BS IEC 62047-31:2019 pdf download – Semiconductor devices – Micro- electromechanical devices Part 31: Four-point bending test method for interfacial adhesion energy of layered MEMS materials.
1 Scope This part of IEC 62047 specifies a four-point bending test method for measuring interfacial adhesion energy of the weakest interface in the layered micro-electromechanical systems (MEMS) based on the concept of fracture mechanics. In a variety of MEMS devices, there are many layered material interfaces, and their adhesion energies are critical to the reliability of the MEMS devices. The four-point bending test utilizes a pure bending moment applied to a test piece of layered MEMS device, and the interfacial adhesion energy is measured from the critical bending moment for the steady state cracking in the weakest interface. This test method applies to MEMS devices with thin film layers deposited on semiconductor substrates. The total thickness of the thin film layers should be 100 times less than the thickness of a supporting substrate (typically a silicon wafer piece). 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. There are no normative references in this document.
5.2 Test machine The test machine is a universal testing machine with a compressive loadcell, a servomotor, a linear guide, and a displacement sensor. Using a four-point bending fixture as shown in Figure 2, a pure bending moment is applied to a test piece with layered materials. The diameter of the loading pins should be larger than the thickness of the test piece and five times less than the length of the test piece. The load and the displacement shall be measured using a loadcell and displacement sensors installed on the universal testing machine during the test. The resolution of the loadcell shall be less than 1/100 of the critical load for interface cracking, and the resolution of the displacement sensor shall be less than 1/100 of the maximum stroke during the test. The loading speed shall be chosen in a range from 0,000 1 mm/s to 0,1 mm/s for steady state interfacial cracking without any inertial effect. The behaviour of crack extension shall be recorded at a speed larger than 10 Hz using a camera with a microscope objective of 20x or more. 5.3 Test procedure The test procedure is as follows: a) Install a test piece on the four-point bending fixture of the test machine. The longitudinal direction of the test piece shall be aligned with the longitudinal direction of the fixture, and the deviation angle shall be less than 1 °. b) Apply a bending moment to the test piece to initiate a crack from the machined pre-crack or notch. This is for introduction of an interface crack at the weakest interface, and the application of bending moment shall be controlled by a displacement of the test machine. When the crack starts to extend, the actuator of the test machine shall be stopped to prevent the test piece from complete delamination. When the interface is brittle, and the adhesion energy is low, the test piece is susceptible to complete delamination after initiation of the crack at the machined pre-crack. W
5.4 Test environment Because mechanical properties are temperature sensitive, fluctuations in temperature during the test shall be controlled to be less than ±2 Certain polymeric materials can be sensitive to humidity; thus, the change in relative humidity (RH) in the testing laboratory shall be controlled to be less than ±5 % RH for such materialsu. 6 Test report The test report shall contain the following information: a) reference to this document; b) test piece identification number; c) test piece preparation procedures; d) test piece dimensions; e) constituent materials and their fabrication methods; f) description of the test machine and four-point bending fixture; g) measured results and properties: applied bending moment versus displacement, critical energy release rate, crack extension behaviour.