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PODCAST: Chris Gregory shares his experience as a test engineer for over 25 years and how test technology has changed over time. Podcast – My Career in Test (12 mins)
1. AbstractAn automated unified test system for printed circuit boards and assemblies is designed around a test hardware and software platform to improve performance, increase throughput, reduce maintenance costs and reduce the amount of test systems required to test a company’s product portfolio. 2. Problem statementIn today’s world of ever-increasing technology advancement, printed circuit boards (PCB’s) continue to become more complex with advanced chips being an integral part of board design. Following manufacture of such boards, they must be tested to ensure they are functionally correct and fit for purpose. With the drive to increase first pass yield (FPY), increase test throughput and reduce PCB costs overall, legacy test systems as described above no longer provide a viable test platform to meet these objectives and a new approach is needed. 3. BackgroundFor many years, test systems have been created specifically to test a particular device under test (DUT) or assembly. These systems usually have a requirements specification created and owned by the product group responsible for the DUT without any regard to a companywide test strategy, if indeed one exists. They are often bespoke designed to meet the requirements of a single DUT. This leads to many test systems incurring:
Assets like the above tend to be used long after the depreciation period due to cost replacement. This leads to the frustration of management with very high costs being involved to maintain systems. The lack of a companywide test strategy was, my experience whilst working as a test engineer for a previous global company for 23+ years. When a new DUT was developed, the responsible product group created the test system requirement based on tests used for design verification. Whilst these tests are somewhat justified for new product introduction (NPI) they will not necessarily be correct for the production environment. For New Product Development (NPD), focus is given to the DUT’s design validation and verification (V&V), where-as production tests revolve around ensuring that the product has been assembled correctly, catches infant mortality, functions as expected, maximizes the first pass yield (FPY) target rate and minimizes test execution time. A companywide test strategy provides:
By removing product groups from the test system design process and creating a test strategy managed by a test management team, manufacturing test issues can be overcome and streamlined. 4. SolutionThe use of NI hardware and software is pivotal to creating a quality unified test system. PXI based modular instrumentation hardware together with the LabVIEW and TestStand software, provide an ideal platform to create systems that are both powerful and flexible in nature. With collaboration between Amfax, NI and the customer, a NI core config rack system was developed that was not only unified in nature, it allowed for many different types of DUT to be tested at production levels. Up to 16 DUTS of the same type can be tested in TestStand batch mode (where applicable) significantly reducing the amount of time required per DUT test.
5. ConclusionUnified test systems can be a far more cost-effective solution even though the initial outlay will be more expensive. The ability to test several DUT’s of the same type concurrently dramatically reduces the test time of each DUT and fits perfectly with the batch production methods of DUT manufacturing.
Test assets are expensive and need to have the agility to test many different types of DUT so they operate and provide great performance at all times. Maintenance and calibration costs are significantly reduced due to the ease of regular maintenance of a common system together with a significantly reduced number of assets requiring calibration. Operators become more knowledgeable of a common system and requiring less training. In summary;
Why a global leader sought a new solution;With expertise in more than 120 countries, our client designs and maintains products globally, often requiring numerous bespoke test solutions throughout their portfolio. They sought to:
The key requirements of the project;The major requirements were as follows:
The collaborative process that drove project success;Collaboration from the first phone call;The team at Amfax worked with the client during the early concept ideas, exploring existing solutions and understanding the long-term needs of the client. An overview of the final test solution;A high functionality common test rack with mass interconnect;The common test rack involves an NI core rack, expanded with additional resources and switching functionality. A mass interconnect system is installed, using direct access kits for connectivity to PXI cards and a custom hybrid module for all other rack resources. The system contains:
 Image modified from © MAC Panel A minimal wiring generic interface test adapter;
The first variant of replaceable port modules;Within each port module is an identifying code that the common rack can interpret to indicate the variant of port module installed. Internal port module current sensors enabled individual supplies to be monitored in real time and internal relays provided 2nd layer switching allowing sophisticated signal routing to be performed. Good quality documentation that supported the programme;The value of a well-executed block diagram;Amfax designed a detailed top-level block diagram early in the project that formed the basis of collaborative design discussions with the client. Later, the initial commissioning of the test system used this block diagram as the primary source of information to identify signal path connectivity during software development. Using the clients preferred drawing and document packages;To make it easy for the client to take ownership of all drawings after project closures, Amfax used the clients preferred drawing and document packages such that the client could port these into their own documentation management system to provide the flexibility for them to maintain the design in the future. This includes using Altium Designer for electrical schematics, step files and DWG files for mechanical drawings, and Microsoft Office programmes for other supporting documents, test procedures, and manufacturing build documents. The resulting impact and on-going success of the test solution;Why modularity simplifies maintenance and support;If there are any issues in-service, the extended modularity reduces downtime by enabling operators to swap out a failed module (i.e. the port module), and replace with a spare and/or send the module off for repair. Proof of concept and rollout;After successful commissioning at a clients’ contract manufacturer, over a 2 year period, a further 8 systems were produced as “Build to Print” and deployed at all the clients contract manufacturers globally. All new DUTS are now tested on these systems with a program in place to convert the testing of all DUTs to the new system. This requires only DUT cassettes to be designed and manufactured along with new software. The overall impact is that the client now sees a significant reduction in the cost of test. In their own words: “This new test system has, and continues to be, a game changer for the company. Typical lead times for supporting new DUT’s has been reduced by approximately 50%”. For our client, it’s now accepted as the global test station; all new product must be designed to be tested on it.
Amfax delivers a new generic ATE for testing aerospace pilot display unit modules. The system enables testing of all module types using the same tester  Amfax have recently designed, built and delivered core PXI based automated test systems to a major aerospace manufacturer. The brief was to come up with a design that could test all the pilots display unit (PDU) modules using a single automated tester. Previously the client had a number of ATE's that each tested just one module. This meant that previously the client not only had to invest in multiple testers but had to obtain support for each unit separately. The ATE used a fully loaded PXI rack to house all of the instrumentation needed to ensure test coverage of all the measurements required for each module. The modules tested included a solar cell, electronic display, interface unit and auxiliary PCBs. System benefits:
System features:
Challenge: To design and develop a revolutionary 3D measurement based Printed Circuit Board Assembly (PCBA) inspection technology to help companies improve the quality of their product. Solution: Combining the benefits of the NI Compact RIO FPGA platform and the user interface qualities of LabVIEW helped Amfax develop the world’s most accurate PCBA inspection system enabling OEM’s and CEM’s to significantly reduce their lifecycle costs. Amfax, are a global Platinum Alliance Partner of 23 years who specialize in designing and manufacturing test engineering solutions for our customers worldwide. Our extensive customer base includes blue chip companies in the aerospace, rail, transport, energy, telecommunications and consumer electronics market sectors. The challenge we have addressed by developing the a3Di PCBA inspection system is that many PCBA manufacturing companies were struggling to solve a problem of accurately and repeatedly inspecting their PCBA to ensure correct component placement and good quality solder joints to improve reliability in use.  Historically, humans have been used to visually inspect PCBA’s at the end of the production line. This is prone to poor repeatability and consistency of inspection and as such many companies have switched to Automated Optical Inspection (AOI) systems. These automated systems use cameras in place of the inspectors to capture images of the board and then subjectively compare these images against a reference standard to check if the PCBA has any faults. Any difference between the image and reference standard is flagged by the AOI as a potential failure. The local system operator must then make the final decision as to whether it is a “real” defect or not. There is always a tradeoff in these systems between generating potential failures that an operator reviews, which are known as false fails or relaxing the rules and allowing false passes. Both incur additional operating cost and can potentially affect the products quality. These systems certainly have their place as they provide significant benefits over the human inspection method and have been the system of choice for PCBA inspection for a number of years. The team at Amfax felt there must be a better, more reliable and ultimately more cost effective solution to the inherent problems associated with AOI systems, so set out to design and build the Amfax a3Di.  What makes a3Di unique? The Amfax a3Di system takes a completely different approach to address the challenges raised by AOI systems. It users a twin metrology based measurement technology to take millions of measurements with accuracies of under 5 microns to build a compete 3D representation of a PCBA or any other object that can fit inside the a3Di. The system scans a PCBA in a matter of a few seconds and the measurements are tested, one to one, against the original CAD dimensional data to determine whether the board has any problems relating to the component or lead location, orientation and size. Solder joints are also reviewed for shape and volume and can be matched to IPC Class 1,2 and 3 recommendations. Uniquely it measures the complete PCBA and thus can find foreign objects between packages or excessive board warpage on the PCBA that can prevent the PCBA mating with its housing at a future stage.  As a3Di is performing real measurement testing, there is no need for an operator as there are no false calls, either the board passes the test or not. That is the advantage of testing against real 3D measurements instead of relying on a comparative methodology such as AOI. The result is zero false calls and no subjective decisions needing to be made by an operator. This means that the users of a3Di save the cost of operators, increase product throughput and more significantly improve their product quality. NI cRIO – The heart of the machine The heart of the a3Di is the control system used to control all aspects of the machines operation. The a3Di was a brand new design for Amfax, so as a Platinum Alliance Partner our first thought was that we must use cRIO. The control system chosen for A3Di is a NI cRIO system using FPGA and the NI 9375D I/O hardware. The performance of this cRIO solution is staggering as it is controlling all of the following I/O and sensors on the a3Di. Machine motors Control switches Optical position sensors Inverters Up and Downstream SMEMA control Light Tower Pneumatics Operator manual controls for width PCB control System side EStop notifications The cRIO has proven to be a completely dependable, reliable and cost effective solution for this high performance, ground breaking application. Using cRIO as the product management system significantly reduced our development time and helped us get the various autonomous state machines of the multiple product control cells run with far tighter timings than the normal 1ms tick of most PLCs.  During development, our developers, who are CLD and CLA level engineers, partnered with the technical support teams in the local NI office in the UK who helped the team overcome some of the detailed control issues raised in the systems design. LabVIEW – The obvious choice for user ergonomics A decision was taken early in the a3Di product specification phase to use LabVIEW to not only provide the control code but to control the system from the user interface perspective also. The ability to design product quality operator interfaces and the flexibility of LabVIEW for creating an engaging user interface environment for the operator makes the software front end of a3Di a unique selling point.  The impact of using NI components within the a3Di product enables Amfax to offer a world class, unique and well supported solution to those OEMs and CEMs looking to improve their PCBA assembly inspection process and significantly reduce their operational costs. The a3Di is also revolutionizing the way PCBA manufacturers can now compete for their customers business. By using a3Di, these manufacturers have a unique selling proposition to their own customers. They can pass on savings made by using a3Di and guarantee that the boards being manufactured are being tested by the most accurate system available to do the job. The importance of this exciting technology has not gone unnoticed, with the British Governments innovation department recognising a3Di as a significant step forward in manufacturing. The Amfax a3Di was a finalist at the 2016 Innovate UK awards hosted at the British Houses of Parliament.   Test systems solution provider Amfax has developed a unique scanning technology that offers manufacturers tighter quality control without an increase in costs. The Amfax system massively outperforms competitor technology for the same cost and could see its use expand from electronics manufacturing to other industries such as semiconductors. The increasingly small size of circuit boards has made traditional inspection systems less reliable. Traditional systems compare images of newly manufactured circuit boards to a reference image. As circuits become more densely packed and components smaller, it becomes difficult to identify any error smaller than a missing component using this method. System uses lasers to check componentsAmfax’s a3Di (automatic 3D inspection) system uses lasers to pinpoint the position of each component and joint to within five micrometres. The technology was developed with help from Innovate UK competition funding for projects investigating ways of manufacturing the electronic systems of the future. An Asia-Pacific hard disc manufacturer is already using the AMFAX a3Di for quality control in very high volume. Rolls Royce Control Data Service has also purchased one for use with its aero engine control and monitoring electronic boards.  Requirement: To develop and manufacture an automated end of line inspection system for the fault recognition of the wire button style connectors.
 Our solution comprised of a high-resolution vision (camera/lens) system, mounted on a precision X, Y motion stage set-up. A plinth was integrated along with special to type fixtures, very accurately locates the connector to be scanned. The system was housed in a light-tight enclosure that contains a series of controlled light sources, to negate the effect of ambient light on the inspection process. A PXI controller/chassis combination provided PC based control of all aspects of the solution. Integrated motion tools allowed us to scan the vision system over the area covered by the connectors, at the very short focal length required (approx. 12mm from the connector surface). The motion system scanned a pre-determined pattern of steps in X & Y, and the vision system acquires an image at each step. The area captured by the vision system enabled testing of a minimum pattern of 16 buttons/plungers, in a 4 x 4 pattern. Further development allowed us to capture a larger image and reduce total inspection time. The image is then transferred to the vision software and processed against a pre-programmed set of pass/fail criteria, the results of which are buffered until all areas have been scanned. When complete the overall result, Pass or Fail, is displayed as a banner on the system display. System hardwareThe system was based on the PXI platform from National Instruments. A 4 slot PXI chassis houses an embedded PXI-8174 controller, PXI-1422 iMAQ vision card, PXI-7344 Motion control card and a PXI-6508 Digital I/O card for interlock monitoring etc. The software was developed using LabVIEW, the Vision and Motion modules for LabVIEW and the Motion assistant software tools, all from National Instruments. Motion/Vision System The motion system wasconstructed from two 150mm (300mm optional) precision motorised translation stages, mounted to provide travel in both X and Y for the camera/lens system. The stages had a resolution of 10um, which was more than sufficient for this application. A 20mm manual Z adjustment was also provided. The camera selected was a high resolution digital, colour model with suitable lens. System SoftwareThe software algorithm developed is split into 7 main sections. The 7 sections are as follows:
Argument sorting The function of this part of the algorithm simply extracts a 2D array from the 1D argument array being passed in by the controlling software. These arguments include which pins must be tested, and their names. Processing of half lit image This section of the algorithm takes an image of the connector lit with the red led array only. Its function is to isolate the wells on the image, and formulate an array of the wells’ coordinates and radii, which is correlated with the test array formulated in the previous section of the algorithm, ie a sorted array is passed out from this function. A general error condition is raised if the algorithm is unable to isolate a full row or a full column on the grid of wells, as this would mean that there is no reference with which to sort the array. The algorithm is capable of making multiple passes of the image to obtain a sorted array, so if the first thresholding value does not yield the correct number of wells, the algorithm will store those values it has already got, reduce the threshold value and try again up to 5 times. This image shows the ideal illumination for the image lit with the red LED array only.The illumination yields a smoothed histogram which should look like this:
The two maxima must be clearly defined, for a valid thresholding value. This shape of graph is important because the two maxima toward the left of the graph represent the well areas and the substrate area repectively, so the algorithm will threshold somewhere to the left of the 2nd Maxima. Processing of fully lit image In this section of the algorithm, the image with both LED arrays illuminated is used. The image should look like this:
Compare the peak to the peak to the right of the histogram with the half lit histogram, this peak represents potential defect material, and has been enhanced with the second LED array. The Algorithm uses the histogram graph to obtain a new threshold value which falls to the left of the large peak to the right of the histogram graph. A particle filter is introduced also which ignores any particle below a certain threshold. This is a critical point in the code, as the value chosen for this area threshold will drastically affect the results of the tests. The default setting is 90 pixels. This section of the algorithm passes out a binary image from the above threshold / filter operations for the test part of the algorithm. Test 1 This test is for wires appearing outside of the well. A ROI is generated above the well in question using the data in the output sorted array from earlier in the algorithm and a small image extracted from the binary image generated in the fully lit image processing. Each pixel is analysed, if the pixel is high, then its distance is measured from the centre of the well. If that distance is greater than the radius of the well then a variable area is incremented. Each time this variable is incremented then the value of area is checked against a set value area threshold. As soon as area is greater than or equal to area threshold, the pin fails and the test terminates.If this condition is not met then the pin passes. The critical areas here are:
Test 2 This test uses the same binary image as the previous test, and is testing to see if there is a pin present in the well, and does this by looking for high pixels within the radius of the connector which form a single blob. The area of this single blob is measured against a constant value. If the area exceeds the value then the test passes, and fails if not. The current setting for the area is 1500 pixels. Display and report This final section of the algorithm overlays test results onto the image, and compiles a report to pass back to the calling vi. Conclusion:The system met all system requirements. The use of the LabVIEW vision and motion tools enabled a much faster and reliable test solution than the old manual test procedure. Additional software has been added to improve the feature set for the customer who is extremely pleased with the result.
Amfax also integrated an image acquisition system to provide handling with vision. This provided the system with the ability to check the device against an absolute and locate it accurately in X, Y and Theta. We were then able to check for missing devices, devices that were misallocated in their pockets and also for devices that were in the incorrect orientation.
The integration of NI LabVIEW and iMAQ and control of the robot was developed by Amfax to provide a completely interactive environment specifically for handling of opto-electronic devices. The depth of field required to capture the image from the devices is restricted to 150um Temperature controlled test pedestals manufactured from elkanite, a tungsten / copper alloy were used to provide the test bed for the UUT controlled using solid state temperature sensors and Keithley controllers. To allow maintenance of the test head such as replacing Peltier heat pumps the pedestal was mounted on X and Y stages integrated into the assembly. This provided the system with fine adjustment for the UUT location and after replacement the stages could be re-taught to their zero position while not needing to re-teach the robot. The probing assembly was located above the test head and lowered into position via precision stages after the robot had placed the device. The wedge probe design from Pico probe, with kelvin probing incorporated was used for testing the chip. The typical tolerance required to make contact with each mirror was + / - 25um A single mode fibre mounted on an X / Y & Z precession stages was used to align with the wave guide of the device and measure the maximum power once voltage was applied to each mirror using the Pico probe. + / - 5um was required to maintain the sweet spot. The system was housed in a lamina flow filter system mounted on an optically flat, vibration isolated table. The chip trays were fed into the system using a mag handler operated via RS232, the system would request a product to test via an agreed RS232 string sent to the controller, the handler would then take all the steps to place the trays in a position ready for the robot to begin pick and place routine to finally test the devise on the test head Low cost, high speed 5x8 RF switch matrixThis rack mounted switch unit is designed and manufactured by Amfax. Inspired by the mobile phone manufacturing industry, this switch is designed to allow vastly reduced tooling costs for mobile phone manufacturing facilities
Key features and system benefitsThis Broadband Switch is a low cost, high speed 5 x 8 RF switch matrix. Benefits of this unit Reduce tooling costs Remove the need for multiple sets of test equipment Increased Longevity This switch matrix is entirely solid state, no more limited life span of electro-mechanical relays. Easy connectivity A single USB connection carries all power and comms to the switch. LabVIEW drivers supplied. RF switch specifications RF connectivity
 S ParametersThe following graphs show typical S parameters for a switch unit. Each unit produced is tested for all 40 possible matrix calculations, to make sure that the unit is within its specification.
Key benefits of Amfax's involvement
The resulting system was a generic test platform which allowed the end customers to strip and test Eurofighter hydraulic components without having to send them back to the manufacturer. This vastly reduced the costs for supporting operational aircraft. System safety and design innovation were keyOperator safety was a key consideration for the hydraulic test rig. Hydraulic power packs capable of delivering 360bar pressure or 180 l/m flow could do serious damage. Our solution's design addressed these concerns
System software and hardware usedLabVIEW LabVIEW was used as the primary development language for this project and delivered the following benefits :
The real time module for LabVIEW allowed us to make use of PXI RT hardware, broadening the scope and capability of this system.
Each type of hydraulic component needed its own test sequence with step by step limits and custom control conditions. TestStand was the natural choice for this and offered these benefits :
Test Bench hardware included
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