2. Externally, the outer layer of the circuit board predominantly displays three colors: gold, silver, and light red. Gold is the most valuable, followed by silver, with light red being the least expensive.
3. These colors can indicate whether hardware manufacturers have economized on materials. Additionally, the circuits within the board consist mainly of pure copper, which oxidizes easily when exposed to air and thus requires the protective layer mentioned earlier.
4. It is incorrect to assume that golden yellow denotes copper; rather, large areas of the circuit board are often gold-plated.
The most expensive type of gold used in circuit boards is genuine gold. Despite its thin layer, it can constitute nearly 10% of the total cost of the board.
There are two primary reasons for using gold: to facilitate soldering and to prevent corrosion.
The gold fingers on an eight-year-old memory stick remain shiny. If they were made of copper, aluminum, or iron, they would rust and become unusable.
Gold-plating is commonly applied to component pads, gold fingers, and connector contacts on circuit boards.
If you encounter circuit boards entirely coated in silver, it indicates cost-cutting in the industry, often referred to as “costdown.”
Most mobile phone motherboards feature gold-plated boards, whereas computer motherboards, audio devices, and small digital circuit boards generally do not.
The exposed parts of the iPhone X circuit board are all gold-plated.
Now, is a golden board made of gold, and a silver one made of silver?
Not exactly; they’re actually made of tin.
A silver board is known as a tin-sprayed board. Applying a layer of tin on the outer layer of the copper circuit aids in soldering but lacks the long-term reliability of gold.
Tin-sprayed boards do not affect already soldered PCB components, but exposed pads like ground pads and spring pin sockets can suffer from oxidation and corrosion over time, leading to poor contact.
Without exception, small digital products use tin-sprayed boards primarily due to cost considerations.
Regarding light red boards:
OSP (Organic Solderability Preservatives), an organic film, is cheaper than tin-spraying because it’s not a metal.
Its sole purpose is to prevent oxidation of the inner copper before soldering. This film evaporates upon heating during soldering, allowing solder to bond copper wires and components.
However, OSP does not protect against corrosion. If an OSP circuit board is exposed to air for ten days, PCB components may fail to solder properly.
Many computer motherboards employ OSP technology due to their large circuit board areas, which make gold plating impractical.
