Intermetallic Compound Formation and Growth Kinetics in Flip Chip Joints Using Sn–3.0Ag–0.5Cu Solder and Ni–P under Bump Metallurgy

Abstract

The interfacial microstructure of Sn-3.0Ag-0.5Cu solder with ENIG (electroless Ni/immersion Au) UBM was studied using scanning electron microscopy and transmission electron microscopy. (Cu,Ni) 6 Sn 5 intermetallic compound layer was formed at the interface between the solder and Ni-P under bump metallization upon reflow. However, after isothermal aging, some AuSn 4 but with a certain amount of Ni dissolved in it, i.e., (Au,Ni)Sn 4 , appeared above the (Cu,Ni) 6 Sn 5 layer. Two distinctive layers, P-rich and Ni-Sn-P, were additionally found from the TEM observation. The analytical studies using EDS equipped in TEM revealed that the averaged composition of the P-rich layer was close to that of a mixture of Ni 3 P and Ni, while that of the Ni-Sn-P layer was analogous to the P-rich layer containing a small amount of Sn in it. The thickness of the (Cu,Ni) 6 Sn 5 layer increased with increasing aging time and temperature. The layer growth of the intermetallic compound satisfied a parabolic law in the given temperature range. The increase of the intermetallic compound layer thickness was mainly controlled by a diffusion mechanism in the temperature range studied, because the values of time exponent (n) were approximately equal to 0.5. The apparent activation energy for the growth of (Cu,Ni) 6 Sn 5 intermetallic compound layer was 55 kJ/mol.

Microstructure and Mechanical Properties of Sn–0.7Cu Flip Chip Solder Bumps Using Stencil Printing Method

“…14) Considering all these data, this ternary phase is believed to be Ni 3 SnP compound. It is noted that this layer was also found in the study about the interfacial reaction between the Sn-Ag-Cu/electroless Ni-P. 20) This means that the Ag element addition to the Sn-Cu solder has not significant influence on the interfacial reactions between solder and Ni-P layer. Figure 4 shows the variations of the IMC layer thickness as a function of square root of aging time for different aging temperatures.…”

“…This was already shown in our previous study concerning the interfacial reaction of Sn-Ag-Cu/Ni-P combination. 20) Huang and Suganuma also reported that the P-rich layer was consisted of Ni 3 P and Ni in the Sn-3.5Ag and Ni-P UBM system with their selected area diffraction (SAD) pattern studies. 14) From our TEM-EDS analyses, the averaged composition of the layer is more close to that of mixture of the Ni 3 P and Ni than that of pure Ni 3 P compound.…”

“…This behavior is very general, and previously reported by others numerously. 17,[20][21][22] In Fig. 4, it can be also seen that the growth of intermetallic compounds followed a parabolic law, implying that the growth of the intermetallic layer is diffusion controlled.…”

Optimal phosphorous content selection for the soldering reaction of Ni-P under bump metallization with Sn-Ag-Cu solder

“…However, a Ni-Sn-P phase formed between IMCs and Ni-P UBM causes IMCs to be spalled into the solder matrix, resulting in a reliability concern. [14][15][16][17][18][19][20][21][22] More recently, the detailed formation configuration for Ni x P y layers and Ni-Sn-P in the Sn-Ag-Cu/Ni-P UBM solder joint was intensively investigated with a newly developed field emission electron probe microanalyzer. 22 It is argued that the formation of Ni-Sn-P is significantly dependent on the phosphorous content of Ni-P UBM.…”

Characterization of Failure Behaviors in Anisotropic Conductive Interconnection

“…Two recent European Union directives, RoHS (Restriction of the use of certain Hazardous Substances) and WEEE (Waste Electrical and Electronic Equipment), require new electrical and electronic equipment produced after July 1, 2006 to be Pb-free. 3,4) In response to these legislations, most major electronic manufacturers have stepped up their search for alternatives to the Sn-37Pb solder.…”