Electromigration of Sn–37Pb and Sn–3Ag–1.5Cu/Sn–3Ag–0.5Cu composite flip–chip solder bumps with Ti/Ni(V)/Cu under bump metallurgy

Self Cite

The Cu pillar is a thick underbump metallurgy (UBM) structure developed to alleviate current crowding in a flip-chip solder joint under operating conditions. We present in this work an examination of the electromigration reliability and morphologies of Cu pillar flip-chip solder joints formed by joining Ti/Cu/Ni UBM with largely elongated $62 lm Cu onto Cu substrate pad metallization using the Sn-3Ag-0.5Cu solder alloy. Three test conditions that controlled average current densities in solder joints and ambient temperatures were considered: 10 kA/cm 2 at 150°C, 10 kA/cm 2 at 160°C, and 15 kA/cm 2 at 125°C. Electromigration reliability of this particular solder joint turns out to be greatly enhanced compared to a conventional solder joint with a thinfilm-stack UBM. Cross-sectional examinations of solder joints upon failure indicate that cracks formed in (Cu,Ni) 6 Sn 5 or Cu 6 Sn 5 intermetallic compounds (IMCs) near the cathode side of the solder joint. Moreover, the $52-lm-thick Sn-Ag-Cu solder after long-term current stressing has turned into a combination of $80% Cu-Ni-Sn IMC and $20% Sn-rich phases, which appeared in the form of large aggregates that in general were distributed on the cathode side of the solder joint.

Section: Electromigration Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electromigration Reliability and Morphologies of Cu Pillar Flip-Chip Solder Joints with Cu Substrate Pad Metallization

Lai

Chiu

Chen

2008

Self Cite

“…[9][10][11][12][13][14][15][16][17] The interfacial reactions between Ni-V alloys and Sn-based solders have also been investigated by many research groups. [18][19][20][21][22] …”

Section: Introductionmentioning

confidence: 99%

Transmission Electron Microscopy Characterization of Ni(V) Metallization Stressed Under High Current Density in Flip Chip Solder Joints

Tsai

Lin

et al. 2010

The Ni(V) under bump metallization (UBM) in flip chip solder joints is known to be consumed in a two-stage process during current stressing. The Ni(V) UBM transforms first to the ''consumed Ni(V)'' state. Then, this consumed Ni(V) transforms to a so-called porous structure. In this study, the details of the consumed Ni(V) and the porous structure were analyzed by transmission electron microscopy. Bright-field images showed that the consumed Ni(V) was a continuous layer without columnar structures and that the porous structure had many voids in the matrix. The compositional analyses showed that V atoms were immobile and trapped in the original Ni(V) layer. Cu and Sn atoms diffused into the original Ni(V) layer, and Ni atoms diffused outward. Selected-area diffraction patterns and high-resolution transmission electron microscopy of the porous structure showed that it was composed of an amorphous matrix with fine crystalline Cu 6 Sn 5 and VSn 2 phases.

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] BasaranÕs group studied stress and deformation in solder joints under high current stressing. [21][22][23][24][25][26] This study examined thermomechanical stress and strain in the different solder joints during steady-state electromigration.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical Stress and Strain in Solder Joints During Electromigration

Zhang

et al. 2009

Thermomechanical stress and strain in the solder joints of a dummy area array package were studied as electromigration occurred. A current density of 0.4 9 10 4 A/cm 2 was applied to this package, constructed with 9 9 9 solder joints in a daisy chain, to perform the electromigration test. After 37 h, the first joint on the path of the electron flow broke off at the cathode, and the first three solder joints all exhibited a typical accumulation of intermetallic compounds at the anode. Different solder joints exhibited dissimilar electromigration states, such as steady state and nonsteady state. Finite element analysis indicated that during steady-state electromigration, although the symmetrical structure produced uniform distributions of current density and Joule heating in all solder joints, the distribution of temperature was nonuniform. This was due to the imbalanced heat dissipation, which in turn affected the distribution of thermomechanical stress and strain in the solder joints. The maximum thermomechanical stress and strain, as well the highest temperature and current crowding, appeared in the Ni/Cu layer of each joint. The strain in the Ni/Cu layer was significant along the z-axis, but was constrained in the x-y plane. The thermomechanical stress and strain increased with advancing electromigration; thus, a potential delamination between the Ni/Cu layer and the printed circuit board could occur.