November_EDFA_Digital

edfas.org 35 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 20 NO. 4 Fig. 14 Signature vs. time. Table 1 Recipe used Process parameters Settings Circulation HE Ratio nitric/sulfuric 5:1 Beginning 20 s Flow 3 ml/min Polarization voltage 15 V Etch time Variable Rinse time 0 s Purge time 20 s Fig. 15 Derivative of amperage shown in Fig. 14. these experiments, the same components with the same recipe (Table 1) were decapsulated using different time durations. As a result, signature changes were observed. (Fig. 14). Four key steps may be observed during acid opening: 1. Exposure of wire bonding is illustrated by measure- ment of a nonzero intensity. T etching = 2 min 2. The die is represented by a little peak of about 10 mA. T etching = 1.8 min 3. When the die is reached during the etching process, one or more peaks appear and can reach 80 mA. T etching = 2 min 4. The peak of the die pad appears at 3.90 min. The first and second derivatives shown in Fig. 15 illustrate the possibility of distinguishing the changes of state, as occurs in laser interferometry for reactive ion etching (RIE). This signature in current polarization does not vary significantly, so it can be used to reach the same step in a packaging decapsulation process with low tolerance variations. In the context of failure analysis, it is common to see components with dies that have become overheated. In such cases, the resin close to the die is repolymerizing and therefore its nature changes. Monitoring the current