Many DIY players will find that the various board products on the market use a dizzying variety of PCB colors. The more common PCB colors are black, green, blue, yellow, purple, red, and brown. Some manufacturers are also creative to develop white, pink and other colors of PCB.
In the traditional impression, black PCB seems to be positioned at the high end, while red, yellow, etc., are low-end dedicated, is that right?
The copper layer of PCB without solder resistance coating oxidizes easily when exposed to air.
We know that both the front and back of PCB are copper layers. In the production of PCB, whether the copper layer is manufactured by the addition method or subtraction method, the final surface will be smooth and unprotected. Although the chemical properties of copper are not as active as aluminum, iron, magnesium, 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 undergo oxidation reaction soon after contact with the air. Because 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 whole PCB.
To prevent copper oxidation, to separate the welded and unwelded parts of the PCB during welding, and to protect the surface of the PCB, engineers developed a special coating. This coating can be easily applied to the surface of the PCB, forming a protective layer of a certain thickness and blocking copper and air contact. This layer of coating is called solder resistance layer and the material used is solder resistance paint.
Since it’s called paint, there must be different colors.
Yes, the original solder resistance paint can be colorless and transparent, but for easy repair and manufacturing, PCBs often need to be printed with tiny text on the board. Transparent solder resistance paint can only show the PCB background color, so whether it is manufacturing, maintenance, or sales, the appearance is not good. So engineers add a variety of colors to the solder resistance paint, and the end result is a black PCB or a red or blue PCB.
Black PCBs are hard to see wiring, which makes maintenance difficult
From this point of view, the color of PCB has nothing to do with the quality of PCB. The difference between black PCB and blue PCB, yellow PCB, and other color PCB lies in the color of solder resistance paint on the final brush. If the PCB is designed and manufactured exactly the same, the color will have no effect on performance, nor will it have any effect on heat dissipation.
As for black PCB, because its surface wiring is almost completely covered, it is very difficult for later maintenance, so it is a color that is not convenient to manufacture and use. Therefore, in recent years, people gradually reform, give up the use of black welding resistance paint, instead of using dark green, dark brown, dark blue, and other welding resistance paint, the purpose is to facilitate manufacturing and maintenance.
At this point, we have basically clear about the problem of PCB color. The reason why “color represents high-grade or low-grade” is because manufacturers like to use black PCB to make high-end products, and red, blue, green, yellow and other low-grade products. To sum up, the product gives meaning to the color, not the color that gives meaning to the product.
Gold, silver and other precious metals are used on PCB what benefit?
The color is clear, let’s talk about the precious metal on PCB! When some manufacturers advertise their products, they will mention that their products are gold-plated, silver-plated and other special processes. So what is the use of this process?
When the PCB surface needs to be soldered, a portion of the copper layer is required to be exposed for soldering. These exposed layers of copper are called pads, and pads are usually rectangular or circular and have a very small area. Above, we know that the copper used in PCB is highly oxidized, so the only copper exposed to the air is the copper on the solder pad after applying the solder resistance 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 final product performance. So engineers have come up with all sorts of ways to protect pads. Such as plating inert metal gold, chemically covering the surface with silver, or covering copper with a special chemical film to prevent contact with the air.
Exposed pads on PCB, the copper layer is directly exposed. This part needs to be protected to prevent it from being oxidized From this point of view, whether gold or silver, the purpose of the process itself is to prevent oxidation and protect the pads so that they can ensure a good yield during the subsequent welding process.
However, the use of different metals will put forward requirements on the storage time and storage conditions of PCB used in the production plant. Therefore, PCB factories generally use vacuum sealing machines to package PCB before the completion of PCB production and delivery to customers, so as to ensure that no oxidation damage occurs to PCB to the maximum extent.
And before the final components on the machine welding, board card manufacturers also need to test the degree of oxidation of PCB, eliminate oxidized PCB, to ensure the rate of good products. The final consumer to get the boarding card, is through a variety of tests, even after a long time of use oxidation will almost only occur in the plug-and-unplug connection, and on the pads and has been welded components, no impact.
Since the resistance of silver and gold is lower, will the use of special metals such as silver and gold reduce the heat generated during PCB use?
We know that the biggest factor affecting calorific value is electrical resistance. Resistance and conductor itself material, conductor cross-sectional area, length related. Pad surface metal thickness is even far less than 0.01 mm, if the use of OSP(organic protective film) treatment of the pads, there will be no excess thickness. The resistance shown by such a small thickness is almost zero, or even impossible to calculate, and certainly does not affect the heat.
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