Test Connections

For the semiconductor test market, manufacturers are continually challenged to drive down costs — including test costs. And controlling the cost of test only becomes more challenging as the ASPs of components trend lower year by year, requiring test engineers to continually look for better and more cost-effective test methods.

Historically, the cost of test has been about four percent of a product’s total cost, as Figure 1 shows. The challenge is that with the continual downward trend for component pricing, keeping test costs just even (as a percentage of total product cost) requires that test costs be reduced in lock–step with overall product costs. Subsequently, the real challenge for test engineers is to identify and create new and better test methods and systems that offer quantum levels of improvement with significantly lower test costs.

Assembly and Test Costs
Figure 1 — Assembly and Test Costs as a Percentage of Total Product Cost Over Time

As markets and products expand, test engineers are looking for more flexible and focused test solutions that can address their needs in the areas of device verification, characterization, failure analysis, and pilot and specialized production runs.

Additionally, the need to address the diverse test requirements associated with components that feature higher levels of integration — such as System on Chip (SoC), MEMs, and System in Package (SiP) devices — is driving test engineers to look for new and different ways to implement, expand, and augment existing ATE platforms.

To meet these challenges, test engineers are turning to COTS hardware and more specifically, the PXI architecture. When compared to proprietary ATE test systems, PXI offers test engineers a greater variety of hardware and software options from more than 60 vendors.

To address the specific needs of the semiconductor test market, Geotest has developed digital instrumentation with features and capabilities tailored for the semiconductor ATE market place. Based on more than 20 years of experience producing card-modular products including market-leading digital instrumentation, Geotest has developed a portfolio of PXI products that offer tester per-pin features and incorporate a Parametric Measurement Unit (PMU) per-pin architecture and per-pin programmability.

The result is the most advanced and full featured PXI digital instrumentation in the industry, providing semiconductor ATE test capabilities at a fraction of the cost of traditional ATE test systems. Geotest’s GX5295, GX5055 and GX5960 digital instruments offer high-performance and cost-effective test solutions and are being used successfully today for characterizing a range of devices including MEMs, mixed-signal, and power-management components.

PXI instrumentation for semiconductor test applications
The requirements for testing digital and mixed-signal semiconductor devices include DC characterization of all I/O pins and functional test verification of the device. The former test needs require the use of DC Parametric Measurement Units (PMU) or Source / Measure Units (SMU), which can be used in one of two modes to perform the DC characterization tests on the device’s inputs and outputs:
Force voltage and measure current. With this method, the PMU applies a constant voltage and, using its on-board measurement capability, measures the current being drawn by the device/pin being tested. The voltage being supplied by the PMU can also be measured.
Force current and measure voltage. With this method, the parametric measurement unit either forces a constant current across a device or sinks a constant current from a device pin and measures the resultant voltage. The PMU sink/source current also can be measured.

Once the DC measurements on a device are completed, digital functional tests are preformed using a digital test instrument that can drive, record , or compare test vectors on multiple pins or channels. With the need to supply and verify the operation of a device using millions of test vectors, the ability for a digital instrument to drive and compare expected test vectors in real time becomes essential in order to minimize overall test time.

The test features described above are attributes normally associated with proprietary ATE systems but lacking in card modular (PXI) or rack-and-stack test systems. For users implementing these features using traditional instrumentation,  a collection of digital instruments, switching modules, and an SMU or PMU instrument is needed, as Figure 2 shows.

Digital and PMU Instrumentation
Figure 2 — Digital and PMU Instrumentation

This implementation, while meeting the DC and functional test needs for testing a device, has several limitations:
Test time — Significant time is incurred performing sequential DC measurements with the PMU and switching the PMU to each device pin to make each DC measurement.
Cost and Footprint — Multiple instruments and a switching matrix, as well as the need for more rack space or PXI card space, can affect overall system cost and the size of the system compared to a single instrument solution.
Measurement compromises caused by switching and cabling effects — The switching matrix can compromise signal bandwidth and low current precision measurements, affecting measurement accuracy and repeatability.
Limited ability to perform shorts and continuity testing — with a single PMU configuration and depending on the specific system / switch matrix, the ability to verify test system connections as well as verify the absence of shorted DUT pins may be very limited.

A superior implementation — and one much preferred by users in the semiconductor industry — is to provide these test features on a per-pin or channel basis, with each test channel capable of operating in PMU or digital functional test mode (with real time compare) and functioning as a tester per pin.

Geotest’s GX5295 is a single-card, 32-channel semiconductor test suite solution combining digital, switching, and PMU functionality into a single-slot, 3U PXI module. Figure 3 depicts the features of the GX5295, which includes programmable drive/sense levels as well as PMU features (VI force/measure) on a per-channel basis.

GX5295 Channel Features
Figure 3 — GX5295 Channel Features

By basing the core ATE system on PXI, test engineers can also realize the many benefits of PXI including:
large portfolio of instruments available from more than 60 vendors, supporting customization and reconfiguring of test systems for different devices and test needs
cost-effective instrumentation resulting in lower test system capital costs
Windows-based software that offers users multiple options for APIs and test languages
compact test system footprint and lower power consumption resulting in lower operating costs

To read more about the GX5295 and its many features, including its use for DC parametric measurements, click here. Click here for product information about the GX5295.

Having trouble finding a PXI solution that meets your needs? Geotest will build it.

To see how Geotest can customize a test solution for you, visit Geotest online or contact your regional sales representative.
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