SEM/EDS is useful for detecting the use of red phosphorus in IC molding compounds.

At one time (~1990s), red phosphorus was introduced as an environmentally-friendly flame retardant in molding compounds for semiconductor devices.

This turned out to be a mistake.

A rash of electrical leakage related failures ensued.

There are now reports of red phosphorus use in wire insulation for cabling and power cords, suggesting that the industry may not have learned its lesson.

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Chlorine residue on this ENIG land caused corrosion of the underlying nickel and copper to form copper and nickel oxides on the gold surface.

Apparently the 3 – 7 micro-inches thick immersion gold layer is not always impervious to chloride migration.

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This is a SE SEM image of the device die. The source bond wire (left) was fused open. The gate bond wire (right) was intact.

This is the source bond pad. This material (arrow) is fused gold-copper-silica-silicon.

The source bond wire is fused open suggesting excessive source current caused the failure.

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This diode failed due to electrical overstress, likely reverse biasing greater than 1000V. The die fractured when it was de-processed. The melt-through site is indicated by the arrow. Quality issues may have been a factor including post and die attach solder voids, and potting voids, which would be expected to impact the maximum power capability of the diode causing it to fail at lower than rated conditions.

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This is a BSE SEM image of the microsection of the tantalum capacitor.

The breakdown site is indicated by the arrow and is associated with the edge of the slug near the lead attachment at the cathode.

This is an EDS dot map that shows the amount of alloying and inter- diffusion associated with the failure event.

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Fracture of this MLCC was most likely caused by PWB bending, and it resulted in an internal short. This can occur during breakout from a panel, or during ICT, or due to PCBA warpage after reflow.

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This is a BSE SEM image of a parallel microsection showing an electrical breakdown site on an inner laminate layer of the PWB. The short developed due to copper electromigration through damaged areas of laminate from a previous operation where excessively warped boards were laminated to heat sinks.

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Surface trace fractured on rigid-flex assembly.

Location of fracture in microsection.

The stiffness of the PTH solder joint far exceeds that of the trace leading to fracture at the transition.

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