From the outside, the outer layer of the circuit board mainly has three colors: gold, silver, and light red. Gold one is the most expensive, silver one is cheaper, and light red one is the cheapest.
It can be seen from the color whether the PCB manufacturer has cut corners. In addition, the circuit lines 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 golden yellow area is copper, but that is wrong.
Gold one is the most expensive, and it’s the real gold. Although there is only a thin layer, it also accounts for nearly 10% of the cost of the circuit board. Some places along the coast of Guangdong and Fujian specialize in purchasing waste circuit boards and peeling off the gold. The profits are considerable.
There are two reasons why use gold, one is to facilitate soldering, and the other is to prevent corrosion.
The gold finger of the memory chip manufactured 8 years ago is still shiny golden. If you change it to copper, aluminum, or iron, it will be rusty and useless.
The gold-plated layer is widely used in the component pads, gold fingers, connector shrapnel and other positions of the circuit board.
If you find that some circuit boards are all 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.
PCB made 4 years ago, still shiny gold color
Gold finger of Memory Module made 8 years ago
Iphone X main board, gold plating PCB
Is the golden one gold, and the silver one silver? Of course not, it's tin.
The silver board is called the spray tin board, also called Hot air solder leveling PCB board. Spraying a layer of tin on the outer layer of the copper circuit 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, such as grounding pads, spring contact sockets, etc., is not enough. Long-term use is prone to oxidation and corrosion, resulting in poor contact.
The circuit boards of small digital PCB products, without exception, are spray tin boards. There is only one reason: cheap!
OSP, short of Organic Solderability Preservatives, called organic soldering aid film. Because it is organic, not metal, so it is cheaper than tin spraying process.
The only function of this organic film is to ensure that the copper foil will not be oxidized before soldering. This layer of film evaporates as soon as it is heated during soldering. Then can solder 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 more than ten days, the components cannot be soldered on it.
Many computer motherboards use OSP technology. Because the circuit board size is too large, it cannot afford gold plating for such big area.