Process step

Equipment

Comments

Format copperclad, backing material and entry foil

drill press, dowel pins

Insert registration holes and assemble "book"

Drill holes

CNC drill

Blow holes clear and spray rinse

compressed air and sink with hand wand

It is necessary to remove all of the dust and drill debris from the drilled holes.

Dry board

oven (100°C for 10 min)

Activate holes with conductive ink

conductive ink, squeegee, vacuum cleaner or compressed air gun

Drilled holes are filled with conductive ink which is blown out leaving a thin, uniform coating on the holewalls.

Cure ink

oven (100°C for 15 min)

Conductive ink is cured at 100°C to maximize adhesion.

Clean copper cladding

abrasive brush, scrub cleaner, sink with hand wand (rinse with tap water)

Residual ink must be cleaned from the surface of the board and the copper roughened to enhance the adhesion of the electroplated copper.

Dry activated board

oven (100°C for 10 min)

No water should be left in the holes. It can impair the adhesion of the plated copper.

Copper plate board for 30 minutes at 20 ASF

acid copper electroplating system

Pull the board out of the plater and examine each hole to ascertain that each hole is plated without gaps or voids.

Flip board top to bottom and reinsert into plater.

Flipping the board will help compensate for the tendency of the plating system to deposit slight more copper on the bottom half of the board.

Copper plate board for 30 minutes at 20 ASF

acid copper electroplating system

Rinse board, blow dry, and dry in oven

triple rinse tanks, sink with hand wand, compressed air,  oven (100°C for 10 min)

All residual plating solution and rinse water must be removed from the board.

Laminate both sides of board with photoresist

roll laminator,  photoresist

Align artwork on both sides of board and expose photoresist with calibrated UV source

UV source, UV exposure gauge

The easiest way to align the artwork is to align the round pads in the circuit pattern with the holes drilled through the substrate.  The eye is surprisingly effective at detecting any misalignment between concentric circles.

Set exposed board aside in a light-tight container for 15 minutes

dark poly bag

Setting the board aside for a few minutes after exposure will give the photopolymer time to fully cross-link. This will insure that optimum results are achieved during developing

Develop photoresist pattern

dry-film developing system

Develop until pattern is fully defined.  If necessary, scrub vigorously with kitchen sponge or soft brush to remove residual photoresist from areas of tight geometry

Rinse board, blow dry, and dry in oven

triple rinse tanks, sink with hand wand, compressed air,  oven (100°C for 10 min)

All residual developing solution and rinse water must be removed from the board.

Dry board / photoresist

oven (100°C for 10 min)

This last drying step will toughen the film and enhance adhesion between the photoresist and copper.

Etch board

etcher

Etch for 1/2 specified time, flip board and etch for remaining half.

Rinse board, blow dry, and examine areas of fine geometry for shorts

triple rinse tanks, sink with hand wand, compressed air,  loupe magnifier or stereo microscope

If shorts are present or the board is not completely etched, return to etcher for 1 minute

etcher

Repeat step above until board is completely etched.

Strip photoresist

Corning Ware dish with 5% solution of NaOH

Lightly scrubbing board after the resist is soft will speed up stripping.

Rinse board

sink with hand wand

All stripping solution must be rinsed from the board.

Microetch circuit

etcher

Dip in the etcher for about 5 seconds to chemically activate the copper surface.

Rinse board, blow dry, and dry in oven

triple rinse tanks, sink with hand wand, compressed air,  oven (100°C for 10 min)

All residual etching solution and rinse water must be removed from the board (especially solution trapped inside through-holes).

Laminate with soldermask

dry-film laminator, soldermask

Laminating the board while it is still hot from the oven will enhance adhesion to the copper.  If the board has areas of closely spaced circuit elements, use wet lamination techniques to insure that no air is trapped between parallel traces.

Image soldermask with "pad master"

UV source, pad master artwork

Using transparent diazo artwork makes aligning the pad master MUCH easier.

Develop imaged soldermask

dry-film developer

Develop until pattern is fully defined.  If necessary, scrub vigorously with kitchen sponge or soft brush to remove residual photoresist from areas of tight geometry

Cure soldermask

UV source, oven (100(C for 30 min)

The post developing curing step renders the soldermask impervious to virtually any solvent or corrosive that the board is likely to be exposed to.  Of course, it also makes the soldermask almost impossible to remove.

De-panel individual circuits if panel consists of multiple, independent circuits

CNC driller/router