There are three types of FPC FPC through holes
1. NC drilling
At present, most of the holes drilled in the double-sided flexible printed board are still drilled by the NC drilling machine. The NC drilling machine is basically the same as that used in the rigid printed board, but the drilling conditions are different. Because the flexible printed board is very thin, multiple pieces can be overlapped for drilling. If the drilling conditions are good, 10 ~ 15 pieces can be overlapped for drilling. The base plate and cover plate can use paper-based phenolic laminate or glass fiber cloth epoxy laminate, or aluminum plate with a thickness of 0.2 ~ 0.4mm. Drill bits for flexible printed boards are available on the market. Drill bits for drilling rigid printed boards and milling cutters for milling shapes can also be used for flexible printed boards.
The processing conditions of drilling, milling, covering film and reinforcing plate are basically the same. However, due to the soft adhesive used in flexible printed board materials, it is very easy to adhere to the drill bit. It is necessary to frequently check the state of the drill bit, and appropriately increase the rotating speed of the drill bit. For multi-layer flexible printed boards or multi-layer rigid flexible printed boards, the drilling shall be particularly careful.
2. Punching
Punching micro aperture is not a new technology, which has been used in mass production. As the coiling process is continuous production, there are many examples of using punching to process the through hole of coiling. However, the batch punching technology is limited to punching holes with a diameter of 0.6 ~ 0.8mm. Compared with the NC drilling machine, the processing cycle is long and manual operation is required. Due to the large size of the initial process, the punching die is correspondingly large, so the die price is very expensive. Although mass production is beneficial to reducing the cost, the burden of equipment depreciation is large, Small batch production and flexibility cannot compete with NC drilling, so it is still not popularized.
However, in recent years, great progress has been made in die precision and NC drilling of punching technology. The practical application of punching in flexible printed board has been very feasible. The latest die manufacturing technology can manufacture holes with a diameter of 75um that can be punched into adhesive free copper-clad laminate with a substrate thickness of 25um. The reliability of punching is also quite high. If the punching conditions are appropriate, holes with a diameter of 50um can even be punched. The punching device has also been numerically controlled, and the die can also be miniaturized, so it can be well applied to the punching of flexible printed boards. CNC drilling and punching can not be used for blind hole processing.
3. Laser drilling
The most fine through holes can be drilled by laser. The laser drilling machines used to drill through holes in flexible printed boards include excimer laser drilling rig, impact carbon dioxide laser drilling rig, YAG (yttrium aluminum garnet) laser drilling rig, argon laser drilling rig, etc.
The impact CO2 laser drilling machine can only drill the insulating layer of the base material, while the YAG laser drilling machine can drill the insulating layer and copper foil of the base material. The speed of drilling the insulating layer is obviously faster than that of drilling the copper foil. It is impossible to use the same laser drilling machine for all drilling processing, and the production efficiency can not be very high. Generally, the copper foil is first etched to form the pattern of holes, and then the insulating layer is removed to form through holes, so that the laser can drill holes with extremely small holes. However, at this time, the position accuracy of the upper and lower holes may restrict the hole diameter of the borehole. If a blind hole is drilled, as long as the copper foil on one side is etched, there is no problem of up and down position accuracy. This process is similar to the plasma etching and chemical etching described below.
