For drilling of FR4 boards with different shapes, resolutions. and densities, LPKF circuit board plotters represent an efficient, low-cost solution. Drill holes with diameters starting at 0.15 mm. LPKF ProtoLaser series laser systems are available if you need even smaller diameters. Our application specialists would be happy to tell you on. which technology is suitable for your application.
How to drill PCB
Drilling is one of the basic, most performed, machining processes. Several methods used for producing micro-holes including conventional punches and dies. electrical discharge machining (EDM), vibration drilling, laser machining, etc.
Electrical discharge machining can used for graphite-epoxy laminates. since the graphite fibers are conductive. Noting that high currents and high temperatures produced. which can cause severe melting of the composite surface. thermal expansion of the graphite fibers in the lateral direction. and debonding between fibers and the matrix. The production rate of an electrical discharge machine is slow .
Vibration drilling is a branch of vibration cutting. which is different from conventional drilling. The conventional drilling is a continuous cutting process. while the vibration-assisted drilling is a pulsed intermittent cutting process. by piezoelectric crystal oscillator. Vibration thrust and torque are smaller than conventional values by 20-30%. under the same drilling condition. Although vibration drilling can avoid burr and improve cutting stability. there are still a lot of problems to conquer.
Laser machining is a process that no contact between the tool. and the workpiece, and it eliminates the delamination. Laser drilling is being developed as a solution for smaller hole sizes. but there are also problems associated with the process. A PCB made up of three materials ——copper, glass fiber and resin. which have very different material and optical properties. This makes it difficult for a laser beam with particular characteristics to cut. and through the board. The hole produced by a laser in a standard PCB is sometimes tapered. Also, very small holes produced by laser have limited to a depth equal to the diameter. The main use of lasers seen to be for small blind and buried vias.
to produce through-holes, the main area of interest in the present research. only mechanical drilling is favorable as hole depth increases. because of the need for high accuracy, low temperature and deformation forces. to produce high quality holes on a glass-epoxy composite board. known as the FR-4 board .
Thrust force and Torque In a drilling process, the drill. and workpiece have a relative motion. along with the axis of the hole so that the surplus material removed. To generate and maintain the relative motion, a thrust force and torque applied to the drill.
Bit temperature. When drilling, temperature usually exceeds the glass transition temperature of adhesive matrix. in the laminate base material. Drilling temperature usually increases with wear of the bit. Gross defects such as land tear out are common at high drilling temperature. Lands are small copper rings in conductive planes that surround plated holes. and provide the connection between the holes and circuit t races. that radiate from the holes.
Prior researches have shown that drilling. affects the quality and reliability of plated hole connections. Many defects in plated holes related to the sensitive nature of the lamina. used in modern circuit boards. considered that problems occur. if temperatures in the work material allowed to rise to too high a level. The difference in the coefficients of linear expansion. between the resin and fibers gives rise to residual stresses. which makes it more difficult to meet high dimensional accuracy. with drilled holes showing a smaller diameter than the drill used. Bolton Robert William developed a suitable on-line measurement system with an infrared pyrometer. documented sensor responses and evaluated the sensitivity of temperature. while drilling printed circuit board stacks.
Radial run-out at the drill tip. Ultrahigh rotational spindles have developed for higher precision. and productivity drilling with smaller micro-drills. PCB manufacturers can use commercial spindles rotating as high as 3×105 min−1 or more. but, high rotational speed might cause a radial run-out at the drill tip.
Hidehito Watanabe observed the drilling behavior at contact. with a work surface using a high-speed video camera (drill diameter is 0.1 mm. rotational speed is 3×105 min−1) and proposed a centering model of micro-drills with some run-out. He concluded that:
(1) Orbital revolving drills. with the radial run-out move toward the centripetal direction. after starting contact with a work surface.
(2) The entry sheet intensifies the centripetal action.
(3) The radial run-out is insensitive to drill wear as well as hole quality. because of the centripetal action. A radial run-out at the drill tip might deteriorate hole quality. such as hole location accuracy or surface roughness on a hole wall.