• Transactions on Electrical and Electronic Materials
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• v.16 no.3
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• pp.112-116
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• 2015

This work studied the thickness and contact angle of solder joints between SAC 305 lead-free solder alloy and a Copper (Cu) substrate. Intermetallic compound (IMC) thickness and contact angle of 3Sn-Ag-0.5Cu (SAC 305) leadfree solder were measured using varying aging times, at a fixed temperature at 30℃. The thickness of IMC and contact angle depend on the aging time. IMC thickness increases as the aging increases. The contact angle gradually decreased from 39.49° to 27.59° as aging time increased from zero to 24 hours for big solder sample. Meanwhile, for small solder sample, the contact angle increased from 32.00° to 40.53° from zero to 24 hours. The IMC thickness sharply increased from 0.007 mm to 0.011 mm from zero to 24 hours aging time for big solder. In spite of that, for small solder the IMC thickness gradually increased from 0.009 mm to 0.017 mm. XRD analysis was used to confirm the intermetallic formation inside the sample. Cu₆Sn₅, Cu₃Sn, Ni₃Sn and Ni₃Sn₂ IMC layers were formed between the solder and the copper substrate. As the aging time increased, the strength of the solder joint mproved due to reduced contact angle.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.84-87
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• 2003

Since Pb-free solder alloys have been used extensively in microelectronic packaging industry, the interaction between UBM (Under Bump Metallurgy) and solder is a critical issue because IMC (Intermetallic Compound) at the interface is critical for the adhesion of mechanical and the electrical contact for flip chip bonding. IMC growth must be fast during the reflow process to form stable IMC. Too fast IMC growth, however, is undesirable because it causes the dewetting of UBM and the unstable mechanical stability of thick IMC. UP to now. Ni and Cu are the most popular UBMs because electroplating is lower cost process than thin film deposition in vacuum for Al/Ni(V)/Cu or phased Cr-Cu. The consumption rate and the growth rate of IMC on Ni are lower than those of Cu. In contrast, the wetting of solder bumps on Cu is better than Ni. In addition, the residual stress of Cu is lower than that of Ni. Therefore, the alloy of Cu and Ni could be used as optimum UBM with both advantages of Ni and Cu. In this paper, the interfacial reactions of Sn-3.5Ag-0.7Cu solder on Ni-xCu alloy UBMs were investigated. The UBMs of Ni-Cu alloy were made on Si wafer. Thin Cr film and Cu film were used as adhesion layer and electroplating seed layer, respectively. And then, the solderable layer, Ni-Cu alloy, was deposited on the seed layer by electroplating. The UBM consumption rate and intermetallic growth on Ni-Cu alloy were studied as a function of time and Cu contents. And the IMCs between solder and UBM were analyzed with SEM, EDS, and TEM.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.192-193
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• 2007

An evaporated Ti/Pd/Ag contact system is most widely used to make high-efficiency silicon solar cells, however, the system is not cost effective due to expensive materials and vacuum techniques. Commercial solar cells with screen-printed contacts formed by using Ag paste suffer from a low fill factor and a high shading loss because of high contact resistance and low aspect ratio. Low-cost Ni and Cu metal contacts have been formed by using electro less plating and electroplating techniques to replace the Ti/Pd/Ag and screen-printed Ag contacts. Ni/Cu alloy is plated on a silicon substrate by electro-deposition of the alloy from an acetate electrolyte solution, and nickel-silicide formation at the interface between the silicon and the nickel enhances stability and reduces the contact resistance. It was, therefore, found that nickel-silicide was suitable for high-efficiency solar cell applications. Cu was electroplated on the Ni layer by using a light induced plating method. The Cu electroplating solution was made up of a commercially available acid sulfate bath and additives to reduce the stress of the copper layer. In this paper, we investigated low-cost Ni/Cu contact formation by electro less and electroplating for crystalline silicon solar cells.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.54-61
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• 2016

Screen printing of commercially available Ag paste is the most widely used method for the front side metallization of Si solar cells. However, the metallization using Ag paste is expensive and needs high temperature annealing for reliable contact. Among many metallization schemes, Ni/Cu/Sn plating is one of the most promising methods due to low contact resistance and mass production, resulting in high efficiency and low production cost. Ni layer serves as a barrier which would prevent copper atoms from diffusion into the silicon substrate. However, Ni based schemes by electroless deposition usually have low thermal stability, and require high annealing process due to phosphorus content in the Ni based films. These problems can be resolved by adding W element in Ni-based film. In this study, Ni-W-P alloys were formed by electroless plating and properties of it such as sheet resistance, resistivity, specific contact resistivity, crystallinity, and morphology were investigated before and after annealing process by means of transmission line method (TLM), 4-point probe, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.260-260
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• 2009

In high-efficiency crystalline silicon solar cell, If high-efficiency solar cells are to be commercialized, It is need to develop superior contact formation method and material that can be inexpensive and simple without degradation of the solar cells ability. For reason of plated metallic contact is not only high metallic purity but also inexpensive manufacture. It is available to apply mass production. Especially, Nickel, Copper are applied widely in various electronic manufactures as easily formation is available by plating. Ni is shown to be a suitable barrier to Cu diffusin as well as desirable contact metal to silicon. Nickel monosilicide has been suggested as a suitable silicide due to its lower resistivitym lower sintering temperature and lower layer stress than $TiSi_2$. In this paper, Nickel as a seed layer and diffusion barrier is plated by electroless plating to make nickel monosilicide.

• Korean Journal of Materials Research
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• v.15 no.5
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• pp.318-322
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• 2005

Ti-capped NiSi contacts were formed on $p^+/n$ junctions to improve the leakage problem and then Cu was deposited without removing the Ti-capping layer in an attempt to utilize as a diffusion barrier. The electrical characteristics of these $p^+/n$ diodes with Cu/Ti/NiSi electrodes were measured as a function of drive-in RTA(rapid-thermal annealing) and silicidation temperature and time. When drive-in annealed at $900^{\circ}C$, 10 sec. and silicided at $500^{\circ}C$, 100 sec., the diodes showed the most excellent I-V characteristics. Especially, the leakage current was $10^{-10}A$, much lower than reported data for diodes with NiSi contacts. However, when the $p^+/n$ diodes with Cu/Ti/NiSi contacts were furnace-annealed at $400^{\circ}C$ for 40 min., the leakage current increased by 4 orders. The FESEM and AES analysis revealed that the Ti-capping layer effectively prohibited the Cu diffusion, but was ineffective against the NiSi dissociation and consequent Ni diffusion.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1019-1022
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• 2004

본 연구에서는 PERC(passivated emitter and rear cell) 구조를 갖는 고효율 단결정 실리콘 태양전지에 도금법을 적용하여 Ni/Cu 전극을 형성하였다. 고효율 태양전지는 제작 비용이 높고 공정이 복잡하기 때문에 실용화에 적용이 어려운 단점이 있다. 따라서 태양전지의 효율은 그대로 유지하고, 공정을 간단하게 줄이면서 저가격화 할 수 있는 방법에 대한 연구가 필요하다. 기존의 고효율 실리콘 태양전지에 가장 일반적으로 적용되고 있는 Ti/Pd/Ag 전극의 경우 고가의 증착 장비를 이용할 뿐만 아니라 재료 자체도 매우 고가의 물질이 사용되고 있다. 도금법으로 Ni/cu 전극을 형성하여 태양전지를 제작한 결과 공정을 간소화하고 비용을 절감 하면서, 20% 이상의 고효율 태양전지를 얻을 수 있었다.

• Journal of Institute of Convergence Technology
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• v.8 no.1
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• pp.33-39
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• 2018

The screen printing method for forming the electrode by applying the existing pressure is difficult to apply to thin wafers, and since expensive Ag paste is used, it is difficult to solve the problem of cost reduction. This can solve both of the problems by forming the front electrode using a plating method applicable to a thin wafer. In this paper, the process conditions of electrode formation are optimized by using LIEP (Light-Induced Electrode Plating). Experiments were conducted by varying the Ni plating bath temperature $40{\sim}70^{\circ}C$, the applied current 5 ~ 15 mA, and the plating process time 5 ~ 20 min. As a result of the experiment, it was confirmed that the optimal condition of the structural characteristics was obtained at the plating bath temperature of $60^{\circ}C$, 15 mA, and the process time of 20 min. The Cu LIEP process conditions, experiments were conducted with Cu plating bath temperature $40{\sim}70^{\circ}C$, applied voltage 5 ~ 15 V, plating process time 2 ~ 15 min. As a result of the experiment, it was confirmed that the optimum conditions were obtained as a result of electrical and structural characteristics at the plating bath temperature of $60^{\circ}C$ and applied current of 15 V and process time of 15 min. In order to form Ni silicide, the firing process time was fixed to 2 min and the temperature was changed to $310^{\circ}C$, $330^{\circ}C$, $350^{\circ}C$, and post contact annealing was performed. As a result, the lowest contact resistance value of $2.76{\Omega}$ was obtained at the firing temperature of $310^{\circ}C$. The contact resistivity of $1.07m{\Omega}cm^2$ can be calculated from the conditionally optimized sample. With the plating method using Ni / Cu, the efficiency of the solar cell can be expected to increase due to the increase of the electric conductivity and the decrease of the resistance component in the production of the solar cell, and the application to the thin wafer can be expected.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.155-161
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• 2018

A Si chip with the Cu/Au bumps of $100-{\mu}m$ diameter was flip-chip bonded using different anisotropic conductive adhesives (ACAs) onto the local stiffness-variant stretchable substrate consisting of polydimethylsiloxane (PDMS) and flexible printed circuit board (FPCB). The average contact resistances of the flip-chip joints processed with ACAs containing different conductive particles were evaluated and compared. The specimen, which was flip-chip bonded using the ACA with Au-coated polymer balls as conductive particles, exhibited a contact resistance of $43.2m{\Omega}$. The contact resistance of the Si chip, which was flip-chip processed with the ACA containing SnBi solder particles, was measured as $36.2m{\Omega}$, On the contrary, an electric open occurred for the sample bonded using the ACA with Ni particles, which was attributed to the formation of flip-chip joints without any entrapped Ni particles because of the least amount of Ni particles in the ACA.

• Transactions of Materials Processing
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• v.6 no.2
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• pp.136-144
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• 1997

(Ag-10%Ni)/Cu clad metals for electric contact switch were fabricated by cold-roll bonding process. 2 or 3 passes of cold-rolling was carried out for each process to investigate the effect of the rolling passes on the bonding property. The effect of the annealing temperature of copper before the cold-roll bonding on the bond strength was also studied. The specimen bonded with copper annealed below 30$0^{\circ}C$ before roll bonding showed good bond strength. This is because high stored energy in copper promoted the short range diffusion and the grain refinement of copper by the static recrystallization increased the degree of the interfacial coherency. The maximum peel strength of clad metals bonded with Cu annealed below 30$0^{\circ}C$ was 120N.