Interfacial reactions and shear strengths between Sn-Ag-based Pb-free solder balls and Au/EN/Cu metallization

Abstract

The morphological and compositional evolutions of intermetallic compounds (IMCs) formed at three Pb-free solder/electroless Ni-P interface were investigated with respect to the solder compositions and reflow times. The three Pb-free solder alloys were Sn3.5Ag, Sn3.5Ag0.75Cu, and Sn3Ag6Bi2In (in wt.%). After reflow reaction, three distinctive layers, Ni 3 Sn 4 (or Ni-Cu-Sn for Sn3.5Ag0.75Cu solder), NiSnP, and Ni 3 P, were formed on the electroless Ni-P layer in all the solder alloys. For the Sn3.5Ag0.75Cu solder, with increasing reflow time, the interfacial intermetallics switched from (Cu,Ni) 6 Sn 5 to (Cu,Ni) 6 Sn 5 ϩ (Ni,Cu) 3 Sn 4 , and then to (Ni,Cu) 3 Sn 4 IMCs. The degree of IMC spalling for the Sn3.5Ag0.75Cu solder joint was more than that of other solders. In the cases of the Sn3.5Ag and Sn3Ag6Bi2In solder joints, the growth rate of the Ni 3 P layer was similar because these two type solder joints had a similar interfacial reaction. On the other hand, for the Sn3.5Ag0.75Cu solder, the thickness of the Ni 3 P and Ni-Sn-P layers depended on the degree of IMC spalling. Also, the shear strength showed various characteristics depending on the solder alloys and reflow times. The fractures mainly occurred at the interfaces of Ni 3 Sn 4 /Ni-Sn-P and solder/Ni 3 Sn 4 .

Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

“…8 Up to now, there have been an umber of studies concerning the solid/liquid interfacial reactions during the reflow soldering process. [9][10][11][12][13][14][15] However, the interfacial IMCs continue to grow at aslow rate during field use and under load conditions in hightemperature environments. The solid/solid interfacial reactions are less understood.…”

Detailed Phase Evolution of a Phosphorous-Rich Layer and Formation of the Ni-Sn-P Compound in Sn-Ag-Cu/Electroplated Ni-P Solder Joints

“…It was revealed that the Ni-Sn-P layer between the solder and P-rich layer caused the spalling of (Ni,Cu) 3 Sn 4 . 12,13,21,22 With the aid of a newly developed FE-EPMA, which exhibits current around one to two orders of magnitude higher than conventional FESEM, better contrast in the BEI image could be provided with superior resolution for quantitatively analyzing the compositions of various phases, as compared with conventional EPMA. Figure 1c and d shows images corresponding to Fig.…”

“…12 Kim et al reported that, with increasing reflow time, more IMCs were spalled into the solder with the Ni-P UBM. 13 It was verified that the spalling phenomena was the result of Ni-Sn-P layer formation between the IMC and the Ni-P metallization. [12][13][14][15][16][17] However, limited data have been reported concerning the formation mechanism of the Ni-Sn-P layer.…”

“…13 It was verified that the spalling phenomena was the result of Ni-Sn-P layer formation between the IMC and the Ni-P metallization. [12][13][14][15][16][17] However, limited data have been reported concerning the formation mechanism of the Ni-Sn-P layer. In this study, the formation of the Ni-Sn-P phase was systematically evaluated, and a description of the corresponding mechanism was proposed.…”

“…IMC spalling, which seriously affects solder joint reliability, was found in the Ni-P metallization. [11][12][13][14] Sohn et al demonstrated the increase of IMC spalling with P content in the Ni-P UBM. 12 Kim et al reported that, with increasing reflow time, more IMCs were spalled into the solder with the Ni-P UBM.…”