Making Printed Circuit Boards Paul Kerchen i3 Detroit

About i3 Detroit ● Educational ● Non-profit ● Volunteer-driven ● Open to the public ● Donations welcome!

Why Make Your Own PCBs? ● Faster turnaround than PCB fab services ● Cheaper for small runs ● More creative freedom

Overview ● Translate schematic to layout ● Transfer layout to blank board ● Remove unwanted copper ● Drill holes ● Solder components ● Enjoy creation

Electrical Schematics ● Describes components and connections between them ● 'Universal' language ● Doesn't necessarily describe the layout of components

From Schematic to Layout ● Design the layout using EagleCAD, ExpressPCB, etc. ● Download from the tubes ● Draw by hand

PCB Layout Software ● Several free/inexpensive options: Eagle CAD, Express PCB, FreePCB, etc. ● Parts libraries and router are key features!

Eagle CAD ● Free version for non- profit/educational use ● Size of boards limited to roughly 3”x4” ● Very popular among hobbyist community ●

Scratch or Etch? ● CNC milling requires milling machine and software ● Chemical etching doesn't require any expensive equipment

Basics of Etching ● Chemicals combine with exposed copper and remove it from substrate ● Copper that is part of circuit is protected from chemicals by mask ● Ferric chloride (FeCl 3 ) is commonly used

Ferric Chloride Safety ● Fairly strong acid (pH ~3) ● Toxic: avoid ingestion! ● Avoid inhaling fumes ● Corrosive to most metals: glass/plastic utensils and containers only ● Stains are permanent in most materials

Masks ● Prevents chemicals from reaching parts of the board that constitute the circuit ● Inert or resistant to chemicals ● Usually removed after etching to allow for easier soldering

Heat Transfer Lamination ● Heat and pressure used to fuse mask to copper board ● Can be done with photo paper and an iron ● Mask bleed can be a problem if pressure applied unevenly ● I3 has a small lamination press

Laser Resist Ablation ● Entire board is covered with masking agent (eg., spray paint) ● Laser cutter used to remove mask from areas that are to be etched by burning mask off ● I3 has a laser cutter

Silkscreen Printing ● Mask is selectively applied to copper via silkscreen mask ● Getting good detail and accuracy is tricky with DIY equipment ● Often used to identify component placement, though

Photomask/Photo-resist ● Photo-reactive chemical coating on board ● Exposed to light with positive or negative mask on it ● Board is developed after exposure but before etching

Exposing the Board ● Put in light frame with mask flat against copper ● Expose for ~10 minutes w/100 watt bulb at ~12” distance ● Develop immediately

Developing the Board ● Put exposed board in developer solution ● Agitate until PCB traces are clearly visible; exposed area should not have any hint of blue/green! ● Rinse in cold water to set remaining mask ● Ready for etching!

Taking the Plunge! ● Once mask is prepared, board is submersed in etching tank ● Heat speeds the etching process ● Agitation makes sure the etching is uniform

Monitoring the Etching Process ● It is possible to over- etch, resulting in thin or broken traces ● Check board every minute or so ● The exposed copper will turn a pinkish color before it is fully etched

Finishing ● Once etching is complete, rinse board thoroughly with cold water ● Remove photoresist with nail polish remover ● Drill & solder