• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.575-579
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• 2004

Package reliability test was conducted to investigate the effect of solder paste composition at BGA Package. It was found that the shape and size of the phase form are affected by the processing parameters. The material have used to fill in the via was Sn/36Pb/2Ag and Sn/0.75Cu type solder paste. Sn/36Pb/2Ag and Sn/0.75Cu paste were fabricated on Tape-BGA substrates by screen printing process, and via ball mount data were characterized with variations of dwell time of 85 seconds at reflow peak temperature at 22$0^{\circ}C$ or 24$0^{\circ}C$. The test condition was MRT 30 $^{\circ}C$/60 %RH/96 HR. Failures formed of a ball-off in solder paste process were observed by using a Optical Microscope and SEM(Scanning Electron Microscope). It was concluded that intermetallic layer growth played important roles in increasing solder fatigue strength for addition of Ag composition. The degradation of shear strength of solder composition is discussed.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.83-89
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• 2014

Solder paste plays a crucial role as the widely used joining material in surface mount technology (SMT). The understanding of its behaviour and properties is essential to ensure the proper functioning of the electronic assemblies. The composition of the solder paste is known to be directly related to its rheological behaviour. This paper provides a brief overview of the solder paste behaviour of four different solder paste formulations, stencil printing processes, and techniques to characterize solder paste behaviour adequately. The solder pastes are based on the Sn-3.0Ag-0.5Cu alloy, are different in their particle size, metal content and flux system. The solder pastes are characterized in terms of solder particle size and shape as well as the rheological characterizations such as oscillatory sweep tests, viscosity, and creep recovery behaviour of pastes.

• Journal of Powder Materials
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• v.24 no.5
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• pp.395-399
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• 2017

Solder paste is widely used as a conductive adhesive in the electronics industry. In this paper, nano and microsized mixed lead-free solder powder (Sn-Ag-Cu) is used to manufacture solder paste. The purpose of this paper is to improve the storage stability using different types of solvents that are used in fabricating the solder paste. If a solvent of sole acetate is used, the nano sized solder powder and organic acid react and form a Sn-Ag-Cu malonate. These formed malonates create fatty acid soaps. The fatty acid soaps absorb the solvents and while the viscosity of the solder paste rises, the storage stability and reliability decrease. When ethylene glycol, a dihydric alcohol, is used the fatty acid soaps and ethylene glycol react, preventing the further creation of the fatty acid soaps. The prevention of gelation results in an improvement in the solder paste storage ability.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.1
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• pp.35-41
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• 2022

In the era of Fifth-Generation (5G), technology requirements such as Artificial Intelligence (AI), Cloud computing, automatic vehicles, and smart manufacturing are increasing. For high efficiency of electronic devices, research on high-intensity circuits and packaging for miniaturized electronic components is important. A solder paste which consists of small solder powders is one of common solder for high density packaging, whereas an electroplated solder has limitation of uniformity of bump composition. Researches are underway to improve wettability through the addition of nanoparticles into a solder paste or the surface finish of a substrate, and to suppress the formation of IMC growth at the metal pad interface. This paper describes the principles of improving the wettability of solder paste and suppressing interfacial IMC growth by addition of nanoparticles.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.55-61
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• 2022

In this study, properties of Pb-free solder joints which were combined using Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder with a mid-temperature type of melting temperature and Sn-57Bi-1Ag Pb-free solder with a low-temperature type of melting temperature were reported. Combined Pb-free solder joints were formed by reflow soldering processes with ball grid array (BGA) packages which have SAC305 solder balls and flame retardant-4 (FR-4) printed circuit boards (PCBs) which printed Sn-57Bi-1Ag solder paste. The reflow soldering processes were performed with two types of temperature profiles and interfacial properties of combined Pb-free solder joints such as interfacial reactions, formations of intermetallic compounds (IMCs), diffusion mechanisms of Bi, and so on were analyzed with the reflow process conditions. In order to compare reliability characteristics of combined Pb-free solder joints, we also conducted thermal shock test and analyzed changes of mechanical properties for joints from a shear test during the thermal shock test.

• ETRI Journal
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• v.35 no.6
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• pp.1152-1155
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• 2013

A cost-effective and simple solder on pad (SoP) process is proposed for a fine-pitch microbump interconnection. A novel solder bump maker (SBM) material is applied to form a 60-${\mu}m$ pitch SoP. SBM, which is composed of ternary Sn3.0Ag0.5Cu (SAC305) solder powder and a polymer resin, is a paste material used to perform a fine-pitch SoP through a screen printing method. By optimizing the volumetric ratio of the resin, deoxidizing agent, and SAC305 solder powder, the oxide layers on the solder powder and Cu pads are successfully removed during the bumping process without additional treatment or equipment. Test vehicles with a daisy chain pattern are fabricated to develop the fine-pitch SoP process and evaluate the fine-pitch interconnection. The fabricated Si chip has 6,724 bumps with a 45-${\mu}m$ diameter and 60-${\mu}m$ pitch. The chip is flip chip bonded with a Si substrate using an underfill material with fluxing features. Using the fluxing underfill material is advantageous since it eliminates the flux cleaning process and capillary flow process of the underfill. The optimized bonding process is validated through an electrical characterization of the daisy chain pattern. This work is the first report on a successful operation of a fine-pitch SoP and microbump interconnection using a screen printing process.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.26-34
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• 2016

Automotive today has been transforming to an electronic product by adopting a lot of convenience and safety features, suggesting that joining materials and their mechanical reliabilities are getting more important. In this study, a Sn-Cu-Cr-Ca solder composition having a high melting temperature ($>230^{\circ}C$) was fabricated and its joint properties and reliability was investigated with an aim to evaluate the suitability as a joining material for electronics of engine room. Furthermore, mechanical properties change under complex environment were compared with several existing solder compositions. As a result of contact angle measurement, favorable spreadability of 84% was shown and the average shear strength manufactured with corresponding composition solder paste was $1.9kg/mm^2$. Also, thermo-mechanical reliability by thermal shock and vibration test was compared with that of the representative high temperature solder materials such as Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb. In order to fabricate the test module, solder balls were made in joints with ENIG-finished BGA and then the BGA chip was reflowed on the OPS-finished PCB pattern. During the environmental tests, resistance change was continuously monitored and the joint strength was examined after tests. Sn-3.5Ag alloy exhibited the biggest degradation rate in resistance and shear stress and Sn-0.7Cu resulted in a relatively stable reliability against thermo-mechanical stress coming from thermal shock and vibration.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2004.09a
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• pp.233-241
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• 2004

A new alloy definition will be presented concerning increasing demands for the board level reliability of miniaturized interconnections. The damage mechanism for LFBGA components on different board finishes is not quite understood. Further demands from mobile phones are the drop test, characterizing interface performance of different package constructions in relation to decreased pad constructions and therefore interfaces. The paper discusses the characterization of interfaces based on SnPb, SnPbXYZ, SnAgCu and SnAgCuInNd ball materials and SnAgCuInNd as solder paste, the stability after accelerated tests and the description of modified interfaces strictly related to the assembly conditions, dissolution behavior of finishes on board side and the influence of intermetallic formation. The type of intermetallic as well as the quantity of intermetallics are observed, primaliry the hardness, E modules describing the ability of strain/stress compensation. First results of board level reliability are presented after TCT-40/+150. Improvement steps from the ball formulation will be discussed in conjunction to the implementation of lead free materials In order to optimize ball materials for area array devices accelareted aging conditions like TCTs were used to analyze the board level reliability of different ball materials for BGA, LFBGA, CSP, Flip Chip. The paper outlines lead-free ball analysis in comparison to conventional solder balls for BGA and chip size packages. The important points of interest are the description of processability related to existing ball attach procedures, requirements of interconnection properties and the knowledge gained the board level reliability. Both are the primary acceptance criteria for implementation. Knowledge about melting characteristic, surface tension depend on temperature and organic vehicles, wetting behavior, electrical conductivity, thermal conductivity, specific heat, mechanical strength, creep and relaxation properties, interactions to preferred finishes (minor impurities), intermetallic growth, content of IMC, brittleness depend on solved elements/IMC, fatigue resistance, damage mechanism, affinity against oxygen, reduction potential, decontamination efforts, endo-/exothermic reactions, diffusion properties related to finishes or bare materials, isothermal fatigue, thermo-cyclic fatigue, corrosion properties, lifetime prediction based on board level results, compatibility with rework/repair solders, rework temperatures of modified solders (Impurities, change in the melting point or range), compatibility to components and laminates.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.3
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• pp.13-19
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• 2018

The soldering property of Pb-containing solder(Sn-Pb) and Pb-free solders(Sn-3.0Ag-0.5Cu and Sn-1.0Ag-0.7Cu-1.6Bi-0.2In) for solar combiner box module was compared. The solar combiner box module was composed of voltage and current detecting modules, diode modules, and other modules. In this study, solder paste printability, printing shape inspection, solder joint property, X-ray inspection, and shear force measurements were conducted. For optimization of Pb-free soldering process, step 1 and 2 were divided. In the step 1 process, the printability of Pb-containing and Pb-free solder alloys were estimated by using printing inspector. Then, the relationship between void percentages and shear force has been estimated. Overall, the property of Pb-containing solder was better than two Pb-free solders. In the step 2 process, the property of reflow soldering for the Pb-free solders was evaluated with different reflow peak temperatures. As the peak temperature of the reflow process gradually increased, the void percentage decreased by 2 to 4%, but the shear force did not significantly depend on the reflow peak temperature by a deviation of about 0.5 kgf. Among different surface finishes on PCB, ENIG surface finish was better than OSP and Pb-free solder surface finishes in terms of shear force. In the thermal shock reliability test of the solar combiner box module with a Pb-free solder and OSP surface finish, the change rate of electrical property of the module was almost unchanged within a 0.3% range and the module had a relatively good electrical property after 500 thermal shock cycles.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.82-82
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• 2010

표면실장 공법을 통해 CSP 패키지를 보드에 실장 하는데 있어 무연솔더 접합부의 신뢰성에 영향을 미치는 인자 중 가장 중요한 것은 접합부에 형성되는 IMC (Intermetallic compound, 금속간화합물)인 것으로 알려져 있다. 접합부의 칩 부분에는 솔더와 칩의 UBM (Under bump metalization)이 접합하여 IMC가 형성되나, 보드 부분에는 솔더와 보드의 UBM 뿐만 아니라 그 사이에 솔더 페이스트가 함께 접합되어 IMC가 형성된다. 본 연구에서는 패키지의 신뢰성 연구를 위해 솔더 페이스트의 유무 및 두께에 따른 무연 솔더 접합부의 미세조직의 변화를 분석하였다. 본 실험에서는 Sn-3.0(Wt.%)Ag-0.5Cu 조성과 본 연구진에 의해 개발된 Sn-Ag-Cu-In 조성의 직경 $450{\mu}m$ 솔더 볼을 사용하였으며, 솔더 페이스트는 상용 Sn-3.0Ag-0.5Cu (ALPHA OM-325)를 사용하였다. 칩은 ENIG (Electroless nickel immersion gold) finish pad가 형성된 CSP (Chip scale package)를, 보드는 OSP (Organic solderability preservative)/Cu finish pad가 형성된 것을 사용하였다. 실험 방법은 보드를 솔더 페이스트 없이 플라즈마 처리 한 것, 솔더 페이스트를 $30{\mu}m$ 두께로 인쇄한 것, $120{\mu}m$의 두께로 인쇄한 것, 이렇게 3가지 조건으로 준비한 후, 솔더 볼이 bumping된 칩을 mounting하여, $242^{\circ}C$의 peak 온도 조건의 oven(1809UL, Heller)에서 reflow를 실시하여 패키지를 형성하였다. 이후 시편은 정밀 연마한 후, OM(Optical Microscopic)과 SEM(scanning electron microscope) 및 EDS(energy dispersive spectroscope)를 사용하여 솔더 접합부 IMC의 미세조직을 관찰, 분석하였다.