Etching Process

What is Etching?

• Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design incised into the metal.

• It is a selective removal of material from the surface of a PCB (Printed Circuit Board) by means of chemical action of an etchant (or etching agent).

• Etching usually removes the copper areas that are not desired on the finished PCB.

What is Incised?

• To incise means to mark or decorate an object or surface with a cut or a series of cuts.

Traditional Etching Process

• In traditional pure etching, a metal (usually copper, zinc, or steel) plate is covered with a waxy ground that is resistant to acid.

• Etching by goldsmiths and other metalworkers has been known in Europe since the Middle Ages, possibly dating back to antiquity.

• Daniel Hopfer (circa 1470–1536) of Augsburg, Germany:

  • A craftsman who decorated armor using etching methods and applied this technique to printmaking.

  • He utilized iron plates for his designs, many of which still exist today.

Basic Ways of Etching

Mechanical Etching

• Involves the use of a machine tool and a special cutter to remove a narrow strip of copper from the boundary of each pad.

• This action electrically isolates the circuit element from the rest of the foil.

Examples of Mechanical Etching

• CNC Milling Machine:

  • A specific form of computer numerical controlled (CNC) machining.

  • Milling is similar to both drilling and cutting and can achieve many operations performed by cutting and drilling machines.

• In milling:

  • A rotating cylindrical cutting tool is utilized.

  • The cutter can move along multiple axes, allowing for the creation of various shapes, slots, and holes.

Materials and Tools needed for Engraving Operations

• Working Fixture:

  • The work surface of the CNC mill should be as level as possible (999; deviation of as little as 0.001" could affect engraving).

• Spindle or Router:

  • Used to level the work surface with an appropriate end mill and must secure the workpiece.

Tooling (Engraving)

• Tooling involves marking or ornamenting with incised letters, designs, etc.

Tooling (Drill Bit)

• Cutting tools used to remove material to create holes, typically of circular cross-section.

Tooling (Endmill)

• A type of milling cutter used in industrial milling applications, distinguished from drill bits in application, geometry, and manufacture.

• Key difference:

  • Drill bits cut only in the axial direction, while milling bits can generally cut in all directions, though not all have axial cutting capabilities.

Copper Clad

• Copper clad is a raw material necessary for making PCBs and is the primary need in the etching process.

CNC Milling Command Codes

• To engrave paths in copper clad boards, CNC milling machines require software such as Eagle CAD, PCB-Probe, or ZEN Toolworks to plan tool movements.

Chemical Etching

• Relies on a corrosive liquid to dissolve unwanted copper, thereby defining the desired circuit.

Materials and Equipment Needed in Chemical Etching Process

• Ferric Chloride:

  • Industrial-scale chemical compound with the formula $ext{FeCl}_3$.

  • Primary use includes impurities removal in water and wastewater treatment; the second-largest application is in PCB production.

  • Hazards:

  • Acute hazards include fire and explosion risks; irritating or toxic fumes released in a fire.

  • Exposure symptoms:

    • Inhalation: Cough, sore throat, redness, pain.

    • Skin: Redness, pain.

    • Eyes: Redness, pain, blurred vision.

    • Ingestion: Abdominal pain, vomiting, diarrhea, shock, or collapse.

• Ammonium Persulfate (APS):

  • Inorganic compound $ext{(NH}<em>4)</em>2 ext{S}<em>2 ext{O}</em>8$; a strong oxidizing agent used as an etchant, cleaner, and bleaching agent.

  • Hazards:

  • Potential fire and explosion risk upon contact with combustibles; irritating or toxic fumes are released in a fire.

  • Exposure symptoms may include:

    • Inhalation: Cough, sore throat, wheezing.

    • Skin: Redness, burning sensation.

    • Eyes: Pain and redness.

    • Ingestion: Nausea, diarrhea, vomiting.

General Safety Precautions

• Wear PPE (Personal Protective Equipment) before engaging in etching processes to ensure worker safety.

• Clean copper clad before quenching it in etchants.

Methods of Etching

• Masking Tape: Used to cover paths to maintain electrical continuity.

• Permanent Pen: Used to draw etching paths; a whiteboard marker can erase it post-etching.

• Software: Utilized to draw etching paths accurately.

Quenching Process

• After planning etching paths, quench the PCB in etchant, ensuring proper removal of the PCB from etchant followed by rinsing with clean water to eliminate excess etchant.

PCB Manufacturing Process

1. Plan the necessary components for the series circuit, including resistors, wire, LED, copper clad, cutter, and schematic drawing.

2. Apply masking tape or permanent pen to protect areas on the copper clad from acid corrosion.

3. After processing, drill the PCB for component assembly and solder components on the board.

Final Steps

• After completion of etching and drilling processes, ensure thorough rinsing and cleaning of the PCB before use.