Bare copper plate
Advantages and disadvantages are obvious: Advantages: low cost, smooth surface and good weldability (In the absence of oxidation). Disadvantages: it is easy to be affected by acid and humidity, and cannot be kept for a long time. It should be used up within 2 hours after unpacking, because copper is easy to oxidize when exposed to air; It cannot be used on double-sided panels because the second side has been oxidized after the first reflow soldering. 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 air, and the outer layer must have the above protective layer. And some people think that golden yellow is copper, which is wrong, because it is the protective layer on copper. Therefore, it is necessary to make a large area of gold plating on the circuit board, which is the gold sinking process that I have shown you before. Second, gold-plated 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. In Shenzhen, there are many merchants who specialize in purchasing used circuit boards. Through certain means to wash out gold, it is a good income. The use of gold as a coating is to facilitate welding and to prevent corrosion. Even the golden fingers of the memory chips that have been used for several years are still flashing as before. If copper, aluminum and iron were used at the beginning, they will now be rusted into a pile of waste products. The gold-plated layer is widely used in the components of the circuit board, such as the pad, the gold finger, and the connector shrapnel. If you find that the circuit board is actually silver, then there is no need to say, directly call the consumer rights hotline, it must be that the manufacturer cut corners, did not use the materials well, and used other metals to fool customers. The mainboards of the most widely used mobile phone circuit boards are mostly gold-plated plates, gold-plated plates, computer mainboards, audio and small digital circuit boards are generally not gold-plated plates. The advantages and disadvantages of the gold precipitation process are not difficult to draw: Advantages: not easy to oxidize, can be stored for a long time, the surface is flat, suitable for welding fine gap pins and components with small solder joints. The first choice for PCB boards with keys (Such as mobile phone Board). Reflow soldering can be repeated many times, which does not reduce its weldability. Can be used as a COB (Chip On Board)The substrate of the line. Disadvantages: high cost, poor welding strength, because the use of non-electro-nickel plating process, easy to have black disk problems. The nickel layer will oxidize with time, and long-term reliability is a problem. Now we know that gold is gold and silver is silver? Of course not, it's tin. Three, tin spray circuit board, silver board is called Tin spray board. Spraying a layer of tin on the outer layer of the copper line can also help welding. But it cannot provide long-term contact reliability like gold. It has no effect on the components that have been welded, but for the pads that have been exposed to air for a long time, the reliability is not enough, such as grounding pads, spring sockets, etc. Long-term use is easy to oxidize and rust, resulting in poor contact. Basically used as a circuit board for small digital products, without exception, is a tin spray board, the reason is cheap. Its advantages and disadvantages are summarized as follows: Advantages: lower price and good welding performance. Disadvantages: not suitable for welding thin gap pins and too small components, because the surface flatness of tin spray plate is poor. Tin beads are easily produced in PCB processing (solder bead), For the fine gap pin (fine pitch)Components are more likely to cause short circuits. When used in the double-sided SMT process, because the second side has passed a high-temperature reflow soldering, it is extremely easy to spray tin and melt again to produce tin beads or similar drops of water into dripping spherical tin spots affected by gravity, the surface is more uneven and affects the welding problem. The cheapest light red circuit board mentioned earlier, namely miner's lamp thermoelectric separation copper substrate IV and OSP process Board organic welding aid film. Because it is organic, not metal, it is cheaper than the tin spray process. Advantages: it has all the advantages of bare copper plate welding, and the expired board can also be treated again. Disadvantages: easily affected by acid and humidity. When used for secondary reflow soldering, it needs to be completed within a certain period of time, and the effect of secondary reflow soldering is usually relatively poor. If the storage time exceeds three months, it must be re-surface treated. Use up within 24 hours after opening the package. OSP is the insulating layer, so the test point must be printed with solder paste to remove the original OSP layer in order to contact the needle 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. When the welding is heated, the film evaporates. Solder can weld copper wire and components together. However, it is not very corrosion resistant. An OSP circuit board cannot weld components if it is exposed to the air for more than ten days. Many computer motherboards use OSP technology. Because the circuit board area is too large, it can't afford gold plating.