JP2003008168A - Board design method, method of implementing the same board design method, and board structure designed thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a problem that, when a board is heated to solder a part to the board, temperature variations on the board caused by a difference in thermal capacity or the like between parts is unknown, so that an excessive temperature increase causes one or ones of the parts are thermally damaged or an insufficient local temperature increase causes improper soldering. SOLUTION: Upon board design, a board temperature distribution (relation between distance from parts A and B and board temperature) in the vicinities of the parts is previously predicted on the basis of premeasured temperature data at the time of heating the board, a temperature change in a solder junction 14 of the other part B affected by the part A via a board C is calculated, and a distance C between the parts necessary to secure a heating temperature for good soldering is determined on the basis of the calculated result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the arrangement position of surface mount components on a printed wiring board or the like.
The present invention relates to a board design method and its implementation means, and a board structure designed by the board design method.

[0002]

2. Description of the Related Art Reflow is used as a method for soldering surface mount components (hereinafter, components) to a substrate. The temperature of each component on the board during reflow varies due to differences in heat capacity and heat transfer. If the variation is large, heat damage to the parts and poor soldering will occur, which will adversely affect the product reliability and yield.

Particularly, when Pb-free solder, which has recently been used, is used for reflow, its allowable melting point is small because of its high melting point. For this reason, even if the board can be reflowed without problems with conventional solder, the possibility of thermal damage to components and defective soldering increases.

When designing a board for a new product, select a large component having a large heat capacity or a component having low heat resistance in component selection,
If the component layout is carried out by trial and error, it is necessary to redesign the board, resulting in an increase in product development period and development cost. In addition, thermal damage to parts is often undetectable by inspection, and may leak to the market and cause failure. Therefore, it is desired to predict the temperature variation in advance and realize a board design that facilitates reflow.

As a conventional board designing method for determining the arrangement position of the surface mount component, for example, in order to suppress the signal delay time and reduce the electrical noise, the MPU is used.
There is a method of arranging the (ultra-compact processor) and the memory (storage device) as close as possible.

Further, as another conventional board designing method when arranging the surface mount components, a board temperature during heating is sequentially simulated, and temperature variations are evaluated from the result of the simulation to determine the component spacing. There is a method of making a decision (disclosed technology in Japanese Patent Laid-Open No. 11-201647).

[0007]

However, in the above-mentioned former board designing method of the related art, when the board is heated for soldering the components, the surface of the board is generated due to a difference in heat capacity of the components. The temperature variation is unknown, and there is a risk that some parts may be thermally damaged due to excessive temperature rise, or that the temperature rise may be insufficient and soldering failure may occur. was there.

Further, in the latter substrate designing method of the related art, it takes time to create an analytical model, and the temperature variation on the substrate surface during heating can be evaluated only after the simulation of heating is performed. There is a problem that trial and error by simulation is necessary to determine the component interval.

The present invention has been made by paying attention to the above-mentioned problems, and its first object is to determine the distance from the component at the time of heating based on the temperature data measured in advance. A board that can quantitatively predict the relationship with the board temperature (hereinafter referred to as the board temperature distribution around the parts) and calculate the part spacing required to secure the soldering temperature of each part with a simple method during board design. It is to provide a design method.

A second object of the present invention is to provide a board designing method capable of checking whether or not the component intervals required for securing a heating temperature at which good soldering can be obtained are appropriate. It is to provide an implementation method.

A third object of the present invention is to arrange a component that easily exceeds the guaranteed heat resistance temperature at a position where the substrate temperature greatly decreases due to the influence of the component, so that the temperature variation during heating is further reduced. An object of the present invention is to provide a substrate structure capable of designing a substrate.

[0012]

In order to achieve the above first object, a board design method according to the present invention is a board around a component at the time of heating based on temperature data measured in advance at the time of board design. Good soldering can be obtained by predicting the temperature distribution (the relationship between the distance from the component and the substrate temperature) and calculating the temperature change that the component exerts on the solder joint of another component through the substrate. The component interval required to secure the heating temperature was decided.

The raw substrate temperature and the substrate temperature distribution around the component may be used as the temperature data, and the temperature data may be measured by limiting the raw substrate and the component.

Here, the component is an electronic component to be mounted on the substrate, for example, a package component such as QFP, BG.
For example, A. The raw board is a board on which no component is mounted. In addition, the component interval is, for example, the interval between the opposite side end portions of the two components or the interval between the centers of the two components.

Therefore, it is possible to predict the temperature drop of the board due to the component among the board temperature variations when the reflow condition is constant, and to determine the soldering temperature from the allowable value of the temperature of the raw board and the temperature drop of the board due to the component. It will be possible to determine the component interval required for securing.

Further, it becomes possible to quantify the relation between the temperature drop of the adjacent parts due to the influence of the large-sized parts whose temperature is hard to rise and the part spacing. In this way, it is possible to quantitatively determine whether or not there is a problem in the reflow temperature, since it is possible to know from a specific numerical value how many mm or more the component interval should be set.

Further, in the board designing method according to the present invention, in the board designing method according to the present invention described above, the temperature of the raw board on which no parts are mounted, and the periphery of each part when heating some parts. By measuring the substrate temperature distribution in advance, it is possible to determine the substrate temperature distribution around the component during heating, such as the type and size of the component, the thickness of the raw substrate, the number of layers and the material, heat capacity, specific heat, heat conduction, heat The factors that affect the transfer and thermal copying were made into parameters as mathematical expressions, so that the substrate temperature distribution around the parts could be quantitatively predicted.

Therefore, the change of the substrate temperature due to the influence of the component on the temperature of the raw substrate and the range of the influence can be easily evaluated, and among the substrate temperature variations when the reflow condition is kept constant, the component due to the component The temperature drop can be predicted, and the component interval required to secure the soldering temperature can be determined from the temperature of the raw substrate and the allowable value of the temperature drop of the substrate due to the component.

When the substrate temperature distribution around the component is predicted by using the type of the component as a parameter, the component classification may be based on the difference in the measured substrate temperature distribution around the component.

Further, the shape of the parts may be used for classifying the parts, the internal structure of the parts may be used for classifying the parts, and the material of the parts may be used for classifying the parts. Alternatively, the position of the solder joint may be used for classifying the parts.

When the substrate temperature distribution around the component is predicted by using the component size as a parameter, the length and width of the component may be used as the component size. At this time, the length and width of the component may be the size excluding the terminal portion.

Then, the substrate temperature distribution around the component may be predicted by dividing the component in the length direction and the width direction.
Further, the thickness of the component may be used as the component size. At this time, the thickness of the component may be the size excluding the terminal portion.

When the number of layers of the raw substrate is used as a parameter to predict the substrate temperature distribution around the component, the presence or absence of the inner layer may be focused on as the number of layers of the raw substrate.

Further, the board designing method according to the present invention is the board designing method according to the above-mentioned present invention, in which a component that greatly reduces the substrate temperature is selected based on the prediction result of the substrate temperature distribution around the component, and another component is selected. By calculating the temperature drop that affects the solder joints of the parts, it was possible to calculate the space between the parts that can secure the soldering temperature.

Therefore, as compared with the method of simulating the substrate temperature at the time of heating, the component intervals necessary to secure the heating temperature at which good soldering is obtained can be obtained without trial and error.
Easy to make decisions in a short time.

The board design method according to the present invention may be such that, in the board design method according to the present invention described above, the board temperature distribution around the component is determined with reference to the center of the component. The substrate temperature distribution may be determined based on the end of the component closest to the center of the component.

Further, it is preferable that the substrate temperature distribution around the component is approximate to a linear shape. Alternatively, it is preferable that the substrate temperature distribution around the component approximates a curve. In this case, linear is, for example, a straight line. The curve may be, for example, a quadratic or cubic polynomial expression or a logarithmic function.

Further, based on the temperature data measured in advance, the components which have a small influence on the substrate temperature and can be judged to be negligible are arranged at arbitrary positions on the raw substrate without predicting the peripheral substrate temperature distribution. Alternatively, as a result of predicting the substrate temperature distribution around the components, components that have a small influence on the substrate temperature and can be determined to be negligible may be arranged at arbitrary positions on the raw substrate. Good. The fact that the influence on the substrate temperature is small and can be neglected is determined in consideration of measurement errors and temperature changes in the furnace.

Further, it is also possible to predict the board temperature at an arbitrary position by superimposing a decrease in board temperature due to a plurality of parts, and to decide a part interval required to secure a heating temperature at which good soldering can be obtained. Good.

Further, the influence of the component on the substrate temperature during heating is evaluated by the difference between the substrate temperature around the component and the temperature of the raw substrate, and the influence of the individual components is overlapped to determine the solder joint temperature of the component. You may make it possible to determine the component interval required for ensuring the heating temperature which can obtain favorable soldering by predicting.

Further, the substrate temperature around the component at the time of heating under a certain constant heating condition may be predicted.

Further, the average value may be predicted inclusive of the substrate temperature around the component during heating under a plurality of heating conditions.

Further, the difference in the substrate temperature around the component at the time of heating depending on the heating condition may be corrected by correcting the mathematical formula by adding measurement data.

Further, in the board design method according to the present invention, in the board design method according to the present invention described above, the board temperature distribution around the component during heating is calculated using spreadsheet software such as a personal computer. .

Then, the interval between parts during heating is calculated by using spreadsheet software such as a personal computer.

Therefore, in order to easily use the board designing method according to the present invention, it is possible to make a tool by using spreadsheet software of a personal computer, and the designer himself can predict the temperature drop of the board and lay out components.

In order to achieve the above-mentioned second object, the method for implementing the board designing method according to the present invention is such that the board temperature around the component at the time of heating is based on temperature data measured in advance at the board designing time. Heating that provides good soldering by predicting the distribution (the relationship between the distance from the part and the board temperature) and calculating the temperature change that the part will exert through the board to the solder joints of other parts It has the function of determining the component spacing required to secure the temperature and checking whether the component spacing is appropriate or not.

Here, the raw substrate temperature and the substrate temperature distribution around the component may be used as the temperature data measured in advance, or the temperature data may be measured by limiting the raw substrate and the component.

It is also possible to display either one or both of the predicted minimum temperature portion and the predicted maximum temperature portion during heating on the board after the components are arranged, and the predicted temperature of the entire board during heating is displayed. You may be able to display.

Further, when an attempt is made to place a component in an area where the necessary component spacing cannot be secured, a message to that effect is displayed,
Alternatively, the component may have a function that cannot be arranged.

Therefore, the check function makes it possible to check whether or not the component intervals are necessary to secure the heating temperature at which good soldering can be obtained.

Further, in order to achieve the above-mentioned third object, the circuit board structure according to the present invention has a board temperature distribution (parts) around the parts at the time of heating based on temperature data previously measured at the time of board design. The relationship between the distance from the substrate temperature and the substrate temperature) was predicted, and the parts where the heat resistance guaranteed temperature was exceeded easily were placed in the parts where the substrate temperature was low.

It is preferable that the component that easily exceeds the guaranteed heat resistance temperature is an aluminum electrolytic capacitor. Further, it is preferable that the component that easily exceeds the heat-resistant guaranteed temperature is an LED.

Therefore, by disposing a component such as an aluminum electrolytic capacitor that easily exceeds the guaranteed heat resistance temperature at a position where the substrate temperature greatly decreases due to the influence of the component, it is possible to design a substrate with less temperature variation during heating.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

The problems caused by variations in substrate temperature during reflow are thermal damage to components and poor soldering. In order to prevent these problems from occurring, it is necessary that the body temperature of the component is lower than the heat resistant temperature (depending on the component) and the terminal temperature is higher than the melting point of the solder.

In the reflow temperature profile, as shown in FIG. 1 for one substrate, the temperature difference between the body temperature of the component whose temperature rises the most and the terminal temperature of the component whose temperature rises the least is shown. appear.

Therefore, it can be defined that the substrate temperature variation ΔT = (maximum temperature of component body) − (minimum temperature of component terminal).

As shown in FIG. 2 (enlarged view of the portion surrounded by a circle in FIG. 1), the substrate temperature variation ΔT is based on the peak temperature when a raw substrate on which no component is mounted is flown into a reflow furnace. The excessive temperature rise ΔT _h seen in a particular part,
It can be considered separately by the temperature decrease ΔT _l due to the heat capacity of the large-sized component.

Although the problem is complicated when the reduction of ΔT is considered in the entire substrate, it can be understood that if ΔTh and ΔTl are individually evaluated for each component, the component having the largest size should be focused on.

Of ΔT _h and ΔT _l , ΔT _h does not affect the temperature of other components. On the other hand, ΔT _l
Influences not only the terminal temperature of the component itself but also the substrate temperature around it. Therefore, the temperature of the terminal of the adjacent component may be lowered, which may cause soldering failure.
Therefore, in the board design, it is necessary to secure a space between adjacent components that does not affect the solderability of each other.

The substrate temperature variation ΔT of the entire substrate is reduced.
In order to_h Or ΔT_l At least one of
However, based on the above matters, in component layout technology
ΔT _l Mainly to reduce

In the reflow oven, HA (Hot Air)
(Hot air) and IR (Infrared Ray) (infrared)
The temperature is raised by the combination of different heating principles, and the temperature profile is relatively determined by various factors such as heating conditions, heat capacity of components, heat absorption, heat transfer, and component layout.

Therefore, the substrate temperature variation ΔT also changes due to these factors. The factors of the substrate temperature variation ΔT can be broadly classified into those related to the component layout and those related to the reflow furnace.

The items caused by the reflow furnace greatly vary depending on the type of furnace and the condition settings. Since the conditions of the reflow furnace are ideally fixed and used in an optimal state, general-purpose optimum conditions were previously determined and fixed.

In order to reduce the substrate temperature variation ΔT, the selection and layout of parts are important. Of these, it is often difficult to change the parts used because of the function of the circuit. Therefore, a component layout is an effective means for reducing the substrate temperature variation ΔT.

Conventionally, in the layout of components, noise reduction and heat dissipation of high-power components as well as productivity were taken into consideration, but the substrate temperature variation ΔT was not taken into consideration because there was no method for quantitatively evaluating it. However, the substrate temperature variation ΔT is in a situation that cannot be ignored due to high density mounting of the substrate and introduction of Pd-free solder. Therefore, it is necessary to have a means capable of quantitatively predicting and evaluating the relationship between ΔT _l and the component spacing D shown in FIG. 3 and determining ΔT _l at the design stage. In FIG. 3, A and B are components and C is a substrate.

Since there are various kinds of parts, the parts are classified into several kinds according to the items that affect the reflow temperature, such as the outer shape, the structure and the material, and the parts having a large ΔT _l shown in FIG. 2 are first clarified.

By classifying the parts by the items shown in [Table 1], the influence of all parts is not considered individually, but
Consider collectively the effects of parts with similar thermal characteristics. Also, we focused on the parts that make reflow difficult.

[0060]

[Table 1]

[0061] In order to accurately predict the ΔT _l, first ΔT _l
Was made into a database so that the validity of the predicted value could be supported. Many components are mounted on the actual board, but for simplification, only two components A and B are taken out,
Consider the relationship between the component spacing D and the reflow temperature.

As described above, the reflow heating conditions are the standard heating conditions set in advance (HA and I which can well compress the substrate temperature variation ΔT in the test substrate on which typical parts are mounted).
The ratio of R, wind speed, conveyor speed) was fixed.

According to the board designing method of the present invention, "the influence of ΔT of the component layout is caused by the phenomenon that the components are lowered in temperature through the substrate, and the larger the component is, the more difficult it is to raise the temperature, the greater the influence on the periphery. Therefore, we focused not on the component temperature itself, but on the “substrate temperature distribution around the component”.

By setting the substrate temperature as the evaluation target, there is versatility that the data once measured can be used regardless of the combination of parts. For example, the substrate temperature distribution around the component A can be used when determining the component spacing D between the component A and other components (including the component A). Also, the substrate temperature around the component can be measured at the same time as the component temperature.

In the board designing method of the present invention, the number of times of temperature measurement for k kinds of parts is k × n times ( _k C ₁ × n), and even if one kind of part is added, additional measurement is performed for that part. Only n times is required. [Table 2] shows a comparison of the number of measurements required for determining the component spacing D between the conventional method and the board design method of the present invention (this method).

[0066]

[Table 2]

In the conventional ΔT evaluation method, only the reflow temperature of the component was measured and evaluated. Therefore, in order to obtain the relationship between the component interval D and the reflow temperature, it is necessary to change the component interval D and measure the reflow temperature. For example, part A
For the component B, the reflow temperature was measured by changing the component interval D several times. Further, the same temperature measurement was required for the parts A and the parts B.

In such a conventional method, it is necessary to set the temperature to _{k + 1} parts C ₂ × x × n times (x: the number of levels of the part distance D, n: the number of repetitions) for the k kinds of parts. Is 1
When the types are added, (k + 1) × x × n additional measurements are required. For this reason, it has been considered that the construction and maintenance of the database are extremely difficult.

In the board designing method of the present invention, first, the peripheral board temperature distribution of each component is measured for each type of component classified as described above. As a result, it was found that the substrate temperature distribution around the component can be approximated to a straight line.

As an example, QFP (Quad) as a component
The state of the substrate temperature distribution around the Flat Package) is shown in (1) of FIG. 4, and the actual measurement data is shown in (2) of FIG. It can be seen from (2) in FIG. 4 that the measured data are in good agreement with the approximate straight line. Further, the influence of the component on the surrounding substrate temperature can be evaluated from the magnitude of ΔT _l .

From the substrate temperature distribution around the parts, 2
If the board temperature distribution between the two parts A and B can be predicted, ΔT
The relationship between _l and the part interval D can be quantified. Therefore, FIG.
Based on the substrate temperature distributions around the components shown in (1) and (2) above, whether or not the substrate temperature between the two components A and B can be predicted was examined.

As a result, it was clarified that the substrate temperature between the two parts A and B can be predicted by superimposing ΔT _l for each part. As an example, FIG. 5 shows a result obtained by measuring the substrate temperature in the middle while changing the component interval D, and comparing it with the predicted value obtained by superimposing the effects of the individual components A and B.

The difference between the measured value and the predicted value was 2-3 ° C., which was within the range of measurement error. It can be seen that the substrate temperature between the two components A and B2 can be predicted by superimposing ΔT _l for each component.

Therefore, by setting the raw substrate temperature and the allowable value of ΔT _l necessary for ensuring solderability, the component interval D at which soldering failure does not occur can be determined. Also, ΔT _l
[Delta] T _h by arranging a large part of the [Delta] T _h to a large portion of the
And ΔT can be further reduced.

That is, the states of the substrate temperature distribution around the component during heating are shown in (1) and (2) of FIG. Board C
On top of that, one component A having a square component shape excluding the terminal portion is mounted.

The graph (2) in FIG. 6 shows the substrate temperature distribution 4 on the center line 3 of the component A during heating. Part A
Due to the influence of the heat capacity of the component A, the temperature of the substrate becomes lower than the substrate temperature 5 at the time of heating in the vicinity of the component A, and the position 6 which is closest to the center of the component A.
However, the influence becomes smaller as the distance from the component A becomes larger, so that the substrate temperature rises and eventually becomes equal to the temperature 5 when the raw substrate is heated.

The substrate temperature distribution 4 is approximated by a straight line. Also, if the part shape excluding the terminals is square,
The substrate temperature around the component is distributed in the shape of a concentric circle 7 around the component A. The substrate temperature distribution 4 may be approximated by a curve.

(1) and (2) of FIG. 7 are schematic views showing an example of a method of determining the component interval D. (1) of FIG.
In FIG. 3, a component A and a component B having a square component shape excluding the terminal portion are mounted on the board C. In (1) of FIG. 7, 10 is the position closest to the center of the component B, and 11 is a concentric circle centered on the component B.

As shown in FIG. 7B, in the board temperature distribution 12 between the parts A and B, the temperature decrease amount H on the part A side is from the temperature 5 when the raw board is heated. Part A
Amount H1 of temperature decrease due to B and an amount H2 of temperature decrease due to component B
Is given by superimposing and
Is given by superimposing the temperature decrease amount I1 due to the component B from the temperature 5 when the raw substrate is heated and the temperature decrease amount I2 due to the component A.

Therefore, the temperature of the solder joint portion 13 of the component A is lowered by the influence of the component B, and similarly, the temperature of the solder joint portion 14 of the component B is lowered by the influence of the component A.

The component spacing D is the solder joint 13 of the component A.
And the temperature of the solder joint portion 14 of the component B is determined to be equal to or higher than the minimum heating temperature 18 required for ensuring good joint. In addition, 9 in FIG. 7 is a substrate temperature distribution at the time of heating the periphery of the component B.

The substrate temperature distribution around the component varies not only with the type of component but also with the component size and the specifications of the substrate.
Therefore, with respect to package components such as QFP, temperature measurements were performed on several size components, and it was evaluated how the peripheral substrate temperature distribution changes depending on the component size.

As a result, the relationship between the component size and the approximate straight line was generalized so that the substrate temperature distribution during reflow can be predicted from the component size. Some of the data used to generalize the relationship between the size of the QFP and the fitted line is shown in FIG.

In FIG. 8, the error between the approximated straight line based on the measured values and the generalized approximated straight line is 3 ° C. or less, and it can be said that the generalized approximated straight line is a substantially appropriate value.

In addition, FIG. 9 shows an example of experimental data showing the relationship between the type of a part and the substrate temperature distribution under a certain heating condition in the case where the part shape excluding the terminal part is a square part. FIG. 10 shows an example of experimental data showing the relationship between the component size and the substrate temperature distribution under a certain heating condition for a component having a square component shape.

From this experimental data, it can be seen that the mounting area and thickness excluding the terminal portion as the component size influences the substrate temperature distribution, and the degree of influence differs depending on the type of component. From this fact, it can be said that the substrate temperature distribution around the component can be predicted from the component type and size by measuring the data in several sizes for each component type. The parts may be classified based on the measurement result, but may be classified according to the shape of the parts, the internal structure, the material, the position of the solder joint, and the like.

FIG. 11 is an example of experimental data showing the relationship with the substrate temperature distribution around the component under a certain heating condition when the component shape excluding the terminal portion is square on the reflow surface. The temperature of the raw substrate is about 230 ° C., which shows that the substrate temperature around the component has decreased and that the substrate temperature distribution around the component can be approximated by a straight line.

FIG. 12 is an example of experimental data showing a relationship with the substrate temperature distribution around the component under a certain heating condition when the component having a rectangular component shape excluding the terminal portion is on the back surface. From this experimental data, it is understood that the board temperature distribution needs to be obtained for each direction because the board temperature distribution differs in the length direction and the width direction.

Similarly to the component size, the difference in the substrate temperature distribution depending on the substrate specifications (plate thickness / number of layers) was confirmed by an experiment using QFP, and based on the data, the relationship between the substrate specifications and the approximate straight line was generally determined. Turned into

Some of the data used to generalize the relationship between the board specifications and the approximation line are shown in FIG. FIG.
In, the error between the approximated straight line based on the measured value and the generalized approximated straight line is 5 ° C. or less, and it can be said that the generalized approximated straight line is a substantially appropriate value as in FIG. 8.

FIG. 14 shows an example of experimental data showing the relationship between the substrate thickness under certain heating conditions and the substrate temperature distribution around the components. It can be seen that the temperature of the raw substrate decreases as the substrate thickness increases.

FIG. 15 is an example of experimental data showing the relationship between the number of layers of the board and the board temperature distribution around the component under a certain heating condition. It can be seen that the temperature gradient of the substrate temperature distribution around the component is different between the double-sided substrate and the multilayer substrate.

FIG. 16 shows an example of the difference in the substrate temperature distribution around the component due to the difference in heating conditions. Same board,
It can be seen that even for the same component, the substrate temperature distribution around the component differs depending on the heating conditions. By adding the temperature data of the components, the difference in the substrate temperature distribution due to the difference in the heating conditions can be corrected.

FIG. 17 shows an example of means for carrying out the board designing method of the present invention, which calculates the component interval by using a commercially available personal computer spreadsheet software.

In FIG. 17, 19 is an input unit, 20 is an approximate expression display unit of the substrate temperature distribution, and 21 is a component interval display unit.

Then, the type of the components A and B, the component size (length, width, thickness, lead length), the thickness and the number of layers of the substrate C, the temperature of the raw substrate, and the like are good in the input section 19. By inputting the minimum temperature for ensuring proper soldering, the board temperature distribution approximation unit 20 predicts the board temperature distribution around the two components A and B, and the component interval display unit 21
Then, the minimum required component spacing D according to the placement surface of the components A and B
Can be instantly calculated without trial and error. here,
The material of the board is glass epoxy board, ceramic board,
A flexible substrate or the like may be selectable.

As described above, the spreadsheet software such as a personal computer is used to calculate the substrate temperature distribution around the component during heating, and the spreadsheet software such as the personal computer is used to calculate the component interval during heating. By performing the calculation, the board design method according to the present invention is made into a tool so that it can be easily used, and the designer himself can predict the temperature decrease of the board and lay out the components.

For components which have a small influence on the substrate temperature and can be neglected based on temperature data measured in advance, the substrate temperature distribution around the components is not predicted, and the components are arranged at arbitrary positions on the raw substrate. Is also possible, and as a result of predicting the substrate temperature distribution around the component,
Parts that have a small influence on the substrate temperature and can be determined to be negligible can be placed at arbitrary positions on the raw substrate.

According to the above-described embodiment of the board designing method of the present invention, it is possible to predict the temperature decrease of the board due to the component among the board temperature variations when the reflow condition is constant, and to estimate the temperature of the raw board and the component. It is possible to determine the component interval required to secure the soldering temperature from the allowable value of the temperature drop of the board due to.

Further, it becomes possible to quantify the relation between the temperature drop of the adjacent parts due to the influence of the large-sized parts which are hard to rise in temperature and the part interval. In this way, it is possible to quantitatively determine whether or not there is a problem in the reflow temperature, since it is possible to know from a specific numerical value how many mm or more the component interval should be set.

Further, according to the embodiment of the board designing method of the present invention, the temperature of the raw board on which no component is mounted and the distribution of the board temperature around each component during heating of some components By pre-measurement, the substrate temperature distribution around the component during heating is modeled, and the substrate temperature distribution around the component is quantitatively predicted using the type and size of the component and the thickness and number of layers of the raw substrate as parameters. I made it possible.

Therefore, the change in the substrate temperature due to the influence of the component on the temperature of the raw substrate and the range of the influence can be easily evaluated, and among the substrate temperature variations due to the constant reflow condition, the component The temperature drop can be predicted, and the component interval required to secure the soldering temperature can be determined from the temperature of the raw substrate and the allowable value of the temperature drop of the substrate due to the component.

Further, according to the embodiment of the board designing method of the present invention, based on the prediction result of the board temperature distribution around the parts, the parts which greatly reduce the board temperature are selected, and the solder joints of other parts are selected. It was made possible to calculate the temperature drop caused by the above, and to calculate the component interval that can secure the soldering temperature for each component.

Therefore, as compared with the method of simulating the substrate temperature at the time of heating, the component intervals necessary for ensuring the heating temperature at which good soldering is obtained can be obtained without trial and error.
Easy to make decisions in a short time.

FIG. 18 is a schematic diagram showing an example of the board designing method according to the present invention implemented by the board designing CAD.

On the design screen, a concentric circle 7 showing the substrate temperature distribution of the component A and its periphery and a concentric circle 11 showing the substrate temperature distribution of the component B and its periphery are displayed. By checking the parts placement position automatically or manually,
It is possible to confirm whether the component interval D is secured.

Further, when the component B is placed on the board C on which the component A is placed, a warning is displayed when the component B is placed and used at a position where the component spacing D cannot be secured, or even if the component B cannot be placed. Good.

After the component placement position is determined, the expected temperature distribution of the entire substrate or at least one of the highest temperature portion and the lowest temperature portion may be displayed.

FIG. 19 is a conceptual diagram showing another example in which the board design method according to the present invention is carried out by board design CAD.

On the design screen, a concentric circle 7 showing the substrate temperature distribution of the component A and its periphery, a concentric circle 11 showing the basic temperature distribution of the component B and its periphery, and a concentric circle 23 showing the substrate temperature distribution of the component E and its periphery. Is displayed. In the case of newly arranging the component E in a state where the arrangement positions of the crystal A and the component B have already been determined, the solder joint of at least one of the component A and the component B has a good solder joint due to the influence of the component E. When the component E is to be placed at a position where the temperature at which the component can be obtained does not reach, a message to that effect is displayed, and a new component interval between the component A and the component B is calculated in consideration of the influence of the component E. So that the parts A and B are separated from each other. Alternatively, the component E may not be placed at such a position.

As described above, the method of implementing the board designing method according to the present invention has a function of checking whether or not the component spacing D necessary for ensuring the heating temperature at which good soldering is obtained is appropriate.

It is also possible to display one or both of the predicted minimum temperature portion and the predicted maximum temperature portion during heating on the board after the components are placed, or the predicted temperature of the entire board during heating can be displayed. It may be displayed, or if a component is to be placed in an area where a required component interval cannot be secured, a message to that effect may be displayed, or the component may be placed.

Therefore, by the check function, it is possible to check whether or not the component intervals are necessary to secure the heating temperature at which good soldering can be obtained.

FIG. 20 shows an embodiment of a board structure using the board designing method of the present invention in which a component 24 that easily exceeds the guaranteed heat resistance temperature is arranged in a portion where the board temperature decreases.

According to the embodiment of the board structure according to the present invention, the board temperature distribution around the part (the distance from the part and the board temperature) around the part at the time of heating is designed based on the temperature data measured in advance at the time of designing the board. (Relationship) is predicted, and parts that easily exceed the guaranteed heat resistance temperature are arranged in the portion where the substrate temperature is low. In this case, the parts that easily exceed the guaranteed temperature for heat resistance are aluminum electrolytic capacitors and LEDs.

Therefore, by disposing a component such as an aluminum electrolytic capacitor that easily exceeds the guaranteed heat resistance temperature at a position where the substrate temperature greatly decreases due to the influence of the component, it is possible to design a substrate with less temperature variation during heating.

[0117]

As described above, according to the board designing method of the present invention, it is possible to predict the temperature drop of the board due to the component among the board temperature variations when the reflow condition is constant, and From the temperature and the allowable value of the temperature drop of the board due to the components, it becomes possible to determine the component interval required to secure the soldering temperature.

Further, according to the method of implementing the board designing method of the present invention, it is possible to check, by the check function, whether or not the component intervals are necessary to secure the heating temperature at which good soldering can be obtained.

Further, according to the substrate structure of the present invention, by disposing a component such as an aluminum electrolytic capacitor that easily exceeds the guaranteed heat resistance temperature at a position where the substrate temperature greatly decreases due to the influence of the component, temperature variation during heating can be further increased. It is possible to design a board with a small size.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a temperature profile of the entire reflow.

FIG. 2 is an explanatory diagram of the definition of a substrate temperature variation ΔT during reflow.

FIG. 3 is an explanatory diagram of a substrate structure for explaining a component interval D.

FIG. 4A is an explanatory diagram of a substrate temperature distribution around a component. (2) is a graph of measured data of substrate temperature distribution around QFP.

FIG. 5 is a graph showing a relationship between a component distance D and a temperature decrease ΔT ₁ due to the heat capacity of components in the middle thereof.

FIG. 6A is an explanatory diagram of a substrate temperature distribution around one component on the substrate. (2) is a graph showing the substrate temperature distribution around one component by temperature and position.

FIG. 7A is an explanatory diagram of a substrate temperature distribution around two components on the substrate. (2) is a graph showing the substrate temperature distribution around two components in terms of temperature and position.

FIG. 8 is a graph of measured data of substrate temperature distribution around QFP.

FIG. 9 shows a square-shaped component excluding the terminal portion,
It is a graph which shows the experimental data which shows the relationship between the kind of components on a certain heating condition, and substrate temperature distribution.

FIG. 10 is a graph showing experimental data showing a relationship between a component size and a substrate temperature distribution under a certain heating condition for a component having a square component shape excluding a terminal portion.

FIG. 11 is a graph showing experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a square component shape excluding a terminal portion is on the reflow surface.

FIG. 12 is a graph showing experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a rectangular component shape excluding the terminal portion is on the back surface.

FIG. 13 is a graph of the data used to generalize the relationship between the board specifications and the approximate straight line.

FIG. 14 is a graph showing the relationship between substrate thickness and raw substrate temperature.

FIG. 15 is a graph showing the relationship between the number of layers on the substrate and the temperature gradient.

FIG. 16 is a graph showing the measured data of the relationship between the distance from the component end closest to the component center and the difference in substrate temperature (raw substrate temperature) due to the difference in heating conditions.

FIG. 17 is an explanatory diagram of an example of an implementation means of a board design method for calculating a component interval by using commercially available personal computer spreadsheet software.

FIG. 18 is a circuit diagram of a board design method according to the present invention.
FIG. 6 is a concept diagram showing an example implemented by D.

FIG. 19 is a circuit diagram of a board design method according to the present invention.
FIG. 8 is an enthusiasm diagram showing another example implemented by D.

FIG. 20 is an explanatory diagram of a board structure in which components that easily exceed the guaranteed heat resistance temperature are arranged in a portion where the board temperature decreases.

[Explanation of symbols]

A parts B parts C board D parts spacing E parts Center line of 3 parts 4 Substrate temperature distribution 5 Temperature when the raw board is heated 6 Position closest to the center of part A 7 Concentric circle centered on part A 9 Board temperature distribution during heating around component B 10 Position closest to the center of part B 11 Concentric circle centered on part B 12 Substrate temperature distribution between parts A and B 13 Solder joint of part A 14 Solder joint of component B 18 Minimum heating temperature 19 Input section 20 Substrate temperature distribution approximate expression display 21 Parts interval display 23 concentric circles 24 Parts that easily exceed the heat resistance guarantee temperature

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Claims (35)

[Claims] 1. When designing a board, the board temperature distribution around the component (the relationship between the distance from the component and the board temperature) at the time of heating is predicted based on temperature data measured in advance, and the component intervenes through the board. Board design method characterized in that the component interval required to secure the heating temperature for obtaining good soldering is determined by calculating the temperature change affecting the solder joints of other components. . 2. The temperature of a raw board on which the component is not mounted and the temperature distribution of the substrate around each of the components when some of the components are heated are measured in advance, whereby The substrate temperature distribution around the component is mathematically expressed as a parameter such as the type and size of the component and the thickness, the number of layers, and the material of the raw substrate, so that the substrate temperature distribution around the component can be quantitatively predicted. The board design method according to claim 1. 3. A component that significantly reduces the substrate temperature is selected based on a prediction result of the substrate temperature distribution around the component, and a temperature reduction exerted on a solder joint portion of the other component is calculated, 1. The component interval capable of ensuring the soldering temperature of the component of FIG. 1 can be calculated.
The board design method described in. 4. The board design method according to claim 1, wherein the raw board temperature and the board temperature distribution around the component are used as the temperature data. 5. The board design method according to claim 1, wherein the temperature data is measured by limiting the raw board and the component. 6. The substrate designing method according to claim 1, wherein the heating time is a time point of the maximum temperature during heating. 7. The substrate designing method according to claim 1, wherein the substrate temperature distribution around the component is determined with reference to the center of the component. 8. The board designing method according to claim 1, wherein the board temperature distribution around the part is obtained based on the end of the part closest to the center of the part. 9. The board designing method according to claim 1, wherein the board temperature distribution around the component is linearly approximated. 10. The board design method according to claim 1, wherein the board temperature distribution around the component is approximated to a curve. 11. For the component that can be judged to have a small influence on the substrate temperature based on the temperature data measured in advance and can be ignored, the substrate temperature distribution around the component is not predicted and the raw substrate The board designing method according to any one of claims 1 to 3, wherein the board designing method is arranged at any position. 12. As a result of predicting the substrate temperature distribution around the component, the component which has a small influence on the substrate temperature and can be determined to be negligible is arranged at an arbitrary position on the raw substrate. The board designing method according to claim 1. 13. When the substrate temperature distribution around the component is predicted using the type of the component as the parameter, the classification of the component is based on the difference in the measured substrate temperature distribution around the component. The board design method according to claim 2. 14. The board design method according to claim 13, wherein the shape of the component is used for classifying the component. 15. The board design method according to claim 13, wherein an internal structure of the component is used for classifying the component. 16. The board design method according to claim 13, wherein a material of the component is used for classifying the component. 17. The board design method according to claim 13, wherein the position of the solder joint is used for classifying the parts. 18. The length and width of the component are used as the component size when predicting the substrate temperature distribution around the component using the size of the component as the parameter. The board design method described in. 19. The board design method according to claim 18, wherein the board temperature distribution around the part is predicted by dividing the part into a length direction and a width direction. 20. The board design method according to claim 18, wherein the thickness of the component is used as the component size. 21. When the number of layers of the raw substrate is used as the parameter to predict the substrate temperature distribution around the component, attention is paid to the presence or absence of an inner layer as the number of layers of the substrate. The board design method described in. 22. The substrate temperature at an arbitrary position is predicted by superimposing influences of the plurality of components on the substrate temperature, and the component interval required to secure a heating temperature at which good soldering can be obtained is determined. The board designing method according to claim 1, wherein 23. The influence of the component on the substrate temperature at the time of heating is expressed by the difference between the substrate temperature around the component and the temperature of the raw substrate, and the influence of the individual components is superposed to obtain the influence of the component. The board design method according to any one of claims 1 to 3, wherein by predicting a temperature of a solder joint portion, the component interval required to secure a heating temperature at which good soldering is obtained is determined. . 24. The board design method according to claim 1, wherein the board temperature around the component is predicted during heating under a certain heating condition. 25. The board design according to claim 1, wherein an average value is predicted by including the board temperature around the component at the time of heating under a plurality of heating conditions. Method. 26. The board designing method according to claim 1, wherein a difference in the board temperature around the component during heating under heating conditions can be corrected. 27. The board design method according to claim 26, wherein the difference in the board temperature around the component is corrected by adding measurement data. 28. The board designing method according to claim 1, wherein the board temperature distribution around the component at the time of heating is calculated using spreadsheet software such as a personal computer. 29. The board designing method according to claim 1, wherein the component interval at the time of heating is calculated by using a spreadsheet software such as a personal computer. 30. When designing a board, predicting a board temperature distribution around the component (relationship between the distance from the component and the substrate temperature) at the time of heating based on temperature data measured in advance, and the component intervenes through the board. By calculating the temperature change over the solder joints of other parts, determine the part spacing required to secure the heating temperature for good soldering, and determine whether this part spacing is appropriate or not. A method of performing a board design method, which has a function of checking 31. The board designing method according to claim 30, wherein one or both of an expected minimum temperature portion and an expected maximum temperature portion at the time of heating can be displayed on the substrate after the component placement. 32. The method of implementing a board design method according to claim 31, wherein an expected temperature of the entire board at the time of heating can be displayed. 33. The board designing method according to claim 30, wherein when the component is to be arranged in an area where the necessary component interval cannot be secured, a message to that effect is displayed or the component cannot be arranged. Implementation method. 34. When designing a board, predicting a board temperature distribution around a component (relationship between the distance from the component and the board temperature) at the time of heating on the basis of temperature data measured in advance, and applying heat resistance to a portion where the board temperature is low. A circuit board structure in which parts that easily exceed the guaranteed temperature are placed. 35. The circuit board structure according to claim 34, wherein the component that easily exceeds the guaranteed heat resistance temperature is an aluminum electrolytic capacitor or an LED.