Get Ready For In-Mold Electronics

Imagine inserting the electronics into a product without using a printed circuit board, a module, or even a system-in-package. That’s the promise of in-mold electronics (IME), a technology that has been around for years, but which is just beginning to see wider adoption.

The technology is related to conductive inks and transparent conductive films. The IME manufacturing process is said to produce less waste than using PCBs or flexible printed cables, making it very friendly to the environment and less costly in the long run.

The electronics are fabricated on a “smart skin” that is flexible, formable, and stretchable. The electronics are then combined with plastic through injection molding or standard thermoforming processes. The “smart plastic” then can be used to make lighter and smaller products, such as human-machine interfaces for automotive electronics or consumer appliances.

Holst Centre, the European research and development organization, worked with DuPont and other industry vendors to develop an IME demonstrator that could serve as a center console in vehicles. The project used DuPont’s thermoformable electronic inks and pastes to produce a 3D plastic surface measuring only 1.5 millimeters in thickness.

Fig. 1: In-mold electronics packaging. Source: DuPont

In-mold electronics enables the development of structural electronics, where the electronics are integrated into the structure, rather than being attached to the structure or connected with wires.

IME should not be confused with molded interconnect devices (MIDs), according to Khasha Ghaffarzadeh, research director at IDTechEx, who has been studying IME for several years. The manufacturing processes for IME and MID are different, he notes.

“The IME process is still relatively immature,” Ghaffarzadeh observes. “The industry had largely been pushed along by material suppliers in search of new market outlets, particularly conductive paste makers. The manufacturing step of the value chain had remained weak and most progress, until recently, had been made at piloting facilities by small to medium-sized firms. This is changing now as we witness strong engagement from large contract manufacturers. The processing know-how is also accumulating, and the industry is learning how to optimize the many tradeoffs involved in going from a pilot design to one streamlined for mass manufacture.

The production cost is still higher than the incumbent solution. As a result, IME products must create additional value, such as better aesthetics or thinner designs. This state, however, is likely to be temporary.

“We anticipate that IME will, in the long run, become cost-competitive with incumbent solutions,” Ghaffarzadeh says. “In-mold electronics is a technology where you can combine two high-through processes. One of them is printing and the other one is thermoforming and molding. In fact, a similar technology is already in use, called in-mold decorating, where you print graphical ink and then you form them and shape them and sometimes mold them. The first application for this technology came about four or five years ago. It was almost a major commercial success. It was an overhead control, over the console of an auto. The idea was that by using in-mold electronics, you could simplify the design, make the circuit part of the structure, and therefore eliminate a lot of the wiring that was going into the console, and that would save space. This product was actually qualified and adopted and rolled out in cars. Very soon, some technical problems became apparent, and the product was recalled. It had a kind of false success, false starts in the past. Now, the industry is progressing along the standing trend, developing touch controllers for the automotive switches, such as lights, air conditioning, wipers, and so on.”

Adventures in packaging
There are a number of new packaging approaches under development across the semiconductor industry, ranging from package-less designs to entirely new types of packages. As it becomes more difficult and much more expensive to develop chips at leading-edge process nodes, packaging has become a major area of research and innovation.

Packaging can affect the entire PPA spectrum in design. A 2.5D package with HBM2 has significantly higher throughput and performance than a single-chip solution and DDR4 DRAM, and it can run at lower power in a smaller form factor. And a fan-out can significantly cut costs by allowing components developed at different process nodes to be packaged more tightly together than on a PCB.

But that’s just the beginning. UCLA’s Electrical Engineering Department has been developing a packageless version of an SoC, for example. In addition, both Intel and Samsung have developed bridge technology for side-by-side chip configurations. At several conferences, Intel has shown slides with an external bridge used to connect side-by-side chips. Samsung approach is to embed the bridge in the redistribution layer.

With fan-out wafer-level packaging, there are likewise a number of different ways to put chips into the package, including chip first, chip last, and multiple variations involving different types of packages. This can address everything from warping and thermal issues to the thickness of various chips in the package, as well as the thermal and electrical characteristics of an entire device.

“Packaging has become a major concern for chip designers,” said Seung Wook Yoon, director of product technology marketing at STATS ChipPAC. “With a package you can change the electrical characteristics, parasitics, and resistance/capacitance, which are all things you need to consider for system integration at the system level. If you change the layers, the parasitics of the materials change.”

Put simply, packaging can alter a device’s performance if it is considered early enough in the design process, and increasingly that is the whole point. In many cases, it is part of the initial architecture.

This is already the case with flexible packaging for some consumer and medical applications. And DARPA has been developing some unique packaging for circuits that are used inside the human body. At last month’s Hot Chips conference, packaging was an important part of many discussions about how to speed up chips or lower power consumption.

And it doesn’t stop there. Some companies are trading in the dull gray or black packages with much more attractive packaging, almost like chrome headers and manifolds on a supercharged car engine. The difference is that in most cases, these devices will never be opened to show off the package.

“We’re seeing much tighter cosmetic specs from some customers,” said Ou Li, senior director of engineering at ASE. “In the past, you had to worry about whether there was chipping or scratches, or a bigger defect that might cause a problem at the system level. Nowadays, customers don’t even want discoloration on the metal, even if it doesn’t cause problems in functionality. In the past all they cared about was the package dimensions and the wattage. Now, we have to look at all six sides, rather than just the top. Traditionally you had a black case. We have customers that want sparkles or other chips with a sky-color case.”

Structured electronics
Transforming the electronics into the structure of a device is one of the more pronounced shifts in the basic concept of packaging. In this case, the electronics functionality is integrated into the structure itself, and in-mold electonics is one approach to embed the electronics.

MIDs, in contrast, are more mature and already in use in automotive systems. The advantage of IMEs is the form factor.

DuPont isn’t the only vendor in this burgeoning segment. AlSentis, Duratech Industries, Eastprint, Sun Chemical, and T+Ink also provide in-mold electronic materials and process technologies.

DuPont is teaming with Finland’s TactoTek to further adoption of IME and structural electronics. TactoTek is a venture-funded company founded in 2011 that focuses on 3D injection-molded structural electronics technology. Faurencia Ventures invested in the company late last year, bringing its total private funding to more than $20 million. TactoTek also has received funding from the European Union.

Fig. 2: 3D injection molded structural electronics. Source: TactoTek

“TactoTek IMSE solutions transform injection-molded plastics into smart molded structures—single parts that encapsulate sophisticated electronic functionality while being light, thin, and durable,” says Ranjana Lakshmi Venkatesh Kumar, a Frost & Sullivan research analyst. “The TactoTek IMSE value proposition spans diverse markets including automotive, appliances, IoT, and wearable technology, and enables OEMs to differentiate their products in the marketplace. Frost & Sullivan is very optimistic about the market for IMSE solutions.”

Michael Burrows, global venture leader for DuPont Advanced Materials, says the primary application for IME is capacitive switch touch panels, as typically seen in automotive vehicles and on home appliances.

“It’s really kind of the nerve center of what would be an in-mold plastic part. We want to be able to turn things on and off, open and close things, use sliders or touch dials to give modulation, for making things hotter or colder, louder or quieter. It’s really a classic touch-switch control panel, the main application that we’re going after,” he notes. “Also embedded in that would be then some lighting effects, as well. It could be lit up for aesthetic reasons, but also to give better hand-eye coordination and feedback.”

IME’s advantages include reducing the parts count, a lower profile shape (saving space), and reducing cost, according to Burrows. It also provides a pleasing differentiator compared with older technology.

Human-machine interfaces (HMI) are a key application for IME, Burrows says. The technology can provide better tactile feedback for users, he adds. Haptics could be involved. “This would certainly be a nice add or new application for IME, or a new embedded technology within IME. So that’s something that we’re working on, that physical feedback or indication coming from the touch panel to the user,” he says.

Auto consoles and consumer appliances are the leading products suitable for IME-based touch panels now. “As auto goes through its own different design phases, you’ll see switches coming in and out, being more and less popular, in different auto suppliers and Tier 1s. Many of them are looking at in-mold and trying to understand that technology better, seeing what they can do with it,” Burrows says. “Right now, the leaders in the space, still confidentially, not yet commercial products, but the leaders are now charging ahead and getting production-ready for bringing out IME-based auto parts.”

As knowledge of IME technology spreads, “we’re seeing more inquiries and more attention coming in,” Burrows says. Potential customers want to talk about using IME for small hand-held devices and hand-held appliances, since IME can make such products lighter in weight. Most interest is coming from North America, while some inquiries are emanating from Japan and other areas of the world.

“We’re moving electronic parts off of PCB boards and into the molded plastic,” the DuPont executive observes. “As well, we’re moving other mechanical buttons and switches. We’re actually pulling some of the discrete parts off the PCB and putting them right into the plastic. We’ve got a mini-industry growing around this technology.”

Given reliability and scaling, IME is considered to be “a disruptive technology within HMI and touch interfaces,” he says. “The industries we’re going after have very strict reliability standards. We need to be able to answer to those reliability standards. The key focus within our group in 2017 is, you know, this isn’t exploration any more. We need to show its reliability and industrial relevance. One of the ways that DuPont is addressing that challenge is that we offer a complete set of electronic materials that are needed to create the circuit within the molded part. And because that material selection, instead of trying to cobble it together, from many different suppliers, or in-house development, you can come to market with a fully compatible system, so it reduces your number of potential errors or defects.”

DuPont has been working on in-mold electronics technology for about five years, according to Burrows.

“This is new,” he said. “If the value is there, it’s likely to go big, and be quite a disrupter. There will be room for many winners within this new industry, and there may be some growing pains for others, as well, that didn’t realize that this was coming, and how much value there was to it.”

Conclusion
Packaging will continue to evolve, both for individual markets and applications, and for mass markets such as the smart phone. In many cases they are an extension of the problem about how to use a limited amount of space more effectively, adding new options and opportunities for innovation that were not required or available in the past.

What ultimately works best for what applications isn’t clear yet. But what is becoming clear is that packaging is a giant knob to turn, and an area where there will continue to be massive experimentation over the next decade as Moore’s Law continues to slow. Adding features, functionality and performance is now being examined from a much broader perspective, and packaging will play a key role in whatever solutions are ultimately created.

—Ed Sperling contributed to this report.

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