Plextek, an electronics design consultancies, provides innovative design of complex communication systems and devices for a wide range of companies and also undertakes supply of the finished products. The consultancy operates across the telecoms, automotive, medical and defence sectors. In addition to supplying a range of its own products for the security market, the company provides an outsourced resource of highly experienced, multidisciplinary engineering skills to organisations that require challenging electronics design projects to be delivered within competitive time and cost constraints.
Its 300 clients encompass a range of global organisations, from BAE Systems, the UK MoD, Qinetiq and Raytheon to TDK and Sony. The company also supplies automotive security products to both LoJack Corporation and Tracker Network (UK) Ltd..
They traditionally designs and manufactures boards of both low-medium value/high volume (i.e. batches of 10,000 boards) and high value/low volume (e.g. batches of 10 boards). In 2000 Plextek began using the Boundary Scan system from Göpel to check for shorts and opens, fault isolation and repair. The methodology was extremely useful for highly complex boards, especially during the integration stage. It helps to eliminate hardware manufacturing problems as a possible cause of any software issues that were seen. Before using Boundary Scan the engineers would face uncertain and potentially lengthy integration times with unknown software and hardware.
Using Boundary Scan
The company utilises Boundary Scan for test and programming of prototypes and final test development. ICs such as CPLDs and E²PROMs are programmed at high-speed and verified. In practice once a board design has been completed, the Boundary Scan test program is written whilst waiting for the first prototypes to be assembled, and then the assembled prototypes are Boundary Scan test verified. The Boundary Scan test program could be done earlier in the design cycle but this is where it best fits in to the process. Doug Reid, Senior Technology Consultant, comments: " We build our own test boards to allow easier debug and test of the prototype. It is critical that the hardware is good, Boundary Scan allows us to test sections of the hardware that the software is not ready for."
The test boards act as a carrier for the boards in a multiboard system, providing easy test and debug access and a means of testing the connections between the different boards. " Design for Test is a key issue" comments Doug Reid. All engineers must utilise it to their benefit at the design and layout stage. The major IC manufacturers now incorporate the Boundary Scan architecture into their components, helping to maximise the testing ability. "We learn from each product to make the test strategy for the next product even better", Doug explains.
Plextek chose the Göpel electronic Boundary Scan system due to the solution being able to offer unique features including an intuitive Graphical User Interface (GUI) with the powerful Caslan programming language, as well as the ability to be able to see the test code which is being applied to the board. Asked if they have ever dealt with other vendors, Doug Reid says, "I don't know why people are using other Boundary Scan systems. We considered other systems – but they either had functionality limitations or we had other concerns. Using this equipment consistently gives us the impression of a well thought out system."
Emphasis is laid on test coverage not test speed. Test speed would be critical for high-volume productions but in these cases Boundary Scan is not utilised, and products are tested with custom test racks running GO/NO GO tests as there's no intention to repair if boards or connections are faulty. For low volume productions Plextek tests for shorts, opens, connectivity, or check of pull-ups on FPGA components. As there's no single Boundary Scan test, the company is applying a Cluster Test. A logic cluster test verifies the connections from Boundary Scan pins to cluster inputs and outputs and connections within the cluster as well as the general cluster functionality. Fault isolation is limited due to missing Boundary Scan access to all cluster-internal nodes. That means that also parts on a board can be tested via Boundary Scan that do not include the required Boundary Scan architecture. Doug Reid says. "Cluster Test is great as it covers much of the boards and includes analog components as well." In particular, since test coverage is highly important for Plextek test engineers, this solutions was found fitting best.
At the moment, the company uses two Göpel electronic PCI Boundary Scan controllers and are very satisfied with the performance of both the hardware and software. All in all, both hardware and software package are doing outstanding jobs, which gives the engineers a good feeling of having decided for the right technology and system. "Overhead is very low. It's always part of the development done by design engineers. Additionally, investment in time is so little", explains Doug Reid. He is a highly satisfied user and can't understand why not many more engineers are utilising Boundary Scan. Ultimately, Plextek knows that anyone not using Boundary Scan gambles away lots of opportunities. Opportunities that definitely play a critical role in the market: namely time, money and technical lead.
Göpel electronic, Jena (Germany)
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