Reliability Studies and Failure Analysis for Fine Cu-Al Bonding System in Microelectronic Packaging

Abstract

Copper thermosonic wire-bonding on aluminum metallization pad applied in high-volume digital microelectronic devices have developed as a mainstream since Cu is a much cheaper material alternative and it also offers several physical advantages as compared to more mature technology of gold wire-bonding In decapsulation technique of Cu-Al binary system in FA analysis a new strategy has been developed for discovering a novel/facile way of etching epoxy molding compounds (IMCs) and polyimide (PI) film It successfully developed a process both including laser and wet treatments of optimum recipe to solve the over-etching and corrosion problems for critical package geometries of ball grid array (BGA) packages The deprocessing technique (drenched alkaline aqueous solution of ethylenediamine and then instantaneously combined with mix acid (2:1 Nitric 90% fuming to Sulfuric mix at 40 °C)) could be extended to remove polyimide in different package geometry and different thickness of film Reverse engineering techniques of Cu wire bonding process used in manufacturing microelectronic packing components are proposed for evaluating Cu-Al intermetallic phases The High Thermal Storage (HTS) in the molded bond reliability test and Cu-Al IMC coverage estimation method on Cu ball-bonded parts contribute to increased production efficiency and improved bonding process quality The results show that distinct intermetallics of microscopic lamellar structures were identified as CuAl2 CuAl and Cu9Al4 after thermal annealing to 2000 h at 150 °C After post annealing process voids appear here are too small to pose a threat to reliability concern and Al fragments emerge during bonding process accompanied with smaller diffusion voids are highly connected to create more robust intermetallics The growth kinetics of Cu-Al intermetallic compound was determined simultaneously during annealing tests From Arrhenius equation the growth rate of intermetallic formation (k) has been obtained under three different annealing temperatures and calculated its activation energy of 76 13 kJ/mol and the growth rate constant of k0=46 47 μm2/s The obtained universal equation of layer thickness can be acted as the prediction model for the guideline of intermetallic growth behavior under thermal effect which diminished the Cu-Al interface failures for practical field application Cu-Al intermetallics coverage inspection and ball shear test was investigated in the unmolded bake reliability test which addressed the specification of IMC coverage>80% and typical minimum shear strength of 6 67 g/mil2 (=10 34 Kg/ mm2) The corrosion issue in the copper ball bonding process and evaluating the selection of the device molding compound (depends on the amount of hydrogen and chloride ions in EMC with ion catcher) for the impact in the Cu-Al interface during bias HAST (highly accelerated temperature and humidity stress test) has addressed Corrosion-induced-degradation issue in Cu stitch bond will also be implemented by electrochemical analysis and validated by practical case study for a comprehensive understanding of the failure mechanisms involved with copper wire bonded semiconductor devices To meet the extensive application in copper wire bond technology identification of corrosion sites and corrosion products on electronic components and devices will be discussed for ensuring a high degree of reliability of the electronic systems where such components or devices are installed in automotive components or even in spaceflight hardware

Date of Award	2019
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)