1. Bare Copper
Advantages: low cost, flat surface, good solderability (without being oxidized).
Disadvantages: easily affected by acid and humidity, can not be stored for a long time, 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 boards, because the Cannot be used for double-sided boards because the second side is oxidized after the first reflow. If there is a test point, it must be printed with solder paste to prevent oxidization, otherwise, it will not be able to make good contact with the probe subsequently.
2. OSP
Advantages: Has all the advantages of bare copper soldering, expired boards can also be re-do a surface treatment.
Disadvantages: susceptible to acid and humidity. Used in the second reflow soldering, need to be completed within a certain period, usually the second reflow soldering results will be worse. If the storage time is more than three months, it must be re-surfaced. If the storage time exceeds three months, it must be re-surfaced. OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer before contacting the needlepoint for electrical properties. OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer to contact the needlepoint for electrical testing. The only function of this organic film is to ensure that the inner copper foil is not oxidized before soldering. As soon as the solder is heated, the film evaporates. film evaporates when the solder is heated. The solder is then able to weld the copper wires and components together.
3. Immersion Gold
Advantages: not easy to oxidize, can be stored for a long time, the surface is flat, suitable for soldering fine gap pins and solder joints smaller components. Preferred PCB boards with buttons (such as cell phone boards) The first choice for PCB boards with buttons (such as cell phone boards). Can be repeated many times over the reflow soldering is not likely to reduce its solderability. Can be used as a base material for COB (Chip On Board).
Disadvantages: Higher cost, poorer solder strength, easy to have black disk problem because of electroless nickel plating process. The nickel layer will oxidize over time, so long-term reliability is a problem.
4. HASL
Advantages: Lower price, good welding performance.
Disadvantages: not suitable for welding fine gap pins and too small components, because the surface flatness of the tin spray board is poor. Easy to produce tin beads in PCB processing (solder bead), the fine gap pin (fine pitch) components are more likely to cause a short circuit. Used in double-sided SMT process, because the second side has a high-temperature reflow soldering When used in double-sided SMT process because the second side has been through a high-temperature reflow soldering, it is very easy to happen that the spray tin re-melts and produces a tin bead or a similar water bead affected by gravity into a drop of spherical tin point, resulting in a more uneven surface and thus affecting the soldering problem.
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