For conventional flexible printed circuit board widely used in industry, jointing islands of electric components with polyimide-supported copper serpentine interconnects is an effective approach to ensure circuit stretchability. The stretchability of the interconnects varies significantly due to the soft elastomer encapsulating the interconnect, as the encapsulation essentially constrains the lateral buckling of the serpentine structure during stretching. Previous studies have indicated that thin encapsulation with a low Young’s modulus is required to maximize stretchability. However, extremely low modulus and thinness lead to the elimination of the encapsulation function, and the design criteria for maximizing stretchability while maintaining adequate modulus and thickness are still unclear. This study investigates the dependence of stretchability on encapsulation stiffness, an index that simultaneously considers modulus and thickness. The interconnects with core–shell and single-elastomer encapsulations, each with a different stiffness, were prepared. The relationships between the elongation to failure of the interconnect and the tensile and bending stiffness of the encapsulation were investigated through experiments and finite element method calculations. The results indicate that the tensile stiffness is a more useful index in encapsulation design than the bending stiffness because the elongation to failure monotonically decreases as the tensile stiffness increases. The results also indicate that the required tensile stiffness to maximize interconnect stretchability, essentially making the interconnect almost freely deformable, ranges from 5 to 34 N m⁻¹ when the interconnects use an 18 μm thick copper and 50 μm thick polyimide.

中文翻译：

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聚酰亚胺支撑铜蛇形互连的软弹性体封装的可拉伸性对刚度的依赖性

对于工业中广泛使用的传统柔性印刷电路板来说，用聚酰亚胺支撑的铜蛇形互连连接电子元件岛是确保电路可拉伸性的有效方法。由于封装互连件的软弹性体，互连件的可拉伸性显着变化，因为封装实质上限制了拉伸期间蛇形结构的横向屈曲。先前的研究表明，需要具有低杨氏模量的薄封装才能最大限度地提高可拉伸性。然而，极低的模量和薄度导致封装功能的消除，并且在保持足够的模量和厚度的同时最大化拉伸性的设计标准仍不清楚。这项研究研究了拉伸性对封装刚度的依赖性，这是一个同时考虑模量和厚度的指标。制备了具有不同刚度的核壳和单弹性体封装的互连件。通过实验和有限元方法计算，研究了互连的失效伸长率与封装的拉伸和弯曲刚度之间的关系。结果表明，在封装设计中，拉伸刚度是比弯曲刚度更有用的指标，因为断裂伸长率随着拉伸刚度的增加而单调减小。结果还表明，当互连件使用¹⁸μ米厚铜和50μ米厚的聚酰亚胺。