JP4682873B2 - Bypass capacitor check method and check device - Google Patents

Description

The present invention relates to a method for checking the effectiveness of a bypass capacitor provided in designing a power supply and a ground of an IC on a printed circuit board, and a check apparatus therefor .

  When the IC performs switching operation from the logical value 0 to 1, or from the logical value 1 to 0, a switching current flows from the power supply pin of the IC to the ground pin. In recent years, the frequency of circuits has increased, and a switching current has flowed in a short switching time. At this time, a sudden change in current causes noise in the power supply and ground, and further causes malfunction of the IC. Therefore, a capacitor (bypass capacitor) that bypasses the current is provided between the power supply pin and the ground pin of the IC, and the constant ( It is desired to optimize (capacitance).

  Bypass capacitor optimization means that the switching current can easily flow between the IC power supply pin and the ground pin with respect to the IC operating frequency. In other words, the bypass capacitor reduces the impedance at the IC power supply pin and the ground pin. It means to do.

  Conventional bypass capacitor effectiveness check methods include the wiring length between the IC power supply pin and the bypass capacitor (wiring inductance), the wiring length between the IC ground pin and the bypass capacitor (wiring inductance), and the bypass capacitor static Some have checked the effectiveness of the bypass capacitor based on the capacitance (see, for example, Patent Document 1). FIG. 9 shows a power supply circuit and a ground circuit of an IC handled by the conventional bypass capacitor effectiveness check method described in Patent Document 1.

In FIG. 9, the resonance frequency and the minimum impedance value are obtained from the capacitance of the bypass capacitor 1102, the power supply pin 1103 of the IC 1101, the length of the power supply wiring 1105 from the ground pin 1104 to the bypass capacitor 1102, and the length of the ground wiring 1106. It was checked whether or not the wiring length was such that the operating frequency was the resonance frequency. That is, it is checked whether the switching current 1113 flowing through the bypass capacitor 1102 is easy to flow. In addition to this, the lengths of the power supply wiring 1107 and the ground wiring 1108 from the bypass capacitor 1102 to the power supply via 1109 and the ground via 1110 are also checked to see if they are equal to or less than a threshold value.
JP 2002-16337 A (page 11, FIG. 1)

  However, in the conventional configuration, only the switching current flowing through the bypass capacitor is considered without considering the switching current flowing between the power plane layer and the ground plane layer through the power via and the ground via (hereinafter referred to as switching current flowing between the plane layers). Since this is not taken into consideration, the switching current flowing between the power supply pin and the ground pin of the IC is different from the actual one. In other words, in the graph showing the relationship between the frequency and the impedance in FIG. 10, there are two impedance minimum values because the switching current flowing through the bypass capacitor and the switching current flowing between the plane layers are easy to flow. In the conventional configuration, only one minimum value (that is, the minimum value) of the impedance of the switching current flowing through the bypass capacitor can be obtained, and the impedance of the power supply circuit and the ground circuit of the IC in which the bypass capacitor is inserted is reduced. It had a problem that it was different from the actual measurement result.

The present invention solves the above-mentioned conventional problems, and considering the switching current flowing between the plane layers as the switching current flowing between the power supply pin and the ground pin of the IC, the impedance of the power supply and ground of the IC in which the bypass capacitor is inserted It is an object of the present invention to provide a method of checking the effectiveness of a bypass capacitor and a device for checking the same , which can be calculated so as to match the actual measurement result.

To achieve the above object, a method for checking a bypass capacitor according to the present invention includes a storage step of storing design data of a printed circuit board and IC information data including at least a capacitance of the bypass capacitor, and the stored design data Inductance H ₁ of the wiring from the power supply pin to the bypass capacitor of the IC, inductance H ₂ of the wiring from the bypass capacitor to the power supply via, and inductance H ₃ of the wiring from the ground pin of the IC to the bypass capacitor And calculating the inductance H ₄ of the wiring from the bypass capacitor to the ground via and calculating the capacitance between the power plane layer and the ground plane layer, the inductance H ₁ , the inductance H ₂ , and the inductance A calculation step for calculating the relationship between the impedance between the power pin of the IC and the ground pin of the IC and the frequency of the impedance based on the inductance H ₃ , the inductance H ₄ , the capacitance, and the information data of the IC A calculation step of calculating a required impedance at the operating frequency of the IC based on the information data of the IC; and an impedance between the power supply pin of the IC and the ground pin of the IC with respect to the operating frequency of the IC; A determination step of comparing the required impedance and determining whether the bypass capacitor is valid or invalid.
The bypass capacitor check device according to the present invention also includes a storage means for storing printed circuit board design data and IC information data including at least the capacitance of the bypass capacitor, and an IC power supply based on the stored design data. Wiring inductance H ₁ from the pin to the bypass capacitor, wiring inductance H ₂ from the bypass capacitor to the power supply via , wiring inductance H ₃ from the IC ground pin to the bypass capacitor, and wiring inductance from the bypass capacitor to the ground via Inductance calculation means for calculating H ₄ , capacitance calculation means for calculating the capacitance between the power plane layer and the ground plane layer, inductance H ₁ , inductance H ₂ , inductance H ₃ , inductance H ₄ and static Calculation means for calculating the relationship between the impedance and the frequency of the impedance between the IC power supply pin and the IC ground pin based on the capacitance and the IC information data, and the IC operating frequency based on the IC information data. A means for calculating the required impedance for calculating the required impedance, and a determination means for comparing the impedance between the IC power supply pin and the IC ground pin with the required impedance with respect to the operating frequency of the IC, and determining the effectiveness of the bypass capacitor. It is characterized by including.

  With this configuration, the switching current flowing between the power supply pin and the ground pin of the IC can also be considered as the switching current flowing between the plane layers, and the impedance between the power supply pin and the ground pin of the IC in which the bypass capacitor is inserted matches the actual measurement result. It is possible to determine whether the bypass capacitor is valid or invalid.

As described above, according to the bypass capacitor check method and the check device of the present invention, the switching current flowing between the power supply pin and the ground pin of the IC can also be considered as the switching current flowing between the plane layers, and the bypass capacitor is inserted. The impedance between the power supply pin and the ground pin of the IC can be calculated so as to match the actual measurement result. Moreover, even if the shape that determines the capacitance between the complicated power plane layer and ground plane layer is not modeled as an equivalent circuit for each minute section of each layer, the effectiveness of the bypass capacitor can be determined, It is possible to design a printed circuit board that suppresses power and ground noise and IC malfunction.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing a power supply circuit and a ground circuit of an IC handled by the bypass capacitor check method according to the first embodiment of the present invention. 1A is a view of the substrate 1 as viewed from above, and FIG. 1B is a cross-sectional view of the substrate 1 taken along the line AA. There is a switching current 8 that flows through the bypass capacitor 7 from the power supply pin 3 and the ground pin 4 of the IC 2 through the power supply wiring 5 and the ground wiring 6. In the present invention, the power supply wiring 9, the ground wiring 10, the power supply via 11, and the ground via are further provided. 12, the switching current 15 flowing between the plane layers of the power plane layer 13 and the ground plane layer 14 of FIG.

  Next, a method for checking the bypass capacitor in the first embodiment of the present invention will be described. FIG. 2 is a diagram showing a configuration of an apparatus used for the bypass capacitor check method. In FIG. 2, the storage means 101 has IC information data 102 and printed circuit board design data 103. The wiring inductance calculation unit 104 calculates the wiring inductance from the printed circuit board design data 103. The capacitance calculating means 105 between the power plane layer and the ground plane layer calculates the capacitance between the power plane layer 13 and the ground plane layer 14 from the printed circuit board design data 103. The calculation means 106 of the relationship between the impedance between the power supply pin 3 and the ground pin 4 of the IC 2 and the frequency of the impedance is a characteristic of the bypass capacitor 7 in the IC information data 102, such as capacitance, resistance value, inductance, and the like. From the result of the inductance calculating means 104 of each wiring in the power circuit and the ground circuit of the IC 2 and the result of the calculating means 105 of the capacitance between the power plane layer and the ground plane layer of the IC 2, the power pin 3 and the ground pin 4 of the IC 2 Between the impedance and the frequency of the impedance is calculated.

  On the other hand, during the operation of IC2, the required impedance calculation means 107, which is the ease of electricity required for each frequency, is calculated from the IC information data 102, the allowable voltage fluctuation range of IC2, and the maximum current amount. Calculate the required impedance at the operating frequency. The judging means 108 for judging the validity / invalidity of the bypass capacitor 7 is that the impedance between the power supply pin 3 and the ground pin 4 of the IC 2 is equal to or lower than the required impedance with respect to the operating frequency of the IC 2. The value is checked, and if it is below, it is valid, and if it is larger, it is invalid. The bypass capacitor check result output means 109 displays the result of checking the bypass capacitor 7 by the determination means 108 for determining whether the bypass capacitor is valid or invalid.

  Next, a method for checking the bypass capacitor will be described. FIG. 3 is a flowchart of the bypass capacitor check method according to the first embodiment of the present invention. A description will be given of how the apparatus according to the first embodiment of the present invention shown in FIG. 2 processes the power supply circuit and the ground circuit of the IC shown in FIG.

  In step 201, the cross-sectional shape (width W [m] and thickness t [m]) of the wiring on the substrate surface, the distance h [m] between the wiring and the plane layer, and the relative permeability μ [H / m] of the dielectric layer From the above, the inductance [H / m] of the unit wiring length is calculated by Equation 1.

ステップ２０２は、ＩＣ２の電源ピン３、グランドピン４からバイパスコンデンサ７までの配線長、バイパスコンデンサ７から電源ビア１１、グランドビア１２までの配線長から、各配線のインダクタンスを数２で計算する。

In step 202, the inductance of each wiring is calculated from the wiring length from the power supply pin 3 and the ground pin 4 of the IC 2 to the bypass capacitor 7 and the wiring length from the bypass capacitor 7 to the power supply via 11 and the ground via 12 by Equation 2.

ステップ２０３は、誘電体層の誘電率ε〔Ｆ／ｍ〕、電源プレーン層１３とグランドプレーン層１４の重なり面積Ｓ〔ｍ^２〕、プレーン層間の距離ｄ〔ｍ〕から、電源プレーン層１３とグランドプレーン１４層間の静電容量を数３で計算する。

Step 203 is based on the dielectric constant ε [F / m] of the dielectric layer, the overlapping area S [m ² ] of the power plane layer 13 and the ground plane layer 14, and the distance d [m] between the plane layers. The capacitance between the ground plane 14 layers is calculated by Equation 3.

ステップ２０４は、各配線のインダクタンスと、プレーン層間の静電容量と、バイパスコンデンサ７の静電容量、抵抗値、インダクタンスから、静電容量、抵抗値、インダクタンスにて構成される回路モデルを作成し、ＩＣ２の電源ピン３とグランドピン４での周波数とインピーダンスの関係を計算し、Ｘ軸が周波数〔Ｈｚ〕、Ｙ軸がインピーダンス〔Ω〕のＸ−Ｙグラフを作成する。ここでは、回路により計算式が異なるが、テブナンの定理を用いて、電圧、電流、インピーダンスの等式を作成することにより、周波数とインピーダンスの関係を計算することができる。例えば、抵抗（抵抗値Ｒ〔Ω〕）、コイル（インダクタンスＬ〔Ｈ〕）、コンデンサ（容量Ｃ〔Ｆ〕）が直列にならんだ回路では、数４で計算できる。

Step 204 creates a circuit model composed of capacitance, resistance, and inductance from the inductance of each wiring, the capacitance between the plane layers, and the capacitance, resistance, and inductance of the bypass capacitor 7. Then, the relationship between the frequency and impedance at the power supply pin 3 and the ground pin 4 of the IC 2 is calculated, and an XY graph in which the X axis is frequency [Hz] and the Y axis is impedance [Ω] is created. Here, although the calculation formula differs depending on the circuit, the relationship between the frequency and the impedance can be calculated by creating a voltage, current, and impedance equation using Thevenin's theorem. For example, in a circuit in which a resistor (resistance value R [Ω]), a coil (inductance L [H]), and a capacitor (capacitance C [F]) are arranged in series, the calculation can be performed using Equation 4.

ステップ２０５は、ＩＣ２の電圧許容変動範囲、最大電流量から、ＩＣ２の動作周波数において要求されるインピーダンスを数５で計算する。

In step 205, the impedance required at the operating frequency of IC2 is calculated by Equation 5 from the allowable voltage variation range of IC2 and the maximum amount of current.

ステップ２０６は、ＩＣ２の動作周波数に対して、ステップ２０４で求められたＩＣ２の電源ピン３とグランドピン４との間のインピーダンスと、ステップ２０５で求めた要求インピーダンスを比較して、要求インピーダンス以下であれば「バイパスコンデンサ有効」、要求インピーダンスより大きな値であれば「バイパスコンデンサ無効」と表示する。

Step 206 compares the impedance between the power supply pin 3 and the ground pin 4 of the IC 2 obtained in Step 204 with the required impedance obtained in Step 205 with respect to the operating frequency of the IC 2 and is less than or equal to the required impedance. If present, “bypass capacitor is valid” is displayed. If the value is larger than the required impedance, “bypass capacitor is invalid” is displayed.

  Here, the check contents and calculation accuracy of the bypass capacitor check method according to the first embodiment of the present invention will be described. FIG. 4 shows an actual measurement result 401 obtained by actually measuring the relationship between the frequency and the impedance, and a calculation result 402 calculated by the bypass capacitor check method according to the first embodiment of the present invention. FIG. 10 described above shows an actual measurement result 1201 obtained by actually measuring the relationship between frequency and impedance, and a calculation result 1202 calculated by a conventional method. The bypass capacitor 7 used in FIG. 4 and the bypass capacitor 1102 used in FIG. 10 use the same bypass capacitor, but as can be seen by comparing FIG. 4 and FIG. 10, FIG. Then, it can be seen that the actual measurement result 401 and the calculation result 402 agree with each other up to a frequency of 3 GHz.

  That is, in calculating the impedance, not only the inductance of each wiring and the capacitance of the bypass capacitor 7 but also the static electricity between the power plane layer 13 to which the power via 11 is connected and the ground plane layer 14 to which the ground via 12 is connected. The capacitance is calculated from the printed circuit board design data and used to determine whether the bypass capacitor 7 is valid or invalid. By handling the switching current 8 flowing through the bypass capacitor 7 and the switching current 15 flowing between the plane layers, the calculation result 402 matches the actual measurement result 401 of the switching current flowing between the power supply pin 3 and the ground pin 4 of the IC 2. In other words, in the graph of FIG. 4 showing the relationship between the frequency and the impedance, the switching current 8 that flows through the bypass capacitor 7 and the switching current 15 that flows between the plane layers are easy to flow. Two can be made, which coincide with the actual measurement result.

  For example, when the impedance needs to be suppressed to 1 or less with respect to the operating frequency of 300 MHz of the IC 2, the method of the present invention can correctly determine that the bypass capacitor 2 is effective, but the conventional method calculates the result 1202. That the bypass capacitor 7 is determined to be “invalid” because the impedance is larger than 1, and an inappropriate bypass capacitor 7 is selected by changing the capacitance of the bypass capacitor 7 or the like. Become.

  According to such a configuration, the switching current flowing between the power supply pin 3 and the ground pin 4 of the IC 2 is obtained by using the capacitance between the power supply plane layer 13 and the ground plane layer 14 as the characteristic between the power supply via 11 and the ground via 12. As a result, the switching current flowing between the plane layers can be taken into consideration, and the impedance between the power supply pin and the ground pin of the IC 2 in which the bypass capacitor 7 is inserted can be calculated so as to match the actual measurement result. Moreover, it is possible to determine whether the bypass capacitor 7 is valid or invalid even if the shapes of the complicated power plane layer 13 and ground plane layer 14 are not modeled.

  The apparatus used in the method of the present embodiment is provided with means for calculating the wiring inductance, the capacitance between the power plane layer 13 and the ground plane layer 14 and the required impedance from the IC information data and the printed circuit board design data. However, a means for directly inputting a specific numerical value may be provided.

  Note that the bypass capacitor 7 is connected not only to a single capacitor but also to a plurality of capacitors in parallel, the wiring is not only based on inductance, but also its capacitance and resistance values, or between the power plane layer 13 and the ground plane layer 14. In addition to the capacitance, the resistance value and inductance may be taken into account.

  As the power supply via 11 and the ground via 12, their capacitance, resistance value, and inductance may be calculated, or specific numerical values may be directly input.

(Embodiment 2)
FIG. 5 is a flowchart of the bypass capacitor check method according to the second embodiment of the present invention. In FIG. 5, the same components as those in FIG. The steps from Step 201 to Step 205 in FIG. 5 are the same as those in FIG. 3, and in the subsequent Step 506, the impedance between the power supply pin and the ground pin of the IC is larger than the required impedance with respect to the operating frequency of the IC. If so, the power supply pin and the ground pin of the IC are highlighted in the drawing on the printed circuit board CAD, assuming that the bypass capacitor is invalid.

  Step 507 then checks to see if bypass capacitors for all power and ground pins of the IC have been checked, and if not, repeats the check from step 201.

  FIG. 6 is a diagram showing a display of check results in the second embodiment of the present invention. In FIG. 6, the same components as those in FIG. When it is determined that the bypass capacitor 7 is invalid, the power supply pin 3 and the ground pin 4 of the IC 2 are highlighted with a double line, for example.

  Note that not only the power supply pin 3 and the ground pin 4 but also the bypass capacitor 7, the power supply wiring 5, the ground wiring 6, the power supply wiring 9, the ground wiring 10, the power supply via 11, and the ground via 12 can be highlighted.

(Embodiment 3)
FIG. 7 is a flowchart of the bypass capacitor check method according to the third embodiment of the present invention. In FIG. 7, the same components as those in FIG. Steps 201 to 205 in FIG. 7 are the same as those in FIG. 3, and then step 706 is performed when the impedance between the power supply pin and the ground pin of the IC is larger than the required impedance with respect to the operating frequency of the IC. Assuming that the bypass capacitor is invalid, the next step 707 is performed. In step 707, the printed circuit board design of the wiring length, the capacitance between the power plane layer and the ground plane layer, or the capacitance of the bypass capacitor is reviewed and checked from step 202 until “bypass capacitor is valid”. repeat.

  FIG. 8 is a diagram showing a comparison between the impedance of the printed circuit board design and the required impedance in the third embodiment of the present invention. If the graph 802 of the calculation result of the relationship between frequency and impedance is equal to or higher than the required impedance 803, that is, if it is determined No in step 706, it is necessary to review the printed circuit board design. In the case of the example in FIG. 8, since the minimum value of the resonance frequency and the impedance is higher than the operating frequency of the IC having the required impedance, the content of step 707 is “reducing the wiring length or increasing the overlapping area of the plane layers. By increasing the capacitance between the plane layers or increasing the capacitance of the bypass capacitor, the resonance frequency can be matched with the operating frequency of the IC, and the impedance can be reduced.

The bypass capacitor check method and the check device according to the present invention use the capacitance between the power plane layer and the ground plane layer, so that the switching current flowing between the power supply pin and the ground pin of the IC can also be switched between the plane layer and the switching current. Therefore, the impedance between the power supply pin and the ground pin of the IC in which the bypass capacitor is inserted can be calculated so as to match the actual measurement result. Moreover, even if the shape of the complicated power plane layer and ground plane layer is not modeled, the effectiveness of the bypass capacitor can be determined, and it can be applied to the printed circuit board design of almost all electric devices such as digital AV products. .

(A) The figure which shows the power supply circuit and ground circuit of IC which are handled with the check method of the bypass capacitor of this invention (b) The AA section arrow figure of this figure (a) The figure which showed the structure of the apparatus used for the check method of the bypass capacitor of this invention Flow chart of bypass capacitor check method Graph of relationship between frequency and impedance in Embodiment 1 of the present invention Flowchart of bypass capacitor check in Embodiment 2 of the present invention The figure which showed the power supply circuit and ground circuit of IC in Embodiment 2 of this invention Flowchart of bypass capacitor check in Embodiment 3 of the present invention Graph of relationship between frequency and impedance in Embodiment 3 of the present invention The figure which showed the power supply circuit and ground circuit of IC in the check of the conventional bypass capacitor Graph of relationship between frequency and impedance in conventional bypass capacitor check

Explanation of symbols

1 Substrate 2 IC
DESCRIPTION OF SYMBOLS 3 Power supply pin 4 Ground pin 5 Power supply wiring 6 Ground wiring 7 Bypass capacitor 8 Switching current 9 Power supply wiring 10 Ground wiring 11 Power supply via 12 Ground via 13 Power supply plane layer 14 Ground plane layer 101 Storage means 102 IC information data 103 Printed circuit board design data 104 Wiring inductance calculation means 105 Capacitance calculation means between power plane layer and ground plane layer 106 Calculation means for calculating relationship between impedance and frequency between power supply pin and ground pin of IC 107 Required impedance calculation means 108 Judgment means for judging validity / invalidity of bypass capacitor 109 Bypass capacitor check result output means

Claims (6)

A method for checking a bypass capacitor provided between a power pin of the IC and a ground pin of the IC when mounting the IC on a printed circuit board,
A storage step of storing the design data and the information data of the IC of the PCB including the capacitance of at least said bypass capacitor,
Stored on the basis of the design data, the inductance H ₁ of the wiring from the previous Symbol supply pins to said bypass _capacitor, inductance of H ₂ wiring from the bypass capacitor to the power supply _via, before Kigu Randopin to said bypass capacitor And calculating the wiring inductance H ₃ and the wiring inductance H ₄ from the bypass capacitor to the ground via,
A calculation step for calculating the capacitance between the power plane layer and the ground plane layer;
Based on the inductance H ₁ , the inductance H ₂ , the inductance H ₃ , the inductance H ₄ , the capacitance and the information data of the IC, the impedance between the power pin of the IC and the ground pin of the IC and the A calculation step for calculating the relationship of impedance to frequency;
A calculation step of calculating a required impedance at an operating frequency of the IC based on the information data of the IC;
A step of comparing the required impedance with the impedance between the power supply pin of the IC and the ground pin of the IC with respect to the operating frequency of the IC, and determining whether the bypass capacitor is valid or invalid. How to check the bypass capacitor. The judgment step is
When the impedance between the power supply pin of the IC and the ground pin of the IC is equal to or lower than the required impedance with respect to the operating frequency of the IC, the bypass capacitor is valid, and when the impedance is larger than the required impedance, the bypass capacitor is invalid. The method of checking a bypass capacitor according to claim 1, wherein the determination is made. Further, an output step for outputting the determined result is included,
The output step includes
3. The method of checking a bypass capacitor according to claim 1, wherein a power supply pin of the IC and a ground pin of the IC on the printed circuit board CAD are highlighted. The output step is
4. The bypass capacitor according to claim 3, wherein a countermeasure content for enabling an impedance between a power supply pin of the IC and a ground pin of the IC is displayed based on a determination result of invalidity of the bypass capacitor in the determination step. How to check. A bypass capacitor check device provided between a power supply pin of the IC and a ground pin of the IC when mounting the IC on a printed circuit board,
Storage means for storing design data of the printed circuit board including at least the capacitance of the bypass capacitor and information data of the IC;
Based on the stored design data, the inductance H ₁ of the wiring from the power supply pin to the bypass capacitor, the inductance H ₂ of the wiring from the bypass capacitor to the power supply via, and the wiring from the ground pin to the bypass capacitor calculation means of the inductance of calculating the inductance H ₄ wiring inductance H ₃ and the bypass capacitor to ground via,
A capacitance calculating means for calculating the capacitance between the power plane layer and the ground plane layer;
Based on the inductance H ₁ , the inductance H ₂ , the inductance H ₃ , the inductance H ₄ , the capacitance and the information data of the IC, the impedance between the power pin of the IC and the ground pin of the IC and the A calculation means for calculating the relationship between the impedance and the frequency;
A required impedance calculating means for calculating a required impedance at an operating frequency of the IC based on the information data of the IC;
Determining means for comparing the impedance between the power supply pin of the IC and the ground pin of the IC with the required impedance with respect to the operating frequency of the IC, and determining whether the bypass capacitor is valid or invalid. Bypass capacitor check device. Furthermore, an output means for outputting the determined result is included,
The output means includes
6. The bypass capacitor checking device according to claim 5, wherein a power supply pin of the IC and a ground pin of the IC are highlighted on the printed circuit board CAD.

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