High cycle fatigue testing of thermosonic ball bonds

• Autores: A. Lassnig, M. Lederer, G. Khatibi, R. Pelzer, W. Robl, M. Nelhiebel
• Localización: Microelectronics reliability, ISSN 0026-2714, Nº. 71, 2017, págs. 91-98
• Idioma: inglés
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• Resumen

  • Abstract During operation, miniaturized thermosonic Cu ball bond interconnects on Al pads occurring in microelectronic devices experience thermomechanical cyclic stresses, which lead to a degradation and subsequent fatigue fracture at the bond interface. Standard static tests, however, ignore the performance of such bonds under cyclic loads. Therefore, a new mechanical fatigue testing method tailored for such interconnects has been introduced, allowing to study their high cycle fatigue behavior in reasonable time. By means of a vibrating system and a special specimen setup cyclic stresses are mechanically induced at the bond interface causing fatigue lift off, where the bond is separated at its weakest site. For this purpose, two distinct specimen preparation methods basing on industrially applicable soldering techniques are suggested and can be used equally, depending on the focus of the investigation and the availability of the required testing structures. The first method - “single bond testing” - allows to test each bond individually regardless of the chip layout. In contrast, the second test method - “multiple bond testing” - allows to test several bonds simultaneously. To interpret and analyze the stresses occurring at the bond interface during these tests, finite element analyses were conducted. In the present study both methods are applied to CuAl ball bonds of the same quality and chip layout. It is shown that the aluminum is responsible for the fatigue crack initiation and propagation processes as confirmed by fractographic analyses of the fatigued bond interfaces. It can be concluded that the proposed fatigue test method is a powerful alternative screening method for such miniaturized bond interfaces, which allows to reveal their mechanical fatigue behavior in reasonable time and to identify the weakest link of the tested bond interface.