A Different Approach To Failure Analysis

Decapsulation of plastic IC packages in different types and size were performed by wet chemical technique. Studied devices were to use in satellites and going to subject a series of test which require the die to be exposed. Different package types with changing sizes and bonding types such as Au- and Cu-bonded packages for unmounted and PCBA-mount components were successfully achieved. A combination of mechanical grinding, acid resistant tape masking and automatic low/high temperature etch instrument – JET Etch, were used in processing. Decapsulation process was carried out successfully for all devices, by preserving IC functionality after decapsulation which was main requirement for executed job.

Introduction
Decapsulation is a procedure which is conventionally used to remove the plastic packaging and allow internal features to be observed in classic FA (Failure Analysis) process. Regardless of the part being inspected, decapsulation must be performed in such a way that it preserves the integrity of the die, die attach, bond pads and wires, and other components within the encapsulation.

In this project DELTA/FORCE was hired by DTU Space (Danish Technical University) for decapsulation of different space components. The task was not a classic FA task, where the aim of decapsulation is exposing die for further failure analysisn. The task was exposing the dies which were going to subject a series of test which require the die to be uncovered.

DTU Space develops advanced space instruments for scientific satellites worldwide. An important part of the classification of the instruments for use in space is the verification of the electronic components used, both in terms of their actual production-quality and their resistance to radiation in space. This process requires that the test specimens are “decapsulated” ie removing parts of the package over the die so that the electronic circuitry is exposed. Delta has skillfully performed this “decapsulation” process for DTU Space for a series of components, some of which have a complex internal structure. The components must be qualified for a variety of aerospace missions include ESA’s formation flight’s mission “PROBA-3” and NASA’s “Mars 2020” rover mission to collect geological samples and try to find traces of prehistoric life on the red planet.

The principal concern in this job was to decapsulate all those packages without damaging sensitive electronic components and keeping the device functional. Some components were Cu-bonded which eliminates the usage of traditional high temperature acid dropping decapsulation technique. Another concern was to avoid damage to PCBA and surrounding components during decapsulation of onboard-mounted components. Physical dimensions for space components are very small in general and this makes local decapsulation – only die area decapsulation – near impossible. In such small sized components (1 mm X 1mm, length and wide) we preferred to remove whole package surface down to die level.

In each case, decapsulation process was started by X-Ray investigation for locating die position and the depth of plastic mold over the die surface. Depth data is important to predict chemical etch time. Next step is mechanical cavity opening, acid resistant tape bordering of decapsulation area and masking of this area in order to limit the etch area, this step is excluded for smaller size devices. Last step was decapsulation of the device in automatic decapsulation instrument, the JetEtch.

Images of decapsulated components

Images show physical sizes of different components which were decapsulated successfully. After decapsulation all the devices tested and approved as functioning correctly.

Images on the page show physical sizes of different components which were decapsulated successfully. All decapsulated device were fully functioning after mounting on PCBA for further tests.

Images show decapsulation of Cu-bonded SMD on board, decapsulation process carried out on board without removing the device.