Stress concentration-relocating interposer in electronic textile packaging using thermoplastic elastic polyurethane film with via holes for bearing textile stretch.

Electronic textile (e-textile) devices require mechanically reliable packaging that can bear up to 30% stretch induced by textile crimp stretch, because the boundary between the rigid electronic components and the soft fabric circuit in the e-textile is prone to rupture due to mismatch of their mechanical properties. Here, we describe a thin stress-concentration-relocating interposer that can sustain a textile stretch of up to 36%, which is greater than the 16% stretch of conventional packaging. The stress-concentration-relocating interposer consists of thin soft thermoplastic polyurethane film with soft via holes and is inserted between the electronic components and fabric circuit in order to move the area of stress concentration from the wiring area of the fabric circuit to the film. A finite element method (FEM) simulation showed that when the fabric is stretched by 30%, the boundary between the electrical components and the insulation layer is subjected to 90% strain and 2.5 MPa stress, whereas, at 30% strain, the boundary between the devices and the wiring is subjected to only 1.5 MPa stress, indicating that the concentration of stress in the wiring is reduced. Furthermore, it is shown that an optimal interposer structure that can bear a 30% stretch needs insulating polyurethane film in excess of 100 μm thick. Our thin soft interposer structure will enable LEDs and MEMS sensors to withstand stretching in several types of fabric.