Recent developments in miniaturization have been the main reason for the strong momentum of the electronics industry. As miniaturization continues to drive the industry, it becomes increasingly challenging to manufacture electronics and manufacture PCBs. The most challenging aspect of PCB manufacturing is the combination of high-density vias and vias used as interconnects. Through holes are used to mount the electronic components that make up the circuit.
As the packing density of through holes in PCB assembly lines increases, so does the demand for smaller holes, respectively. Mechanical drilling and laser drilling are the two main techniques used to produce microscopic holes with precise and repeatable diameters. Using these PCB drilling techniques, vias can range from 50-300 microns in diameter and about 1-3 mm in depth.
PCB Drilling Considerations
The drill press consists of a high speed spindle that rotates at approximately 300k RPM. These speeds are critical to achieving the precision required for micron-scale drilling on PCBs.
To maintain accuracy at high speeds, the spindle uses an air bearing and a direct drill bit assembly held by a precision collet chuck. Also, control the vibration of the drill tip to within 10 microns. To maintain the exact position of the holes on the PCB, the drill is mounted on a servo table that controls the movement of the table in the X and Y axes. The channel actuator is used to control the movement of the PCB in the Z axis.
As the pitch of holes in a PCB assembly line continues to decrease and the need for higher throughput, respectively, increases, the electronics that control the servos may fall behind at some point. Using laser drilling to create the vias used to make PCBs can help reduce or eliminate this lag, a next-generation requirement.
Laser drills used in the PCB manufacturing process consist of a complex set of optics that control the precision of the laser needed to punch holes.
The size (diameter) of the hole to be drilled on the PCB is controlled by the hole diameter of the mounting, and the depth of the hole is controlled by the exposure time. Also, the beam is split into multiple energy bands to further provide control and precision. The moving focusing lens is used to focus the energy of the laser beam precisely at the drilling position. Galveno sensors are used to move and position PCBs with high accuracy and precision. Galveno sensors capable of switching at 2400 KHz are currently used in industry.
Alternatively, a novel method called direct exposure technology can also be used to drill holes in circuit boards. The technology is based on the concept of image processing, where the system increases accuracy and speed by creating an image of the PCB and converting that image into a position map. Then use the position map to align the PCB under the laser during drilling.
Advanced research in image processing algorithms and precision optics will further improve the productivity and yield of PCB manufacturing and high-speed drilling used in the process.