FPC series article directory
4. The difference between rolled copper and electrolytic copper for FPC substrates
5. Auxiliary materials for FPC
7. Introduction to the production process of FPC
8. Introduction to the production process of R-FPC
9. Development and application of FPC
10. Control method of expansion and contraction of FPC materials
11. FPC development requirements for FCCL
13. Several factors affecting the price of FPC
15. Three methods of FPC hole processing
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15. Three methods of FPC hole processing
The through hole of FPC can also be drilled by CNC like PCB, but it is not suitable for hole processing of double-sided metallized hole circuit. With the high density of circuit patterns and the small aperture of metallized holes, and the aperture of CNC drilling has a certain limit, many new drilling technologies have been put into practical application.
These new drilling technologies include plasma etching, laser drilling, micro-aperture punching, chemical etching, etc. These drilling technologies are easier to meet the hole-forming requirements of the tape-and-roll process than CNC drilling. Below we briefly introduce the three methods of FPC through-hole processing:
1. CNC drilling : Most of the through holes drilled in double-sided FPC are still drilled with CNC drilling machines. The CNC drilling machine is basically the same as the CNC drilling machine used in PCB, but the drilling conditions are different. Since FCCL is very thin, it is possible to drill multiple overlapping sheets. If the drilling conditions are good, it is even possible to overlap 10 to 15 sheets for drilling.
Backing board and cover board can use paper-based phenolic laminated board or glass fiber cloth epoxy laminated board, and can also use aluminum board with a thickness of 0.2-0.4mm. Drills for FPC drilling are available on the market, and drills for PCB drilling and milling cutters for milling shapes can also be used for FPC. The processing conditions for drilling the base material hole, milling the cover film and the shape of the reinforcement plate are basically the same, but because the adhesive used in FCCL is soft, it is very easy to attach to the drill bit, and the status of the drill bit needs to be checked frequently, and It is necessary to properly increase the speed of the drill bit, and be particularly careful when drilling multi-layer FPC or R-FPC.
2. Punching : Punching micro-aperture is not a new technology, it has been used as a mass production. Since the coiling process is continuous production, there are many examples of using punching to process the through holes of the coiling. However, the batch punching technology is limited to punching holes with a diameter of 0.6-0.8mm. Compared with CNC drilling machine drilling, the processing cycle is long and expensive. Manual operation is required; due to the large size of the initial process, the punching mold is correspondingly large, so the price of the mold is very expensive. Although mass production is beneficial to reduce costs, the burden of equipment depreciation is large, and small batch production and Flexibility can't compete with CNC drilling, so it's still not widely available.
However, in recent years, great progress has been made in the mold precision and CNC drilling of punching technology, and the practical application of punching on FPC is very feasible; the latest mold manufacturing technology can manufacture The 75um-diameter hole of the adhesive-free FCCL with a substrate thickness of 25um is also quite reliable. If the punching conditions are suitable, it can even punch a 50um-diameter hole. The numerical control of the punching device and the miniaturization of the mold can be well applied to FPC punching, but neither numerical control drilling nor punching can be used for blind hole processing.
3. Laser drilling : lasers can be used to drill the finest through holes. The laser drilling machines used for FPC drilling through holes include excimer laser drilling, impact carbon dioxide laser drilling, and YAG (yttrium aluminum garnet) laser drilling. , Argon laser drilling machine, etc.
The impact carbon dioxide laser drilling machine can only drill the insulating layer of FCCL, while the YAG laser drilling machine can drill the insulating layer and copper foil of FCCL. The speed of drilling the insulating layer is obviously faster than that of the copper foil. It is impossible to use the same laser drilling machine to perform all the drilling processes. The production efficiency is not very high; generally, the copper foil is first etched to form a hole pattern, and then the insulating layer is removed to form a through hole, so that the laser can drill For holes with extremely small apertures, the position accuracy of the upper and lower holes may restrict the drilling diameter. If drilling blind holes, as long as the copper foil on one side is etched away, there is no problem with the position accuracy of the upper and lower holes.
At present, the holes processed by the excimer laser are the smallest. The excimer laser is ultraviolet light, which directly destroys the structure of the base layer resin, makes the resin molecules discrete, and generates very little heat, so it can dissipate the heat to the damage around the hole. The degree is limited to the minimum range, and the hole wall is smooth and vertical. If the laser beam can be further narrowed, holes with a diameter of 10-20um can be processed. Of course, the larger the plate thickness-to-aperture ratio, the more difficult it is to wet copper plating.
The problem with excimer laser technology drilling is that the decomposition of polymers will produce carbon black attached to the hole wall, so some means must be taken to clean the surface before electroplating to remove carbon black. In addition, when laser processing blind holes, there are also certain problems in the uniformity of the laser, which will produce bamboo-like residues. The biggest difficulty of the excimer laser is that the drilling speed is slow and the processing cost is too high, so it is limited to high-precision applications. , High reliability micro-hole processing.
The impact carbon dioxide laser generally uses carbon dioxide gas as the laser source, and the radiation is infrared. Unlike the excimer laser, which burns and decomposes resin molecules due to thermal effects, it belongs to thermal decomposition, and the processed hole shape is worse than that of the excimer laser. Much, the aperture that can be processed is basically 70-100um, but the processing speed is significantly faster than the excimer laser, and the cost of drilling is much lower. The impact carbon dioxide laser should pay attention to when processing blind holes. , the laser can only be emitted to the surface of the copper foil, and there is no need to remove the organic matter on the surface. In order to clean the copper surface stably, chemical etching or plasma etching should be used as post-treatment. From the perspective of technical possibility, there is basically no difficulty in using the laser drilling process for the tape process, but considering the balance of the process and the proportion of equipment investment, it does not have an advantage.