• Van Put, Steven
• Yang, Yang
• Dunphy, Sheila
• Guillaume, Joren
• Vervust, Thomas
• Vanfleteren, Jan
• Dhaenens, Kristof
• Bossuyt, Frederick
• Plovie, Bart

Abstract

This contribution describes an efficient process flowfor production of one-time deformable electronic devices basedon standard circuit board technology and demonstrates multipledevices fabricated using this technique. The described technologyhas the potential to streamline and simplify the production ofcomplex user interfaces which typically require extensivemechanical design and many components. The employedtechnique allows for the production of complex 3D shapeswithout the need to modify existing circuit board manufacturingequipment or processes significantly. To achieve this the device ismanufactured in a flat state, encapsulated in a thermoplasticpolymer laminate and deformed afterwards. This allows theusage of standard electronic components in surface mountpackages, which are assembled using lead-free high-temperaturesolder. The circuit is deformed using a high-volume cost-effectivethermoforming approach, where the encapsulating polymer isheated above its glass transition temperature and forced againsta mold where it is allowed to cool down again. To enablesignificant out-of-plane deformations stretchable meanderinginterconnects are used, which were traditionally developed fordynamically stretchable devices. Fabrication of the circuit startsusing a standard flexible copper clad laminate which is processedusing the default techniques, the resulting circuit is then attachedto a carrier board coated with a reusable high-temperaturepressure sensitive adhesive. The interconnect and circuit outlineis then defined using laser routing or punching, cutting theflexible circuit without damaging the carrier. The residuals notpart of the circuit are removed, in a process akin to protectivefilm removal, and solder paste is stencil printed on the circuit.Afterwards components are placed using a pick-and-placemachine and the boards are reflow soldered. After functionaltesting and repair (if necessary) the circuits are placed in avacuum press with a thermoplastic laminate, consisting of athermoplastic elastomer and a rigid thermoplastic sheet. Duringthis lamination the components are protected by a highlyconforming press pad. Because the adhesion between theelastomer and the circuit far exceeds that between the circuit andthe carrier the circuit is released readily as the thermoplasticlaminate is peeled away. The resulting laminate is built upfurther using thermoplastic films and sheets, and finallydeformed using a vacuum forming machine. The resultingdevice, which is trimmed to remove the clamping edges, can thenbe mounted in the final assembly. The advantages of thisapproach are demonstrated using a series of test vehicles,demonstrating the integration of complex circuits, connectors,and power circuitry. Finally, a series of design considerationsthat became apparent after initial reliability testing arediscussed, together with the resulting design rules.

Topics

• impedance spectroscopy
• surface
• glass
• glass
• copper
• glass transition temperature
• forming
• thermoplastic
• elastomer