by Jack Goho
Gideon Analytical Laboratories received several Bourns Trimpot Trimming Potentiometers for failure analysis. A Potentiometer (known as a pot) is a three terminal resistor with a sliding contact that forms an adjustable voltage divider. They are widely used for volume control in radio and television receivers. The Bourns Trimpot Trimming Potentiometer 3006P 203 has a standard resistance range of 10 to 5 megohms, power rating of 400 volts maximum, and is ROHS compliant. Gideon Analytical Laboratories received several good and several bad units for comparison. The failures were addressed as having higher resistance or open.
Failure analysis ensued. There were no mechanical marks or bifurication marks along the package housing. This Trimpot was non-hermetic and vulnerable to fluid ingress. The adjustable screw, which allows the wiper to move, was made of brass. FTIR analysis was used to examine an unknown, colorless, viscous material that was found on the bottom of the 3006P 203 potentiometer. FTIR analysis revealed this substance to be a mixture of several substances, including polypropylene glycol and carboxylic acid salt.
FTIR analyis was followed by SEM-EDS analysis to determine another corrosive substance on the 3006P 203 potentiometer. SEM-EDS analysis revealed copper coming from the wiper, the presence of silica coming from silicone oil, and also the presence of chloride. Chloride is a foreign substance that corrodes ruthenium. Chloride was also present on the resistance runway; it had reacted with silver.
Overall results from the failure analysis performed by Gideon Analytical Laboratories were informative. There were chlorides present on the active resistive line on both the failures and the good parts, which was corrosive to ruthenium.
Gideon Analytical Laboratories provided the analytical services of FTIR and SEM-EDS for this failure analysis case. Gideon Analytical Laboratories uses state of the art diagnostic tools to glean and compile evidence to build a case outlining the cause of failure. We have the experience, the knowledge and technical expertise, and the scientific equipment to get the job done. If you need any failure analysis work performed or are in need for any analytical services to be carried out, call Gideon Analytical Laboratories.