Test, test and test again…
We can provide support to prepare for reliability tests and help you with the statistical analysis as necessary.
Without reliability, WLP or any bumping is useless. There are a number of essential tests that need to be performed to validate the reliability of processes and performance of completed parts. For example:
- Bump shear
- Pressure cooking test
- Temperature cycling
- High temperature storage
- Temperature and humidity under electrical bias
- Surface leakage tests
- Dielectric constant (e' and e") vs. frequency
- Dielectric constant (e' and e") vs. humidity
Accelerated testing is a widely used technique for obtaining reliability information quickly by extrapolation. Test units are subjected to higher-than-usual levels of variables such as humidity or temperature. However, the acceleration factor is limited to stress levels related to realistic use conditions.
Reliability of flip-chips is ultimately limited by the mechanical fatigue of the solder bumps originating during temperature cycling. There is no recourse to this reliability limit other than changing solder, which is in many cases not an option. It is therefore the goal of any flip-chip or WLP fabrication processes to reach a minimum reliability level where failures modes are not related to degradation of the polymer, interconnect, or UBM.
The quickest common indicator of polymer and metallization reliability is a 100 hours pressure-cooking test. This test is equally demanding for metallization and polymers and will reveal process issues such as contamination. Corrosion and delamination due to moisture permeability, ionic contamination and other flaws will be readily apparent during an SEM/EDX examination at the end of the test. Parts failing this test are very unlikely to make it through the other tests.
Statistical data analysis
There are a number of statistical tools available to us for analyzing accelerated life and performance degradation data.
Rely on our experience to help analyze reliability failures. We are familiar with many polymers and their failure modes as well as thin film metallurgy and deposition methods that are potential sources of problems. We can assist you distinguish between random failures and difficulties rooted in materials or processes.