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Research Papers

Numerical and Experimental Analysis of Solder Joint Self-Alignment in Fiber Attachment Soldering

[+] Author and Article Information
Wei Zhang1

Microjoining Laboratory, School of Material Science and Engineering,  Harbin Institute of Technology, Harbin 150001, P.R.C.zmacho@hit.edu.cn

Chunqing Wang, Yanhong Tian

Microjoining Laboratory, School of Material Science and Engineering,  Harbin Institute of Technology, Harbin 150001, P.R.C.

1

Corresponding author.

J. Electron. Packag 130(1), 011009 (Feb 12, 2008) (9 pages) doi:10.1115/1.2837518 History: Received October 28, 2006; Revised June 25, 2007; Published February 12, 2008

Fiber attachment soldering is low cost and high-precision technology in direct-coupling optoelectronic packaging. For accurate alignment, it is crucial to understand the self-alignment behavior of solder joint. In this research, the self-alignment method by using surface tension of molten solder and by adopting specific pad shape was proposed. First, the self-alignment model of solder joint in fiber attachment soldering was developed by using the public domain software called SURFACE EVOLVER and the three-dimensional geometry of solder joint with different solder volume was analyzed. Then, the self-alignment behavior of solder joint with an initial yaw misalignment was discussed and the theoretical equilibrium positions of ellipse and square pad were calculated. Next, based on the minimum potential energy theorem and data from geometry simulation, the influences of design and material parameters on the standoff height (SOH) were analyzed. Furthermore, experiments were done to examine the theoretical equilibrium positions of ellipse and square pad and the SOHs of solder joints were measured by using confocal scanning laser microscope. The numerical results show that the theoretical equilibrium positions of ellipse and square pad are the major axis of ellipse and the diagonal of square, respectively. SOH can be controlled by adopting proper solder volume, which is above the critical value for specific pad. The experimental results show that the solder joint with initial yaw angle can be self-aligned to the theoretical equilibrium position of pad and solder joint with ellipse pad substrate demonstrates smaller alignment error than those with square pad substrate. The measurement results of SOH are in agreement with the simulation results.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Numerical model of fiber attachment soldering

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Figure 2

Effects of solder volume on 3D geometry and self-alignment: (a) when solder volume does not wet the pad boundary completely, the fiber is pulled out of alignment, (b) when the solder splits on top of the fiber, it is favorable to self-alignment, and (c) when the solder encircles the fiber, the restoring force and torque are too small for self-alignment

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Figure 3

Effects of contact angle on critical solder volume (the diameter of the fiber is 128μm, the ellipse pad has major and minor axes of 576μm and 384μm, respectively, and the SOH is zero)

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Figure 4

Principle of self-alignment of fiber (a) putting the fiber on solder paste, (b) reflowing and aligning by surface tension, and (c) accomplishing the self-alignment

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Figure 5

Total system energy and restoring torque varying with the yaw of fiber: (a) ellipse pad and (b) square pad

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Figure 6

Effects of solder volume on self-alignment of fiber in cases involving ellipse pads (solder volume exceeds the lower critical value)

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Figure 7

Effects of surface tension coefficient on self-alignment of fiber in cases involving ellipse pads

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Figure 8

Effects of contact angle on self-alignment of fiber in cases involving ellipse pads: (a) contact angle on the fiber and (b) contact angle on the pad

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Figure 9

Effects of solder volume on SOH in cases involving ellipse pads

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Figure 10

Effects of pad size on SOH in cases involving ellipse pads

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Figure 11

Effects of pad shape on SOH in cases involving ellipse pads

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Figure 12

Effects of surface tension coefficient on SOH in cases involving ellipse pads

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Figure 13

Pictures of pad with different shapes: (a) ellipse (6×4mm2) and (b) square (4×4mm2)

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Figure 14

Ellipse pad with solder paste and copper rod deposited before reflowing

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Figure 15

Relationship between initial angle and alignment final angle: (a) ellipse pad and (b) square pad

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Figure 16

The 3D geometry of solder joint with ellipse pad (solder volume adopted is 19.23×10−6cm3)

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Figure 17

The SOH and profile of solder joint with ellipse pad (solder volume adopted is 19.23×10−6cm3)

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Figure 18

Numerical results of SOH compare with the experimental results (ellipse pad is 874×437μm2)

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