Application-Specific 3D Machine Vision Systems For The Electronic Industry

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. ‘bow 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 moiré.  Shadow moiré 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.

3.  What are critical 3D machine vision system performance criteria?

[Patrick] Repeatability, reproducibility, throughput/speed across all applications.  Some applications demand very high levels of sensitivity and accuracy.

[Frank] Height resolution at 10µm per gray value.

[Stacy/Glen] Throughput, low false fails, high call accuracy and repeatability are typically performance criteria consider when comparing machine vision systems.

[Shavi]       
- Speed of inspection - better than the automatic line tact time
- Accuracy of results  (in PCB assemble Gage R&R better than 10% on smallest deposits) 
- Fast set up time 
- Support all PCB materials and finishes 
- Less expensive than previous generation 
- Connection of measurements to process control SW ( real time SPC) 

4.  What changes have been taking place in the technologies that are the basis of 3D machine vision systems used in the electronic industry that has resulted in improved performance?

[Frank] For triangulation applications partly improved resolution by enhanced laser optics. 

• Faster data acquisition by specially designed ASICs, e.g. for triangulation evaluation directly on the camera chip.
• Advantages for stereoscopic approaches using megapixel camera chips (increased resolution at given overlap).
• Faster calculators/processors allow for more complicated 3d data evaluations
• (Advantages for phase shifting approaches, real-time suppression/correction of artifacts etc.)

[Shavi] New sensors (large foot print – higher resolution) and ability to control the data extraction algorithms.

[Stacy/Glen] The evolution of solid shape modeling (SSM) to provide a full 3D view of components and solder paste deposits has taken the 3D machine vision concept for AOI to a new level.  This technology gives users the ability to maintain higher call accuracy and additionally gives users rotatable views of images that can assist them with process understanding.  Improved imaging technologies and the continuing improvement in price/performance of computers increase system performance while reducing system cost.

[Patrick] Shadow moiré algorithms are getting smarter and more robust  - readily increasing the range of surfaces that can be analyzed with the technique.  Also, we are seeing better off-the-shelf image processing tools that help our analyses operate faster and more robustly. Image processing tools (such as part finder algorithms) represent good opportunities to increase performance at reduced cost.  For example, less accuracy is needed for part delivery into the inspection head to achieve the same quality level of measurement .  

5.  Where do you see breakthroughs coming in the technologies that are the basis of 3D machine vision systems used in the electronic industry that will result in further improvements in the near future - next three years?

[Stacy/Glen] Camera technologies and computer performance continue to advance and thus allow speeds and throughputs to be positively impacted.  The evolution of software solutions such as Agilent's solid shape modeling (SSM) also provides users with more information to make improvements and facilitate understanding about their process, products, etc. The evolution of these two areas will drive 3D imaging.

[Shavi] Better sensors (faster) that will allow further improvement in speed and larger sensor dimension that will allow larger FOV or longer line scanning.

[Frank] Perhaps more intensive use of ‘‘3D-ASICs’‘ with faster performance

[Patrick] Cost, processing speed and multifunctional systems (bundled capabilities) are always of interest to our customer’s future needs.  We are only adopting/developing techniques that can move from the laboratory to the production floor. 

6.  Are there market changes in the electronic industry that are driving the adoption of 3D machine vision?

[Frank] Smaller structures (0201, pitch 0.3mm) needs test gates behind every production step due to higher possibility of faults.

[Stacy/Glen] There are two main drivers for these changes and their adoption in the industry.  One category is quality and the other is technology.  The interest in quality is increasing as companies compete for assembly contracts, quality can be linked to 3D information in many cases with inspection and as such, 3D imaging is critical.  With regards to technology, smaller pitches, increased circuit density and speeds, advances in component technologies and the emergence of lead-free are impacting interested in 3D machine vision.

[Patrick] In our business, yes.  There are definite issues with warpage for fine pitch devices that are on the leading edge of assembly technologies.  Larger BGA devices (40mm +), Lead-free processing techniques, bromine-free laminates materials, expanded options of underfill and encapsulants products – all require characterization for impact on warpage.  Warpage can heighten defects dramatically on fine pitch assemblies.

[Shavi] Yes - finer components and finer pitches of paste deposits require 3D view on them because the volume of the deposits is the main indicator of the level of good soldering. In addition it is also height. Imagine a BGA where not all deposits are the same height - not all balls will be soldered correctly.

7.  How will 3D machine vision systems have to change to meet emerging applications in the electronic industry?

[Patrick] Depends on the application.  But for our business we will seek to add additional functionality to our systems and/or incorporate our technology into existing/other inspection systems.

[Shavi] 1) meet line speed 2) less expensive, 3) able to detect small deposits.

[Stacy/Glen] Continuous evolution of speed and call accuracy, always with an eye toward cost, are typically required to meet the needs of emerging applications.  

[Frank] Perhaps more intuitive system operation.

8.  As a supplier of 3D machine vision systems for the electronic industry what are some challenges you face in marketing such systems?

[Frank] The market misunderstanding of what 3D really means.  Staying on the price performance curve.

[Patrrick] As an emerging company, we are faced with a wide range of issues including: Distribution channels (i.e. indirect sales force); on-site demonstration systems; paradigm shift (i.e. new approach versus old approach) required for inspection mentality in some application areas.

[Shavi] 1) Pass the accuracy test at each customer in order to meet requirements. 2) Education of market on the importance of 3D versus 2D systems.

[Stacy/Glen] Customers' assembly lines continue to run faster and faster, and competition among suppliers of imaging equipment are driving the industry to design and build faster, more reliable, and less costly systems.

9.  What are your thoughts on the future of 3D machine vision in the electronic industry?

[Stacy/Glen] 3D techniques have the potential to offer a quantum leap in performance levels from advanced test and measurement equipment, particularly as densities increase, double sided boards become the norm, and end customers' reliability expectations continue to rise.  The powerful advantages of 3D techniques mean they are rapidly becoming the only safe bet for future test and inspection.

[Patrick] We feel the future is very positive.  And not just in the electronics industry.  We are looking aggressively at other markets/industries that will benefit from our existing technologies and optical/non-contact metrology tools as a whole.

[Shavi] There are a lot of segments that will require 3D inspection - Ball inspection, memory cards and also some semiconductor applications.

[Frank] The importance of 3D inspection will increase for a certain (but as well limited) range of applications.  3D will NOT replace 2D-solutions for all applications!

10.  What advice would you give to a company investigating the purchase of a 3D machine vision system for an electronic industry application?

[Shavi] 1) Check that the AOI machine is really meeting your specification of inspection: speed, setup time and accuracy. In addition a full solution is required to improve the process and additional SW tools should be available to make process improvements.

[Frank] Analyze why you want 3D and the benefits that it brings your company before you review the possible solutions.

[Patrick] Don’t buy more than you need.  We see numerous customers with a performance list (and/or wish list) that is far in excess of their primary applications.  All this excess can greatly impact your price, cost of ownership and the ROI. Of course, one must think of future application needs, but see if the platform is upgradeable to accommodate future improvements that will cost less at a later date.

[Stacy/Glen] Considering a portfolio solution can improve the cost of ownership for the customer.  Be sure to include the cost of ownership and system flexibility in your considerations. These often impact the bottom line more than feature-based investigation of machine vision solutions.   Also, a realistic analysis of the cost of passing along defects instead of finding and fixing them as early as possible will demonstrate the economics of 3D inspection.