shop air, use your air nozzle to blow the water off. Handle the board carefully to avoid scratching the sensitizer left on the PCB, since it will protect that area from the etchant during the next step.

Picture 5 shows the five PCB’s that were exposed and developed this day. Note that it is impossible to tell which one was exposed for 2 minutes and which one had 6 minutes.

Leaving the PCB in the developer too long will result in all sensitizer being removed, which will mean your board is unusable. Picture 6 shows a PCB which was left too long in the developer. All nomenclature is gone, and the pads in the lower right corner are almost completely gone. Don’t wait to long to remove your board or this can happen to you.

The mixed developer may be stored in a clean glass or plastic container if desired. I don’t know what its shelf life under storage conditions is, however. It can be discarded in the sink drain, and washed down with lots of water.

Etching the developed PCB

Place one or both PCB’s, fully dry, in the bottom of the Pyrex or glass pan, copper side up. Pour the etchant, in this case ferric chloride, over the PCB’s enough to cover them reasonably well. It will probably take about 5 ounces or so of ferric chloride to cover the PCB’s. As in the developer process, alternately lift one side of the pan then the other, to move the etchant across the face of the PCB’s. Be careful not to slop the ferric chloride out of the pan, cause it is messy and very active at eating and staining things. Note the condition of my sink in these photos. You don’t want to do that to mama’s sink.

Heating the ferric chloride will increase its effectiveness, but it will get the job done at room temperature. It will just take a bit longer, and ferric chloride is not something I really want to mess with any more than necessary. Adding about 25 percent volume of hot water to the ferric chloride will increase its efficiency, so I usually do that. Picture 1 shows the PCB’s just beginning the etch process.

Continue to rock the etchant across the faces of the PCB’s to help remove the dissolved copper from the faces. It will probably take about 30 minutes to eat off all the exposed copper. Picture 2 shows them almost clear of all undesired copper. Only a small smudge is left under the nomenclature. When all the exposed copper is gone, remove the PCB’s from the pan by lifting them out of the etchant with a popsicle stick or wooden pencil. I handle them by the edges bare handed, but you may want to wear a heavy set of rubber gloves if you have sensitive skin. Rinse them in your sink under running water till all etchant is removed. Rinsing is shown in Picture 3. At this time, I also use the steel wool pad to remove the sensitizer which covers the copper left. It comes off easily, leaving a printed circuit board which only needs holes to be useable. This is shown in Picture 4. Be careful not to drip ferric chloride on the floor or countertop, since it can cause nasty stains.

Disposal of the used ferric chloride can be accomplished by rinsing it down the drain along with lots of water. Since it can stain things, be careful when disposing of it. Picture 5 shows the five etched PCB’s built this day.

Drilling the PCB's

All holes in the PCB can be drilled with a hand drill, but a small drill press is much easier to use. I drill the holes for components with a #48 drill, which is .076 inches. That is maybe larger than necessary, but not so big as to make soldering a chore. The iron core choke on this PCB is mounted with #4-32 screws, so it’s mounting holes are drilled with a #31 drill. The corner mounting holes are drilled with a #27 drill for #6 screws. The first picture shows the drill bits awaiting use.

Drill all holes with the smallest drill bit first, because the smaller bits tend to want to find the center of the pad easier than the large bits. Picture two shows the small bit about to drill the first hole. The larger bits then center themselves on the small hole already drilled.

Picture 3 shows me drilling one of the PCB's. Note the small magnetic flashlight placed on the base of the drill press. It shines up through the hole in the work platform and through the PCB making it easier to see the little hole where I need to drill.

The fourth picture shows all five PCB’s made today.

Assembly of the crossover PC board

Mount the crossovers parts to the PCB, and solder them on the back. I bend the leads over against the PCB to make the connection a little more secure, and to increase the surface area of the solder joint, lowering the resistance somewhat.

Zilch likes to secure the parts to the PCB, since he once traced a warble in a speaker to a capacitor vibrating on the crossover PCB. Hasn’t happened to me, but why push my luck. An application of RTV Silicone underneath all parts will help secure them to the PCB, and is mandatory for the small air core choke, since it isn’t physically held in any other way.

The picture shown is of crossovers previously built using this printed circuit board. It utilizes the third order HP, but for EconoWave use, the capacitor on the right would be replaced with a jumper. .

And, if you have gotten this far, and completed your own crossovers, you can be very proud of the professional looking crossovers you have made, even though no one will likely ever see them. But in your heart, you will know!

Congratulations.

Will you be making film positives for EconoWave and Indignia available to AKers, Jack, for those who want to DIY them according to this method?

If so, I suppose we can simply PM you for costs and arrangements to obtain them?

Zilch said:

Will you be making film positives for EconoWave and Indignia available to AKers, Jack, for those who want to DIY them according to this method?

If so, I suppose we can simply PM you for costs and arrangements to obtain them?

Click to expand...

Yes, Rick has saved the artworks for both on his computer, so buying more should not be a problem. Anyone interested, PM me, and I will get cost and delivery info. This is a really fun way to build crossovers.

jackgiff said:

This is a really fun way to build crossovers.

Click to expand...

Or an easier way fur us dummies to build crossovers. :stupid:

Your life has officially ended! Your mailbox will look like Michael Jackson's after his first big hit I can see it now, boxes and boxes of request and purchase orders litter the front lawn,:yippy:

Incredible display of talent, patience and ingenuity. Thanks so much for the presentation.

I was serious about the work orders, will there be various xovers coming down the pipe???

That is too cool. It almost looks like it is too nice to be mounted on the inside of the box, I'm thinking maybe a standalone glass enclosure for the eyes to behold:scratch2:
Great work!!

Thanks,
Rick

I see there are different sizes of sensitized boards available at PE. Is that part of the "secret" here, to lay out the artwork for one of the stock sizes, or can they be cut to any desired size before processing?

I can see how with a double layout of 3" x 6", a 6" square board might be cut in two after etching. Does that work, or is it not worth the hassle?

Must bookmark this thread for future studies, thanks for the detailed post. Some day this will come in handy!

this is probably one of the best DIY instructions I have ever read.

good job!:tresbon:

Very Very nice Jack!

I use a hot glue gun to secure the pieces to the board, just a dab under each
Xover part holds them in place and is a nice anti shock device at the same time.
(Comes apart fairly well if you decide to change something later)

Very very nice work. It looks like I'll have to try the UV method next time. Toner transfer method has failed me in the past

Brilliant tutorial, all 'round!


Philip.

Zilch said:

I see there are different sizes of sensitized boards available at PE. Is that part of the "secret" here, to lay out the artwork for one of the stock sizes, or can they be cut to any desired size before processing?

I can see how with a double layout of 3" x 6", a 6" square board might be cut in two after etching. Does that work, or is it not worth the hassle?

Click to expand...

I choose stock sizes to avoid having to cut them apart. I am not so good with a hacksaw. That said, the guides used in the tutorial were made from the strip cut off a 4X6 board to build your Indignia crossover which is 3X6.

A single 6X6 PCB costs $8.53 from PE while two 3X6's cost $4.32 each. A savings of 11 cents is not worth my time cutting a board in half. To make a custom sized PCB, a board could be trimmed, but since it goes into a speaker, and may never see the light of day again, why bother minimizing floor space?

I need to point out that I am not in the PC making business. This is strictly for my own use. The five PCB's made in the tutorial were for my HT project. I did end up giving two of them away for a special project, and will need to make two more. I wanted to share the absolute joy of doing something for yourself that most people wouldn't even dream of trying. Who do you know who etches their own PC boards?

The positives used in the tutorial and the Indignia 3.5 may be available if Rick wants to make some more copies for me. But you will need to expose, develop and etch them yourself. That is the real joy part of building crossovers with printed circuit boards.

This is just crying out to be made a Sticky, whether here or in the DIY forum.
Brilliant tutorial jackgiff. :thmbsp:
As soon as I finish twisting all my speaker cables and ICs and after I finally do a TT acrylic cover and.........aah, this is what AK is all about.:yes:

tx_polkhead said:

Must bookmark this thread for future studies, thanks for the detailed post. Some day this will come in handy!

Click to expand...

Have added this to the reference sticky thread. :yes: