Moisture failures induced

In IC packaging, the carrier case also provides a moisture barrier. Often, failure in a microdevice is the contact between the metal wires and the metal contacts on the substrate due to moisture-induced corrosion. For microelectromechanical system (MEMS) devices, moisture presents more of a threat than for conventional IC devices [1]. Many micromechanical MEMS components (such as a microcantilever beam) are positioned a few micrometers from the substrate. Moisture condensing on the surface of the substrate will pull down the MEMS devices due to surface tension. The micromechanical component will no longer be functional. 

In IC packaging, the carrier case also provides a moisture barrier. Often, failure in a microdevice is the contact between the metal wires and the metal contacts on the substrate due to moisture-induced corrosion. For... 

Moisture induced failures have been the most persistent, and thus the most intensively studied, of all the reliability hazards of plastic encap-... 

Conditions Which Will Result in Unacceptable Moisture Induced Failure Rates... 

Although the last decade has seen sustained improvements, in both moulding compounds and passivation layers, which have lessened the risk of moisture induced failure, it is still considered necessary to perform regular product evaluation. 

From Fig. 6.8 it also follows that there will be no risk of moisture induced failure occurring in service in the UK, if internal power dissipation raises the die temperature by only 16°C above the uncontrolled ambient temperature. (The corresponding figure for tropical climates is 18°C.) Although there are many technologies (such as bipolar TTL) which satisfy this criterion, there are others (such as CMOS) where the internal heating is minimal, and consequently ambient moisture will present a significant reliability hazard. 

The confinement of the cracks to a specific area of the cooler suggests that condensate from atmospheric moisture initially formed in this area and dissolved a corrodent from the atmosphere such as ammonia, sulfur dioxide, or oxides of nitrogen. Since the previous cooler had been in service for 20 years, it is conjectured that the rapid failure of this exchanger was due principally to very high bending stresses, which may have been induced during construction of the cooler. 

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

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