Vision for Solder Paste Depositing Review by Jeremy LeFevre Authors Yongcong Kuang the College of Mechanical Engineering South China University of Technology Guangzhou China Shenglin Lu ID: 261433
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Slide1
An Integrated Inspection Method based on Machine
Vision for Solder Paste Depositing
Review by Jeremy
LeFevreSlide2
Authors
Yongcong
Kuang
the College of Mechanical Engineering
South China University of TechnologyGuangzhou, China
Shenglin Luthe College of Mechanical EngineeringSouth China University of TechnologyGuangzhou, Chinajoolu@163.com
Xianmin Zhangthe College of Mechanical EngineeringSouth China University of TechnologyGuangzhou, Chinazhangxm@ scut.edu.cn
Publishing Information:
2007
IEEE International Conference on Control and Automation
WeC5-3
Guangzhou
, CHINA - May 30 to June 1, 2007Slide3
Purpose of Article
Demonstrate that 2D automated
imaging of Stencil Printing Process (SPP) for solder application to
IC boards
can be used to identify soldered areas, determine defects, and prevent component destruction during board testing. This paper mentions that 50-70% of Printed Circuit Board (PCB) defects are caused by the SPP process or other solder depositing methods.Slide4
Importance
While inspection methods already exist, they use a laser that determines
where solder has been placed and take measurements to determine whether defects are present. They are capable of finding three dimensional soldering errors by directly measuring the thickness of the solder compared to known height of the contact base. However, laser imaging techniques are slow and generally take too much time. They’re not practical to perform on every PCB that undergoes the SPP.Slide5
References
[1] Nepcon
South China 2007, [Online]. Available
: http://www.nepconchina.com
[
2] Glenn Wyllie, Mark Norris, "2D or Not 2D, That Is TheQuestion!" ,Conference: SMTA International, 2003[3] D. Burr, "Solder paste inspection: process control for defect reduction,"
Test Conference, 1997. Proceedings., International, Nov. 1997,pp.1036.[4] T. Okura, M. Kanai, S. Ogata, T. Takei, and H. Takakusagi,"Optimization of solder paste printability with laser inspectiontechnique," Electronics Manufacturing Technology Symposium, 1995.Manufacturing Technologies - Present and Future' SeventeenthIEEEICPMT International, 1995, pp.361 - 365.
[5] Omron Inc. "AOI Inspection in Pb Free Craft," Equipment forElectronic Products Manufacturing, 2003, Vol64.[6] J. Mahon, "Automatic 3-D inspection of solder paste on surface mountprinted circuit boards ," Journal of Materials Processing Technology,Volume 26, Issue 2, June 1991, pp. 245-256.[7] Rafael C. Gonzalez Richard E. Woods Digital Image Process Publishing
House of Electronics Industry, 2004
.
[8]
National
lnstruments
, IMAQ Vision Concepts Manual,2003, pp.10-1.Slide6
Design
Immediately before the SPP, the imaging system helps line up the PCB and stencil system. Then the inspection system takes a photo of the contacts. When the image has been taken, the previous image can be used to compare the change in surface texture. Looking at a couple of fixed points, the images can be rotated or translated to line up the images. This system used a 3 axis SPP system with a squeegee and the mentioned imaging system.Slide7
Design
After aligning the images of the before and after shots, the inspection system needs to find whether the solder paste has been successfully deposited on the desired site. To make such a determination, the image is sharpened around the average
greyscale
color of the solder beads. This requires a somewhat complex, but common imaging algorithm.Slide8
Pseudo 3D Solder Analysis
This is the major part of the article that made me skeptical, as it is not well explained and uses inherently uses some assumptions that can’t be right all of the time, and probably would rarely be correct. Whether or not this yields a good estimate to the amount of solder deposited on the contacts is poorly explained by the authors, though they seem to think that this yields a good estimate.Slide9
Potential Industries Affected
If this method proves successful, this could be extended to multiple electronics companies. This would lower rejection rates significantly by allowing the board to be cleaned and fixed before the reflow process and more importantly, before the board testing process which could potentially damage or destroy components with bad connections.
This process could be applied to desktop computers, notebook computers, calculators, cell phones, planners, GPS navigation systems, televisions, and any other electronics that include an IC with logic components.
That includes of course, Mitsubishi projectors.
Images courtesy of Global SMT and Packaging.
<http://www.globalsmt.net/troubleshooter/printing_paste_misalignment.htm>