Ground Allocation of Multi Tier Hardware Warranty Liabilities
Ground allocation distributes warranty liability across hardware tiers based on integration depth, physical root cause, and explicit contract caps.
Kirkendall Voiding
Meaning
Metallurgical defect characterized by the formation of microscopic cavities at the interface between two dissimilar metals. Kirkendall voiding occurs when the atoms of one metal diffuse into the other at a higher rate than the return flow of atoms. This imbalance creates vacancies that coalesce into physical gaps, which eventually compromises the mechanical and electrical integrity of the joint.
Diffusion Mechanism
Copper atoms move into the tin layer of a solder joint more rapidly than the tin atoms migrate in the opposite direction. This directional flux of matter creates a surplus of empty lattice sites on the copper side of the boundary. These vacancies aggregate into small clusters that grow over time as the device remains at operating temperature.
Thermal Acceleration
High temperature environments increase the rate at which atoms move through the metal lattice. Systems that operate under continuous heavy loads or in uncooled enclosures experience faster development of these cavities. Long term aging at elevated temperatures can cause the voids to form a continuous line of failure along the intermetallic interface.
Joint Reliability
Mechanical strength of the interconnection drops as the total area of the voids increases. A joint affected by kirkendall voiding is prone to brittle fracture when subjected to vibration or mechanical shock. Testing for this condition usually involves cross sectional imaging of the solder interface after several hundred hours of heat soaking.