The Call That Inspired This Guide

A few weeks ago, the phone rang. On the other end was John Keith, W5BWC, calling from his electronics workshop in Texas. John's been an Extra Class ham radio operator for decades, and his website, W5BWC Electronics, is a treasure trove of technical articles and projects for amateur radio operators and engineers.

"I wanted to let you know," John said, "I've been using your ferric chloride for years to etch my PCBs. Still doing it the old-school way—toner transfer, ferric chloride bath, the whole process. It works for my RF designs and prototype boards."

That call reminded us of something important: while commercial PCB fabrication has become faster and cheaper, there's still tremendous value in the traditional, hands-on approach to circuit board etching.

John's projects on W5BWC Electronics—including RF amplifiers, antenna matchers, and sophisticated radio circuitry—demonstrate that the traditional ferric chloride etching process can produce professional-quality results when done correctly.

Why Ferric Chloride Remains the Go-To Etchant

Walk into any amateur radio operator's workshop, any electronics hobbyist's garage, or any engineering lab doing PCB prototyping, and chances are you'll find a bottle of ferric chloride. For over 50 years, this chemical has been the workhorse of DIY and professional circuit board etching.

After supplying ferric chloride to makers, engineers, and radio enthusiasts like John Keith for over two decades, we've learned something important: the quality of your etchant directly affects the quality of your finished boards.

Ferric chloride selectively removes exposed copper, leaving your circuit traces intact

Understanding the Chemistry: How Ferric Chloride Etches Copper

Ferric chloride (FeCl₃) works through a straightforward chemical reaction that selectively dissolves copper while leaving your resist material untouched.

The Etching Reaction

When ferric chloride contacts exposed copper on your PCB, this reaction occurs:

2 FeCl₃ + Cu → 2 FeCl₂ + CuCl₂

What's happening: The ferric ions (Fe³⁺) oxidize the metallic copper (Cu) into soluble copper chloride (CuCl₂), which dissolves into the solution. The ferric chloride is reduced to ferrous chloride (FeCl₂) in the process.

This reaction continues until either:

• All exposed copper is removed (your board is etched)
• The ferric chloride is depleted (solution turns greenish-black)
• The solution becomes saturated with copper chloride

Why This Chemistry Works So Well

Ferric chloride's popularity in PCB etching comes down to several practical advantages:

• Room temperature operation: No heating required, though gentle warming (90-110°F) speeds the reaction
• Resist compatibility: Doesn't attack most common resist materials (toner transfer, photoresist, permanent markers)
• Predictable etch rates: Typically 0.001" to 0.002" per minute depending on concentration and temperature
• Visual feedback: Fresh solution is amber/yellow-brown; spent solution turns dark green-black

Step-by-Step: Etching Your PCB with Ferric Chloride

The complete PCB etching process from design to finished board

Whether you're creating a simple RF filter for your ham radio station or prototyping a complex microcontroller board, the process is fundamentally the same.

Materials You'll Need

• Copper-clad PCB blank (single or double-sided)
• Ferric chloride solution (40%)
• Resist material: Toner transfer paper, photoresist film, or UV-sensitive presensitized boards
• Etching tank or tray: Plastic or glass container (never metal!)
• Agitation method: Aquarium pump with air stone, or manual rocking
• Safety equipment: Nitrile gloves, safety glasses, apron
• Baking soda solution: For neutralizing spills

The Etching Process

1. Prepare Your Resist Pattern

   Apply your circuit pattern to the copper using your chosen resist method. For toner transfer, print your design mirrored on glossy paper, then iron onto clean copper at high heat. For photoresist, expose and develop according to the resist manufacturer's instructions.

   Critical: Ensure complete coverage where you want copper to remain. Any pinholes or gaps will etch through.

2. Inspect Your Resist

   Hold the board up to light and check for any incomplete coverage, bubbles, or lifted edges. Touch up problem areas with a permanent marker or additional resist application.

3. Prepare the Etching Bath

   Pour ferric chloride into your etching container. Use enough to fully submerge the PCB with at least 1/2" above and below the board. Room temperature works, but heating to 90-110°F speeds etching significantly.

   Pro tip: If using an aquarium pump for agitation, position the air stone to create circulation across the board surface without splashing.

4. Begin Etching

   Submerge your board copper-side up. If etching multiple boards or working without agitation, periodically lift and rock the container to move fresh solution across the copper.

   Typical etch times:

   • With agitation at 100°F: 15-30 minutes
   • Room temperature, no agitation: 45-90 minutes
   • Cold solution, no agitation: 2-3 hours

5. Monitor Progress

   Check every 10-15 minutes. As copper dissolves, you'll see the bare substrate (usually tan/yellow fiberglass) showing through. The solution will darken as it becomes loaded with copper.

   Watch for: Undercutting (solution etching underneath resist) if left too long, especially on fine traces.

6. Rinse Thoroughly

   Once all exposed copper is removed, immediately remove the board and rinse under running water for at least 2 minutes. Pat dry with paper towels.

7. Remove Resist

   Use acetone (for toner transfer) or appropriate resist stripper to remove the protective layer, revealing your clean copper traces underneath.

8. Clean and Finish

   Scrub with steel wool or ScotchBrite to brighten copper. Apply flux or solder to traces within a few hours to prevent oxidation, or coat with solder mask or clear acrylic spray.

Troubleshooting Common Etching Problems

Slow or Incomplete Etching

Causes:

• Depleted or old ferric chloride solution (dark green-black color)
• Too cold (below 70°F significantly slows reaction)
• Insufficient agitation (copper-saturated layer forms at surface)
• Solution too diluted

Solutions:

• Use fresh ferric chloride—etchant depletes with use
• Warm solution to 90-110°F (use water bath, not direct heat)
• Add agitation via air pump or periodic manual rocking
• Replace with full-strength solution

Excessive Undercutting

Causes:

• Over-etching (left in solution too long)
• Poor resist adhesion allowing solution underneath
• Solution too hot or too concentrated

Solutions:

• Check boards more frequently; remove as soon as copper clears
• Ensure resist is properly adhered with good pressure/heat
• Keep temperature below 110°F
• For very fine traces (<0.010"), consider cooler solution for more control

Pitting or Rough Copper Surface

Causes:

• Contaminated or degraded etchant
• Dirty copper surface before resist application
• Fingerprints or oils on copper

Solutions:

• Use fresh ferric chloride
• Clean copper thoroughly with ScotchBrite and acetone before resist application
• Wear gloves when handling bare copper

Resist Lifting During Etching

Causes:

• Poor adhesion of resist to copper
• Contaminated copper surface
• Inadequate heat/pressure during toner transfer

Solutions:

• Clean copper with ScotchBrite, then acetone immediately before resist application
• Increase heat and pressure during toner transfer (if using that method)
• Let photoresist dry/cure fully before etching
• Touch up edges with permanent marker before etching

Safety and Handling: The Non-Negotiables

Ferric chloride is an effective etchant, but it requires respect. After two decades supplying this chemical to electronics hobbyists and professionals, we've learned that safe handling starts with understanding the hazards.

Key Safety Considerations

Corrosivity: Ferric chloride is acidic and corrosive. Contact with skin causes irritation; prolonged contact can cause chemical burns.

Staining: This is perhaps the most underestimated hazard. Ferric chloride leaves permanent rust-brown stains on nearly everything:

• Clothing (permanent, will NOT wash out)
• Concrete floors and driveways
• Porcelain sinks
• Wood surfaces
• Skin (fades in days but is initially very noticeable)

Container compatibility: NEVER use metal containers. Ferric chloride attacks most metals. Use only:

• HDPE or PP plastic containers
• Glass (handle carefully—breakage is catastrophic)
• Chemical-resistant trays designed for photographic or chemical use

Emergency Procedures

Skin contact: Immediately flush with copious running water for 15 minutes. Wash with soap. If irritation persists, seek medical attention.

Eye contact: Flush immediately with water for 15 minutes minimum while holding eyelids open. Seek medical attention immediately.

Spills: Neutralize with baking soda solution (1/2 cup baking soda per gallon of water). The fizzing reaction indicates neutralization is occurring. Soak up with paper towels or absorbent material. Be aware that even neutralized solution will still stain.

Disposal

Spent ferric chloride must NOT be poured down the drain. The copper content makes it hazardous waste in most jurisdictions.

Proper disposal methods:

1. Neutralization: Slowly add baking soda until pH reaches 7-8 (test with pH strips)
2. Precipitation: Let copper compounds settle (may take several days)
3. Decanting: Pour off clear liquid, which can then be disposed of per local regulations
4. Solids disposal: Copper-containing sludge must go to hazardous waste facility

Best practice: Contact your local hazardous waste facility for specific disposal requirements in your area. Many facilities have specific collection days for hobbyist chemicals.

Ferric Chloride vs. Other Etchants: The Comparison

Real-World Applications: From Ham Radio to Professional Prototypes

The Old-School Method That Still Works

John Keith, W5BWC, represents thousands of amateur radio operators and electronics engineers who continue using the traditional ferric chloride etching method. Why? Because it works, it's reliable, and it gives you complete control over the process.

"When I'm developing a new RF circuit or need to modify a design," John explains, "I can make a board change in the morning and have the new version etched and populated by afternoon. That rapid iteration is invaluable for prototyping."

Amateur Radio PCB Projects

Amateur radio operators have been etching their own PCBs for decades—filters, antenna tuners, QRP transceivers, and countless other projects. The W5BWC Electronics website showcases excellent examples of professional-quality homebrew RF circuits created using the traditional ferric chloride etching process.

Common ham radio PCB projects perfect for old-school ferric chloride etching:

• RF filters: Low-pass, high-pass, and band-pass filters for harmonic suppression
• Antenna matchers and tuners: Custom impedance matching networks
• QRP transceivers: Low-power transmitter/receiver circuits
• Audio interfaces: Computer sound card interfaces for digital modes
• Power supplies and controllers: Station control and power management boards
• RF amplifiers: Linear amplifiers and driver stages for homebrew transmitters

Engineering and Prototype Development

Professional engineers use ferric chloride for rapid prototyping before committing to production PCB fabrication:

• Proof-of-concept testing: Quick turnaround for circuit validation
• One-off repairs: Custom adapter boards and repair patches
• Small production runs: 5-50 boards for limited production
• Educational demonstrations: Teaching circuit design and fabrication

When to Etch vs. When to Order

Ferric chloride etching makes sense when:

• You need a board TODAY (no wait for fabrication)
• Prototyping with frequent design changes
• Single-sided or simple double-sided boards
• Relatively large traces (>0.015" / 0.4mm)
• Learning and education

Commercial fabrication is better for:

• Fine-pitch surface mount (< 0.010" traces)
• Multilayer boards (4+ layers)
• Production quantities (>10 boards)
• Plated through-holes
• Solder mask and silkscreen