• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.442-446
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• 1999

Melting behavior and bridge phenomenon of solder paste, which is essential for surface mount technology in packaging, were investigated. solder paste of Sn-37%Pb was printed on Sn-coated Cu-pattern of PCB, and heated over melting point. Melting behavior of the paste was observed using CCD-camera. In order to modelize the melting and agglomeration phenomena of the paste, two solder balls of 0.76mm diameter were used. As experimental results, the paste start to melt from the margin of the printed shape. The hight of the melted paste decreased from 270 $\mu$m to 200 $\mu$m firstly, and finally recovered to 250 $\mu$m. During the melting procedure, pores were evolved from the molten paste. Bridge Phenomenon of the molten Paste depends upon the pitch of the pattern.

• 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 Institute of Control, Robotics and Systems
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• v.8 no.2
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• pp.151-157
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• 2002

A 3-dimenstional automatic solder paste inspection system is described that can be used to find defects occurring in solder paste printing process. This system extracts height and volume information very fast as well as area of solder paste printed, using multiple slit ray projection and Galvano-mirror scanning. Methods are presented on calibration of camera and slit projector, real-time image processing of multiple slit images, determination of reference height, and extraction of paste height information are proposed. Performance of the system was successfully demonstrated through field tests.

• 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.22 no.1
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• pp.69-74
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• 2015

With difficulties during the cleaning of reflow flux residues due to the decrease of the part size and interconnection pitch in the advanced electronic devices, the need for the no-clean solder paste is increasing. In this study, an epoxy curable solder paste was made with SAC305 solder powder and the curable flux of which the main ingredient is epoxy resin and its reflow solderability, flux residue corrosivity and solder joint mechanical properties was investigated with comparison to the commercial rosin type solder paste. The fillet shape of the cured product around the reflowed solder joint revealed that the curing reaction occurred following the fluxing reaction and solder joint formation. The copper plate solderability test result also revealed that the wettability of the epoxy curable solder paste was comparable to those of the commercial rosin type solder pastes. In the highly accelerated temperature and humidity test, the cured product residue of the curable solder paste showed no corrosion of copper plate. From FT-IR analysis, it was considered to be resulted from the formation of tight bond through epoxy curing reaction. Ball shear, ball pull and die shear tests revealed that the adhesive bonding was formed with the solder surface and the increase of die shear strength of about 15~40% was achieved. It was considered that the epoxy curable solder paste could contribute to the improvement of the package reliability as well as the removal of the flux residue cleaning process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5269-5279
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• 2014

The cause of defects in the PCB SMT assembly is mostly solder paste deposits. Conventional inspection methods for solder paste deposits suffer from slow speed, low reliability and high cost. Therefore, this paper proposes a method for calculating the height and region of solder paste on PCB using the 3D profiles without measuring the 2D image. The solder paste region is detected by the phase difference in the measurement points and the average phase on the whole surface of PCB. The high reliable height of the solder paste region is computed by the average of the measurement points' phase with repeatability and reliability. The experimental results revealed improvements of 17% in inspection time and 29% repeatability in the height calculation of the solder paste region, resulting in a high speed and less expensive system.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.1
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• pp.5-11
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• 2001

Melting behavior and bridge phenomenon of solder paste, which is essential for surface mount technology in pachaging, were investigated. Solder paste of Sn-37%Pb was printed on Cu-pattern of PCB, and heated over melting point. Melting behavior of the paste was observed using CCD-camera. In order to modelize the melting and agglomeration phenomena of paste, two solder balls of 0.76 mm diameter were used. As experimental results, the paste start to melt from the margin of the printed shape. The height of the melted paste decreased from 270 $\mu\textrm{m}$ to 200 $\mu\textrm{m}$ firstly, and finally recovered to 250 $\mu\textrm{m}$ During the melting procedure, pores were evolved from the molted paste. Concerning melting model of solder ball, relationship between contact area of solder ball and soldering time was derived as $\chi^2/t=4r \; \gamma/\eta=7.56 m^2$/s at $280^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.35-39
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• 2020

Nonwet (Head in Pillow) defect is one of the defects in SMT (surface mount technology) process, the defect is caused by several factors, such as solder paste misalignment, reflow condition, package warpage and package ball size. This paper focused on ① reflow condition ② package ball & solder paste misalignment ③ package ball size for nonwet experiment. The first, on the case of reflow condition, there would be high risk of nonwet defect when the soldering time was increased, but N₂ was adopted to reflow process, there could be no or low risk of nonwet defect because of oxidation barrier control. And when the contact depth between Solder ball and solder paste was below 20 ㎛, there could be high risk of nonwet defect. Also smaller package ball would have low risk of nonwet defect.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.91-97
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• 2022

The wettability and rheological properties of solder paste with the size of the solder powder were evaluated. To formulate the solder paste, three types of solder powder were used: T4 (20~28 ㎛), T5 (15~25 ㎛), and T6 (5~15 ㎛). The viscosities of the T4, T5, and T6 solder pastes at 10 RPM were 155, 263, and 418 Pa·s, respectively. After 7 days, the viscosity of the T4 solder paste slightly increased by 2.6% and that of T5 was increased by 20.6%. The viscosity of the T6 solder paste after 7 days could not be measured due to high viscosity. The viscosity variation with solder particle size also affected on the printability of the solder. In the case of the T4 solder paste, printability, slump, bridging, and soldering properties were excellent. On the other hand, T5 showed slight dewetting and solder ball defects. Especially, T6, which the smallest powder size, showed poor printability and dewetting at the edge of solder.