Prototyping Center

In addition to Dry Film Negative Resist (Cat. No. 416-DFR), the following items from MG Chemicals, or their equivalent, are required:

• Negative Developer (Cat. No. 4170-500ML)
• Exposure Kit (Cat. No. 416-X)
• Transparency Film (Cat. No. 416-T)
• Foam Brush (Cat. No. 416-S)

These items are also required, but not supplied by MG Chemicals:

• Laminator – any baseline laminator from an office supply store will do
• Cutting device – sharp scissors or fabric cutter
• Safelight – a working area lit by a yellow or red 40 watt incandescent bulb.
• 2 glass or plastic trays - one to contain the developer solution and one for rinsing water
• A measuring cup and water

Overview
Working under safelight, a portion of dry film resist is cut from the roll and laminated onto the prototype board.

There are five steps to using this resist:

• Printing the circuit on a transparency
• Creating a safelight environment
• Application
• Exposure
• Development
• Stripping (after use)

Printing the circuits on transparencies
Before beginning this step you will need to print the circuits for each side of the board onto heat stabilized transparencies (MG Cat. No. 416-T) using a laser printer, 600 dpi or greater. An ink jet printer will not work because the ink is not sufficiently opaque.

In the Professional Prototyping Process, and generally whenever the resist is acting as a plating resist, the artwork should be positive, so the black ink on the printed transparency covers the desired circuit.

In the Basic Prototyping Process and generally when the resist is acting as an etch resist, the artwork should be negative, so black ink on the printed transparency covers the copper that will be etched off.

Ideally, artwork should be mirrored before printing, so that when the transparency is placed on the board, the ink will be on the bottom and thus flush against the board, although this is not always critical. If the ink is on the top of the transparency, during exposure light hitting at an angle can potentially get under the edges of the image, resulting in a fuzzy exposure.

Creating a safelight environment
Dry film resist is exposed by ambient light, so a dimly lit work area must be created. A darkroom lit by a red or yellow 40 watt incandescent bulb is optimal, but a plain 40 watt bulb across of the room with a little stray light coming in here or there will be fine for short intervals. Fluorescent lighting and sunlight will expose the resist prematurely.

Application
Clean the board using fine steel wool or similar abrasive pad and rinse well with water. Dry the board quickly with a hair dryer to prevent corrosion. Enter your safelight environment, and take the resist out of the package. Cut off a portion of resist large enough to cover both sides of your board, folded over one side, leaving 1 cm of excess resist on all sides except the side the resist is folded over. The easiest way to do this is to lay the resist flat, lay the board on it, and then cut around the board with a fabric cutter, flipping the board over one side while cutting to double the area. If you do not have a fabric cutter, sharp scissors or an exacto knife will work fine.

If it is a single sided board, the process is almost the same but the back side of the board does not need to be covered. Make sure, however, that there is at least 1” folded over one edge; this edge will be the first one through the laminator.

Exposure
In the safe light environment, set up the Exposure Kit (Cat. No. 416-X), but do not turn it on. Place the laminated board under the center of the light fixture. Place the appropriate transparency on the board, being very careful to align it properly. 

Carefully place the clear acrylic cover included in the Exposure Kit (or similar clear weight) over the transparency to hold it in place. 

Turn on the exposure light and expose the board for 12 minutes. Turn off the exposure light, and remove the acrylic cover and transparency.

If the board is double sided, flip the board over, place the transparency printed with the circuit for that side on the board, replace the acrylic cover, and then turn on the exposure light on for another 12 minutes. Turn off the light and then remove the board. 

Examine the board to ensure the exposed resist has turned from green to blue, indicating a successful exposure.

Development
While the board is exposing, dilute one part MG Negative Developer (Cat No. 4170-500ML) with 10 parts room temperature water into a tray large enough to comfortably fit the board being developed. Mix enough solution to be 1” – 2” deep in the tray.

After the board is exposed, still in safelight, remove the outer protective coating from the resist (which might take time, be patient), and place the board into the developing solution. Gently agitate the solution with the smoother brush, flipping the board over now and then to ensure both sides develop evenly, and keeping an eye on the board’s progress. Towards the end of the process, take the board out of the solution now and then and inspect it closely to determine if it is done developing or if you need to submerge it back into the solution.

When the board is placed into the developing solution, all of resist that was not exposed to light will be removed, but the time can vary greatly, between 30 to 120 seconds. Because of this variance, it is important that developing be observed instead of timed. The development stage is completed when the desired circuit and through-holes are bare copper, and the remaining copper that will later be etched off of the board is still completely covered with dry film resist.

When development is completed, quickly rinse the board in water and dry with a hair dryer. After this it is ok to work with the board in normal light again.

Stripping
After plating or etching is complete, remove the resist by submerging it in Resist Stripper (Cat. No. 4185-500ML).