SMART Group Webinar: Advances in AOI technology


Reading time ( words)

Systems for automated optical inspection (AOI) of electronic assemblies have undergone dramatic evolution and development in recent years, from very basic 2D image recognition via “2.5D” and “pseudo 3D” to full 3D techniques. SMART Group recently presented a webinar to clarify the fundamentals of AOI technology and discuss the strengths and weaknesses of the equipment options currently available. SMART Group Chairman Keith Bryant drew upon many years’ experience as a specialist in X-ray and AOI techniques to give a clear and comprehensive overview, with detailed explanations of attributes and applications.

“Through the eye of a needle” was the analogy that Bryant used to illustrate the trend in component size and spacing. Indeed the eye of a needle and the head of a pin looked huge compared with the 01005 chips he showed next to them. And when these chips were placed at 0.1 mm spacing, covering up to 83% of the local real estate, inspecting them for placement accuracy and solder joint quality became a real challenge. At the other end of the packaging scale were the Z-axis issues of inspecting BGAs and QFNs for coplanarity and PoPs for warpage.

Keith Bryant.jpgLots of good equipment was available for traditional inspection: Magnifiers, comparators, digital imaging devices, and video microscopes, but all depended ultimately on the human eye. “Is there a standard eye test for assembly operators?” Bryant asked. (Apparently there is in some aerospace specifications!). But in reality, the missed-defects rate was disturbingly high. The second consideration was the inconsistency of “judgement of what is acceptable.” Guidelines existed, for example IPC-A-610, but it was the operator’s interpretation that determined whether a defect was rejectable.

So what were the automated options? Bryant listed functional test of finished product, electrical test of partial or finished assemblies, in-circuit test of circuits and components, automated X-ray inspection for soldering and presence of components, AOI for soldering and components, and automatic solder paste inspection. He chose to focus on AOI for detail discussion.

First decision to be made was whereabouts in the process to use AOI most effectively--inspection of solder paste, component placement, solder post-reflow, or all three? Three machines on-line or a single machine off-line, able to perform all three functions on a sample basis? Whatever the decision, AOI would give more consistent results than the human eye, and, if used pre-reflow, would check for attributes such as component presence and position, component identity, orientation, polarity, and alignment. Most importantly in Bryant’s view, it would replace the “dangerous tweezer-people.” Post-reflow, the inspection task became particularly demanding. In Bryant’s words, “It’s hard to define a good solder joint--it’s even harder to define a good-enough solder joint!”

Bryant went on to explain the principles of AOI technology, the various illumination, image-capture, and image-analysis techniques available, their relative costs and capabilities, and the differences between the terms “2D,” “2.5D,” “pseudo 3D,” and “real 3D.” He discussed in detail the value of true z-axis information, particularly in solder paste inspection, citing the widely accepted view that over 60% of assembly defects originate from the solder paste printing stage, then showed several examples illustrating the limitations of 2D post-reflow inspection and some of the of subtle defects that could be revealed by high-end 3D systems.

Share

Print


Suggested Items

Juan Arango on Koh Young’s New U.S. Headquarters

10/27/2019 | Andy Shaughnessy, I-Connect007
At a recent open house, Managing Director Juan Arango talks about his role in the company’s transition from their Arizona facility to a new headquarters located outside of Atlanta, Georgia. Juan details many of the benefits customers can expect, including brand new spaces dedicated to customer demos as well as training.

SMTAI 2019: Chris Bastecki on Low-temperature Solder Challenges and Products

10/14/2019 | Real Time with...SMTAI
Chris Bastecki, director of global PCB assembly at Indium Corporation, discussed challenges of low-temperature solder and the company's new product, Durafuse LT, which provides novel properties and reliability.

Real Time with... SMTAI 2019 Video Interviews

10/09/2019 | Real Time with...SMTAI
The SMTA International Conference and Exhibition 2019, which took place September 22–26, 2019, at the Donald E. Stephens Convention Center in Rosemont, Illinois, concluded successfully. For those of you who were not able to make it to the show, catch our video interviews with the movers and shakers of the electronics industry. We've updated our video presentation for a better experience for our users, so check it out!



Copyright © 2019 I-Connect007. All rights reserved.