Magnetic-Based Interfacial Adhesion Measurement Technique with Environmental Conditions

Abstract

This paper presents the experimental results of the continued development of a magnetically actuated interfacial adhesion measurement technique. Beneficial characteristics of the technique are that it is fixtureless, can be incorporated in an environmental chamber, can test a range of mode mixities, and has the ability to perform monotonic and cyclic loading.A common mode of failure in electronic packages is interfacial fracture that occurs between layers of dissimilar materials. These failures can appear during assembly, reliability testing, and normal operating conditions and are also influenced by environmental conditions such as temperature and humidity. In order to prevent interfacial fracture, is it necessary to have methods to measure and characterize the interfacial mechanical parameters subjected to various environmental conditions that can be subsequently utilized in finite-element models of electronic packages. But as the dimensions of electronic packages have continued to decrease, these mechanical parameters have become more difficult to measure with traditional techniques due to the need for small sample fixtures to hold samples and to apply loads during testing. In this paper, the experimental results from the continued development of a magnetically actuated test method used to assess the reliability of material interfaces of electronic packages such as Backend of Line (BEOL) layers and metallization layers are presented. This method uses magnetic forces to apply external forces to the electronic package and cause mechanical failure at the interface using either monotonic or fatigue loading. This is achieved by attaching a small-scale permanent magnet to the electronic package’s features that are to be tested and then subjecting the magnet to an external electromagnetic field. The force applied to the test sample is controlled by the voltage of an external electromagnet and the separation distance between the electromagnet and the permanent magnet attached to the sample. During the magnetically actuated tests, a maximum force of 4.3 N was achieved for the specific permanent and electromagnet utilized. Monotonic testing was performed by increasing the voltage of the electromagnet or deceasing the separation distance until mechanical failure of the sample was observed, while fatigue loading was created by cycling the electromagnetic field below the monotonic failure threshold of the material interface. These tests were conducted on a range of material interfaces including copper, epoxy, and dielectrics with measured maximum loads of 3.5-3.7 N at failure during monotonic tests and additional fatigue tests with mechanical failure occurring at ~785 cycles. An additional advantage of the electromagnetic actuation approach of this test method is its ability to be easily incorporated into an environmental chamber during testing. Experiments investigating the effect of temperature and humidity on the mechanical reliability of relevant material interfaces of commercially available chips using this test method are presented and discussed.