JP2001345542A - Structure for mounting electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure reliability by increasing bonding strength with respect to the substrate of a relatively large electronic component, and to provide a wiring board mounted with an electronic component, having increased bonding density with respect to the wiring board. SOLUTION: Electrode pads 5, having nearly the same size and shape as those of terminal electrodes 4 located at the bottom face of a rectangular electronic component 2, are provided on the wiring board 1. Extended electrode pads 6 are formed from electrode pads which are disposed at each corner of the electronic component 2 or nearby. A solder fillet is formed on respective end face near each corner of the electronic component 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component mounting structure, and more particularly to an electronic component mounting structure for mounting electronic components on a wiring board at high density.

[0002]

2. Description of the Related Art In recent years, telephones, audio products, various video equipment, notebook personal computers, and the like have been portable, and further reductions in size and weight have been pursued. In particular, as electronic components are being miniaturized and highly integrated, the wiring board is also designed with a high-density mounting board design with no wasted space by devising wiring patterns and electrode pads on the surface.

As a method for mounting electronic components on a wiring board, a reflow soldering method is generally used. That is, electrode pads are formed on the surface of a wiring board made of glass epoxy resin, glass ceramic, or the like, and cream solder is applied thereon by a printing method or the like, and electronic components such as chip capacitors, chip resistors, and oscillators housed in a package. The terminal electrode portion of the component is placed, passed through a reflow furnace, heated to a predetermined temperature, and soldered.

FIG. 7 shows a mounting structure of a conventional electronic component.
As shown in the drawing, an electrode pad 25 having substantially the same size as a terminal electrode (not shown) of an electronic component 23 (shown by a two-dot chain line) on a wiring board 24, and a lead electrode pad 26 extending outside the electrode pad 25. Are formed. This is because a reliable connection can be achieved even when the mounting position of the electronic component 23 is slightly displaced, and a self-alignment effect of returning the electronic component to a predetermined position due to the surface tension of the molten solder can be exhibited even if the mounting position is slightly displaced. is there. Further, the melted solder creeps up along the end surface of the electronic component 23 to form a so-called solder fillet to increase the bonding strength to the wiring board 24.

In order to mount electronic components of various sizes on a wiring board at a high density, it is necessary to arrange electrode pads of adjacent electronic components as close as possible without interfering with each other. A filletless mounting that achieves solder mounting only on the bottom surface of the electronic component is desirable to satisfy this requirement. By using filletless mounted electronic components, it becomes possible to mount components on the surface of a wiring board without gaps between the electronic components in extreme cases.

[0006]

However, when examining the bonding strength of such a filletless mounted electronic component to a wiring board, the strength is lower than that of a conventional mounting method in which a fillet is formed.

As a method for evaluating the bonding strength of parts, a bending strength test of a substrate is used. In the board bending strength test, the electronic component is mounted on two horizontal bars spaced at a predetermined interval of, for example, 90 mm with the component mounting surface facing down. (For example, a sink of 3 mm), and a test is performed to determine whether or not an abnormality occurs at the solder connection point.

In the conventional mounting method in which a fillet is formed, a force for pulling the terminal electrode on the end face downward is generated as the substrate is bent. That is, a shearing force parallel to the terminal electrode surface on the end face is applied.
On the other hand, in the case of the filletless mounting, a peeling force perpendicular to the electrode surface is applied to the outer edge of the terminal electrode provided on the bottom surface of the electronic component. Comparing the terminal electrodes of the same size, the bonding strength with the fillet formed parallel to the terminal electrode shows a much larger value, and the filletless mounting is weaker in the board bending strength test.

In particular, the board bending strength of electronic components having large external dimensions is reduced. This is because as the component size increases, the distance between the terminal electrodes of the electronic component increases, and a bending moment proportional to the distance between the terminal electrodes is applied to the terminal electrode, and the distance between the terminal electrode on the bottom of the electronic component and the electrode pad on the wiring board is increased. This is considered to be because the force for peeling off becomes large, and peeling occurs relatively easily.

As described above, when a filletless electronic component is employed to increase the mounting density of the electronic component, if the variation of the component and the variation of the assembling process are not strictly controlled, the stress applied to the wiring board at the time of assembling and the equipment may be reduced. Electronic components with low board joint strength will cause open failure or dropout between the terminal electrode and the electrode pad of the wiring board due to external vibration etc. at the stage of incorporating it into the electronic device, making it an electronic device with low connection reliability Be in danger.

The present invention has been made in view of the above problems, and has a substrate bonding density close to that of filletless mounting of electronic components.
It is an object of the present invention to provide a wiring board having an electrode pad structure of a wiring board having high substrate bonding strength and high connection reliability.

[0012]

In order to solve the above-mentioned problems, the present invention provides an electronic component having a plurality of terminal electrodes formed on a bottom surface of a rectangular electronic component at a position facing the terminal electrodes. An electronic component which is mounted on a wiring board on which an electrode pad having substantially the same size as the terminal electrode is formed, and which joins each terminal electrode of the electronic component and each electrode pad of the wiring board via solder Mounting structure, wherein, among a plurality of terminal electrodes formed on the bottom surface of the electronic component, a part of a terminal electrode formed at or near a corner of the electronic component is connected to the electronic component via a lead-out portion. An electronic component, which extends to an end surface of the component, and a part of an electrode pad of a wiring board facing a terminal electrode on which the lead-out portion is formed extends to outside of the electronic component. Provide the mounting structure of

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a surface mounting electrode pad according to the present invention will be described below in detail with reference to the drawings. FIGS. 1 and 2 relate to a first embodiment of the present invention. FIG. 1 shows a situation in which a chip type electronic component 2 housed in a ceramic package 3 is mounted on the surface of a wiring board 1 and soldered. FIG. FIG. 2 is a pattern diagram showing a situation when the electronic component 2 and another electronic component are arranged close to each other. 2
The dashed-dotted line is the external position of the electronic component 2 to be soldered and joined.

The wiring board 1 is composed of a glass epoxy laminated board,
Electrode pads connected to terminal electrodes of chip components are provided on the surface of the substrate by etching a copper foil. The chip components S1 to S9 are relatively small electronic components, and electrode pads of equal or slightly larger size are formed on the wiring board 1 so as to face a plurality of terminal electrodes on the bottom surface.

The electronic component 2 has a rectangular shape as shown in FIG. 6, and is formed by mounting a SAW filter element, an oscillation circuit and the like inside a ceramic package 3 made of alumina or the like. On its bottom surface, for example, six terminal electrodes 4-
1 to 4-6 are formed. In the center of the terminal electrode 4-2 or the terminal electrode 4-5, the end face through holes 4-20, 4-
50 are formed, and the through-holes 4-10, 4-30, 4-40, and 4-6 at the corners of the electronic component 2 are also formed.
0 are formed, and all of them are drawn out from the terminal electrodes 4-1 to 4-6 to the side surface.

The end face through holes 4-10 to 4-60
After laminating ceramic green sheets to form through holes at predetermined positions and forming an electrode film on the inner surface,
It is cut through the center line of the through hole to form a part of the terminal electrode. End face through hole 4-10-4-6
Some of the zeros reach the upper surface and are electrically connected to a metal lid (not shown) for seam sealing on the upper surface to give the package a shielding effect.

The end face through holes 4-10, 4-3
Although 0, 4-40, and 4-60 are formed along the side wall of the corner of the electronic component, the invention is not limited to this, and they may be formed on the end face near the corner.

FIG. 2 shows the structure of the electrode pads provided on the surface of the wiring board 1. The portion indicated by the dotted line is the mounting position of each electronic component 2. Terminal electrodes 4-1 to 4-6 of electronic component 2
The electrode pads 5 (5-1 to 5-6) having substantially the same size as the terminal electrodes 4-1 to 4-6 are provided on the wiring board 1 facing the. The electrode pads 5-1 to 5-6 are formed inside the region X of the electronic component 2 indicated by the dotted line, and small extension electrodes 6 (6-1 to 6-6) extending outside the region X are provided. I have. The shape of the extended electrode 6 surrounds the corners of the electrode pads 5-1, 5-3, 5-4 and 5-6 at the corners of the electronic component 2 in an L-shape with a width of 0.1 to 0.5 mm. It is formed as follows. The electrode pad 5 on which the extension electrode 6 is formed as described above faces the terminal electrodes 4-1, 4-3, 4-4 and 4-6 formed at or near the corners of the bottom surface of the electronic component 2. Is formed on the electrode pad.

Although the extension electrode 6 extends from the corner of the electrode pad 5, it is not limited to this, and may extend to a corner other than the corner of the electrode pad 5. In this case, it is necessary to match the positions of the end face through holes 4-10, 4-30, 4-40, and 4-60 with the extension electrodes 6. In short, of the plurality of terminal electrodes 4, they extend to the electrode pads facing the terminal electrodes 4-1, 4-3, 4-4 and 4-6 formed at or near the corners of the bottom surface of the electronic component 2. As long as the electrode 6 can be formed, the formation position of the extension electrode 6 does not matter.

For bonding the wiring board 1 and the electronic component 2, cream solder is printed on the electrode pads 5-1 to 5-6 and the extended electrodes 6-1 to 6-6 of the wiring board 1, The wiring board 1 is placed by placing the component 2 and passing it through a reflow furnace.
Can be electrically and mechanically joined to the terminal electrodes 4 of the electronic component. The solder melted at this time is applied to the extension electrodes 6-1, 6-3, 6- 6 at the corners.
4, 6-6 to terminal electrodes 4-1 at the corners of the electronic component,
4-3, 4-4, 4-6 end face through-hole 4-10,
A fillet 7 is formed in a shape in which the solder creeps up along 4-30, 4-40, and 4-60.

The bonding state between the terminal electrodes 4-2 and 4-5 and the electrode pads 5-2 and 5-5 is determined by the electrode pads 5-2 and 5-5.
Since -5 does not extend from under the electronic component, it is not apparent in appearance as shown in FIG. However, by observing the fillet formation states formed on the extension electrodes 6-1, 6-3, 6-4, and 6-6 at the corners, it is possible to estimate the solder connection state of these terminal electrodes sandwiched therebetween. It is possible to easily confirm the working conditions of the solder reflow.

When a fillet is formed at a corner as shown in FIG. 1, compared with a case without a fillet,
The solder joint strength can be increased 2 to 10 times. These are through holes 4-10, 4-30, 4-40, 4
Since solder is attached to −60 to form a solder fillet, a shearing force acts on the end face through-hole electrode in a direction parallel to the electrode surface during the board bending test. Since this durability is generally higher than the peel strength with respect to the electrode surface when there is no fillet, the bonding strength is expected to increase.

By forming a fillet at a corner portion of the terminal electrode, the joining strength can be made more effective. That is, as shown in FIG. 5, when the length of the side is 2D, the length of the diagonal line is 2L, and the force acting on the solder fillet 7 of the electronic component 2 by bending the board is F, the DF of the side direction is not bent. The bending moment is LF for diagonal bending. The magnitude of the bending moment generated by actual substrate bending is between DF and LF. Therefore, it is most effective to form a fillet at the corner where the maximum bending moment is generated to provide strength. For example, if the shape of the electronic component is a square base, L =
Although the bending moment is 1.4D and a large bending moment is generated, the joint strength can be effectively increased by forming a fillet there.

By applying the extended electrodes of the electrode pads to the corners in this manner, it is possible to form a region having no extended electrodes in the middle of the side, thereby leading the wiring pattern and other chips. A space in which components can be arranged close to each other is secured. Thereby, high-density mounting can be achieved.

Here, the example in which the extended electrodes 6 of the electrode pads 5 are provided at the four corners of the electronic component has been described. However, even if the extended electrodes 6 are provided at at least one corner, the molten state of the solder is confirmed. In addition, the substrate bending test strength can be partially increased. It may be provided at two or three diagonal positions.

Although the case where the terminal electrodes are formed at the corners of the electronic component has been described, even when the terminal electrodes are not at the corners, the extension electrodes are provided at the terminal electrodes furthest from the plurality of terminal electrodes. It is important to provide.

FIG. 3 shows another embodiment of the present invention. Although the shape of the extension electrode of the electrode pad is L-shaped at the corner of the terminal electrode, the same effect can be obtained even if the narrow electrode pad extends in the direction in which the diagonal line of the electronic component is extended. be able to. At this time, the electrode width is 0.1 to 0.3 mm and the length is 0.1 to 0.5 mm. Thereby, there is an advantage that a solder fillet is formed to secure the bonding strength of the substrate and the area of the electrode pad can be further reduced.

FIG. 4 shows an embodiment in which the present invention is applied to an electrode of a two-terminal electronic component. Electrode pad 15-
Reference numerals 1 and 15-2 correspond to the positions of the terminal electrodes, and at the corners on both sides of each of the electrode pads 15-1 and 15-2, the extension electrodes 16-1, 16-2 and 16- 3, 16
-4. The same effect as the embodiment of FIG. 1 can be obtained. A two-terminal electronic component is a general electronic component in which electrode films are formed on upper, lower, and end surfaces at both ends. Also for these, the mounting strength of the substrate can be increased by forming the extension electrode and mounting the substrate.

As described above, by forming the extended electrodes only at the corners, a space is formed between them, and it becomes possible to arrange the adjacent electronic components close to each other, thereby increasing the degree of freedom in design. it can.

Although the size of the extension electrode is not always larger than that of the conventional one, the formation of the extension electrode exerts a self-alignment effect of correcting the displacement of the electronic component from the electrode pad during mounting by solder reflow. be able to. This is particularly effective due to the presence of overhangs at the corners.

[0031]

Embodiment A specific embodiment will be described with reference to FIG. In FIG. 1, the wiring board 1 is a glass epoxy laminated board having a thickness of 0.75 mm. The electronic component 2 is a crystal oscillator in which a crystal unit and an integrated circuit are incorporated in an alumina ceramic package 3 and has a bottom surface of 3.5 mm * 3.5 mm and a thickness of 1.0 mm rectangular parallelepiped. is there. The upper surface is sealed by seam welding a lid made of Kovar.

The terminal electrodes 4-1, 4-2,..., 4-6
Are formed on the bottom surface of the ceramic package 3 near the front and rear end faces, and are 0.8 mm square electrode pads.
Their spacing is 0.5 mm. 0.2 mm overhangs from the terminal electrode on the bottom side with a through hole on the end face,
An electrode whose outer side has a length of 0.4 mm is formed. As the electrode material, nickel plating is plated with gold.

The electrode pads of the wiring board 1 correspond to the terminal electrodes of the ceramic package, and each electrode dimension is 0.8 mm * 0.8 mm. It is a copper foil electrode subjected to a flux treatment. The extension electrode of the electrode pad 5 is 0.2
It is millimeter wide.

The creamy 6 is applied to the electrode pads of the wiring board 1.
/ 4 solder is applied, and the electronic component 2 is placed on the
Keep solder for 2 seconds to melt and join solder.

For comparison of the bonding strength of the substrate, the case of an electrode pad (0.8 mm * 1.3 mm) having a length of 0.5 mm extending from the end face of a commonly used electronic component was compared with that of the present invention. Electrode pad (0.8 mm * 0.8 mm electrode pad, 0.
The test pattern consists of three types of electrode pads: 2 mm overhang length, 0.4 mm on each side, and an electrode pad without any extension electrodes (0.8 mm * 0.8 mm). The formed wiring board is prepared. The wiring board is a paper phenol board having a thickness of 1.6 mm.

In the board bending test, a wiring board having the above-mentioned electronic component mounted on its lower surface is placed on a round bar on which electronic components are mounted and arranged at an interval of 90 mm. Is pressed from above to gradually sink the center of the wiring board. The amount of sinking when an abnormality occurs in the terminal electrode is measured and compared. The occurrence of abnormalities is monitored for abnormalities in the electric circuit, and the terminal is checked for any peeling off with a microscope.

As a result, the one having no extension electrode is destroyed by 1 to 3 mm, whereas the present invention in which the extension electrode is provided at the corner portion is 4 to 5 mm. When the electrode was provided, the value was 5 to 6 mm. In practical use, the strength that can withstand impacts such as dropping is 3
Mm or more, which indicates that the present invention has sufficient strength.

[0038]

As described above in detail, the present invention is directed to a part of a terminal electrode formed at or near a corner of the electronic component among a plurality of terminal electrodes formed on the bottom surface of the electronic component. To extend to the end face of the electronic component through the lead portion, and because a part of the electrode pad of the wiring board facing the terminal electrode on which the lead portion is formed extends to the outside of the electronic component. Therefore, the electrode pad protruding from the region of the wiring board facing the electronic component and the terminal electrode at or near the corner of the electronic component are joined by reflow soldering, whereby a solder fillet is formed at the corner of the electronic component. Is formed so that the bonding strength of the substrate can be sufficiently increased, and another electronic component can be arranged close to the side surface of the electronic component while avoiding a corner of the electronic component. As a result, high reliability against drop impact and the like can be achieved, and high-density mounting can be achieved, thereby contributing to miniaturization of electronic devices.

A solder fillet is formed from the extension of the electrode pad on the wiring board to the through hole electrode at the end face of the corner of the electronic component, and the corner of the electronic component is moved toward the extension of the electrode pad by the surface tension of the solder. The pulling self-alignment effect (self-position correction function) is exhibited,
Since the electronic components roughly mounted on the wiring board by the ordinary chip mounter are joined at predetermined positions by reflow solder mounting, a mounting process that can be easily assembled with an inexpensive device becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a pattern diagram showing a structure of an electrode pad on a wiring board in the first embodiment of the present invention.

FIG. 3 is a pattern diagram showing a structure of an electrode pad according to a second embodiment of the present invention.

FIG. 4 is a pattern diagram showing a structure of an electrode pad according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a state in which a bending moment is generated in a solder fillet on a side surface of an electronic component during a board bending test in an electronic component on a wiring board.

FIG. 6 is a perspective view illustrating a structure of a terminal electrode on a bottom surface of the electronic component used in the first embodiment of the present invention.

FIG. 7 is a diagram illustrating a structure of an electrode pad of a wiring board on which a conventional electronic component is mounted.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wiring board 2, 12 ... Electronic component 3 ... Ceramic package 4, 4-1, 4-2, 4-3, 4-4, 4-5, 4-6
... Terminal electrodes 5, 5-1, 5-2, 5-3, 5-4, 5-5, 5-
6, 15-1, 15-2 ... electrode pad 6, 6-1, 6-2, 6-3, 6-4, 6-5, 6
6, 16-1, 16-2, 16-3, 16-4: extended electrode pad 7: solder fillet S1 to S9: mounting position of other chip components

Claims (1)

[Claims] An electronic component having a plurality of terminal electrodes formed on a bottom surface of a rectangular electronic component, and a wiring board having an electrode pad substantially the same size as the terminal electrode formed at a position facing the terminal electrode. A mounting structure for an electronic component, which is mounted on the terminal and bonded to the respective terminal electrodes of the electronic component and the respective electrode pads of the wiring board via solder, wherein a plurality of electronic components are formed on a bottom surface of the electronic component. Of the terminal electrodes, a part of the terminal electrode formed at or near the corner of the electronic component extends to the end face of the electronic component via a lead portion, and the lead portion is formed. A part of an electrode pad of a wiring board facing a terminal electrode extending to the outside of the electronic component.