FEATURE TEST & MEASUREMENT
Developments in inspection and test of electronic assemblies
n line with the ever more complex demands being made of electronic systems and more intricate manufacturing processes, inspection and test has ne eded to keep evolving. A consequence of this process, over the last 20 years, has been the development of highly sophisticated inspection and test capabilities, which are as critical to the success of a contract electronic manufacturer’s (CEM) business as the design and manufacturing elements. A simple Google search highlights a vast array of online tutorials, guidelines and parameters to accompany a range of complex test and inspection equipment.
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WHAT DO WE MEAN BY INSPECTION AND TEST? Inspection is the part which ensures the printed circuit board assembly (PCBA) looks good. The test ensures that the PCB’s function correctly. Both aspects need to pass acceptability criteria. A PCBA could function correctly, but fail completely on a cursory visual inspection, suggesting the potential for early failure in the field. Achieving cosmetic perfection is a CEM’s primary objective. However, a PCBA could look visually
perfect, but still fail to function correctly when customers first power up for test. This is an occupational hazard for CEMs, which manufacture small batches of PCBAs, and particularly for new products where functional test routines are not available. A special responsibility
therefore falls on the CEM to ensure the PCBAs look perfect, because perfect looking PCBAs have a higher probability of passing functional test first time. Fortunately, Automatic Optical
Inspection (AOI) machines have become increasingly sophisticated and effective in achieving visual assembly perfection. They have transformed quality standards for small batch CEM, and increased the expectations of customers that look for 100 per cent functional test pass, despite the CEM not having the opportunity to power up the device under test. Most AOI systems compare component
2D images with known good library images, to check presence or absence and orientation of components. The condition of solder joints is checked by comparing the amount of light reflected from a ‘good solder fillet’, to that from an ‘absent solder fillet’. In practice, this is not a precise criteria, and results can be variable. Slightly lifted SMD IC legs (which cause opens) cannot be identified by 2D systems, and they cannot indicate the condition of under component solder joints. Looking down in 2D the camera images simply cannot see these faults. The solution is to take ‘z’ axis
measurements across the entire circuit under inspection, i.e. the heights of all the components. This is what 3D AOI machines do, in addition to conventional 2D inspection. It works by projecting a pixelated matrix of light dots onto the circuit and calculating the position of
Improved troubleshooting and productivity
The VDV II cable verifier series from Ideal Networks is helping network installers to keep productivity high and operational costs low when it comes to troubleshooting in voice, data and video cable installation. Unlike LED verifiers, where the user must decode a sequence of blinking
lights to identify the cabling fault, the display panel on an LCD verifier has intuitive graphics to provide far more comprehensive details on cabling faults, allowing for faster repair. To improve productivity, LCD verifiers can also offer support for multiple
remotes. Using several inexpensive, numbered remotes, a single installer can connect to numerous cables at once and test each one from the patch panel in seconds. The LCD verifier then displays the test result along with the ID number of the remote, ensuring that single-person testing of a jobsite can be completed more efficiently, saving installers both time and money. To ensure that technicians can select the cable verifier which best suits their copper cable testing needs, the series includes a choice of three models, VDV II, VDV II Plus and VDV II Pro.
Ideal Networks
www.idealnetworks.net 16 DECEMBER/JANUARY 2017 | ELECTRICAL ENGINEERING
each dot in space with angled viewing cameras. With comprehensive ‘Z’ axis data, tests can be performed which can measure if solder fillets exist, whether legs are lifted, and whether BGAs are soldered flat, using accurate dimensional data and not guessed light levels. These new 3D machines provide the tools to identify a raft of circuit faults previously invisible to 2D AOI’s. Unfortunately, possible solder faults
evidenced by 3D inspection if they are beneath components, will not be visible by eye, so they must additionally be X- ray inspected. But, at least this extra work can be focussed on potential faults, rather than a mass general inspection.
SO WHAT DOES ALL THIS MEAN FOR SUPPLIERS AND PURCHASERS? Customers need to be confident that the boards they are purchasing are being inspected to the highest level. An expectation of a field life of 15 years is not unreasonable, and the cost of a board failure cannot only be costly but the reputational damage is hard to measure, and even harder to reverse. For manufacturers investing in the 3D automated optical inspection solutions and high resolution X-ray equipment, whilst it is a significant initial outlay, such equipment will undoubtedly provide a recognisable return on investment. CEMs able to guarantee high precision,
non-contact inspection will be at the forefront of the market, providing their clients with higher first time functional test pass rates and much longer mean time before failure in the field. In short, lower lifetime costs.
Newbury Electronics
www.newburyelectronics.co.uk
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