One method of reducing costs in the packaging sector is to switch from gold bond wires to copper. Thicker copper wires (over 2 mils) can be safely decapsulated using a ratio mixture of fuming acids. Some surface etching of the copper will occur, but the wire will remain electrically viable. Microwave Plasma can provide a safer alternative for decapsulating packages with copper bondwires and exposed copper metallization. In this paper, experimental deprocessing of copper bond wire and copper metallization using laser ablation and downstream microwave plasma has found that 1 mil stressed wires can be safely exposed and examined, showing slip plane fractures in the corner wires. Topside copper metallization remains intact, even the thin protective nickel plating. Sensitive copper metal structures on top of the passivation (such as antennas) will remain electrically viable following decapsulation with plasma, but are often lost and defective following acid decapsulation.

With the introduction of new packaging technologies and the great variety of semiconductor devices, new decapsulation tools are needed to improve failure analysis with a higher success rate, and to improve quality control with a higher confidence level. Conventional downstream microwave plasma etchers use CF4 or other fluorine containing compounds in the plasma gas that causes unwanted overetching damage to Si3N4 passivation and the Si die, thus limiting its use in IC package decapsulation. The approach of atmospheric pressure O2-only Microwave Induced Plasma (MIP) successfully solves the fluorine overetching problem. Comparison between MIP, conventional plasma, acid etching based on several challenging decapsulation applications has shown the great advantage of MIP in preserving the original status of the die, wire bonds, and failure sites. One of the challenging failure analysis cases is Bond-Over-Active-Circuit (BOAC) devices with exposed thin copper metallization traces on top of Si3N4 passivation. The BOAC critical die structures present a challenge to both conventional plasma and acid decapsulation. The use of MIP to solve the BOAC device decapsulation problem will be discussed in detail through multiple case studies. It appears that the MIP machine is the only approach to decapsulate BOAC devices without causing any damage to the exposed copper on passivation critical structure, which demonstrates the failure analysis capabilities of the MIP system.

The decapsulation process in today’s failure analysis labs can become complicated with the smaller size of the package and the surface mount methods of attachment. Some failure modes recover when a part is removed from the application and remounted after decapsulation, and some parts are simply too fragile to handle for re-mounting after decapsulation. Decapsulating the failing device in-situ (on the board or DIP adapter) allows us to analyze the part in its original mounting condition, without exposing it to additional solder temperature stress, broken wires, or tweezer damage. This poses a challenge, as the fuming acids used for decapsulation most likely will spill onto the circuit board, dissolving the package leads, damaging the resin layers, and potentially corroding and shorting the circuit board traces.

Soft Defect Localization (SDL) is a dynamic laser-based failure analysis technique that can detect circuit upsets (or cause a malfunctioning circuit to recover) by generation of localized heat or photons from a rastered laser beam. SDL is the third and seldom used method on the LSM tool. Most failure analysis LSM sessions use the endo-thermic mode (TIVA, XIVA, OBIRCH), followed by the photo-injection mode (LIVA) to isolate most of their failures. SDL is seldom used or attempted, unless there is a unique and obvious failure mode that can benefit from the application. Many failure analysts, with a creative approach to the analysis, can employ SDL. They will benefit by rapidly finding the location of the failure mechanism and forgoing weeks of nodal probing and isolation. This paper will cover circuit signal conditioning to allow for fast dynamic failure isolation using an LSM for laser stimulation. Discussions of several cases will demonstrate how the laser can be employed for triggering across a pass/fail boundary as defined by voltage levels, supply currents, signal frequency, or digital flags. A technique for manual input of the LSM trigger is also discussed.

Cold temperature failures are often difficult to resolve, especially those at extreme low levels (< -40°C). Momentary application of chill spray can confirm the failure mode, but is impractical during photoemission microscopy (PEM), laser scanning microscopy (LSM), and multiple point microprobing. This paper will examine relatively low-cost cold temperature systems that can hold samples at steady state extreme low temperatures and describe a case study where a cold temperature stage was combined with LSM soft defect localization (SDL) to rapidly identify the cause of a complex cold temperature failure mechanism.