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TECHNICAL PAPERS

# Study on Embedding and Integration of Microsensors Into Metal Structures for Manufacturing Applications

[+] Author and Article Information
Xudong Cheng, Arindom Datta, Hongseok Choi, Xugang Zhang

Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706

Xiaochun Li

Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706xcli@engr.wisc.edu

J. Manuf. Sci. Eng 129(2), 416-424 (Sep 25, 2006) (9 pages) doi:10.1115/1.2515456 History: Received November 29, 2005; Revised September 25, 2006

## Abstract

Real time monitoring, diagnosis, and control of numerous manufacturing processes is of critical importance in reducing operation costs, improving product quality, and shortening response time. Current sensors used in manufacturing are normally unable to provide measurements with desired spatial and temporal resolution at critical locations in metal tooling structures that operate in hostile environments (e.g., elevated temperatures and severe strains). Microsensors are expected to offer tremendous benefits for real time sensing in manufacturing processes. Rapid tooling, a layered manufacturing process, could allow microsensors to be placed at any critical location in metal tooling structures. However, a viable approach is needed to effectively integrate microsensors into metal structures during the process. In this study, a novel batch production of metal embedded microsensor units was realized by transferring thin-film sensors from silicon wafers directly into nickel substrates through standard microfabrication and electroplating techniques. Ultrasonic metal welding (USMW) was studied to obtain optimized process parameters and then used to integrate nickel embedded thin-film thermocouple (TFTC) units into copper workpieces. The embedded TFTCs successfully survived the welding tests, validating that USMW is a viable method to integrate microsensors to metallic tool materials. Moreover, the embedded microsensors were also able to measure the transient temperature in situ at $50μm$ directly beneath the welding interface during welding. The transient temperatures measured by the metal embedded TFTCs provide strong evidence that the heat generation is not critical for weld formation during USMW. Metal embedded microsensors yield great potential to improve fundamental understanding of numerous manufacturing processes by providing in situ sensing data with high spatial and temporal resolution at critical locations.

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## Figures

Figure 1

Illustration of using rapid tooling for in situ integration of metal embedded sensor unit

Figure 2

Schematic diagram of dielectric multilayer for microthin-film sensors

Figure 3

Sensor fabrication and embedding process

Figure 4

3D illustration of “L” shape embedded sensor unit for ultrasonic welding test

Figure 5

Geometry of each layer of the sensor unit for welding test

Figure 6

Dimensions of TFTCs’ sensing tip

Figure 7

Image of microbumps created at the electroplating interface

Figure 8

Picture of the multiple “L” shape embedded sensor units fabricated by the batch production technique

Figure 9

Single nickel embedded sensor unit with lead wires attached

Figure 10

Calibration of TFTC before and after embedding

Figure 11

Comparison of the noise level of TFTCs with or without additional titanium layer

Figure 12

Dynamic response of TFTC: (a) a temperature peak captured by TFTC; and (b) detailed peak for response time estimation

Figure 13

Sample dimensions for welding parameter optimization

Figure 14

3D response surface and contour plot of break load versus amplitude and welding optimization (clamping pressure at 58.38MPa)

Figure 15

SEM and EDS examination on welded sample

Figure 16

Ultrasonic welding test setup for sensor unit integration: (a) sensor clamped in the fixture prior to the welding; and (b) after copper was welded to the sensor substrate (connection wires detached)

Figure 17

In situ temperature measurement results (welding parameters: vibration amplitude at 23μm, welding duration at 0.2s, and clamping pressure at 58.4MPa)

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