What is the difference between gold plating and silver plating on PCB boards?

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Many DIY players will find that the PCB colors used in various board products in the market are dazzling. The more common PCB colors are black, green, blue, yellow, purple, red, brown.

In addition, 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 not the case?

  1. The copper layer of the PCB without solder mask is easily oxidized when exposed to the air

We know that the front and back sides of the PCB are copper layers. In the production of PCBs, whether the copper layers are manufactured by the additive method or the subtractive method, they will get a smooth and unprotected surface.

Although the chemical properties of copper are not as active as aluminum, iron, magnesium, etc., in the presence of water, pure copper and oxygen are easily oxidized in contact; because of the presence of oxygen and water vapor in the air, the pure copper surface is Oxidation reactions occur very quickly.

Since 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 coating can be easily applied to the surface of the PCB, forming a protective layer with a certain thickness and blocking 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 print small text on the board.

The transparent solder mask can only reveal the background color of the PCB, so whether it is manufacturing, maintenance or sales, the appearance is not good enough. Therefore, engineers added various colors to the solder mask to form a black or red and blue PCB.

 

  1. The black PCB is difficult to see the traces, which brings difficulties for maintenance

From this point of view, the color of the PCB has nothing to do with the quality of the PCB. The difference between the black PCB and the blue PCB, yellow PCB and other color PCBs is that the color of the solder resist paint on the brush is different.

If the PCB design and manufacturing process are exactly the same, the color will not have any impact on performance, nor will it have any impact on heat dissipation.

Regarding the black PCB, since its surface traces are almost completely covered, it is very difficult for later maintenance, so it is a color that is not very convenient to manufacture and use.

Therefore, in recent years, people have gradually reformed, giving up the use of black solder resist paint, and switching to dark green, dark brown, dark blue and other solder resist paints, the purpose is to facilitate manufacturing and maintenance.

Having said that, everyone has basically understood the problem of PCB color. The reason for the “color representation or low-end” statement is that manufacturers like to use black PCBs to make high-end products, and use red, blue, green, yellow, etc. to make low-end products.

To sum up a sentence is: the product gives the color meaning, not the color gives the product meaning.

 

  1. What are the benefits of using precious metals such as gold and silver on PCBs?

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?

If components need to be soldered on the surface of the PCB, a part of the copper layer is required to be exposed for soldering. These exposed copper layers are called pads, and the pads are generally rectangular or circular 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 is greatly increased, which seriously affects the performance of the final product. Therefore, engineers have come up with various ways to protect the pads. For example, the inert metal gold is plated, or the surface is covered with a layer of silver through a chemical process, or the copper layer is covered with a special chemical film to prevent the 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 stop 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 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, the PCB factory generally uses a vacuum plastic packaging machine to package the PCB before the PCB production is completed and delivered to the customer to ensure that the PCB does not suffer from oxidation damage.

Before the components are soldered on the machine, the board manufacturer also needs to detect the degree of oxidation of the PCB, remove the oxidized PCB, and ensure the yield. The boards obtained by the end consumers have passed various tests. Even if they are used for a long time, oxidation will almost only occur at the plug-in connection, and it has no effect on the pads and components that have been soldered.

 

Since silver and gold have lower resistance, will the use of special metals such as silver and gold reduce the heat generated when the PCB is used?

We know that the factor that affects heat generation is resistance; 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 treated by the OST (organic protective film) method, there will be no excess thickness at all. The resistance shown by such a tiny thickness is almost 0, and it cannot even be calculated. Of course, it will not affect the heat generation.

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