Best Practices for Machining Circuit Boards with Bantam Tools
Electrical engineers who are looking to add a Bantam Tools milling machine to their shop often ask, “What’s the smallest trace size you can mill?” Using both the Bantam Tools Desktop CNC Milling Machine and the Bantam Tools Explorer™ CNC Milling Machine, we’ve been able to mill boards with 6 mil traces. However, to machine 6 mil traces there are a few best practices to keep in mind when working with our desktop CNC machines.
Prepping Your Machining Bed
Whenever we’re machining PCBs, our machine bed of choice is our PCB pallets (or spoilboard). Unlike the T-slot bed and fixturing pallets there are no gaps on the surface of the bed and that means more surface area to fixture to. This is important because to fixture single- or double-sided FR-1 to the pallet, you’ll use High-strength, Double-Sided Nitto Tape.
Additionally, you’ll want to make sure that the PCB pallet is F-L-A-T. We’re talking granite table flat! All of our machining beds are manufactured in-house and are held to tight tolerances. However, sometimes these tolerances can vary by thousandths of an inch. That’s why for the best results we recommend facing the spoilboard.
Proper Fixturing & Z-height Offsets
Like we mentioned, you’ll want to use High-strength, Double-Sided Nitto Tape to adhere you PCB to the freshly faced PCB pallet. This tape is designed for heavier milling jobs and is P-02 double-coated. In other words, it’s incredibly sticky and designed to keep your boards securing throughout your milling job. When applying the tape to your board, cover as much surface area on the underside of the board as possible. But make sure the strips of tape don’t overlap and that there aren’t and ripples in the tape. You want to have a uniform thickness because failure to do so will impact the Z-height of your board and result in the machine milling deeper cuts on certain parts of the board.
On that note, it’s important to account for the thickness of the Nitto tape. The Nitto tape we carry in our store is 0.006” thick and so this is the value you’ll want to enter for the Z Offset in the Bantam Tools software’s Material Setup Tab.
Choosing the Right End Mill
Tool selection plays an important role in machining 6 mil traces using your Bantam Tools milling machine. We tend to keep a separate set of end mills on reserve to be used specifically for machining circuit boards. This ensures that we’re not using a tool that’s become dull from machining harder materials like aluminum.
Additionally, we like to use a combination of 1/32” and 1/64” flat end mills and then PCB Engraving Bits. We’ve found that using a combination of end mills helps cut down on milling time (and save our tooling from wearing out too quickly). After loading your file into the Bantam Tools software, you can select these tools under Milling Tools. We also recommend setting the Trace Depth to 0.003” for the best results.
Minimizing Tool Runout
Tool runout is the measurement of how far the end mill rotates off its true axis while machining. When runout is extreme it can look like the tool is wobbling in its holder. But typically, tool runout is not something you would notice.
Runout is minimal on the Bantam Tools Desktop CNC Milling Machine and the Bantam Tools Explorer™ CNC Milling Machine. Nevertheless, when it comes to nailing 6 mil traces, we want to make sure precision. For ultimate performance, we use our High-Precision Collet Set because it offers twice as much grip strength compared to the ER-11 collet that ships standard with every Bantam Tools milling machine, and so this helps prevent the smallest amount of runout that might occur.
Accessory Recommendations for Electrical Engineers
We called out a number of useful accessories for those planning to use our milling machines for electronics. Here is a full list of items we mentioned:
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