PCB Milling – All You Need to Know
People are familiar with PCB etching but seldom do they know what PCB milling is and how it works. Similar to the etching process, milling is the process of electrical isolation. Copper is removed from the PCB’s sheet according to the layout design to for the creation of signal traces and pads. Ground planes are created with the removal of copper. Yet quite unlike the etching process, milling is not chemical based. Essentially a non-chemical process, the target is accomplished in an ordinary environment with zero chances of interaction with hazardous chemicals.
Which process is more accurate?
Both milling and etching can produce high end circuit boards. While it is the quality of the photomasking and chemicals in etching that makes the process more accurate, it is the accuracy of the milling system that determines the precision if the PCB. The control, rpm, condition of the bits and the sharpness of the tools also determine the quality of the PCB manufactured from milling.
How is milling done?
Milling is done with the help of a CNC machine which can create the entire prototype of a PCB. However, milling machines can neither insert through hole plates nor vias. The software is provided by the manufacturer. The mechanics of PCB milling is fairly similar to a computer numeric control system. The system is highly accurate and commands are sent through a serial or parallel port via milling specific software to the machines controller which in turn positions the milling head accordingly. It also controls the spindle speed (the higher the rpm, the better is the accuracy), monitors and drives the gantry. Stepper motors are used to control the x and y axis. Pneumatic cylinder or solenoid is used to control the z axis. D-bit cutters, spade mills and endmills are used as tools for cutting out the traces.
Advantages of milling
The turnaround of prototypes through PCB milling is faster than regular etching process. This is because it does not undergo the wetting processes. This subtractive process is favorable for profiling the outiline and drilling. You may use a single CNC milling machine that has the capability to tackle drilling, cutting and milling processes which reduces the registration and scaling faults in the circuit boards. In most situations, layouts that are easy to create with milling are difficult to attain by wet etching and manual drilling processes unless you use extremely expensive lab equipment. Even though the CNC technology is gaining pace, it is still highly unlikely that for the mass production of PCBs milling will be preferred over the chemical etching process.
Are there any other processes for creating electrical isolation?
Yes, one such method is laser drilling. It is better for etching circuit boards than both chemical etching and PCB milling with respect to the variations exerted upon the circuit boards. Since it does not come into the physical contact with the board, the stress is negligible. For this reason, microwave and RF designs prefer laser drilling. The laser drilling process is expensive but it is eco-friendly and offers the highest precision and requires minimal maintenance.