JP2013131513A - Surface-mounted electronic device and mounting method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-mounted electronic device capable of maintaining strength of a joint portion by suppressing reduction in solder joining strength caused by void formation without reducing as much as possible an area of a joint surface of a terminal pad and a mounting terminal, and to provide a mounting method of the same.SOLUTION: The mounting method of the surface-mounted electronic device comprises steps of: providing a small hole 10 which captures a bubble at each central part of a plurality of mounting terminals 5 of a surface-mounted electronic device 100 which is mounted by connecting to a terminal pad 9 of a mounting substrate 200; and joining both by a solder reflow process while maintaining a surface of the terminal pad 9 formed on the mounting substrate 200 to be flat.

Description

  The present invention relates to a mounting structure of an electronic device for surface mounting, and in particular, a surface that prevents a crack or the like of a solder layer connecting a terminal and a terminal pad of a mounting board after surface mounting and enables a strong connection. The present invention relates to a mountable electronic device and a mounting method thereof.

  With the widespread use of mobile information terminals such as mobile phones and so-called tablets or various on-vehicle electronic devices, many of the electronic components mounted on these devices are small and low-profile devices called surface mounting devices. It came to be considered as a special part. A surface-mounted device has a flat connection terminal (surface-mounted terminal) on its abdominal surface (surface facing the mounting substrate) and faces a terminal pad (also referred to as a land or land pattern) formed on the surface of the mounting substrate. -Connected via solder film in a surface-compatible manner. Here, a crystal resonator will be described as an example of the surface mount device. However, the present invention is not limited to this, and can be similarly applied to crystal-related parts such as crystal oscillators and SAW filters, laminated circuit parts, and various discrete parts.

  Since the quartz crystal resonator described as an example here is small and light, it can be used alone as a reference source for frequency or time, or incorporated in various electronic devices by being incorporated in an oscillation circuit. In recent years, in electronic devices such as in-vehicle devices that have a large change in impact and temperature environment, solder cracks due to differences in thermal expansion coefficient due to changes over time (heat cycle) or stress changes such as substrate strain due to external force application Therefore, there is a demand for preventing damage to the substrate or the component body.

  FIG. 5 is a plan view for explaining a conventional example of a planar mounting type mounting terminal provided in an electronic device. Note that the mounting substrate is provided with terminal pads, which are also referred to as lands or land patterns, depending on the mounting terminals of the surface mounting type electronic component to be mounted. In the figure, reference numeral 5 (5a, 5b, 5c, 5d) is a mounting terminal formed on the abdominal surface of the electronic device 100, and 11 is a groove provided in the mounting terminal. The mounting terminals 5 (5a, 5b, 5c, 5d) are joined to each of terminal pads provided on a mounting substrate (not shown) by solder reflow.

  In FIG. 5, the mounting terminals 5 (5a, 5b, 5c, 5d) are provided with vertical and horizontal grooves 11 that intersect through the center and open to the outside at their ends. With this configuration, bubbles generated in the melted solder layer during the solder reflow process when the mounting terminals 5 (5a, 5b, 5c, 5d) are joined to the terminal pads formed on the mounting substrate with a solder film. Is released to the outside from the groove to prevent generation of voids formed by hardening of the solder (see Patent Document 1).

JP 2009-141455 A

  The mounting terminals of the surface mounting type electronic component are joined via a solder film welded to a terminal pad provided on the mounting substrate. The bonding strength increases as the area of the bonding surface between the mounting terminal and the terminal pad increases as long as the welding strength of the solder film is equal. Therefore, if the mounting terminal is provided with a groove whose both ends are open to the outside as in the prior art described above, the area of the joint surface with the terminal pad is reduced, and the joint strength may be reduced accordingly.

  In addition, if such a groove exists in the mounting terminal, the stress is concentrated in the groove due to the application of external force or temperature stress to the mounting board or mounting component, and the bonding force distribution becomes unbalanced. There is a risk that cracks may occur in the separation of the parts or in the joints, resulting in destruction of the fixed parts, the electronic components, or the mounting substrate.

  An object of the present invention is to solve such a problem in the prior art, and is due to the formation of voids without reducing the area of the joint surface between the mounting terminal of the electronic device and the terminal pad of the mounting substrate as much as possible. An object of the present invention is to provide a surface-mount type electronic device that can suppress a decrease in solder joint strength and maintain the strength of a joint portion, and a mounting method thereof.

  In order to achieve the above object, the present invention provides a small hole for capturing bubbles in each central portion of a plurality of mounting terminals of a surface mounting type electronic device that is connected to and mounted on a terminal pad of a mounting board. The surface of the terminal pad to be formed is kept flat and both are bonded by a solder reflow method. That is, the small holes provided only in the plurality of mounting terminals provided in the electronic device pass through the mounting terminals and reach the surface of the container body of the electronic device. That is, the surface of the mounting substrate is exposed at the bottom of the small hole. The container body of the electronic device is made of an insulating material such as a glass epoxy plate or a ceramic plate. In the embodiments of the present invention to be described later, one made of a ceramic plate is used.

  In the case where the joint surface between the mounting terminal of the electronic device and the terminal pad of the mounting substrate is flat, that is, when the groove as described above is not formed, bubbles generated in the solder film due to melting of the solder are melted solder film. Experience has shown that there is a tendency to gather in the middle of The technical idea of the prior art is to prevent voids from being formed in the solidified solder film by discharging the generated bubbles to the outside through the grooves formed in the mounting terminals. On the other hand, in the present invention, bubbles generated by melting of the reflow solder are trapped in small holes provided at the center of a plurality of mounting terminals provided in the electronic device.

  By providing a small hole in the electronic device for capturing air bubbles on the mounting terminal side, even if the amount of air bubbles is large to some extent, the air bubbles are less likely to wet the solder than the terminal pad side where the solder is present. It tends to be closer to the surface side (bottom of small holes). The molten solder wets and flows over the entire surface of the continuously flat terminal pad of the mounting substrate below the small hole, and remains spread over the entire surface of the terminal pad. Therefore, the reduction of the joint area between the two is limited to the small hole provided in the mounting terminal, and the reduction of the joint area is suppressed to the minimum.

It is explanatory drawing of Example 1 of the mounting method and its mounting substrate of the surface mounted type electronic device by this invention. It is explanatory drawing of the crystal oscillator which is an example of the electronic device in this invention. It is explanatory drawing of the structural example of the quartz crystal vibrating piece which comprises the crystal oscillator which is an example of the electronic device in this invention. It is a top view which shows the principal part of the mounting terminal explaining Example 2 of the electronic device which concerns on this invention. It is a top view explaining the prior art example of the mounting terminal of the surface mounting type provided in an electronic device. It is a top view which shows the principal part of the mounting terminal explaining Example 3 of the electronic device which concerns on this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings of the examples.

  FIG. 1 is an explanatory view of a mounting method of a surface-mount type electronic device according to the present invention and a mounting substrate of a first embodiment. FIG. 1A is a cross-sectional view of a principal part showing a state where a surface-mount type electronic device is mounted on a mounting substrate, FIG. 1B is a plan view of a mounting terminal formed on the electronic device, and FIG. It is a schematic diagram which expands and shows the A section of the figure (a) which expands and shows the adhering state of a terminal and a terminal pad.

  In FIG. 1A, a surface-mount type electronic device 100 (hereinafter referred to as a crystal resonator 100) is mounted on a mounting substrate 200. A plurality of mounting terminals 5 are provided on the abdominal surface (mounting surface) of the electronic device 100, and a plurality of land patterns corresponding to the mounting terminals, that is, terminal pads 9, are provided on the main surface (mounting surface) of the mounting substrate 200. Is formed. All the surfaces (outer surfaces) of the terminal pads 9 on the mounting substrate 200 side are flat surfaces. On the other hand, as shown in FIG. 1B, a small hole 10 is formed in the center portion of the mounting terminal 5 on the crystal resonator 100 side. The small hole 10 penetrates the mounting terminal 5 toward the container body of the crystal unit 100 and reaches the surface of the container body. In the present embodiment, the mounting terminal 5 of the crystal unit 100 shown by the solid line in FIG. 1B is shown smaller than the terminal pad 9 of the substrate 200, which is general. However, some of the mounting terminals 5 are larger than the terminal pads 9.

  To mount this type of electronic device on a mounting device board, a solder film 12 is applied to the terminal pad 9 of the mounting board 200, the electronic device 100 is mounted on the terminal pad 9, and the mounting terminal 5 is the terminal pad 9. A reflow process is performed using a heating furnace or a hot plate in a state in which it is positioned so as to coincide with this position. In the reflow process, the solder film 12 is melted and spreads on the surface of the mounting terminal 5 of the electronic device 100, and the solder film is filled between the terminal pads 9. Thereafter, the electronic device 100 is mounted on the substrate 200 as the solder film cools and hardens.

  In this solder reflow process, the solvent contained in the solder film is vaporized and bubbles are generated in the solder film. The bubbles move in the molten solder film toward the center of the terminal pad 9 and stay in the small holes 10 provided in the terminal pad 9. In the process of cooling the solder film 12 at the later stage of the reflow process, the bubbles 8 are reduced, and the solder film is hardened in a state where the void 80 is formed in the portion where the bubbles are present.

  FIG.1 (c) is a schematic diagram which expands and shows the A part of the same (a). As described above, the solder melted in the solder reflow process covers substantially the entire surface of the terminal pad 9 and flows on the surface of the mounting terminal 5 so as to circumvent the periphery of the small hole 10. It is filled between the mounting terminals 5. Since the bottom surface of the small hole 10 (the surface of the container body of the electronic device) has low wettability with respect to the molten solder, the solder hardly flows into the bottom surface of the small hole 10. Therefore, even if the bubbles are in contact with the surface of the terminal pad 9, the solder exists between the bubbles in the contacted portion and the terminal pad 9. As a result, the bubbles are stopped by approaching the quartz resonator 100 side of the small hole 10.

  When the temperature of the solder is lowered and the solder film 12 is cooled and hardened, a void (space) 80 is formed in a portion where bubbles exist. As the temperature of the solder film decreases, the bubbles shrink, and the solder film still exists in the region indicated by arrow B of the terminal pad 9. The void 80 is formed so as to be away from the terminal pad 9 and close to the crystal unit 100 side, is smaller than the original bubble and is formed on the crystal unit side, and as a result, a void is formed in this portion. The small hole 10 is not limited to a round hole, and may be a polygon more than a triangle, but it is desirable that the corner be as obtuse as possible. In FIG. 1C, the void 80 is illustrated so as to protrude greatly toward the terminal pad 9 than the mounting terminal 5, but the void 80 is formed at a position lower than the surface of the mounting terminal 5. In some cases.

  FIG. 2 is an explanatory diagram of a crystal resonator which is an example of an electronic device according to the present invention. 2A is a side view partially showing a cross section, and FIG. 2B is a plan view showing an abdominal surface which is a mounting surface. In this crystal resonator 100, the crystal resonator element 2 is installed in the internal space (also referred to as a recess or a cavity) of the container body 1 that is rectangular in plan view. The container body 1 is formed of a multilayer ceramic substrate, and four mounting terminals 5 (5a, 5b, 5c, 5d) are provided on the back surface as a mounting surface. The mounting terminal 5 is also referred to as an external terminal of the crystal resonator, and is bonded to a terminal pad 9 formed on a mounting substrate of a device on which the crystal resonator is mounted by reflow processing of a solder film. The solder pad 9 is a portion also called a land pattern connected to a wiring / circuit pattern formed on the mounting substrate. The small holes 10 (10a, 10b, 10c, 10d) are formed in the mounting terminals 5 (5a, 5b, 5c, 5d).

  The container body 1 is a laminate of a bottom wall 1a and a frame wall 1b, and a conductive adhesive 4 (4a, 4b) is attached to a crystal terminal (not shown) provided on the inner bottom surface of a recess 1c surrounded by the frame wall 1b. It is fixed with. The concave portion 1 c to which the crystal vibrating piece 2 is attached is sealed by fixing a lid body 7 made of a metal plate through a metal film 6. In FIG. 2B, the orientation identifying part 50 is formed only on the mounting terminal 5c. The orientation identification unit 50 is an index for identifying the orientation at the time of mounting when the crystal unit 100 is mounted by an automatic machine.

  FIG. 3 is an explanatory diagram of a configuration example of a crystal resonator element that constitutes a crystal resonator that is an example of an electronic device according to the present invention. The quartz crystal vibrating piece 2 has excitation electrodes 2 (2a, 2b) formed on the front and back of a thin rectangular quartz piece 20 having a substantially rectangular shape. The excitation electrode 2 (2a, 2b) is drawn to one end of the quartz crystal vibrating piece 2 by the extraction electrode 3 (3a, 3b). This end is fixed to a crystal terminal provided on the inner bottom surface of the recess 1c using the conductive adhesive 4 (4a, 4b) described above.

  According to the first embodiment, the solder film 12 that is interposed between the terminal pad 9 formed on the mounting substrate 200 and the mounting terminal 5 of the crystal unit 100 and bonds the two is provided in the small hole 10 provided in the mounting terminal 5. Also on the surface of the terminal pad 9 at the position of. Therefore, even if a small hole is formed in the mounting terminal of the electronic device, there is little decrease in the bonding area between the two, and there is no significant decrease in bonding strength. In addition, by forming a small hole in the center of the mounting terminal, the imbalance of the bonding strength of the connection area due to external force application or temperature stress is suppressed, and cracks and poor connection of electronic devices are avoided. The

  FIG. 4 is a plan view showing a main part of a mounting terminal for explaining an embodiment 2 of the electronic device according to the present invention. In the second embodiment, a plurality of small holes 10 are provided in a mounting terminal of a crystal resonator 100 which is an example of an electronic device. FIG. 4A shows a case where nine small holes are formed inside the mounting terminal 5 (5a, 5b, 5c, 5d). FIG. 4B shows the mounting terminal 5 (5a, 5b, 5c, 5d). 5 small holes are formed inside. 4 (a) and 4 (b) show only the mounting terminal 5a and only the small hole 10a.

  In this embodiment, the mounting terminals 5 (5a, 5b, 5c, 5d) of the crystal unit 100 are formed with small holes 10 (10a, 10b, 10c, 10d) arranged in a balanced manner at the respective central portions. ing. One of these small holes is preferably provided at the center of the mounting terminal 5. Furthermore, it is possible to make variations such as making the small hole located at the center larger than other small holes. Since the other steps and configuration of the second embodiment are almost the same as those of the first embodiment, the description thereof is omitted.

  Also in the second embodiment, the solder film 12 that is interposed between the terminal pad 9 formed on the mounting substrate 200 and the mounting terminal 5 of the crystal unit 100 and joins them is formed by the small hole 10 provided in the mounting terminal 5. Even at the position, it exists on the entire surface of the terminal pad 9. Therefore, even if a plurality of small holes are formed in the mounting terminal of the electronic device, the reduction of the joint area between the two is relatively small, and the joint strength is not significantly reduced. For this reason, cracks in the bonding region and a decrease in bonding strength due to external force application and temperature stress are suppressed, and the occurrence of defective mounting of the crystal resonator is avoided.

  FIG. 6 is a plan view showing a main part of a mounting terminal for explaining an embodiment 3 of the electronic device according to the present invention. In Example 3, the mounting terminal 5 (5a, 5b, 5c, 5d) of the crystal unit 100 was formed with a cross-shaped small hole 10 at each central portion thereof. The cross-shaped arms may be gradually narrowed toward the outside to form a substantially star shape. Although the cross-shaped small hole 10 shown in FIG. 6 is shown to be relatively large for the sake of explanation, the size of the mounting terminal 5 is actually smaller than the illustrated relative size. In any case, it is desirable to make each corner as obtuse as possible. Since the other steps and configuration of the third embodiment are substantially the same as those of the first and second embodiments, the description thereof is omitted.

  Also in the third embodiment, the solder film 12 that is interposed between the terminal pad 9 formed on the mounting substrate 200 and the mounting terminal 5 of the crystal unit 100 and joins them is formed by the small hole 10 provided in the mounting terminal 5. Even at the position, it exists on the entire surface of the terminal pad 9. Therefore, even if a plurality of small holes are formed in the mounting terminal of the electronic device, the reduction of the joint area between the two is relatively small, and the joint strength is not significantly reduced. For this reason, cracks in the bonding region and a decrease in bonding strength due to external force application and temperature stress are suppressed, and the occurrence of defective mounting of the crystal resonator is avoided.

  The present invention is not limited to the mounting of the crystal resonator on the mounting substrate described in each embodiment, but can be similarly applied to mounting of a crystal oscillator, a SAW filter, a discrete component, and other surface-mount type electronic devices. .

  DESCRIPTION OF SYMBOLS 1 ... Container main body, 1a ... Bottom wall, 1b ... Frame wall, 1c ... Recessed part, 2 ... Crystal vibrating piece, 2a, 2b ... Excitation electrode, 3 (3a, 3b) ... Extraction electrode, 4 (4a, 4b) ... Conductive adhesive, 5 (5a, 5b, 5c, 5d) ... Mounting terminal, 50 ... Direction identification part, 6 ... Metal film , 7 ... Lid, 8 ... Bubble, 80 ... Void, 9 (9a, 9b, 9c, 9d) ... Terminal pad, 10 (10a, 10b, 10c, 10d) ... Small Hole: 100 ... Electronic device (quartz crystal), 200 ... Mounting substrate.

Claims (6)

A surface mount type electronic device having a plurality of mounting terminals for mounting a surface mount type electronic device on a mounting substrate,
A surface-mount type electronic device having a small hole that penetrates from the surface of the mount terminal to the surface of the container body of the electronic device at each central portion of the mount terminal. In claim 1,
A surface-mount type electronic device, wherein one small hole is formed in each terminal pad. In claim 1,
A plurality of the small holes are formed in each terminal pad. In claim 3,
One of the plurality of small holes is formed at the center of each terminal pad. A plurality of mounting terminals for mounting a surface mounting type electronic device on a mounting substrate is formed, and a small hole that penetrates at the center of each mounting terminal and from the surface of the mounting terminal to the surface of the container body of the electronic device A surface-mount type electronic device mounting method for mounting a surface-mount type electronic device having a terminal pad on a mounting substrate,
Covering the upper layer of the terminal pad of the mounting substrate, to form a solder film for bonding the mounting terminal of the electronic device by reflow,
By heating and reflowing the solder film with the mounting terminal of the electronic device positioned on the terminal pad of the mounting substrate, bubbles generated by melting of the solder film are retained in the small holes of the mounting terminal. ,
A method for mounting a surface-mount type electronic device, wherein the solder film is solidified to form voids due to the bubbles in the small hole portions. In claim 5,
A method for mounting a surface mount electronic device, comprising: forming a solder film bonded to the terminal pad between the void formed in the small hole portion of the terminal pad and the terminal pad of the mounting substrate.

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