Huizhou double-sided FPC manufacturing process full solution process

FPC cutting - double-sided FPC manufacturing process  

FPC In addition to some materials, FPC materials 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 FPC metallized hole drilling, currently can only be drilled in the sheet form, so double-sided FPC 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 tape etching process after the FPC for automatic cutting, using 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  

The through holes of FPC can be drilled numerically as well as those of rigid printed boards, but are not suitable for hole machining of circuits with double-sided metallized holes.  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.  

The through holes of FPC can be drilled numerically as well as those of rigid printed boards, but are not suitable for hole machining of circuits with double-sided metallized holes.  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 FPC through the drilling is now mostly still with CNC drilling machine drilling, CNC drilling machine and FPC use of CNC drilling machine is basically the same, but the drilling conditions are different.  Because FPC is very thin, it can be drilled by overlapping multiple pieces. If the drilling conditions are good, 10 to 15 pieces can be drilled together.  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 FPC are available on the market. Drill bits for rigid printed board drilling and cutter for contour milling can also be used for FPC.  

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.  Special care should be taken in drilling multi-layer or double-layer FPC.  

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 FPC practical application 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 FPC punching, CNC drilling and punching can not be used for blind hole processing.  

3.  Laser drilling  

With laser can drill the most fine hole, for FPC 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 FPC manufacturing process product drawing  

Hole metallization - double-sided FPC manufacturing process  

The hole metallization of FPC is basically the same as the hole metal process of rigid printed board.  

In recent years, instead of electroless plating, direct electroplating has been used to form carbon conductive layer.  The hole metallization of FPC also introduces this technique.  

FPC, because of its softness, requires a special 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 the flexible printed board perforation experience of the factory, if there is no FPC special plating line, the quality of the hole is not guaranteed.  

Surface cleaning of copper foil -FPC manufacturing process  

In order to improve the adhesion of resist mask, the surface of copper foil should be cleaned before coating resist mask. Even such simple procedure needs special attention for FPC.  

FPC generally cleaning chemical cleaning process and mechanical grinding process, for the manufacture of precision graphics, most occasions are to combine the two clean flow process for surface treatment.  Mechanical grinding using brush method, brush material too hard will cause damage to the copper foil, too soft and insufficient grinding.  Nylon brush is generally used, and the length and hardness of the brush must be carefully studied.  Use two brush rollers, placed on the conveyor belt, the direction of rotation is opposite to the direction of belt transmission, but at this time if the brush roller pressure is too large, the substrate will be stretched by a great tension, which is one of the important reasons for the size change.  

FPC if the copper foil surface treatment is not clean, then the adhesion to the resist mask is poor, which will reduce the qualified rate of the etching process.  Due to the recent improvement in the quality of copper foil, the surface cleaning process can also be omitted in the case of single circuit.  However, surface cleaning is an essential process for precision graphics below 1OOμm.  

Now, the coating method of resist is divided into the following three methods according to the precision and output of circuit graphics: screen leakage method, dry film/photosensitive method, liquid resist photosensitive method.  

Now, the coating method of resist is divided into the following three methods according to the precision and output of circuit graphics: screen leakage method, dry film/photosensitive method, liquid resist photosensitive method.  

FPC anticorrosive ink uses screen printing method to directly print the line graphics on the surface of copper foil, which is the most commonly used technology, suitable for mass production, low cost.  The accuracy of FPC line graphics can reach line width/spacing of 0.2 ~.3 mm, but is not suitable for more precise graphics.  With refinement this method gradually fails to adapt.  Compared with the dry film method described below, the operator has to be trained for many years, which is a disadvantage.  

The line width of 70 ~ 80μm can be prepared by FPC dry film method as long as the equipment and conditions are complete.  Now most of the precision graphics below 0.3mm can be used to form corrosion resistant circuit graphics by dry film method.  Using dry film, its thickness is 15 ~ 25μm, conditions allow, batch level can produce 30 ~ 40μm line width graphics.  

FPC when choosing dry film, must be based on the matching with copper foil, process and through the test to determine.  Even if the experimental level has good resolution, it does not necessarily have a high pass rate when used in mass production.  Flexible printed boards are thin and easy to bend. If you choose a hard dry film, it is brittle and poor follow-up, so it will crack or peel off so that the qualified rate of etching is reduced.  

FPC dry film is rolled, the production equipment and operation is relatively simple.  Dry film is composed of thin polyester protective film, photoresist film and thick polyester release film.  In the film before the first release film (also known as diaphragm) stripping, and then the hot roll will be pressed on the surface of the copper foil, before development and then tear off the above protective film (also known as carrier film or covering film), general FPC on both sides of the guide positioning hole, dry film can be slightly narrower than the flexible copper foil film to film.  The automatic laminating device for FPC is not suitable for the laminating device for FPC and some design changes must be made.  Due to dry film and other processes compared with the linear speed, so many factories do not use automatic film, but the use of manual film.  

After the dry film of FPC is affixed, it should be placed for 15 ~ 20 minutes before exposure in order to make it stable.  

If the line width of FPC line graph is less than 30μm, the qualified rate will decrease obviously when the graph is formed by dry film.  Liquid photoresist is usually used instead of dry film for mass production.  Different coating conditions, coating thickness will change, if the thickness of 5 ~ 15μm liquid photoresist coating on 5μm thick copper foil, laboratory level can etching line width less than 10 μm.  

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