Investigation of the Bending Process and Theory in Free-Boundary Pneumatic Film-Forming for Curved Image Sensors
<p>Principle comparison of imaging methods: (<b>a</b>) distortion principle of traditional image sensor due to Petzval field curve; (<b>b</b>) imaging principle of curved image sensor inspired by human eye.</p> "> Figure 2
<p>Forming principle; the left side is the traditional fixed-boundary mold forming, while the right side is the free-boundary pneumatic film forming.</p> "> Figure 3
<p>When using free-boundary mold molding, the molding method has been changed from “projection” to “wrap”.</p> "> Figure 4
<p>If the difference between the displacement in the x and y direction and the displacement in diagonal direction is too large, there will be a tendency of out-of-plane deformation.</p> "> Figure 5
<p>Points x, y and d in the figure represent the intersection of the dividing line and the lines in the x, y and d directions. Make the x, y, and d points on the fitting boundary located on the same section diagram. The points representing the diagonal direction on the fitting boundary gradually approach and exceed the x and y points during the forming process. It indicates that the fitting speed in the d direction is faster than that in the x and y directions.</p> "> Figure 6
<p>Structure diagram of free-boundary pneumatic film forming method.</p> "> Figure 7
<p>Edge fitting direction.</p> "> Figure 8
<p>At the beginning of bending, the Mises stress was mainly affected by the length of the chip, and the Mises stress on the <span class="html-italic">y</span> axis increased to distinguish the low stress in the middle of the chip. (<b>a</b>) Before the division of the middle low-stress region; (<b>b</b>) After the segmentation of the low stress region in the middle.</p> "> Figure 9
<p>Diagram of stress distribution when edge fitting is completed (S11 represents radial stress, and S22 represents circumferential stress): (<b>a</b>) the shaded area indicates where bonding is complete, forming an arcuate boundary line near the edges. Stress concentration occurs in the central part of the unbonded arc; (<b>b</b>) circumferential stress distribution after edge fitting.</p> "> Figure 10
<p>Buckling from the diagonal caused by the chip being too thin.</p> "> Figure 11
<p>Repeated changes of the chip edge midpoint displacement and subsequent laminating progress reduce the edge fitting speed. (<b>a</b>) Displacement changes during normal forming process; (<b>b</b>) The change of displacement at the midpoint of the edge before buckling occurs.</p> "> Figure 12
<p>Three forming directions in the forming stage.</p> "> Figure 13
<p>Affected by the direction of the diagonal fit, the shape of the fit boundary changes: (<b>a</b>) after the end of edge fitting for a period of time, the arc boundary line from the four corners gradually replaces the rectangular boundary line; (<b>b</b>) boundary shape near the end of molding.</p> "> Figure 14
<p>Mises stress distribution during molding process: (<b>a</b>) Mises stress distribution at the beginning of the molding process; (<b>b</b>) Mises stress distribution during molding; (<b>c</b>) Mises stress distribution change during molding process.</p> "> Figure 15
<p>On the boundary point d passes point x and does not reach point y: (<b>a</b>) The circular boundary line from the four corners has just swallowed up the short boundary line diagram; (<b>b</b>) at this time, the compressive stress in this region reaches its peak, and the maximum stress and range in this region are smaller than that in the concentrated region near the edge; (<b>c</b>) at this time, the area indicated in Figure (<b>c</b>) has been fitted and there is no longer any stress concentration. Taking the region c in the Figure as an example, it is shown that the stress will produce a concentrated phenomenon of regional stress change process.</p> "> Figure 16
<p>In the center of the chip appears a droplet area symmetrical about the <span class="html-italic">y</span>-axis.</p> "> Figure 17
<p>Radial stress distribution at the end of molding.</p> "> Figure 18
<p>Strain distribution in the chip after molding: (<b>a</b>) radial strain results; (<b>b</b>) tangential strain results.</p> ">
Abstract
:1. Introduction
2. Bending Theory
3. Setup of Simulation Parameters
3.1. Elastic Modulus for Polymer Films
3.2. Parameters of CMOS Chips
3.3. Selection of Mould Materials
4. Process of Bending
4.1. Edge Fitting Stage
4.1.1. Edge–Middle Contact
4.1.2. Edge Fitting
4.2. Molding Stage
5. Summarize the Outlook
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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E | 10 | 100 | 300 | 500 | 800 | 1200 | 3000 |
Mises | 1375 | 1375 | 1373 | 1375 | 1377 | 1375 | 1376 |
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Zheng, W.; Li, C.; Hu, J.; Guo, L. Investigation of the Bending Process and Theory in Free-Boundary Pneumatic Film-Forming for Curved Image Sensors. Sensors 2024, 24, 6428. https://doi.org/10.3390/s24196428
Zheng W, Li C, Hu J, Guo L. Investigation of the Bending Process and Theory in Free-Boundary Pneumatic Film-Forming for Curved Image Sensors. Sensors. 2024; 24(19):6428. https://doi.org/10.3390/s24196428
Chicago/Turabian StyleZheng, Weihan, Chunlai Li, Jiangcheng Hu, and Liang Guo. 2024. "Investigation of the Bending Process and Theory in Free-Boundary Pneumatic Film-Forming for Curved Image Sensors" Sensors 24, no. 19: 6428. https://doi.org/10.3390/s24196428