While a complete screening program includes a range of Optical, X-Ray, CSAM, chemical resistance and other physical inspections, this post will focus specifically on electrical test and how curve trace fits the requirement very well. Curve tracing is generic and can apply to any electronic technology without knowing, in depth, the function of the device. We can adjust sensitivity of the curve trace process to meet the needs of an organization and use resources efficiently.
Pin 470 (AD9), S/N368, Leakage on IO pin
The 3 Methods
The same methods used for failure analysis can adapt to aid in the screening of devices for signs of counterfeiting.
- Unpowered curve tracing is used to inspect the input protection diodes of a device regarding grounding the supply pins or all other pins. Subtle differences in semiconductor processing and a range of failure related damage can be detected.
- Powered curve tracing shows that all power pins and IO pins are working and also gives a reading of the device supply current under various states of the input pins. Variation of the IV or IDD curves shows a potential device failure or mismatch. IV curve traces often contain information that can match to the DC specifications table in the datasheet.
- Supply current test is a simplified test that samples the supply current under 1 or more static states of the input pins. A good deal of metrics of the device must match to pass the test. This test easily repeats for multiple input states, thus amplifying its usefulness.
Unpowered Curve Tracing
Think of the curves in a curve trace as analogous to the ridges on a fingerprint. If we collect many of these curves from all pins of the device, the fingerprint takes shape. If more test conditions are tried, then the resolution gets even better. Unlike a real fingerprint, all devices should be the same with only a narrow range of variation allowed. A fake, reused, or rejected device has a good probability of showing curves that are not the same as the average of the lot.
Unpowered curve trace is very good at screening for gross defects and more obvious footprint mismatches. It can detect open and shorted pins caused by incorrect die inside, or by a range of electrical failures like EOS and bond wire failures. It can also detect leakage often caused by ESD when the device is handled incorrectly without ESD protection or reprocessed as counterfeit devices often are. The ‘all pins grounded’ test condition is used on all devices tested which simplifies test condition choices.
Powered Curve Tracing
Powered curve tracing results in many IDDQ readings as inputs are toggled from low to high input levels during the curve trace process. Besides the I-V curves which offer additional evidence that the pin function is correct. The supply current is a very useful signature. If you looked at several IDDQ values at several input states, it would be a sensitive screen that all other devices can attain the same operational states at the same supply current. This requires many metrics to match from function to semiconductor process and may even correlate to aging in extreme cases. Some basic information from a datasheet is needed for this analysis, such as the pin names, pin types (Power, Gnd, I, IO and O), Nominal voltage levels are often enough. The DC specifications table and pin names, or pin function, are often enough to get through the analysis. Most of the middle part of the datasheet is not used to set up or interpret curve trace results.
Powered Curve trace pin 22 only, showing 200 devices overlaid with similar results. Red is IV Curve, Green is IDD1 which remains low and Blue is IDD2 which has 2 distinct levels at VIL and VIH with a distinct transition in the middle.
Sample size of the units inspected applies to the sensitivity of the test. If you have a known good device, the process is straightforward. You can directly compare a small sample of devices to the golden device using any valid test condition. However, often no prior experience with the device means no golden device results to compare to. In this case, the more devices tested the better. But at least 5 devices are needed to arbitrate any variation that might occur in a smaller set. Exceptions to the exact match of curve traces apply to power pins, so when this happens, it is important to sample a larger set to verify it is bi-stable and not failed.
MultiTrace & DataTrace
RTI’s MultiTrace automated curve tracer is a very efficient tool for collecting curve trace data with the methods discussed here. DataTrace software has specific features designed to simplify collecting this data, especially when the device lot size is large, or the testing requirement is 100%. Batch comparison mode and advanced test sequencers with automatic trace compare logging are available to those who need more efficient tools. DataTrace has the power to load and compare hundreds of device’s worth of data at one time. With the save one image per trace feature, documentation of the results in a format anyone can read.
DataTrace Batch comparison results grid
Screening counterfeit IC devices with curve tracers is effective if there is a known good device, or golden device, to compare against. Powered, unpowered curve tracing or supply current tests are the main methods of RTI’s curve tracers to screen for counterfeit ICs. When coupled with Datatrace’s batch comparison tool, hundreds of devices can be tested at the same time against the golden device.
If you have questions or want more technical information on RTI’s curve tracers and software abilities, please contact us.