Gideon Analytical Labs received three partial boards with four coupling Vishay MKT 1817 63V ERO 0225 film capacitor failures. After electrical measurements and considerable testing, the ESR was found to be the cause of the failure, however, what caused the ESR to elevate?
It was determined the packaging on the capacitor was not adequately protecting the terminal end from the outside environment. Moisture ingress elevated the ESR and with higher ESR, the higher the heat produced in the circuit.
Film capacitors are widely used because of their superior characteristics. This capacitor type is not polarized, which makes them suitable for AC signal and power use. Film capacitors can be made with very high precision capacitance values, and they retain that value longer than other capacitor types. This means that the aging process is generally slower than in other capacitor types, such as the electrolytic capacitor. Film capacitors have a long shelf and service life, and are very reliable, with a very low average failure rate.
Gideon Analytical Labs received a cold rolled steel plate with two corrosion blemishes on the plating. The black corrosion deposition is on zinc plating, which has oxidized with chlorine forming zinc chloride.
The SEM-EDS spectrum shows an excessive amount of chlorine. The chloride is reacting with the zinc. Chlorides are very corrosive to electronic parts, plating, and metals. On copper trace lines the resistance increases, metals discolor, and on aluminum, it acts as a corrosive catalyst causing opens and pitting to metal.
Three lots of capacitors were submitted Gideon Analytical Labs for chloride and zinc contamination analysis on the terminal leads of the electrolytic capacitors.
The analysis was performed using an SEM-EDS system giving elemental analysis in relation to the intensity of the element at a specific wavelength or energy level (Kev). Since Kev (energy levels) for specific elements do not change, these are used to identify the elements in the sample.
Gideon Analytical Labs received a contaminated white translucent adhesive at the edge of a polyimide strip under a rubber keypad. Since most of the materials were organic, FTIR was the method of analysis first used to determine the foreign material.
The polyimide is a double-sided adhesive based flexible laminate (Kapton) film coated with adhesive on one or both and laminated to copper. There are two kinds of adhesive used in flex, epoxy, and acrylic.
This filter is used in a water filter system for water consumption. The filters were plugging up rather fast with the pink material shown in the photograph below.
Since these problem types are unknown, one must choose the appropriate analysis method for material identification. Methods used are Fourier transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) and Gas Chromatography-mass Spectrometry (GCMS)) since the filters were designed to filter out organics and inorganics.
This is a picture of a copper wire that used to have tin plating and nickel plated pad. The wire was running 120V at 60Hz. The connection was placed in a non-hermetical container where chlorides in the atmosphere were high. Over time the chlorides attacked the exposed copper and undermined the tin plating on the copper wires. The resistance in the wire increased, the copper arced due to this increased resistance and the socket assembly failure to corrosion.
This a micrograph of copper oxide deposits on nickel plating. The copper oxide is inhibiting the electrical conduction of a 120V light on terminals of a light bulb. This is an environmental failure stemming from the fact that the exposed copper on another part of this circuit, deposited copper oxide by arching, and this, in turn, caused an eventual loss in conduction to the bulb.
This arcing happens when low-level contaminants are present and concentrate over time.
The analysis was performed on ten failed microwave capacitors. They were Samwha vintage 2100VAC .65uF with 3 percent tolerance with a maximum temperature rating of 85oC. All the capacitors were tested for shorts or opens. The resistance of the integrated resistor was measured also. None of the integrated resistors failed. They all varied from 9.75-M ohms to 10.85M ohms. Many of the capacitors saw considerable heat. This was evident by the bulging deformed metal can housing.
Gideon Analytical Laboratories received two integrated load switches and two small signal diodes for analysis. The integrated load switches are particularly suited for compact power management in portable electronic equipment where 2.5V to 8V input and 2.8A output current capability are needed. They have an operating voltage range 1.2V-20.V. The signal diodes are non-linear semiconductor devices generally used in electronic circuits, where small currents or high frequencies are involved such as in radio, television and digital logic circuits.
