No abstract

The introduction of copper as wire bonding material brings about a new challenge of aluminum bond pad bimetallic corrosion at the copper/aluminum galvanic interface. Aluminum is well known to undergo pitting corrosion under halide-contaminated environments, even in slightly acidic conditions. This paper aims to study the corrosion morphology and progression of aluminum influenced by different halide contaminations in the presence and absence of galvanic contact with copper. We used a new corrosion characterization platform of the micropattern corrosion screening to simulate the copper wire bonding on the aluminum bond pad. The corrosion screening data and subsequent SEM–EDX analyses showed a striking difference in morphology and progression between chloride-induced and fluoride-induced aluminum corrosion. The corrosion products formed play a vital role in the resulting morphology and in sustaining further aluminum corrosion.

Accelerated reliability testing of integrated circuit (IC) packages, such as wire-bonded devices, is a useful tool for predicting the lifetime corrosion behavior of real-world devices. Standard tests, such as highly accelerated stress test, involves subjecting an encapsulated device to high levels of humidity and high temperature (commonly 85–121 ⁰C and 85–100% relative humidity). A major drawback of current reliability tests is that mechanistic information of what occurs between t = 0 and device failure is not captured. A novel method of in-situ investigation of the device corrosion process was developed to capture the real time mechanistic information not obtained in standard reliability testing [1] . The simple, yet effective methodology involves: Immersing a micropattern or device directly into contaminant-spiked aqueous solution, and observing its morphological changes under optical microscope paired with a camera. Short (2–48 h) time required for testing (compared to 24–300 h of standard tests). No need for humidity chambers.

Copper has rapidly replaced gold as the preferred wire bonding material in microelectronic packaging due to its lower cost and many performance advantages. However, halides induced corrosion-related failures need to be carefully controlled to ensure maximum bonding reliability. Literature reported corrosion studies mostly focus on intermetallic compounds as the corrosion vulnerability. Utilizing a novel corrosion screening approach, we established that the bimetallic contact between Cu balls and Al bond pad is the real driver for the observed heavy Al pad corrosion induced by chloride ions [1]. We identified, for the first time, H2 evolution was the coupling cathodic half reaction to the Al bond pad corrosion. With these improved mechanistic insights, we developed an effective corrosion inhibition strategy that utilizes chemical vapor deposition to selectively bond corrosion inhibitors to these critical Cu ball/Al pad interfaces. A new corrosion-screening platform was developed to evaluate the effectiveness of this inhibitor protection treatment. After intentionally loaded chloride contaminants on the die surface, the molded Cu wire bonded devices with selected inhibitor treatment were subjected to PCT stress tests. The subsequent failure analyses, showed selected inhibitor treatment is highly effective of preventing Al bond pad corrosion even under the massive attack of heavy Cl− ion contamination and extensive delamination.