Topics Mechanical Engineering - IC Packaging ( 3D packaging) project report

Electronic Packaging Fundamentals Course Project Report

Automotive MEMS and Sensors Technology

INTRODUCTION

Micro-electromechanical systems (MEMS) are developed as a result of technological advancement in integrated circuits and micromanufacturing, and its technology has become the backbone of many sensor technologies in automobiles. Although faced with many challenges such as device miniaturization, quality, and reliability testing, and high cost from packaging and testing, emerging solutions such as MEMS packaging standardization and wafer level testing can be adopted to overcome these setbacks.

LITERATURE REVIEW

Device Miniaturization [1]

Device miniaturization has been the ongoing trend in the electronic industry, and the demand for advancement in MEMS technology reflects the drive as well. The recent development in autonomous vehicles and portable devices are calling for higher integration of MEMS sensors to support its increasing capabilities. As these devices increase in function and complexity, the available footprint within the device is continuously limited by the ever-decreasing device size. The manufacturing technique that enables the production of MEMS technology is bulk surface machining, where layers of mechanical structures and features are created through a combination of etching and layer deposition. As the demand for smaller and more intricate features rises, the industry must provide an answer in terms of improved and more advanced manufacturing techniques to address the miniaturization trend.

Component Testing [2]

Many MEMS devices serve as accelerometers, gyroscopes, and sensors for critical data acquisition applications; therefore, the reliability and quality of these devices must be ensured. Extensive reliability testing is performed at the device or package level to ensure that the product meets requirements and specifications. When it comes to testing MEMS products, both electrical and mechanical analysis is required for a thorough examination of the product performance. The coupling relationship of the mechanical parts with electrical circuitry results in a complex system that requires unique testing equipment. The cost of testing equipment and setups such as testing stations can easily exceed millions of dollars in capital investment from the device manufacturer. The Challenge of high testing cost poses a roadblock in the MEMS market and innovative solutions are needed for a cost-saving solution.

MEMS and CMOS Integration [3]

As shown in Fig. 1, MEMS structure is often coupled with integrated circuitry to perform sensing and analysis of the acquired data. The industry's drive to lower the production cost and device size calls for the tackling of the challenge in MEMS and CMOS process integration. The current method for system integration involves the manufacturing of the MEMS and electrical circuitry on different substrates, and interconnects or direct bonding of the two chips are performed for device integration. This approached is forced by the high cost associated with monolithic integration. Challenges foreseen within the industry would be to lower the cost associated with the integration of MEMS with IC fabrication.

Figure 1 Acceleration sensor internal layout and MEMS structure [4]

MEMS Packaging [5]

Packaging serves a crucial function in providing the proper mechanical protection and environmental control for the MEMS device. Given the role of packaging and its value in ensuring the reliability and function of the device, packaging and testing can often take up to 90% of the total production cost. The key challenge in the area of MEMS packaging falls in the design of the enclosure to provide the proper protection against temperature, shock, moisture, and stress while allowing data of interest to be collected through a specified medium. In the case of pressure sensors used in pressure monitoring and control, package engineers must ensure that a sufficient and controlled amount of desired inputs can be registered by the MEMS device. This process proves to be difficult in that many of the elements the sensor is designed for monitoring can easily cause device malfunction if the input is let uncontrolled (ex: pressure, temperature).

Co-design Requirement [6]

The name "micro-electromechanical system" clearly indicates the need for the collaboration of mechanical and electrical engineering disciplines when developing MEMS technologies. Although the development of MEMS did not revolutionize the world of engineering and design, it does, however, pose the challenge and requirement for a higher level of co-design initiative and execution. In the past, mechanical and electrical engineers each have simulation and design software dedicated to their area of interest and expertise. The gap between these software (ex: FEA and EDA) pose many issues when designing MEMS devices. The lack of communication between the software and engineering groups means that critical design considerations and simulation results were not being shared efficiently. To successfully develop a product to ensure that quality and reliability performance are meeting requirements, there is a growing challenge for software developers and designers to come up with a solution and initiative for co-designs.

DESCRIPTION

Standardized Package Solutions

As previously mentioned, packaging and testing can often take up to 90% of the total production cost of MEMS devices. Unlike conventional IC packages, where package options have been standardized and thoroughly tested by many manufacturers, MEMS packaging still proves to be challenging due to the high level of customization and variation in the package design [7]. The high cost associated with packaging can be resolved by introducing a company or industry-wide package standard. To establish a standardized package model for MEMS devices, characteristics such as package dimension, I/O count, connection type, and material sets must be defined. Key ideas to keep in mind when defining such parameters should be designed for manufacturability and for reliability, where these two factors can greatly influence the resulting cost of the device if left unconsidered. Each characteristic mentioned above warrants extensive testing and review because the chosen package types will replace many customized package designs and must be capable of providing the package solution needed for a wide range of products.

Wafer Level Testing

The general approach for MEMS device testing has been at the component level, where the quality of the product is inspected at the end of the fabrication process. This approach inherently increases the cost of MEMS fabrication because faulty devices are identified at the end of the manufacturing process, leading to higher waste of resources and time since the products have been processed and packaged. A recent approach taken by many device manufacturers is the testing of the MEMS device at the wafer level – wafer-level testing.

Wafer-level testing involves providing the device with required electrical stimulation, as well as required testing input such as sound, light, vibration, temperature, and pressure depending on the sensor application [8]. Traditional IC testing often requires input and output both in the form of an electrical signal. Wafer-level testing of MEMS devices requires not only the electrical input but also output as a result of the mechanical input to the system (ex: sensor applications). To conduct tests at the wafer level, testing devices such as test probes and controllable testing chambers must be acquired. Depending on the device/sensor application, the chamber needs to be capable of creating an inert environment with controlled environmental specifications targeting different types of MEMS sensors.

INFERENCES/ADVANTAGES-DISADVANTAGES

With the application of both package standardization and wafer level testing in MEMS design and manufacturing, issues and challenges such as high-reliability requirements, manufacturing cost, and testing difficulty can be resolved.

In the case of MEMS package standardization, research and testing effort can be focused and allocated for a selective number of package solutions. This approach can allow companies to develop reliable material sets, process control parameters, and design guidelines for those specific packaging solutions. By developing a mature design model and manufacturing approach by standardizing the package types, companies can increase the quality and reliability of the product while driving costs down. A drawback to this approach is the requirement of boundary and design limitations placed on MEMS designers. No longer designers can utilize the versatility of custom package design options for MEMS since the design of the MEMS and electrical circuitry have to take into consideration of the available package types available.

Wafer-level testing provides a significant advantage over component level testing due to the prevention of resource and time wasted on failed components identified at the wafer level. By identifying the failed parts early on, additional processing and packaging effort can be preserved, thus lowering the cost of manufacturing (Fig. 2). The challenge associated with this approach is the large investment needed for purchasing of testing equipment and setup. The required equipment must be capable of both delivering mechanical input while retrieving the electrical signal and response; the test environment needs to provide the ability for fine control of the testing environment to ensure test accuracy and repeatability.

Figure 2 Cost comparison with and without wafer-level testing [8]

CONCLUSIONS

As the demand for MEMS technology grows with the increasing complexity of application areas, many challenges have and will continue to pose design and application issues for MEMS devices. It is paramount that the industry position the necessary resources and effort in tackling those challenges mentioned in this paper to improve the function and performance of MEMS products. In the case of this review paper, package standardization and wafer level testing are discussed and analyzed to align focuses on the potential benefits capable of receiving from these two approaches. The number of automobiles produced and purchased is growing at an upward trend, meaning MEMS are being incorporated in more and more of our daily lives. This trend requires the continual advancement of MEMS products through methods such as those described in this paper.

REFERENCES

[1] Marek, J. “MEMS for Automotive and Consumer Electronics.” 2010 IEEE International Solid-State Circuits Conference - (ISSCC), vol. 53, IEEE, 2010, pp. 9–17, doi:10.1109/ISSCC.2010.5434066.

[2] Muhammad, et al. “A Review on Key Issues and Challenges in Devices Level MEMS Testing.” Journal of Sensors, Hindawi, 21 Feb. 2016, www.hindawi.com/journals/js/2016/1639805/.

[3] Villanueva, et al. “Grand Challenge in N/MEMS.” Frontiers, Frontiers, 11 Nov. 2015, www.frontiersin.org/articles/10.3389/fmech.2015.00015/full.

[4] Marek, J. “Automotive MEMS Sensors - Trends and Applications.” Proceedings of 2011 International Symposium on VLSI Technology, Systems and Applications, IEEE, 2011, pp. 1–2, doi:10.1109/VTSA.2011.5872208.

[5] Bhat, K N, and M M Nayak. MEMS Pressure Sensors- An Overview of Challenges in Technology and Packaging. pdfs.semanticscholar.org/b3ab/9fd4fcae88c557c7d7ccd7e26472a50c4b60.pdf.

[6] Karam, J. M., et al. “MEMS: The New Challenge for the Electronic Design Automation Vendors.” SpringerLink, Springer, Berlin, Heidelberg, 1 Jan. 1998, link.springer.com/chapter/10.1007/978-3-662-39696-4_11.

[7] Bauer, Charles E. Packaging MEMS, The Great Challenge of the 21st Century. TechLead Corporation, 2000, www.osti.gov/etdeweb/servlets/purl/20136250#page=40.

[8] Werner, Frank-Michael. “Wafer Level Test: Significant Time and Cost Reduction of MEMS Production.” Electron-Mec, SUSS MicroTec Test Systems GmbH, www.electron-mec.com/wp-content/uploads/applications/Publication-2003_Wafer_Level_Test_Significant_Time_and_Cost_Reduction_of_MEMS_Production.pdf.

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