• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.204-207
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• 2003

The flip chip bonding utilizing self-aligning characteristic of solder becomes mandatory to meet to tolerances for the optical device. In this paper, a parametric study of aging condition and pad size of sample was conducted. A TiW/Cu UBM structure was adopted and sample was aging treated to analyze the effect of intermetallic compound with time variation. After aging treatment, the tendency to decrease in shear strength was measured and the structure of the fine joint area was observed by using SEM, TEM and EDS. In result, the shear strength was decreased of about 20% in the $100{\mu}m$ sample at $170^{\circ}C$ aging compared with the maximum shear strength of same pad size sample. In the case of the $120^{\circ}C$ aging treatment, 17% of decrease in shear strength was measured at the $100{\mu}m$ pad size sample. Also, intremetallic compound of $Cu_6Sn_5$ and $Cu_3Sn$ were observed through the TEM measurement by using an FIB technique that is very useful to prepare TEM thin foil specimens from the solder joint interface.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2007.04a
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• pp.49-65
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• 2007

• ETRI Journal
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• v.38 no.6
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• pp.1163-1171
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• 2016

Integration technologies involving flexible substrates are receiving significant attention owing the appearance of new products regarding wearable and Internet of Things technologies. There has been a continuous demand from the industry for a reliable bonding method applicable to a low-temperature process and flexible substrates. Up to now, however, an anisotropic conductive film (ACF) has been predominantly used in applications involving flexible substrates; we therefore suggest low-temperature lead-free soldering and bonding processes as a possible alternative for flex-on-flex applications. Test vehicles were designed on polyimide flexible substrates (FPCBs) to measure the contact resistances. Solder bumping was carried out using a solder-on-pad process with Solder Bump Maker based on Sn58Bi for low-temperature applications. In addition, thermocompression bonding of FPCBs was successfully demonstrated within the temperature of $150^{\circ}C$ using a newly developed fluxing underfill material with fluxing and curing capabilities at low temperature. The same FPCBs were bonded using commercially available ACFs in order to compare the joint properties with those of a joint formed using solder and an underfill. Both of the interconnections formed with Sn58Bi and ACF were examined through a contact resistance measurement, an $85^{\circ}C$ and 85% reliability test, and an SEM cross-sectional analysis.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.35-40
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• 2010

In this study, the reliability of thermal shock, thermal cycle, and complex vibration test at high temperature were examined for 3 types of lead-free solder alloys, Sn-3.5Ag, Sn-0.7Cu and Sn-5.0Sb. For the reliability test, daisychained BGA chips with ENIG-finished Cu pad was assembled with the three lead-free solders on OSP-finished PCBs. Among the 3 types solder alloys, Sn-3.5Ag solder alloy showed the highest degradation rate of electrical resistance and joint strength. On the other hand, Sn-0.7Cu solder alloy had high stability after the reliability tests.

• Journal of Applied Reliability
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• v.7 no.2
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• pp.45-55
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• 2007

In this study, two types of fatigue tests were conducted. Firs, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. Creep deformation was dominant in thermal fatigue and plastic deformation was main parameter for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.143-146
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• 2005

In modern automotive control modules, mechanical failures of surface mounted electronic components such as microprocessors, crystals, capacitors, transformers, inductors, and ball grid array packages, etc., are mai or roadblocks to design cycle time and product reliability. This paper presents a general methodology of failure analysis and fatigue prediction of these electronic components under automotive vibration environments. Mechanical performance of these packages is studied through finite element modeling approach fur given vibration environments in automotive application. Using the results of vibration simulation, fatigue lift is predicted based on cumulative damage analysis and material durability information. Detailed model of solder/lead joints is built to correlate the system level model and obtain solder strains/stresses. The primary focus in this paper is on surface-mount interconnect fatigue failures and the critical component selected for this analysis is 80 pin plastic leaded microprocessor.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.151-155
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• 2003

The requirements for harsh environment electronic controllers in automotive applications have been steadily becoming more and more stringent. Electronic substrate technologists have been responding to this challenge effectively in an effort to meet the performance, reliability and cost requirements. An effect of the plasma cleaning at the alumina substrate and the IMC layer between $Sn-37wt\%Pb$ solder and Ag-Pd thick film conductor after reflow soldering has been studied. Organic residual carbon layer was removed by the substrate plasma cleaning. So the interfacial adhesive strength was enhanced. As a result of AFM measurement, Ag-Pd conductor pad roughness were increased from 304nm to 330nm. $Cu_6Sn_5$ formed during initial ref]ow process at the interface between TiWN/Cu UBM and solder grew by the succeeding reflow process so the grains had a large diameter and dense interval. A cellular-shaped $Ag_3Sn$ was observed at the interface between Ag-Pd conductor pad and solder. The diameters of the $Ag_3Sn$ grains ranged from about $0.1\~0.6{\mu}m$. And a needle-shaped $Ag_3Sn$ was also observed at the inside of the solder.

• Journal of Welding and Joining
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• v.25 no.2
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• pp.82-88
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• 2007

Sn-3.0Ag-0.5Cu lead fee solder was generally utilized in electronics assemblies. But it is insufficient to research about activation energy(Q) that is applying to evaluate the solder joint reliability of environmental friendly electronics assemblies. Therefore this study investigated Q values which are needed to IMC formation and growth of Sn-3.0Ag-0.5Cu/Cu and Sn-40pb/Cu solder joints during aging treatment. We bonded Sn-3.0Ag-0.5Cu and Sn-40Pb solders on FR-4 PCB with Cu pad$(t=80{\mu}m)$. After reflow soldering, to observe the IMC formation and growth of the solder joints, test specimens were aged at 70, 150 and $170^{\circ}C$ for 1, 2, 5, 20, 60, 240, 960, 15840, 28800 and 43200 min, respectively. SEM and EDS were utilized to analysis the IMCS. From these results, we measured the total IMC$(Cu_6Sn_5+Cu_3Sn)$ thickness of Sn-3.0Ag-0.5Cu/Cu and Sn-40Pb/Cu interface, and then obtained Q values for the IMC$(Cu_6Sn_5,\;Cu_3Sn)$ growth of the solder joints.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.311-316
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• 2001

This paper presents that the affecting factors to the solderability and initial reliability. It is the factor that the coefficient of thermal expansion between package and PCB(Printed Circuit Board), the quantity of solder paste and reflow condition, and Au thickness of the solder ball pad on polyimide tape. As the reflow soldering condition for 48 ${\mu}BGA$ is changed, it is estimated that the quantity of Au diffusion at eutectic Sn-Pb solder surface and initial bonding strength of eutectic Sn-Pb solder and lead free solder. It is the result that quantitative measurement of Au diffusion quantity is difficult, but the shear strength of eutectic Sn-Pb solder joint is 842 mN at first reflow and increases 879 mN at third reflow. The major failure mode in solder is judged solder fracture. So, Au diffusion quantity is more affected by reflow temperature than by the reflow times.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.1-7
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• 2006

A major failure mode for wafer level chip size package (WLCSP) is thermo-mechanical fatigue of solder joints. The mechanical strains and stresses generated by the coefficient of thermal expansion (CTE) mismatch between the die and printed circuit board (PCB) are usually the driving force for fatigue crack initiation and propagation to failure. In a WLCSP process peripheral or central bond pads from the die are redistributed into an area away using an insulating polymer layer and a redistribution metal layer, and the insulating polymer layer affects solder joints reliability by absorption of stresses generated by CTE mismatch. In this study, several insulating polymer materials were applied to WLCSP to investigate the effect of insulating material. It was found that the effect of property of insulating material on WLCSP reliability was altered with a solder ball layout of package.