How to Know the Surface Finish From PCB Color?

How to know the surface finish from PCB color?

 

From the PCB surface, there are three main colors: gold, silver, and light red color. The PCB with gold color is the most expensive, the silver color is cheap, and the light red color is the cheapest.

 

You could know if the manufacturer have cut corners or not, from the surface color.

Besides, the circuit inside the board is mainly pure copper. The Copper is easily oxidized when exposed to air, so the outer layer must have the above protective cover.

 

  1. Gold color

Some people say that gold color is copper, that is not right.

Please refer to the picture with gold plating on the board as below:

 

immersion gold pcb board

 

The golden circuit board is the most expensive and is the real gold. Although it is thin, it also accounts for nearly 10% of the cost of the board.

There are two advantages for using gold, One is for welding conveniently and the other is for anti-corrosion.

 

As shown below, this is the golden finger of the memory stick 8 years ago. It is still golden and shining.

 

plated gold finger pcb

 

The gold-plated layer is widely used in circuit board component pads, gold fingers, connector shrapnel etc.

If you find that some boards are all silver, it must be cut corners. We call it "costdown."

Generally speaking, the motherboards of mobile phone are gold-plated boards, but computer motherboards and small digital boards are not gold-plated.

Please refer to the board of iPhone X as below, The exposed parts are all gold plated.

gold plated pcb

 

 

  1. Silver color

Gold color is gold, silver color is silver? Of course not, it is tin.

immersion silver pcb board

 

The silver board is called a HASL board. Spraying tin on the outer layer of the copper, it also could help to welding, but it is not as stable as gold.

There is no effect on already welded components for HASL board. However, if pads are exposed to the air for a long time, such as ground pads and pin sockets etc, It is easy to oxidize and rust, resulting in poor contact.

 

All the small digital products are HASL boards. There is only one reason: cheap.

 

HASL PCB Board

 

  1. Light red color

OSP(Organic Solderability Preservatives), it is organic, not metal, So it is cheaper than the HASL process.

The only function of the organic membrane is to ensure the inner copper foil will not be oxidized before soldering.

This membrane evaporates as soon as it is heated. Then you could solder the copper wire and components together.

But it is easy to be corroded. An OSP board can't be soldered if it is exposed to the air for more then 10 days.

There are many OSP processes in computer motherboards. Because the board size is too large.

 

osp pcb board