Abstract
The interfacial reactions and shear strength of joints between Sn–9Zn solder and two different kinds of BGA (ball-grid-array) substrates (Cu and Au/Ni–P/Cu) were investigated for reflow conditions of 230 °C up to 60 min. For the Cu substrate, only Cu 5Zn 8 intermetallic compound was observed and other Cu–Sn IMCs were not observed. For the Au/Ni/Cu substrate, an AuZn 3 IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, some of the AuZn 3 IMC layer was detached from the interface after reflow. The thickness of the AuZn 3 layer did not change with reflow time because the Au was consumed during the initial reflow process. After being reflowed for 60 min, a Ni 5Zn 21 IMC formed between AuZn 3 IMC and Ni substrate. Also, many voids existed inside the upper AuZn 3 IMC layer. Ball shear tests for the Cu substrate showed the shear strength significantly decreased after reflow for 60 min. A Cu 5Zn 8 IMC was also observed on the fracture surface. For the Au/Ni/Cu substrate, the shear strength value did not change much as a function of reflow time and fractures occurred within the solder.
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