PCB manufacturers take you through the various surface processes of circuit boards
With the rapid and continuous development of today's technology, the production of PCB technology has also undergone great changes, with the precision grasp, the manufacturing process also needs to progress. At the same time each industry on the PCB circuit board process requirements have also gradually improved, such as today's cell phones and computers in the circuit board, the use of gold also used copper, resulting in the advantages and disadvantages of the circuit board has gradually become easier to distinguish.
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 circuitry inside the board is primarily pure copper, which means bare copper boards. The advantages and disadvantages of bare copper board is obvious, advantages: low cost, flat surface, good solderability (in the absence of being oxidized) disadvantages: easy to be affected by acid and humidity, can not be placed for a long time, after unpacking need to be used up within 2 hours, because the copper is exposed to the air is easy to oxidation; can not be used for double-sided, because after the first reflow soldering the second side has been oxidized. If there is a test spot, solder paste must be added to prevent oxidation, otherwise it will not make good contact with the probe subsequently. 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 protective layer above the copper. So it requires a large area of gold plating on the board, which is the same process I took you through before for sinking gold. The second is the gold-plated board, as the name implies is to the substrate plated with a layer of gold, of course, is really gold, even if only a very thin layer of plating, it has accounted for nearly 10% of the cost of the board. In Shenzhen there are many families specializing in acquiring scrap circuit board businessmen, through certain means of washing out the gold, is a good income.
PCB manufacturers use gold as a plating layer, one is to facilitate welding, the second is to prevent corrosion. Even after several years of memory sticks of gold fingers, still shining as before, if the initial use of copper, aluminum, iron, now has rusted into a pile of scrap. Gold plating is used in large numbers on circuit boards for component pads, gold fingers, connectors, 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 of the main board is mostly gold-plated board, sinking gold board, computer motherboard, audio and small digital circuit boards are generally not gold-plated board.
Through the above, it is not difficult to draw the advantages and disadvantages of gold-plated board, advantages: not easy to oxidation, can be stored for a long time, the surface is flat, suitable for welding fine gap pins and solder joints of smaller components. There are keys PCB board of choice (such as cell phone board). 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. So now many partners will ask, yellow is gold, then the silver is silver? Of course not, the correct answer is: tin. This board is called spray tin circuit board. Spray a layer of tin in the outer layer of copper lines, but also be able to help solder. But not as long as gold to provide contact reliability. 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 not difficult to summarize, 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 gap pin components easier to cause a short circuit. When used in the 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.
The last one is the OPS process, simply put, is the organic flux film. Because it is organic, not metal, so it is cheaper than the spray tin process. The advantage is that it has all the advantages of bare copper soldering, and the expired board can also be redone once the surface treatment. Disadvantages: It is easily affected by acid and humidity. When used in secondary reflow, it needs to be completed within a certain period of time, and the effect of the second reflow will usually be poor. 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. The OSP process is mainly experienced on computer motherboards, because computer circuit boards are too large, if you use gold plating, the cost will be very high.