How-To Instructions for Making Printed Circuits

How to Make PCB'S with Dalpro Products

Making high quality printed circuit boards with Dalpro products is easy -- all you need is a negative of your design, a water source, a glass tray, an electrical outlet, and a timer ... in minutes you can have a board ready for assembly.

The purpose of this How-To discussion is to help you become familiar with how Dalpro products are used, when they're used and what you might need to complete your boards. Processing your boards will require use of chemicals; as with all chemicals, using common sense and carefully reading the instructions will help you properly handle any Dalpro materials. All chemistries you receive from Dalpro will include instructions for proper usage and Material Safety Data sheets.

Throughout this discussion, you will find Catalog Product Numbers in bold type. A chart at the bottom of this discussion lists additional data on these products. And we've even included a simple "glossary of common terms" in case there's terminology that's new to you.

Dalpro has been providing hobbyists and the electronics industry with supplies and equipment to produce professional prototype and short-run circuit boards� easily and economically. And we stand behind everything we do. . . so if you have any questions or problems with any Dalpro product, just give us a call. Technical representatives are always available to answer any question you may have. We'll be glad to help any way we can.

E-Mail: sales@dalpro.net or Call: 1-800-325-3878

Before you start. . . please remember that all Dalpro pre-sensitized copper clad is negative acting, which means you'll need a negative to produce your boards. A "negative" will have a black background and the circuit board pattern will be clear; a "positive" will have a clear background and the circuit board pattern will be black.
Don't have a negative, see heading  If You Have a Positive ....... 2

 

USING YOUR NEGATIVE    .....2

You will need a UV (ultraviolet) light source for exposing all Kepro photosensitive materials. The best source is a BX-101 UV Fluorescent Tube. Some people prefer to use natural sunlight, but it is not a consistent exposure source. You need a UV light source with a spectral intensity of 350-425 nanometers, or your exposure results could be affected.

When UV light strikes the panels, it hardens the resist but if your light source is marginal, the resist may not harden properly and could slip or slide in the developing process.

you will need to decide which type of presensitized photoresist copper clad boards you prefer to use. There are two kinds:

• Dry Film Resist DF-type material

Dry Film Resist (DF) is pre-laminated to the copper surfaces and is ready for exposure. This resist is a 1.3 mil thick, scratch resistant, hard to damage, high resolution mask for print-etch and plating applications. Developing and stripping chemistries associated with dry film are mild, aqueous-based chemicals and do not require use of solvents.

Pre-sensitized DF-type copper clad boards are available in various copper foil weights and substrates, one-sided and two-sided, in various sizes from 3"x6" up to 12"x24".

Each Dalpro photoresist requires its compatible Dalpro developer and stripper. For your convenience, here's a simple chart showing the compatibility and different chemistries required for each process:

 

  If You Have a Positive ....... 2

You will need to turn your positive into a negative in order to proceed. If you're working with a board pattern from a magazine .......

• you can just transfer the positive pattern onto a sheet of our Copy Film, CF-8115 using a plain paper copier .......
• then use our Photo Reversing Kit FK-701 to reverse your positive into a negative in just two simple steps.

NOTE: If your positive is already on transparent media (film), you can eliminate the Copy Film step in the reversal procedure listed above. Also available is our all-in-one Copy & Reversing Kit CR-705. This kit contains all the materials you'll need to reverse a positive into a negative.

IMPORTANT:

Be sure to cut your film slightly larger than your design (1/2"-1 " ) so that you'll have room to handle the film on the edges later.

Once you have reversed your positive, you're ready to continue....

 EXPOSE    .....3

With your negative, your light source and your boards, you will need to be able to monitor UV light intensity during exposure of the board. For that, use an ST-21 Exposure Step Tablet. You just place the Step Tablet alongside your negative and you will be able to determine the level of exposure as the pattern is being exposed on the board. The Step Tablet is reusable.

For Dry Film Photoresist-DF and Liquid Photoresist-S. . . your work area should be dimly lit, using a yellow "bug light" or gold fluorescent light�they provide a high level of light, but will not expose the photosensitive emulsion. A "red darkroom safety light" is not necessary.

You'll then expose your negative to the copper clad laminate with a BX-101 UV Fluorescent light source. Just sandwich the negative between the piece of glass and the board. Emulsion side for the copper clad (the side of the board with the copper) and emulsion side down for the negative. You can determine the emulsion side of the negative by scratching an edge outside the image area with a sharp point which will remove the colored emulsion�only the emulsion side will scratch. Exposure time will vary depending upon the light source you select. UV light hardens the light struck portions of the photoresist. Check your instructions for exact times and procedures.

 DEVELOP   .....4

For Dry Film Photoresist (DF). . . the developing process requires DFD-12G dry concentrate mixed with hot tap water. Remove the protective film and place the board in the heated developing solution. Gently rock the container for 45 seconds to one minute. Then carefully wipe the panel with the soft, wet sponge until the exposed pattern is all that remains. The areas of the board that have been exposed to ultraviolet light will be hardened and cannot be removed by the developing solution.

(S). . . the developing process requires KD-type solvent based developing solution which softens unhardened emulsion. In a metal or glass tray you'll thoroughly submerge and agitate your board in the solution for 1-1� minutes and immediately rinse it in lukewarm tap water. Your pattern will then be visible on the board.

Small voids or scratches may be found in the exposed pattern, if so you need to repair these areas on the resist prior to etching. To touch up these areas you can use Kepro's lacquer based etch resist marking pen RMP-700A.

To etch your boards you can use E-type Ferric Chloride or SP-type Sodium Persulfate. Ferric Chloride is a liquid, ready to use etchant with unlimited shelf life. Sodium Persulfate is a dry crystal that mixes with water and has a limited shelf life after it is mixed, but unlimited when it is dry. To successfully etch your boards you'll need to constantly agitate the panels in the etchant. Warming the etchant greatly accelerates the etchant's reaction to the copper, but do not exceed 110 degrees Fahrenheit. Then rinse and dry the panels. Carefully follow the instructions accompanying the etchant you select.

It is at this point that we recommend you re-inspect your boards and complete any mechanical processing you may have planned, such as drilling, notching, etc .

Prior to using the circuit board you'll need to remove the photoresist from the etched panel. The copper under the photoresist is clean and ready to be soldered.

For Dry Film Photoresist, you'll use DFS-12G, Stripper, a dry concentrate which mixes with water. For Liquid Photoresist, you need PRSK Stripper, a liquid solution.

If you handle your boards and the copper has become oxidized, dirty or fingerprinted, you may want to use CU3A, a chemical used to clean raw copper. and/or FSB-500 a very fine non-metallic cleaning pad, to clean especially dirty or oxidized boards.

You may choose to tin plate your panels to enhance soldering. Tin plating must be completed just prior to soldering. You can use ITP  an immersion tin plating solution which deposits an extremely thin layer of tin on the bare copper surface of circuit boards.

In addition to supplies and equipment for the hobbyist and prototyper, Kepro provides complete Print-Etch and Plate-Thru Facilities for in-house operations. All Kepro Bench-Top units are pre-engineered for easy installation and set-up, they are simple to use and are backed by Kepro's unconditional service commitment.

CAUTION:

For disposal of all Kepro chemistries, please check with your local EPA.

Go to END of Document

Glossary of Common Terms

• Aqueous-based: Chemistries shipped in a dry state that require the addition of water prior to use.  
• Exposure: To subject the photoresist to an ultraviolet light source. 
• Nanometer: Unit of measure of light wavelength.  
• Negative: Artwork/film in which the desired pattern is clear on an opaque background.  
• Negative-acting: Refers to photoresist that requires the board's pattern to be in a negative form to produce the correct image when processed.  
• PCB: Printed circuit board; interchangeable term with "printed wiring board" (PWB).  
• PWB: Printed wiring board; interchangeable term with "printed circuit board" (PCB).  
• Photoresist: Coating applied to copper clad, which is light sensitive.  
• Photosensitive: Properties are altered by exposure to light.  
• Plate-Thru: A deposit of metal in the holes of a 2-sided PCB to establish electrical continuity between the two sides.
• Positive: Artwork/film in which the desired pattern is opaque and the background is clear.
• Pre-laminated: Material that has a dry film photoresist already applied to the copper clad surface.  
• Print-Etch: To apply (print) the desired pattern on the copper clad laminate and remove (etch) the unwanted copper.  
• Resists: Material applied to the copper clad to protect copper from etching solution. 
• UV: Ultraviolet light.

Return to Top