Why move from packet-level reliability testing to wafer-level reliability testing?
Ayscom works with the experience of the world leader in the design and development of wafer-based test & measurement solutions, Cascade Microtech now FormFactor. In this post we intend to tell you about the factors that may motivate you to move from packet-level reliability testing to wafer-level reliability testing.
But… What are these factors? Mainly two: lower cost of ownership and better data integrity.
Wafer-Level testing lowers operating expense
Cost of ownership is one reason to consider EM WLR. EM PLR requires the use of expensive ceramic packages for each framework to be tested. In addition to the packages themselves, the costs are incurred in the packaging process (whether done in-house or by a third party) to cube the wafer, join the DUTs into the packages, and send wafers and packages; it also requires effort to manage the process. These expenses do not decrease over time: they continue throughout the life of the testing program and accumulate into a significant investment.
EM WLR systems are more expensive per channel compared to EM PLR systems. However, this difference in initial investment may eventually be recovered through cost savings on the ongoing package.
Wafer-Level Testing Provides Safer Approach, Better Data Integrity
Reliability margins have been drastically reduced with recent nodes, making simple «worst-case» analysis and one-size-fits-all analysis work for everyone. To get the most out of each CI element, the design rules have become progressively more sophisticated; this requires a wider range of test conditions to verify all corner cases and applications and requires increasingly accurate data for each tested case.
Data integrity is therefore essential, but DUT packaging comes with multiple damage threats. Sawing of the wafer to individualize the test structures uses water, which can be absorbed by the low k or ultra low k dielectric. Worse still, multiple opportunities for electrostatic discharge (ESD) damage to the DUTs arise during package bonding, shipping, handling and charging of the packages into the system for testing.
Water and ESD damage is sometimes apparent (hard fault DUTs are easily removed prior to testing), but sometimes these can be latent effects that arise later in the test and can bias the results. These problems are especially traumatic for technology development when protective rings cannot be present, but can also negatively affect the assessment of process reliability.
EM WLR provides a safer approach to testing, without the risk of EM PLR of potential damage to data due to moisture absorption and ESD during bonding, shipping, handling and loading.
Accelerate your reliability program with electromigration testing directly on the wafer. Check out the FormFactor product line, which we market, and select the equipment that will help you improve your efficiency and accuracy in electrical measurements.