External Package Contamination

External package contamination is the presence of a foreign material, whether attached or unattached, anywhere on the external portions of the package body and/or its interconnection features (e.g., leads, solder balls, etc.). Since certain contaminants can affect the performance and reliability of the device, external contaminants need to be identified promptly and, if necessary, traced to their root cause. Corrective actions may then be implemented to prevent recurrence.

The criteria for rejecting external contamination depends on its location, extent, and composition. Some contaminants are rejected because it results in cosmetic failure, while others are rejected because of the reliability risk involved, mainly with regard to lead corrosion and solderability issues, as well as electrical leakage between pins.

External contaminants can come from anywhere. If all the units are affected, it is likely that it has come from an equipment used in the process, or a bad batch of raw material has been used. If the contaminated units are isolated, it may have been produced by a random or non-repeating event.

External contaminants, depending on their identity, can lead to various failures, including excessive current leakage, pin-to-pin shorts, corrosion, solderability failures, and visual-mechanical failures.

Figure 1. Lead contamination in PDIP (left) and metal can (right)

Common external contaminants include but are not limited to the following : grease or oil from equipment; flux or solder on package; oxides on leads; human contaminants such as spittle and fingerprint residues; and organic contaminants on package or leads.

Examples of FA techniques used for identifying external contaminants include: EDX Analysis, FTIR Analysis, and Ion Chromatography. The corrosive effects of contaminants may be accelerated by PCT and HAST.

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