PCB Milling Master Class Part 5: Soldering, Testing & Protection

You have built the machine. You have designed the circuit. You have milled the board. Now, you are holding a piece of fiberglass with raw copper traces on it.

Welcome to the final installment of our PCB Milling Master Class. Today, we turn that milled board into a functioning device. However, soldering on a DIY milled board is different from soldering on a commercially manufactured one. There is no solder mask to stop bridges, and bare copper loves to oxidize.

Let's walk through the final steps to bring your creation to life.

Step 1: Post-Processing the Board

Fresh off the CNC machine, your board likely has "fuzzies" (burrs) and copper dust. If you don't clean this, you will have short circuits.

1. Deburring: Take a piece of Steel Wool (Grade 0000) or a Scotch-Brite pad and scrub the board vigorously under running water. This removes the burrs and polishes the copper.
2. Inspection: Hold the board up to a bright light. Look for tiny slivers of copper bridging the isolation paths. Use a sharp knife or a pick to scrape them away.
3. Cleaning: Wipe the entire board down with Isopropyl Alcohol (IPA). Do not touch the copper with your fingers after this (oils prevent solder adhesion).

Step 2: The "Bare Copper" Challenge

Commercial boards come with a coating (HASL or ENIG) that makes solder stick easily. Your board is bare copper. It oxidizes in minutes, making soldering difficult.

Step 3: Assembly Order

Since we don't have a silkscreen (the white text printed on boards), you need to keep your EasyEDA diagram open on your computer screen to know where parts go.

The Rule of Height: Always solder from shortest to tallest.

1. Vias / Rivets: If you have a double-sided board, do your vias first.
2. Resistors & Diodes: These lay flat against the board.
3. IC Sockets: Never solder a chip directly if you can avoid it. Use a socket.
4. Capacitors & Transistors: These stand up a bit higher.
5. Connectors & Headers: These are the tallest and hardest to work around.

Step 4: The "Smoke Test" (Testing)

Before you plug in power, you must check for shorts. Milled boards are notorious for having microscopic copper bridges that you can't see with the naked eye.

The Continuity Check

1. Set your Multimeter to Continuity Mode (the one that beeps).
2. Touch one probe to your VCC (Positive) line.
3. Touch the other probe to your GND (Ground) line.
4. If it beeps, STOP. You have a short circuit. Do not power it on. Inspect your isolation paths with a magnifying glass.
5. If it stays silent, you are generally safe to plug it in.

Step 5: Protection (Optional but Recommended)

Bare copper will turn green and corrode over time. To make your project last, you need to seal it.

• Spray Lacquer: A simple clear coat spray paint works well for non-critical hobby projects.
• Conformal Coating: A specialized chemical designed for electronics (available on Amazon).
• Liquid Tin: A chemical bath that plates your copper with tin (expensive, but professional).

Conclusion: You Are Now a Maker

Congratulations! You have gone from a blank idea to a physical, functioning electronic device—all within your own workshop. This is a superpower. You are no longer limited by what you can buy; you are only limited by what you can design.

We hope you enjoyed this Master Class series. Now go build something amazing.