From the PCB surface, the outer layer of the circuit board mainly has three colors: gold, silver, and light red. It can be seen from the color whether the manufacturer has cut corners. In addition, the internal circuit of the circuit board is mainly pure copper, which is easily oxidized if exposed to the air, and the outer layer must have a protective layer. There are several knowledge points about how to judge the PCB surface process of circuit boards by color.
1. Golden PCB board
Plated Gold circuit board projects are the most expensive. Although there is only a thin layer, they also account for nearly 10% of the cost of the circuit board. There are two reasons why gold is used, one is to facilitate welding, and the other is to prevent corrosion. The gold-plated layer is widely used in the component pads, gold fingers, and connector shrapnel of the circuit board. Most mobile phone motherboards are gold-plated boards; computer motherboards, audio, and small digital circuit boards are generally not gold-plated boards.
2. Silver PCB
The silver printed circuit board is called the spray tin board. Spraying a layer of tin on the outer layer of the copper circuit can also help to solder. But it cannot provide long-term contact reliability like gold-plated PCB. The tin-spraying board has no effect on the components that have been soldered, but the reliability of the pads that have been exposed to the air for a long time, such as ground pads, spring pin sockets, etc., is not enough. Long-term use is prone to oxidation and corrosion, resulting in poor contact. The circuit boards of small digital products, without exception, are spray tin boards.
3. Light red PCB
OSP, organic soldering film. Because it is organic, not metal. The only function of this organic film is to ensure that the inner copper foil of rigid-flex PCB will not be oxidized before welding. This layer of film volatilizes as soon as it is heated during welding. The solder can weld the copper wire and the components together. But it is not resistant to corrosion. If an OSP circuit board is exposed to the air for ten days, the components cannot be welded. Many computer motherboards use OSP technology because the circuit board area is too large.