Flip chip packaging

Soldering-induced Cu diffusion and intermetallic compound formation between Ni/Cu under bump metallization and SnPb flip-chip solder bumps

“…[8][9][10][11] Copper metallization is widely used as the conductor material in flip-chip interconnects because of its excellent conductivity. 12 Recently, the effect of Ni thickness and reflow times on the interfacial reactions between PbSn solder and the Ni/Cu UBM was reported. 13,14 The phase transformation of IMCs and related phase-equilibrium behaviors were also discussed.…”

Interfacial reactions and compound formation in the edge of PbSn flip-chip solder bumps on Ni/Cu under-bump metallization

“…The morphology of (Cu 1-y Ni y ) 6 Sn 5 could be revealed from the x-ray color mapping of Ni, Cu, and Sn elements. The formation of (Cu 1-y Ni y ) 6 Sn 5 indicated that Cu diffused through Ni and the (Ni 1-x Cu x ) 3 Sn 4 IMC and then reacted with Sn and Ni, as discussed elsewhere. 7,8 The amounts of the (Cu 1-y Ni y ) 6 Sn 5 IMC were dependent on the degrees of Cu atoms diffusing through the electroplated Ni.…”

“…The formation of (Cu 1-y Ni y ) 6 Sn 5 indicated that Cu diffused through Ni and the (Ni 1-x Cu x ) 3 Sn 4 IMC and then reacted with Sn and Ni, as discussed elsewhere. 7,8 The amounts of the (Cu 1-y Ni y ) 6 Sn 5 IMC were dependent on the degrees of Cu atoms diffusing through the electroplated Ni. As a result, with increasing cycles of reflow, the amounts of the (Cu 1-y Ni y ) 6 times, two or three Cu-Ni-Sn IMCs could be found between the solder and Ni.…”

“…In fact, only 4at.% and 2at.%Cu dissolved in the Ni 3 Sn 4 IMC and Ni metallization, respectively. It should be mentioned that the monotonic variations of y in the (Cu 1-y Ni y ) 6 Sn 5 IMC formed in the sideway of the Ni/Cu UBM were detected after point-by-point detailed quantitative analysis by EPMA. However, because of the limit of the pixel resolution in the color mapping images, only two tones of blue (i.e., light and dark) represent the concentration variation of the (Cu 1-y Ni y ) 6 Sn 5 IMC in Fig.…”

“…4,5 The Cu metallization is widely used as the conductor material in flip-chip interconnects because of its electrical conductivity. 6 For Ni/Cu UBM, the effect of Ni thickness and reflow times on the interfacial reactions between PbSn solder and metallized layers in the central portion of the solder joints was recently reported. 7 The phase transformation of intermetallic compounds (IMCs) and related phase-equilibrium behaviors were also discussed.…”