Open material is the original copper-clad board cut into the production line can be made in the process of the board, first of all, let's understand a few concepts: (1) UNIT: UNIT refers to the PCB design engineers to design the unit graphics.
(2) SET: SET refers to engineers in order to improve production efficiency, ease of production and other reasons, more than one UNIT put together into a whole graphic. It is also often referred to as a patchwork, which includes unit graphics, process edges, and so on.
(3) PANEL: PANEL refers to the production of PCB manufacturers, in order to improve efficiency, ease of production, etc., will be more than one SET put together and add the tooling board edge, composed of a board.
Two, the inner layer of dry film (INNER DRY FILM)
Inner dry film is the inner layer of the line graphics transferred to the PCB board process. In the PCB production we will mention the concept of graphic transfer, because the production of conductive graphics is the fundamental PCB production. So the graphic transfer process has a very important meaning for PCB production. The inner layer of dry film, including the inner layer of film, exposure and development, inner layer of etching and other processes. The inner layer of the film is in the copper plate surface with a layer of special photosensitive film, is what we call dry film. This film will be cured by light, forming a protective film on the board. Exposure development is to paste the film on the board for exposure, the light transmittance of the part is cured, no light transmittance of the part or dry film. Then after developing, the uncured dry film is removed and the plate with the cured protective film is etched. And then after the film treatment, the inner layer of the line graphics will be transferred to the board. The entire process flow is as follows:
For designers, our main consideration is the minimum line width of the wiring, spacing control and uniformity of the wiring. Because the pitch is too small will cause the clip film, the film can not be faded out resulting in a short circuit. Line width is too small, the film adhesion is not enough, resulting in open circuit. So the circuit design of the safe spacing (including line and line, line and pad, pad and pad, line and copper surface, etc.), must be considered for the production of the safe spacing.
1, pre-treatment: grinding plate
The main role of the grinding plate: the basic pre-treatment is mainly to solve the problem of surface cleanliness and surface roughness. Remove oxidation, increase the roughness of the copper surface, easy to film attached to the copper surface.
2, film
The processed substrate by hot pressing or coating the way to apply a dry film or wet film to facilitate the subsequent exposure production.
3, exposure
The negative and the dry film pressed on the substrate alignment, in the exposure machine using ultraviolet light, the negative graphic transfer to the light-sensitive dry film.
4. Developing
The unexposed dry film/wet film is dissolved and rinsed away by the weak alkalinity of the developing solution (sodium carbonate), and the exposed portion is retained.
5, etching
Non-exposed dry film / wet film by the developer to remove the copper surface will be exposed, with acidic copper chloride will be exposed to this part of the copper surface of the dissolution of the corrosion, to get the desired line.
6, the film
Will protect the copper surface has been exposed to the dry film with sodium hydroxide solution to peel off, revealing the line graphic.
Three, browning
Purpose: is to make the inner copper surface to form a microscopic rough and organic metal layer, enhance the adhesion between the layers.
Process principle: through chemical treatment to produce a uniform, good adhesive properties of the organic metal layer structure, so that the inner layer of the copper layer before bonding the surface of the controlled roughening, for the enhancement of the inner layer of copper layer and semi-cured sheet between the pressure plate after the bonding strength.
Four, lamination
Lamination is the pp sheet with the help of the adhesive properties of the various layers of the line bonded into a whole process. This bonding is through the interface between the macromolecules of mutual diffusion, penetration, and then produce intertwined and realize the discrete multilayer board and pp sheet together with the press into the required number of layers and thickness of the multilayer board. In practice, the copper foil, bonding sheet (semi-cured sheet), inner plate, stainless steel, isolation plate, kraft paper, outer steel plate and other materials are laminated according to the process requirements.
For designers, the first thing to consider with lamination is symmetry. Because the board in the process of lamination will be affected by the pressure and temperature, in the laminated after the completion of the board there are still stresses within the board. Therefore, if the laminated board is not uniform on both sides, then the stress on both sides is not the same, resulting in board bending to one side, greatly affecting the PCB performance. In addition, even in the same plane, if the distribution of copper cloth is not uniform, will cause the resin flow rate is not the same at all points, so that the thickness of copper cloth less places will be slightly thinner, while the thickness of copper cloth more places will be slightly thicker. In order to avoid these problems, in the design of the uniformity of the copper cloth, the symmetry of the laminated, blind buried hole design layout and other aspects of the factors must be considered in detail. Fifth, drill holes
To make the circuit board layer to produce through-hole, to connect the purpose of the interlayer.
Legendary drill
Six, copper-plated
1, copper-plated
Also known as the chemical copper, after drilling the PCB in the copper cylinder redox reaction occurs, the formation of a copper layer so that the hole hole metallization, so that the original insulation of the surface of the substrate deposited on the copper to achieve the interlayer electrical interconnection.
2, plate plating
To make just copper out of the PCB board for the board surface, hole copper thickening to 5-8um, to prevent the thin copper in the holes in the graphic plating before the oxidation of the holes, micro-etching off and leakage of the substrate.
Seven, the outer dry film
and the inner dry film the same process.
Eight, the outer layer of graphic plating, SES
Holes and lines of copper plating to a certain thickness (20-25um) to meet the requirements of the final PCB board finished copper thickness. And the board surface is not used to etch off the copper, revealing the useful line graphics.
Nine, soldermask
Soldermask, also known as anti-solder, green oil, is one of the most critical processes in the production of printed circuit boards, mainly through screen printing or coating soldermask ink, coated with a layer of soldermask on the surface of the board, through the exposure of the development, revealing to be welded to the plate and the hole, and elsewhere covered with a layer of soldermask, to prevent short-circuiting when welding.
Ten, screen printing characters
The desired text, logo or parts symbols, printed on the board surface by stencil printing, and then exposed to ultraviolet radiation on the board surface.
Eleven, surface treatment
Bare copper itself is very good solderability, but long-term exposure to the air is susceptible to moisture oxidation, tend to exist in the form of oxides, is unlikely to remain for a long time for the original copper, so the need for surface treatment of the copper surface. The most basic purpose of surface treatment is to ensure good solderability or electrical properties.
Common surface treatment: spray tin, immersion gold, OSP, immersion tin, immersion silver, nickel and palladium gold, electric hard gold, electric gold finger.
Twelve, molding
The PCB will be CNC molding machine to cut into the required dimensions.
Thirteen, electrical test
Simulation of the state of the board, power on the electrical properties of the inspection, whether there is an open or short circuit.
Fourteenth, final inspection, sampling, packaging
The appearance of the board, size, aperture, thickness, marking and other checks to meet customer requirements. The qualified products will be packaged into bundles for easy storage and transportation.