Chip Resistor Corrosion
SEM Lab, Inc. has seen the same type of resistor failures repeatedly since ~ 1997 when we were founded. The trigger appears to be the local environment where the resistors are deployed, for example ...
- A computer module in a tractor.
- Fireworks display controller. Boards coated with ~ 0.300 inches of Dow Corning "tough gel".
- A display at an outdoor drive-up kiosk.
- Many other previous analysis efforts where the source of sulfur is unexplained.
The problem, sulfur pollution and corrosion of silver, is illustrated in Fig. A and explained thoroughly in references  & . The resistors increase in value and eventually fail open.
 Craig Hillman, Joelle Arnold, Seth Binfield, Jeremy Seppi, "Silver And Sulfur: Case Studies, Physics, And Possible Solutions", DfR Solutions, College Park, MD, USA, 2007, email - firstname.lastname@example.org, http://www.dfrsolutions.com/uploads/publications/2007_10_silver_and_sulfur.pdf. link
 Marie Cole et al, "Harsh Environment Impact On Resistor Reliability", SMTA International 2010 Conference Proceedings, http://researcher.ibm.com/researcher/files/us-kleinl/Resistor_Harsh_Environ_final_SMTAI2010.pdf.