Introduction
Semiconductor digital tests, especially digital test programs converted from simulation files such as STIL, WGL, VCD, EVCD or ATP, are often required to be expanded into multiple DUT test sites. This article discusses the system hardware and software requirements to perform multi-site testing using the GtDio6x product line and ATEasy®, to provide a cost effective solution.
Digital Design Considerations
When designing a multi-site test program the tradeoffs between cost and performance may not be completely understood. After evaluating the performance and capability of the GX5296 or the GX5964 series of dynamic digital instruments, it may be logical to assume that the large number of channels of a single GtDio6x board should be capable of providing a multi-site digital test solution. While this solution is possible, it cannot yield the performance of a system that uses a digital resource or board per DUT test site.
Domain Per Site Solution
Marvin Test Solutions recommends that multi-site test systems be designed such that each DUT test site uses its own digital domain, as shown in Figure 1. This solution provides the fastest multi-site test performance, as each DUT test site can be run independently.
Figure 1 – Multi-Domain Solution Block Diagram
Using this configuration, all digital resources are available for each DUT test site. The test status of each DUT test site can be instantly identified by reading the Real Time Compare (RTC) error status register. In addition, the system can be designed such that each DUT test site will use the same digital test file and test program. DUT test sites can be can easily be expanded by adding additional digital domains. Using ATEasy® a multi-threaded test program can easily be created to perform this testing.
Table 1 – The relative merits of the Multi-Domain Solution
Single Domain Solution
A multi-site digital test system designed using a single digital domain as shown in Figure 2 has several disadvantages. First, each test site can no longer use the same digital file. This solution will require a separate application to create the additional test sites from the original digital file. This additional application would need to copy the original channel and vector data to all of the new DUT test sites.
Figure 2 – Single Domain Solution Block Diagram
This also requires a much more complicated test program to determine DUT test site status. As with the multi-board solution if the RTC error status register is zero then all DUT test sites pass. But when a failure occurs, the status of each DUT test site cannot be determined by simply reading the RTC error status register. The DUT test status must be determined by reading the RTC Error Address and or the record memories.
The record memory alone could be read and evaluated to determine the status of all DUT sites, but as the sizes of most of these digital tests are very large, the approach is not practical as it would consume too much test time.
The RTC Error address memory contains the failing vector addresses up to 1K failures. The record memory for each of these addresses can then read to determine the failing DUT site(s). As each entry indicates a failing location time is not wasted reading large sections of record memory to determine the test failures. Unless the number of failures is less than 1k or all DUTs have failed as indicated above, the status of all DUTs cannot be determined. In this case the test program must disable the failing test sites and rerun the digital test until the status of all DUT test sites are known. The GtDio6x series of digital instruments provides a method to abort the test sequence if a failure is detected; this feature can save test time when a failure occurs.
Table 2 – The relative merits of the Single-Domain Solution
Summary
The following table compares the two solutions:
| Multisite in a Single Domain Solution | Single Site Per Domain Solution |
|---|
| Programming is required to Create Digital Test File | Automatic Generation of Digital Test File |
| Reduced number of PXI Slots and Boards | More Slots/Digital Test Boards |
| Lower Hardware Cost | Higher Hardware Cost |
| Slower Deployment | Faster Deployment |
| Requires complicated programming to find the faulty DUT | Better Diagnostics |
| Lower Test Yield | Maximum Test Yield |
Table 3 – Pros and Cons of Single vs. Multiple Domain Solutions
Conclusion
Unless the space (PXI slots) in the semiconductor test system is at premium, a multi-site test system should always be designed using one digital domain for each DUT test site. The upfront costs of adding the additional hardware will pay large dividends, guarantying the fastest possible test times and simplifying test programming. Careful consideration of these capabilities is paramount in the design of a multi-site digital test system.