JP2005116897A - Circuit board, apparatus and method for supporting design thereof, design support program and recording medium thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board wherein its probing performed by a third party is so made difficult as to improve its tamper resistance, while solving the problems associated with the aspects of its present art and its manufacturing cost. <P>SOLUTION: When a secret information flows from the terminal 116 of a component 111 to the terminal 117 of a component 112 (through a foil 121, a via 122, a foil 123, a via 126, and a foil 127), the component 111 outputs a predetermined sensing signal for an unjust access in a predetermined timing. The component 112 receives this sensing signal for an unjust access, and decides securely whether a change appears in the wave shape of the received signal or not. When sensing the change of the wave shape, the component 112 so decides that there has been performed by the connection of a probe, etc. the unjust access to the place of the secret information flowing as to restrict a predetermined circuit operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a circuit board, a circuit board design support apparatus and method, a design support program, and a design support program recording medium. More specifically, the present invention relates to a circuit board having tamper resistance and supports the design of the circuit board. The present invention relates to an apparatus and method for performing the method, a program for executing the method, and a computer-readable recording medium on which the program is recorded.

  In recent years, with the development of digital information technology and the explosive spread of digital information communication infrastructure, it has become common to process content such as music, images, videos and games as digital information. The contents converted into digital information can easily be illegally obtained by eavesdropping, eavesdropping, impersonation, etc., or illegally copied or illegally tampered with a recording medium storing content data. For this reason, it is a big problem to establish a security system that protects the rights of the copyright holder of the content and the profits of the distributor, and a technology for protecting the digitalized work is required. In the following description, the difficulty of unauthorized access to confidential information such as content and signals is referred to as tamper resistance.

  Various security techniques with improved tamper resistance using communication media have been known. In many cases, discrimination of a legitimate system and data encryption are realized by an encryption / authentication technique or the like. As a typical example, when accessing the confidential data storage area where confidential data that requires protection of copyrighted work is stored, exchange of random numbers and response values between devices is performed to authenticate each other. In addition, there is a challenge response type mutual authentication technology that permits access only when it is legitimate. Also, for secret data communication, cryptographic communication using random numbers or response values for mutual authentication is performed to prevent unauthorized decryption.

  On the other hand, in order to improve tamper resistance in a circuit board on which components and the like are mounted and wired, one of the conditions is the difficulty of probing a signal line for transmitting digital information. This is because information converted into digital signals can be easily reproduced with the same quality as long as the signal can be probed to determine its logic. The more difficult it is to read a signal on the circuit board, that is, the probing, the more difficult it is to analyze and copy digital information by unauthorized access from the outside. The easier the probing, the easier the signal extraction. Digital information can be easily analyzed and copied.

Various security technologies for circuit boards have been known. For example, there is a technique in which a circuit portion that processes confidential information is made into a one-chip IC so that a signal of the confidential information does not flow on the circuit board. Moreover, the circuit part which processes confidential information is included by resin etc. In addition, there is a technique in which components are arranged so as to cover a probable portion on a signal line through which a signal of confidential information flows (see Patent Document 1).
JP 2002-299842 A

  However, the method of making the circuit portion for processing the confidential information into a single chip IC or including it with a resin or the like cannot use an off-the-shelf IC or care for all the chips and wiring on the circuit board. It is unrealistic considering the current technology and manufacturing cost. In addition, not only a third party but also a developer or a designer (hereinafter, referred to as a designer or the like) cannot confirm a confidential signal after making a one-chip IC or including a resin. In addition, when a conventional encryption / authentication technology in communication is applied to a circuit board, it is necessary to incorporate logic for realizing the technology into all LSIs that handle digital information. It is unrealistic considering the aspect. In addition, as disclosed in Patent Document 1, the method of covering the signal line of the confidential information with a component has a problem that it can be easily probed if the component is removed. Thus, with the conventional technology, it is very difficult to completely conceal the signal line on which the confidential information on the circuit board flows.

  Therefore, an object of the present invention is to provide a circuit board having improved tamper resistance by making probing difficult by a third party while solving problems in the current technology and manufacturing cost. In addition, an object of the present invention is to provide a circuit board design support apparatus and method, a design support program, and a design support program recording medium.

  The present invention is directed to a circuit board on which components are mounted. And in order to achieve the said objective, the circuit board of this invention has mounted the 1st component and the 2nd component at least.

  The first component outputs a predetermined signal to a predetermined signal line. The second component receives a predetermined signal output from the first component via a predetermined signal line, confirms a change in the waveform of the received signal with respect to the predetermined signal, and a change is observed in the signal waveform. In this case, a predetermined restriction is added to the circuit operation.

  Typically, a signal whose value is periodically inverted is used as the predetermined signal, and the second component is at least the duration of the signal stable state on the high potential side, or the low potential side as the change in the signal waveform. Either the duration of the stable signal state or the occurrence of ringing is checked.

  Here, the first component outputs a predetermined signal to a predetermined signal line at a predetermined timing, and the second component checks the waveform change of the signal received at the predetermined timing via the predetermined signal line. It is preferable to do. When the predetermined signal line is composed of a plurality of signal lines, the first component outputs a predetermined signal to one or more predetermined signal lines, and the second component is 1 Only the waveform change of signals received from one or a plurality of signal lines may be confirmed. The first component can also output a predetermined signal superimposed on a signal that originally flows on a predetermined signal line. Note that the predetermined signal is desirably a signal having a higher frequency component than the signal originally flowing through the predetermined signal line. Further, an element for detecting the temperature is further mounted, and a change in the signal waveform due to the temperature detected by the element is confirmed as a waveform of a predetermined signal output from the first component or a signal waveform change in the second component. It is preferable to reflect the above.

  Further, in order to enable a specific user to observe a signal, the second part is configured to stop the function of applying a predetermined restriction to the circuit operation by enabling a predetermined key. Also good. This predetermined key may be realized using a memory area in which a semiconductor element on the circuit board can be written only once, or may be realized by mounting / non-mounting a jumper component that can be built in the circuit board. .

  More preferably, the distance from the observation point at which the signal flowing in the predetermined signal line can be observed to the location where the ground signal is exposed, even if the ground signal is not exposed on the substrate surface or is exposed. Is not less than a predetermined length.

  The present invention is also directed to a design support apparatus that supports circuit board design. And in order to achieve the said objective, the design assistance apparatus of this invention is provided with the arrangement | positioning part, the wiring part, and the check part.

  The placement unit designs a circuit by placing components. The wiring unit designs a circuit by wiring parts. The check unit checks a portion where the ground signal is exposed on the substrate surface in the circuit designed by the placement unit and the wiring unit, and notifies the user of the exposed portion. The preferred check unit further checks whether or not the portion where the ground signal is exposed on the substrate surface is more than a predetermined length away from the observation point where the predetermined signal can be observed, and is not more than the predetermined length. The part is notified to the user.

  Each process performed by the placement unit, the wiring unit, and the check unit of the design support apparatus described above can be regarded as a design support method that provides a series of processing procedures. In other words, in the design support device, the circuit is designed by arranging the components, the circuit is designed by wiring between the components, and the portion where the ground signal is exposed on the substrate surface is checked in the arranged and wired circuit. The design support method notifies the user of the portion where the ground signal is exposed on the substrate surface based on the check result.

  Preferably, the design support method is provided in the form of a program for causing the design support apparatus to execute a series of processing procedures. This program may be recorded on a computer-readable recording medium.

  According to the present invention described above, a predetermined signal for detecting unauthorized access is supplied to a predetermined signal line to observe a change in the signal, and when the signal is changed, a predetermined restriction is applied to a circuit operation or the like. . This makes it possible to perform control such as detecting the probing of the secret signal by a third party and stopping the circuit operation, thereby improving tamper resistance. Further, by releasing the restriction using a predetermined key, the designer or the like can observe and control the secret signal, which has the effect of improving the tamper resistance and the development efficiency. Furthermore, it is possible to reliably detect unauthorized access by considering the temperature change of the circuit board and the position of the ground signal. Furthermore, these circuit boards with improved tamper resistance can be easily designed with the above design support apparatus and method. Even if the design is not successful, a warning is notified to the designer and the like, so that a circuit design error can be prevented.

  The circuit board with improved tamper resistance according to the present invention is produced by using a general single-layer board technique, a multilayer board technique in which components can be incorporated in an internal layer between the boards, and the like. Hereinafter, a characteristic circuit board structure according to the present invention will be described with reference to the drawings.

(First embodiment)
The first embodiment of the present invention can observe the waveform of a signal that requires tamper resistance, such as confidential information, and can limit the circuit operation when the waveform changes due to probing or the like. This is a circuit board having the structure as described above. In the present embodiment, a case where the circuit board is a six-layer multilayer board will be described as an example.

  FIG. 1 is a cross-sectional view of a circuit board 100 using a board structure according to a first embodiment of the present invention. As shown in FIG. 1, the circuit board 100 is configured by bonding five substrates 11 to 15 together. The signal line (foil) includes the first layer 101 and the sixth layer 106 (surface layer) appearing on the substrate surface, and the second layer 102, the third layer 103, the fourth layer 104, and the fifth layer 105 (not appearing on the substrate surface). 6 layers in total with the inner layer). The component 111 and the component 112 are placed on the surface of the circuit board on the first layer 101. In FIG. 1, it is assumed that the signal line A connecting the terminal 116 of the component 111 and the terminal 117 of the component 112 is a signal line through which a signal requiring tamper resistance flows. That is, the signal line A includes the foil 121, the via 122, the foil 123, the via 126, and the foil 127. A signal that requires tamper resistance refers to a signal that a circuit board designer, such as a microcomputer memory bus or a debugging signal line, does not want a third party to observe or control. Hereinafter, this signal is referred to as a secret signal. The signal line A is wired via the second layer 102 which is an internal layer. The foil 123 is connected to an observation point 113 exposed on the surface (first layer 101) of the circuit board 100 via the via 124. The observation point 113 is a part for external connection such as a test pad, a test pin, or a connector. In addition, a ground plane 133 is wired in the third layer 103, and the terminal 115 of the component 111 and the terminal 118 of the component 112 are respectively connected to the first layer foil 131 and the via 132, the first layer foil 135 and The via 134 is connected to the ground plane 133.

  In the present invention, in order to detect unauthorized access by a third party, the component 111 that outputs a secret signal is provided with an unauthorized access detection signal output function. Further, the component 112 for inputting the confidential signal is provided with an unauthorized access detection signal monitoring function and a circuit board control function. These functions may be separated from the component that processes the confidential signal, or may be integrated into one component together with the function that processes the confidential signal. In the latter case, it may be incorporated in advance at the design stage. Hereinafter, these three functions will be described in detail.

  First, the unauthorized access detection signal output function provided in the component 111 outputs a predetermined unauthorized access detection signal to the signal line A through which the confidential signal flows at a predetermined timing. The unauthorized access detection signal is a test signal for detecting unauthorized access, and is a signal whose value (or polarity) is periodically inverted as shown in FIG. This unauthorized access detection signal can be freely set as long as it is consistent with the unauthorized access detection signal monitoring function provided in the component 112. The predetermined timing may be the time when the operation of the circuit is started, for example, before or after the flow of the confidential signal, at regular intervals. This timing can also be freely set as long as it is consistent with the unauthorized access detection signal monitoring function provided in the component 112. Further, the unauthorized access detection signal may be output by being interrupted in the middle of the secret signal, or may be output by being superimposed on the secret signal.

  Next, the unauthorized access detection signal monitoring function provided in the component 112 receives the unauthorized access detection signal output from the component 111 via the signal line A. At this time, if the unauthorized access is not made to the signal line A, the waveform of the received signal should not be changed from the waveform of the unauthorized access detection signal (FIG. 2A) (here, the signal No delay is considered). However, when the signal line A is illegally accessed by probing the observation point 113 or the like, the waveform of the received signal changes from the waveform of the unauthorized access detection signal due to the inductance component of the probe. For example, the rising and falling of the waveform are dull as shown in FIG. 2B, or ringing occurs at the rising and falling of the waveform as shown in FIG. 2C. Therefore, the unauthorized access detection signal monitoring function stores in advance information related to the normal reception signal (FIG. 2A) when the unauthorized access detection signal is normally received, and information on the received signal for this information. Check for changes in

  This confirmation may be performed as follows, for example. For the waveform dullness, a high reference potential 301 and / or a low reference potential 302 for extracting a stable state of a normal reception signal is determined in advance (FIG. 3A). Then, between the normal reception signal (FIG. 3A) and the received signal (FIG. 3B), the high-potential side duration t (or the number of data) that exceeds the high reference potential 301 and stabilizes the signal. ), Or the low potential side duration t (or the number of data) at which the signal stabilizes below the low reference potential 302 is compared. As a result of the comparison, if there is a predetermined difference between the two, it is determined that there is a change. In this case, the information regarding the normal reception signal includes the high reference potential 301 and / or the low reference potential 302, the duration of only the portion where the unauthorized access detection signal exceeds or falls below the high reference potential 301 and / or the low reference potential 302, A bit is fine.

  Also, for the ringing of the waveform, a high reference potential 303 or a low reference potential 304 that is equal to or greater than the amplitude of the normal reception signal is determined in advance (FIG. 3A). Then, it is determined whether a part of the received signal (FIG. 3C) is higher than the high reference potential 303 or lower than the low reference potential 304. As a result of the determination, it is determined that there is a change when the received signal is above or below the potential. In this case, the information regarding the normal reception signal may be the high reference potential 303 and / or the low reference potential 304.

  The frequency of the unauthorized access detection signal is not particularly limited, but is preferably different from the frequency of the secret signal. In particular, it is preferable to use an unauthorized access detection signal having a high-frequency component so that the waveform changes greatly when probing is performed. This has the effect of making it easier to detect unauthorized access. In general, the ground of the probe is basically as close as possible to the probing point. This is because as the ground moves away from the probing point, the waveform of the observed signal is disturbed. For this reason, it is desirable that the ground terminals such as observation points and components provided on the circuit board 100 be arranged apart from the observation point 113 of the secret signal by a predetermined length or more so that unauthorized access can be easily detected. . For example, as shown in FIG. 4, the ground plane 133 is connected via a via 136 to the substrate surface (sixth layer 106) opposite to the substrate surface (first layer 101) on which the secret signal observation point 113 is provided. The ground observation point 114 is provided.

  Further, when there are a plurality of concealment signals having a single meaning, for example, a 32-bit bus signal, the unauthorized access detection signal is sent to any one or a plurality of buses instead of all the 32-bit bus lines. You may output only to the line. Which bus line to output may be based on an instruction from a designer or the like. The unauthorized access detection signal output from the component 111 may change in waveform depending on the temperature of the circuit board 100. Therefore, an element capable of detecting a change in temperature, such as a temperature sensor, is mounted on the circuit board 100 so that unauthorized access can be detected correctly even if the waveform changes with temperature, and the influence of the waveform change due to temperature can be measured from the component 111 It is preferably reflected when an unauthorized access detection signal is output or when a change in the signal is confirmed in the component 112.

  Finally, when a signal change is detected by the unauthorized access detection signal monitoring function, the circuit board control function provided in the component 112 determines that unauthorized access has been made, and the circuit board 100 or the circuit board 100 is incorporated. A predetermined restriction is added to the operation of the specific device. A typical predetermined limit is a method of stopping the operation of all or part of the circuit. It may be stopped for a certain period, or may be continuously stopped until an instruction from a designer or the like is given. Moreover, you may notify a predetermined place that there was unauthorized access. The restriction on the circuit board may be applied directly to the circuit board 100 or may be indirectly applied by outputting a restriction signal to other components.

  By the way, even when a designer or the like observes a secret signal for debugging or the like, since the observation point 113 is probed, the change in the unauthorized access detection signal is confirmed and the circuit board 100 is restricted as described above. Become. Therefore, when the designer or the like wants to observe the confidential signal, for example, the operation of the unauthorized access detection signal output function is stopped using a predetermined key so that the waveform of the confidential signal can be observed or controlled from the observation point 113. To do. The key may be inserted by connecting a recording medium such as a memory card storing key information to the circuit board 100, or using a storage area (register) of a semiconductor that can be rewritten only once. Good. Further, if the circuit board is a board in which components can be embedded, a jumper corresponding to a key may be mounted on the inner layer.

  As described above, the circuit board according to the first embodiment of the present invention observes a signal change by flowing a predetermined unauthorized access detection signal through a signal line through which a confidential signal requiring tamper resistance flows. When there is a change, a predetermined restriction is added to the circuit operation or the like. This makes it possible to perform control such as detecting the probing of the secret signal by a third party and stopping the circuit operation, thereby improving tamper resistance. Further, by releasing the restriction using a predetermined key, the designer or the like can observe and control the secret signal, which has the effect of improving the tamper resistance and the development efficiency. Furthermore, it is possible to reliably detect unauthorized access by taking into account the temperature change of the circuit board and the position of the ground.

  In the first embodiment, an unauthorized access is detected by using a signal for detecting unauthorized access and confirming a change in the signal due to probing. However, the unauthorized access may be detected by confirming the change of the secret signal that flows during the actual operation without using the unauthorized access detection signal.

(Second Embodiment)
In the second embodiment, a device (CAD device or the like) that supports the design of the circuit board described in the first embodiment will be described. A feature of the circuit board design support apparatus and method according to the second embodiment is that a well-known circuit board design apparatus and method make it possible to consider a secret signal. A known circuit board designing apparatus and method are described in detail in, for example, Japanese Patent Application Laid-Open No. 2000-242647.

  FIG. 5 is a functional block diagram conceptually illustrating a circuit board design support apparatus according to the second embodiment of the present invention. 5, the design support apparatus includes a command input unit 501, a data input unit 502, a command input analysis unit 503, a design information storage unit 504, a display unit 505, a tamper resistance signal detection unit 506, A tamper-resistant wiring unit 507 and a tamper-resistant signal check unit 508 are provided.

  The command input unit 501 is an input interface such as a keyboard and a mouse, and receives input of various design commands by a user operation. The data input unit 502 inputs circuit diagram information and the like created by a circuit diagram creation CAD device or the like (not shown). The command input analysis unit 503 analyzes the design command input to the command input unit 501 and determines the command type. This design command includes a component placement command and a wiring command. The design information storage unit 504 includes design information necessary for circuit board design, such as circuit diagram information, board information, layer configuration information, component information, connection information, signal information, and design reference information input from the data input unit 502. Remember. Information regarding whether or not the signal is a confidential signal is included in the signal information, for example, by being specified by a designer or the like. The display unit 505 displays a display screen corresponding to the design process of the circuit board to be designed.

  As a method for specifying a secret signal, a designer or the like may instruct signal names such as TCKTDI, TMS, TDO, NRD, and NWT one by one. Alternatively, a predetermined spelling such as * CS * or ADR * may be designated and a signal including the specified spelling may be used as a secret signal. Alternatively, the signals included in the circuit board may be grouped, and one of the groups may have a tamper-resistant attribute, thereby providing a secret signal.

With further reference to FIG. 6, a circuit board design support method related to tamper resistance will be described.
The tamper resistant signal detection unit 506 detects a secret signal from the signal information stored in the design information storage unit 504 (step S601). When the tamper resistant signal detection unit 506 detects components connected to the secret signal, a design process for arranging these components is performed (step S602). The component placement method in this design process may be a method used in a conventional CAD apparatus, or a designer or the like may instruct from the command input unit 501.

  The tamper resistant wiring unit 507 routes the secret signal in the area of the inner layer so that only the observation point is exposed on the circuit board after the components are arranged, and routes other wiring in the area where wiring is possible. A design process is performed (step S603). In addition, with respect to the ground net, wiring is performed in the inner layer as much as possible, and a design process is performed so that the ground is not exposed near the observation point (step S604). The tamper resistant signal check unit 508 observes whether or not a portion of the circuit board designed for processing by the tamper resistant wiring unit 507 that can observe a secret signal other than the observation point is exposed on the surface layer of the circuit board. It is checked whether or not the length from the point to the ground signal is equal to or longer than a predetermined length (step S605). If the observable part is exposed or does not have a predetermined length, a warning is notified to the designer or the like (steps S606 and S607). Note that the observable part and the ground signal part exposed on the circuit board may be selectively displayed on the CAD screen or the like without notifying the warning. As a warning notification means, a message may be displayed on the screen of the display unit 505, a warning part may be highlighted, or a beep sound or the like may be notified. A log may be left. The designer who has received the warning performs component placement and signal wiring again (repeating from step S602).

  As described above, by using the circuit board design support apparatus and method according to the second embodiment of the present invention, the circuit board with improved tamper resistance described in the first embodiment can be easily designed. It becomes possible. Even if the design is not successful, a warning is notified to the designer and the like, so that a circuit design error can be prevented. In particular, it is possible to easily design a circuit board in which the place where the probe ground is connected is limited, so that even if the probe is connected incorrectly, the probe inductance component increases and the influence on the signal waveform increases. There is an effect that unauthorized access can be easily detected.

  The circuit board, the circuit board design support apparatus and method of the present invention makes it difficult to probe a secret signal that requires tamper resistance flowing through the circuit board, and enables the designer and the like to observe and control it. This is useful for improving tampering properties.

Sectional drawing of the circuit board 100 using the board | substrate structure which concerns on the 1st Embodiment of this invention. The figure explaining an example of the signal for unauthorized access detection which flows between the components 111 and 112 The figure explaining an example which detects an unauthorized access using the waveform change of the signal for unauthorized access detection Another sectional view of circuit board 100 using the substrate structure concerning a 1st embodiment of the present invention. The functional block diagram which illustrates notionally the design support apparatus of the circuit board based on the 2nd Embodiment of this invention The flowchart which shows the process sequence of the design support method of the circuit board based on the 2nd Embodiment of this invention.

Explanation of symbols

11 to 15 substrate 100 circuit boards 101 to 106 layers 111 and 112 parts 113 and 114 observation points 115 to 118 terminals 121, 123, 127, 131, 135 foils 122, 124, 126, 132, 134, 136 vias 133 ground plane 501 Command input section 502 Data input section 503 Command input analysis section 504 Design information storage section 505 Display section 506 Tamper resistance signal detection section 507 Tamper resistance wiring section 508 Tamper resistance signal check section

Claims (17)

A circuit board on which components are mounted,
A first component that outputs a predetermined signal to a predetermined signal line;
When the predetermined signal output from the first component is received via the predetermined signal line, a change in the waveform of the received signal with respect to the predetermined signal is confirmed, and a change is observed in the signal waveform A circuit board on which a second component that imposes a predetermined restriction on circuit operation is mounted. The predetermined signal is a signal whose value is periodically inverted,
The second component confirms, as the change in the signal waveform, at least one of the duration of the signal stable state on the high potential side, the duration of the signal stable state on the low potential side, or occurrence of ringing. The circuit board according to claim 1, wherein the circuit board is characterized. The first component outputs the predetermined signal to the predetermined signal line at a predetermined timing,
The circuit board according to claim 1, wherein the second component confirms a waveform change of a signal received at the predetermined timing via the predetermined signal line. When the predetermined signal line is composed of a plurality of signal lines,
The first component outputs the predetermined signal to one or more predetermined signal lines,
The circuit board according to claim 1, wherein the second component confirms only a waveform change of a signal received from the one or more signal lines.   The circuit board according to claim 1, wherein the first component outputs the predetermined signal superimposed on a signal that originally flows through the predetermined signal line.   The circuit board according to claim 1, wherein the predetermined signal is a signal having a higher frequency component than a signal that originally flows through the predetermined signal line.   An element for detecting the temperature is further mounted, and a change in the signal waveform due to the temperature detected by the element is confirmed as a waveform of the predetermined signal output from the first component or a signal waveform change in the second component. The circuit board according to claim 1, wherein the circuit board is reflected on the circuit board.   The circuit board according to claim 1, wherein the second component stops a function of applying a predetermined restriction to the circuit operation by enabling a predetermined key.   9. The circuit board according to claim 8, wherein the predetermined key is realized by using a storage area in which a semiconductor element on the circuit board is writable only once.   9. The circuit board according to claim 8, wherein the predetermined key is realized by mounting / non-mounting a jumper component that can be built in the circuit board.   The circuit board according to claim 1, wherein the ground signal is not exposed on the surface of the board.   2. The circuit board according to claim 1, wherein a distance from an observation point at which a signal flowing through the predetermined signal line can be observed to a portion where a ground signal is exposed is a predetermined length or more. A design support device for supporting circuit board design,
An arrangement part for arranging parts and designing a circuit;
A wiring part for wiring between parts and designing a circuit;
In the circuit designed by the said arrangement | positioning part and the said wiring part, a design support apparatus provided with the check part which checks the part which a ground signal is exposed to the board | substrate surface, and notifies a user of the exposed part.   The check unit further checks whether or not the portion where the ground signal is exposed on the substrate surface is more than a predetermined length away from an observation point where the predetermined signal can be observed, and is not more than the predetermined length. The design support apparatus according to claim 13, wherein a part is notified to a user. A design support method for supporting circuit board design,
Placing components and designing the circuit;
Designing the circuit by wiring between parts;
In the circuit designed in the placing step and the wiring step, checking a portion where a ground signal is exposed on the substrate surface;
And a step of notifying a user of a portion where the ground signal is exposed on the substrate surface based on a check result obtained by the checking step. A program executed by a design support device that supports circuit board design,
In the design support device,
Placing components and designing the circuit;
Designing the circuit by wiring between parts;
In the circuit designed in the placing step and the wiring step, checking a portion where a ground signal is exposed on the substrate surface;
And a step of notifying a user of a portion where the ground signal is exposed on the substrate surface based on a check result obtained by the checking step. A computer-readable recording medium that records a program executed by a design support device that supports design of a circuit board,
In the design support device,
Placing components and designing the circuit;
Designing the circuit by wiring between parts;
In the circuit designed in the placing step and the wiring step, checking a portion where a ground signal is exposed on the substrate surface;
A recording medium for recording a program for executing a step of notifying a user of a portion where a ground signal is exposed on a substrate surface based on a check result obtained by the checking step.

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