How much surface finished do you know 你知道多少种表面处理

Anyone involved within the printed circuit board industry understand that PCB's have copper finishes on their surface. If they are left unprotected then the copper will oxidize and deteriorate, making the circuit board unusable. The surface finish forms a critical interface between the component and the PCB. The finish has two essential functions, to protect the exposed copper circuitry and to provide a solderable surface when assembling (soldering) the components to the printed circuit board.

 

HASL / Lead Free HASL

HASL is the predominant surface finish used in the industry. The process consists of immersing circuit boards in a molten pot of a tin/lead alloy and then removing the excess solder by using 'air knives', which blow hot air across the surface of the board. One of the unintended benefits of the HASL process is that it will expose the PCB to temperatures up to 265°C which will identify any potential delamination issues well before any expensive components are attached to the board.

Advantages: Low Cost Widely AvailableRe-workableExcellent Shelf Life. Disadvantages: Uneven SurfacesNot Good for Fine PitchContains Lead (HASL)Thermal ShockSolder BridgingPlugged or Reduced PTH's (Plated Through Holes)

 

Immersion Tin

According to IPC, the Association Connecting Electronics Industry, Immersion Tin is a metallic finish deposited by a chemical displacement reaction that is applied directly over the basis metal of the circuit board, that is, copper. The ISn protects the underlying copper from oxidation over its intended shelf life.Copper and tin however have a strong affinity for one another. The diffusion of one metal into the other will occur inevitably, directly impacting the shelf life of the deposit and the performance of the finish. The negative effects of tin whiskers growth are well described in industry related literature and topics of several published papers.

Advantages: Flat SurfaceNo PbRe-workableTop Choice for Press Fit Pin Insertion. Disadvantages: Easy to Cause Handling DamageProcess Uses a Carcinogen (Thiourea)Exposed Tin on Final Assembly can CorrodeTin WhiskersNot Good for Multiple Reflow/Assembly ProcessesDifficult to Measure Thickness

 

OSP / Entek

OSP (Organic Solderability Preservative) or anti-tarnish preserves the copper surface from oxidation by applying a very thin protective layer of material over the exposed copper usually using a conveyorized process.

It uses a water-based organic compound that selectively bonds to copper and provides an organometallic layer that protects the copper prior to soldering. It's also extremely green environmentally in comparison with the other common lead-free finishes, which suffer from either being more toxic or substantially higher energy consumption.

Advantages:

Flat SurfaceNo PbSimple ProcessRe-workableCost Effective

Disadvantages:

No Way to Measure ThicknessNot Good for PTH (Plated Through Holes)Short Shelf LifeCan Cause ICT IssuesExposed Cu on Final AssemblyHandling Sensitive

 

Electroless Nickel Immersion Gold (ENIG)

ENIG is a two layer metallic coating of 2-8 μin Au over 120-240 μin Ni. The Nickel is the barrier to the copper and is the surface to which the components are actually soldered to. The gold protects the nickel during storage and also provides the low contact resistance required for the thin gold deposits. ENIG is now arguably the most used finish in the PCB industry due the growth and implementation of the RoHs regulation.

Advantages:Flat SurfaceNo PbGood for PTH (Plated Through Holes)Long Shelf Life

Disadvantages:ExpensiveNot Re-workableBlack Pad / Black NickelDamage from ETSignal Loss (RF)Complicated Process

Gold – Hard Gold

Hard Electrolytic Gold consists of a layer of gold plated over a barrier coat of nickel. Hard gold is extremely durable, and is most commonly applied to high-wear areas such as edge connector fingers and keypads.

Unlike ENIG, its thickness can vary by controlling the duration of the plating cycle, although the typical minimum values for fingers are 30 μin gold over 100 μin nickel for Class 1 and Class 2, 50 μin gold over 100 μin nickel for Class 3.

Hard gold is not generally applied to solderable areas, because of its high cost and its relatively poor solderability. The maximum thickness that IPC considers to be solderable is 17.8 μin, so if this type of gold must be used on surfaces to be soldered, the recommended nominal thickness should be about 5-10 μin.

 

Advantages: Hard, Durable SurfaceNo PbLong Shelf Life

Disadvantages: Very ExpensiveExtra Processing / Labor IntensiveUse of Resist / TapePlating / Bus Bars requiredDemarcationDifficulty with Other Surface FinishesEtching Undercut can Lead to Slivering / FlakingNot Solderable Above 17 μinFinish Does Not Fully Encapsulate Trace Sidewalls, Except in Finger Areas

 

任何关系到印制电路板的人都了解印刷电路板的表面上有铜。如果他们得不到保护,铜会氧化变质,使电路板无法使用。表面光洁度构成组件和印刷电路板之间的一个关键接口。表面处理有两个基本的功能,来保护暴露的铜电路和当表面组装时(焊接)到印刷电路板器件时提供可焊性。

 

喷锡/无铅热风整平

在工业上的应用中,喷锡是主要的表面处理。这个过程包括将电路板在熔锅的锡/铅合金,然后用空气刀除去多余的焊料,在板的表面吹热风。一个过程的所有意想不到的好处是它会使PCB的温度高达265°C将在任何昂贵的部件识别任何潜在的分层问题连接到板。

优势:低成本;广泛使用;再操作;保质期

缺点:不平的表面;不好的间距;含有铅(HASL);热冲击;焊料桥接;插入或减少PTH的(镀通孔)

 

浸锡

根据IPC,连接电子工业协会,浸锡是一种金属通过化学置换反应,在电路板上,这是基础金属直接沉积铜。在其预定的保质期,保护了基本铜的氧化。铜和锡对彼此有很强的亲和力。一个金属进入其他的扩散就会不可避免的发生,直接影响存款的保质期和性能。锡晶须生长是它的负面影响,在工业有关的文献和几个已发表论文主题中有涉及。优势:平面;无铅;可操作性;压接pin首选. 缺点:容易造成损坏;过程使用致癌物(硫脲);暴露锡总装可以腐蚀;锡晶须;多回流焊/装配工艺不好;很难测量的厚度。

 

OSP / Entek

OSP(有机可焊性防腐剂)或防锈保护铜面氧化,在应用材料中利用输送过程暴露的铜通常是一个非常薄的保护层。

优势:平坦的表面,无铅,工艺简单,可操作性强,成本效益

缺点:没有办法测量厚度,PTH不好(镀通孔),保质期短,导致ICT问题,暴露的铜在最后装配,处理敏感

 

化学镀镍浸金(ENIG

ENIG是一二层金属层2-8μAu120-240μ镍。镍对铜的屏障,是表面的组件实际上是焊接。金在储存期间保护镍,并提供薄的金矿床所需的低接触电阻。ENIG是现在可以说是由于RoHS规定的增长和实现PCB行业最常用的完成。

优势:表面平整,无Pb,良好的PTH(镀通孔),保质期长

缺点:昂贵的,不可重复的,黑色的垫/黑色镍,损坏等,信号损失(射频),复杂的过程

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镀金

镀硬金是由一层镀金的镍镀层。硬金是非常耐用,是最常用于高磨损区域如边缘连接器的手指和键盘。

优势:坚硬,耐用的表面,没有铅,保质期长

缺点:很贵,额外的处理/劳动密集型,使用抗/磁带,电镀/母线的要求,划分,与其他表面处理的难度,侧蚀会导致切丝/剥落,不可焊17μin,完成不完全封装了微量的侧壁,除了手指