Korean Institute of Surface Engineering

pISSN : 1225-8024 | eISSN : 3399-8403


공학

한국표면공학회지 (36권5호 373-378)

Fluxless Plasma Soldering with Different Thickness of UBM Layers on Si-Wafer

Si 웨이퍼의 UBM층 도금두께에 따른 무플럭스 플라즈마 솔더링

문준권;강경인;이재식;정재필;주운홍;

서울시립대학교 신소재공학과;University of Waterloo, 기계공학부;

Abstract

With increasing environmental concerns, application of lead-free solder and fluxless soldering process have been taken attention from the electronic packaging industry. Plasma treatment is one of the soldering methods for the fluxless soldering, and it can prevent environmental pollution cased by flux. On this study fluxless soldering process under $Ar-H_2$plasma using lead free solders such as Sn-3.5 wt%Ag, Sn-3.5 wt%Ag-0.7 wt%Cu and Sn-37%Pb for a reference was investigated. As the plasma reflow has higher soldering temperature than normal air reflow, the effects of UBM(Under Bump Metallization) thickness on the interfacial reaction and bonding strength can be critical. Experimental results showed in case of the thin UBM, Au(20 nm)/Cu(0.3 $mu extrm{m}$)/Ni(0.4 $mu extrm{m}$)/Al(0.4 $mu extrm{m}$), shear strength of the soldered joint was relatively low as 19-27㎫, and it`s caused by the crack observed along the bonded interface. The crack was believed to be produced by the exhaustion of the thin UBM-layer due to the excessive reaction with solder under plasma. However, in case of thick UBM, Au(20 nm)/Cu(4 $mu extrm{m}$)/Ni(4 $mu extrm{m}$)/Al(0.4 $mu extrm{m}$), the bonded interface was sound without any crack and shear strength gives 32∼42㎫. Thus, by increasing UBM thickness in this study the shear strength can be improved to 50∼70%. Fluxed reflow soldering under hot air was also carried out for a reference, and the shear strength was 48∼52㎫. Consequently the fluxless soldering with plasma showed around 65∼80% as those of fluxed air reflow, and the possibility of the $Ar-H_2$ plasma reflow was evaluated.

Keywords

Plasma Reflow Soldering;Fluxless Soldering;Lead free Solder;UBM;Shear Strength;Bonded Interface;