The growth of electronic industry as a whole, and the demand to support the expansion of its underlying infrastructure will continue to drive the improvements in electroplating

process. In order to improve existing electroplating process, the study of fundamentals aspects for electroplating process has become important

Aziz, N

Idris, M. N.

Miskam, M.A.

Noordin, N.

Samad, Z

Siah, C.H.

English

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" Proceedings of the 18th Symposiwn ofMalaysian Chemical EngineersFUNDAMENTALS STUDIES OF ELECTRO~SILVERPLATING PROCESSC. H. Siah2, N. Aziz1,*, Z. Samad2, N. Noordint, M. N. Idris3 and M. A. Miskam21 School of Chemical Engineering, Universiti Sains Malaysia, Sen Ampangan,14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia.2 School ofMechanical Engineering, Universiti Sains Malaysia, Seri Ampangan,14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia.3 School ofMaterial & Mineral Resources Engineering, Universiti Sains Malaysia, SeriAmpangan, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia~*Corresponding author. Phone: Tel: +6045937788 Ext 6457, Fax: +604 5941013Email: chnaziz@eng.usm.my;siah~choonhwa@yahoo.com.myABSTRACTThe growth of electronic industry as a whole, and the demand to support the expansion ofits underlying infrastructure will continue to drive the improvements in electroplatingprocess. In order to improve existing electroplating process, the study of fundamentalsaspects for electroplating process has become important. The influences of severalelectroplating parameters such as geometry of the path, the movement of electrolyte,electrodeposition current, and bath temperature on the unifonnity of the electrodepositionhave been widely investigated. In this paper, the study of fundamentals aspect forelectroplating will focus on silver plating due to" this process currently play very importantrole in semiconductor industry especially in lead f"ra.ffie manufacture process. In order tostudy the fundamentals aspect, a simple lab scale silver plating experiment will be carriedout to deposit a silver coating on a copper electrode by using a cyanide based plating bath.Based on the experimental re~ult, the influence of bath concentration and current densityto the process current efficiency will be presented. By combining the suitableconcentration and type of plating bath, amount of current density and appropriate anode, itwill contribute to the enhancement of uniformity for the electrodeposition. The optimumconditions of the silver plating process are proposed at the end of the paper.Keywords: Electroplating, Silver Plating, Fundame~talsAspect, Optimum Cond~tions1 INTRODUCTIONElectroplating is one of the important processes in electronic industries. The originalpurpose of electroplating process is to enhance the value of metal articles by improvingtheir appearance. However, the importance of metal finishing for purely decorativepurposes has decreased. Currently, the trend is toward surface treatments which willimpart corrosion resistance or particular physical or mechanical properties to the surface(e.g. conductivity, heat or wear resistance, lubrication or solderability), and hence to makepossible the use of cheaper substrate metals or plastics covered to give essential metallicsurface properties or decorative for coating purposes (Pletcher, 1982).Electrochemical technology entered the electronics industry about 50 years ago as amanufacturing process for low-end printed-circuit boards. Today, electrochemicaltechnology is employed widely for the processing of advanced microelectroniccomponents, including copper (eu) chip, high end packages and interconnects, thin filmmagnetic heads and micro-electro-mechanical systems (MEMS). The continuingimprovements in photo lithography and the theoretical understanding of theelectrochemical engineering principles including cu"rrent distribution, mass transport,electrode kinetics and nucleation and growth phenomena help to develop electrochemicaltechnology in advanced miCroelectronic industry. At the same time, ~aterials science and1-424': :'. "Pro¢e"edings of the 18th Symposium ofMalaysian Chemical Engineers .'engineering provided the experimental and theoretical tools pennitting to relate theproperties of electrochemically produced materials to their structure. All thesedevelopments led to new sophisticated cell designs and to improved reliability ofelectrochemical microfabrication processes permitting their industrial implementation forautomated large scale manufacturing. Electrochemical microfabrication technology isexpected to play an important role in ~e electronics and microsystems industry because ofits cost effectiveness and high precision. In addition, electrochemical processes areattractive from an environmental point of view because material deposition or removal ishighly selective thus minimizing waste (Datta &Landolt, 1999). With the miniaturizationof electronic devices, the connection reliability between integrated circuit (Ie) and theexternal circuits has become important. Electroplating and electroless plating have beenapplied for the metallization of electronic components. Recently, advanced· platingtechnology is strongly in demanded for the manufacturing of electronic components,because many oevices are becoming finer and more complicated (Honma, 2001).. The use of electrochemical technologies is increasing in the semiconductor industry. Inpackaging, electrochemical materials are used to address power delivery and dissipation,including electroless deposition and electroplating for substrates, electroplating bumps toconnect die to substrate, plating for die sacking and 3D interconnects. In chipmetallization, electrochemical materials are used to reduce RC delay and increaseelectromigrration resistance, includil.lg electroplated damascene interconnects with lowresistivity and higher electromigration resistance than Al interconnects, and electrolessplating tor cladding, barrier and seed layer applications. In transistor, electrochemicalmaterials are used to form silicon on isolator (Sal) by employing porous silicon to reducetransistor leakage. Electrochemical processing offers low cost, excellent scalability tosmaller feature sizes and the capability of preferential, selective growth to fonn patterns(Dub-in, 2003).A thorough understanding of the underlying principles of mass transport and currentdistribution is crucial for. successful industrial implementation of electrochemicalmicrofabrication processes. Mass transport limits the ultimate rate in an electrochemicalmicrofabrication process and therefore has a direct implication on throughput andinvestment cost. The current distribution on a macroscopic level detennines the uniformityof the thickness of an electrodeposits auf! the depth of dissolution in an anodic process(Datta & Landolt, 1999). To s~dy the effects of offset voltage on electroplatinguniformity, the degree of uniformity has improved with decreasing offset voltage. Highertemperature and changmg anode position have also influenced the uniformity positively.With the introduction of agitation during electroplating, the current distribution unifonnitywould be improved through the more equalized feeding of depleted metal ions. Loweroffset voltages, suitable amount of bath agitation, elevated temperatures, appropriatecathode-anode separation and bath concentration were found to contribute to theenhancement of current distribution unifonnity when they were assessed individually.However, it is also been foUnd that the combination of these parameters did not producethe expected synergistic effect in unifonnity improvement (Datta & Landolt, 1999).Electrochemical or electroplating process is rapidly evolving as a technology ofchoice in the electronics and microsystems industries. The successful implementation ofelectroplating process in manufacturing industry has become possible thanks to progressachieved through· fundamental research in electrochemistry, electrochemical materialsscience and electrochemical engineering. However, further miniaturization trends of themicroelectronics industries provide new opportunities and challenges which include issuesrelated to nanoscale structuring, fabrication of high aspect ratio structures, new functionalalloys, multidimensional interconnects, and automated large scale processes includingadditive control and recycling of electrolytes. To successfully overcome such challenges,fundamentals as well technology oriented research will be needed and interactionsbetween the two should be stimulated (Datta & Landolt, 1999).Silver is a soft, white metal with pleasing appearance~ It is malleable and ductile andan excellent conductor of heat and electricity. The good conductivity of silver contributesto the use of the metal in decorative as well as technical applications. Silver plating,'developed well over one hundred years ago, was one of the earliest electroplatingsuccesses (Mohler, 1969). Currently, silver plating is one of the important processes inlead frame manufacture industry. Silver was selectively coated on the copper leadframe to1-425Proceedings of the 18th Symposium ofMalaysian Chemical Engineersimprove the conductivity and also act as protection layer to avoid oxidation. during ,wirebonding process.In this study, the electro-silver plating experiment is carried out in a cyanide basedplating solutio:t:l with a copper cathode and a platinum anode. Silver deposits are chosen tobe evaluated with different parameters of electroplating because of its importance usagesuch as in electronic, jewelry and decorative industries. The electroplating process will beevaluated for certain parameters that will greatly affect the process. The parameters are thetype and plating bath concentration and the amount of current supply during platingprocess. Finally, the optimum conditions that result in a unifonn deposit are proposed.2EXPERIMENTAL SETUPThe experiment consisted of an electrolysis cell with 100 ml electrolyte in a 100 mlbeaker. The anode was a 5 cm platinum wire and the cathode was a 5 cm x lcm copperplate with a 0.004 dm2 as plating surface area. The electrolyte was considered to be wellmixed by a constant stirring rate of a magnetic stirrer. For the stirring and heating source,a hotplate stirrer LMS-I003E Carolina plate was used. The experiments were conductedwith different concentration of electrolyte, current supplied, stirring rate and temperature.To study the effect of bath concentration, the concentration for potassium argentumcyanide was varied from 66.87g/1 to IOOg/1 with 5 different concentrations were used ~(66.87g/1, 70g/1, 80g/1, 90g/1, 100g/l). The increasing of concentration of potassiumargentum cyanide was followed by increasing of potassium cyanide to maintain the freecyanide level in solution bath (35g1l, 36.63g1l, 4 1.86g1l, 47.09g11, 52.32g1l).In the experiment to study the effect of current density, the current supplied to thebath was varied from 0.04 Ampere to 0.2 Ampere with 5 different current supplies wereused (O.04A, O.08A, O.12A, O.16A, O.20A). In this study, 2 set of experiment were carriedout with different potassium argentum cyanide concentration (66.87g1l, 80g/1). Thepurpose using two different concentration baths is to study the effect of CWTent densityand concentration when it applied together in the solution~v3 RESULTS AND DISCUSSION100·-rfl. 90>:uc:CD'(3::= 80·w-c:~:s 70o---'-"--'- --------_ __.__.._-_ _.- .."'-"'--- _ - _. _ _.!I60·95 100 105908580757065Potassium Argentum Cyanide Concentration(g/l)6055I 5050L.~ .. _.. __ __ .._. ._.. ._ ." _-FIGURE 1. The effect of Potassium Argentum Cyanide concentration to current efficiencyof the process; Plating Temperature 27°C, Plating time 30 minutes, Bath pH 12, Agitation.360rpm, Current density IA/dIn2, K2C03 40g/l, KNOJ 40gll, KOH 19l1.1-426·

Fundamentals Studies Of Electro-Silver Plating Process.

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Fundamentals Studies Of Electro-Silver Plating Process.

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