JP2017117919A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board which is simplified, improved in workability and capable of suppressing fault occurrence further than the prior arts.SOLUTION: A circuit board 10 comprises a resin 13 which is a material having a linear expansion property having directivity along a flow during molding and includes holes 13a in a predetermined shape provided at both sides in a width direction along lead frames 12a-12d for disposing mounting components 11a-11d therein. In such a configuration, a cross-linking part 13b of the resin 13 that is formed mutually between the holes 13a is capable of such constant orientation that a linear expansion coefficient in a length direction becomes smaller than that in a width direction. Even if the resin 13 is expanded or shrunk in accordance with the presence/absence of heat or a temperature change in an ambient environment, influences to be exerted upon the lead frames 12a-12d being held can be suppressed. Therefore, even if the circuit board 10 is used for a long time, fault occurrence can be suppressed further than the prior arts. Further, the need of special processing for a fault of a solder is eliminated, such that the circuit board is simplified and improved in workability.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit board having a plurality of lead frames, one or more mounting components, and a resin.

  Conventionally, for example, the following Patent Document 1 discloses a technique related to a lead frame structure for the purpose of preventing warpage caused by reflow. This lead frame structure includes an inner lead on which a mounted component is mounted by reflow, an outer lead to which an external electrode is electrically connected, and a reinforcing resin that maintains the shape of the inner lead.

JP2015-103790A

  However, the reinforcing resin described in Patent Document 1 expands or contracts in accordance with the presence or absence of heat generated from the mounted components with energization and the temperature change in the surrounding environment. In particular, since the inner lead held by the reinforcing resin moves under the influence of the linear expansion of the reinforcing resin, stress is generated in the solder portion where the mounted component and the inner lead are electrically connected. This stress accumulates in the solder part as it is used for a long time. When the accumulated fatigue of the solder part exceeds the limit, there is a problem that a failure occurs. The failure corresponds to, for example, a crack or a disconnection.

  The present disclosure has been made in view of such points, and an object thereof is to provide a circuit board that is simple and has good workability, and that can suppress the occurrence of failure more than conventional ones.

  The invention made in order to solve the above-mentioned problems is arranged between a plurality of lead frames (12a, 12b, 12c, 12d) partially exposed for electrical connection to the outside and the lead frames. In the circuit board (10) having one or more mounting parts (11a, 11b, 11c, 11d) that are electrically connected to each other and a resin (13) that molds and holds the lead frame and the mounting parts The resin is a material having a linear expansion characteristic with directionality along the flow during molding, and a predetermined shape provided on both sides in the width direction along the lead frame on which the mounting component is arranged Hole (13a).

  According to this configuration, a hole having a predetermined shape is provided on both sides in the width direction along the lead frame on which the mounting component is arranged. The portions of the resin formed between the hole portions can ensure a constant orientation in which the linear expansion coefficient is smaller in the longitudinal direction than in the width direction. Even if the resin expands or contracts in accordance with the presence or absence of heat and the temperature change in the surrounding environment, the influence on the held lead frame can be suppressed. Therefore, even if the circuit board is used for a long period of time, the occurrence of failure can be suppressed as compared with the conventional case. Further, since no special measures are required for solder failure, it is easy and easy to process.

  The “external device” is optional as long as power and signals can be transmitted to and from the circuit board. “Multiple lead frames” are an outer lead frame that protrudes from the circuit board and is electrically connected to an external device, an inner lead frame that forms an electric circuit on the inner side of the circuit board, and a combination of the outer part and the inner part. Includes one or more of the lead frames. The outer lead frame corresponds to a terminal, a lead wire, a connection pin, or the like. The inner lead frame corresponds to a circuit pattern or wiring included in the electric circuit. As the “resin”, any material may be applied as long as it has a directional linear expansion characteristic along the flow during molding. For example, a fiber reinforced plastic containing a liquid crystal polymer is applicable. The “mounting component” is arbitrary as long as it is an electronic component that can be mounted on a circuit board. For example, an integrated circuit element such as an IC or an LSI, a resistor, a capacitor, a coil, a module element in which a plurality of electronic components of the same type or different types are sealed, and the like are applicable. The “linear expansion characteristic” is a characteristic related to the linear expansion coefficient included in the thermal expansion coefficient.

It is a top view which shows typically the 1st structural example of a circuit board. It is sectional drawing of the II-II line | wire shown in FIG. It is sectional drawing of the III-III line shown in FIG. It is a top view which shows typically the example of composition of a plurality of lead frames. It is a top view which shows typically the example of shaping | molding of resin to mold. It is a top view which shows typically the flow of the resin between metal mold | dies. It is a top view explaining the linear expansion coefficient in the bridge part which is a part of resin. It is a graph which shows typically the example of a relationship between a linear expansion coefficient and a failure rate. It is sectional drawing which shows the 2nd structural example of a circuit board typically. It is sectional drawing which shows the 3rd structural example of a circuit board typically.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that unless otherwise specified, “connecting” means electrically connecting. Each figure shows elements necessary for explaining the present invention, and does not necessarily show all actual elements. When referring to directions such as up, down, left and right, the description in the drawings is used as a reference. Alphanumeric continuous codes are abbreviated using the symbol “˜”. For example, “mounted components 11a to 11d” mean “mounted components 11a, 11b, 11c, and 11d”. In this embodiment, an ECU or a computer is applied as an external device. ECU is an abbreviation consisting of the acronym “Electronic Control Unit”.

  The circuit board 10 shown in FIGS. 1 to 3 corresponds to, for example, a sensor that detects a state related to a vehicle. The circuit board 10 includes a plurality of mounting components 11a to 11d, a plurality of lead frames 12a to 12d, a resin 13, and the like. The “state relating to the vehicle” includes, for example, one or more of throttle opening, brake stroke amount, steering angle, rotation speed, speed, acceleration, yaw rate, rotation angle, occupant load, and the like. “Vehicle” is arbitrary as long as it is a mobile device, and in this embodiment, an automobile is applied regardless of the number of wheels and the power source (for example, an internal combustion engine, a rotating electrical machine, etc.).

  The plurality of mounting components 11a to 11d correspond to integrated circuit elements, resistors, capacitors, coils, module elements, and the like. Each mounting component may be a surface mounting component that is mounted on the surface of the lead frame, or may be a through-hole mounting component that fixes the lead to a hole in the lead frame. The mounting components 11a to 11d are joined and connected to the corresponding lead frames 12a to 12d by flow or reflow, respectively. Joining includes soldering and welding. In this embodiment, an example of connection by solder 14 is shown in FIG. Moreover, the example of arrangement | positioning of the mounting components 11a-11d with respect to the lead frames 12a-12d is shown with a dashed-two dotted line in FIG.

  The plurality of lead frames 12a to 12d are used for connection to an external device, or used as a circuit pattern or wiring that constitutes an electric circuit. In the example of FIG. 1, the lead frames 12a and 12b correspond to “shared lead frames”, and the lead frames 12c and 12d correspond to “inner lead frames”. In this embodiment, a part of the lead frames 12a, 12b is exposed for connection with an external device. As shown in FIGS. 2 and 3, portions of the lead frames 12a to 12d that are not held by being sealed with a resin 13 described later are exposed. Although not shown, the lead frames 12a and 12b may be “outer lead frames” for connection to an external device. Each lead frame may be made of any material as long as it shows electrical conductivity, for example, copper, aluminum, alloy, conductive resin, and the like. A configuration example in which the lead frames 12a to 12d are arranged on the same surface is shown by a solid line in FIG.

  The resin 13 seals and holds the plurality of mounting components 11a to 11d, the plurality of lead frames 12a to 12d, and the like except for the exposed portions described above. In this embodiment, a liquid crystal polymer is applied as the resin 13. A mold that is molded into a finished shape using the melted resin 13 has a general configuration, and is not shown. The completed shape may be arbitrarily set according to the shape of the mounting components 11a to 11d, the purpose of use of the circuit board 10, and the like, and a polyhedron is applied in this embodiment.

  As shown in FIG. 5, the resin 13 after being molded by the mold and cured has a plurality of holes 13a, a plurality of bridge portions 13b, and the like. However, in FIG. 5, illustration of the plurality of mounting components 11 a to 11 d is omitted. The plurality of hole portions 13a are formed on both sides of the bridge portion 13b along a plurality of bridge portions 13b described later. In other words, as shown in FIGS. 1 and 5, the holes 13 a are provided on both sides in the width direction along the lead frames 12 a to 12 d where the mounting components 11 a to 11 d are arranged. The hole 13a of the present embodiment is a through-hole that is formed by a predetermined portion 15 of a mold shown in FIG. The width and length of the hole portion 13a may be arbitrarily set as long as a linear expansion coefficient α of a bridge portion 13b described later is satisfied.

  As shown in FIG. 5, each of the plurality of bridge portions 13 b exposes two or more lead frames 12 a to 12 d, and corresponding mounting components 11 a to 11 d are arranged and connected between the exposed lead frames. Provided for. Each bridge part 13b may shape a cross-sectional shape with an arbitrary geometric shape, and the longitudinal direction may be linear or non-linear. The bridge portion 13b of this embodiment has a cross-sectional shape of a square shape and is formed in a straight line shape in the longitudinal direction.

  As shown in FIG. 6, each bridge portion 13 b is cured after flowing in the direction of arrow D in a molten state during molding by a mold. That is, the flow of the molten resin 13 is regulated in the direction of arrow D by the two predetermined portions 15 included in the mold. Depending on the location where the molten resin 13 is introduced into the mold, the direction may be opposite to that of the arrow D.

  Each bridge portion 13b after curing has a linear expansion coefficient α as shown in FIG. However, in FIG. 7, the lead frame and the mounted components are not shown. The linear expansion coefficient α corresponds to “linear expansion characteristics” and is included in the thermal expansion coefficient. The linear expansion coefficient α includes a longitudinal direction linear expansion coefficient αL and a width direction linear expansion coefficient αW. The longitudinal direction linear expansion coefficient αL is a longitudinal direction linear expansion coefficient, and the width direction linear expansion coefficient αW is a width direction linear expansion coefficient. The longitudinal direction linear expansion coefficient αL is smaller than the width direction linear expansion coefficient αW, and an inequality of αL <αW is established.

  FIG. 8 shows an example of a characteristic line L in which the horizontal axis is the linear expansion coefficient difference αD and the vertical axis is the solder strain ST. The linear expansion coefficient difference αD is a value that expresses the difference from the linear expansion coefficient β of the mounting components 11a to 11d as a percentage based on the linear expansion coefficient α of the resin 13. When expressed by a mathematical formula, αD = (| α−β | / α) × 100. Since the linear expansion coefficient α is different for each of the mounting components 11a to 11d, a mounting component that maximizes the linear expansion coefficient β (for example, an integrated circuit element or a coil that generates a large amount of heat) may be selected. As the linear expansion coefficients α and β, either the longitudinal direction linear expansion coefficient αL or the width direction linear expansion coefficient αW may be applied. From the viewpoint of suppressing the expansion or contraction of the resin 13, the longitudinal direction linear expansion coefficient αL is more suitable than the width direction linear expansion coefficient αW.

  In the characteristic line L shown in FIG. 8, as the linear expansion coefficient difference αD increases, the vertical axis also increases the solder strain ST. As the solder strain ST increases, a failure such as a crack or disconnection is likely to occur early in the solder connecting the mounting components 11a to 11d and the lead frames 12a to 12d. Therefore, it is preferable to set a predetermined range AR in which the linear expansion coefficient difference αD is equal to or less than the allowable coefficient difference αDa so that the solder distortion ST is equal to or less than the allowable distortion value STa. When the predetermined range AR is expressed by a mathematical expression, (| α−β | / α) × 100 ≦ αDa. In order to suppress the failure, the resin 13 and the mounting components 11a to 11d may be set so that the linear expansion coefficient α and the linear expansion coefficient β are within a predetermined range AR.

  According to the embodiment described above, the following operational effects can be obtained.

  (1) In the circuit board 10 shown in FIGS. 1 to 3, the resin 13 is a material having a directional linear expansion characteristic along the flow during molding, and the lead frame on which the mounting components 11a to 11d are arranged. It was set as the structure which has the hole 13a of the predetermined shape provided in the both sides of the width direction along 12a-12d. According to this configuration, the bridge portion 13b of the resin 13 formed between the hole portions 13a can ensure a constant orientation in which the linear expansion coefficient α is smaller in the longitudinal direction than in the width direction. Even if the resin 13 expands or contracts according to the presence or absence of heat, the temperature change of the surrounding environment, etc., the influence on the held lead frames 12a to 12d can be suppressed. Therefore, even if the circuit board 10 is used for a long period of time, the occurrence of failure can be suppressed as compared with the conventional case. Further, since no special treatment is required for the failure of the solder 14, it is simple and has good workability. Similar effects can be obtained by welding other than solder.

  (2) As shown in FIGS. 1 to 3, the hole portion 13a is a through hole. According to this structure, since it can shape | mold easily by the predetermined | prescribed site | part 15 of a metal mold | die, it is easy and workability is good.

  (3) As shown in FIGS. 1 to 3, the hole 13 a has a configuration in which the opening has a long groove shape. According to this structure, since it can shape | mold easily by the predetermined | prescribed site | part 15 of a metal mold | die, it is easy and workability is good.

  (4) As shown in FIG. 8, the linear expansion coefficient α of the resin 13 and the linear expansion coefficient β of the mounting components 11 a to 11 d are configured to be within a predetermined range AR. According to this configuration, since the linear expansion coefficient difference αD between the resin 13 and the mounted components 11a to 11d is small, the influence on the lead frames 12a to 12d can be more reliably suppressed. Therefore, even if the circuit board 10 is used for a long period of time, the occurrence of failure can be further suppressed than in the past.

  (5) The resin 13 is a liquid crystal polymer. According to this configuration, since the liquid crystal polymer has a small linear expansion coefficient difference αD in the longitudinal direction in the resin 13 (particularly the bridge portion 13b), the influence on the lead frames 12a to 12d can be more reliably suppressed. Therefore, even if the circuit board 10 is used for a long period of time, the occurrence of failure can be further suppressed than in the past.

[Other Embodiments]
Although the form for implementing this invention was demonstrated above, this invention is not limited to the said form at all. In other words, various forms can be implemented without departing from the scope of the present invention. For example, the following forms may be realized.

  In the above-described embodiment, as shown in FIGS. 1 and 5, the bridge portion 13 b of the resin 13 does not cover the mounting components 11 a to 11 d and the lead frames 12 a to 12 d but holds the lead frames 12 a to 12 d. . Instead of this form, as long as the influence on the joining portion including the solder 14 is negligible, the mounting components 11a to 11d and the lead frames 12a to 12d may be covered and held as shown in FIG. Good. Since the longitudinal direction linear expansion coefficient αL is small in the longitudinal direction of the bridge portion 13b, expansion or contraction is suppressed, and since the width direction is the same width as the lead frames 12a to 12d, the influence due to expansion or contraction can be ignored. Therefore, it is possible to obtain the same operational effects as those of the above-described embodiment.

  In the above-described embodiment, as shown in FIGS. 1 to 3, the hole portion 13 a is configured by a through hole. Instead of this form, as shown in FIG. 10, when the linear expansion coefficient α in the bridge portion 13 b is within the predetermined range AR shown in FIG. 8, the one side (the lower side in FIG. 10) of the resin 13 does not penetrate. You may comprise by a through hole. Although illustration is omitted, as shown in FIG. 9, the mounting components 11a to 11d and the lead frames 12a to 12d may be covered and held. In any configuration, since the bridge portion 13b has a linear expansion coefficient α, it is possible to obtain the same effects as those of the above-described embodiment.

  In the above-described embodiment, as shown in FIG. 1, the circuit board 10 is configured to include four lead frames 12a to 12d, four mounting components 11a to 11d, and the like. Instead of this form, the number of lead frames corresponding to the number of connections with external devices, circuit patterns, wirings, etc. may be set to an arbitrary number of two or more. The number of mounted components may be set to an arbitrary number of one or more according to an electric circuit having a target function. Since only the number of elements is different, it is possible to obtain the same effect as the above-described embodiment.

  In the above-described embodiment, as shown in FIGS. 1, 5, and 7, the cross-sectional shape is a square shape, and the shape is linearly formed in the longitudinal direction. Instead of this form, although not shown, one or more of the bridge portions 13b may have a cross-sectional shape other than a square shape, or may be formed in a non-linear shape in the longitudinal direction. Examples of the cross-sectional shape other than the quadrangular shape include a polygonal shape including a triangular shape and a pentagonal shape, a circular shape including a semicircular shape and an elliptical shape, and a combined shape obtained by combining a plurality of shapes. The non-linear shape corresponds to a polygonal shape that is equal to or greater than a triangular shape, a circular shape including an arc shape or an elliptical shape, a step shape including a crank shape, and a branched shape that branches into one or more in the middle. Since only the shape of the bridge portion 13b is different, the same effect as the above-described embodiment can be obtained.

  In the embodiment described above, the resin 13 is formed using a liquid crystal polymer. Instead of this form, other fiber reinforced plastics that have a directional linear expansion characteristic along the flow during molding may be applied. For example, a glass fiber reinforced plastic, a glass long fiber reinforced plastic, a carbon fiber reinforced plastic, a boron fiber reinforced plastic, an aramid fiber reinforced plastic, a polyethylene fiber reinforced plastic, a xylon reinforced plastic, and the like are applicable. Other resins capable of having a linear expansion characteristic with a direction along the flow during molding may be used. Even in other materials, the longitudinal direction linear expansion coefficient αL of the bridge portion 13b is smaller than the width direction linear expansion coefficient αW. Therefore, it is possible to obtain the same effect as the above-described embodiment.

  In the embodiment described above, the circuit board 10 is configured to apply a sensor that detects a state related to the vehicle, and to apply an automobile to the vehicle. Instead of this form, it may be applied to other devices capable of transmitting power and signals to / from an external device, or other mobile devices other than automobiles may be applied. The other device corresponds to any part mounted on the mobile device. Other mobile devices include railway vehicles, ships, and aircraft. Since the object is merely different, the same effect as the above-described embodiment can be obtained.

DESCRIPTION OF SYMBOLS 10 Circuit board 11a-11d Mounting parts 12a-12d Lead frame 13 Resin 13a Hole part 13b Bridge part

Claims (5)

A plurality of lead frames (12a, 12b, 12c, 12d) partially exposed for electrical connection with the outside, and one or more mountings disposed between and electrically connected to the lead frames In a circuit board (10) having components (11a, 11b, 11c, 11d) and a resin (13) for molding and holding the lead frame and the mounting component,
The resin is a material having a linear expansion characteristic with directionality along the flow at the time of molding, and has a predetermined shape provided on both sides in the width direction along the lead frame on which the mounting component is arranged. A circuit board having a hole (13a).   The circuit board according to claim 1, wherein the hole is a through hole or a non-through hole.   The circuit board according to claim 1, wherein the hole portion has an elongated groove shape.   4. The circuit board according to claim 1, wherein a linear expansion coefficient (α) of the resin and a linear expansion coefficient (β) of the mounting component are within a predetermined range (AR). 5.   The circuit board according to claim 1, wherein the resin is a liquid crystal polymer.

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