Investigation of durability of TSV interconnect by numerical thermal fatigue analysis

Abstract

3D packaging using through silicon via (TSV) technology is becoming important in IC packaging industry. However, increased number of interconnects and extreme miniaturization suggest that thermo-mechanical reliability and fatigue will aggravate. In traditional package, thermo-mechanical fatigue failure mostly occurs as a result of damage in the solder joint. In TSV technology, however, the driving failure may be the TSV via or TSV interconnects. In this study, the durability of TSV technology is investigated using finite element method. Thermal fatigue phenomenon due to the plastic strain caused by repetitive temperature cycling is analyzed, and possible failure locations are discussed. In particular, the effects of via size, underfill material, and via filling material on the thermal fatigue reliability are investigated. The expected fatigue life indicates that the presence of underfill material is essential in improving the durability of the TSV structure. The plastic strain increases with the via size increases, therefore the thermal fatigue life increases as the via size decreases. For different via filling materials such as copper, nickel and tungsten, amount of plastic strain is very similar, suggesting that nickel could be used for via filling material. However, the locations of the maximum strain are different for each filling material.

Microvia Filling with Nickel-Tungsten Alloy to Decrease the Coefficient of Thermal Expansion of Electronic Circuit Interconnections

“…2d, 2e. The high CTE of the filled copper (i.e., 17 × 10 14,15,18 led to copper protrusion on the TSV due to copper atom movement. On the basis of mass balance, several copper cracks and voids (i.e., copper vacancies) remained in the TSV because the copper atoms thermally moved and got out the TSV, [18][19][20][21][22] as confirmed in Fig.…”

“…18,19 The copper protrusion on the TSV caused respectively by thermal expansion and diffusion of copper lattices and atoms may destroy stacked IC chips. [20][21][22] Copper must be replaced by tungsten 23 or nickel 24,25 to overcome the issue of CTE mismatch.Although the CTE of tungsten is very low, 14,26 it cannot be electrochemically plated in an aqueous electrolyte. Fortunately, tungsten can be induced to co-deposit with nickel.…”

“…[14][15][16][17] Copper atoms diffuse from the TSV due to thermal cycling, leading to void formation in the TSV. 18,19 The copper protrusion on the TSV caused respectively by thermal expansion and diffusion of copper lattices and atoms may destroy stacked IC chips.…”

“…Although the CTE of tungsten is very low, 14,26 it cannot be electrochemically plated in an aqueous electrolyte. Fortunately, tungsten can be induced to co-deposit with nickel.…”

Evaluation of sensitivity and linearity for touch-mode capacitive pressure sensor measuring the inner bladder pressure

“…Diaphragm made from bulk silicon has elastic modulus of 130 GPa and Poisson's ratio of 0.3 (Table 1). 10 Finite element modeling is made after the selection of three design variables: size of square diaphragm, diaphragm's thickness, and gap distance between diaphragm and insulator (Fig. 1).…”