BS IEC 62951‑4:2019 pdf download – Semiconductor devices – Flexible and stretchable semiconductor devices Part 4: Fatigue evaluation for flexible conductive thin film on the substrate for flexible semiconductor devices.
4.2 Preparation of a test piece The test piece shall be prepared using the same fabrication process as the real device fabricated for flexible electronics and flexible semiconductor devices, because the mechanical and electrical properties depend on the fabrication processes. Thin conductive film shall be carefully prepared to prevent formation of cracks or flaws and delamination from the substrate. 4.3 Measurement of dimensions The thickness and width of the conductive thin film and flexible substrate shall be accurately measured respectively, because the dimensions are used to determine the mechanical and electrical properties of test materials. Each test piece should be measured directly. Both the thickness and width of the test piece shall be specified within the maximum error of ± 1 % for the thickness and ± 5% for the width. Thickness measurement shall be performed according to Clause 4 and Annex C of IEC 62047-2:2006. There can be some combinations of thin film and substrate where it is difficult to fulfil the tolerance of thickness measurement. In this case the average and the standard deviation of the thickness measurement should be reported. 4.4 Storage prior to testing Care should be taken on the storage environment, because for thin films and flexible substrates there is a great risk to affect the electromechanical properties of the film by the storage environment. For example, oxidation on the test piece surface will deteriorate the electrical and mechanical properties of the test piece. If there is a longer duration between final preparation and testing, particular care should be taken in storing the test pieces, and the specimens should be examined by appropriate means to ensure that the surface has not deteriorated during the storage period. If any deterioration is observed that was not present after the specimens were prepared, testing shall not be performed.
5 Testing method and test apparatus 5.1 General The test is performed by bending a test piece. The bending strain induced by the tensile or compressive load shall be uniform in a pre-defined gauge section in the elastic region of the substrate and the thin film. To measure the change in electrical resistance along with the change in mechanical strain, carefully select the gauge section. The gauge section for measuring mechanical strain shall be coincident with or scalable to that for measuring electrical resistance. 5.2 Test apparatus The cyclic bending test equipment includes the clamp to hold a bending test sample, the moving part to shuttle, and control system which regulates cyclic bending number, moving distance, and moving speed while testing. Specimen should be securely clamped with gripping part during the test. Several cyclic bending test equipments are available and described in Annex A. It is not necessary that a certain type of bending test equipment be preferred. During the test, however, the test apparatus shall not cause any unintended damage to the test piece such as scratches and other defects. 5.3 Method of gripping It is recommended that the test piece be tightly clamped. However, this should be carefully done in order to prevent local stress concentration in the clamped region.
5.6 Static bending fatigue test This test is to provide a standard procedure for determining the bending fatigue properties of flexible semiconductor devices to withstand the same strain for a certain period of time. Each specimen is bent at fixed bending radius for a certain period of time. There are several types of bending test equipments to measure the static bending fatigue property of the semiconductor device. It is not necessary that a certain type of bending test method be preferred. Mandrel or round bar with a certain radius can be used. In order to make sure that the specimen is bent at a fixed bending radius, the specimen should be safely clamped with pressing tool or securely adhere to the test equipment. 5.7 Bending fatigue test of flexible substrate The bending fatigue properties of the conductive thin films or semiconductor devices deposited on flexible substrates are influenced by the fatigue properties of flexible substrates. Therefore, the dynamic or static bending fatigue testing of the substrate itself is recommended prior to fatigue testing of the conductive thin films or semiconductor devices. Any damages, deformation, or cracks of the substrate should be carefully monitored during the bending fatigue test.