Ceramic Capacitor Aging and Restoration

[Retrovert]

I have no idea if this is useful, or if it applies to the vintage ceramic caps we encounter, but I found this description from Johanson Dielectrics of the aging process for ceramic capacitors:

The effect of time imposes a predictable loss of capacitance when comparing Class II and IV capacitors. For X7R and X5R the loss is calculated at -2.5% per decade hour and for Y5V it is -7% per decade hour. After manufacturing, the crystalline structure of the dielectric material is reset. It is due to the realignment of these crystals after firing that the capacitor goes through a logarithmic loss of capacitance.

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This aging rate is expressed in decade hours. This means after manufacturing the loss of capacitance is calculated at 1hr, 10hrs, 100hrs, 1000hrs etc….. This means at 10 hours the capacitance changes the same percentage as it will when measured at 100 hours and 1000 hours. As time goes on the aging process slows.

Now what's interesting is that this process can be reversed:

The aging process is reversible. By heating the capacitors over the "Curie Point" (approx 125°C for Barium Titanate capacitors), the crystalline structure of the capacitor is returned to its original state and the capacitance value observed after manufacturing. This process is referred to as "De-Aging". The amount of De-Aging is dependant on the level of temperature and how long the capacitors are exposed to it. Exposure to 150°C for one half hour or exposure to 125°C for one hour is sufficient to return the capacitor to its original value. The soldering process is also an effective De-Aging process.

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After the soldering process, the capacitors have essentially been De-Aged. Capacitance measurements may be erratic in the initial 10 hours after testing. This is due to the initial capacitance value, dielectric type and the time between reflow and the capacitance measurement. For this reason, it may be necessary to wait for the capacitance to stabilize after reflow before testing. In "High K" dielectrics, the capacitance may also appear slightly high after the soldering process. This is normal as the capacitance is intended to be stable after 1000 hours so that there is adequate capacitance throughout the life of the circuit.

The full technical note is available both as HTML and as a PDF.

I haven't tried this, don't know if it is typically necessary, nor do I know if it is practical to heat up a chassis up to 125 degrees and not destroy everything. My guess is that it likely isn't that far above the normal operating temperature, but baking geriatric circuity likely is not a good idea and you can't blame me if you turn a radio or TV into burnt toast.