With the continuous development of electronic science and technology, PCB technology has also undergone great changes, and the manufacturing process also needs to progress. At the same time each industry on the PCB board process requirements have gradually improved, such as cell phones and computers in the circuit board, the use of gold, but also the use of copper, resulting in the advantages and disadvantages of the board has gradually become easier to distinguish.

We take you to understand the surface process of the PCB board, compare the advantages and disadvantages of different PCB board surface finish and applicable scenarios.

Purely from the outside, the outer layer of the circuit board has three main colors: gold, silver, light red. According to the price categorization: gold is the most expensive, silver is the next, light red is the cheapest, from the color is actually very easy to determine whether the hardware manufacturers have cut corners. However, the circuit board internal circuit is mainly pure copper, that is, bare copper board.

A, Bare copper board
Advantages: low cost, flat surface, good solderability (in the case of not being oxidized).

Disadvantages: easy to be affected by acid and humidity, can not be stored for a long time, and need to be used up within 2 hours after unpacking, because copper is easily oxidized when exposed to air; can not be used for double-sided, because the second side has been oxidized after the first reflow. If there is a test point, must add printed solder paste to prevent oxidation, otherwise the subsequent will not be able to contact with the probe well.

Pure copper can be easily oxidized if exposed to air, and the outer layer must have the above protective layer. And some people think that the golden yellow is copper, that is not the right idea, because that is the copper above the protective layer. So it needs to be a large area of gold plating on the board, that is, I have previously brought you to understand the sink gold process.

B, Gold-plated board

The use of gold as a plating layer, one is to facilitate the welding, the second is to prevent corrosion. Even after several years of memory sticks of gold fingers, still shining as before, if the original use of copper, aluminum, iron, now has rusted into a pile of scrap.

Gold plating layer is heavily used in the circuit board component pads, gold fingers, connector shrapnel and other locations. If you find that the circuit board is actually silver, it goes without saying, call the consumer rights hotline directly, it must be the manufacturer cut corners, did not use the material properly, using other metals to fool customers. We use the most widely used cell phone circuit board is mostly gold-plated board, sunken gold board, computer motherboards, audio and small digital circuit boards are generally not gold-plated board.

The advantages and disadvantages of the sunken gold process is actually not difficult to draw.

Advantages: not easy to oxidation, can be stored for a long time, the surface is flat, suitable for welding fine gap pins and components with small solder joints. Preferred for PCB boards with keys (such as cell phone boards). Can be repeated many times over reflow soldering is not likely to reduce its solderability. It can be used as a substrate for COB (Chip On Board) marking.

Disadvantages: Higher cost, poor solder strength, easy to have the problem of black plate because of the use of electroless nickel process. The nickel layer will oxidize over time, and long-term reliability is a problem. 

Now we know that the gold is gold, silver is silver? Of course not, is tin.

C, HAL/ HAL LF
Silver-colored board is called spray tin board. Spraying a layer of tin in the outer layer of copper lines can also help soldering. But can not provide long-lasting contact reliability as gold. For components that have been soldered has little effect, but for long-term exposure to air pads, reliability is not enough, such as grounding pads, bullet pin sockets, etc.. Long-term use is prone to oxidation and rust, resulting in poor contact. Basically used as a small digital product circuit board, without exception, is the spray tin board, the reason is cheap.

Its advantages and disadvantages are summarized as follows

Advantages: lower price, good soldering performance.

Disadvantages: not suitable for soldering fine gap pins and too small components, because the surface flatness of the spray tin board is poor. In the PCB processing is easy to produce tin beads (solder bead), the fine pitch pins (fine pitch) components easier to cause a short circuit. When used in double-sided SMT process, because the second side has been a high-temperature reflow, it is easy to melt the spray tin again and produce tin beads or similar water droplets by gravity into drops of spherical tin spots, resulting in a more uneven surface and thus affect the soldering problem.

Previously mentioned the cheapest light red circuit board, that is, the mine lamp thermoelectric separation copper substrate.

4, OSP process board

Organic flux film. Because it is organic, not metal, so it is cheaper than the spray tin process.

Its advantages and disadvantages are

Advantages: has all the advantages of bare copper board soldering, expired boards can also be redone once the surface treatment.

Disadvantages: Easily affected by acid and humidity. When used in secondary reflow, it needs to be done within a certain period of time, and usually the second reflow will be less effective. If the storage time exceeds three months, it must be resurfaced. OSP is an insulating layer, so the test point must be stamped with solder paste to remove the original OSP layer in order to contact the needle point for electrical testing.

The only purpose of this organic film is to ensure that the inner copper foil is not oxidized before soldering. Once heated during soldering, this film evaporates away. Solder is then able to solder the copper wire and components together.

But it is very resistant to corrosion, an OSP board, exposed to the air for ten or so days, you can not solder components.

Computer motherboards have a lot of OSP process. Because the board area is too large to use gold plating.