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Pressurex-micro® is a surface pressure imaging material that reveals the pressure distribution profile between any two contacting or impacting surfaces. It was designed with low contact pressures in mind. Pressurex-micro® is perfect for any load less than 20 psi (1.5 kg/cm). Simply place Pressurex-micro® between two surfaces and apply pressure. Then, remove it and a grayscale pressure distribution profile is revealed. The color intensity of the resulting image shows the relative amount of pressure applied to it: the greater the pressure, the darker the color.

While Pressurex-micro® is a stand-alone product, it may be combined with the Topaq® Analysis System. This easy-to-use Windows®-based system renders high resolution, color-calibrated images in seconds that accurately reflects how force is dispersed. The system consists of a scanner (pictured below) and Topaq® software. Virtually no training is required to use this product.

Kwan-yu Lai, Dean Spicer, Kevin Kornelsen, and Aruna Brennan of Micralyne Inc. wrote a White Paper with Jeffrey Stark, president of Sensor Products, on the use of Pressurex-micro® entitled, Pressure Indicating Film Characterization of Wafer-to-Wafer Bonding. Figure 1 illustrates the wafer bonding process and the use of Pressurex-micro®.

wafer bonding process

Fig 1: Wafer Bonding Process and the Use of Pressurex-micro®

By running a bond recipe with Pressurex-micro®, a direct imprint is formed as shown in Figure 2a, which is an image of Pressurex-micro® sensor film taken from a 6 diameter bonding tool with poor pressure uniformity. Through analyzing the pressure distribution with Topaq® this image is transformed into the color coded pressure map in Fig. 2b. which shows a donut-shaped high pressure ring with relatively little pressure applied at the center. The line scan in Figure 2c further illustrates the pressure variations.

analysis of wafer bonding

Fig 2a, 2b, and 2c: Analyses of Wafer Bonding Pressure Distribution.

A series of adjustments to the pressure column of the bond tool were then made, and the pressure uniformity was checked each time by running the same bond recipe on the Pressurex-micro®. The resulting series of images are shown in Figure 3 that confirms that the adjustments have made the actual pressure more uniform.

improved pressure uniformity

Fig 3: Bond Tool Images Show Improvement To The Pressure Uniformity as Captured by Pressurex-micro® and Topaq® Imaging