1. Gerber file preprocessing
The wiring and functional characteristics on the FPC are designed by the customer, and the circuit board factory is only responsible for manufacturing it. The circuit board factory often finds that the design information sent by the customer does not meet the board’s process capabilities, such as line width, line The distance is too small, the aperture is too small, etc. At this time, the engineer of the circuit board factory will communicate with you to confirm. Then, the data required for each process of FPC production is exported from the Gerber file, such as: each layer of circuit, solder mask, silk screen layer, surface treatment, drilling and other data, which are then input to the production device equipment corresponding to the process in.
2. Circuit board negative output
Under the strict temperature and humidity control environment, a laser negative film plotter is used to draw the negatives of the circuit board. These negatives are used as the image exposure of each circuit layer in the subsequent circuit board manufacturing process, and are used in the solder mask green oil process. You also need to use the bottom film. In order to make the X-Y relative position of each layer of the circuit correct, a laser is used to punch holes in each film for subsequent positioning of different circuit layers.
3. Circuit board inner layer forming
The inner layer structure of a multilayer circuit board usually uses a whole copper foil substrate as the material, and then each step will clean the surface of the copper foil by pickling to ensure that there are no other dust or impurities on it, as long as there is any tint The foreign matter will affect the subsequent circuits. Then the surface of the copper foil will be roughened by mechanical grinding to enhance the adhesion between the dry film and the copper foil, and then a dry film will be coated on the surface of the copper foil. An inner circuit film is attached to each side of the copper foil substrate and set up on the exposure machine. The positioning film and vacuum are used to precisely attach the film to the copper foil substrate. The ultraviolet light is used in the yellow light area to make the negative film. The unshielded dry film is chemically changed and cured on the copper foil substrate, and finally the unexposed dry film is removed with a developing solution.
4. Etching of inner circuit
Generally, a strong alkaline solution is used to dissolve and etch away the exposed copper surface. That is to say, remove the copper surface that is not covered by a dry film. When etching, pay attention to the formula and time of the potion. The thicker the copper foil, the longer it takes. The wider the time and the wider the gap is, the wider the wiring is kept, because the etching will corrode the exposed copper foil, and the copper surface at the edge of the dry film will be more or less corroded. Then, the cured dry film that was originally covered on the copper foil is removed with a film removing solution, and only the copper foil of the circuit should be left on the copper foil substrate.
5. Image positioning target hole
In order to accurately align the inner and outer copper skins, CCD positioning is used to find the target position that has been preset on the negative film in advance and drill the required positioning target holes. The movement of the target hole must also be performed on all the inner and outer layers of the circuit, so that the copper foil circuits of the inner and outer layers can be positioned on the same datum in subsequent processes.
6. Lamination and Lamination
Generally, the surface of copper is oxidized with an alkaline solvent to produce black copper oxide. The crystals of the copper oxide are needles and can be used to strengthen the contact strength between layers. Next, the completed inner layer and the copper layer of the outer layer of the film machine are overlapped. Here, the inner layer and the outer layer must be accurately positioned by means of the positioning holes drilled in advance, and then the high temperature and high pressure laminator will be used to align each other. Tightly integrated.
7. Mechanical drilling
The main purpose of drilling is to make vias to connect lines that need to communicate between layers. The rotation speed of the drill bit, the speed of drilling and the feed rate of the drill bit, and the life of the drill bit are all important factors that affect the quality of the circuit board after forming. And cause CAF phenomenon in the future.
8. Chemical precipitation
Because the high-speed rotation of the drill bit will generate high temperature, when high temperature exceeds the Tg point of the substrate, slag will be generated. If it is not removed, the inner copper foil will not be able to form a channel through the electroplated copper, or the channel will be formed but unstable. . When removing the rubber residue, it will be soaked with a leavening agent for about 1-10 minutes to allow the various rubber residues to swell and relax before removal. A thin layer of copper is then chemically applied to the walls of the non-conductive holes.
9. Electroplated copper / resist layer
Copper is then plated into the vias by electroplating until the customer’s requirements are met.
10. Etching Outer Circuits
After the circuit board is etched, the outer layer of the circuit is already formed, and it is the same as the designed circuit. At this time, the etching resist film is no longer necessary and must be removed to avoid affecting the subsequent surface treatment. Stripping the resist layer is usually performed by high-pressure spraying. get on.
11. Solder mask
The main purpose of the solder mask layer is to distinguish the soldered assembly area from the non-soldered area. In addition, it can also prevent the copper layer from oxidizing and achieve aesthetic requirements. If it is a relatively simple solder mask or a solder mask with a large dimensional tolerance, you can also use screen printing to selectively print the solder mask.
12. ENIG Chemical Nickel Gold
The ENIG surface treatment process is generally used to make chemical nickel deposits on copper pads. The thickness of the nickel layer is controlled by controlling time and temperature. Then the fresh nickel activity just deposited is used to put the nickel pads into the acidic gold water. The substitution reaction displaces gold from the solution to the surface of the pad, that is to say, nickel is replaced, and part of the surface nickel will be dissolved in the gold water. The replaced gold will gradually cover the nickel layer. After the nickel layer is completely covered, the replacement reaction will automatically stop, and the process can be completed after cleaning the pad surface dirt.
13. Electroplated hard gold
The purpose of electroplating hard metal in selective electroplating is to increase its resistance to friction. Therefore, it can be seen in the film that the parts that do not need to be plated with hard gold are pasted to reveal only the areas that need to be plated. Only part of the film is FPC. Soak in the plating solution.
14. Silk screen
The early text (white paint) was almost all completed by screen printing, but the silk screen printing ink needs to be added with solvents and volatile, which is not good for the human body. Now some new text printing has switched to inkjet printing, and it is also very fast accurate. After screen printing or inkjet printing, it needs to go through the oven to fix white paint.
15. Flying Probe Test
The flying board test is usually used for the circuit board test. If the quantity is large, the needle bed test can also be used to save time. The test is mainly open / short circuit test.
16. Forming splits
The shape of the circuit board is usually formed by using a milling machine and a CNC machine to control the shape of the circuit board.
If there is a board with V-Cut requirements, it is necessary to cut out V-grooves in the defined place.
18. Visual inspection and packaging
Final visual inspection and vacuum packaging