PCB Technical - Method of judging PCB board surface process by color

There is gold and copper in the PCB circuit boards of mobile phones and computers. Therefore, the recycling price of used circuit boards can reach more than 30 yuan per kilogram. It is much more expensive than selling waste paper, glass bottles, and scrap iron.

From the outside, the outer layer of the circuit board mainly has three colors: gold, silver, and light red. Gold is the most expensive, silver is the cheapest, and light red is the cheapest.

It can be seen from the color whether the hardware manufacturers have cut corners,

In addition, the circuits inside the circuit board are mainly pure copper, which is easily oxidized if exposed to the air, and the outer layer must have the above-mentioned protective layer. Some people say that golden yellow is copper, which is wrong.

Large area gold plating on the circuit board

The most expensive gold is 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 finger of the 8 years old memory stick below is still shiny. 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, and connector shrapnel of the circuit board.

If you find that some circuit boards are all silver, you must be cutting corners. The industry term is called "costdown".

Most mobile phone motherboards are gold-plated boards, while computer motherboards, audio and small digital circuit boards are generally not gold-plated boards.

The exposed parts of the circuit board of iPhone X are all gold-plated.

silver

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. 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 PCB 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 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. There is only one reason: cheap

Small digital products like to use spray tin plate

Light red:

OSP, 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, PCB components cannot be soldered.

Many computer motherboards use OSP technology. Because the area of the circuit board is too large, it cannot be used for gold plating.