Chiho Kim
Pusan National University
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Publication
Featured researches published by Chiho Kim.
Microelectronics Reliability | 2018
Hyunju Lee; Cheolmin Kim; Cheolho Heo; Chiho Kim; Jae-Ho Lee; Yangdo Kim
Abstract The electroless nickel immersion gold (ENIG) process results in surface defects, such as pinholes and black pads, which weaken the solder joint and eventually degrade the reliability of the PCB. Contamination of the plating solutions, including dissolution of the solder resist (SR), can be a cause of the pinholes and black pads. This study examined the effects of SR dissolution on the solder joint reliability and electroless Ni plating properties. Electroless Ni plating was performed by adding 1 to 10 ppm hardener (melamine) to the fresh Ni solution. Many black pads were observed in the 7 and 10 ppm hardener-added surfaces. In addition, the content of P was highest when 7 and 10 ppm hardener was added. The ball shear tests were carried out to confirm the joint reliability between the ENIG surface with hardener-added and the Sn-3.0Ag-0.5Cu solder (SAC 305). The ball shear strength decreased with increasing dissolution of the hardener. In particular, the shear strength was the lowest at 7 and 10 ppm hardener addition. In addition, the failure mode of the solder joint was changed from ductile to brittle mode with increasing hardener addition. That is, as the hardener additive increases, intermetallic compound (IMC) phases were changed from (Cu,Ni)6Sn5 to (Cu,Ni)3Sn4 and Cu6Sn5 (brittle structure).
Journal of Welding and Joining | 2015
Jeong-Chul Seo; Ildong Choi; Hong-Rea Son; Chang-Wook Ji; Chiho Kim; Sung-Bu Suh; Jinseok Seo; Yeong-Do Park
With using adaptive control of the resistance spot welding machine, the advantage on electrode life time for galvanized steels has been addressed. This study was aimed to evaluate the electrode life time of galvanized steels with applying the constant current control and the adaptive control resistance spot welding process for a comparison purpose. The growth in diameter of electrode face was similar for both the constant current and the adaptive control up to 2000 welds. The button diameter was decreased with weld numbers, however, sudden increase in button diameter with use of the adaptive control after 1500 welds was observed. The peak load was continuously decreased with increasing number of welds for both the constant current and the adaptive control. The current compensation during a weld was observed with using the adaptive control after 1800 welds since the -peak on dynamic resistance curve was detected at later weld time. The current compensation with adaptive control during resistance spot welding enhanced the nugget diameter at the faying interface of steel sheets and improved the penetration to thinner steel sheet.
Physical Review B | 2012
Chiho Kim; Y. H. Jang; S. J. Seo; C. H. Song; Jong Yeog Son; Y. S. Yang; J. H. Cho
Current Applied Physics | 2016
Sangmin Shin; Chansu Park; Chiho Kim; Yangdo Kim; Sungkyun Park; Jae-Ho Lee
Journal of the Korean Physical Society | 2009
Z.H. Sun; Chiho Kim; Hak Beom Moon; Y. H. Jang; J. H. Cho; C.H. Song; Y. S. Yang
Thin Solid Films | 2013
Y. H. Jang; Chiho Kim; S. J. Seo; J. H. Cho
Journal of the Korean Physical Society | 2012
S. J. Seo; J. H. Cho; Y. H. Jang; Chiho Kim
Journal of the Korean Physical Society | 2007
K. S. Song; Chiho Kim; Hak Beom Moon; S. S. Min; J. H. Cho
Journal of the Korean Physical Society | 2007
Hak Beom Moon; Chiho Kim; S. S. Min; Jin-Hong Ahn; J. H. Cho; Young-Myeong Kim; R. Hyun
Journal of Electronic Materials | 2018
Hyunju Lee; Jaewook Jung; Cheolho Heo; Chiho Kim; Jae-Ho Lee; Yangdo Kim