How do I print PCB?

Printed circuit boards (PCBs) provide the foundation for electronics that power devices we use every day. Printing a properly designed PCB turns a circuit schematic into a functional real-world product. While professionals typically handle PCB fabrication and assembly for mass production, DIY methods allow hobbyists and prototypers to print PCBs themselves. Understanding PCB printing techniques helps bring custom electronics ideas to life.

PCB Printing Overview

PCB printing transfers a layout pattern onto a copper-clad nonconductive substrate that becomes the electronics foundation. Typical steps include:

Design

• Draw schematic capturing components and connectivity
• Create PCB layout positioning parts and routing copper traces to connect them

Print Circuit Layout

• Print layout pattern onto transfer paper or photo board using laser/UV printer
• Some DIY methods directly laser print onto copper clad instead

Etch Board

• Chemically etch copper not covered by printed toner mask, removing unneeded copper
• Leave desired conductive traces protected by printed resist
• Generates conductors allowing soldering of components

Printed Circuit Boards – Materials and Tools

Printing PCBs uses various materials and equipment:

Substrate

• Fiberglass epoxy resin sheets clad with thin copper foil on one or both sides
• FR-4 glass epoxy is common – flame resistant and more resilient than paper or phenolic

Transfer Medium

• Laser printer transfer paper, photo paper, magazine paper pages
• Some methods directly print toner onto copper clad instead

Etchant Solutions

• Ammonium persulfate, ferric chloride, or sodium persulfate etchants eat away exposed copper
• Convert coated copper foil into isolated PCB traces

Equipment

• Laser/inkjet printer, laminator, clothes iron, chemicals, etching tank, safety gear

PCB Printing Methods

Common DIY PCB printing approaches include:

Photoengraving

1. Print layout on transparency film sheets using a laser/UV printer
2. Use photosensitive presensitized copper clad boards
3. Expose board to UV light covered by printed transparencies
4. Develop out unexposed photoresist, etch to remove copper, strip resist

Toner Transfer

1. Print mirror image of layout using a laser printer onto glossy paper
2. Use clothes iron to transfer toner onto copper clad blank
3. Chemically etch away copper without toner resist protecting it

Direct Toner

1. Print layout pattern directly onto copper clad substrate in laser printer
2. Fuse toner onto board using hot plate or laminator
3. Etch copper without fused toner resist guarding it

Method	Description	Pros	Cons
Photoengraving	Use transparencies and photosensitive boards	Higher resolution traces	Special materials, process steps
Toner Transfer	Clothes iron transfers laser printer toner	Simple process using common materials	Lower consistency, hard to align
Direct Toner	Print directly onto copper boards	Eliminates transfer step	Requires modified printer, lower toner adherence

Steps to Etch Printed Circuit Boards

With boards printed by the desired method, follow this process to etch conductive traces:

Prepare Etchant Tank

• Fill glass or plastic tank with ferric chloride or other etchant solution
• Include cooling coils, air pump, and heating element to maintain proper temperature
• Use safe handling procedures working with harsh chemicals

Add Boards and Adjust Flow

1. Secure printed circuit boards inside tank using non-metallic clips
2. Position boards ensuring solution flows evenly across surfaces
3. Circulate etchant via pump and coils maintaining uniform temperature

Monitor and Remove Boards

1. Check boards frequently as some sections etch faster
2. Use microscope to periodically inspect trace integrity
3. Take boards out immediately once unprinted copper fully etches away
4. Rinse thoroughly with water to halt etching action

Clean Boards

• Use abrasives like steel wool to scrub off toner and photoresist
• Clean with alcohol, acetone, or commercial resist strippers
• Avoid damaging conductive traces when cleaning

The etched and cleaned PCB blank becomes ready for drilling holes and assembling components to build finished boards.

Assembling Printed Circuit Boards

With custom PCB boards etched, printed and cleaned, they now undergo assembly adding components:

Drill Holes

• Use drill press to bore holes aligned to mounting pad locations
• Drill size determined by leads or fasteners used
• Holes plated to carry signals between board layers

Stuff Board

• Insert component leads or connectors into holes
• Press fit or glue wires and non-leaded parts
• Use vise to prevent boards warping when applying pressure

Solder Joints

• Flow solder along pads wetting leads and/or pad perimeters
• Ensure solder joints fully cover joints for electrical connectivity
• Visual inspect joints identifying cold solder points or bridges

Clean Flux

• Remove corrosive flux residues cleaning under joints
• Use solder wick to desolder bridged pins if found
• Touch up imperfect fills reapplying solder if needed

Thoroughly inspecting finished boards validates the PCB printing and assembly process, checking for issues needing correction before further system integration.

FAQ

What resolution traces can be produced with PCB printing?

Typical minimum trace/space capabilities for hobbyist PCB printing methods fall around:

• Photoengraving – 200 micron traces
• Toner transfer – 250 microns with difficulty below 500
• Direct toner etching – 100 microns, sometimes finer

High-end professional photoengravers print down to 30-50 micron traces for more sophisticated boards.

Can I etch double-sided boards at home?

While possible, simultaneously etching both sides of a homemade double-sided board proves quite challenging:

• Tricky aligning separate toner prints onto each side
• Hard visually monitoring two etch fronts as they progress
• Typically etches faster on side exposed to air bubbles
• Rotating boards helps but still tends to come out lopsided

Easier to either hand wire or use wire jumpers between dual single-sided boards.

What metals can substitute copper for etching PCBs?

While copper serves as the standard for professional PCB fabrication, hobbyists can experiment with alternatives:

• Brass shim stock works with similar methods to copper foil
• Some etch steel or zinc plates by modifying processes
• Avoid lead due to toxicity – research handling precautions
• Results vary greatly – can’t match copper’s solderability

Can I use a clothes iron when toner transferring onto copper?

Yes, clothes irons commonly apply printouts onto household copper clad boards. However, challenges exist:

• Difficult ensuring uniform pressure when ironing
• Dropping or shaking transfer paper shifts alignment
• Works for simple designs – inconsistent for fine pitch ICs

Use laminators or purpose-built PCB hot presses for more reliable toner transfers.

How long does a batch PCB etch cycle take?

Typical amateur etch times in small tanks run 30-60 minutes, but can vary widely depending on:

• Etchant used and concentration
• Temperature
• Copper thickness/density
• Agitation level

Pay close attention near the end when going from partial to complete etching to avoid over-etching traces.