Some history about the development of stretch PCB
The definition of the original development project, Stretchable Electronics Technology for Large Area Applications (STELLA) did among others include the integration of electronic circuitry, stretch up to 50% and a circuitry which could withstand machine washing. During the development program a large number of possible solutions were evaluated, some of them were already in the early development phase stopped, several were developed up to prototype circuitry.
The project with an additive Cu process on a breathing layer as the substrate was stopped as the substrate layer was heavily affected by the chemistry. Another technology which was explored was the creation of conductive polymers on non-woven substrates.
The advantage is the breathing of the substrate, however this technology turned out to be very unreliable.
The stretchable copper board technology, which makes use of a polyurethane type basis, is not breathable though turned out to have some big advantages. The productions processes are rather similar to the traditional production technology of PCBs. Stretch can be up to 30% depending on the design chosen for the circuitry and a reliable interconnection can be created. The polyurethane base material can be contact with the skin, the disadvantage of the non-breathing of the material can be overcome by a patron of small holes in the poly urethane substrate.
Development of SCB technology
The development of new stretchable and flexible substrates carrying stretchable conductors does include a few additional challenges. Electronics cannot stretch and also the interconnection of the components with the substrate should not bend and/or stretched. Therefore several new interconnection technologies are developed to assure reliable circuitry.
- Interposer technology. The active electronics are placed on a interposer to assure that no stress is put on the electronics and the interconnection of the components
- Stretch-rigid. Similar to the technology of Flex-rigid a circuitry is built with a stretchable interconnection part and a rigid part on which the electronics are mounted
- In case of a limited amount of electronics also a stiffener like solution can be an option. The effect of stretching is hardly noticeable on these reinforced islands.
Stiffener construction to support the mounted parts