As Huawei breaks through the U.S. blockade in the field of mobile phone chips, the United States has begun a new round of sanctions against China. This time they have targeted Graphics Processing Unit (GPU) chips. Currently, there are more than 10 Chinese chip companies. The company was sanctioned. Next, let’s take a look at the chip production process and why ferric chloride is used.
Photolithography is the process of transferring patterns to photoresist that covers the surface of a semiconductor silicon wafer. These patterns must then be transferred to the thin layers that make up the device under the photoresist. This process is called etching, which selectively etches away the unmasked parts of the thin layer. Today we will briefly talk about one of the methods of photolithography: wet chemical etching.
The mechanism of wet chemical etching mainly includes three stages: the reactants diffuse to the reactant surface, the chemical reaction proceeds on the surface, and then the reaction products are removed from the surface through diffusion.
The stirring and temperature of the corrosive solution will affect the corrosion rate. In the integrated circuit process, most wet chemical etching involves immersing the silicon wafer in a chemical solvent or spraying etching solvent on the silicon wafer. For immersion etching, the silicon wafer is put into a chemical solvent, and stirring is required to ensure that the etching process proceeds at a consistent or constant rate; spray etching greatly increases the efficiency by continuously providing new etchant to the surface of the silicon wafer. In terms of etching rate and consistency, the spray type is better than the immersion type.
And if it is a circuit board made of copper, then ferric chloride is the perfect etching machine, because 2FeCl3+Cu=2FeCl2+CuCl2 , the +3-valent iron ions are reduced to +2-valent iron ions, and the copper element is Oxidized to +2-valent copper ions. In addition, the cost of ferric chloride determines that it is a high-quality and low-cost etchant.
Let’s take a look at the circuit board production process
Part 1
The first step in PCB production is to organize and check the PCB layout (Layout). The PCB production factory receives the CAD files from the PCB design company. Since each CAD software has its own unique file format, the PCB factory will convert it into a unified format – Extended Gerber RS-274X or Gerber X2. Then the factory engineers will check whether the PCB layout complies with the manufacturing process and whether there are any defects or other problems.
Part 2
Cleaning the copper-clad board. If there is dust, it may cause a short circuit or open circuit in the end . At this time, you need to use cleaning agents such as inorganic acids, organic acids, and surfactants.
Part 3
The picture below is an illustration of an 8-layer PCB. It is actually composed of 3 copper-clad laminates (core boards) plus 2 copper films, and then glued together with prepreg. The production sequence is to start from the middle core board (4th and 5th layer circuits), continuously stack them together, and then fix them. The production of 4-layer PCB is similar, except that only one core board and two copper films are used . The composition of the prepreg is 20-70% glass fiber cloth, 10-40% silica, and 20-40% epoxy resin.
Part 4
First, make the two layers of circuits on the middle core board (Core). After the copper clad laminate is cleaned, a layer of photosensitive film will be covered on the surface. This film will solidify when exposed to light, forming a protective film on the copper foil of the copper-clad laminate.
Insert the two layers of PCB layout film and the double-layer copper clad laminate into the upper layer of PCB layout film to ensure the accurate stacking position of the upper and lower layers of PCB layout film .
The photosensitive machine uses UV light to illuminate the photosensitive film on the copper foil. Under the light-transmitting film, the photosensitive film is cured, but under the opaque film, there is still no cured photosensitive film. The copper foil covered under the cured photosensitive film is the required PCB layout circuit, which is equivalent to the role of laser printer ink for manual PCB.
Then use alkali solution to clean the uncured photosensitive film, and the required copper foil circuits will be covered by the cured photosensitive film.
Then use a strong alkali, such as NaOH, to etch away the unnecessary copper foil. Peel off the cured photosensitive film to expose the required PCB layout circuit copper foil.
Part 5
A new raw material is needed here called prepreg, which is the adhesive between the core board and the core board (number of PCB layers > 4), as well as the core board and the outer copper foil, and also plays an insulating role.
The lower copper foil and two layers of prepreg have been fixed in position through the alignment holes and the lower iron plate in advance. Then the prepared core board is also placed into the alignment holes. Finally, the two layers of prepreg, one layer of copper foil and A layer of pressure-bearing aluminum plate covers the core plate.
The above is the whole process of circuit board production.
