In order to increase the efficiency of testing, one of the things that manufacturers have been doing over the years is trying to see whether they should test every component on the board or do selective testing.
Let’s say, you have a cellphone which has 15-20 components—one big ASIC, amplifier, receiver, antenna and so on. Ideally, you would like to test every component on the board to ensure that everything is working perfectly.
With functional testing, you need not test every component. You just test the functions that the cellphone is expected to do. So, typically, functional testing is end-to-end testing where an input is given and output checked. If the whole device is working, it is assumed that all its components are working.
There is also a possibility that critical limits aren’t met. So manufacturers do sample testing. In sample testing, some samples are tested for complete test. The samples are tested for every aspect—voltage level, current level, functionality, etc.
If the manufacturing volume is high and you have a very standard parts supplier, you have a certain level of confidence over the supplier that the parts being supplied are certified and wouldn’t like to do the testing exercise over all the components. However, you still do sample testing to ensure parts’ quality. For a new product launch, obviously every component is tested because you haven’t built the confidence yet over the vendor that the components supplied are good.
So for mass manufacturing, there could be a mix of functional testing and complete parametric measurements for sample devices.
To make testing simpler, boundary scan has become an essential tool. It enables much of a board to be tested with minimal access. Over a period of time, JTAG port has become a standard connector on many devices by accessing which you can do many things on the device—you can test the device, program the device and so on. It was introduced primarily to reduce the cost of test. The maximum cost of test in manufacturing is involved in ICT. ICT means every pin of the device has to be accessed for testing. Traditionally, for a 144-pin device, you need to probe every pin, apply signal and check the response. With JTAG, even if it’s a 144- or 200-pin device, through only five pins you can check the functionality of the device.
“In today’s production process, automation is the key for optimising the cost of the final product. With interfacing of test equipment with PCs and PLCs, and features like pass/fail, these are being integrated within the process chain. These instruments not only measure the parameters but also do data logging for documentation, statistical quality controls, etc. When a component fails to comply with specifications, a solenoid control signal is generated and the faulty part moved out. An example is a high-precision multimeter with pass/fail output used in a resistor, capacitor or inductor component manufacturing unit,” adds P. Prabhu, general manager (technical), Scientific Mes-Technik.
According to Jayaram Pillai, managing director, National Instruments IndRA (India, Russia and Arabia), key technology trends that increase test efficiency and reduce test costs include organisational test integration, system software stack, heterogeneous computing and IP to the pin.
Organisational test integration. Throughout the electronics design and manufacturing industry, test teams are improving integration across the organisation to gain a competitive edge. In the past, validation (the process of testing a product during design to guarantee that it meets feature specifications) and manufacturing test teams had few opportunities to work together. However, test managers seeking to decrease time to market and reduce test costs see that improving. Increased use of automation across both the groups has shown that they can share a common software and instrumentation. Hence one of the top goals for test engineering organisations is to increase reuse between validation and production.
System software stack. Software has been a critical component of automated test systems since it was first used to control standalone instruments more than 40 years ago. In fact, software development costs are often two to ten times more than capital costs of most test systems today. In response to rising software development costs and accelerated product development cycles, today’s industry-leading companies emphasise on designing a robust system software stack to ensure maximum longevity and reuse of their software investments.
From a system software perspective, most companies are moving away from monolithic software stacks that often contain fixed-constant code and direct driver access calls to the instruments. Alternatively, they are seeking modular software stacks in the form of separate yet tightly integrated elements for test management software, application software and driver software. This type of system software stack helps engineers apply optimal tools for each area and choose between standardised commercial off-the-shelf (COTS) and in-house tools at each level. A key trend is the extension of modularity into each layer of the software stack, including the increasing use of process models, code module libraries and hardware abstraction layers.