Mechanical and Electrical Properties of Cu/Sn-3.5Ag/Cu Ball Grid Array (BGA) Solder Joints after Multiple Reflows

The in situ intermetallic compound (IMC) growth in Cu pillar/Sn bumps was investigated by isothermal annealing at 120°C, 150°C, and 180°C using an in situ scanning electron microscope. Only the Cu 6 Sn 5 phase formed at the interface between the Cu pillar and Sn during the reflow process. The Cu 3 Sn phase formed and grew at the interfaces between the Cu pillar and Cu 6 Sn 5 with increased annealing time. Total (Cu 6 Sn 5 + Cu 3 Sn) IMC thickness increased linearly with the square root of annealing time. The growth slopes of total IMC decreased after 240 h at 150°C and 60 h at 180°C, due to the fact that the Cu 6 Sn 5 phase transforms to the Cu 3 Sn phase when all of the remaining Sn phase in the Cu pillar bump is completely exhausted. The complete consumption time of the Sn phase at 180°C was shorter than that at 150°C. The apparent activation energy for total IMC growth was determined to be 0.57 eV.

Section: Resultsmentioning

confidence: 99%

Temperature Effect on Intermetallic Compound Growth Kinetics of Cu Pillar/Sn Bumps

Lim

Kim

Lee³

et al. 2009

“…This type of spalling occurs by transformation from a hemispherical to a more spherical type of particle, driven by lowering of the total surface and interfacial energies in conservative ripening. 4,5,[23][24][25] After 1000 h of storage the Sn-Ag-0.5Zn/Cu system showed significant spalling at the interface, marked by arrows in Fig. 4a.…”

Section: Effect Of Solder Alloy Composition On Melting and Solidificamentioning

confidence: 99%

Reactions of Sn-3.5Ag-Based Solders Containing Zn and Al Additions on Cu and Ni(P) Substrates

Kotadia

Mokhtari

Bottrill

et al. 2010

In this study we consider the effect of separately adding 0.5 wt.% to 1.5 wt.% Zn or 0.5 wt.% to 2 wt.% Al to the eutectic Sn-3.5Ag lead-free solder alloy to limit intermetallic compound (IMC) growth between a limited volume of solder and the contact metallization. The resultant solder joint microstructure after reflow and high-temperature storage at 150°C for up to 1000 h was investigated. Experimental results confirmed that the addition of 1.0 wt.% to 1.5 wt.% Zn leads to the formation of Cu-Zn on the Cu substrate, followed by massive spalling of the Cu-Zn IMC from the Cu substrate. Growth of the Cu 6 Sn 5 IMC layer is significantly suppressed. The addition of 0.5 wt.% Zn does not result in the formation of a Cu-Zn layer. On Ni substrates, the Zn segregates to the Ni 3 Sn 4 IMC layer and suppresses its growth. The addition of Al to Sn-3.5Ag solder results in the formation of Al-Cu IMC particles in the solder matrix when reflowed on the Cu substrate, while on Ni substrates Al-Ni IMCs spall into the solder matrix. The formation of a continuous barrier layer in the presence of Al and Zn, as reported when using solder baths, is not observed because of the limited solder volumes used, which are more typical of reflow soldering.

“…7,8 This requirement would cause damage to other devices on the chip or to polymer materials that are sensitive to heat when the device is treated to temperatures of 400°C to 450°C. 6,9 Thus, the Cu-Cu thermocompression bonding process should be accomplished at low temperatures (below 400°C). Several studies on Cu-Cu thermocompression bonding have been reported, varying bonding process parameters such as the Cu surface quality, bonding temperature, applied pressure, and postannealing conditions.…”

Section: Introductionmentioning

confidence: 99%

Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

Jang

Hyun

Lee

et al. 2009

Quantitative analysis of the interfacial adhesion energy of Cu-Cu thermocompression bonds was performed using the four-point bending method with various wet pretreatment conditions. The evaluated interfacial adhesion energies for 1-lm-thick Cu bonding layers were 0.29 J/m 2 , 1.28 J/m 2 , 1.64 J/m 2 , 1.17 J/m 2 , and 0.43 J/m 2 for different acetic acid pretreatment times of 0 min, 1 min, 5 min, 10 min, and 15 min, respectively. There exists an optimum wet etch time for maximum adhesion strength. The change of surface properties with increasing wet etch time was believed to result in the variation of the interfacial adhesion energy. The decrease in interfacial adhesion energy after 5 min seems to result from a decrease in the plastic dissipation energy during interfacial crack propagation with thinner Cu film thickness caused by overetching.