Poster “Testing Challenges for IoT Smart Sensors”

Introduction:

According to many market predictions, the IoT will drive a “third wave” of semiconductor growth to enable over 25 billion sensors by 2020 for end-node applications in multiple market segments [1].  These IoT end nodes are smart, connected ‘things’ that typically consist of 3 key elements: sensors, microcontrollers (including flash memory) and low-power wireless interfaces.

Fig.1.  IoT end nodes: ‘Connected Smart Things’

This functional integration, combined with the need to perform final test and calibration of different kinds of sensor nodes, is creating a multi-dimensional test challenge in manufacturing. This discussion will review aspects of the different test challenges and propose solutions to answer them in a cost effective way.

IoT Sensor Trends

The Internet of Things (IoT) is the network of physical objects that contain embedded technology to communicate and sense or interact with their internal states or the external environment [2].

In recent years, many sensor types migrated from larger, analog architectures into semiconductor (MEMS) implementations, enabling several factors of miniaturization and resulting cost reduction. This high level of sensor integration has supported the smartphone revolution, delivered new levels of automotive performance and enabled many other new applications.

A general challenge for sensor manufacturing is the requirement to calibrate the sensor at the end of the manufacturing process, prior to shipment. This requires a non-electrical stimulation (e.g. gravity, pressure, light, magnetic field) applied to the sensor during electrical final test.

Microcontrollers in IoT end nodes are SOCs in their own right, with embedded memory, mixed-signal functions and security features that require more complex test capabilities.

Numerous RF protocols and interfaces are being proposed for various industrial, personal and domestic IoT applications, requiring a flexible and low-cost RF test solution.

It can be seen that the connection of the sensors via RF communication links and the integration of data processing using an integrated micro controller is further increasing the complexity and diversity of manufacturing test requirements.

IoT Test and Manufacturing Challenges

A universal challenge is the cost pressures driven by falling ASPs for sensors, microcontrollers and wireless ICs. Low cost test solutions are required, but new technologies and applications are making it difficult to define and stick to a cost-effective IoT test standard:

  • Innovative and smaller packaging (WLCSP, SiP, 3D, Embedded) with finer contact pitches, must be handled reliably with lowest conversion efforts and costs
  • New sensor applications require significant test setup adaptations: every kind of sensor (e.g. accelerometer, gyroscope, magnetometer, pressure, humidity, light, IR, …) requires a new stimulus module.
  • Diverse market segments (consumer, automotive, industrial, medical) are demanding solutions at different specifications and conditions (ambient vs. tri-temp).
  • Continuous ASP reduction drives a need for higher parallelism to achieve acceptable cost of test, which in turn mandates tester architectures with high Multi-Site Efficiency (MSE).

Other challenges come from the higher levels of integration

  • Multiple sensors integrated in one package will require different types of stimulus and this could become a cost of test roadblock, unless multiple stimuli can be combined in one system.
  • The integration of low-power microcontroller cores, memory, RF, sensors and smart power leads to contradictory test scaling requirements and capabilities, where the boundaries might come from the tester instrumentation or the test handler interfaces.

Other IoT Market Pressures

IoT solutions are targeting a broad mix of applications, many of which will drive high volumes with short product life-cycles.

Dynamic market requirements may include new wireless protocols, new sensor functions and protocol-based programming.

Ultimately this will lead to ramp requirements that exceed the slope of today’s mobility product ramps

Solutions for IoT End Node Test

In order to address the test and manufacturing challenges of IoT products, we have defined 3 key characteristics for an IoT end node test cell:

  1. Low Cost of Test
  2. Flexible to meet today’s challenges
  3. Adaptable to future needs

In addition the test cell needs to support the different test requirements of all the end node components,

  • Specific sensor stimulus
  • Power management technology
  • Low cost RF covering all wireless protocol standards
  • Digital protocol engines

All of these test requirements need to implemented in-line with high volume production requirements:

  • Multi-package handling technology
  • High Multi-Site Testing Capability
  • Robust Contacting
  • Performance optimized, flexible test cell

Fig.2. Key capabilities for IoT Test Cell

Even though these are general requirements, it is mandatory to support them at all component levels of the test cell: the tester, the test handler, the stimulus module and the interface products. Typically this can only be managed with a holistic approach that provides a common point of ownership for the key test cell components.

References

  1. Integrated Circuit Market Drivers 2016; Rob Lineback, Bill Mc Clean, Brian Matas; IC Insights, Inc; Nov 24, 2015.
  2. Gartner Online IT Glossary; http://www.gartner.com/it-glossary/internet-of-things/ 2016.

Version: May 2016
Presented by: Peter Cockburn
Presented at: IEEE European Test Symposium