• Proceedings of the KWS Conference
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• 2005.11a
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• pp.219-221
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• 2005

Sn-9Zn solder balls were bonded to Cu, ENIG (Electroless Nickel/Immersion Gold) and electrolytic Au/Ni pads, and the effect of aging on their joint reliability was investigated. The interfacial products were different from the general reaction layer formed in a Sn-base solder. The intermetallic compounds formed in the solder/Cu joint were $Cu_{5}Zn_{8}$ and $Cu_{6}Sn_{5}$. After aging treatment, voids formed irregularly at the bottom side of the solder because of Sn diffusion into the $Cu_{5}Zn_{8}$ IMC. In the case of the solder/ENIG joint, $AuZn_{3}$ IMCs were formed at the interface. In the case of the Au/Ni/Cu substrate, an $AuZn_{3}$ IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, the $AuZn_{3}$ IMC layer became detached from the interface after reflow. When the aging time was extended to 100 h, $Ni_{5}Zn_{21}$ IMC was observed on the Ni substrate.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.2
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• pp.25-30
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• 2018

Sn-Pb solder has been used in automotive electronics for decades. However, recently, due to the environmental and health concerns, some international environmental organizations such as the end-of-life vehicle (ELV) enacted legislation banning of the Pb usage in automotive electronics. For this reason, many studies to develop and promote Pb-free soldering have been significantly reported. Meanwhile, because of flexibility and lightweight, flexible printed circuit boards (FPCBs) have been increasingly used in automotive electronics for lightweight to improve fuel efficiency and space utilization. Although the properties of lead-free solders for automotive electronics have been widely studied, there is a lack of research on the reliability performance of the lead-free solder joint on FPCB under user conditions. This study reported the properties of solder joints between Pb-free solders such as Sn3.0Ag0.5Cu, Sn0.7Cu and Sn0.5Cu0.01Al (Si), and various FPCBs finished with organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG). To evaluate on joint properties and reliabilities with different solder compositions and surface-finishing materials, pull strength test, thermal shock test, and bending cycle test were performed and analyzed. After the bending cycle test of solder joint on OSP-finishing, the fractures were occurred in solder and the lifetime of Sn3.0Ag0.5Cu solder joint was the longest.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.2
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• pp.47-53
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• 2015

The effects of electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes on the in-situ intermetallics reaction and the electromigration (EM) reliability of Sn-3.0Ag-0.5Cu (SAC305) solder bump were systematically investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of the ENIG surface finish at solder top side, while at the OSP surface finish at solder bottom side,$ Cu_6Sn_5$ and $Cu_3Sn$ IMCs were formed. Mean time to failure on SAC305 solder bump at $130^{\circ}C$ with a current density of $5.0{\times}10^3A/cm^2$ was 78.7 hrs. EM open failure was observed at bottom OSP surface finish by fast consumption of Cu atoms when electrons flow from bottom Cu substrate to solder. In-situ scanning electron microscope analysis showed that IMC growth rate of ENIG surface finish was much lower than that of the OSP surface finish. Therefore, EM reliability of ENIG surface finish was higher than that of OSP surface finish due to its superior barrier stability to IMC reaction.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.4
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• pp.65-70
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• 2008

The mechanical shear strength of BGA(Ball Grid Array) solder joints under high impact loading was investigated. The Sn-37Pb solder balls with a diameter of $500{\mu}m$ were placed on the pads of FR-4 substrates with ENIG(Electroless Nickel Immersion Gold) surface treatment and reflowed. For the High Temperature Storage(HTS) test, the samples were aged a constant testing temperature of $120^{\circ}C$ for up to 250h. After the HTS test, high speed shear tests with various shear speed of 0.01, 0.1, 1, 3 m/s were conducted. $Ni_3Sn_4$ intermetallic compound(IMC) layer was observed at the solder/Ni-P interface and thickness of IMC was increased with aging process. The shear strength increased with increasing shear speed. The fracture surfaces of solder joints showed various fracture modes dependent on shear speed and aging time. Fracture mode was changed from ductile fracture to brittle fracture with increasing shear speed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.24-24
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• 2009

ENIG(Electroless Nickel Immersion Gold) is the surface treatment method that is used most widely at fine pitch's SMT and BGA packaging process. In this paper, we have studied the effect of P content variation during ENIG process on those phenomena related to the solder joint. The effect of P content was discussed using the results obtained from FE-SEM, EPMA, EDS and FIB. Finally, it was concluded that the more P-content in Ni layer, the thicker P-rich layer.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.250-255
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• 2008

This study utilized a high speed lap-shear test to evaluate the mechanical behavior of Sn-37Pb/Cu and Sn-37Pb/Electroless Nickel immersion Gold under bump metallization solder joints under high speed loading and hence the drop reliability. The samples were aged for 120 h at different temperatures ($120^{\circ}C,\;150^{\circ}C,\;170^{\circ}C$) and afterward tested at different displacement rates (0.01 mm/s to 500 mm/s) to examine the effects of aging on the drop life reliability. The combination of the stress-strain graphs captured from the shear tests and identifying a fracture mode dominant in the samples for different strain rates leads us to conclude that the drop reliability of solder joints degrades as the aging temperature increases, possibly due to the role of the IMC layer. This study successfully demonstrates that the analysis based on a high speed lap-shear test could be critically used to evaluate the drop reliability of solder joints.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.25-27
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• 2005

Sn-9Zn solder balls were bonded to Cu and ENIG (Electroless Nickel/Immersion Gold) pads, and the effect of aging on their joint reliability was investigated. The interfacial products were different from the general reaction layer formed in a Sn-base solder. The intermetallic compounds formed in the solder/Cu joint were $Cu_{5}Zn_{8}$ and $Cu_{6}Sn_{5}$. After aging treatment, voids formed irregularly at the bottom side of the solder because of Sn diffusion into the $Cu_{5}Zn_{8}$ IMC. In the case of the solder/ENIG joint, $AuZn_{3}$ IMCs were formed at the interface. In the case of the Sn-9Zn/ENIG, the shear strength remained nearly constant in spite of aging for 1000 hours at $150^{\circ}C$. On the other hand, in the case of the Sn-9Zn/Cu, the shear strength significantly decreased after aging at $150^{\circ}C$ for 100hours and then remained constant by further prolonged aging. Therefore, the protective plating layer such as ENIG must be used to ensure the mechanical reliability of the Sn-9Zn/Cu joint.

• Korean Journal of Metals and Materials
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• v.47 no.4
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• pp.261-266
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• 2009

The mechanical and electrical properties of ball grid array (BGA) solder joints were measured, consisting of Sn-3.5Ag, with organic solderability preservative (OSP)-finished Cu pads and Electroless Nickel/Immersion Gold (ENIG) surface finishes. The mechanical properties were measured by die shear test. When ENIG PCB was upper joint and OSP PCB was lower joint, the highest shear force showed at the third reflow. When OSP PCB was upper joint and ENIG PCB was lower joint, the highest shear force showed at the forth reflow. For both joints, after the die shear results reached the highest shear force, shear force decreased as a function of increasing reflow number. Electrical property of the solder joint decreased with the function of increasing reflow number. The scanning electron microscope results show that the IMC thickness at the bonding interface gets thicker while the number of reflow increases.

• Korean Journal of Metals and Materials
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• v.46 no.2
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• pp.80-87
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• 2008

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than $1,000{\Omega}$. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.1
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• pp.35-39
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• 2011

Shearing characteristics of Sn-3.0wt%Ag-0.5wt%Cu ball for standardization of high speed shear test were investigated. The solder ball of 450 ${\mu}m$ in diameter was reflowed at $245^{\circ}C$ on FR4 PCB (Printed Circuit Board) to prepare a sample for the high-speed shear test. The metal pads on the PCB were OSP (Organic Solderability Preservative, Cu pad) and ENIG (Electroless Nickel/Immersion Gold, i.e CulNi/Au). Shearing speed was varied from 0.5 to 3.0 m/s, and tip height from 10 to 135 ${\mu}m$. As experimental results, for the OSP pad, a ductile fracture increased with tip height, and it decreased with shearing speed. In the case of ENIG pad, the ductile fracture increased with the tip height. The tip height of 10 ${\mu}m$ (2% of solder ball diameter) was unsuitable since the fracture mode was mostly pad lift. Shear energy increased with increasing shearing tip height from 10 to 135 ${\mu}m$ for both of OSP and ENIG pads.