Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Studies on the Interfacial Reaction of Screen-Printed Sn-37Pb, Sn-3.5Ag and Sn-3.8Ag-0.7Cu Solder Bumps on Ni/Au and OSP finished PCB

Ni/Au 및 OSP로 Finish 처리한 PCB 위에 스크린 프린트 방법으로 형성한 Sn-37Pb, Sn-3.5Ag 및 Sn-3.8Ag-0.7Cu 솔더 범프 계면 반응에 관한 연구

  • Nah, Hae-Woong (Department of Materials Sci. & Eng., Korea Advanced Institute of Science and Technology) ;
  • Son, Ho-Young (Department of Materials Sci. & Eng., Korea Advanced Institute of Science and Technology) ;
  • Paik, Kyung-Wook (Department of Materials Sci. & Eng., Korea Advanced Institute of Science and Technology) ;
  • Kim, Won-Hoe (Circuit R&D Center, Samsung Elecrto-Mechaics Co. LTD) ;
  • Hur, Ki-Rok (Package Team, MicroScale Co.LTD)
  • 나재웅 (한국과학기술원 재료공학과) ;
  • 손호영 (한국과학기술원 재료공학과) ;
  • 백경욱 (한국과학기술원 재료공학과) ;
  • 김원회 (삼성전기(주)) ;
  • 허기록 (마이크로스케일(주))
  • Published : 2002.09.01
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Abstract

In this study, three solders, Sn-37Pb, Sn-3.5Ag, and Sn-3.8Ag-0.7Cu were screen printed on both electroless Ni/Au and OSP metal finished micro-via PCBs (Printed Circuit Boards). The interfacial reaction between PCB metal pad finish materials and solder materials, and its effects on the solder bump joint mechanical reliability were investigated. The lead free solders formed a large amount of intermetallic compounds (IMC) than Sn-37Pb on both electroless Ni/Au and OSP (Organic Solderabilty Preservatives) finished PCBs during solder reflows because of the higher Sn content and higher reflow temperature. For OSP finish, scallop-like $Cu_{6}$ /$Sn_{5}$ and planar $Cu_3$Sn intermetallic compounds (IMC) were formed, and fracture occurred 100% within the solder regardless of reflow numbers and solder materials. Bump shear strength of lead free solders showed higher value than that of Sn-37Pb solder, because lead free solders are usually harder than eutectic Sn-37Pb solder. For Ni/Au finish, polygonal shaped $Ni_3$$Sn_4$ IMC and P-rich Ni layer were formed, and a brittle fracture at the Ni-Sn IMC layer or the interface between Ni-Sn intermetallic and P-rich Ni layer was observed after several reflows. Therefore, bump shear strength values of the Ni/Au finish are relatively lower than those of OSP finish. Especially, spalled IMCs at Sn-3.5Ag interface was observed after several reflow times. And, for the Sn-3.8Ag-0.7Cu solder case, the ternary Sn-Ni-Cu IMCs were observed. As a result, it was found that OSP finished PCB was a better choice for solders on PCB in terms of flip chip mechanical reliability.

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