Gideon Analytical Laboratories received several GE Aviation 144A9284P4 carbon film resistors for failure analysis evaluation. A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Their purpose is for creating a precise quantity of resistance for insertion into a circuit; they are typically constructed of metal wire or carbon and engineered to maintain a stable resistance value over a wide range of environmental conditions. They are frequently integrated within integrated circuits within the silicon; the resistor changes the voltage or the current in the line. It's measured in ohms (Ω). There were five working and five failed 144A9284P4 carbon film resistors. The failed resistors exceeded the 2% tolerance designated for this type of carbon film resistor.
The resistor consists of a ceramic substrate with two through holes for leads soldered to two tin strips, which make contact a carbon film coated under a blue epoxy cover coat. The blue epoxy functions as a scratch protection and seals the underlying carbon film from the outside environment. The five failures had resistance measurements of 17.3-17.6 ohms. This exceeded the manufacturers 2% tolerance. The virgin resistors were about 16.8 ohms.
The failed resistors were electrically tested for their respective resistances. Then they were baked and retested; it was found that their resistance actually increased. Silicon was removed and the resistors were retested. The epoxy was removed and the resistors retested. FTIR analysis was conducted to see what exactly was contributing to the increased resistance. There was no spectrum able to be obtained. The cause of the increased resistance was a porosity and permeability of the epoxy.
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