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Adrian Wilson

Editor's Viewpoint

12th February 2019, UK

IME: A complex field with high potential

DuPont has teamed up with Tactotek to advance IME developments. © DuPont

DuPont has teamed up with Tactotek to advance IME developments. © DuPont

It’s often not always immediately clear where some emerging new technologies sit in the bigger picture, and a good case in point is in mould electronics (IME).

As a hybrid of the techniques for making composites and plastics, PCBs and printed electronics, IME, while still very much a niche field, in many ways represents the next potential level of convergence for material technologies and electronics.

IME techniques promise to enable the high-volume production of structural electronics where the electronic circuitry and functionality are part of a 3D-shaped structure itself, in order to save weight and space and enable elegant new designs.

As Dr Khasha Ghaffarzadeh, research director for IDTechEx points out in a useful new report*, IME is not exactly new and in many ways is an evolution of the well-established IMD – in mould decoration – in which moulding or other ways of 3D forming are combined with graphic printing.

The transition from IMD to IME however is not straight forward, he observes, especially on a commercial scale. This partially explains why it has taken this long for IME to establish lasting commercial success despite all the efforts and false starts.

IMS is an engineering-based company, based in Phoenix, Arizona, with the technical knowledge base and resources to develop, install and maintain vertically integrated production cells for IME. © IMS

IMS is an engineering-based company, based in Phoenix, Arizona, with the technical knowledge base and resources to develop, install and maintain vertically integrated production cells for IME. © IMS

This is now changing, IDTechEx believes, predicting that the market will grow to a value of more than $250 million by 2024, but many things still need to move forward. New materials must be developed that can survive requirements such as stretching and 3D forming, new processes must be perfected to combine 2D printing, 3D forming and rigid component placement, and new design procedures and product concepts are still required.

Material trends

Functional materials in IME must survive a one-off significant stretching event as the 2D printed sheet is formed into a 3D object. This is much more challenging to achieve for functional, rather than merely graphical inks, since elongation can disrupt the function, e.g., break the conduction path in conductive inks.

There is no single required degree of stretching, Ghaffarzadeh says, but in general higher levels of stretchability are desired. As a crude rule of thumb, 20% elongation is the minimum, whereas 60% or higher is in many cases preferred. Suppliers already seek to differentiate by the stretchability of the material since it eases process development and provide more design freedom.

Reliability

Functional materials must also be reliable under harsh field conditions.

“This is critical, particularly in automotive and similar applications,” Ghaffarzadeh says. “This aspect, surprisingly, was often neglected in the early days. Indeed, famous IME product failures and recalls have been caused by unreliability. The properties of utilized materials can often change significantly during high humidity and high temperature tests. This change should be factored into the design of the product.”

A stack of materials need to be printed to achieve the required effect. This stack can include graphic inks, conductive inks, dielectrics, transparent conductive inks, carbon overcoats, and so on.

IMS is an engineering-based company, based in Phoenix, Arizona, with the technical knowledge base and resources to develop, install and maintain vertically integrated production cells for IME. © IMS

IMS is an engineering-based company, based in Phoenix, Arizona, with the technical knowledge base and resources to develop, install and maintain vertically integrated production cells for IME. © IMS

So far, the most studied functional material has been the conductive ink. Today, there are multiple suppliers across the world offering conductive inks for IME. Metal filled conductive inks (almost always silver) represent the most expensive and high value material in the stack and because they are the most sensitive to changes in the conduction, e.g., elongation.

Other materials are also critical in the process, in particular, low-temperature printable conductive adhesives that also exhibit some stretchability. In general, all functional materials must be compatible with one another. This compatibility is critical, especially during the forming process and significantly impacts final properties. Even the sequences in which the materials are deposited can have an impact.

This is a development challenge but also an opportunity to develop and sell complete IME material portfolios, IDTechEx says.

The substrate also represents a development and supply opportunity. Most have thus far utilised a polycarbonate substrate due to its good formability, but now special PETs are being developed.

Process trends

The IME process involves printing and drying/curing multiple functional and graphical materials on a 2D formable substrate such as PC. It then involves converting the 2D sheet into the 3D shape via thermo or vacuum moulding under elevated temperatures. The overmoulding must then take place at high temperatures too.

The question of pick-and-placing rigid components is also challenging. If the pick-and-place takes place after forming, then the pick-and-place machine must be able to handle placement in a 3D space. This will require specialised pick-and-place as well as adhesive dispensing tools, and will almost certainly slow down the process. The pick-and-place could also take place on a 2D sheet prior to forming. This would however require special adhesives as well as careful product and process design to ensure that the rigid components will remain attached after all the forming steps.

DESIN is a manufacturer of Human Machine Interface (HMI) sensors based in San Luis Potosi. © DESIN

DESIN is a manufacturer of Human Machine Interface (HMI) sensors based in San Luis Potosi. © DESIN

“In general, the process development is complex,” says Ghaffarzadeh. “It requires deep knowledge of the materials as well as all the process steps. The question of yield is a persistent and particular challenge because defects cannot be repaired since the electronics are embedded or structurally integrated. As such, defects are expensive since they waste the fully formed devices. In general, there is a steep learning curve to be travelled.

“This has created the need for centres or entities with accumulated know-how and expertise to cut down development time and technical barriers to entry. It has also meant that many traditional membrane switch or other functional printers with low risk appetites and/or tight cash flows have had to wait for the industry to mature further before investing to evolve their business towards IME. This evolution will increasingly become inevitable and will accelerate as IME achieves a higher level of technical maturity and perhaps modularity.”

Design challenges

The design of IME products is also not straight forward, the IDTechEx report points out.

It is not a streamlined process yet, lacking established software packages with drop-and-place component/functional libraries. This is in stark contrast to design processes found, say, in standard PCBs. The market requirements are also not clear-cut, well-established or convergent yet. This is because despite years of development, the industry is still in an exploratory phase where it is developing numerous prototypes and running qualification processes. The products and prototypes are still mainly custom made, without standard design.

“These all complicate the product development process, prolong the time-to-market, and form barriers to entry for users as well as potential producers,” Ghaffarzadeh concludes. “However, the industry is responding now, and some firms are positioning to fill exactly this need, thus helping accelerate overall commercialisation.”

*For further details of the new IDTechEx report, In-Mold Electronics 2019-2029: Technology, Market Forecasts, Players, visit www.IDTechEx.com/IME

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