Apparatus and method for screening electrolytic capacitors
View Patent ↗A method for screening electrolytic capacitors places a capacitor in series with a resistor, applying a test voltage and following the charge curve for the capacitor. A high voltage drop across the capacitor indicates high reliability and a low voltage drop is used to reject the piece. The leakage current is not adversely affected during the test.
1. A method for screening a population of electrolytic capacitors comprising:
separating said population of electrolytic capacitors into a first subpopulation of electrolytic capacitors and a second subpopulation of electrolytic capacitors;
determining an average breakdown voltage of said first subpopulation of electrolytic capacitors
applying a dc voltage of no less than said average breakdown voltage to the combination of each test capacitor of said second subpopulation of electrolytic capacitors and a series connected resistor;
monitoring a voltage drop in a charge curve across said test capacitor until up to either said average breakdown voltage or until a predetermined time is reached; and
sorting said test capacitors into at least two groups wherein in a first group of said groups said voltage drop is below a predetermined level and in a second group of said groups said voltage drop is above a predetermined level.
2. The method for screening a population of electrolytic capacitors of claim 1 said series resistor has a resistance of at least 0.1 Mohm to no more than 10 Mohm.
3. The method for screening a population of electrolytic capacitors of claim 1 wherein said predetermined time is at least 0.5 min to no more than 5 min.
4. The method for screening a population of electrolytic capacitors of claim 1 further comprising removing capacitors from said first group.
5. A method for screening a population of electrolytic capacitors of claim 4 wherein said first group represents 1% to 10% of said population.
6. The method for screening a population of electrolytic capacitors of claim 1 further comprising screening said capacitors.
7. The method for screening a population of electrolytic capacitors of claim 6 wherein said screening is selected from the group consisting of ageing at elevated temperature, ageing at elevated voltage, surge test and re-flow test.
8. The method for screening a population of electrolytic capacitors of claim 6 said screening is after said determining an average breakdown voltage.
9. The method for screening a population of electrolytic capacitors of claim 1 further comprising determining a resistance of said series resistance.
10. The method for screening a population of electrolytic capacitors of claim 9 wherein said determining a resistance is prior to a screening.
11. The method for screening a population of electrolytic capacitors of claim 1 wherein said dc voltage is no more than 1.5 times average breakdown voltage.
12. A method for screening a population of electrolytic capacitors comprising:
applying a dc voltage of no less than an average breakdown voltage to a combination of each electrolytic capacitor of said electrolytic capacitors and a series connected resistor;
monitoring a voltage drop in a charge curve across said electrolytic capacitor until up to either said average breakdown voltage or a predetermined time is reached; and
sorting said electrolytic capacitors into at least two groups wherein in a first group of said groups said voltage drop is below a predetermined level and in a second group of said groups said voltage drop is above a predetermined level.