Is there a difference between gold plating and silver plating on PCB?
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【Jie Duo Bang PCB】Today, the editor will introduce some small knowledge about PCB. For example, whether different colors of PCB affect its performance, whether there is a difference between gold plating and silver plating on PCB, the following will explain them one by one. 01 The Secret of Colorful PCB Colors 51)]Many DIY players will find that the PCB colors used in various board products on the market are dazzling. The more common PCB colors are black, green, blue, yellow, purple, red and brown. Some manufacturers have also developed PCBs in different colors such as white and pink. In the traditional impression, black PCB seems to be positioned at the high end, while red, yellow, etc. are dedicated to the low end. Is that true? The copper layer of the PCB without solder mask coating is easily oxidized when exposed to the air. 51)]We know that both sides of PCB are made of copper layer. In the production of PCB, no matter whether the copper layer is made by additive method or subtractive method, it will get a smooth and unprotected surface. Although the chemical properties of copper are not as active as aluminum, iron, magnesium, etc., pure copper is easily oxidized when it comes into contact with oxygen in the presence of water; because there is oxygen and water vapor in the air, the pure copper surface will soon undergo oxidation reaction after coming into contact with air. Since the thickness of the copper layer in 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 soldering part and non-soldering part of PCB during soldering, and to protect the surface of PCB, engineers have invented a special coating. This coating can be easily applied to the surface of PCB to form a protective layer with a certain thickness and block the contact between copper and air. This coating is called solder mask, and the material used is solder mask paint. Since it is called paint, it must have different colors. Yes, the original solder mask paint can be made colorless and transparent, but for the convenience of maintenance and manufacturing of PCB, it is often necessary to print small text on the board. Transparent solder mask paint can only reveal the base color of the PCB, so whether it is manufactured, repaired or sold, the appearance is not good enough. Therefore, engineers added various colors to the solder mask paint, and finally formed black or red or blue PCBs. 02 51)]Black PCB is difficult to see the wiring, which makes maintenance difficult 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 is the color of the solder mask applied at the end. 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 black PCB, since its surface traces are almost completely covered, it makes it very difficult to repair in the later stage, so it is not a color that is convenient to manufacture and use. Therefore, in recent years, people have gradually reformed and abandoned the use of black solder mask paint, and switched to dark green, dark brown, dark blue and other solder mask paints, the purpose is to facilitate manufacturing and maintenance. Speaking of this, everyone has basically understood the issue of PCB color. As for the saying that "color represents high-end or low-end", it is because manufacturers like to use black PCB to manufacture high-end products, and use red, blue, green, yellow and other colors to manufacture low-end products. In a word, it is the product that gives the color meaning, not the color that gives the product meaning. 03 What are the benefits of using precious metals such as gold and silver on PCBs? Now that we have explained the colors, let's talk about the precious metals on PCBs! 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? If components need to be soldered on the surface of the PCB, a part of the copper layer must be exposed for soldering. These exposed copper layers are called pads, which are generally rectangular or circular and have a small area. In the above, we know that the copper used in PCBs is easily oxidized, so after applying solder mask, the only copper exposed to the air is the copper on the pads. If the copper on the pad is oxidized, it will not only be difficult to solder, but also the resistivity will increase greatly, seriously affecting the performance of the final product. Therefore, engineers have come up with various ways to protect the pad. For example, plating with inert metal gold, or covering a layer of silver on the surface through chemical processes, or covering the copper layer with a special chemical film to prevent the pad from contacting the air. The exposed pad on the PCB has the copper layer directly exposed. This part needs to be protected to prevent it from being oxidized. From this point of view, whether it is gold or silver, the purpose of the process itself is to prevent oxidation and protect the pad so that it can ensure the yield rate in the subsequent welding process. However, the use of different metals will put forward requirements for the storage time and storage conditions of the PCB used by the production factory. Therefore, the PCB factory generally uses a vacuum plastic sealing machine to package the PCB after the PCB production is completed and before it is delivered to the customer for use, to maximize the guarantee that the PCB will not be damaged by oxidation. Before the components are finally soldered on the machine, the board manufacturer must also test the oxidation degree of the PCB and remove the oxidized PCB to ensure the yield rate. The boards that consumers finally get have already passed various tests. Even if oxidation occurs after long-term use, it will almost only occur at the plug-in connection parts, and will have no effect on the pads and already soldered components. Since silver and gold have lower resistance, will the use of special metals such as silver and gold reduce the heat generated by the PCB during use? We know that the biggest factor affecting heat generation is resistance. Resistance is related to the material of the conductor itself, the cross-sectional area of the conductor, and the length. The thickness of the metal material on the surface of the pad is even much less than 0.01 mm. If the pad is treated with OST (organic protective film), there will be no excess thickness at all. The resistance shown by such a small thickness is almost equal to 0, and it cannot even be calculated. Of course, it will not affect the heat generation.
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