JP2008060182A - In-vehicle electronic circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a solder thickness varies depending on variation in component dimensions, plating dimensions, substrate electrode dimensions, and manufacture conditions when connecting an electronic component with a circuit board, resulting in variation of a solder connection service life. <P>SOLUTION: The in-vehicle electronic circuit device is equipped, on the circuit board 2, with solder resist 4, the substrate electrode 2a, silk ink 5, or a protrusion 2b for bringing the electronic component 1 onto the circuit board 2 by their combinations. Since the variation can thus be reduced in an interval between the circuit board 2 and the electronic component 1, the variation can be reduced in the thickness of a solder layer 3. Therefore, the service life of the solder connection can be stabilized with its variation reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an on-vehicle electronic circuit device, and more particularly to a mounting structure that improves the reliability of solder connection between an electronic component and a circuit board.

  In an in-vehicle electronic circuit device used for an automobile engine control device or the like, an electronic component and a circuit board on which the electronic component is mounted are electrically connected mainly by solder. On the other hand, these on-vehicle electronic circuit devices and solder joints are required to have high reliability to withstand fatigue due to long-term thermal cycles and vibrations. It is essential that the solder connection portion is not disconnected in order for the electronic circuit device to operate normally, and particularly high connection reliability is required.

  The solder connection life is largely influenced mainly by the difference in coefficient of linear expansion (α) between connected members. Therefore, for example, when dissimilar materials having different linear expansion coefficients, such as a glass epoxy substrate (eg, α≈13) and a ceramic (alumina, α≈7) resistance, are joined, the life is likely to be shortened. Compared to this, for example, when a ceramic resistor is mounted on a ceramic substrate, it is possible to expect a longer life than when a glass epoxy substrate is used.

  On the other hand, considering the competitiveness of products, we would like to mount ceramic resistors and capacitors with a small area and high productivity on a glass epoxy substrate that is advantageous in terms of cost. Against this background, a mounting method that improves the solder connection life is required. As a soldering method for improving the solder connection life between different kinds of materials having different linear expansion coefficients, for example, a method for reducing the distortion generated in the solder due to the thermal cycle by characterizing the shape of the electrode of the electronic component (Patent Document 1).

JP 2005-183468 A

  FIG. 5 shows a general relationship between the solder thickness and the solder connection life. Increasing the solder thickness can reduce the strain generated in the solder layer, thus improving the connection life. In the above prior art, by increasing the thickness of the solder layer, the concentration of strain is reduced and the connection life is improved.

In addition, the continuous line part of FIG. 5 has shown that the solder connection lifetime improves with the increase in solder thickness. The broken line portion in FIG. 5 indicates that the solder connection life is expected to be saturated when the solder thickness exceeds a certain value. Here, since the relationship between the solder thickness and the solder connection life varies depending on the material and size of the target electronic component, the material of the circuit board, the size of the board-side electrode, the solder fillet shape, etc., FIG. Keep on. As an example, a calculation result that can increase the solder connection life by about 1.5 times by increasing the solder thickness by 2.5 times was obtained. As described above, generally, the distortion generated in the solder can be reduced by increasing the thickness of the solder layer, and thus the solder connection life can be improved.

  However, in the actual manufacturing process, the thickness of the solder layer varies due to various factors of the manufacturing state. For example, in the electronic component mounting process of an in-vehicle electronic circuit device, the steps of (1) printing of solder paste, (2) mounting of electronic components, and (3) solder connection using a reflow furnace are performed. In the process, variations in the solder layer thickness occur due to [1] variations in component dimensions and plating dimensions, [2] variations in circuit board electrode (land) dimensions, [3] variations in reflow conditions, and the like. Therefore, it is difficult to keep the thickness of the solder layer within a certain range without special measures, and as a result, the solder connection life is varied. In the above-described conventional technology, no special contrivance has been made for this problem.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a mounting method and a circuit board that reduce the variation in the thickness of the solder layer with respect to the above problems.

  A convex part for contacting the electronic component is provided on the circuit board, and the distance between the substrate electrode provided on the circuit board and the component electrode provided on the electronic component is adjusted to the height of the convex part. Specifically, a circuit board, an electronic component mounted on the circuit board, a substrate electrode provided on the circuit board, and a solder layer that electrically connects the component electrode provided on the electronic component. In the on-vehicle electronic circuit device provided, a convex portion that comes into contact with the electronic component is provided at a portion of the circuit board on which the electronic component is mounted, and the height of the convex portion is configured to be higher than the substrate electrode. This convex portion can be provided by solder resist, Cu land, silk ink, or a combination thereof on the circuit board. Moreover, the said convex part can also be formed by providing a dent in a circuit board and providing the electrode of a circuit board in a dent.

  The variation in the distance between the substrate electrode provided on the circuit board and the component electrode provided on the electronic component, that is, the variation in the thickness of the solder layer is suppressed within the manufacturing tolerance range of the convex portion. Therefore, the variation in the thickness of the solder layer is smaller than that in the prior art, and the variation in the solder connection life is reduced.

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

  FIG. 1 shows a first embodiment. FIG. 1 is a schematic cross-sectional view of an electronic circuit device in which an electronic component 1 is connected to a circuit board 2 with a solder layer 3.

  Specific examples of the electronic component 1 include a ceramic resistor and a ceramic capacitor. Specific examples of the circuit board 2 include a glass epoxy board and a ceramic board. Specific examples of the solder layer 3 include eutectic solder and Pb-free solder. The present invention can be widely applied regardless of the combination of these members, but is particularly effective when the difference in linear expansion coefficient is large, such as a glass epoxy substrate and a ceramic resistor or ceramic capacitor.

  Component electrodes 1 a are formed on both ends of the electronic component 1. The component electrode 1a is mainly Sn (tin) -based plating. On the circuit board 2, a substrate electrode (land) 2a is formed at a position facing the component electrode 1a, and a convex portion 2b is formed at an intermediate position between these substrate electrodes. The material of the substrate electrode 2a and the convex portion 2b is mainly Cu (copper). A solder resist 4 is applied to the surface of the circuit board 2 except for the substrate electrode 2a and its periphery.

  The convex portion 2b provided on the circuit board 2 is an independent land that is not electrically connected to other lands or circuits. The solder resist 4 is applied so as to cover the convex portion 2 b, and the silk ink 5 is further applied on the solder resist 4, thereby forming the convex portion 5 b that contacts the electronic component 1. The height of the convex portion 5b is obtained by adding the height corresponding to the thickness of the solder resist 4 and the silk ink 5 to the height of the convex portion 2b.

  Here, the thickness of the solder resist 4 can be adjusted to a predetermined thickness by the mask thickness at the time of printing or the amount of spray, and the thickness of the silk ink 5 can be adjusted by the mask thickness at the time of printing. The height can be limited within the range of variations in the height of the convex portion 2b. Therefore, by performing soldering while the electronic component 1 is in contact with the convex portion 5b, the thickness variation of the solder layer 3 can be limited within the range of the height variation of the convex portion 2b. Thus, by making the thickness of the solder layer 3 within a predetermined range, it is possible to reduce the variation in the solder connection life. As shown in FIG. 1, it is desirable that the upper surface of the convex portion 5b be planar.

  As an example of the thickness configuration of the solder resist 4 and the silk ink 5, when the solder resist is 5 microns and the silk ink is 20 microns, a convex portion of 25 microns can be formed by the solder resist 4 and the silk ink 5.

  FIG. 2 is an example in which a plurality of convex portions 2 b formed on the circuit board 2 are provided. By using a plurality of protrusions 2b, the electronic component 1 can be prevented from being inclined. When the number of the convex portions 2b is one, the electronic component 1 may be inclined. When the electronic component 1 is tilted, the distance between the substrate electrode 2a and the component electrode 1a varies depending on the location. Therefore, the thickness of the solder layer 3 therebetween varies depending on the location, thereby increasing the variation of the solder connection life. there is a possibility. Specifically, in the example of FIG. 1, the thickness of the solder on the right side of the electronic component 1 is different from the thickness of the solder layer 3 on the left side. Furthermore, if the electronic component 1 is greatly inclined, there is a possibility that electrical connection between the component electrode 1a and the substrate electrode 2a cannot be secured. Therefore, when only one convex part 2b is provided, it is necessary to pay close attention so that the electronic component 1 does not tilt in the manufacturing process.

  On the other hand, in this embodiment, a plurality of convex portions 2b are provided to prevent the electronic component 1 from being tilted. This makes it easier to hold the electronic component 1 so as not to tilt in the manufacturing process as compared to the first embodiment, and is formed between the component electrodes 1a at both ends of the electronic component 1 and the corresponding substrate electrodes 2a. The thickness of the solder layer 3 can be made more uniform. Therefore, it is possible to reduce the variation in the solder connection life.

  In the case where a plurality of convex portions 2b are provided, it is desirable that the necessary minimum number (two locations) be used in order to prevent inclination due to height variation between the convex portions, but there may be three or more locations.

  FIG. 3 shows a third embodiment. This embodiment is effective when it is desired to more strictly limit the height of the convex portion or when both solder connection reliability and heat dissipation are desired.

In Example 1, since the height of the convex portion 2b is equal to that of the other substrate electrode 2a, the thickness of the solder layer 3 is substantially defined by the thickness of the solder resist 4 and the silk ink 5. On the other hand, in this embodiment, as shown in FIG. 3, the convex part 2b formed on the circuit board 2 is formed thicker (higher) than the board electrode 2a, and the electronic component 1 is formed without applying the solder resist 4 or the like. The convex part to contact | abut is formed. In this method, as compared with the formation of the convex portion by the solder resist 4, variation in the height of the convex portion can be reduced. Therefore, since the thickness of the solder layer 3 can be controlled more strictly, the solder connection life can be further stabilized. The convex part 2b by this method can be formed by lamination | stacking of the copper foil used for Cu plating or circuit pattern formation.

  In addition, in the structure of a present Example, since the metal (Cu) which is excellent in heat conductivity is made to contact with the electronic component 1, the heat dissipation of the electronic component 1 can be improved with respect to Example 1,2.

  The fourth embodiment shown in FIG. 4 is particularly effective when the height when the electronic component 1 is mounted is limited.

  In FIG. 4, in the circuit board 2, a recess 2 c is provided at a position facing the component electrode 1 a of the electronic component 1, and a protrusion 5 c is formed at a position immediately below the component of the circuit board 2. In the present embodiment, the convex portion 5c is formed by the land 2b independent of the remaining portion 5d left by creating the concave portion 2c. Here, the depth of the recess 2c is formed deeper than the plating thickness of the component electrode 1a. When the electronic component 1 is mounted on the circuit board 2, the antinode of the electronic component 1 and the protrusion 5c of the circuit board 2 It has a structure that contacts. The component electrode 1 a and the substrate electrode 2 a are electrically connected by the solder layer 3. According to the above configuration, the thickness of the solder layer 3 is determined by the difference between the depth of the recess 2c and the plating thickness of the component electrode 1a. Therefore, the thickness of the solder layer 3 can be set within a predetermined range, and variations in the solder connection life can be reduced.

  In the example of FIG. 4, in order to minimize the mounting height of the electronic component 1 while ensuring the maximum thickness of the solder layer 3, the solder resist 4 and silk ink 5 are applied to the convex portions 5c. Not done. However, if the mounting height allows, it is desirable to apply the solder resist 4 and the silk ink 5 in order to ensure insulation.

  When a multilayer board is used as the circuit board 2, the inner layer pattern can also be used as the board electrode 2a.

Sectional drawing of the vehicle-mounted electronic circuit apparatus concerning the 1st Example of this invention. Sectional drawing of the vehicle-mounted electronic circuit apparatus concerning the 2nd Example of this invention. Sectional drawing of the vehicle-mounted electronic circuit apparatus concerning the 3rd Example of this invention. Sectional drawing of the vehicle-mounted electronic circuit apparatus concerning the 4th Example of this invention. Graph showing the general relationship between solder thickness and solder connection life.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electronic component, 1a ... Component electrode, 2 ... Circuit board, 2a ... Board electrode, 2b ... Convex part of a circuit board, 2c ... Concave part of a circuit board, 3 ... Solder layer, 4 ... Solder resist, 5 ... Silk ink,
5b, 5c ... convex part, 5d ... remaining part.

Claims (9)

A circuit board;
Electronic components mounted on the circuit board;
A solder layer for electrically connecting a substrate electrode provided on the circuit board and a component electrode provided on the electronic component;
The circuit board is a vehicle-mounted electronic circuit device having a convex portion that abuts the electronic component at a portion where the electronic component is mounted, and the height of the convex portion is higher than that of the substrate electrode.   The in-vehicle electronic circuit device according to claim 1, wherein the convex portion on the circuit board is formed by a solder resist applied to the circuit board.   The in-vehicle electronic circuit device according to claim 1, wherein the convex portion on the circuit board is formed by a pattern for performing electrical wiring on the circuit board.   The in-vehicle electronic circuit device according to claim 1, wherein the convex portion on the circuit board is formed by silk ink applied on the circuit board.   The in-vehicle electronic circuit device according to claim 1, wherein the convex portion on the circuit board is formed by using two or more of the methods according to claim 2.   The in-vehicle electronic circuit device according to claim 1, wherein two or more convex portions on the circuit board are provided for one electronic component. The electronic component has a plurality of the component electrodes,
The in-vehicle device according to claim 1, wherein the convex portion is formed by providing a concave portion in a portion facing the plurality of component electrodes on the circuit board, and providing the substrate electrode in each of the plurality of concave portions. Electronic circuit device.   The on-vehicle electronic circuit device according to claim 7, wherein the height of the convex portion is adjusted by the method according to claim 2.   The in-vehicle electronic circuit device according to claim 1, wherein an upper surface of the convex portion is planar.

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