JP3879453B2 - Capacitor pass / fail judgment method - Google Patents
Capacitor pass / fail judgment method Download PDFInfo
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- JP3879453B2 JP3879453B2 JP2001230014A JP2001230014A JP3879453B2 JP 3879453 B2 JP3879453 B2 JP 3879453B2 JP 2001230014 A JP2001230014 A JP 2001230014A JP 2001230014 A JP2001230014 A JP 2001230014A JP 3879453 B2 JP3879453 B2 JP 3879453B2
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- capacitor
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Description
【0001】
【発明の属する技術分野】
この発明は、コンデンサの良否判定方法に関し、特に、たとえばコンデンサの信頼性を判定するためのコンデンサの良否判定方法に関する。
【0002】
【従来の技術】
近年、誘電体層と内部電極とを積層した積層セラミックコンデンサなどにおいては、誘電体層の薄層化により、小型で大容量の製品が開発されている。このような積層セラミックコンデンサの良否を判定する方法として、たとえば測定用の直流電圧をコンデンサに印加し、充分に充電された後にコンデンサの漏れ電流を測定することにより、コンデンサの絶縁抵抗を測定する方法が知られている。このような絶縁抵抗の測定方法としては、JIS−C5102で規定されている方法がある。
【0003】
【発明が解決しようとする課題】
しかしながら、誘電体層が薄層化すると、その比抵抗は小さくなり、さらに、薄層・大容量のコンデンサに電圧を印加すると、誘電体は高電界にさらされ、その抵抗は一層小さくなる。そのため、コンデンサに電圧を印加すると、電流が流れやすくなり、特に誘電体層に構造欠陥などがあると、欠陥部分に電流が集中してジュール熱が発生する。このような発熱のために、コンデンサの静電容量や絶縁抵抗などの特性が変化し、特性の変化が安定するまで、最終的な充電が始まらない。このように、電圧印加後、ある時点の電流値を測定する場合、欠陥の大小によって検知される電流は複雑に変化する。そのため、安定した漏れ電流を測定するのに、5〜30秒と長時間かかることになる。
【0004】
それゆえに、この発明の主たる目的は、短時間で、正確にコンデンサの良否を判断することができるコンデンサの良否判定方法を提供することである。
【0005】
【課題を解決するための手段】
この発明は、コンデンサに直流電圧を印加し、コンデンサが発熱したときの充電電流の時間特性において、単調減少以外の充電特性を示したものを不良品であると判断することを特徴とする、コンデンサの良否判定方法である。
このようなコンデンサの良否判定方法において、コンデンサに直流電圧を印加し、時間を変えて充電電流を測定したとき、最初に測定した電流値よりコンデンサの発熱後に測定した電流値が大きい場合に不良品であると判断することができる。
【0006】
コンデンサにおいて、誘電体層に大きい内部欠陥がある場合には不良品となるが、このようなコンデンサでは欠陥部分に電流が集中し、大きいジュール熱が発生する。このような発熱により、コンデンサを構成する誘電体層の絶縁抵抗や静電容量が変化し、充電電流が不規則に変動する。内部欠陥のないコンデンサや内部欠陥の小さいコンデンサでは、発熱が少ないために充電電流が単調減少するため、電流値が単調減少しないコンデンサは不良品であると判断することができる。
このように、不良品の充電電流は不規則に変動するため、コンデンサに直流電圧を印加して、最初の測定時より後の測定時の電流値が大きいとき、そのコンデンサは不良品であると判断することができる。
【0007】
この発明の上述の目的,その他の目的,特徴および利点は、図面を参照して行う以下の発明の実施の形態の詳細な説明から一層明らかとなろう。
【0008】
【発明の実施の形態】
ここでは、代表的なコンデンサとして、積層セラミックコンデンサの信頼性を判断する方法について説明する。図1は、信頼性の高い積層セラミックコンデンサ(良品)と信頼性の低い積層セラミックコンデンサ(不良品)の充電特性を示すグラフである。ここで、良品とは、内部の誘電体層に欠陥がないか、または欠陥があっても小さい欠陥であって、長期間の使用に耐えるコンデンサのことを示す。また、不良品とは、内部の誘電体層に欠陥があり、初期の特性は良好であっても、時間が経過すると特性が劣化するものを示す。
【0009】
図1において、点線は良品の充電特性を示し、実線は不良品の充電特性を示す。図1から、良品では、単調に電流が減少しているのに対して、不良品では、電流が一旦上昇し、最終的に電流が減少している。この理由について、以下に説明する。
【0010】
良品でも、最初の充電電流が流れたあと、漏れ電流によるジュール熱が発生するが、その電流値が非常に小さいため、コンデンサの温度上昇が僅かで、特性に影響を及ぼさない。一方、不良品の電流変化は、初期の充電が完了するまえに、漏れ電流によるジュール熱によってコンデンサ内部の温度が上昇し、誘電体の温度特性により絶縁抵抗や静電容量が変化し、この変化が安定するまで最終的な充電が始まらないことによる。すなわち、電圧印加後、ある時点の電流値を測定する場合、欠陥の大小により検知される電流は複雑に変化する。
【0011】
そこで、このような電流値が複雑に変化するコンデンサを不良品であると判断することができ、この場合、電流値の変動が観測できれば、電流値が安定するまで待つ必要がない。具体的には、コンデンサに直流電圧を印加し、電圧印加後に2回電流を測定し、最初の測定値より後の測定値のほうが大きい電流値であるときに不良品であると判断することができる。このような測定は、直流電圧印加後、0.1秒と0.2秒の電流値を測定し、これらの電流値を比較することにより、良品であるか不良品であるかを判断することができる。
【0012】
【実施例】
まず、3.2×1.6×1.6mmのサイズで、静電容量10μFの積層セラミックコンデンサを準備した。この積層セラミックコンデンサに直流電圧を印加して、電流値を測定した。なお、良品においても、印加する電圧と印加されるコンデンサの熱容量、およびコンデンサに電圧を印加するために接続された端子の熱容量によって、単調減少でなく、温度上昇を起こして、一旦電流が上昇する特性を示すものもある。そこで、次のような条件のもとで、充電電流を測定した。
【0013】
コンデンサを搭載する基板として、幅40mm、長さ100mm、厚み1.58mmのガラスエポキシ樹脂基板を準備した。また、コンデンサに接続する端子としては、直径1mm、長さ12mmのステンレスに金めっきを施した端子を使用した。この基板上に搭載したコンデンサに、制限電流50mAで、200V(電界強度66kV/mm)の直流電圧を1秒間印加した。このときの周囲温度は25℃で、無風状態であった。
【0014】
この状態で測定した充電特性の代表例を図2および図3に示す。そして、充電特性が単調減少カーブを示すコンデンサと、そうでないコンデンサに分類し、それぞれについて、105℃の雰囲気温度において、コンデンサに12.6Vの直流電圧を印加し、360時間経過後の絶縁抵抗値を測定した。このとき、コンデンサに6.3Vの直流電圧を印加し、5分後の絶縁抵抗値を測定した。そして、その結果を表1に示した。
【0015】
【表1】
【0016】
表1から、充電特性が単調減少を示したグループは、高温負荷試験前後の絶縁抵抗の変化率が僅かであるのに対して、そうでないグループでは、全て抵抗値が劣化していることがわかる。すなわち、コンデンサおよび回路の熱容量を固定した状態で、印加する電圧を適当に選ぶことにより、その充電特性から確実にコンデンサの良否を判定することができる。また、図3から、電圧印加後、0.1秒と0.2秒の電流値を比較すると、高温負荷試験で特性の劣化した全てのコンデンサにおいて、電圧印加後0.2秒の値が0.1秒の値より大きくなっていた。したがって、コンデンサの良否の判定に要する時間は、電圧印加後0.2秒以下で充分である。
【0017】
この実施例では、積層セラミックコンデンサについて説明しているが、セラミック以外の誘電体材料を用いたコンデンサにおいても、この発明の方法を採用することができる。このとき必要なことは、コンデンサに直流電圧を印加し、自己発熱により温度上昇を起こす場合であっても、そのコンデンサが絶縁破壊を起こさないという条件を満たすことである。もちろん、この条件は、正常品に適用されるものである。
【0018】
【発明の効果】
この発明によれば、コンデンサに直流電圧を印加後、0.2秒以下でコンデンサの良否の判定を確実に行なうことができる。
【図面の簡単な説明】
【図1】信頼性の高い積層セラミックコンデンサと信頼性の低い積層セラミックコンデンサの充電特性を示すグラフである。
【図2】実施例において、充電電流が単調減少したコンデンサの充電特性を示すグラフである。
【図3】実施例において、充電電流が単調減少しなかったコンデンサの充電特性を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitor quality determination method, and more particularly, to a capacitor quality determination method for determining the reliability of a capacitor, for example.
[0002]
[Prior art]
2. Description of the Related Art In recent years, small and large-capacity products have been developed for multilayer ceramic capacitors and the like in which a dielectric layer and internal electrodes are laminated, by reducing the thickness of the dielectric layer. As a method for judging the quality of such a multilayer ceramic capacitor, for example, a method of measuring the insulation resistance of a capacitor by applying a DC voltage for measurement to the capacitor and measuring the leakage current of the capacitor after being sufficiently charged It has been known. As a method for measuring such an insulation resistance, there is a method defined in JIS-C5102.
[0003]
[Problems to be solved by the invention]
However, when the dielectric layer is thinned, its specific resistance decreases, and when a voltage is applied to a thin layer / high capacity capacitor, the dielectric is exposed to a high electric field and its resistance is further reduced. For this reason, when a voltage is applied to the capacitor, current easily flows, and particularly when there is a structural defect or the like in the dielectric layer, the current concentrates on the defective portion and Joule heat is generated. Due to such heat generation, characteristics such as capacitance and insulation resistance of the capacitor change, and final charging does not start until the change in characteristics is stabilized. As described above, when a current value at a certain time point is measured after voltage application, the current detected depending on the size of the defect changes in a complicated manner. Therefore, it takes a long time of 5 to 30 seconds to measure a stable leakage current.
[0004]
Therefore, a main object of the present invention is to provide a capacitor quality determination method capable of accurately determining a capacitor quality in a short time.
[0005]
[Means for Solving the Problems]
The present invention is characterized in that when a DC voltage is applied to a capacitor and the capacitor generates heat , the time characteristic of the charging current is determined to be a defective product that exhibits a charging characteristic other than monotonous decrease. This is a pass / fail judgment method.
In such a capacitor quality determination method, when a DC voltage is applied to the capacitor and the charging current is measured at different times, if the current value measured after heat generation of the capacitor is larger than the current value measured first, the product is defective. Can be determined.
[0006]
In a capacitor, when a dielectric layer has a large internal defect, it becomes a defective product. However, in such a capacitor, current concentrates on the defective portion, and a large Joule heat is generated. Due to such heat generation, the insulation resistance and capacitance of the dielectric layer constituting the capacitor change, and the charging current fluctuates irregularly. In a capacitor without an internal defect or a capacitor with a small internal defect, since the heat generation is small, the charging current monotonously decreases. Therefore, a capacitor whose current value does not monotonously decrease can be determined as a defective product.
In this way, since the charging current of defective products fluctuates irregularly, when a DC voltage is applied to the capacitor and the current value at the time of measurement after the first measurement is large, the capacitor is considered to be defective. Judgment can be made.
[0007]
The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the drawings.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Here, as a typical capacitor, a method for determining the reliability of a multilayer ceramic capacitor will be described. FIG. 1 is a graph showing charging characteristics of a highly reliable multilayer ceramic capacitor (non-defective product) and a low reliability multilayer ceramic capacitor (defective product). Here, the non-defective product refers to a capacitor that has no defect in the internal dielectric layer or is a small defect even if it has a defect and can withstand long-term use. In addition, a defective product refers to a product in which an internal dielectric layer has a defect and the characteristics deteriorate over time even though the initial characteristics are good.
[0009]
In FIG. 1, the dotted line indicates the charging characteristics of the non-defective product, and the solid line indicates the charging characteristics of the defective product. From FIG. 1, the current decreases monotonously in the non-defective product, whereas the current temporarily increases and finally decreases in the defective product. The reason for this will be described below.
[0010]
Even in the non-defective product, Joule heat is generated due to the leakage current after the initial charging current flows. However, since the current value is very small, the temperature rise of the capacitor is slight and does not affect the characteristics. On the other hand, the current change of defective products is caused by the rise of the internal temperature of the capacitor due to the Joule heat due to the leakage current before the initial charging is completed, and the insulation resistance and capacitance change due to the temperature characteristics of the dielectric. This is because the final charge does not start until the battery stabilizes. That is, when a current value at a certain point in time after voltage application is measured, the current detected due to the size of the defect changes in a complicated manner.
[0011]
Therefore, it is possible to determine that a capacitor whose current value changes in a complicated manner is a defective product. In this case, if fluctuations in the current value can be observed, there is no need to wait until the current value becomes stable. Specifically, applying a DC voltage to the capacitor, measuring the current twice after applying the voltage, and determining that the product is defective when the measured value after the first measured value is a larger current value. it can. Such measurement is to determine whether the product is good or defective by measuring current values of 0.1 seconds and 0.2 seconds after applying a DC voltage and comparing these current values. Can do.
[0012]
【Example】
First, a multilayer ceramic capacitor having a size of 3.2 × 1.6 × 1.6 mm and a capacitance of 10 μF was prepared. A DC voltage was applied to the multilayer ceramic capacitor, and the current value was measured. Even in a non-defective product, the current temporarily rises due to a temperature rise, not a monotonous decrease, due to the applied voltage, the applied heat capacity of the capacitor, and the heat capacity of the terminal connected to apply the voltage to the capacitor. Some exhibit properties. Therefore, the charging current was measured under the following conditions.
[0013]
A glass epoxy resin substrate having a width of 40 mm, a length of 100 mm, and a thickness of 1.58 mm was prepared as a substrate for mounting the capacitor. In addition, as a terminal connected to the capacitor, a terminal obtained by applying gold plating to stainless steel having a diameter of 1 mm and a length of 12 mm was used. A DC voltage of 200 V (electric field strength 66 kV / mm) was applied to the capacitor mounted on the substrate at a limiting current of 50 mA for 1 second. At this time, the ambient temperature was 25 ° C., and there was no wind.
[0014]
Representative examples of the charging characteristics measured in this state are shown in FIGS. Then, the capacitor is classified into a capacitor whose charging characteristics show a monotonically decreasing curve and a capacitor that does not, and for each, a DC voltage of 12.6 V is applied to the capacitor at an ambient temperature of 105 ° C., and an insulation resistance value after 360 hours has elapsed. Was measured. At this time, a DC voltage of 6.3 V was applied to the capacitor, and the insulation resistance value after 5 minutes was measured. The results are shown in Table 1.
[0015]
[Table 1]
[0016]
Table 1 shows that the rate of change in insulation resistance before and after the high-temperature load test is small in the group in which the charging characteristics show a monotonous decrease, while the resistance value is deteriorated in all other groups. . That is, it is possible to reliably determine the quality of the capacitor from its charging characteristics by appropriately selecting the voltage to be applied in a state where the heat capacity of the capacitor and the circuit is fixed. Further, from FIG. 3, when the current values at 0.1 seconds and 0.2 seconds are compared after voltage application, the values at 0.2 seconds after voltage application are 0 for all capacitors whose characteristics were deteriorated in the high temperature load test. It was larger than the value of 1 second. Therefore, the time required for determining the quality of the capacitor is sufficient to be 0.2 seconds or less after voltage application.
[0017]
In this embodiment, a multilayer ceramic capacitor is described. However, the method of the present invention can also be adopted in a capacitor using a dielectric material other than ceramic. What is necessary at this time is satisfying the condition that the capacitor does not cause dielectric breakdown even when a DC voltage is applied to the capacitor and the temperature rises due to self-heating. Of course, this condition applies to normal products.
[0018]
【The invention's effect】
According to the present invention, it is possible to reliably determine the quality of a capacitor within 0.2 seconds after applying a DC voltage to the capacitor.
[Brief description of the drawings]
FIG. 1 is a graph showing charging characteristics of a multilayer ceramic capacitor with high reliability and a multilayer ceramic capacitor with low reliability.
FIG. 2 is a graph showing charging characteristics of a capacitor whose charging current monotonously decreases in the example.
FIG. 3 is a graph showing charging characteristics of a capacitor whose charging current did not monotonously decrease in the example.
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