Yes, the parts will age and change. Any of the "high-k" dielectric materials (required for physically small caps for electrically large values) have surprisingly wide ranges of variations in value. The dielectric name (X7R, Z5U, etc.) only specifies temperature related performance. The capacitance - vs. - applied voltage is often much worse, with parts from different vendors often having significant performance differences for the "same" part. For a good scare, check out the article at: https://www.edn.com/design/analog/4402049/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor .
Later,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask] http://cipherengineering.com
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Dennis Fritz
Sent: Wednesday, July 18, 2018 9:07 AM
To: [log in to unmask]
Subject: Re: [TN] capacitor measurement
Duh, chemical engineer question - I understand that you can make the
caps read correctly by baking them. However, what happens when you
solder them on to the board - i.e., won't they "age" on the assembly and then again function differently from caps just out of the 150C oven?
Denny
On 7/18/18, John Maxwell <[log in to unmask]> wrote:
> At 150C the parts are above the Curie temperature
>
> Sent from my iPhone
>
>> On Jul 18, 2018, at 11:48 AM, John Maxwell <[log in to unmask]> wrote:
>>
>> High dielectric constant ceramic capacitors all exhibit aging due to
>> the crystal structure changing from ferroelectric (tetragonal or
>> diamond) to paraelectric (cubic) structures. Higher the dielectric
>> constant (k) and the thinner the dielectric the more rapidly the
>> parts age or lose capacitance.
>>
>> John
>>
>>
>> Sent from my iPhone
>>
>>> On Jul 18, 2018, at 11:10 AM, Guy Ramsey <[log in to unmask]> wrote:
>>>
>>> Well, I'll Be. I cooked them at 150C for an hour and they measure
>>> 100uF I learned something today.
>>>
>>>> On Wed, Jul 18, 2018 at 8:08 AM <[log in to unmask]> wrote:
>>>>
>>>> Guy,
>>>>
>>>> Read this and try putting the parts through their Curie point and
>>>> test them again. We have seen this on some parts here.
>>>>
>>>> https://www.johansondielectrics.com/ceramic-capacitor-aging-made-si
>>>> mple
>>>>
>>>> Drew
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
>>>> Sent: Wednesday, July 18, 2018 7:00 AM
>>>> To: [log in to unmask]
>>>> Subject: [TN] capacitor measurement
>>>>
>>>> I got pulled into a Receiving Inspection problem. Our test
>>>> instrument, an old HP 4192A impedance meter, and a newer Instek
>>>> 6020 tell us that our X5R capacitors are out of spec.
>>>> A 100uF, 10%, 6.3V capacitor measures between 25% and 30% below the
>>>> nominal value. The instruments have Kelvin probes and are zero
>>>> calibrated at frequrency, 120Hz the test waveform is 500mV rms.
>>>> Does anyone have any advise?
>>>>
>
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