DIY Etching of Printed Circuit Boards (PCB) | Home, DIY & Stuff

DIY Etching of Printed Circuit Boards (PCB)

PCB Screen PrintingMaking your own PCB boards for DIY electronics projects is not difficult.  Doing so as a DIY project is extremely handy and allows almost anyone to custom design one-off, or small batch circuit layouts relatively quickly and cheaply, without the need for the volumes or costs involved in using the services of professional circuit board manufacturers.   With care, DIY PCB project results are usually of extremely high quality and are very satisfying.  Even more interest can be added to projects when printed circuit boards are combined with CNC cutter designs for shaping of the circuit boards.

There are various different methods for making PCB boards.  Each method has various pros and cons, with most considerations being linked to cost, quality of finished product, accuracy required for fine circuits and availability of chemicals and materials.

Here we describe the UV exposure method for transfer of circuit layout image to a pre-sensitized Copper coated PCB blank, followed by etching with Ferric Chloride.  The technique is accurate, convenient and provides a high quality etching.

 

Warning: This method uses toxic and highly corrosive chemicals. Suitable safety, ventilation and personal protective gear is a must. Additionally, the use of Ferric Chloride to etch Copper produces Copper Salts in the form of Copper Chloride. All Copper salts are extremely toxic to the environment. Even small amounts kill aquatic organisms and other animals if it gets into waterways and soil. Please ensure ALL leftover liquids from PCB making are disposed of in an environmentally responsible manner.

 

Basic Outline of Steps Required



The UV exposure and etching method requires 6 main steps:

  1. Design and print the circuit layout onto transparency
  2. Transfer the circuit design onto a Copper coated PCB blank using UV light exposure
  3. Develop the exposed image using Sodium Hydroxide
  4. Etch away Copper between the required circuit tracks and contacts
  5. Drill holes in the PCB for placement of components (for through-hole PCB designs)
  6. Screen print and protect the PCB

 

Required Materials

In the past, perhaps the biggest hindrance in using the UV exposure method was perhaps the availability of the required UV sensitized PCB blanks.  However, these days, the copper coated PCB blanks and all other chemicals and materials are readily available online or from any good chemical or electronics supply outlet.  Our preferred brand and supplier for many electronics and circuit board materials, from Japan is Sunhayato.

  • (Optional) Circuit Board Design Software to produce layout design
  • UV sensitive PCB board Blanks
  • UV light source (UV lamp, tungsten element spot light, or in a pinch, bright sunshine)
  • Personal Protection Equipment (chemical resistant gloves, eye goggles, chemical resistant apron, etc)
  • Sodium Hydroxide Solution for developing  – ie: highly corrosive!
  • Ferric Chloride (for Copper etching) – ie: also highly corrosive and toxic!
  • Ample running wash water
  • Shallow plastic trays (x2)  nb: Do not use metal!
  • Wood or plastic tongs
Making DIY printed circuit boards (PCB) can be easy, fun and cheap, especially when coupled with a CNC cutter.

Making DIY printed circuit boards (PCB) can be easy, fun and cheap, especially when coupled with a CNC cutter to design board shapes for specific project requirements.

 

 

Computer Design Software Available

Computer circuit and PCB design packages with Opensource GPL, free or  sponsored licenses will more than likely satisfy the needs of many DIY electronics hobbyists.  Some examples include:   Fritzing, PCB Artist, DipTrace, XCircuit and gEDA to name a few.  These are listed without order or preference and offer differing features, capability and quality.

Many commercial design packages are also available, but can be pricy if you are just messing with home DIY projects.  Such an option that we like however is Eagle PCB by CadSoft, which offers a non-profit, DIY hobbyist license of Eagle PCB (free at time of writing) if you are able to truthfully sign and comply with their non-profit declaration.

 

So, with all the above said …. LET’S GET STARTED!

 

Making Your Printed Circuit Board

 
Step 1 – Design and Printing

Print the negative of the desired circuit layout onto a transparent film.

Print the negative of the desired circuit layout onto a transparent film, with the design oriented such that the toner side can sit directly against the Copper coating of the PCB.

Various computer packages are available for assisting with electronic circuit design, testing and even simulation.   After initial circuit design, such packages allow for placement of the circuit tracks and components onto a virtual PCB of a desired size.

The PCB layout design is printed on to a transparent film using  a laser printer or photocopier. Try not to touch the surfaces of the transparency sheet both before and after printing as the oils in your fingers can often degrade print quality.

This printed transparency will be used in a similar way to a photographic film negative, so the aim is to make the circuit tracks on the print as dark, sharp and as well defined as possible.

In this exposure method for marking PCBs, where the ink is black and solid on the design, the Copper on the etched PCB will remain.  Image sharpness and a print that totally blocks light where circuit Copper is required  provides the best results for image exposure on the PCB board.

Warning: Careful you choose a transparency film suitable for heated drum, toner transfer type printers and photocopiers rather than inkjet type transparency. Don’t use the melt-able plastic inkjet transparencies! It is easy to end up with a melted mess of plastic on your toner drum and destroy your printer if using the wrong type of transpareny film. Just saying.

Even for a DIY PCB maker, the UV exposure method allows development of extremely fine circuit tracks.  It is part of the reason we like the method over other methods.

When using a computer generated layout, ensure it is printed at a 1:1 size ratio.  Otherwise chips and other components will not match up with your circuit contacts.

In the case where a computer or photocopier is not available for printing, a black permanent  marker pen can also be used to mark up a transparency sheet to produce the circuit lines and contacts required.

Tip: For printers that leave toner holes or do not image darkly enough to stop light passing through the printed areas, you can tape multiple layers of transparency together.

Tip: It is usually a good idea to mark your transparency image with corner locating marks so it is easy to exactly position the transparency image over the PCB blank. This is extra important if your are printing double sided circuit boards as components and pin holes will need to line up perfectly on both side of the board.

 

Step 2 – Exposing the UV Sensitive PCB Board

Light and UV Sensitive PCB Blanks

A blank Copper coated PCB.

A blank Copper coated PCB.

Now we transfer the transparency image onto a Copper coated PCB blank using UV light.

The pre-UV sensitized sheets of PCB blanks come packaged in light proof bags, inside an outer sealed envelop.  Do not open the inner bag in bright light or remove the PCB blank(s) until ready to use them.

Move to a dimly lit workspace (away from sunshine, fluorescent and incandescent lights).  A work area with a red or yellow light can used if you prefer to work in well lit rooms.  These colored globes are  available from most hardware stores.  Absolute darkness is not usually required as long as you work quickly and are careful not to expose the blanks to light unnecessary.  It is wise to use a darkroom bag to open multi-board packets, so not to unnecessarily or accidentally expose other boards in the packet while removing a working PCB blank.

Blanks can be cut to required size by scoring on both sides with a sharp blade and then snapping.

 

Exposing Light Source

UV lamps and dedicated light boxes are faster at exposing boards, but are not absolutely necessary.    Halogen or incandescent work lamps (200-500W) and fluorescent tubes work just fine.    At an exposure distance of approximately 15cm (6 inches), these light sources will normally require 5-12minutes exposure time.

UV light boxes expose very quickly.  Approximately 30 seconds to 1 minute is all that is usually required.  (Be careful of sunburn if using these over prolonged periods and wear UV eye protection!)

In a pinch, bright sunshine and a little exposure time guesswork can also be used to expose PCBs.

 



Exposing Arrangement and Exposure

Remove the PCB blank from the protective cover in very dim light.  Peel away the thin top (white) protective plastic layer.

Assuming the light source is placed above, lay the PCB flat with the printed transparency film lined up exactly as required for the exposure.  Ensure the toner print side of the transparency is directly against the Copper coating of the PCB blank (ie: ensure the circuit is printed the right way around to allow this).  This prevents light leaking under the print edges.

Place a sheet of clean heavy glass or acrylic on top of both the PCB and transparency film.  Ensure the transparency is pressed firmly and flat against the PCB blank.

Switch the light source on and expose the PCB blank for the required exposure time (as mentioned above).
Upon finishing the exposure time, you should be able to see a slight discoloration of the exposed circuit board tracks on the PCB.

 
Step 3 -Developing the Exposed PCB

Developer

Sodium Hydroxide (NaOH), otherwise known as Caustic Soda or Lye,  is used to develop the exposed PCB.  This comes in either granular, powdered or liquid form.  The exact solution strength is not essential for development.  It will simply affect development time.

Developing a UV Exposed PCB Board

A UV exposed PCB board after the developing stage.

We use 25g of granulated Sodium Hydroxide in 500 mL of deionized  water (ie: pure water).  This allows development of the exposed PCB within a matter of seconds and is perhaps overkill.  But this stuff is cheap and can be bought from hardware and chemical supply stores for a few bucks a kilogram.

Smaller specialty (expensive) satchels or pre-mixed liquids can also be obtained from electronics stores for this purpose.  Use as per the directions if you purchase from electronics stores, as working concentrations and requirements will depend on product brand and supply concentration.

Keep in mind that Sodium Hydroxide in granular form is an extremely strong Alkaline.  It will quickly and painlessly burn holes in you!  All you feel is slipperiness as your skin fats are destroyed and turned to soap.  Use of suitable eye and skin safety gear is a must.

 

Developing

Place a centimeter or so depth of the mixed NaOH solution into into a shallow plastic tray.

Immediately after UV exposure, place the PCB into the NaOH liquid face down and continuously agitate with tongs.  The printed circuit develops quickly.  Allow to develop until all circuit tracks are distinct and clear and there is no remaining discoloration in exposed areas.

Remove and wash thoroughly under running water.

 

Step 4 – Etching the PCB Copper Coating

Ferric Chloride Fe(III)Cl3 for Etching

Etching Copper PCB with Ferric Chloride

Leave the PCB in the Ferric Chloride solution until all UV exposed areas are free of Copper.

Ferric Chloride is a toxic and highly acidic chemical.  All suitable ventilation and safety precautions require suitable attention.  Do not get it anywhere near the alkaline Caustic Soda from the previous step as any mixing may cause a dangerously violent chemical reaction!  Further, Ferric Chloride is a dark red/brown color that stains anything and everything.  Clothes, stainless steel sinks, skin, etc, etc.  Be warned!  Due to environmental dangers, it is illegal to dispose of Ferric Chloride down drains.

Ferric Chloride is available relatively cheaply from laboratory supply companies, or (more expensively) from electronics suppliers.

 

The Copper Etching Process

Pour a small amount of Ferric Chloride into a shallow plastic tray.

Place the developed and washed board from Step 3 face down in the shallow solution and agitate until all Copper has been thoroughly etched from exposed areas of the PCB.

Remove and  wash thoroughly under running water.

 

Step 5 – Drill Hole-Throughs for Components Pins

Holes drilled in PCB

Holes are drilled in a sample circuit board at positions required for component hole throughs.

Once the etching process is complete, the PCB can by placed on a CNC drilling machine, or drilled manually by mini drill press, in all contact positions that require holes for component pin throughs.  Selection of drill bit will vary depending on component leg and pin sizes, but 0.5 – 1.0mm diameter bits are typical.

Larger corner screw-down holes are also usually handy on most circuit board designs.

 

 

 

Step 6 – Screen Printing and Coating

If the PCB is to be used for repeated production or requires a professional looking finish, it is often useful to screen print component and circuit information onto the board. This requires oil based screen printing ink.

Clear epoxy coating can also be applied to the bare Copper coating for protection against tarnishing and corrosion.

 PCB Screen Printing

 

Please Note:  This process and chemicals involved have potential to be dangerous and environmentally damaging!  The information on this page is therefore offered for the reader’s consideration and examination only, and it is the reader’s responsibility to satisfy him or herself that information is suitable and complete for needs before use.

Read and understand all associated Materials and Safety Data Sheets for chemicals before starting and ensure all suitable safety measures and protections are taken when handling them. The writer and Home DIY & Stuff  are not responsible or liable for any injury, damage, or loss as a result of using this information or process.








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