How to Judge PCB Surface Process by Color
There are gold and copper in the circuit boards of mobile phones and computers, so the recycling price of waste circuit boards is much more expensive than selling waste paper, glass bottles, and scrap iron. From the surface, the outer layer of the circuit board mainly has three colors: gold, silver, and light red. Gold is the most expensive, silver is cheap, and light red is the cheapest one.
It can be seen from the color whether the PCB manufacturing plant 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. The outer layer must have the above-mentioned protective layer. Some people say that the golden yellow one is copper, which is wrong.
The gold circuit board is the most expensive, whose material contains real gold. Although there is only a thin layer, it also accounts 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. If you find that the surface color of a PCB fabrication is silver, it must be cutting corners. The industry term is called "cost down". Most mobile phone motherboards are gold-plated boards, while computer motherboards, audio, and small digital circuit boards are generally not gold-plated boards.
Does the golden color is gold, and the silver color is real silver? Of course not, it is tin. The silver board is called the spray tin board. Spraying a layer of tin on the outer layer of the copper circuit board can also help soldering. But it cannot provide long-term contact reliability like gold. 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 is not enough, such as grounding pads, probe sockets and so on. 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. There is only one reason that is cheap.
OSP is an organic soldering film. Because it is organic, not metal, it is cheaper than tin spraying. The only function of this organic film is to ensure that the inner copper foil 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 area of the circuit board is too large, its gold plating cannot be affordable.