Laser-based PCB assembly inspection

Author : Ian Crighton, Head of Sales and Marketing at Amfax

12 September 2017

Electronic products typically have stringent testing requirements, particularly as the PCBs that power them have become more complex, miniaturised and mass-produced. Accurately and repeatedly inspecting PCB assemblies improves product quality and ensures reliability in use, helping to reduce the negative impact of field failures and product recall events, ultimately improving brand reputation. But doing so has traditionally been both difficult and costly.

This article originally appeared in the September 2017 issue of Electronic Product Design & Test; to view the digital edition, click here – and to register to receive your own printed copy, click here.

This article explains how the test system solutions provider developed its a3Di PCBA inspection system to help electronics manufacturers overcome this challenge.

Amfax specialises in designing and manufacturing test engineering and inspection solutions for customers worldwide, including blue chip companies in aerospace, rail, transport, energy, telecommunications and consumer electronics. A common challenge we have observed across our customer base is that PCB manufacturers have struggled for years to accurately and repeatedly inspect their PCB assemblies to ensure correct component placement and good quality solder joints.

In response to such a problem, Amfax has developed the a3Di, a revolutionary XYZ measurement-based PCBA inspection machine, combining the benefits of 3-dimensional laser-based metrology and new patented software algorithms to produce the world’s most accurate PCB assembly inspection system. This enables OEMs and CEMs to significantly reduce their lifecycle PCBA inspection costs – and ultimately improve their brands’ reputations.

Historically, human inspectors have been used to inspect PCBs at the end of the production line. However, as this became uneconomical and prone to poor repeatability (particularly for volume production), due to the limited concentration span of most human inspectors, many companies switched instead to Automated Optical Inspection (AOI) systems. These automated systems use cameras to capture images of the board, before comparing and contrasting them against a ‘gold reference standard’ to check whether the PCB assembly passes or fails.

These systems certainly provide significant benefits over the inherently flawed human inspection method: AOI systems rely on a comparison technique, and every difference identified between the images results in a failure being reported.

Many of these identified ‘failures’, however, can end up being misnomers: flagged as potential failures, the system’s local operator must make the final decision after manual visual inspection. These incorrect potential failures are known as ‘false calls’. Their high occurrence rate on 2D and 3D AOI systems means that there needs to be an operator present when the PCBAs are under inspection. This incurs additional operating costs, and the machine must be halted every time a potential failure occurs to enable the operator to visually inspect the PCBA before deciding whether it can be passed (a ‘false call’) or failed.

The Amfax a3Di system employs a completely different approach to overcome these challenges: it uses twin laser-based metrology technology to take millions of XYZ measurements across the whole of the PCBA under inspection – scanning the board assembly down to sub-micron level in just a few seconds. These measurements can then be validated directly against the original CAD data, in order to determine whether the board has any issues relating to the solder joints, component placement and orientation, foreign objects or board warpage.

The benefit of working with absolute 3D measurements, rather than a comparative methodology such as AOI, is near zero false calls, removing the need for operator inspection and subjective decisions. Either the board passes or it doesn’t, and this reduces cost and significantly improves both quality and production throughput.

The a3Di system is capable of repeatedly taking highly accurate and precise measurements, resulting in superior system uptime; this means that significant increases in OEE (overall equipment effectiveness) can be achieved, potentially helping to introduce Six Sigma techniques to PCBA manufacturing lines. One consumer electronics manufacturer in Asia is currently testing over 18,000 boards per day using one a3Di, a significant improvement over their previous solution.

At the heart of the machine, the a3Di control system uses FPGA-based National Instruments CompactRIO (cRIO) and LabVIEW technology to manage all aspects of the machine’s operation, I/O and sensors, including:

  • Machine motors

  • Control switches

  • Optical position sensors

  • Inverters

  • Up and downstream SMEMA (Surface Mount Equipment Manufacturers Association) conveyor control

  • Light tower

  • Pneumatics

  • Operator manual controls for width PCB control

  • System emergency stop

Using cRIO as the control system significantly reduced our development time and helped us get the various autonomous state machines of the multiple control cells running with far tighter timings than the normal 1ms tick of most PLCs.

The cost and efficiency savings a3DI enables are important, of course; however, the real benefit in using the technology is that the system can restrict the shipping of potentially poor quality products into the market. With 100% board coverage and absolute measurement testing, a3Di not only helps improve the final board inspection, but has also found its way into the NPI (new product introduction) process. New product design prototypes can be checked and validated quickly and accurately, with 100% confidence, resulting in faster time to market and significant reductions in field failures.

The advanced technology and sophisticated techniques used by the a3Di system enables Amfax to offer a unique, world-class and well-supported solution to OEMs and CEMs looking to improve their PCBA assembly inspection process and significantly reduce their operational costs. The a3Di is also revolutionising the way PCBA manufacturers can now compete for their customers’ business.

By using a3Di, these manufacturers have a unique selling proposition to offer their own customers. They can pass on savings made by using a3Di and guarantee that the boards being manufactured are tested by the most accurate system available for the job.

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