Semiconductor devices are almost always part of a larger, more complex piece of electronic equipment. These devices will operate in unison with other circuit elements and be subject to system, subsystem, and environmental influences.
As so often happens after an equipment failure, a technician will troubleshoot the unit and determine that a particular device is at fault. The device then will be removed, often using thermal and mechanical stresses, after which the device will be submitted to the laboratory for fault analysis.
Isolating the failure
When the subsystem responsible for the failure has been identified, the fulty section must be further isolated to the board or smallest mechanical structural level containing all related parts and components.
The ultimate goal in failure analysis is to arrive at an accurate determination of the cause of failure. In semiconductor failure analysis, destructive testing is necessary in a large portion of the analytical effort. Tasks such as decapsulation and cross sectioning are acceptable techniques. Performed prematurely, however, thes procedures can result in irreversible damage and a ruined analysis.
Decapsulation
The goal in decapsulation is to expose the failure and internal construction of the device without alerting the failure mode. Depending on the suspected failure mode, the appropriate techniques for opening a device generally are mechanical and chemical. Mechanical techniques usually apply to metal, glass and ceramic packages. Chemical techniques generally are used on plastic or epoxy encapsulated devices.
Topside decapsulation (analysis that is carried out on the circuitry populated side of the wafer material) using primarily chemicals is a well established application that is carried out with manual protocols, or more frequently with automated acid etch systems.
These methods produce fast and effective results on standard plastic packaged parts. However, several factors make acids incapable of processing all package styles. Fro instance, when the package contains materials that are slow or impossible to remove with acids, or when the total package cross-sectional thicknesss is large (this exacerbates the non-directionality of the acid attack and potentially leads to harmful corrosion of the bond pads and wires) it has been found that initial mechanical decapsulation offers key advantages.
Internal Visual Examination
Following decapsulation, optical microscopes or a scanning electron microscope (SEM) can be used to evaluate physical anomolies, damaged areas, or electrically overstressed areas.
Failures that can be successfully located using Logitech technology include :
- Bond wire snapping due to EOS (Electrical Over Stress)
- Deformation of bond wires due to improper bonding
- Cracks at the bonding pad-bond wire junction
- Metallization damage due to EOS, ESD (Electro Static Discharge), corrosion
- Hillock formation by metal ions
- Oxide layer faults due to impurities, ESD damage, pin-hole due to etching processes
- Defects in the bulk semiconductor material , such as crystal defects
- Design and fabrication faults, misalignment of layers, geometric defects
- Cracks at the lead body interface leading to open-circuit