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dw black nickel over brass tube lugs

author:MF manufacturerstime:2022-03-17 22:05:08

(dw black nickel over brass tube lugs)There are manyPCBSurface treatment process,Common is hot air leveling、Organic coatingOSP、Electroless Nickel/Immersion gold、Soak、Tin and electroplated nickel gold and other processes。

(dw black nickel over brass tube lugs)dw black nickel over brass tube lugs(dw black nickel over brass tube lugs)

picture1 Type of surface processing of the circuit board

1. Hot air levelHASL

Hot air and fine, name, hot air, solderHASL (Hot Air Solder Leveled),It isPCBSurface coating molten tin lead solder and use heating compressed air(blow)Flat process,Make it forms a layer of anti-copper oxidation,Good weldability coating。Good weldability,Hot air intensity welding and copper form copper tin metal compounds at binding。Figure1middlea)Shown。

PCBTake hot air and usually immersed in molten solder;Heavy blown solder before solder solidification;The wind knife can minimize the meniscoids of the solder on the copper surface and prevent the solder bridge。Hot air is divided into vertical and horizontal,Generally speaking, horizontal is better,Mainly the horizontal hot air and the plating layer is relatively uniform.,Automated production。The general process of hot air leveling process is:Abnormal→Preheat→Welding flux→Spray→Cleaning。

HASLThe thickness of the solder and the flatness of the pad(Garden)It is difficult to control,It is difficult to mount narrow pitch components。Lead-freeHASLIt is replaced with non-lead metal or lead-free solder alloyPb-Sn。

2. Organic coatingOSP

Organic coating processOSP(Organic SolderabilityPreservative)Unlike other surface treatment processes,Figure1middleb)Shown。It is acting as a barrier between copper and air;Simple organic coating process、low cost,This makes it widely used in the industry。Early organic coated molecules are imidazole and benzotriazole for rust,The latest molecules are mainly benzimidazole,It is a chemical bonded nitrogen function group toPCBCopper。During the subsequent welding process,If there is only one layer of organic coating on the copper surface, it is not possible.,Must have a lot of layers。This is why the copper fluid is usually needed in the chemical tank.。After coating the first layer,Coating layer adsorption copper;Then the organic coating molecule of the second layer is combined with copper,Until twenty or even hundreds of organic coating molecules are assembled in copper,This ensures multiple reflow soldering。the experiment shows:The latest organic coating process maintains good performance during multiple lead-free welding。

General process of organic coating processes is:Degreasing→Abnormal→Pickle→Pure water cleaning→Organic coating→Cleaning,Process control is relatively easy for other surface treatment processes。

3. Electroless Nickel/Immersion goldENIG

(1) Process

dw black nickel over brass tube lugs(dw black nickel over brass tube lugs)

picture2 ENIGStructure of surface pads

(dw black nickel over brass tube lugs)Electroless Nickel/The general process of the immersion process is:Acidic cleaning→Abnormal→Prepreg→activation→Electroless Nickel→Chemical immersion gold,There are6Chemical tank,Involve nearly100Chemicals,Therefore, the process control is difficult。

(2) application

Chemical platingNiAnd dip gold(ENIG)Good weldability,Printing plug(Golden finger)、Touch screen switch。NiAs the isolation layer and solderable coating,Require thickness≥3um;AuYesNiProtective layer ,AuCan be used in solderSnCo-covalent compound forming gold tin(AuSn4),More than gold in the solder joint3%Will brittle the solder joint,OvermuchAuAtom replacementNiatom,Because too muchAuDissolve into the solder joint(Whether it isSn-PbstillSn-Ag-Cu)All“Crispy”。So must defineAuLayer thickness,WeldingAuLayer thickness≤1µm (ENIG :0.05~0.3µm)。

If the nickel plating process control is unstable,Will cause“Black pad”Phenomenon。Figure3Exquisite example,

dw black nickel over brass tube lugs


(dw black nickel over brass tube lugs)In the figureaIs the welding rear components fall off, Can see the pad black;

(dw black nickel over brass tube lugs)bIs no weldingQFPWelding on the circuit board before the components;

cAfter zoomingQFPThe corresponding air welding has a black phenomenon;

(dw black nickel over brass tube lugs)dIs the metallographic slice of components pin and pads,Cracks appeared on the welded contact surface;

eDuring the padSEMScanning electron microscopy analysis,It can be seen that the nickel layer has a rough gap production.。

(dw black nickel over brass tube lugs)(3) “Black pad”Causes of phenomena

(a)PCBThe solder plating and nickel plating structure is not dense,Surface is crack,The water in the air is easy to enter,And the acid solution in the immersion process is easy to remain in the nickel plating。In gold plating,due toNiAtomic radius ratioAuSmall,Thus, inAuAtomic arrangement depositionNiAt the time,Its surface crystal grains will be rough、sloppy、Multi-well morphology forms a number of voids,And the plating will continue through these gapsAuBelowNiAtomic reaction,MakeNiAtom continues oxidation,Not dissolvedNiIons are trappedAuBelow,Form nickel oxide(NixOy)。When the nickel layer is excessively oxidized,The so-called black soldering plate is formed。

(b)Nickel-plated phosphorus content is high or low,Poor resistance to acid resistance resistance,Easy to corrode discoloration,appear“Black tray”Phenomenon,Western weldability。(PHfor3~4better)

(c)Nickel plating is not cleaned with acid plating solution,Long time NiBe sour。

(d)Welding,Thin thin, weldable protective coatingAuThe layer is quickly spread into the solder,Exposed excessive oxidation、Low weldabilityNiLayer surface,Be bound to makeNiIt is difficult to form a uniform and solder.、Continuous intermetallic compound(IMC),Impact the combination of solder joint interface,And may trigger along the solder joint/Cracking of plating,Severe can lead to poor surface wetting to make components fromPCBDeclined or nickel,Commonly known as“Black nickel”。

A large number of research and practical conditions show,PlatingPThe content is the key to the quality of the entire coating。whenPContent7%-10%Between time,NiThe quality of the layer is better。

4. Soak

(dw black nickel over brass tube lugs)Silver process(Immersion Silver) Figure1middled)Shown,Introduction of organic coating and chemical plating/Immersion,Simple process、fast;Unlike chemical plating nickel/Soil is as complex,Not givenPCBWear a thick armor,But it still provides good electrical performance。Silver is only gold,Even exposure to heat、Wet and polluted environment,Silver still maintains good solderability,But lose gloss。Silver silver does not have chemical plating nickel/The good physical intensity of the immersion gold is no nickel under the silver layer.。Also impregnated silver has good storage,After leaching silver, put a few years, it will not have a big problem.。

(dw black nickel over brass tube lugs)Silver silver is a replacement reaction,It is almost a submicron sterling silver coating。Sometimes some organic matter,Mainly to prevent silver corrosion and eliminate silver migration;It is generally difficult to measure this thin organic matter,Analysis shows that the weight of the body is less than1%。

5. Immersion tin

Immersion tin(Immersion Tin),Figure1middlee)Shown。Since all solders are currently based on tin,Therefore, tin can match any type of solder.。From this point of view,Immersion processes have great development prospects。But beforePCBTin must,Tin and tin migration will bring reliability issues during welding,Therefore, the adoption of the soaking process is limited.。Later, an organic additive was added to the Tin solution,The tin layer structure can be made into a granular structure,Overcoming the previous problem,And also have good thermal stability and solderability。

Tinkin process can form a flat copper tin metal compound,This feature makes immersion tin with a good weldability as hot and free, without hot wind, flatness, headache, flatness;Tin is also no chemical nickel plated/Diffusion problem between immersion metal——Copper tin metal compounds can be combined together。Tin plate is not too long,It must be performed according to the order of Tin during assembly.。

6. Electroplated nickel gold

Electroplated nickel gold(Electrolytic Nickel/ Gold)YesPCBSurface treatment process,sincePCBThere is an appearance,Slowly evolve into other ways later。Figure7-17middlef)Shown.It isPCBThe surface conductor is plated with a layer of nickel to platen a layer of gold.,Nickel plating is mainly to prevent proliferation between gold and copper。Now electroplated nickel gold has two types:Software(Pure gold,Gold surface looks unlucky)Plating hardware(Surface smooth and hard,Wear-resistant,Contains other elements such as cobalt,Gold surface looks brighter)。Flooding is mainly used for chip packaging;Hardware is mainly used in non-welded electrical interconnections。

Take into account the cost,Industry often selectively plated with image transfer to reduce gold。Currently selective electroplated use in the industry's use continues to increase,This is mainly due to chemical plating nickel/The impregnation process control is more difficult。

Under normal circumstances,Welding can cause electric plating,This will shorten the service life,Therefore, avoid welding on electroplating gold;Chemical nickel/Iryekin is very thin,And very consistent,Crisp phenomenon rarely occur。

7. Other surface treatment processes

(dw black nickel over brass tube lugs)There are fewer applications in other surface treatment processes.,Let's see the relatively more chemical plating processes。

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