Rigid-flex electronics with printed passives

Summary form only given. Flat rigid circuit boards housed in prismatic casings are convenient for the office or industrial products, but the rigid prismatic form is not the most sensible and unobtrusive for portable or wearable products. Flexible forms with small rigid portions are accommodating to curved shapes to improve portability, and they can be easily fitted into tight spaces to enable deployment of ubiquitous computing devices. A large part of the rigid circuit board is occupied by passive components. Transformation of rigid boards into flexible ones would require successful conversion of rigid passive components on rigid board into flexible passives on flexible substrate. In this study, the conversion of a rigid wireless transmitter into a flexible rigid-flex module is investigated. Low profile polymeric printed resistors, capacitors and etched metal inductors were used as flexible components for rigid-flex conversion on flexible polyimide. Their physical behaviors as a function of geometries and tolerances were evaluated, and design rules were established for rigid-flex component circuit design. On this basis, a RF transmitter module is used as a system implementation case study for the flexible printed passives on polyimide technologies. The transmitter's passives count is reduced by more than 50% after redesign. The redesigned flexible circuits with passives were fabricated using printing technologies and the few remaining rigid components were mounted separately. Functional system tests on the RF signal behaviors demonstrated that the rigid-flex RF transmitter has comparable functionalities with the rigid version even when bent to radius of 4 cm. Rigid-flex transmitter built using printed passive technologies is demonstrated as a potential low cost route towards portable products and that electronics can be built conformal to curve shapes and surfaces