1. Bare copper plate
The advantages and disadvantages are obvious:
Advantages: low cost, smooth surface, good weldability (in the absence of oxidation).
Disadvantages: It is easy to be affected by acid and humidity and cannot be stored for a long time. It should be used up within 2 hours after unpacking, because copper is easily oxidized when exposed to the air; it cannot be used on double-sided PCB because it is second after the first reflow soldering. The noodles are already oxidized. If there is a test point, solder paste must be printed to prevent oxidation, otherwise it will not be in good contact with the probe.
Pure copper is easily oxidized if exposed to the air, and the outer layer must have the above-mentioned protective layer. And some people think that the golden yellow is copper, which is wrong because it is the protective layer on the copper. Therefore, it is necessary to plate a large area of gold on the circuit board, which is the immersion gold process that I have taught you before (such as: 6 layer Rigid-flex Immersion Gold PCB).
Second, the gold plate
Gold is real gold. Even if only a very thin layer is plated, it already accounts for nearly 10% of the cost of the circuit board. Use gold as a plating layer, one is to facilitate welding, and the other is to prevent corrosion. Even the gold finger of the memory stick that has been used for several years still flickers as before. If copper, aluminum, and iron were used in the first place, they have now rusted into a pile of scraps.
The gold-plated layer is widely used in the electronic component pads, gold fingers, connector shrapnel and other positions of the circuit board. If you find that the circuit board is actually silver, then needless to say, it must be the manufacturer cutting corners, not using the materials properly, and using other metals to fool customers. Most of the motherboards of the most widely used mobile phone circuit boards are gold-plated PCBs and heavy gold PCBs. Computer motherboards, audio and small digital circuit boards are generally not gold-plated boards.
The advantages and disadvantages of immersion gold technology are not difficult to draw:
Advantages: It is not easy to oxidize, can be stored for a long time, and the surface is flat. It is suitable for welding small gap pins and electronic components with small solder joints. The first choice of PCB boards with buttons (such as mobile phone boards). Reflow soldering can be repeated many times without reducing its solderability. It can be used as a substrate for COB (Chip On Board) wire bonding.
Disadvantages: high cost, poor welding strength, because the electroless nickel plating process is used, it is easy to have the problem of black disk. The nickel layer will oxidize over time, and long-term reliability is a problem.
Now we know that gold is gold and silver is silver? Of course not, it is tin.
Three, spray tin circuit board
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 PCBA Manufacturing. But it cannot provide long-term contact reliability like gold. It has no effect on the electronic components that have been soldered, but the reliability is not enough for the pads that have been exposed to the air for a long time, such as grounding pads and spring pin sockets. Long-term use is prone to oxidation and corrosion, resulting in poor contact. Basically, it is used as a circuit board for small digital products, without exception, the spray tin board, the reason is cheap pcb manufacturing.
Its advantages and disadvantages are summarized as:
Advantages: lower price and good welding performance.
Disadvantages: It is not suitable for soldering pins with fine gaps and electronic components that are too small, because the surface flatness of the spray tin plate is poor. In PCBA Manufacturing, solder bead is easy to produce, and it is easy to cause short circuit to fine pitch components. When used in double-sided SMT chip processing, because the second side has already undergone a high temperature reflow soldering, it is very easy to spray tin and re-melt to produce tin beads or similar water drops into spherical tin spots that are affected by gravity, resulting in a better surface. Unevenness affects welding problems.
Before talking about the cheapest light red circuit board, that is, the miner’s lamp thermoelectric separation copper substrate
Four, OSP craft board
Organic soldering film. Because it is organic, not metal, it is cheaper than tin spraying.
Advantages: It has all the advantages of bare copper plate welding, and the expired board can also be surface treated again.
Disadvantages: easily affected by acid and humidity. When used in the secondary reflow soldering, it needs to be completed within a certain period of time, and usually the effect of the second reflow soldering will be relatively poor. If the storage time exceeds three months, it must be resurfaced. It must be used up within 24 hours after opening the package. OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer before it can contact the pin point for electrical testing.
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 evaporates 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, the components cannot be welded.
Many computer motherboards use OSP technology. Because the area of the circuit board is too large, it cannot be used for gold plating.
