Application-Specific 3D Machine Vision Systems For The Electronic Industry
by Nello Zuech, President, Vision Systems International, Consultancy
(posted 08/09/2004)

By far the largest application of 3D-based machine vision techniques in the electronic industry is for solder paste inspection. Systems are in widespread use to measure the volume, height, coverage and position of the solder paste after screen-printing and before component placement. As IC package interconnect densities increase and surface mount devices continue to decrease their footprints, the volume of solder paste becomes an even greater factor in determining the ultimate quality of the solder joint. Hence, monitoring and controlling solder paste volume are critical to successful first pass yields and reduction of corresponding rework. Solutions addressing 3D volume measurements have been around for some time. However, the market has been relatively slow to embrace them. While interconnects were less dense, the actual solder paste volume was not as critical. At the same time, the early systems were slower and more suitable for offline measurements than online measurements. With the advances in the underlying technologies that make up a machine vision system (higher resolution, digital cameras; application-specific LED lighting arrangements; better, faster, cheaper computing power, etc.), many systems are available that can keep up with the output of a screen printer making online measurements possible to provide immediate feedback to conditions that will result in out of spec conditions. While there are several companies that specialize in solder paste volume inspection systems, most of the companies that offer machine vision-based AOI post-component placement inspection systems also offer 3D-based systems for solder paste inspection as well. By using multiple camera arrangements some of these same systems are able to extract 3D data for solder fillet inspection, for example. Another 3D machine vision application in the electronic industry involves preloaded board inspection for warpage. As interconnect densities increase, local area (i.e. component site) warpage is becoming a significant factor when it comes to both solder joint yield and reliability.  New specifications are beginning to appear for finished board flatness that go beyond traditional bow and twist by including component site flatness requirements. 3D machine vision includes acquiring image data, operating on that data, and analyzing the data so as to automatically make decisions without operator intervention for the purpose of control: quality control, process control, machine control, robot control, etc. The method for acquiring the 3D image data could be based on using area-based cameras, line scan-based cameras, laser scanners, x-ray, infrared, etc. The principles used in capturing 3D data could be stereovision, laser triangulation, laser ranging, structured light, photogrammetric, systematic cross-sectioning, etc. Companies known to be suppliers of 3D-based machine vision systems for these applications in the electronic industry were asked to contribute to this article. They were forwarded a questionnaire and asked for their responses accordingly. Those contributing were:

• Stacy Kalisz Johnson, Product Manager and Glen Leinbach 5DX Technical Marketing Engineer, Agilent Technologies Patrick Haskell, President, AkroMetrix Shavi Spinzi, Director of Marketing, Orbotech
• Frank Marangell, VP of Sales, Viscom

1.  What are some specific applications in the electronic industry that your company addresses with 3D machine vision technology? [Stacy Kalisz Johnson and Glen Leinbach] Agilent technologies has a portfolio of imaging solutions that include 3D machine vision imaging for solder paste inspection (SPI) for checking the screen print process, in-line automated optical inspection (AOI) for testing components and joints and x-ray systems for solder joint testing. [Frank Marangell] Viscom offers 3D solder paste inspection and wire bond inspection (loop height). [Shavi Spinzi] Orbotech uses 3D machines to inspect solder paste deposits in the electronic PCB assembly industry. [Patrick Haskell] AkroMetrix offers 3D-based machine vision systems for the general applications of substrate, package and assembly warpage/flatness measurement.  A laboratory product line (TherMoire) enables the unique ability to measure flatness during thermal loading (i.e. reflow processing, curing and operating environments).   A production level product line (LineMoire) enables volume inspection of bare PCB warpage (a.k.a. 慴ow and twist? at room temperature in volume; localized (i.e. key BGA component site) flatness on PCBs; semiconductor chip-carrier flatness (i.e. coplanarity) prior to die placement; flatness of metal lids and cavities for semiconductor packages; parallelism.
2.  Can you provide a general description of the approach your products use to arrive at 3D image data? [Shavi] We use laser triangulation method, which is quite well known in the industry. The main advantage that we deliver (from optical head aspects) is a very fast speed of inspection - up to 40 sq-cm/second with X-Y resolution of 20 X 20 microns and height resolution of 5 microns. [Stacy/Glen] For solder paste inspection, the Agilent solution uses laser triangulation to provide 3D image data. This is coupled with solid shape modeling, a revolutionary method for mapping the already available laser triangulation data into a full 3D rendering.  For component inspection, the Agilent solution uses color visible light coupled with solid shape modeling to give 3D AOI information. For xray, the Agilent solution uses cross-sectional x-ray test, which provides 3D information by extracting visible 'slices' at the desired level for automatic analysis while rendering features at other levels invisible.   This allows x-ray inspection of double-sided PCAs and inspection of BGA and CCGA component solder joints at multiple heights. [Frank] The principle is laser triangulation by use of two laser lines combined with an area-based camera with integrated triangulation calculation.

[Patrick] We use a measurement technique known as shadow moir?  Shadow moir?is an interferometric technique that is optical (white light), non-contact and full-field in nature.  Getting data involves handling/presentation of the sample to the measurement head.  A phase-stepping process that involves multiple image collection (approximately 3), and algorithmic processing of the images collected to create an out-of-plane displacement matrix for the surface under investigation. Speed (1 second data acquisition regardless of area), resolution (2.5 microns or better) and cost are core advantages to the technique.