How to understand the surface finish from PCB color?
From the surface of the PCB, there are three main colors: gold, silver and light red. The gold PCB is the most expensive, silver is the cheapest, and light red is the cheapest.
You can know whether the manufacturer is cutting corners from the surface color.
In addition, the circuit inside the circuit board is mainly pure copper. Copper is easily oxidized when exposed to the air, so the outer layer must have the above-mentioned protective layer.
Some people say that gold is copper, which is wrong.
Please refer to the gold picture plated on the circuit board as shown below:
The most expensive gold circuit board is real gold. Although it is very thin, it also accounts for nearly 10% of the cost of the board.
There are two advantages to using gold, one is convenient for welding, and the other is anti-corrosion.
As shown in the picture below, this is the golden finger of the memory stick 8 years ago. It is still golden sparkling.
The gold-plated layer is widely used in circuit board component pads, gold fingers, connector shrapnel, etc.
If you find that some circuit boards are silver, it must be cut corners. We call it “price reduction”.
Generally speaking, mobile phone motherboards are gold-plated, but computer motherboards and small digital boards are not gold-plated.
Please refer to the iPhone X board below, the exposed parts are all gold-plated.
Gold is gold, silver is silver? Of course not, it is tin.
The silver board is called the HASL board. Spraying tin on the outer layer of copper also helps soldering, but it is not as stable as gold.
It has no effect on the already welded parts of the HASL board. However, if the pad is exposed to the air for a long time, such as grounding pads and sockets, it is easy to oxidize and rust, resulting in poor contact.
All small digital products are HASL boards. There is only one reason: cheap.
OSP (Organic Solderability Preservative), it is organic, not metallic, so it is cheaper than HASL process.
The only function of the organic film is to ensure that the internal copper foil will not be oxidized before soldering.
Once the film evaporates, it will evaporate and be heated. Then you can solder the copper wire and the component together.
But it is easily corroded. If the OSP board is exposed to the air for more than 10 days, it cannot be soldered.
There are many OSP processes on the computer motherboard. Because the circuit board size is too large.