Effect of 0.5 wt % Cu addition in Sn–3.5%Ag solder on the dissolution rate of Cu metallization

Abstract

The dissolution of thin film under-bump-metallization ͑UBM͒ by molten solder has been one of the most serious processing problems in electronic packaging technology. Due to a higher melting temperature and a greater Sn content, a molten lead-free solder such as eutectic SnAg has a faster dissolution rate of thin film UBM than the eutectic SnPb. The work presented in this paper focuses on the role of 0.5 wt % Cu in the base Sn-3.5%Ag solder to reduce the dissolution of the Cu bond pad in ball grid array applications. We found that after 0.5 wt % Cu addition, the rate of dissolution of Cu in the molten Sn-3.5%Ag solder slows down dramatically. Systematic experimental work was carried out to understand the dissolution behavior of Cu by the molten Sn-3.5%Ag and Sn-3.5%Ag-0.5%Cu solders at 230-250°C, for different time periods ranging from 1 to 10 min. From the curves of consumed Cu thickness, it was concluded that 0.5 wt % Cu addition actually reduces the concentration gradient at the Cu metallization/molten solder interface which reduces the driving force of dissolution. During the dissolution, excess Cu was found to precipitate out due to heterogeneous nucleation and growth of Cu 6 Sn 5 at the solder melt/oxide interface. In turn, more Cu can be dissolved again. This process continues with time and leads to more dissolution of Cu from the bond pad than the amount expected from the solubility limit, but it occurs at a slower rate for the molten Sn-3.5%Ag-0.5%Cu solder.

Dissolution Kinetics of Nickel in Lead-free Sn-Bi-In-Zn-Sb Soldering Alloys

“…[1][2][3][4][5][6][7][8]. To avoid the excessive loss of solid metals in contact with the alloys during soldering, data on metal dissolution rates in molten solders are needed.…”

The Failure Mechanism of Recrystallization – Assisted Cracking of Solder Interconnections

“…I t s h o u l d a l s o b e n o t i c e d t h a t i n p r a c t i c e t h e m i c r o s t r u c t u r e s f o r m e d o n o t h e r p a d metallizations can differ notably, even though the same solder compositions are used (see, e.g., [15,30,31]). The dissolution of the contact pads or pad metallizations of packages and printed wiring boards during reflow changes the composition of the molten solder.…”

Effect of Ni-P Plating Temperature on Growth of Interfacial Intermetallic Compound in Electroless Nickel Immersion Gold/Sn-Ag-Cu Solder Joints

“…[10][11][12] The P content in the Ni-P layer affects the interfacial IMC thickness, joint strength, and solder wettability. [10][11][12] These properties of the Ni-P layer depend on the Ni-P electroless plating conditions, including temperature, pH, additives, etc. Hence, the effects of these conditions on the properties of the Ni-P layer and the solder joint must be evaluated.…”