Processing tantalum capacitors on assembled PWAs to yield low failure rate

A method of conditioning and screening tantalum capacitors, the method comprising:

• for each tantalum capacitor to be tested, applying a series of voltage pulses across the capacitor to induce a series of surge currents through the capacitor,
• applying a predetermined voltage across the capacitor and measuring leakage current flowing through the capacitor at predetermined intervals of time after the predetermined voltage has been applied across the capacitor,
• determining whether the capacitor is acceptable on the basis of the leakage current measurements taken for the capacitor,
• the capacitor being determined to be acceptable where the capacitor has a level of leakage current that is decreasing over time, or that is less than a predetermined current level at a selected one of the predetermined intervals of time,
• the capacitor being determined to not be acceptable where the capacitor has a level of leakage current that is increasing over time, or that is equal to or greater than the predetermined current level at the selected one of the predetermined intervals of time;
• wherein the predetermined intervals of time at which leakage current through the capacitor is measured begin at a predetermined amount of time after the end of the third pulse period, and
• wherein the predetermined amount of time after the end of the third pulse period is equal to the duration of time for each pulse period.

A method of aging tantalum capacitors to thereby condition the capacitors for screening to yield capacitors that are usable without de-rating at low failure rates, the method comprising:

• for each tantalum capacitor to be tested, aging the capacitor by applying over each of a plurality of pulse periods having a predetermined duration of time, a series of voltage pulses across the capacitor to induce a plurality of surge currents through the capacitor,
• subsequent to aging the capacitor, applying a predetermined DC voltage across the capacitor for a predetermined period of time and measuring leakage current a plurality of times at predetermined intervals of time after the predetermined DC voltage has been applied across the capacitor,
• grading the capacitor on the basis of the results of the leakage current measurements taken for the capacitor,
• the capacitor being determined to have a passing grade where the capacitor has a level of leakage current that is decreasing over time, or that is less than a predetermined current at a predetermined one of the predetermined intervals of time,
• the capacitor being determined to have a failing grade where the capacitor has a level of leakage current that is increasing over time, or that is greater than a predetermined current at a predetermined one of the predetermined intervals of time.

A circuit for aging tantalum capacitors to thereby condition the capacitors for screening to yield capacitors that are usable without de-rating at low failure rates, the circuit comprising:

• a first voltage supply that applies across a capacitor to be tested a first DC voltage,
• a circuit that switches the first DC voltage applied across the capacitor so as to age the capacitor by applying several series of voltage pulses across the capacitor over a plurality of pulse periods of predetermined duration,
• a second voltage supply that applies across the capacitor, subsequent to aging the capacitor, a second DC voltage different from the first DC voltage,
• a circuit that measures leakage current a plurality of times over predetermined intervals of time after the second DC voltage has been applied across the capacitor,
• wherein the capacitor is determined to be acceptable or not on the basis of the results of the leakage current measurements taken for the capacitor,
• the capacitor being determined to be acceptable where the capacitor has a level of leakage current that is decreasing over time, or that is less than a predetermined current at a predetermined one of the predetermined intervals of time,
• the capacitor being determined to not be acceptable where the capacitor has a level of leakage current that is increasing over time, or that is greater than a predetermined current at a predetermined one of the predetermined intervals of time.