A bare copper
Advantages and disadvantages are obvious:
Advantages: low cost, surface smoothness, good weldability (without being oxidized).
Disadvantages: acid susceptible and humidity, not keep, after unpacking need to be used within 2 hours as exposed copper is easily oxidized in air; not be used for dual-panel, because the second surface after the first reflow It has been oxidized. If there are test points, to prevent oxidation of the solder paste to be printed, otherwise it will not be a good follow-up contact with the probe.
If the exposed copper is easily oxidized in air, the outer layer of the protective layer must be. Therefore, it is necessary for the surface treatment of the circuit boards.
Two, OSP process plate
OSP is different from the other surface treatment is: its role is to serve as a barrier layer between copper and air, simply, OSP is on bare copper surfaces clean, chemically grown to an organic thin film layer. Because it is organic, not metal, so cheaper than the HAL process.
This unique effect of the organic thin film layer is to ensure that prior to welding the inner foil is not oxidized. When a heating welding, this membrane volatilized off. It is possible to solder and copper components welded together. However, this layer of the organic film is very resistant to corrosion, an OSP board, exposed to air ten days, the components can not be welded. There are many computer motherboards using OSP process. Since the circuit board area too, OSP more affordable.
Advantages: All the advantages of bare copper welding expired board can do a re-surface treatment.
Disadvantages:
1.OSP transparent and colorless, so check more difficult, it is difficult to distinguish whether through OSP treatment.
2.OSP itself is insulated, non-conductive, it will affect the electrical testing. Therefore, test points must open stencil printed solder paste to remove the OSP layer to the original point of contact pins for electrical testing. More OSP electrical contact can not be used as a surface treatment, such as a keyboard surface keys.
3.OSP susceptible to acid and temperature. When used in the second reflow, should be completed within a certain time, typically a second reflow of the effect will be relatively poor. Stored for longer than three months must be re-surface treatment. After opening the package needs to be used within 24 hours
Third, the hot air leveling (HASL)
HASL Hot Air Solder Leveling known, it is in a molten tin-lead and the PCB surface is coated with a leveling process heated air (blowing level), to form a layer of cupric oxide against both turn provides good solderability of the coating layer. HASL usually formed of copper solder and copper-tin intermetallic compound at the joint, which has a thickness of about 1 ~ 2mil.
Perforation means in the case where the dominant, wave soldering is the best method, but is sufficient to meet the technical requirements HASL wave, of course, for the high strength requirements of the multi-node method electroless nickel / gold.
Pros: Low cost
Disadvantages:
Technical treated 1.HASL not flat pad coplanarity can not meet the technical requirements fine pitch pads.
2. not environmentally friendly, lead and harmful to the environment
Fourth, gold plate
Plated real gold is used, even if only a thin plating layer, has accounted for nearly 10% of the cost of the circuit board. Gold plating as, first, in order to facilitate welding, and second, in order to prevent corrosion. Even with the memory cheat several years, it is still shining ever, if the same time using a copper, aluminum, iron, rust now into a pile of scrap.
Component widely used in gold plating layer pads of the circuit board, finger, shrapnel and the like connected position. Most motherboards most widely used mobile phone circuit board we use gold-plated plates, gold-plate, computer motherboards, digital sound and a small circuit board generally are not gold plate.
Advantages: conductive, good oxidation resistance, and long life. Dense coating, more wear-resistant, generally used in bonding, welding and the case plug
Disadvantages: high cost, poor bonding strength.
Five of the gold / immersion gold (ENIG)
Nickel Immersion Gold (ENIG), also known as nickel gold, ENIG, Immersion Gold and short of gold. ENIG is a copper surface by chemical means thick layer of wrapping, good electrical properties of nickel-gold alloy may be long-term protection and PCB. The thickness of nickel deposited the inner layer is generally 120 ~ 240μin (about 3 ~ 6μm), gold was deposited to a thickness of the outer layer is generally 2 ~ 4μinch (0.05 ~ 0.1μm). OSP as not only rust-preventive barrier layer, which can be a useful and good electrical properties during long-term use in the PCB. In addition it also has tolerance to environmental additional surface treatment is not available.
advantage:
1.ENIG PCB treated surface is very smooth, good coplanarity, suitable for button contact surface.
2.ENIG be excellent solderability, gold will rapidly melt into solder which solder is formed with Ni Ni / Sn intermetallic compound.
Disadvantages: complex process, but also want to achieve good results requires strict control of process parameters. Most troublesome is, EING treated surface of the PCB in the ENIG or welding process is easy to produce black plate benefits. Direct Black disk performance is Ni excessive oxidation, gold is too large, brittle weld will affect reliability.
Six, palladium electroless nickel immersion gold (ENEPIG)
Compared nickel gold, nickel, and gold ENEPIG between more than a layer of palladium, gold displacement deposition reaction, a palladium plating layer, the nickel protective layer will prevent it from being excessive displacement gold deposit corrosion, palladium prevent displacement reaction At the same time lead to corrosion phenomena, well prepared for the leaching of gold. The thickness of the nickel deposition is generally 120 ~ 240μin (about 3 ~ 6μm), thickness of the palladium is 4 ~ 20μin (about 0.1 ~ 0.5μm). Thickness of the gold deposited is generally 1 ~ 4μin (0.02 ~ 0.1μm).
Advantage: its wide range of applications, while the chemical treatment NiPdAu opposite surface of the nickel metal surface treatment can effectively prevent the connection reliability black plate (Black Pad) defects caused, gold, nickel may be used instead.
Drawback: ENEPIG Although there are many advantages, but palladium is expensive, is a scarce resource. At the same time as gold and nickel, the process requires strict control.
Seven board HASL
The board called the silver spray tin plate. Spray a layer of tin on the copper wiring layer, it is possible to contribute to welding. But it can not provide long-term contact reliability like gold. For the soldered components has no effect, but long-term exposure to air pads, the reliability is not sufficient, such as ground pads, spring pin socket. Long-term use of easily oxidized corrosion, resulting in poor contact. Basically as a small digital products circuit board, without exception, is sprayed tin plate, the reason is cheap.
Advantages: low price, good weldability.
Disadvantages: not suitable for fine pitch solder pins and the components too small, because of the poor surface smoothness of HASL. In PCB processing easily solder balling (solder bead), for fine pitch pins (fine pitch) Component easily cause a short circuit. When using double sided SMT process, since the second surface has passed a reflow temperature, discharge occurs very easily re-melted tin solder balls or the like to produce drops by gravity into a spherical solder joint dropped, resulting in less surface thereby affecting the level of welding problems.
Eight, immersion silver
Silver immersion processes between OSP and electroless nickel / immersion gold between, the process is relatively simple and fast. Silver immersion is a substitution reaction, it is almost submicron silver coating (5 ~ 15μin, about 0.1 ~ 0.4μm). Silver leaching process may further contain organic substances, mainly of silver to prevent corrosion and eliminating silver migration problems, it is generally difficult to measure the organic thin layer analysis indicated that less than 1% by weight of the organism. Even when exposed to heat, humidity and pollution of the environment, it can still provide good electrical properties and good weldability, but will lose their luster. Because there is no silver layer under the nickel, it does not have the silver impregnated nickel / immersion gold all good physical strength.
Advantages: immersion silver solder surface good weldability, good coplanarity while the OSP not exist as a conductive barrier, but as the contact surface (e.g., surface buttons), the strength is not good gold.
Disadvantages: immersion silver have an important issue is the problem of silver migration of electrons, when exposed to a damp environment, silver generated electron mobility under the action of the voltage can be reduced by adding an organic electron migration into the silver component.
Nine, immersion tin
Since all frames are tin-based solder, the tin layer can be matched with any type of solder. However, after a previous PCB by immersion tin process prone to tin whisker, welding and tin migration over Chengzhong Xi shall bring reliability problems, thus limiting the use of immersion tin process. After immersion tin solution was added to the organic additives, tin granular structure layer structure, it overcomes previous problems, but also has good thermal stability and weldability.
Soldering greatest weakness is short-lived, especially when stored at high temperature and humidity environment between the Cu / Sn intermetallic compound will continue to grow until the loss of solderability. Tin deposited to a thickness of not less than 40μin (1.0μm) is reasonable, in order to provide a pure tin surface, in order to meet the weldability requirements.
Disadvantages: Soldering greatest weakness is short-lived, especially when stored at high temperature and humidity environment between the Cu / Sn intermetallic compound will continue to grow until the loss of solderability. No electroless nickel / immersion gold diffusion problems between the metal; but not stored for too long dip tin plate
X. summary
Since each have unique surface treatment, the application range is not quite the same. However, palladium nickel immersion gold (ENEPIG) is a versatile processing method, which can be assembled to meet the requirements of various applications on more knowledge on the pcb Czech distribution network, www.jiepei.com / g532