Precautions for measuring the capacitance of chip multilayer ceramic capacitors

Precautions for measuring capacitance


Do any of the following problems occur when measuring the capacitance of chip multilayer ceramic capacitors (hereinafter, "MLCC")?

Let's resolve these problems!!

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When measuring the capacitance of a TC-related low capacity MLCC,
the measured value is greater or smaller than the nominal value.




     
When measuring the capacitance of a HiK-related high capacity MLCC,
the measured value is smaller than the nominal value.


 
       
*Please check the detailed specs sheet for the capacitance measuring conditions.

*Please see the attached reference material『Basics of capacitors [Lesson 7] Measurement Method for the Electrostatic Capacitance of Ceramic Capacitors』which provides an overview of capacitance measurements.


Precautions when taking a TC-related low capacity measurement

     
When measuring the capacitance of a TC-related low capacity MLCC, the measured value is greater or smaller than the nominal value.


     

The process is explained using the following steps.

1) What is the test fixture zero point adjustment?

2) The distance between the terminals and the capacitance measurement value during OPEN correction

3) The reason why the capacitance measurement value changed

4) Precautions during measurement

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1)What is the test fixture zero point correction?


1. The MLCC is measured as shown in the figure below, but the following issues occurred, and the actual MLCC capacitance cannot be accurately measured.

・There is series resistance and series inductance in the measuring cable
・There is stray capacitance in the measuring terminal, which interposes the MLCC

Therefore, the action, which cancels out each parameter when the MLCC being measured is not present, is called the "Test Fixture Zero Point Correction."
This corresponds to the OPEN correction and SHORT correction actions taken before the measurement.


2. The OPEN correction cancels out the stray capacitance of the measuring terminal which interposes the MLCC while the SHORT correction cancels out the series resistance and inductance in the measuring cable.

3. After performing this OPEN correction and SHORT correction, you can ensure the accuracy of the MLCC measurement.


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2)The distance between the terminals and the capacitance measurement value during OPEN adjustment


The capacitance of a 1 pF MLCC was measured while changing the distance between the terminals of the test fixture during the OPEN correction.
As a result, when the distance between the terminals during the OPEN correction is greater than the L dimension of the MLCC being measured, the capacitance increases, and decreases when it is smaller.

■Measurement conditions
Test sample: GRM0334C1H1R0B
Measuring instrument: HP4278A
Measuring jig: HP TEST FIXTURE16034E (insertion type)
Conditions: 1±0.1 MHz/1±0.2 Vrms

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3)The reason why the capacitance measurement value changed


■Why does the capacitance change depending on the distance between the terminals during OPEN correction?

    Capacitance occurs when there is an insulator between two pieces of metal.
The air is also an insulator, so capacitance occurs between the measuring terminals.

The capacitance increases as the distance between the two pieces of metal decreases.
Therefore, as the distance between the terminals gets smaller, the capacitance gets larger.
 
     

■Distance between the terminals during OPEN correction and the capacitance measurement results



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4)Precautions during measurement

<Key points during OPEN correction>

Set the distance between the fixture terminals during OPEN correction to the same value as the L dimension of the chip being measured.


If OPEN correction is performed when the distance between the fixture terminals is long, the fixture stray capacitance during correction will be smaller than the capacitance during the actual measurement.
 
 C=ε・S/d ・・・・・ Because "d" increases in formula (1)

C :stray capacitance (capacitance)
ε:dielectric constant
S :electrode surface area
d :distance between terminals (distance between electrodes)
   

If the zero point correction is performed when the distance between the fixture terminals differs from the dimensions of the MLCC being measured, the stray capacitance of the fixture itself will not be accurately corrected to zero.

When the distance between the terminals during OPEN correction is smaller than the L dimension of the MLCC, the stray capacitance of the fixture is corrected to the zero point at a distance greater than reality, so the post-correction measurement result will decrease.

Conversely, if the distance between the terminals is set to greater than the L dimension of the MLCC, the post-correction measurement result will increase.
The variation in the distance between the terminals during OPEN correction is greater when using a tweezer-type of fixture (Ex. Agilent16334) than it is when using an insertion-type of fixture (Ex. Agilent16034).


Compared to the insertion-type of fixture, the tweezer-type has a measuring terminal tip with a larger surface area (S in formula 1), so the fluctuation in the capacitance measurement value increases according to the difference in the distance between the terminals.


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Precautions for an HiK-related high capacity measurement


When measuring the capacitance of a HiK-related high capacity MLCC, the measured value was less than the nominal value.

     

The process is explained using the following steps.

1) Example of a high capacity MLCC measurement

2) Reason why the capacitance falls below the measured value

3) Precautions during measurement

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1)Example of a high capacity MLCC measurement


The capacitance was measured with high capacity and regular MLCCs with the ALC (Automatic Level Control) in the ON/OFF state.
The results are shown below.


■Measurement conditions

Test sample: GRM21BB31C106K/ GRM21B1C1H223J
Measuring instrument: Agilent E4980A
Measuring jig: Agilent TEST FIXTURE16334 (tweezer-type)
Conditions: GRM21BB31C106K; 1±0.1 KHz/0.5±0.1 Vrms
GRM21B1C1H223J; 1±0.1 KHz/1.0±0.2 Vrms
=> When measuring the high capacity capacitance, the measurement result was smaller compared to when the ALC was turned ON only when the ALC was OFF.


■Capacitance measurement results


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2)Reason why the capacitance falls below the measured value


The results of measuring the voltage with a tester in each case are as follows.
In a high capacity MLCC measurement, the measurement voltage does not meet the standard conditions when the ALC is OFF.


■Measurement conditions:1±0.1KHz/0.5±0.1Vrms

■Measurement conditions:1±0.1KHz/1.0±0.2Vrms


■Why does the measurement voltage Vc decrease when the capacitance increases?
     
The capacitance C is expressed as
 

When the capacitance C increases,
Zc decreases.
In addition, the measurement voltage Vc in the measurement circuit can be expressed as

 
Therefore, the measurement voltage Vc decreases when Zc drops.
   
   
 
■Why does the capacitance measurement result decrease when the measurement voltage Vc decreases?
     

The MLCC capacitance changes based on the ambient temperature and the applied voltage.
The AC voltage characteristics of the MLCC at measurement conditions of 20°C and 1 KHz are shown in the figure on the right.
The capacitance changes when the AC voltage changes, and when the applied voltage is less than 0.5 Vrms, the capacitance also decreases.

   


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3)Precautions during measurement


■When the capacitance drops, use the tester to measure the measurement voltage.


If the measurement voltage is less than the standard measurement voltage, perform the following steps


①Turn the ALC ON

②Switch to a measuring instrument which exhibits the standard measurement voltage.


To measure the measurement voltage, apply the tester to each of the measuring terminals during the MLCC measurement as shown in the photograph below.



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Supplemental:GRM21B1C1H223J measurement comparison


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