Many DIY players will find that the PCB colors used by the various board products in the market are dazzling. The more common PCB colors are black, green, blue, yellow, purple, red and brown. Some manufacturers have ingeniously developed PCBs of different colors such as white and pink.
In the traditional impression, black PCB seems to be positioned at the high end, while red and yellow are dedicated to the low end. Isn’t that true?
PCB copper layer that is not coated with solder mask is easily oxidized when exposed to the air
We know that both sides of the PCB are copper layers. In the production of PCB, the copper layer will get a smooth and unprotected surface regardless of whether it is made by additive or subtractive methods.
Although the chemical properties of copper are not as active as aluminum, iron, magnesium, etc., in the presence of water, pure copper is easily oxidized in contact with oxygen; because oxygen and water vapor exist in the air, the surface of pure copper is exposed to air Oxidation reaction will occur soon.
Because the thickness of the copper layer in the PCB is very thin, the oxidized copper will become a poor conductor of electricity, which will greatly damage the electrical performance of the entire PCB.
In order to prevent copper oxidation, to separate the soldered and non-soldered parts of the PCB during soldering, and to protect the surface of the PCB, engineers invented a special coating. This kind of paint can be easily applied to the surface of the PCB to form a protective layer with a certain thickness and block the contact between copper and air. This layer of coating is called solder mask, and the material used is solder mask.
Since it is called lacquer, it must have different colors. Yes, the original solder mask can be made colorless and transparent, but for the convenience of maintenance and manufacturing, PCBs often need to be printed with small text on the board.
Transparent solder mask can only reveal the PCB background color, so the appearance is not good enough whether it is manufacturing, repairing or selling. Therefore, engineers added various colors to the solder mask to form a black or red, blue PCB.
The black PCB is difficult to see the trace, which brings difficulties to maintenance
From this point of view, the color of the PCB has nothing to do with the quality of the PCB. The difference between black PCB and other color PCBs such as blue PCB and yellow PCB lies in the color of the solder mask.
If the PCB design and manufacturing process are exactly the same, the color will not have any effect on performance, nor will it have any effect on heat dissipation.
Regarding the black PCB, its surface layer traces are almost completely covered, which causes great difficulties in later maintenance, so it is a color that is not convenient to manufacture and use.
Therefore, in recent years, people have gradually reformed, abandoning the use of black solder mask, and instead use dark green, dark brown, dark blue and other solder masks, the purpose is to facilitate manufacturing and maintenance.
Having said that, everyone has basically understood the problem of PCB color. Regarding the “color representation or low-end” statement, it is because manufacturers prefer to use black PCBs to make high-end products, and red, blue, green, and yellow to make low-end products.
The summary is: the product gives the color meaning, not the color gives the product meaning.
3.What are the benefits of using precious metals such as gold and silver on PCB?
The color is clear, let’s talk about the precious metals on the PCB! When some manufacturers promote their products, they will specifically mention that their products use special processes such as gold plating and silver plating. So what is the use of this process?
The PCB surface requires soldering components, so a part of the copper layer is required to be exposed for soldering. These exposed copper layers are called pads. The pads are generally rectangular or round with a small area.
In the above, we know that the copper used in the PCB is easily oxidized, so after the solder mask is applied, the copper on the pad is exposed to the air.
If the copper on the pad is oxidized, it is not only difficult to solder, but also the resistivity greatly increases, which seriously affects the performance of the final product. Therefore, engineers came up with various methods to protect the pads. For example, it is plated with inert metal gold, or the surface is covered with a layer of silver through a chemical process, or a special chemical film is used to cover the copper layer to prevent contact between the pad and the air.
For the exposed pads on the PCB, the copper layer is directly exposed. This part needs to be protected to prevent it from being oxidized.
From this perspective, whether it is gold or silver, the purpose of the process itself is to prevent oxidation, protect the pad, and ensure the yield in the subsequent soldering process.
However, the use of different metals will impose requirements on the storage time and storage conditions of the PCB used in the production plant. Therefore, PCB factories generally use vacuum plastic packaging machines to pack PCBs after PCB production is completed and before delivery to customers to ensure that PCBs are not oxidized to the limit.
Before the components are welded on the machine, the board card manufacturer must also check the oxidation degree of the PCB, eliminate the oxidation PCB, and ensure the yield. The board that the end consumer gets has passed various tests. Even after long-term use, the oxidation will almost only occur at the plug-in connection part, and it will have no effect on the pad and the already soldered components.
Since the resistance of silver and gold is lower, after using special metals such as silver and gold, will the heat generation of PCB be reduced?
We know that the factor that affects the amount of heat is resistance. The resistance is related to the material of the conductor itself, the cross-sectional area and length of the conductor. The thickness of the metal material on the surface of the pad is even far less than 0.01 mm. If the pad is processed by the OST (organic protective film) method, there will be no excess thickness at all. The resistance exhibited by such a small thickness is almost equal to 0, even impossible to calculate, and of course it will not affect the heat generation.