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<p>In this study, the mechanical properties and stress–strain constitutive relations of electroless and electroplated Ni layers are investigated and their influence on Si chip warpage in Si/Sn58Bi/FR4 structure specimens are examined via nanoindentation testing, finite element inverse analysis, tensile testing, microstructural characterization, warpage testing, and finite element simulation. The results demonstrate that the elastic modulus of electroless Ni is 152.975&#xa0;GPa, which is 31.75% lower than that of electroplated Ni. This reduction can be attributed to the increased atomic spacing in amorphous structures, which weakens atomic bonding, and to the greater ease of local atomic rearrangement in such structures. However, the yield strength of electroless Ni is considerably higher than that of electroplated Ni owing to the solid-solution strengthening effect of the P atoms. Warpage measurements demonstrate that the room-temperature initial warpage of the electroless Ni Si/Sn58Bi/FR4 structure specimens before the reliability testing of the Si chip, is 25.1–2.7&#xa0;μm higher than that of the electroplated Ni specimens. This enhancement indicates the considerable influence of the Ni layer type on Si chip warpage. During high-temperature storage and thermal cycling (TC) reliability processes, the warpage of the Si chip exhibits power-law-type and exponential-type decreases, respectively, with TC causing more pronounced warpage reductions. The warpage simulation results of the Si/Sn58Bi/FR4 finite element (FE) model, based on the mechanical properties and constitutive equations of the two Ni layers, are in excellent agreement with the experimental results. Furthermore, this study found that using the mechanical properties of electroplated or bulk Ni for the electroless Ni layer in FE simulations could lead to inaccurate warpage predictions, compromising reliability assessments.</p>

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Comparative analysis of mechanical behavior between electroless and electroplated Ni layers and their influence on Si chip warpage

  • 期刊论文

  • 发表日期：

    2025年7月25日

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  • Hongbo Qin,
  • Shaohao Zhu,
  • Jian Huang,
  • Quanzheng Tan,
  • Jizhan Lin,
  • Lili Wang,
  • Guolin Lin,
  • Caihang Liang,
  • Jiaqiang Huang

摘要

In this study, the mechanical properties and stress–strain constitutive relations of electroless and electroplated Ni layers are investigated and their influence on Si chip warpage in Si/Sn58Bi/FR4 structure specimens are examined via nanoindentation testing, finite element inverse analysis, tensile testing, microstructural characterization, warpage testing, and finite element simulation. The results demonstrate that the elastic modulus of electroless Ni is 152.975 GPa, which is 31.75% lower than that of electroplated Ni. This reduction can be attributed to the increased atomic spacing in amorphous structures, which weakens atomic bonding, and to the greater ease of local atomic rearrangement in such structures. However, the yield strength of electroless Ni is considerably higher than that of electroplated Ni owing to the solid-solution strengthening effect of the P atoms. Warpage measurements demonstrate that the room-temperature initial warpage of the electroless Ni Si/Sn58Bi/FR4 structure specimens before the reliability testing of the Si chip, is 25.1–2.7 μm higher than that of the electroplated Ni specimens. This enhancement indicates the considerable influence of the Ni layer type on Si chip warpage. During high-temperature storage and thermal cycling (TC) reliability processes, the warpage of the Si chip exhibits power-law-type and exponential-type decreases, respectively, with TC causing more pronounced warpage reductions. The warpage simulation results of the Si/Sn58Bi/FR4 finite element (FE) model, based on the mechanical properties and constitutive equations of the two Ni layers, are in excellent agreement with the experimental results. Furthermore, this study found that using the mechanical properties of electroplated or bulk Ni for the electroless Ni layer in FE simulations could lead to inaccurate warpage predictions, compromising reliability assessments.