Technology

Stretchable Islands

To make it possible to deform a flat assembly to the desired 2.5D shape the embedded electronics have to be able to deform as well. This is achieved by introducing the concept of stretchable circuits by which flexible or rigid component islands are interconnected using stretchable electrical interconnects. This way a flat circuit can be deformed to any desired shape and still remain functional.

For embedding and forming these structures in combination with a wide variety of materials the consortium relies on the expertise of several industrial partners, together with the expertise of a world renowned institute on injection molding (PEP), to offer a wide variety of possibilities. By doing so, we hope to meet the requirements for the most challenging applications.

Niebling Formtechnologie, the inventors of isostatic high pressure forming, brings their expertise in the forming of polymers and conductive features to the project. High pressure forming offers, among many other benefits, very high positioning tolerances and compatibility with a wide variety of materials. For industrial scale vacuum forming and injection molding SINTEX NP is the partner of choice, having a long track record of high volume production for various industries like automotive, aeronautics and medical. They are able to bring even the largest scale applications to life.

Technologies:

SMI

Stretchable Mould Interconnect

Imec’s SMI technology was previously used to encapsulate fully stretchable circuits in both silicone (PDMS) and thermoplastic polyurethane (TPU). It is based on copper meanders supported by polyimide. By introducing a high temperature carrier with a reusable adhesive, to which the polyimide substrate is attached during production, it is within TERASEL the only technology which allows high temperature lead-free soldering. In fact the carrier allows the use of standard printed circuit board processing without any further modifications to the process. After the definition of the meanders the circuit is transferred to a polyurethane film and embedded in a thermoplastic material using lamination or injection moulding.

SCB

Stretchable Circuit Board

Fraunhofer IZM’s Stretchable Circuit Board (SCB) technology directly integrates a copper layer on a polyurethane film which is mounted on a temporary carrier. The copper meanders are patterned using conventional photolithography and etching steps. Subsequently, the patterned copper is covered with polyurethane. The components are assembled using low temperature solder and capped off by polyurethane. The end result is embedded in a thermoplastic sheet, which can be deformed later on, using lamination or injection moulding.

SPF

Stretchable Plastic Film

TNO Holst’s Stretchable Plastic Film technology takes a different approach by introducing the concept of additive manufacturing to the printed circuit board world. The process starts by screen printing a layer of conductive paste on a thin plastic film. The electronic components are assembled using conductive adhesive. To protect the components, and to embed the film in a thermoplastic material, the whole system is first embedded in a layer of thermoplastic polyurethane which is then laminated to a thermoplastic material.

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High Pressure Forming

High Pressure Forming is one of several methods to deform sheets to a desired free-form shape. It works by heating the sheet to its glass transition temperature using contactless infrared heaters. Next, the sheet is formed against a metal tool using compressed air. Its main characteristics are support for a wide variety of materials, lower temperatures, and high positioning tolerances.

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Injection Molding

Injection molding is one of the most common techniques to make plastic parts. It offers high precision, the ability to make complex parts, and above all flexibility in choice of materials. The process starts by melting plastic pellets; these are then injected under high pressure in a mold. After a short cooling time the mold opens and the part is ejected.

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Vacuum Forming

Vacuum forming is one of the workhorses of the plastics industry. It is a cheap and reliable way to make plastic parts with low setup costs. This makes it an economic approach for both low and high volume applications. First the sheet is heated to the point where the plastic becomes formable using a variety of methods (e.g. infrared heaters). It is then drawn into a forming tool using a strong vacuum. This forces the plastic to take the shape of the forming tool.