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1、電鍍工作原理大綱,一.電鍍原理 (1)電鍍定義 (2)電鍍目的 (3)電鍍槽的組成 (4)電鍍化學反應 二.連接器電鍍的特異性 (1)Nickel Plating (2)Gold Alloy Plating (3)Pd/Ni Plating (4)Tin/Lead Plating 三.選擇性電鍍 四.電鍍工作站簡介,一.電鍍工作原理,(1)定義: Definition 從牛津字典來定義“Plate”: 1.Apply a thin coat esp of silver gold or tin to (another metal) 2. Cover(esp a ship) with plates
2、 of metal esp for protection 而 “Electroplating”就是:Electroplating is the process of depositing a metallic coating upon a negatively charged electrode by the passage of an electric current 電鍍是一種將金屬沉積在帶負電的電極上的過程.一般工業界常用的電鍍金屬如表1,表1,Typical Electrodeposited Metals Used in Surface Finishing Brass Palladiu
3、m Cadmium Palladium-Nickal Chromium Palladium-Silver Copper Tin Gold Tin-Lead Gold-Cobalt Tin-Nickel Gold-Nickel Rhodium Nickel Silver Nickel-Iron Zine,Typical Electrodeposited Metals Used in Surface Finishing Brass Palladium Cadmium Palladium-Nickal Chromium Palladium-Silver Copper Tin Gold Tin-Lea
4、d Gold-Cobalt Tin-Nickel Gold-Nickel Rhodium Nickel Silver Nickel-Iron Zinc,2.電鍍的目的,1.美觀,耐用 2.防鏽 3.防磨耗 4.提高電氣特性 5.提高潤滑性 6.提高強度,硬度 7.耐熱性,耐候性 8.浸炭防止,氮化防止,3.電鍍槽的組成,電鍍槽的組成含tank、電解液、直流電源、電極,參考簡圖Fig.1 【1】電鍍液(Plating solution):或稱electrolyte電解質,提供導電的功能,補充被鍍的金屬鹽,維持電鍍槽內化學平衡,及PH值的穩定。 【2】直流電源(DC power supply):
5、一直是用整流器(Rectifier)來控制DC電流的供出。 【3】陽極(Anode):電解用陽極,可分為可溶性或非可溶性電極.可溶性陽極因電解而溶解,作為補充金屬離子在陰極析出的量為目的,非可溶性電極其材質甚多,如碳極(Carbon anode)陶瓷或鈦合金底材塗裝貴金屬氧化物或白金鈮網等。,【4】電鍍化學反應 電鍍槽內的化學反應分陰極反應如Fig2及陽極反應 Fig3。陰極反應,鍍層會沉積(deposit)在底材上,附產品是氫氣等。陽極則是“反電鍍反應”亦是電解反應可溶性陽極在電鍍過程中解離成金屬離子,而不溶性陽極只產生氧氣,本身并無解離發生,+,-,-,+,Anode,Cathode,-,
6、-,+,+,Figure1:Schemati of the plating process,Cathode Reactions Cathode Reduction of ions Draw Electrons from extermal circuit Typical Reactions Mn+ne-M0 2H+2e-H2 4H2O+4e-2H2+4(OH)-,Figure 2,Anode Reactions Anode Oxidation of metal to ions Release of electrons to extermal circuit Typical Reactions M
7、0Mn+ne- 4OH-O2+2H2O+4e- 2H2OO2+4H+4e-,Figure 3,二.Connectors電鍍的特異性,一般用在connector industry的電鍍工程是鍍鎳(Nickel),鍍金鈷合金(Gold/Cobalt alloy),鍍鈀鎳合金(Palladium-Nickel alloy), 及鍍錫鉛合金(Tin/Lead alloy)等工藝。 (1)Nickel Plating 鍍鎳是應用在電鍍底層,因為可提供對環境腐蝕的抵抗力,且防止銅合金底材的銅、鋅擴散,因為電鍍后的端子經儲藏過一段長時間后,會被覆蓋一層來自外界的氧化膜包括氧化鋅、氧化銅或硫化銅,導致可靠性降
8、低而鋅或銅的氧化會因鎳當擴散障礙(diffusion barrier)而降低。其三的原因是在鍍金區打鎳底可改善金接觸區的耐磨性。其四也因鎳層的存在使porosity問題減少嚴重程度,參考Figure4,2.Gold Alloy Plating 金是一種貴重金屬,本身不易與它種物質發生反應,也不與空氣反應,所以也不易在表面形成氧化物或污染的膜層,電流很容易穿越過去,因此當connector需要handle低層次(low-level)的信號電壓和電流使其具有高可靠度的信賴性必須選用鍍金。純金本身的硬度極低故為增加wear res stance我們會在鍍液內添加微量的鈷,使其在鍍層共同析出鈷約占0.
9、15%至0.25%,而鍍層的硬度由低于50 knoop增加至200knoop,3.PdNi Plating 鈀鎳合金電鍍因本身密度比硬金小(11.2 v.s 17.5)、硬度、延展性、多也性都遠優于金,陰抗電陰亦與金相近,原料价線遠低于金(鈀鎳合金鍍層與金鍍層相比,成本可降低3070%)是一種代金鍍層,如果在Pd/Ni鍍層再加上一層閃亮薄金鍍層,不但其性能獲得改善,并且符合客戶喜愛金色外觀的心理。 4.Tin/Lead Plating 錫鉛電鍍顧名思義是為改善connector的焊接性(solderability)而設計。,三.選擇性電鍍,在connectors的貴重金屬電鍍上常選用遮蔽性罩頭
10、來達成省金的目的,罩頭制造的廳特更是know-how的所在。以其應用的技朮,可概分2種,一是masking如Figure5 Spot plating,另一種則是brush plating,其工作原理如Figure6,其效果如 Figure7a ,7b,四.電鍍工站的簡介,良好的電鍍皮膜須具備 a.密著性的確保 b.具備色深,緻密,連續性且美觀 c.均一電著性且被覆力優良 d.無殘留應力且机械強度高 e.化學性安定且耐葯品性高,參考Figure8 電鍍所涉及的工站相當的多,需控制的項目亦極繁雜,如各鍍液的濃度、PH、過濾、溫度、走速、電流等等,一般可依其止的,而概分如下: 【1】清洗脫脂:去除油
11、污以待電鍍的准備 【2】酸活化:將氧化膜由被鍍物去除,提供新鮮的表面,以增進附著性 【3】各電鍍槽:提供各机能性電鍍所需的葯水 【4】水洗:阻止前制程的葯水沾附在端子上而污染了后制程的槽液 【5】QA:提供制程的管制,皮膜厚度,焊錫性的測量 一個優良的電鍍制程:除了良好的電鍍机外,仍需有化學實驗室提供正確的分析,嚴格的現場管理,SOP的作業,QA的協助,新技朮的開發,才能構筑成功的電鍍工站。,UNREEL,ELECTROCLEAN,RINSE,ACID ACTIVATE,RINSE,NICKEL PLATE,RINSE,PdNi PLATE,RINSE,SELECTIVE GOLD,GOLD
12、RECOVERY,RINSE,SnPb PLATE,RINSE,HOT RINSE,HOT AIR DRY,REEL,REEL-TO-REEL ELLCTROPLATING FLOW CHART,上料,脫脂,水洗,酸活化,水洗,鎳,水洗,鈀鎳,水洗,水洗,水洗,熱水洗,選擇鍍金,金回收,錫鉛,烘干,下料,Foreign Material,DEFINITION Foreign material is any substance on the gold surface PROBABLE CAUSE When the electroplating procedure is the cause of
13、foreign material adhering to contact parts,the problem can often be solved by filtration.(See the section on Nodules) It is usually desirable to boil a new cloth or plastic filter element is a 10 percent sulfuric acid solution before using it for the first time.This removes the sizing agents and pla
14、sticizers which might otherwise alter the brightness of the plate. Other sources of foreign material include packaging materials .solder,air-borne particles attracted to the surface by electrostatic charges,epidermal matter from physical handling,etc. Foreign material can impair the products perform
15、ance in several ways.First,organic type material could cause high resistance or open-circuit contacts.Second,any materials harder than the gold would cause excessive wear or gouging of the gold surface,Indentations,DEFINITION An indentation is a surface recess of depression formed by imperfections i
16、n the immediate or underlying layers PROBABLE CAUSE Most indentations are the result of poorly prepared base material with nicks.scratches*,and dents on the surface.indentations can occur during some types of plating such as rack of selective strip plating.In these cases,if the indentations cannot b
17、e eliminated,Scratches,DEFINITION A scratch is a potential defect,depending upon its depth, caused by a scraping action over the surface of the plated or bare contact and characterized by sharp edges. PROBABLE CAUSE Scratches are obviously the result of physical abrasion with a jagged or sharp objec
18、t scratches,these detects may expose the metal to the atmosphere. Characteristic sharp edges inherent to scratches,Blisters,DEFINITION A blister occurs when there is a localized failure of the gold to adhere to its underlying material. It appears as a spherical or raised area. PROBABLE CAUSE Large,s
19、eparate blisters are caused by poor adhesion between the gold and the underlying nickel or copper. This type of blister can be easily flattened or punctured with the tip of a razor blade while being examined with tip of a razor blade while,Blisters,Being examined with a low power microscope,and rhe
20、blister can then be seen to be hollow. To eliminate the problem,follow the procedures listed under adhesion failure. Blisters are considered defects because any physical contact with the gold surface such as a mating part may break the bubble,exposing the base layers to the atmosphere and potential
21、corrosion. Blisters caused by poor adhesion of gold to nickel,Drawing D,and nickel to base,Drawing E.,Blisters,base,Drawing E. Blisters as they appear at the gold surface due to a nickel to base adhesion failure.,Nodules,Figure 26 illustrates a gross nodular condition in which,at low magnification (
22、10x),the nodules appear as bright spots. Figure 27,at higher magnification, shows an elongates module surrounded by smaller ones. Figure 28 is an SEM revealing the nodular morphology at 700x.,Porosity,DEEINITION Porosity is a defect of minute size, introduced during the plating operation,which resul
23、ts in an opening extending to underlying layers. Porosity tests should be conducted per X-18453. FAILURE DESCRIPTION The porosity test, when performed with nitric acid vapor, results in corrosion normally ranging in color from blue,green,or blue-green to green-white,blue-white,or white. In some case
24、s,Porosity,Particularly on nickel underplated parts, corrosion may or white. In some cases,particularly on nickel underplated parts, corrosion may appear as transparent amorphous spots. Figures 29 and 30 illustrate porosity “decorations” on typical on nickel under underplated parts. Note the deep bl
25、ue color. Figures 31and 32 are couuosion decorations on product with nickel underplating. Note the white color. All porosity test results should be carefully viewed to insure that the decorations are not,Porosity,Actually foreign material or staining. The porosity test,when performed with polysulfid
26、e, results in a black corrosion product. “NOTE: The word”decoration”is used to describe the colored corrosion product which is a result of the porosity test. The pore decorations are simply the salts which form form the acid vapor reacting with the base metals.,Adhesion Failure,Polished cross sectio
27、ns illustrating the previous pictorials. Additional copper layer was plated on for edge protection during polishing. Most of the cross sections used in this book will also have copper overplating. PROBABLE CAUSE In cases in which a nickel underplate is used,the first thing to do in seeking the cause
28、 of poor adhesion is to look for nickel on the underside of the peeled-off gold foil,If Ni is present,the failure is likely to be caused by inadequate cleaning of the basis,Adhesion Failure,Metal. Scribbing several parts by hand,before the nickel plating,can aid in determining whether cleaning was a
29、ctually the important factor. If so, an experimental cleaning procedure for copper or copper alloy basis metal should be tried,including the following steps: 1.Degrease in methyiene chloride, using hand scrubbing or ultrasonic agitation. 2.Ringe in isopropanol or denatured ethanol(which are compatib
30、le with both the organic solvents and the aqueous cleaners).,Adhesion Failure,3.Rinse in water. 4.Use an alkaline cleaner with hand scrubbing or anodic electroclean. 5.Rinse in water. 6.Mild acid bright dip or pickle(1% HCl by volume,20% HNO3,40% H2SO4,39% H2O or uninhibited proprietary mixture). 7.
31、Rinse in water. 8.Rinse in deionized water. If this sequence cures the problem,some of the steps can be eliminated, one at a time,Adhesion Failure,Until the most effective procedure is found. Many types of part can be adequately cleaned by very simple methods such as electrocleaning. However,a commo
32、n cause of adhesion failure in such cases is accumulation of a floating oil layer on the surface of the aqueous cleaner. Because of agitation,this may not be visible while the bath is being used. If it is a suspected cause, the top layer of the solution should be skimmed off.,TIN COMMANDMENTS,TIN OR
33、 TIN ALLOY COATINGS ARE COST EFFECTIVE AND RELLABLE ALTERNATIVES TO GOLD IF USED ACCORDING TO THE FOLLOWING GUIDELINES: 1.Tin coated contacts should be mechanically stable in the mated condition 2.Tin coated contacts need at least 100 grams contact normal force 3.Tin coated contacts need lubrication
34、 4.Tin coating is not recommended for,TIN COMMANDMENTS,For continuous service at high temperatures 5.The choice of plates,reflowed, hot air leveled,or hot tin dipped coatings does not strongly affect the electrical performance of tin or tin alloy coated contacts. 6.Electroplated tin coatings should
35、be at least 100 microinches thick 7.Mating tin coated contacts to gold coated contacts is not recommended 8.Sliding or wiping action during contacts is not recommended with tin coated contacts,TIN COMMANDMENTS,9.Tin coated contacts should not be used to make or bread current 10.Tin coated contacts c
36、an be used under dry circuit or low level conditions,Porosity,Figures 29 and 30 illustrate pore decorations resulting from a one-hour nitric acid vapor test on gold plated parts with copper underplating.Figures 31 and 32 show pore decorations resulting from a two-hour nitric vapor test on gold plated parts with nickel underplating.,