PCB Technical - What are the benefits of gold and silver plating on PCB boards

Many DIY players will find the wide variety of PCB board colors available on the market bewildering. More common PCB colors are black, green, blue, yellow, purple, red, and brown. Some manufacturers have also developed different colors such as white and pink PCB.

In the traditional impression, black PCB seems to be positioned at the high end, while red, yellow and so on are dedicated to the low end, is that true?

The copper layer of PCB without solder resistance coating is easily oxidized when exposed to air

As we know, both sides of PCB are copper layers. In the production of PCB, the copper layer will get smooth and unprotected surface no matter it is made by addition method or subtraction method. Although the chemical properties of copper is not as active as aluminum, iron, magnesium and so on, but in the presence of water, pure copper and oxygen contact is easily oxidized; Because of the presence of oxygen and water vapor in the air, the surface of pure copper will oxidize quickly upon contact with the air. Because the thickness of copper layer in PCB is very thin, the oxidized copper will become a bad conductor of electricity, which will greatly damage the electrical performance of the whole PCB.

To prevent copper oxidation, to separate the welded part of the PCB from the non-welded part during welding, and to protect the surface of the PCB, engineers developed a special coating. This coating can be easily applied to the PCB surface, forming a protective layer of a certain thickness and blocking the contact between copper and air. This layer of coating is called solder blocking and the material used is solder blocking paint.

If it's called paint, it must be a different color. Yes, raw solder paint can be made colorless and transparent, but

PCBS often need to print tiny text on the board for easy maintenance and manufacturing. Transparent solder resistance paint can only show the PCB background, so whether manufacturing, maintenance or sales, the appearance is not good enough. So engineers add a variety of colors to the solder resist paint to create black or red or blue PCBS.

What are the benefits of gold and silver plating on PCB boards

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Black PCB is difficult to see the line, which brings difficulties for maintenance

From this point of view, the PCB color and PCB quality is not related. The difference between black PCB and blue PCB, yellow PCB and other color PCB lies in the color of solder resistance paint on the brush. If the PCB is designed and manufactured exactly the same, the color will not have any effect on performance, nor will it have any effect on heat dissipation.

As for the black PCB, its surface wiring is almost completely covered, which causes great difficulties to the later maintenance, so it is not very convenient to manufacture and use the color. Therefore, in recent years, people gradually reform, abandon the use of black welding paint, to use dark green, dark brown, dark blue and other welding paint, the purpose is to facilitate manufacturing and maintenance.

Speaking of which, we have basically understood the problem of PCB color. The reason for the "color representative or low grade", it is because manufacturers like to use black PCB to manufacture high-end products, with red, blue, green, yellow and other low-end products caused by. The conclusion is: the product gives color meaning, rather than color gives product meaning.

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What are the advantages of gold, silver and other precious metals used in PCB?

Now that the colors are clear, let's talk about the precious metals on the PCB! When some manufacturers advertise their products, they will make special mention of their products using special processes such as gold plating and silver plating. So what is the use of this technique?

When soldering elements are required on the PCB surface, a portion of the copper layer is required to be exposed for soldering. These exposed layers of copper are called pads, which are usually rectangular or round and have a small area. As mentioned above, we know that the copper used in PCB is easily oxidized, so it is exposed to air on the pad after brushing with anti-welding paint.

If the copper on the pad is oxidized, it is not only difficult to weld, but also increases the resistivity, which seriously affects the performance of the final product. So engineers have come up with all sorts of ways to protect pads. Such as coating the pad with inert metal gold, or chemically coating the surface with silver, or covering the pad with copper with a special chemical film that prevents air contact.

Exposed pads on PCB, the copper layer is directly exposed. This part needs to be protected from oxidation

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 to ensure good yield during the subsequent welding process.

However, the use of different metals will require the storage time and storage conditions of the PCB used in the production plant. Therefore, PCB factories generally use vacuum molding machine to pack PCB before PCB production is completed and delivered to customers, so as to ensure no oxidation damage to PCB.

Before the components are welded on the machine, the board card manufacturers also need to detect the oxidation degree of PCB and eliminate the oxidized PCB to ensure the good yield. The board card that consumer gets eventually, it is already passed all sorts of detection, although the oxidation after using for a long time also can happen to be in plug and unplug connecting place almost only, and to welding plate and already welded component, without what effect.

Since the resistance of silver and gold is lower, will the use of silver and gold and other special metals reduce the heat when using PCB?

We know that the factor that affects calorific value is resistance. The resistance is related to the material, cross-sectional area and length of the conductor. The thickness of the metal material on the surface of the pad is even 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 tiny thickness is almost zero, even incalculable, and of course does not affect the calorific value.