Many DIY players will find that the PCB colors used by 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 also developed PCB with 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 PCB are dedicated to the low end. Is that so?
01 PCB copper coating without coating of solder resist is easy to oxidize in air. We know that both sides of PCB are copper layers. In the production of PCB, the copper layer is made smooth or unprotected by both addition and reduction. Although the chemical properties of copper are not as active as aluminum, iron and magnesium, the contact between pure copper and oxygen is easy to oxidize under water conditions; because there are oxygen and water vapor in the air, the surface of pure copper will react quickly with air. Because the thickness of copper layer in PCB is relatively thin, the oxidized copper will become a poor conductor of electricity, which will greatly damage the electrical performance of the whole PCB. In order to prevent copper oxidation, and in order to separate the welding parts and non welded parts of PCB during welding, engineers also invented a special coating to protect the surface of PCB. The coating can be easily brushed on the PCB surface, forming a protective layer with a certain thickness, and blocking the contact of copper and air. This coating is called solder mask, and the material used is solder mask.
Since it's called lacquer, there must be different colors. Yes, the original solder resist paint can be made into colorless and transparent, but PCB often needs to print small words on the board for maintenance and manufacturing convenience. Transparent solder resist can only reveal the background color of PCB, so the appearance is not good enough for manufacture, repair or sale. So engineers added a variety of colors to the solder resist paint, and finally formed black or red or blue PCB.
02 The black PCB is hard to see clearly and brings difficulties to maintenance. From this point of view, the color of PCB has nothing to do with the quality of PCB. The difference between black PCB and other color PCB, such as blue PCB and yellow PCB, is that the color of solder resist paint on the final brush is different. If the PCB design and manufacturing process are exactly the same, the color will not have any effect on the performance, nor will it have any effect on the heat dissipation.
As for the black PCB, because its surface line is almost completely blocked, resulting in greater difficulties for later maintenance, so it is not easy to make and use a color. Therefore, in recent years, people gradually reform, abandon the use of black solder resist paint, turn to use dark green, dark brown, dark blue and other solder resist paint, the purpose is to facilitate manufacturing and maintenance.
Speaking of this, you have basically understood the problem of PCB color. The reason for the emergence of "color represents high-grade or low-grade" is that manufacturers prefer to use black PCB to make high-end products, and produce low-end products with red, blue, green, yellow and so on. To sum up, the product gives color meaning, not color gives product meaning.
03 What are the advantages of gold, silver and other precious metals used in PCB? Let's talk about the precious metals on the PCB. Some manufacturers, when promoting their products, will specifically refer to their products using gold-plated, silver plated and other special processes. So what is the use of this process?
PCB surface needs welding components, so a part of copper layer is required to be exposed for welding. These exposed copper layers are called pads, and the pad is generally rectangular or round, with a smaller area. In the above, we know that copper used in PCB is easy to oxidize, so the only exposure to air in the air is the copper on the pad.
If the copper on the pad is oxidized, it is not only difficult to weld, but also the resistivity increases greatly, which seriously affects the final product performance. So engineers came up with all kinds of ways to protect the pads. For example, plating inert metal gold, or covering a layer of silver on the surface by chemical process, or covering the copper layer with a special chemical film, preventing the contact between the pad and air.
For the solder pad exposed on PCB, the copper layer is directly exposed. This part needs to be protected from oxidation. From this point of view, whether gold or silver, the purpose of the process itself is to prevent oxidation and protect the pad, so as to ensure the yield in the next welding process.
However, the use of different metals will require the storage time and storage conditions of PCB used in the production plant. Therefore, PCB factories usually use vacuum plastic packaging machine to pack PCB after PCB production and before it is delivered to customers for use, so as to ensure PCB does not suffer oxidation damage to a large extent.
Before the final components are welded, the board manufacturer should check the oxidation degree of PCB once, remove the oxidized PCB, and ensure the yield. Finally, the boards and cards that consumers get have passed various tests. Even after a long time of use, the oxidation will almost only occur at the plug-in connection part, and have no impact on the pads and the components that have been welded.
Because the resistance of silver and gold is lower, will the heat generated in PCB use be reduced after special metals such as silver and gold are used?
We know that resistance is the major factor affecting the calorific value. Resistance is also related to the material of the conductor itself, the cross-sectional area of the conductor and the length of the conductor. The thickness of the metal material on the pad surface is even far less than 0.01mm.
