PCB production process two: graphic electroplating process description
We use the process flow of multi-layer board as the lead of PCB process introduction, and select the graphic electroplating process to explain the process. It is specifically divided into eight parts for introduction. The classification and process are as follows:
A. Inner layer circuit (photographic process) → B. Lamination → C. Drilling → D. Hole metallization (wet area process) → E. Outer layer dry film (photographic process) → F. Outer circuit → G. Screen printing → H. Surface technology → I. Post process
A. Inner line
Utilizing UV light irradiation, the photosensitive initiator in the resist in the exposed area decomposes into free radicals, and the free radical initiation unit undergoes a cross-linking reaction to form a space network macromolecular structure that is insoluble in dilute alkali, while the unexposed part is due to It is soluble in dilute alkali. Utilize the different solubility properties of the two in the same solution to transfer the graphics on the negative film to the substrate, that is, image transfer.
b. lamination
Lamination, as the name suggests, is the process of bonding each layer of circuit sheets into a whole. The whole process, including kiss pressure, full pressure, cold pressure. During the kissing stage, the resin wets the bonding surface and fills the voids in the circuit, and then enters full pressure, bonding all voids. The so-called cold pressing is to quickly cool the circuit board and keep the size stable.
C. Drilling
In general, drilling refers to a processing method in which a drill bit is used to process holes on a product display. Generally speaking, when drilling a product on a drilling machine, the drill bit should complete two movements synchronously:
①Main movement, that is, the rotational movement of the drill bit around the axis (cutting movement);
②Secondary movement, that is, the linear movement of the drill bit against the workpiece along the axis (feed movement).
D. Hole metallization
A very important process in the PCB processing process is to change the non-metallized hole into a metallized hole to realize the conduction of the hole, that is, the via hole. At present, PCB hole metallization uses several common processes in the industry: chemically deposited foil copper, chemically deposited copper, chemically deposited thick copper, and direct electroplating processes.
E. Outer dry film
Transfer the outer layer circuit image on the film to the copper clad board that has completed the copper plating or board electroplating process to form an anti-plating dry film image.
F. Outer line
A layer of photosensitive film will be pasted on the treated same surface, and under the irradiation of ultraviolet light, the pattern on the film negative will be transferred to the copper surface to form a corrosion-resistant mask pattern.
G. silk screen
It can prevent circuit bridging during soldering, provide long-term electrical environment and chemical resistance protection, and form a beautiful "coat" for printed boards, including two systems: thermosetting epoxy green oil and liquid photosensitive solder resist ink.
H. Surface technology
At present, the common PCB instant noodle treatment processes in domestic board factories include: spray tin (HASL, hot air solder leveling hot air leveling), OSP (anti-oxidation), chemical immersion gold (ENIG), electroplating gold, etc. Of course, special applications are also available. There will be some special PCB surface treatment processes. Comparing different PCB surface treatment processes, their costs are different, and of course the occasions used are also different.
Only choose the right one and not the expensive one. At present, there is no perfect PCB surface treatment process (this is about cost performance, that is, it can meet all PCB application scenarios at the lowest price), so there are so many processes. Let us choose, of course, each craft has its own merits, the existence of which is reasonable, the key is that we must know them and make good use of it.
I. Post process
That is, outer processing, testing and inspection.