Title :
Spalling suppression by Sn-3.5Ag incorporated with Cu particles
Author :
Liu, C.Y. ; Wang, S.J.
Author_Institution :
Dept. of Chem. Eng. & Mater. Eng., Nat. Central Univ., Chung-li, Taiwan
Abstract :
Spalling phenomenon is one of the current urgent reliability issues for the Pb-free solder implementation in flip chip technology. Essentially, spalling was caused by high interfacial energy between intermetallic compound and Cr, which dewetted the layer compound into a spherical compound. In this paper, we report that spalling of Ni thin UBM (Under Bump Metallization) can be prevented during the soldering reaction, if a Cu reservoir is introduced into the structure of C4 (Controlled Collapse Chip Connections) solder joints. Once molten Sn-3.5Ag solder was saturated with Cu atoms, Cu precipitated out as a layer of Cu-Sn compound on Ni thin UBM. Cu-Sn compound layer served as a reaction barrier to retard the consumption of Ni thin UBM. So, spalling is retarded. After prolonged reflowing, Ni thin UBM was converted to ternary Cu-Sn-Ni compounds. Remarkably, we found that Cu-Sn-Ni compound still resided on the Cr surface without spalling. Unlike interfaces of Cu-Sn compound/Cr or Ni-Sn compound/Cr, the interface of Cu-Sn-Ni compound/Cr is very stable and has a low interfacial energy. Hence, spalling effect on Ni thin UBM is prevented.
Keywords :
circuit reliability; copper; flip-chip devices; reflow soldering; silver alloys; tin alloys; C4 solder joints; Cr; Cu particles; Cu-Sn compound layer; CuSnNi; Ni; Ni thin under bump metallization; Pb-free solder implementation; Sn-3.5Ag solder; SnAgCu-Cr; controlled collapse chip connections solder joints; flip chip technology; intermetallic compound; reaction barrier; reliability issues; spalling suppression; Artificial intelligence; Atomic layer deposition; Chromium; Electronics packaging; Flip chip; Gold; Reservoirs; Soldering; Substrates; Tin;
Conference_Titel :
Electronic Materials and Packaging, 2002. Proceedings of the 4th International Symposium on
Print_ISBN :
0-7803-7682-X
DOI :
10.1109/EMAP.2002.1188866