Design for Test: What Is a Streaming Scan Network (SSN)?

Finding manufacturing defects in integrated circuit (IC) chips is hard to do.  Automatic test pattern generation (ATPG) and on-chip compression logic have been fundamental in allowing engineers to create reliable manufacturing test patterns for many years.  As designs continue to grow in size and complexity however, this leads to challenges in regard to:

  • Limited number of scan channels available
  • Routing and timing closure
  • Test time and data volume
  • Test planning and implementation flow
  • Diagnosis and debugging of defects

To help resolve these issues the Tessent design-for-test division has created and released a product called Tessent Streaming Scan Network, or SSN for short.  But what is a streaming scan network?

For those who create ATPG manufacturing test patterns with Tessent TestKompress, adding SSN to their design is an important solution using proven technology to help overcome the challenges listed previously.  At a basic level, SSN adds a test data streaming network into the design for very efficient delivery of test pattern data wherever it is needed throughout the design, and then getting the test results back out for comparison on the tester equipment.

The SSN solution relies on the IEEE standard 1687, commonly called IJTAG, as a test infrastructure or framework.  SSN also adds a streaming scan host (SSH) piece of logic into each design block or core.  The SSH is the interface between the SSN streaming data bus and the TestKompress logic within the cores.  The SSN data bus is kind of like a conveyor belt and the SSH nodes know exactly when to grab the right pieces of data off the bus that are needed for their core, performs the test, then places the test response back on the data bus/belt.  This process is very efficient and automated by the tool, so the user gets the benefits without doing complicated setup work.  If any test results don’t compare correctly on the tester, the test failure information can be used with the Tessent Diagnosis tool to determine the defect type and location.

The SSN data bus traverses throughout the design to deliver the test pattern data and return the results to the tester.

To learn all about SSN and how to insert the necessary logic into your design in the Tessent Shell environment, you can register for our self-paced on-demand course HERE.

We also have virtual instructor led (VILT) classes offered by experienced instructors. You can read about and register for the Tessent SSN VILT class HERE.

Note that this is an advanced Tessent training and students should be familiar with IJTAG and the Tessent Integrated Flow for creating and inserting test logic into their designs. 

Author: Bruce Swanson, Principal Customer Training Engineer, Siemens EDA Learning Services

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This article first appeared on the Siemens Digital Industries Software blog at https://blogs.sw.siemens.com/xcelerator-academy/2022/03/21/design-for-test-what-is-a-streaming-scan-network-ssn/