Why Etch When We Can CNC Mill?

Milling Copper Clads to make Circuit Boards

On average, a CNC Mill will run you around $2,388. Here’s a handy chart from the MicroMill Folks.

Real Deal

First of all, any one that’s used a CNC machine will tell you that it’s housing cannot be made out of plastic, or any material that cannot dampen vibrations (i.e. not stiff enough).  Take for example a LPKF ProtoMat Series CNC machine, a reputable company that has been in the business for almost two decades. Getting a used ProtoMat (say a 93S) will be around $5,000, and for good reason. You may be tempeted to go after the cheapest option there is, a chinese CNC mill, for about $300-$400,  and they may be okay, but here’s what they will lack.

Chinese CNC Mill

You’ve probably seen them online, at places like eBay. Looks cheap, and could do the business. Two great combinations. But here’s what you find:

  • Loud
  • Slow

Notice the difference in routing a trace. On the left is a standard CNC Mill, and on the right is a etchant. Perhaps its subtle to the average person, but mechanical stresses on the circuit board will cause stress fractures and cracks along the crevice. It’s very similar to chopping trees down, when an axe hits the tree laterally, its creating a wedge, and the tree will crack under its own weight .

Image source: FamilyHandyman

Breath In Breath Out

Did you read that is breath or breath?

CNC milling will generate a lot of dust in the air, and not just ordinary asthma causing dust, but fiberglass dust or carcinogen dust. Anyone remember “Don’t breath this!”? Okay lets say that you don’t mill literally where you work (i.e. not exactly a desktop situation), you’ll have other issues. Here’s a couple of overlooked ones:

  • The copper clad needs to be exactly flat, otherwise your going to have a bad cut.
  • Bits and end mills can be expensive, and don’t take much to wear out.
  • Isolation size is a function of bit size and milling accuracy.
  • As the bit wears out, your traces will vary in widths (non uniform traces).