Chip resistors can corrode and increase in resistance or go open circuit due to sulfur in atmospheric pollution.

Here is another example …

The conformal coating was removed to exposed the top of the resistor.

SEM/EDS analysis of an apparent corrosion bloom suggest that it is silver sulfide.

This is a higher magnification image showing the structure of the bloom.

Solder mask defined pads are considered undesirable since they require exacting mask alignment. In this case misalignment likely contributed to weakness in the ball attachment.

Check out SEM Lab, Inc.  to learn more.

Pad lift can be caused by excessive heat during reflow soldering or poor copper adhesion to the PWB laminate.

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This is an LED microsection where the open circuit failure was caused by the die and lens material separating from the bottom of the cup and rupturing the die attachment.

Check out SEM Lab, Inc.  to learn more.