The wiring and functional characteristics on the PCB are designed by the customer, and the PCB board factory is only responsible for manufacturing it, so it is the same as that there is often communication between most designers and manufacturers. The board factory often It is found that the design materials sent by the customer do not meet the process capability of the board factory, such as the line width, the line spacing is too small, and the aperture is too small. Communication confirmation. Then, the data required for each process of PCB 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 film plotter is used to draw the film of the circuit board (Film). These films are used for the image exposure of each circuit layer in the subsequent circuit board manufacturing process. It is also used in the oil process. 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.
This film is actually a transparent PET material printed with a black image, similar to the film used on the projectors we used in early school.
3. Circuit board inner layer forming
The inner layer structure of a multilayer circuit board (more than 4 layers) usually uses a whole copper foil substrate as the material, and then each step will clean the copper foil surface by pickling to ensure that there are no other dust or impurities on it. As long as there is any foreign matter, it 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. Then, a dry layer will be coated on the surface of the copper foil membrane. 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
Etching-"peeling film
Generally, a strong alkaline solution is used to dissolve and etch away the exposed copper surface, that is, 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 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
Copper surface oxidation treatment-"disc version"-"pressing-" edge fishing target
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 laminating machine will Tightly integrated.
7. Mechanical drilling
The main purpose of drilling is to make vias to connect the lines that need to communicate between the layers. The vias of the multilayer board will have different conduction requirements. Here, the simplest 4-layer board is used as an example, so blind buried holes are not involved. In order to save time and improve efficiency, three PCBs can be stacked and drilled at the same time. In order to avoid burrs, an aluminum plate is placed on the top and a pad is placed on the bottom to avoid the drill directly hitting the table. In fact, it is not necessary to work with three PCBs. The board manufacturer will determine the number of PCBs and stacks according to factors such as PCB thickness, aperture size, and hole location accuracy.
According to experience, the rotation speed of the drill bit, the speed of drilling and the speed of the drill, and the life of the drill are important factors affecting the quality of the circuit board after molding. The porosity of the fibers causes CAF in the future.
In addition, there are laser drilling processes for more demanding boards. Lasers can drill finer micro holes (Micro Via), but the cost is relatively high. Generally, high-density (HDI) boards use laser holes, and they are blindly buried Most of the holes in the board are laser holes.
8. Chemical precipitation
Deslagging-"chemical copper-" electroplated copper
Because the high-speed rotation of the drill will generate high temperature, when the high temperature exceeds the Tg point of the substrate (glass transition temperature), slag will be generated. If it is not removed, the inner copper foil will not be able to pass through the electroplated copper to form channels, Channels are 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. Development of outer laminated film
Its production method and principle are the same as the development method of the inner laminated film, but at this time there are already PTH metallized holes on the layout.
10. Electroplated copper / resist layer
Next, copper is plated into the through-holes by electroplating until the customer's requirements are met, which generally requires more than 25um. Please note that the place where the dry film is at this time can prevent being plated with copper, but other places not covered by the dry film will also add about 25um of copper.
11. 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 needed and must be removed to avoid affecting the subsequent surface treatment. Stripping the resist layer is usually performed by high pressure spraying get on.
12. 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. Originally thought that the solder resist layer was selectively printed on it, I did not expect to print the entire board with solder resist paint, then enter the baking box for pre-baking, and then use the film to make contact exposure Transfer the image on the negative to the solder mask, then use UV to dry the area not covered by the light to allow the solder mask to truly adhere to the circuit board, and finally clean the mask area in the chemical tank. To expose the copper surface that can be soldered.
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.
13. 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 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.
14. Electroplated hard gold
The purpose of electroplating hard metal for 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 PCB is shown in the film. Soak in the plating solution.
15. Silkscreen
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. However, most of the domestic mass-produced PCBs still use the screen printing process.
At this point, the manufacturing process of the circuit board is completed, and the electrical measurement, analysis, and packaging are only included later.
16. Flying Probe Test
The prototype test of the circuit board usually uses the flying probe test. If the quantity is large, the needle bed test can also be used to save time. The test is mainly open / short test
17. Molded split board
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 and divide the board.
18. V-Cut
If there is a board with V-Cut requirements, it is necessary to cut out V-grooves in the defined place.
19. Visual inspection and packaging
Final visual inspection and vacuum packaging