​An 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.

In 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.
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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.

For 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:
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• A high value of assets.
• Increased cost of maintenance.
• High levels of real estate required at the contract manufacture.
• Test systems being continually designed and built from the ground up.
• Large NRE costs and long build lead times.

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:
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• Increased agility, a single hardware/software test platform that can be utilized on many different types of DUT’s.
• Ease of use by system operators with comprehensive documentation.
• Involvement of test engineering within DUT design development process. 
• Ability to test multiple DUT’s in batch mode within the same test cycle.
• Reduction in the amount of floor space required to test the DUT portfolio.
• Auto uploading of test logs for analysis and data mining.
• Reduction of NRE costs.
• Reduced time to market. 
• Eliminate test bottlenecks.
• Reduction and ease of maintenance tasks due to a common platform.
• Access by remote test engineers to perform upgrades and fault diagnosis.
• Reduce the overall cost of test.

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.

The 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.

Unified 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.
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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. 

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:

• decrease cost of ownership,
• maximise the use of common resources to test different units, and
• reduce downtime through easier replaceability and maintenance.

The major requirements were as follows:

• ability to test multiple units and different types of units at the same time with one test solution,
• enabling parallel testing of both identical and eventually different types of units and
• be modular in design to quickly enable replacement when required.

​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.

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:

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.

​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.

​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.

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.

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:

For our client, it’s now accepted as the global test station; all new product must be designed to be tested on it.

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:

• The test system was easy to use by the operators. This was achieved by careful design of the GUI
• The client could take up ownership easily to due the modular nature of the system
• The self test fixture enables easy and regular maintenance of the system
• Modular design enables easy repeat system build

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.
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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.

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.

The 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.

​The software algorithm developed is split into 7 main sections.  The 7 sections are as follows:

• Argument sorting.
• Processing of half lit image.
• Processing of fully lit image.
• Test 1.
• Test 2.
• Image report preparation.
• Report generation.

 
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:     

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:

1. The radius of the well
2. The area threshold variable.

 It should be noticed that these two values will have significant impact on   the results of the test.
 
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.

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.  
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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. 
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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

LabVIEW
LabVIEW was used as the primary development language for this project and delivered the following benefits :

• Rapid development
• Hardware support
• Accredited code standards
• Wide industry support

LabVIEW Real Time
The real time module for LabVIEW allowed us to make use of PXI RT hardware, broadening the scope and capability of this system.

• Deterministic Epoch
• Safety critical

TestStand
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 :

• Separate test from application
• Custom step types
• Separate installers