Non-destructive degradation study of copper wire bond for its temperature cycling reliability evaluation

• A non-destructive electrical measurement method for degradation monitoring of bonded copper wires under temperature cycling
• Degradation is significant after 700 temperature cycles.
• Correlation exists between non-destructive electrical method and conventional mechanical wire pull test method.
• Differences in wire loop configuration and failure region influence pull test results.
• Wire pull test is less sensitive as compared to the non-destructive electrical method in detecting wire degradation.

Wire bonding is essential for the electrical connection of integrated circuit (IC) devices, therefore its quality and reliability is of utmost importance. During the wire bonding process, several parameters need to be well controlled in order to achieve a well bonded wire. Furthermore, the migration to copper (Cu) wire from gold (Au) due to its high cost has resulted in an even more stringent and narrow process window. Current industrial practices to evaluate wire bond quality after the assembly and packaging process are either done destructively which may result in loss of critical information, or non-destructively which are limited by resolution, cost and time. In this work, the quality of copper wire bond is being evaluated by electrical means that is non-destructive, fast and accurate. This makes it suitable for use in the production line for wire bond quality evaluation. Experimental results showed that there is a good correlation with conventional wire assessment methods. Furthermore the electrical method is sensitive enough to pick out degraded wires that conventional methods are unable to identify.