TEST & MEASUREMENT u SWINDON SILICON SYSTEMS Production test: the key to supplying
the highest quality ASICs Andrew McDerment, operations manager at ASIC design and supply specialist, Swindon Silicon Systems, says one of the most desirable trends in electronics system design is to push as much functionality as possible into a single device. To achieve that, it is favourable to use an application specific integrated circuit (ASIC) over an off-the-shelf IC.
T
o ensure ASICs retain their edge over their standardised counterparts, each device must undergo a stringent
production test regime to confirm its functionality and adherence to specification. First, let’s begin by defining an ASIC design
flow. A design flow is a proven design process that follows various stages of IC development. The process starts from the customer concept and progresses to the ASIC specification, then onto an early design and simulation, through to layout, prototype verification and production test engineering. It’s here at production test engineering
where we see the results of the customer’s ASIC transform from a checklist of design requirements to a production-released and fully specification-adherent custom IC.
PUTTING ASICS TO THE TEST Production test forms a critical part of the supply chain. It’s essential all ASICs are thoroughly tested to ensure that they meet customers’ complex system requirements and are specification conformant. Opting for a custom IC brings many benefits, not least because it ensures bespoke and optimised performance to the customer, but it also delivers a production test procedure specific to their requirements. This test procedure may differ with regards
to having wafer probe and automatic test equipment (ATE), or both, and may have different temperature insertions and with calibration over an extended measurement range. In current times, as the shortage of commercial off-the-shelf chips continues, custom ASICs can also help deliver security of supply. The major differentiator, however, comes when an ASIC developer can offer all production test and software and hardware development in house. This is typically known as a full turnkey (FTK) offering.
DESIGN FOR TEST The production test of today’s highly integrated ASICs is complex. A major advantage that an FTK ASIC company can deliver is by planning the test
16 January 2024 Irish Manufacturing
regime and coverage of the device during the design phase.
This is commonly known as design for test (DFT) where developing circuit design and test strategies occur concurrently. DFT is challenging for the engineers but the benefits far outweigh the frustrations. The additional circuitry that may be required when incorporating DFT techniques, can marginally increase the amount of silicon required to implement the design. The savings however from enhanced testability will materialise in shortening test time, increasing yields and reducing early life field failures. And all these benefits result in a reduction in overall cost.
ATE AND WAFER PROBE There are several elements that are paramount to a thorough ASIC test schedule. The first makes use of ATE, which refers to any apparatus that performs parametric tests on a device, known as the device under test (DUT), equipment under test (EUT) or unit under test (UUT). ATE systems are designed to minimise the amount of test time needed to verify that a particular device works, or to quickly find its
faults, prior to the part being used in an end customer product. Expertise in the test of ASICs at this phase is crucial to the end customer.
QUALITY GUARANTEED During prototype verification tests, if the ASIC is not performing as expected, changes may need to occur. While making changes to the chip, known as respinning, may seem like a daunting, unwanted process, it is an occurrence that will avoid future test failures. Production test can also identify anomalies. Yield alerts on test systems can detect whether a yield drops below a certain level, alerting the operators to take action. Swindon’s real time yield analysis (RTYA) runs on all production cells, helping to identify any areas that require attention before they can turn into problematic issues. This can range from a wafer batch discrepancy or to a contact continuity fault within the ATE. Several elements go into production test to
ensure a high yield and on time delivery of the final product. By opting for an ASIC supplier with an in-house production test facility, will ensure delivery of the highest quality of ASIC and an elevated level of service.
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