• ETRI Journal
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• v.35 no.4
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• pp.625-631
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• 2013

For the formation of solder bumps with a fine pitch of 130 ${\mu}m$ on a printed circuit board substrate, low-volume solder on pad (LVSoP) technology using a maskless method is developed for SAC305 solder with a high melting temperature of $220^{\circ}C$. The solder bump maker (SBM) paste and its process are quantitatively optimized to obtain a uniform solder bump height, which is almost equal to the height of the solder resist. For an understanding of chemorheological phenomena of SBM paste, differential scanning calorimetry, viscosity measurement, and physical flowing of SBM paste are precisely characterized and observed during LVSoP processing. The average height of the solder bumps and their maximum and minimum values are 14.7 ${\mu}m$, 18.3 ${\mu}m$, and 12.0 ${\mu}m$, respectively. It is expected that maskless LVSoP technology can be effectively used for a fine-pitch interconnection of a Cu pillar in the semiconductor packaging field.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1018-1024
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• 1999

The effects of operating temperature and stress on degradation of components in high temperature steam generator were investigated. Several 2.25CrlMo tubes which had operated over 20 years and an unused 9CrlMoVNb tube were tested. For the former samples, the amount of $\textrm{M}_{6}\textrm{C}$ carbide and its size are increased with the aging or operating time. The precipitation behavior of carbides ($\textrm{M}_{2}\textrm{O}$, $\textrm{M}_{6}\textrm{C}$) is changed with the operating temperature of the tubes. However, unused 9CrlMoVNb samples show a different carbide precipitation process due to high chromium, vanadium, and niobium contents. The amount of Cr-rich $\textrm{M}_{23}\textrm{C}_{6}$ carbide is significantly increased with aging time, but that of $\textrm{M}_{6}\textrm{C}$ type carbide is rarely changed with aging time at elevated temperatures.

• Journal of Welding and Joining
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• v.17 no.3
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• pp.90-95
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• 1999

The increase in high speed, multi-function and high I/O pin semiconductor devices highly demands high pin count, very thin, and high density packages. BGA is one of the solutions, but the package has demerits in package reliability, surface mounting problems due to the PCB warpage and solder joint crack related with TCE mismatch between the materials. On this study to verify the thermal fatigue lifetime of the solder joint FEM and experiments were performed after surface mounting BGA with different solder composition and reliability conditions. FEM showed optimum composition of Ag3.2-Sn96.5 and under the composition minimum creep deformation of the solder joint was calculated, and the thermal fatigue lifetime was improved. In view of temperature cycle condition, the conditions of $-65^{\circ}C$to $150^{\circ}C$ showed minimum lifetime and t was 1/3 of $0^{\circ}C$ to $125^{\circ}C$ condition. Test board was prepared and solder joint crack was verified. Until 1000cycle on soder joint crack was observed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.134-139
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• 2007

This paper presents a computer-based analysis on the thermal shock characteristics of Pb-free solder joints and UBM in flip chip assemblies. Among four types of popular UBM systems, TiW/Cu system with 95.5Sn-3.9Ag-0.6Cu solder joints was chosen for simulation. A simple 3D finite element model was first created only including silicon die, mixture between underfill and solder joints, and substrate. The displacements due to CTE mismatch between silicon die and substrate was then obtained through FE analysis. Finally, the obtained displacements were applied as mechanical loads to the whole 2D FE model and the characteristics of flip chip assemblies were analyzed. In addition, based on the hyperbolic sine law, the accumulated creep strain of Pb-free solder joints was calculated to predict the fatigue life of flip chip assemblies under thermal shock environments. The proposed method for fatigue life prediction will be evaluated through the cross check of the test results in the future work.

• Proceedings of the Korean Society for Quality Management Conference
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• 2004.04a
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• pp.298-301
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• 2004

European Union Member States shall ensure that, from 1 July 2006, new electrical and electronic equipment put on the market does not contain mercury, cadmium, lead, hexavalent chromium, polybrominated biphenyls(PBB) or polybrominated diphenyl ethers(PBDE) (by Directive 2002/95/EC of The European Parliament and the Council of 27 january, 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment ). So, It is important to develop lead free solder and to assure the reliability of appliance. But lead free solder(i.e. Sn-3Ag-0.5Cu) have some problems such as lift off, whisker, migration and crack, etc. In this paper we discuss the reliability assurance method in lead free solder and appliance.

• Proceedings of the Korean Reliability Society Conference
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• 2005.06a
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• pp.385-392
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• 2005

The restriction of the use of hazardous substances in electrical and electronic equipment legislation mandates the substitution of lead and other hazardous substances in electronics products by July 2006. Due to this legislative pressure, the electronics industry is moving to adoption of lead free solders. In this paper, we investigated a flux to restrict generating electrochemical migration in lead-free solder. The lead-free solders used in this study were Sn-0.7Cu-0.01P and Sn-3.0Ag-0.5Cu. To measure the resistance of electrochemical migration, the dew-cycle test and water drop test were adopted. As the result, now flux having high durable of electrochemical migration was developed.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.22-30
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• 2013

Due to ELV banning, automotive electronics cannot use four kinds of heavy metal element (Pb, Hg, Cd, $Cr^{6+}$) from 2016. Therefore, this study was focused on degradation characteristics of Sn-3.0Ag-0.5Cu Lead-free solder joint with OSP and ENIG finsh under various reliability assessment method, as like to thermal shock test and high temeprature/high humidity test with test duration for cabin electronics. Also, we compared bonding strength degradation to other advanced research results of electronic control unit for engine room because of difference service temperature with mount location in automotive. Whisker growth phenomenon and mitigation method which were essentially consideration items for Pb-free car electronics were examined. Conformal coating is a strong candidate for mitigating whisker growth in automotive electronics. Necessary condition to adapt Pb-free in car electronics was shown.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.6
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• pp.90-96
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• 2011

In this study, the characteristic of fractured portion and shape on solder joints were investigated according to the thermal shock test for Automotive Application Component using Sn-3.0Ag-0.5Cu solder, which has a outstanding property as Lead-free solder. The value of pull and shear strength was decreased in principle after 432 cycles thermal shock test. In addition, fracture mode was verified by using EDS and SEM to observe fractured shape on the solder joints before and after thermal shock. In before thermal shock test, the fracture mode revealed typically solder layer's fracture mode. In after thermal shock test, we identified multiple fracture mode of the ductile and brittle fracture. Even though same composition of solder was used to experimental for estimating. the fracture mode varied on the fracture portion's height and the directional angles of shear strength. In conclusion, we identified that mechanical strength was affected on the solder layer's fracture mode.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.1-9
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• 2011

Understanding the void characterization in the solder joints has become more important because of the application of lead free solder materials and its reliability in electronic packaging technology. According to the JEDEC 217 standard, it describes void types formed in the solder joints, and divides into some categories depending on the void position and formation cause. Based on the previous papers and the standards related to the void, reliability of the BGA solder joints is determined by the size of void, as well as the location of void inside the BGA solder ball. Prior to reflow soldering process, OSP(organic surface preservative) finished Cu electrode was exposed under $85^{\circ}C$/60%RH(relative humidity) for 168 h. Voids induced by the exposure of $85^{\circ}C$/60%RH became larger and bigger with increasing aging times. The void position has more influence on mechanical strength property than the amount of void growth does.

• 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.