Double-sided flexible circuit board FPC manufacturing process solution

FPC cutting - double-sided FPC manufacturing process

Except for some materials, the materials used in flexible printed boards are basically rolled. Because not all processes must be processed with the roll tape process, some processes must be cut into the sheet to process, such as double-sided flexible printed board metallized hole drilling, currently can only be drilled in the form of sheet, so double-sided flexible printed board the first process is to open.

Flexible copper-clad laminates are easy to be injured due to their poor bearing capacity to external forces. If the material is damaged during opening, it will have a serious impact on the pass rate of subsequent processes. Therefore, even if it appears to be very simple material, in order to ensure the quality of the material, it must be given enough attention. If the amount is relatively small, you can use manual shears or hob cutters, large quantities, available automatic shears.

Whether it is single side, double side copper foil laminate or covering film, the precision of cutting size can reach ± o.33. High reliability of opening material, open good materials automatically neatly stacked, in the exit does not need personnel to collect material. Can control the damage to the material in the minimum, using the change of the size of the feeding roller, the material almost no wrinkle, scar. And the latest device can also roll strip etching process after the flexible printed board for automatic cutting, the use of optical sensors can detect the corrosion positioning graphics, automatic opening positioning, opening precision up to O. 3mm, but can not be this opening frame as the next process positioning.

FPC drilling through hole - double-sided FPC manufacturing process

Through holes of flexible PCB can also be drilled by NUMERICAL control as well as rigid PCB, but it is not suitable for hole machining of coil with double-sided metallized hole circuits. With the high density of the circuit graphics and the small aperture of the metallized hole, plus the aperture of nc drilling has a certain limit, now many new drilling technology has paid the practical application. These new drilling techniques include plasma etching hole, laser drilling, micro-aperture punching, chemical etching hole, etc. These drilling techniques are easier to meet the hole formation requirements of the winding process than CNC drilling.

Through holes of flexible PCB can also be drilled by NUMERICAL control as well as rigid PCB, but it is not suitable for hole machining of coil with double-sided metallized hole circuits. With the high density of the circuit graphics and the small aperture of the metallized hole, plus the aperture of nc drilling has a certain limit, now many new drilling technology has paid the practical application. These new drilling techniques include plasma etching hole, laser drilling, micro-aperture punching, chemical etching hole, etc. These drilling techniques are easier to meet the hole formation requirements of the winding process than CNC drilling.

1. Nc drilling

Double-sided flexible PRINTED board through the drilling hole is now mostly still with CNC drilling machine, CNC drilling machine and rigid printed board use of CNC drilling machine is basically the same, but the drilling conditions are different. Because the flexible PCB is very thin, it can overlap many pieces of drilling, if the drilling conditions are good, 10 to 15 pieces can be overlapped together for drilling. The backing plate and cover plate can use paper based phenolic laminate or glass fiber cloth epoxy laminate, and also can use 0.2 ~ 0.4mm thick aluminum plate. Drill bits for flexible PCB are available on the market. Drill bits for rigid PCB drilling and cutter for contour milling can also be used for flexible PCB.

Drilling, milling cover film, and reinforcement plate profiles are basically the same, but due to the softness of the adhesive used by the flexible PRINTED board material, it is very easy to adhere to the bit, requiring frequent testing of the bit condition and increasing the bit speed. For multi-layer flexible PCB or multi-layer rigid flexible PCB drilling should be especially careful.

2. punching

Microaperture punching is not a new technology and has been used for mass production. Because the winding process is continuous production, there are many examples of using punching to process the winding through hole. But batch punching technology is limited to blunt o. diameter 6 ~ 0.8 mm hole, compared with nc drilling machine drilling processing cycle is long and need manual operation, due to the large size of original process, the punching mould accordingly, so the mold price is very expensive, although mass production to reduce the cost advantage, but the burden of equipment depreciation, Small volume production and flexibility cannot compete with CNC drilling, so it is still not popular.

However, in recent years, the die precision of punching technology and numerical control drilling have made great progress, punching in the practical application of flexible printed board has been very feasible. The latest mold manufacturing technology can produce a hole with a diameter of 75um that can punch and cut the base material 25um thick non-adhesive adhesion-type copper clad foil laminate. The reliability of punching is also quite high. If the punching conditions are suitable, it can even punch holes with a diameter of 50um. Punching device has also been CNC, mold can be miniaturized, so it can be well applied to flexible printed board punching, CNC drilling and punching can not be used for blind hole processing.

3. Laser drilling

With laser can drill the smallest hole, for flexible printed board drilling hole laser drilling machine has excited excimer laser drill, impact carbon dioxide laser drill, YAG(yttrium aluminum garnet) laser drill, argon laser drill, etc..

Impact type carbon dioxide laser drill only can carry on the drilling to the base material of insulation layer, and YAG laser drill insulating layer of the base material and copper foil for drilling, drilling and the speed of the insulating layer significantly faster than the speed of drilling and copper foil, in just the same kind of laser drilling machine for all drilling could not have a high production efficiency. Copper foil is etched first to form a pattern of holes, then the insulation is removed to create a through-hole, so that lasers can drill holes of extremely small sizes. However, due to the position accuracy of upper and lower holes, the hole diameter may be restricted. If the blind hole is drilled, as long as the copper foil etching off one side, there is no up and down position accuracy problem. The process is similar to the plasma and chemical etching holes described below.

At present, the holes processed by excimer laser are the smallest. Excited excimer laser is ultraviolet light, directly destroy the structure of the base layer resin, so that the resin molecules dispersed, the heat generated is very small, so you can limit the damage degree of heat around the hole to the minimum range, the hole wall is smooth and vertical. If the laser beam could be shrunk further, it would be possible to process holes between 10 and 20 µ m in diameter. Of course, the larger the plate thickness aperture ratio, the more difficult the wet copper plating. The problem with stimulated excimer laser drilling is that the breakdown of polymers results in carbon black sticking to the hole wall, so some means must be taken to clean the surface to remove the carbon black prior to plating. However, when laser processing blind holes, there are also some problems in laser uniformity, which will produce bamboo-like residues.

The biggest difficulty of excimer laser is slow drilling speed and high processing cost. Therefore, it is limited to the processing of small holes with high precision and high reliability.

Impact type carbon dioxide laser is generally used carbon dioxide gas as laser source, radiation is infrared, and excited excimer laser combustion decomposition resin molecules due to thermal effect is different, it belongs to thermal decomposition, processing hole shape is much worse than the excited excimer laser, can be processed aperture is basically 70 ~ 100um, But the processing speed is significantly faster than the excited excimer laser speed, and the cost of drilling is much lower. Even so, the processing cost is much higher than plasma etching hole method and chemical etching hole method described below, especially if there are many holes per unit area.

It should be noted that when processing blind holes, the laser can only be fired to the surface of the copper foil, and the organic matter on the surface need not be removed at all. In order to stably clean the copper surface, chemical etching or plasma etching should be used as post-processing. Considering from the possibility of technology, laser drilling process is basically no difficulty in winding process, but considering the balance of the process and the proportion of equipment investment, it is not dominant, but the width of the Tape chip Automated welding process (TAB, Tape Automated Bonding) is narrow, Practical examples have been made of the use of a winding process to increase the rate of drilling.

Double-sided flexible circuit board FPC manufacturing process product drawing

Hole metallization - double-sided FPC manufacturing process

The hole metallization of flexible PCB is basically the same as the hole metal process of rigid PCB.

In recent years, instead of electroless plating, direct electroplating has been used to form carbon conductive layer. Hole metallization of flexible printed boards also introduces this technique.

Flexible printed board because of its softness, need to have a special fixed fixture, fixture can not only fix the flexible printed board, but also must be stable in the plating solution, otherwise the copper plating thickness is not uniform, which is also an important cause of wire breaking and bridging in the etching process. To achieve uniform copper plating, the flexible PCB must be taut in the fixture, and the position and shape of the electrodes must be worked out.

Hole metalization outsourcing processing, as far as possible to avoid outsourcing to no flexible printed board perforation experience of the factory, if there is no flexible printed board special electroplating line, the quality of perforation is not guaranteed.

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