Cos'è un circuito stampato2020-06-02
What is a circuit board
Printed circuit board (eg, printed circuit board, PCB or printed wiring board, PWB)-a dielectric board that forms a conductive circuit of an electronic circuit on the surface and/or inside it. Printed circuit boards are designed for electrical and mechanical connection of various electronic components. The electronic components on the printed circuit board are usually found through solder to connect the elements connected to the conductive pattern by soldering.
Unlike surface mounting, the printed circuit board is made of foil and is completely located on a solid insulating base. The printed circuit board contains mounting holes and pads for mounting output or planar components. In addition, the printed circuit board has through holes for electrically connecting foil portions located on different layers of the board. A protective coating (“solder mask”) and markings (according to the auxiliary drawings and text of the design document) are usually applied on the board from the outside.
According to the number of layers with conductive patterns, printed circuit boards are divided into:
One side (OPP): Only one layer of foil is attached to one side of the dielectric sheet.
Double-sided (DPP): two-layer foil.
Multi-layer (MPP): not only on both sides of the board, but also on the inner layer of the dielectric with foil. The multilayer printed circuit board is obtained by bonding several single-sided or double-sided boards together.
As the complexity of design equipment and mounting density increase, the number of layers on the board also increases.
The basis of the printed circuit board is dielectric, and the most commonly used materials are glass fiber and wood grain paint. Furthermore, the substrate of the printed circuit board may be a metal substrate coated with a dielectric (for example, anodized aluminum), and a copper foil on which tracks are applied. Such printed circuit boards are used in power electronic equipment to efficiently remove heat from electronic components. In this case, the metal base of the circuit board is connected to the heat sink. As a material for printed circuit boards operating in the microwave range and at temperatures up to 260°C, glass fiber reinforced fluoroplastics (such as FAF-4D) and ceramics are used. The flexible board is made of polyimide material (for example, kapton).
What material will we use to make the circuit board
The most common and affordable materials used to manufacture circuit boards are Getinax and Fiberglass. Getinax paper is impregnated with bakelite paint and epoxy glass fiber for textiles. We will definitely use fiberglass!
Foil-shaped glass fiber is a sheet made of glass fiber, impregnated with an epoxy resin-based adhesive, and lined with 35 μm thick electrolytic foil on both sides. The maximum allowable temperature is -60ºС to +105ºС. It has very high mechanical and electrical insulation properties, and is very suitable for cutting, drilling and stamping.
Glass fiber is mainly used on one or both sides, with a thickness of 1.5 mm, and the thickness of copper foil is 35 microns or 18 microns. We will use a single-sided glass fiber with a thickness of 0.8 mm and a foil with a thickness of 35 μm (why will be discussed in detail below).
Method for making printed circuit board at home
The board can be made by chemical and mechanical methods.
When using chemical methods, apply protective ingredients (varnish, toner, paint, etc.) to the foil on the board where there should be traces (painting). Next, immerse the circuit board in a special solution (ferric chloride, hydrogen peroxide, and other solutions) that “corrodes” the copper foil but does not affect the protective components. As a result, copper remains in the protective composition. The protective compound is subsequently removed with a solvent, and the finished board is retained.
Mechanical methods use scalpels (for manual manufacturing) or milling machines. A special cutter slotted the aluminum foil, and eventually left the aluminum foil-the necessary pattern on the island.
Milling machines and milling cutters themselves are expensive and have few resources. Therefore, we will not use this method.
The simplest chemical method is manual. Risograph paint draws the track on the board, and then etch the solution. This method does not allow the production of complex circuit boards with very fine tracks-so this is not the case.
The next method of manufacturing the board is to use photoresist. This is a very common technique (plates are manufactured in this way at the factory) and often used at home. On the Internet, there are many articles and methods that introduce the method of manufacturing circuit boards using this technology. It gives very good and repeatable results. However, this is not our choice. The main reasons are quite expensive materials (photoresist, which will deteriorate over time), and other tools (UV, laminator). Of course, if you can mass-produce circuit boards at home-then photoresist will be unmatched-we recommend that you master it. It is also worth noting that the photoresist equipment and technology allow us to produce screen printing and protective films on circuit boards
Millions of articles on the Internet describe how to use this technology to make circuit boards. However, this technology has many disadvantages, requires direct hands-on and takes a long time to expand. That is, it must be felt. The payment does not appear for the first time, but is obtained every other time. There are many improvements-the use of a laminator (rework required-usually insufficient temperature) can achieve very good results. There are even methods for constructing special hot presses, but all of these require special equipment. The main disadvantages of LUT technology:
Overheating-the path spreads-getting wider and wider
Overheating-traces left on the paper
The paper is “fried” onto the board (it is difficult to leave even when soaked), and as a result, the toner may be damaged. There is a lot of information to choose from on the Internet.
Porous toner-After removing the paper, there are still micropores in the toner-the board is also etched through them-will produce dents
Repeatability of results-today is excellent, tomorrow is bad, and then good-it is difficult to obtain stable results-you need a strictly constant temperature to heat the toner, you need to apply a steady pressure on the board.
By the way, I can’t make planks in this way. I tried to do this in both magazines and coated papers. As a result, he even destroyed the circuit board-copper overheated due to overheating.
For some reason, there is little information on the Internet about another toner transfer method (cold chemical transfer method). Based on the fact that the toner is not soluble in alcohol, but soluble in acetone. Therefore, if choosing a mixture of acetone and alcohol will only soften the toner, you can “glue” it from the paper to the board. I really like this method and get immediate rewards-the first board is ready. However, it was later discovered that I could not find any detailed information that could provide 100% results. We need a method that even children can afford. But the second time, the board of directors did not work, and then it took a long time to pick the necessary ingredients.
As a result, after taking a series of long-term measures, all ingredients were selected, even if not 100%, it can reach 95%. The most important thing is that this process is very simple and children can pay completely independently. This is the method we will use. (Of course, you can continue to make it ideal-if it works better for you, please write). The advantages of this method:
All reagents are cheap, affordable and safe
No other tools needed (iron, lamp, laminator-nothing, although not-you need a pan)
There is no way to destroy the circuit board-the circuit board will not heat up at all
The paper leaves by itself-the result of the toner transfer is visible-the translation is not performed
No holes in the toner (they are sealed by paper)-so no kimchi
Do 1-2-3-4-5 and always get the same result-almost 100% repeatability
Before we start, let us see which boards we need and what we can do at home using this method.
Basic requirements for wood-based panels
We will use modern sensors and microcircuits to make devices on the microcontroller. Microchips are becoming smaller and smaller. Therefore, the following board requirements must be met:
The board should be double-sided (usually, it is very difficult to separate the single board, it is very difficult to make a four-layer board at home, the microcontroller needs a ground layer to protect them from interference)
The track should be 0.2 mm thick-this size is sufficient-0.1 mm or even better-but there may be pickling, the path will be left when welding
The spacing between the tracks-0.2mm-is suitable for almost all schemes. Reducing the gap to 0.1mm is full of the merge of traces and the difficulty of monitoring whether the circuit board is shorted.
We will not use protective masks or screen printing, as this complicates production, and it is not necessary if you make your own circuit boards. Similarly, there is a lot of information on the Internet. If you want, you can make a “marafet” yourself.
We will not deceive the circuit board, which is also unnecessary (unless you manufacture the device for 100 years). For protection, we will use varnish. Our main goal is to quickly, efficiently and inexpensively manufacture the circuit board of the device at home.
This is the appearance of the finished board. Made by our method-tracking 0.25 and 0.3 with a distance of 0.2