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Will wearable devices be reliable?

17 Oct 2014  | Greg Caswell and Craig Hillman

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Editor's Note: Here are several factors and components that wearables designers and manufacturers should consider when making these devices in order to ensure reliability.

The wearables market is perhaps $3 billion to $5 billion today, rising to perhaps $30 billion to $50 billion over the next three to five years, the analysts forecast, adding that there may be upward of 15 per cent of smartphone owners who end up buying a wearable.

The breadth of applications is staggering as shown in Figure 1 from Beecham Research.

 Ubiquitous markets for wearable electronics

Figure 1: Ubiquitous markets for wearable electronics

The question is will the wearable electronics be reliable? Reliability is defined as the measure of a product's ability to perform its specified function, in the customer's use environment, over the required or desired lifetime. From this perspective we need to think about what the product is supposed to do, where it is going to be used, and how long should it last?

Wikipedia defines wearable electronics as "miniature electronic devices that are worn by the bearer under, with or on top of clothing." DfR has come up with what we feel is a better definition. "Technology attached to the human body or clothing that allows the wearer to monitor, engage with and control devices, themselves or their social network.

Wearable electronics falls into the categorisation of "Next Generation Technologies." DfR defines these technologies as those the supply chain or the user will implement because they are cheaper, faster, stronger, etc.

One of the most common drivers for failure is inappropriate adoption of new technologies. As most of us have little or no influence over the packaging technologies chosen for implementation we need to be aware of the pitfalls and what actions need to be taken to assure that the new technologies are reliable. As typically occurs with new markets of electronics, there are several issues that need to be addressed from a reliability perspective to assure these new applications are safe and reliable.

Market studies and mobile phone markets can skew the reality of market adoption as annual sales of >100 million may be due to one or two customers. As such, mobile phone requirements may not match the needs of wearable electronics.

A good example of this issue is the 0201-size ceramic capacitor. Initially, "the smaller the better," was the mantra for electronics. Figure 2 illustrates that the 0201 size capacitor was 25 per cent of the multi-layer ceramic capacitor market in 2010. So what happened?

 Ceramic capacitor usage

Figure 2: Ceramic capacitor usage

Attempts to integrate 0201 capacitor technology into more demanding applications, such as medical implants, resulted in quality issues, unexpected degradation and major warranty returns.

When you look at wearable electronics, the products are utilising many different "Next Generation Technologies." For example, 01005 capacitors (think 0201s); Polyethersulfone, polyethylene terephthalate (PET), polyethylene napthalate (PEN) substrate materials; printed connections such as silver inks, nanosolders and conductive polymers; organic displays; and supercapacitors as the power source. Each of these technologies must be explored to assure they are reliable with respect to wearables.

Similarly, the durability of the wearable products must be examined. The compact fluorescent lamp (CFL) is a perfect example of what can happen if durability becomes an issue. Figure 3, from a CFL Market Profile: Data Trends and Market Insights, U.S. Dept. of Energy, September 2010, illustrates the drop-off in usage. Why did this happen?

 Market share drop for CFLs

Figure 3: Market share drop for CFLs

Two different studies indicated that the failure rate for CFLs was between 2 per cent and 13 per cent, with returns from thermally challenging environments being higher. The consumer was impacted by the failure levels and moved over to LED lighting which is even newer.

Therefore, it is necessary to pay attention to the reliability issues at the design stage of a new product. The designer must look at derating and uprating of the components selected; must design for manufacturability, and must understand the Physics of Failure of the product to properly predict degradation in the electronics involved. The designer must capture at the concept stage the influence of reliability by defining the reliability expectations for the product and also by thoroughly understanding the use environment.

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