Stud bumping using a traditional wire bonding process followed by the severing of the wire material from the ball bond has been widely applied in flip chip packages. Traditionally, Au stud bumps were employed because of the physical properties of gold, but the mediocre reliability of Au with Al pads and the cost of gold make this material unfavorable for industrial needs. Copper stud bumps were also considered, but the intrinsic features of Cu, such as its high hardness and ease of oxidation, present no advantages over gold stud bumps. However, Ag-alloy stud bumps exhibit satisfactory bondability and have been proposed as the optimal substitute for Au stud bumps to ensure better reliability in soldering and better intermetallic growth kinetics with Al bond pads. In this article, the intermetallic growth of Ag stud bumps alloyed with 2%, 10%, and 12% Pd after high-temperature storage tests (HTSTs) is investigated. The results indicated that the Pd atoms remained immobile in the bump-side matrix without diffusing into the aluminum pad side. Alloying with higher Pd content enhanced the formation of the favorable Ag ₂ Al intermetallic compound (IMC), whereas lower Pd content resulted in severe cracking due to the formation of Ag ₃ Al IMC. Compositional analysis showed that continuous layers of Ag–Al IMCs doped with large amounts of Pd formed at the interfaces close to the Ag stud bumps, but no Pd was detected on the Al pad side. The bonding strength increased after aging at 150 °C and 200 °C for 200 h, but it decayed drastically after aging at 250 °C for 200 h. The relationship between intermetallic growth and failure mode was established.

中文翻译：

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Ag-Pd合金凸块凸点与Al垫界面处的金属间化合物

使用传统的引线键合工艺进行的柱形凸点焊，然后将球材料从球形键合中切断，已广泛应用于倒装芯片封装中。传统上，由于金的物理特性而使用Au柱形凸块，但是带有Al垫的Au的中等可靠性以及金的成本使这种材料不适用于工业需求。还考虑了铜柱形凸块，但是Cu的固有特征（例如，高硬度和易氧化性）与金柱形凸块相比没有优势。但是，银合金凸块具有令人满意的粘结性，并已被提议作为金凸块的最佳替代品，以确保焊接时的可靠性更高，并且与Al焊盘的金属间生长动力学也更好。在本文中，Ag柱形凸点的金属间生长与2％，10％，研究了高温储存测试（HTST）之后的12％Pd。结果表明，Pd原子在凸块侧基体中保持不动，而没有扩散到铝焊盘侧。高Pd含量的合金化促进了有利Ag的形成 ₂ Al金属间化合物（IMC），而较低的Pd含量则由于形成了Ag ₃ Al IMC而导致严重的开裂 。成分分析表明，连续的Ag-Al IMC层掺杂有大量的Pd，形成在靠近Ag柱形凸点的界面上，但在Al焊盘侧未检测到Pd。在150°C和200°C老化200 h后，粘结强度增加，但在250°C老化200 h后，粘结强度急剧下降。建立了金属间生长与破坏模式之间的关系。