November_EDFA_Digital

ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 20 NO. 4 36

by laser ablation and to treat those packages separately during acid decapsulation. Due to the new epoxy molding compound (EMC) now in widespread use, manual decapsulation is less and less possible. EMC requires a positive pressure that canonly be obtainedwith an acid pump. In addition, the introduction of copper and silver forwires aswell as polyimides requires a shorter contact time for the wires and acid. Using polarization at 40°C offers the advantage of consuming less acid compared to use of acid at a lower temperature (10°C or lower). Use of the proposed new techniques alsonecessitates updating older equipment of all brands, by exchanging the pump for amore adaptable one and adding new embedded electronics. ACKNOWLEDGMENTS Many of Digit Concept’s global customers have inquiredabout decapsulation including copperwires, thus wewould like to thank EDFA magazine for the opportunity to publish this article. The author would like to thank his colleagues M. Bezard, A. Guerry, V. Poulain, and B. Zitouni for their helpful suggestions and work on hardware and software developments on our equipment. Thanks also to Y. Legoff for sharing his ANADEF presentation. REFERENCES 1. Joined CNES/DC Patent WO 2008/090281 and European project in collaboration with ST Microelectronics, Thales, Infineon, Bosch, Digit Concept, DC Engineering, and others, and the best German- French research centers. 2. A. Aubert, et al.: “Failure Analysis Case Study on a Cu/low-k Technology in Package: New Front-Side Approach using Laser and Plasma De-Processing,” Proc. 21st European Symposium on Reliability of Electron Devices, (ESREF), 2010. 3. M.J. Lefevre, P. Gounet, and S. Barberan: “New Method for Decapsulationof CopperWireDevices using Laser andSub-Ambient Temperature Chemical Etch,” Proc. Int. Symp. Test.Fail. Anal. (ISTFA), 2011. 4. Y. Legoff: “Décapsulation de Composant fils Cuivre avec de l’Acide Saturé en Cuivre,” 16th ANADEF Workshop, 2018. 5. R. Wolf: AS2000 acid decapsulation tool produced in 1992 by Apparate System. 6. S. Manoharan, et al.: “Failure Mechanisms in Encapsulated Copper Wire-bondedDevices,” Proc.Int.Symp.Phys.Fail.Anal.Integr.Circuits (IPFA), 2016. 7. B. Domenges, et al.: “Comparative Study on Decapsulation for Copper and Silver Wire-Bonded Devices,” Proc. Int. Symp. Test. Fail. Anal. (ISTFA), 2014.

signature as it changes over time can allow one to tem- porarily adapt the decapsulation process. This is also true for decapsulation after aging tests on the components. Observation of the current signature permits adaptation of the parameters, mainly during decapsulation, but alsoduring the necessary temperature increases of the acid, which are observed in many cases. Finally, observation of the current signature provides feedback that can be used as an end point. Currently, the plasma decapsulation process suffers from this lack of end point detection. Due to the possibility of localization during chemical etching, this novel technique is called iGPS. The i stands for current intensity andGPS for global positioning system during acid decapsulation. This iGPS technique canbe simply implemented inside all automated decapsulators. It can also be used to stop decapsulation at the rightmoment onmaterials likeGaAs. ONE MORE THING One case not covered by polarization is the protection of Cu wires between dies inside a multiple-die package. The combined use of HNO 3 saturation with Cu + polariza- tion + the localizationby iGPS offers a solution to this case. SAMPLE RINSE There are many ways of rinsing after acid decapsula- tion. Experiments have been published in an article [3] dealing with the decapsulation of packages with copper wires. Transfer times during the acid tool step and the automated rinsing tool stepmust be as short as possible, thus Digit Concept designed a standard and compatible holder for components. Once it is inserted in the rinsing tool, the time needed for the different steps can be adjust- ed: acetone, isopropanol, hot water, drying N 2 , and CO 2 . SUMMARY This article demonstrates the capability of combining current intensity and position information to indicate the acid etch localization with regard to wire position and, more importantly, to die position. In the case of multi- die packages, it is necessary to make uniform precavities

ABOUT THE AUTHOR Michael Obein has more than 30 years of failure analysis experience and received his diploma in electronics from the University of Caen in 1987. He began his career as a designer of FA tools and later designed microwave tools. He co-founded Digit Concept in 1992 where he is now vice president and also serves as R&Dmanager. He has an extensive background in chip access using wet/dry chemical, mechanical, and laser techniques.

edfas.org