Transmission Electron Microscopy of Interfaces in Joints between Pb-Free Solders and Electroless Ni-P

Abstract

Microstructures of joints between a Ni-8 mass%P UBM (under bump metallization) and three different Pb-free solders, i.e., Sn-Ag, SnAg-Cu and Sn-Ag-Cu-Bi were studied by transmission electron microscopy. The phases formed near the joint interfaces as well as inside the solders during soldering were identified on the basis of electron diffraction and EDX analysis without ambiguity. In the Ni-P under bump metallization near the interface with the solders, P-denuded Ni-20 mass%P layer was observed, where a high density of columnar voids were formed. Also, in Ni(Cu) SnP intermetallic, which is adjacent to the P-denuded Ni-20 mass%P, a high density of spherical voids were observed. These voids degrade the joint strength. Change of the above microstructures during thermal cycling between 253 K and 453 K was also observed.

Characterization of Interfacial Reaction Layers Formed Between Sn-3.5Ag Solder and Electroless Ni-Immersion Au-Plated Cu Substrates

“…[15][16][17][18][19][20] Hwang et al examined the interfacial reaction between the Sn-3.5Ag solder and Au (0.06 lm)/ Ni-6wt.%P (5 lm) plated layer at a reflow temperature of 230°C for 40 s and reported that Ni 3 SnP formed on top of the Ni 3 P layer in Sn-3.5Ag/Ni-P joints. 20 Lin and Duh reported the transformation of Ni 2 P-Ni 2 SnP as a result of the in-diffusion of Sn.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Of the many different solder alloys that have been proposed as potential Pb-free solders, the alloy families of Sn-Ag and Sn-Ag-Cu have shown the greatest promise. 4,11 In addition to solder, printed circuit boards (PCBs) and component surface finishes also need to be Pb-free.…”

“…11 Therefore, many studies have examined the interfacial reaction of SnAg/ENIG. 17,20,22 Various analysis techniques, such as scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), and transmission electron microscopy (TEM), have been used to examine interfacial reaction. Of these, TEM equipped with analytical attachments offers the most complete tool for characterizing the formation of these additional layers.…”

Mechanical and electronic properties of Ag3Sn intermetallic compound in lead free solders using ab initio atomistic calculation

“…HCl for 24-48 h with intermittent cleansing in detergent solution in ultrasonic cleaning environment and a large number of small crystals are freed from ingot in this manner. Torazawa et al [51] using transmission electron microscopy (TEM) study confirmed the crystal structure of Ag 3 Sn as Pmmn (59) without ambiguity. The crystal structure of Ag 3 Sn is shown in Fig.…”

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.…”