• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.88-93
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• 2003

무전해 Ni-P와 Sn의 반응 및 Ni-P의 결정화에 대한 P 함량의 영향을 세 가지 다른 조성의 Ni-P (P 4.6, 9, 13 $wt.\%$)를 이용하여 연구하였다. $300^{\circ}C$까지 열처리한 모든 시편에서 $Ni_3Sn_4$ intermetallic compound (IMC)가 생성되었고 이들 시편을 $450^{\circ}C$까지 열처리한 경우 Sn 두께가 $0.5{\mu}m$로 작을 때 $Ni_3Sn_4$가 모두 $Ni_3Sn_2$로 변화하였다. nanocrystal인 Ni-4.6P는 Ni (111) texture를 유지하며 결정화되었고 Sn과의 반응시 형성되는 $Ni_3Sn_4$ IMC 또한 비정질인 Ni-9P, Ni-13P 경우보다 강한 (111) texture를 가짐이 확인되었다. Ni-P 막의 P 함량이 작은 경우 $Ni_3Sn_4$ IMC는 두껍고 조밀하게 형성되는 반면 P-rich layer 두께는 작아졌다.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.59-63
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• 2010

Immersion Sn plating was produced on Cu foil by distributing nano-sized diamonds (ND). The ND distributed on the coating surface broke the continuity of Sn-oxide layer, therefore leading to penetrate the molten solder through the oxide and retarding the wettability degradation during a reflow process. Furthermore, the ND in the Sn coating played a role of diffusion barrier for Sn atoms and decreased the growth rate of intermetallic compound ($Cu_6Sn_5$) layer during the solid-state aging. The study confirmed the importance of ND to improve the wettability and reliability of the Sn plating. Complete dispersion of the ND within the immersion Sn plating needs to be further developed for the electronic packaging applications.

• Journal of Welding and Joining
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• v.24 no.6
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• pp.21-27
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• 2006

This study was focused on the evaluation of the thermo-mechanical board-level reliability of Pb-bearing and Pb-free surface mount assemblies. The composition of Pb-bearing solder was a typical Sn-37Pb and that of Pb-free solder used in this study was a representative Sn-3.0Ag-0.5Cu in mass %. Thermal shock test was chosen for the reliability evaluation of the solder joints. Typical $Cu_6Sn_5$ intermetallic compound (IMC) layer was formed between both solders and Cu lead frame at the as-reflowed state, while a layer of $Cu_3Sn$ was additionally formed between the $Cu_6Sn_5$ and Cu lead frame during the thermal shock testing. Thickness of the IMC layers increased with increasing thermal shock cycles, and this is very similar result with that of isothermal aging study of solder joints. Shear test of the multi layer ceramic capacitor(MLCC) joints was also performed to investigate the degradation of mechanical bonding strength of solder joints during the thermal shock testing. Failure mode of the joints after shear testing revealed that the degradation was mainly due to the excessive growth of the IMC layers during the thermal shock testing.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.95-103
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• 2005

The interfacial reaction between 42Sn-58Bi solder (in wt.$\%$ unless specified otherwise) and electroless Ni-P/immersion Au has been investigated before and after thermal aging, with a focus on formation and growth of an intermetallic compound (IMC) layer, consumption of under bump metallurgy (UBM), and bump shear strength. The immersion Au layer with thicknesses of 0 (bare Ni), 0.1, and $1{\mu}m$ was plated on the $5{\mu}m$ thick electroless Ni-P ($14{\~}15 at.\%$P) layer. Then, the 42Sn-58Bi solder balls were fabricated on three different UBM structures by screen-printing and pre-reflow. The $Ni_3Sn_4$ layer (IMC1) was formed at the joint interface after pre-reflow for all the three UBM structures. On aging at $125^{\circ}C$, a quaternary phase (IMC2) was observed above the $Ni_3Sn_4$ layer in the Au-containing UBM structures, which was identified as $Sn_{77}Ni{15}Bi_6Au_2$ (in at.$\%$). The thick $Sn_{77}Ni{15}Bi_6Au_2$ layer deteriorated the integrity of the solder joint and the shear strength of the solder bump was decreased by about $40\%$ compared with non-aged joints.

• Journal of Welding and Joining
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• v.18 no.3
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• pp.89-96
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• 2000

As solder becomes small and fine, the reliability and solderability of solder joint are the critical issue in present electronic packaging industry. Besides the use of lead(Pb) containing solders for the interconnections of microelectronic subsystem assembly and packaging has enviromental problem. In this study, using Sn/Pb and Sn/Ag eutectic solder paste, in order to obtain decrease of solder joint strength with increasing aging time, initial solder joint strength and aging strength after 1000 hour aging at $100^{\circ}C$ were measured by peel test. And in order to obtain the growth of intermetallic compound(IMC) layer thickness, IMC layer thickness was measured by scanning electron microscope(SEM). As a result, solder joint strength was decreased with increasing aging time. The mean IMC layer thickness was increased linearly with the square root of aging time. The diffusion coefficient(D) of IMC layer was found to $1.29{\times}10^{-13}{\;}cm^2/s$ at using Sn/Pb solder paste, 7.56{\times}10^{-14}{\textrm}{cm}^2/s$ at using Sn/Ag solder paste.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.2
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• pp.59-64
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• 2013

In-situ annealing tests of Cu/Ni/Au/Sn-Ag/Cu micro-bump for 3D IC package were performed in an scanning electron microscope chamber at $135-170^{\circ}C$ in order to investigate the growth kinetics of intermetallic compound (IMC). The IMC growth behaviors of both $Cu_3Sn$ and $(Cu,Ni,Au)_6Sn_5$ follow linear relationship with the square root of the annealing time, which could be understood by the dominant diffusion mechanism. Two IMC phases with slightly different compositions, that is, $(Cu,Au^a)_6Sn_5$ and $(Cu,Au^b)_6Sn_5$ formed at Cu/solder interface after bonding and grew with increased annealing time. By the way, $Cu_3Sn$ and $(Cu,Au^b)_6Sn_5$ phases formed at the interfaces between $(Cu,Ni,Au)_6Sn_5$ and Ni/Sn, respectively, and both grew with increased annealing time. The activation energies for $Cu_3Sn$ and $(Cu,Ni,Au)_6Sn_5$ IMC growths during annealing were 0.69 and 0.84 eV, respectively, where Ni layer seems to serve as diffusion barrier for extensive Cu-Sn IMC formation which is expected to contribute to the improvement of electrical reliability of micro-bump.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.195-202
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• 2003

In this study, failure mechanisms of Au stud bumps/ACF flip chip joints were investigated underhigh current stressing condition. For the determination of allowable currents, I-V tests were performed on flip chip joints, and applied currents were measured as high as almost 4.2Amps $(4.42\times10^4\;Amp/cm^2)$. Degradation of flip chip joints was observed by in-situ monitoring of Au stud bumps-Al pads contact resistance. All failures, defined at infinite resistance, occurred at upward electron flow (from PCB pads to chip pads) applied bumps (UEB). However, failure did not occur at downward electron flow applied bumps (DEB). Only several $m\Omega$ contact resistance increased because of Au-Al intermetallic compound (IMC) growth. This polarity effect of Au stud bumps was different from that of solder bumps, and the mechanism was investigated by the calculation of chemical and electrical atomic flux. According to SEM and EDS results, major IMC phase was $Au_5Al_2$, and crack propagated along the interface between Au stud bump and IMC resulting in electrical failures at UEB. Therefore. failure mechanisms at Au stud bump/ACF flip chip Joint undo high current density condition are: 1) crack propagation, accompanied with Au-Al IMC growth. reduces contact area resulting in contact resistance increase; and 2) the polarity effect, depending on the direction of electrons. induces and accelerates the interfacial failure at UEBs.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.402-407
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• 2007

In electronics manufacturing processes, soldering process has generally been used in surface mounting technology. Because of environmental restriction, lead free solders as like a SnAgCu ternary system are being used widely. After soldering process, the formation and growth of intermetalic compounds(IMCs) are formed in the interface between solder and Cu substrate as follows isothermal temperature and time. In this studies, therefore, we investigated the effects of the Cu substrate thickness on the IMC formation and growth of Sn-40Pb/Cu and Sn-3.0Ag-0.5Cu/Cu solder joints, respectively. The effect of the Cu thickness in PCB Cu pad and pure Cu plate was analyzed as measuring of thickness of each IMC. After solder was soldered on PCB and Cu plate which have different Cu thickness, we measured the IMC thickness in solder joints respectively. Also we compared with the effectiveness of Cu thickness on the IMC growth. From these results, we calculated the activation energy.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.1
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• pp.35-41
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• 2002

Flip-chip interconnection that uses solder bump is an essential technology to improve the performance of micro-electronics which require higher working speed, higher density, and smaller size. In this paper, the shear strength of Cr/Cr-Cu/Cu UBM structure of the high-melting solder bump and that of low-melting solder bump after aging is evaluated. Observe intermetallic compound and bump joint condition at the interface between solder and UBM by SEM and TEM. And analyze the shear load concentrated to bump applying finite element analysis. As a result of experiment, the maximum shear strength of Sn-97wt%Pb which was treated 900 hrs aging has been decreased as 25% and Sn-37wt%Pb sample has been decreased as 20%. By the aging process, the growth of $Cu_6/Sn_5$ and $Cu_3Sn$ is ascertained. And the tendency of crack path movement that is interior of a solder to intermetallic compound interface is found.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.