JPWO2018159728A1 - Mounting structure - Google Patents

Abstract

The mounting structure of the present invention is a mounting structure in which a plurality of terminals of a mounted component are self-aligned to a plurality of lands of a wiring board by reflow of solder, and the lands and the terminals are formed by combining one or more squares in plan view. And the center of gravity of the land main part having the largest area among one or more squares of the land planar shape, and the terminal main part having the largest area among one or more squares of the terminal planar shape. The position of the center of gravity matches.

Description

  The present invention relates to a mounting structure. This application claims priority based on Japanese Patent Application No. 2017-039796 filed on Mar. 2, 2017, and incorporates all the contents described in the above Japanese Application.

  2. Description of the Related Art There is known a self-alignment technique for positioning an electrode of an electronic component at the center of a land by the surface tension of reflowed solder when mounting the electronic component with solder.

  In some electronic components, the planar shape of the electrode may be asymmetric, for example, L-shaped. When soldering an electronic component having such a deformed electrode, self-alignment due to the surface tension of the solder may not function sufficiently.

  On the other hand, for example, Japanese Patent Application Laid-Open No. 2007-250765 discloses that an electronic component (LED) has an electrode mounting portion having a planar shape along the outer periphery of an electrode of an electronic component (LED). It is described that mounting accuracy can be improved.

JP 2007-250765 A

[Means for solving the problem]
A mounting structure according to one embodiment of the present invention is a mounting structure in which a plurality of terminals of a mounted component are self-aligned on a plurality of lands of a wiring board by reflow of solder, and the lands and terminals have one or more planar shapes. It is a combination of squares, the center of gravity of the land main part having the largest area among one or more squares of the land shape, and the largest area among one or more squares of the terminal planar shape. The position of the center of gravity of the terminal main part matches.

FIG. 1 is a schematic plan view of an electronic component having a mounting structure according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of the electronic component taken along line AA of FIG.

[Problems to be solved by the invention]
In recent years, there has been a demand for further improving the mounting accuracy of electronic components, and the mounting accuracy of electronic components is not sufficient simply by setting the planar shape of the land along the outer periphery of the electrode as disclosed in the above publication. May occur.

  The present invention has been made in view of the above circumstances, and has as its object to provide a mounting structure capable of improving mounting accuracy by self-alignment.

[The invention's effect]
The mounting structure according to one embodiment of the present invention can improve mounting accuracy by self-alignment.

[Description of Embodiment of the Present Invention]
A mounting structure according to one embodiment of the present invention is a mounting structure in which a plurality of terminals of a mounted component are self-aligned on a plurality of lands of a wiring board by reflow of solder, and the lands and terminals have one or more planar shapes. It is a combination of squares, the center of gravity of the land main part having the largest area among one or more squares of the land shape, and the largest area among one or more squares of the terminal planar shape. The position of the center of gravity of the terminal main part matches.

  The mounting structure allows the surface tension of the reflowed solder to act appropriately by matching the center of gravity of the land main part with the center of gravity of the terminal main part, thereby improving mounting accuracy by self-alignment. can do.

  It is preferable that the minimum value of the distance between the outer edge of the land main portion and the outer edge of the terminal main portion is 25 μm or more and the maximum value is 35 μm or less. As described above, when the minimum value and the maximum value of the distance between the outer edge of the land main portion and the outer edge of the terminal main portion satisfy the above conditions, the surface tension of the solder acts more appropriately.

Preferably 0.10 mm ² or more 0.30 mm ² or less as the area of the land main unit. As described above, when the area of the land main portion is within the above range, the effect of appropriately applying the surface tension of the solder becomes more remarkable.

  The wiring board preferably has a wiring portion connected to the land main portion, and a width of a portion of the wiring portion connected to the land main portion is preferably 0.05 mm or more and 0.20 mm or less. As described above, the wiring board has the wiring portion connected to the land main portion, and the width of the portion of the wiring portion connected to the land main portion is within the above range. The reliability of the wiring can be secured while suppressing the influence of the parts.

  Preferably, the mounting component is a light emitting diode. As described above, when the mounted component is a light emitting diode, the mounting accuracy is significantly improved by the mounting structure.

[Details of Embodiment of the Present Invention]
Hereinafter, embodiments of a mounting structure according to the present invention will be described in detail with reference to the drawings.

  1 and 2 show an electronic component having a mounting structure according to an embodiment of the present invention. In this electronic component, a mounted component 1 (the main body is indicated by a chain line) is mounted on the surface of a printed wiring board 2 using solder 3. In the mounting structure, the mounted component 1 is self-aligned (positioned) with respect to the printed wiring board 2 by reflow of the solder 3.

〔Mounting parts〕
The mounted component 1 in the present embodiment is a chip-type LED (light emitting diode), and the electronic components in FIGS. 1 and 2 are intended to be used as, for example, an edge light in an edge light type backlight device for a liquid crystal display panel. You. As described above, when a light emitting diode is used as the mounted component 1, there is an effect such that a light irradiation range is shifted due to a mounting error, and the effect of improving mounting accuracy by the mounting structure is remarkably exhibited as a performance of the electronic component.

  The mounted component 1 has a plurality of (two in this embodiment) terminals 4. The planar shape of the terminal 4 is a combination of one or more (two in this embodiment) squares.

  In the case where the planar shape of the terminal 4 is a combination of a plurality of squares, the terminal main part 5 having the largest square area and the terminal sub-part 6 having one or more square areas smaller than the terminal main part 5 are provided. And divided into When the planar shape of the terminal 4 is a single rectangular shape, it is understood that the terminal 4 includes only the terminal main portion 5. When the planar shape of the terminal 4 is divided into a plurality of squares, there may be a plurality of combinations of dividing lines (shown by two-dot chain lines), but the dividing line that maximizes the area of the terminal main portion 5 is assumed. And

[Printed wiring board]
The printed wiring board 2 includes a flexible and insulating base film 7, a conductive pattern 8 formed on the surface of the base film 7, and a cover lay 9 covering the surfaces of the base film 7 and the conductive pattern 8. Configuration.

<Base film>
Examples of the material of the base film 7 include polyamide, polyimide, polyamideimide, and polyester. Above all, polyamide, polyimide and polyamideimide are preferably used from the viewpoint of heat resistance at the time of reflow of the solder 3.

  The thickness of the base film 7 is appropriately set according to the use of the electronic component and is not particularly limited. However, as a general theory, the lower limit of the average thickness of the base film 7 is preferably 5 μm, and more preferably 10 μm. Is more preferable, and 25 μm is further preferable. On the other hand, the upper limit of the average thickness of the base film 7 is preferably 500 μm, and more preferably 150 μm. When the average thickness of the base film 7 is less than the above lower limit, the strength of the base film 7 may be insufficient. Conversely, when the average thickness of the base film 7 exceeds the upper limit, the flexibility of the printed wiring board 2 may be insufficient, or the printed wiring board 2 may be unnecessarily thick.

<Conductive pattern>
The conductive pattern 8 is formed by patterning a layered conductor laminated on the base film 7. The conductive pattern 8 includes a plurality of lands 10 to which the terminals 4 of the mounting component 1 are connected, and one or a plurality of wiring portions (the first wiring portion 11 and the second wiring portion 11 in this embodiment) connected to each land 10. 12).

  The method for laminating the conductor constituting the conductive pattern 8 on the base film 7 is not particularly limited. For example, a bonding method in which a sheet-shaped conductor is bonded with an adhesive, a casting method in which a resin composition as a material of the base film 7 is applied on the sheet-shaped conductor, a thickness formed on the base film 7 by sputtering or vapor deposition. A sputtering / plating method of forming a metal conductor layer by plating on a thin conductive layer (seed layer) of several nm, a lamination method of sticking a sheet-like conductor to the base film 7 by hot pressing, and the like can be used.

  The material for forming the conductive pattern 8 is not particularly limited as long as it is a material having conductivity, and examples thereof include metals such as copper, aluminum, and nickel. Used. Further, the conductive pattern 8 may be subjected to plating on the surface.

  The lower limit of the average thickness of the conductive pattern 8 is preferably 2 μm, more preferably 5 μm. On the other hand, the upper limit of the average thickness of the conductive pattern 8 is preferably 500 μm, more preferably 100 μm. When the average thickness of the conductive pattern 8 is less than the above lower limit, the conductivity may be insufficient. On the other hand, when the average thickness of the conductive pattern 8 exceeds the upper limit, it may be difficult to attach the solder 3 with a uniform thickness.

(land)
The planar shape of the land 10 is a combination of one or more (two in this embodiment) squares.

  In the case where the planar shape of the land 10 is a combination of a plurality of squares, the land main portion 13 having the largest area and the land sub-portion 14 having one or more squares smaller in area than the land main portion 13. And divided into If the planar shape of the land 10 is a single rectangular shape, it is understood that the land 10 includes only the land main portion 13. In the case where the planar shape of the land 10 is divided into a plurality of squares, there may be a plurality of combinations of dividing lines (shown by two-dot chain lines), but the dividing line that maximizes the area of the land main portion 13 is assumed. And

  The land main part 13 is designed such that the position of the center of gravity thereof matches the position of the center of gravity of the terminal main part 5 of the terminal 4. In other words, the arrangement pattern of the center of gravity of the plurality of terminal main parts 5 of the plurality of terminals 4 of the mounted component 1 matches the arrangement pattern of the center of gravity of the land main part 13 of the corresponding land 10. This allows the surface tension of the reflowed solder 3 to act appropriately, thereby allowing each terminal 4 to face the corresponding land 10 relatively accurately. That is, the mounting structure is excellent in mounting accuracy by self-alignment.

  From the viewpoint of design (including an expected manufacturing error), the lower limit of the minimum distance between the outer edge of the land main portion 13 and the outer edge of the terminal main portion 5 of the mounted component 1 is preferably 25 μm, more preferably 28 μm. On the other hand, the upper limit of the maximum value of the distance between the outer edge of the land main portion 13 and the outer edge of the terminal main portion 5 of the mounted component 1 is preferably 35 μm, more preferably 32 μm. If the minimum value of the distance between the outer edge of the land main portion 13 and the outer edge of the terminal main portion 5 of the mounted component 1 is less than the above lower limit, the planar component of the surface tension of the solder 3 acting on the terminal 4 may be small. Therefore, the positioning accuracy of the terminal 4 may be insufficient. Conversely, when the maximum value of the distance between the outer edge of the land main portion 13 and the outer edge of the terminal main portion 5 of the mounting component 1 exceeds the above upper limit, the surface tension component of the solder 3 acting on the terminal 4 is also a planar component. And the rate of change of the position of the terminal 4 with respect to the amount of displacement is small, so that the positioning accuracy of the terminal 4 may be insufficient.

Preferably 0.10 mm ² as the lower limit of the area of the land main portion 13, 0.15 mm ² is more preferable. On the other hand, preferably 0.30 mm ² as the upper limit of the area of the land main portion 13, 0.25 mm ² is more preferable. If the area of the land main portion 13 is less than the above lower limit, the component of the surface tension of the solder 3 acting on the terminal 4 in the planar direction becomes small, so that the positioning accuracy of the terminal 4 may be insufficient. Conversely, when the area of the land main portion 13 exceeds the upper limit, the rate of change of the surface tension component of the solder 3 acting on the terminal 4 in the planar direction and the amount of displacement of the terminal 4 becomes small, thereby positioning the terminal 4. The accuracy may be insufficient.

  The land sub-portion 14 is provided corresponding to the terminal sub-portion 6, and is provided so that the land 10 includes the terminal 4 in plan view. The planar component of the surface tension of the solder 3 acting between the land sub-portion 14 and the terminal sub-portion 6 is the planar direction of the surface tension of the solder 3 acting between the land main portion 13 and the terminal main portion 5. And the influence on the positioning accuracy of the self-alignment is relatively small. However, the minimum value and the maximum value of the distance between the outer edge of the land sub-portion 14 and the outer edge of the terminal sub-portion 6 are the minimum and maximum values of the distance between the outer edge of the land main portion 13 and the outer edge of the terminal main portion 5. It is preferred to be similar to.

(Wiring section)
The first wiring section 11 is connected to the land main section 13. On the other hand, the second wiring part 12 is connected to the land sub part 14.

  It is preferable that the first wiring portion 11 and the second wiring portion 12 of the conductive pattern 8 are each formed in a band shape having a substantially constant width. In addition, substantially constant means that the difference between the width and the average width in each part is 20% or less.

  It is preferable that the width of the portion of the first wiring portion 11 connected to the land main portion 13 is smaller than the width of the portion of the second wiring portion 12 connected to the land sub-portion 14. This makes it possible to reduce the influence of the first wiring portion 11 on the self-alignment while increasing the total sectional area of the first wiring portion 11 and the second wiring portion 12.

  The lower limit of the ratio of the width of the portion of the first wiring portion 11 connected to the land main portion 13 to the width of the portion of the second wiring portion 12 connected to the land sub-portion 14 is preferably 0.3, and 0.3. 4 is more preferred. On the other hand, the upper limit of the ratio of the width of the portion of the first wiring portion 11 connected to the land main portion 13 to the width of the portion of the second wiring portion 12 connected to the land sub-portion 14 is preferably 0.7, 0.6 is more preferred. If the ratio of the width of the portion of the first wiring portion 11 connected to the land main portion 13 to the width of the portion of the second wiring portion 12 connected to the land sub-portion 14 is less than the lower limit, the first wiring portion 11 May be insufficiently conductive. If the ratio of the width of the portion of the first wiring portion 11 connected to the land main portion 13 to the width of the portion of the second wiring portion 12 connected to the land sub-portion 14 exceeds the upper limit, the first wiring portion 11 The effect on self-alignment may not be sufficiently reduced.

  The lower limit of the width of the portion of the first wiring portion 11 connected to the land main portion 13 is preferably 0.05 mm, more preferably 0.08 mm. On the other hand, the upper limit of the width of the portion of the first wiring portion 11 connected to the land main portion 13 is preferably 0.20 mm, more preferably 0.15 mm. If the width of the portion of the first wiring portion 11 connected to the land main portion 13 is less than the above lower limit, the conductivity may be insufficient. Conversely, if the width of the portion of the first wiring portion 11 connected to the land main portion 13 exceeds the upper limit, the first wiring portion 11 affects the tension of the solder 3 at the time of self-alignment and lowers the positioning accuracy. May be caused.

<Coverlay>
The coverlay 9 is a layer that protects the conductive pattern 8. The coverlay 9 has an opening 15 exposing the land 10. The coverlay 9 can be configured to have a resin film and an adhesive layer laminated on the back surface of the resin film.

  Examples of the material of the resin film of the coverlay 9 include polyimide, epoxy resin, phenol resin, acrylic resin, polyester, thermoplastic polyimide, polyethylene terephthalate, fluororesin, and liquid crystal polymer.

  Although the lower limit of the average thickness of the resin film of the coverlay 9 is not particularly limited, it is preferably 3 μm, more preferably 10 μm. The upper limit of the average thickness of the resin film of the coverlay 9 is not particularly limited, but is preferably 500 μm, and more preferably 150 μm. When the average thickness of the resin film of the coverlay 9 is less than the above lower limit, the protection of the conductive pattern 8 may be uncertain. On the other hand, when the average thickness of the resin film of the cover lay 9 exceeds the upper limit, the cover lay 9 may interfere with the mounted component 1 and hinder the positioning of the mounted component 1.

  As the adhesive for forming the adhesive layer of the coverlay 9, a material having excellent flexibility and heat resistance is preferable. Examples of such adhesives include various resin adhesives such as nylon, epoxy resin, butyral resin, and acrylic resin.

  The lower limit of the average thickness of the adhesive layer of the coverlay 9 is preferably 15 μm, more preferably 20 μm. On the other hand, the upper limit of the average thickness of the adhesive layer of the coverlay 9 is preferably 100 μm, and more preferably 50 μm. When the average thickness of the adhesive layer of the coverlay 9 is less than the above lower limit, the adhesive strength may be insufficient. Conversely, when the average thickness of the adhesive layer of the cover lay 9 exceeds the upper limit, the cover lay 9 may interfere with the mounted component 1 and hinder the positioning of the mounted component 1.

〔solder〕
Any solder can be used as the solder 3, but it is preferable to use a solder paste which is a kneaded product of a flux and fine solder powder. By using a solder paste as the solder 3, it is possible to relatively accurately apply the required amount of the solder 3 to each land 10 using, for example, a printing technique.

<Mounting method>
As a method of mounting the mounted component 1 on the printed wiring board 2, a step of holding the printed wiring board 2 on a jig (holding step) and a step of attaching the solder 3 to the plurality of lands 10 of the printed wiring board 2 respectively. A method including a (soldering step), a step of arranging the mounted component 1 on the printed wiring board 2 (a mounted component arranging step), and a step of reflowing the solder 3 by heating (reflow step) can be provided.

(Holding process)
In the holding step, the printed wiring board 2 is held by a jig in order to easily and accurately handle the printed wiring board 2 in the subsequent steps. For efficiency, a plurality of printed wiring boards 2 may be held in one jig.

(Soldering process)
In the soldering step, for example, a solder (solder paste) 3 is applied to the land 10 of the printed wiring board 2 with a constant thickness using a metal mask, for example. The thickness of the metal mask can be, for example, 0.5 mm or more and 1.5 mm or less.

(Mounting component placement process)
In the mounting component placement step, the mounting component 1 is placed on the land 10 using, for example, a mounter.

(Reflow process)
In the reflow step, the printed wiring board 2 together with the jig is placed in a heating furnace and heated to reflow the solder 3. The reflowed solder 3 causes the terminals 4 of the mounted component 1 to face the respective lands 10 of the printed wiring board 2 by the surface tension.

<Advantages>
According to the mounting structure, since the position of the center of gravity of the land main portion 13 of the land 10 and the position of the center of gravity of the terminal main portion 5 of the terminal 4 coincide with each other, it is possible to appropriately apply the surface tension of the reflowed solder 3. Excellent in mounting accuracy by self-alignment.

[Other embodiments]
The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the appended claims, and is intended to include all modifications within the scope and meaning equivalent to the appended claims. You.

  In the mounting structure, the cover lay of the wiring board may be omitted, and a solder resist patterned so as to open a land portion may be provided instead of the cover lay.

  A plurality of mounting components may be mounted on one wiring board, and the mounting structure can be employed for a part or all of the mounting structure of the plurality of mounting components.

  The mounting components mounted in the mounting structure are not limited to LEDs.

  Hereinafter, the present invention will be described in detail with reference to Examples. However, the present invention should not be construed as being limited based on the description of the Examples.

  In order to verify the effect of the present invention, Tests 1 to 3 in which the same mounting component was mounted on lands having different shapes were performed. In each test, 32 flexible printed wiring boards having the same shape were formed by forming a conductive pattern on one base film. Each flexible printed wiring board was configured to mount ten mounting components. Note that the same LED was used for all the mounted components.

  The LED terminal is composed of a terminal main part having a width of 0.30 mm and a length of 0.51 mm, and a terminal sub part having a width of 0.15 mm and a length of 0.14 mm which is continuous with one end of the terminal main part. And had a substantially L-shape.

<Test 1>
In Test 1, a land of the wiring board was formed with a land main portion having a width of 0.36 mm and a length of 0.57 mm, and a land having a width of 0.15 mm and a length of 0.20 mm continuous to one end side of the land main portion. It was formed in a substantially L-shape having a land sub-portion. Each land was disposed such that the center of gravity of the land main part matched the center of gravity position of the LED terminal main part. In addition, the conductive pattern connects the first wiring portion having a width of 0.10 mm to the center of the other edge of the terminal main portion, and has a width of 0.20 mm to the center of the side edge of the land sub portion opposite to the land main portion. Of the second wiring portion.

  After baking (removing moisture) such a wiring board at 120 ° C. for 1 hour in a thermostat, a 0.8 mm-thick metal mask is placed on the surface of the wiring board, and a solder paste is placed and scraped. A 0.8 mm thick layer of solder paste was formed on each land. Subsequently, the LEDs were mounted using a mounter such that the terminals were located on the lands. Then, the wiring board on which the LED was mounted was placed in a furnace, and heated at 230 ° C. for 140 seconds to reflow the solder, thereby obtaining a prototype of an electronic component on which the LED was mounted.

<Test 2>
In Test 2, a land of the wiring board was formed with a land main part having a width of 0.40 mm and a length of 0.61 mm, and a land having a width of 0.15 mm and a length of 0.24 mm continuous to one end side of the land main part. A prototype of an electronic component was obtained in the same procedure as in Test 1, except that the prototype was formed in a substantially L-shape having a land sub-portion.

<Test 3>
In Test 3, a land of the wiring board was formed with a land main part having a width of 0.34 mm and a length of 0.55 mm, and a land having a width of 0.15 mm and a length of 0.18 mm continuous to one end side of the land main part. A prototype of an electronic component was obtained in the same procedure as in Test 1, except that the prototype was formed in a substantially L-shape having a land sub-portion.

<Shift amount>
For all the LEDs of the prototypes of the electronic components obtained in Tests 1 to 3, the amount of deviation in the length direction from the center of gravity position to the design position was measured.

  The maximum value, minimum value, standard deviation, average value, the process capability index (Cp, Cpk) of the double-sided standard and the process capability index (Cpkl, Cpkl, Cpku) was calculated. The results are shown in Table 1 below.

  In all of Tests 1 to 3, the industrial capability index exceeded 1.33, which is the standard. The relatively high mounting accuracy was achieved by matching the center of gravity of the land main part with the center of gravity of the terminal main part. Probably obtained. Above all, in Test 1 in which the distance between the outer edge of the land main portion and the outer edge of the terminal main portion was set to 30 μm, particularly high mounting accuracy was obtained.

DESCRIPTION OF SYMBOLS 1 Mounting component 2 Printed wiring board 3 Solder 4 Terminal 5 Terminal main part 6 Terminal sub part 7 Base film 8 Conductive pattern 9 Coverlay 10 Land 11 First wiring part 12 Second wiring part 13 Land main part 14 Land sub part 15 Opening

Claims (5)

A mounting structure in which a plurality of terminals of a mounted component are self-aligned on a plurality of lands of a wiring board by solder reflow,
The land and the terminal are formed by combining one or more square shapes in a plane shape,
The center of gravity position of the land main part having the largest area among the one or more squares of the planar shape of the land, and the center of gravity position of the terminal main part having the largest area among the one or more squares of the planar shape of the terminal are as follows. Matching implementation structure.   The mounting structure according to claim 1, wherein a minimum value of a distance between an outer edge of the land main portion and an outer edge of the terminal main portion is 25 μm or more and a maximum value is 35 μm or less. Mounting structure according to claim 1 or claim 2 area of the land main portion is 0.10 mm ² or more 0.30 mm ² or less.   3. The wiring board having a wiring portion connected to the land main portion, and a width of a portion of the wiring portion connected to the land main portion is 0.05 mm or more and 0.20 mm or less. Or the mounting structure according to claim 3.   The mounting structure according to claim 1, wherein the mounting component is a light emitting diode.

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