20/03/2021
With the continuous development of electronic science and technology, PCB technology has also undergone great changes, and the manufacturing process needs to be improved.At the same time, the process requirements of PCB circuit boards in each industry are also gradually improved. For example, in the circuit boards of mobile phones and computers, gold and copper are used, leading to the advantages and disadvantages of the circuit boards gradually becoming easier to distinguish.
Take you to understand the surface process of PCB board, compare the advantages and disadvantages of different PCB board surface treatment process and application scenarios.
Purely from the appearance of the outer circuit board there are three main colors: gold, silver, light red.According to the price classification: gold is the most expensive, silver is the second, light red is the cheapest, from the color is actually very easy to judge whether the hardware manufacturers are jerry-building behavior.But the wiring inside the circuit board is mostly pure copper, or bare copper.
The pros and cons are obvious:
First, naked copper plate
Advantages: low cost, smooth surface, good weldability (in the case of no oxidation).
Disadvantages: easy to be affected by acid and humidity, can not be put for a long time, need to be used up within 2 hours after unwrapping, because copper exposure in the air is easy to oxidize;Cannot be used on double panels because the second side is oxidized after the first reflow.If there are test points, the solder paste must be printed to prevent oxidation, otherwise subsequent contact with the probe will not be good.
Pure copper, which is easily oxidized when exposed to air, must be covered with the above protective coating.And some people think that the golden color is copper, which is a wrong idea, because that is the protective coating on the copper.So you need a large area of gold plating on the circuit board, which is what I took you to know about the gold sinking process.
Two, gold-plated plate
Gold is real gold.Even a very thin coating accounts for nearly 10% of the cost of a circuit board.In Shenzhen, there are a lot of merchants specializing in the acquisition of scrap circuit boards, through certain means to wash out gold, is a good income.
The use of gold as a coating, one is to facilitate welding, and the other is to prevent corrosion.Even the golden fingers of memory chips, which have been used for years, still gleam as before. If copper, aluminum, and iron were used, they would now rust into a pile of waste.
Gold plating layer is widely used in circuit board components pads, gold fingers, connector shrapnel and other positions.If you discover the circuit board is actually silvery, that need not say, dial consumer rights and interests hotline directly, certainly is the manufacturer to cut corners, did not use materials well, used other metals to fool customers.We use the most extensive mobile phone circuit board motherboard is mostly gold-plated plate, gold plate, computer motherboard, audio and small digital circuit board are generally not gold-plated plate.
The advantages and disadvantages of gold sinking process are not difficult to get:
Advantages: not easy to oxidize, can be stored for a long time, smooth surface, suitable for welding fine gap pins and components with small solder joints.Preferred PCB board with buttons (such as mobile phone board).The ability to repeat reflow multiple times does not necessarily reduce its solderability.Can be used as the base material of COB(Chiponboard) playing line.
Disadvantages: high cost, poor welding strength, because the use of nickel plating process, easy to have the problem of black plate.Nickel layers oxidize over time, and long-term reliability is an issue.
Now do we know that gold is gold and silver is silver?Of course not, it's tin.
Three, spray tin circuit board
The silver panels are called tinjet panels.Spraying a layer of tin on the copper wires can also aid welding.But it doesn't provide the long-term contact reliability that gold does.There is little effect on already soldered components, but reliability is not sufficient for pads that are exposed to the air for long periods, such as ground pads, poppin sockets, etc.Long-term use is easy to oxidize 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 welding performance.
Disadvantages: not suitable for welding fine gap pins and too small components, because of the surface roughness of the tinjet plate is poor.It is easy to produce solderbead in PCB processing, which is easy to cause short circuit to finepitch components.When used in double-sided SMT process, because the second side has undergone a high temperature reflow soldering, it is very easy to re-melt tin spray and produce tin beads or similar water beads into dropping spherical tin points under the influence of gravity, resulting in more uneven surface and thus affecting the welding problem.
We talked earlier about the cheapest light red circuit board, the mine lamp thermoelectric separation copper substrate
Four, OSP process board
Organic solder aid film.Because it's organic, not metal, it's cheaper than tin spraying.
Advantages: With all the advantages of bare copper plate welding, expired boards can also be re-done surface treatment.
Disadvantages: susceptible to acid and humidity.Used in the second reflow soldering, need to be completed within a certain time, usually the second reflow soldering effect will be poor.If it is stored for more than three months, it must be refinished.Use 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 contacting the needle point for electrical test.
The only purpose of this organic film is to ensure that the inner copper foil does not oxidize before soldering.The film evaporates when heated during welding.The solder can then weld the copper wire to the component.
But it is not corrosion resistant, an OSP circuit board, exposed to the air for more than ten days, can not be welded components.
Many computer motherboards adopt the OSP process.Because the circuit board area is too large to afford gold plating
