JP2007294649A - Surface-mounting electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, when connecting nearly rectangular mount electrodes formed on the bottom face of a package of a surface-mounting electronic device and lands on a circuit board by solder, large stress is applied to solder connecting portions located away from the center of the bottom face of the electronic device due to heat cycles, vibrations, shocks, etc., which easily causes cracks. <P>SOLUTION: The surface-mounting electronic device comprises a package 2 whose bottom face has a nearly rectangular shape, and nearly rectangular mount electrodes 5 formed on the bottom face of the package along with at lest one side, respectively. At two corners at a side proximate with one side of the bottom face of the package in the corners of the mount electrodes, a linear chamfered part 5a is provided which is formed by cutting the corners in a right triangle shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an improvement of a mounting electrode formed on the bottom surface of a surface mount electronic device, and in particular, for solving a problem that a crack is formed by a stress applied to a solder portion when the mounting electrode is soldered on a circuit board. Regarding technology.

As a surface-mount type electronic device, for example, a device in which various circuit components are mounted on a wiring pattern formed on the surface of an insulating substrate (printed substrate) provided with a mounting electrode at the bottom is known. Examples of such surface mount electronic devices include piezoelectric devices such as crystal resonators, crystal filters, and crystal oscillators. A surface-mount type crystal resonator or crystal filter has a crystal resonator element (an element in which an excitation electrode is formed on a crystal substrate) mounted in a surface recess of a package having a mounting electrode at the bottom, and the crystal resonator element The concave portion on the insulating substrate is hermetically sealed with a metal lid.
A surface-mount type piezoelectric device includes a substantially rectangular mounting electrode on a bottom surface of a substantially rectangular package, and is surface-mounted by connecting the mounting electrode to a land formed on the upper surface of a circuit board using solder.

By the way, in a state where the piezoelectric device is solder-connected on the circuit board, the larger the solder connection portion located farther from the center point of the bottom surface of the substantially rectangular package, the larger the mechanical stress is received. For this reason, a crack may be formed in the solder connection part far from the center point depending on the use conditions such as the application, use environment, and installation location of the piezoelectric device. In other words, when used in a harsh environment, such as when a crystal resonator is mounted on an in-vehicle circuit board, it is exposed to high and low temperatures in addition to vibration and impact. The durability of the solder connection due to the heat cycle becomes a problem.
As one of the specifications required for a crystal resonator, a heat cycle test (−40 to +125)
However, since the stress is likely to concentrate at one place in the solder connection part farthest from the center of the bottom of the package, cracks due to heat cycles occur in this part. It is easy to produce defective products that do not meet the specifications.

In Patent Document 1, the occupancy rate of the mounting electrode with respect to the rectangular bottom area of the container body of the crystal resonator is 5
A surface-mount crystal resonator is disclosed in which the bonding strength is improved by disposing the pair of mounting electrodes in the width direction close to 0% or close to the crystal piece and the thermal shock resistance is eliminated. According to this, since the joint area due to the solder becomes large, fatal connection failure is less likely to occur, and on the other hand, the large joint area increases stress strain due to the difference in thermal expansion coefficient, and the solder connection part This causes a problem that cracks are likely to occur. Furthermore, there is a problem that the layout flexibility of the mounting electrodes on the bottom surface of the package is reduced due to an excessive increase in the area occupied by the mounting electrodes on the bottom surface of the package. In addition, since the capacitance between the terminals of the package increases,
This is disadvantageous in terms of characteristics such as frequency variable sensitivity characteristics.

In order to deal with such problems, Patent Document 2 describes the shape of the outer edge of the rectangular mounting electrode formed along the corners and the edges of the bottom surface of the rectangular package from the center point of the package bottom surface. By adopting an arc shape along the arc formed by r, heat cycle, vibration,
A technique is disclosed in which solder is not present at a specific portion of the bottom surface of the package where cracks are most likely to occur due to impact or the like.
However, if a part of the mounting electrode is chamfered in a circular arc shape, the shape of the land on the circuit board side as an object on which the electronic device is mounted is also designed to be a partial arc shape in accordance with the shape of the mounting electrode. The need increases. It is difficult to design a wiring pattern including lands on a circuit board in an arc shape or a curved shape, resulting in an increase in the number of circuit board manufacturing steps and a decrease in the degree of freedom in wiring pattern design.

On the other hand, the shape of the mounting electrode and the shape of the land on the circuit board are different from each other when the mounting electrode having the arc-shaped portion is solder-connected to the rectangular land not having the arc-shaped portion corresponding to the mounting electrode shape. If there is too much difference in area or shape during this period, excess solder is generated and solder balls are easily formed, or the ideal fillet shape cannot be stably formed as a solidified shape of solder. Arise.
JP 2004-064701 A JP 2006-5027 A

As described above, if the shape and area of the mounting electrode provided on the bottom of the package of the surface-mount device are significantly different from the shape of the land on the circuit board, the design work of the wiring pattern on the circuit board side will increase. There is a problem that a solder ball formed by excess solder on the land moves out of the land to cause a short circuit and other problems, or the fillet shape is not stably formed when the solder is solidified. .

The present invention has been made in view of the above. When a substantially rectangular mounting electrode provided on the bottom of a package of a surface-mount electronic device is soldered to a land on a circuit board, the heat cycle, vibration, impact, etc. In order to solve the problem that a large stress is applied to the solder connection part located far from the center point of the bottom surface of the electronic device and the solder is likely to crack, a straight chamfered part is formed on a part of the mounting electrode. And providing a surface mount type electronic device having a mounting electrode shape capable of preventing complication of land pattern design change by minimizing changes to the shape of the land pattern on the circuit board. It is an object.

In order to solve the above problems, a surface-mount electronic device according to the present invention includes a package having a substantially rectangular bottom surface shape, and a substantially rectangular mounting electrode formed along at least one end side of the bottom surface of the package. In the surface-mount type electronic device, the corner electrodes are formed by cutting out the corner portions at two corners on the side close to the one end side of the bottom surface of the package among the corner portions of the mounting electrodes. A straight chamfered portion is provided.

When connecting the mounting electrode and the land of the circuit board by solder, the solder part located farther from the center of the bottom of the package is more likely to be cracked due to damage caused by stress concentration due to heat cycle or impact. Become. Attempts have been made to prevent solder cracks that are likely to occur when solder is placed in the cut part by cutting off a part of the mounting electrode in a place where stress distortion is large. The land side on the circuit board side needs to be processed into an arc shape corresponding to the arc-shaped mounting electrode portion. Since it is technically difficult to process the land pattern into an arc shape or a curved shape, there are problems in terms of productivity and cost when manufacturing a circuit board.

In the present invention, of the four corners of the substantially rectangular mounting electrode, the chamfered portion extends in an obliquely linear manner at two corners along the one end edge of the bottom surface of the package (portion far from the package center point). Therefore, it is possible to increase the productivity by preventing the formation of the land pattern on the circuit board side from being arc-shaped or curved, while preventing cracks in the solder connection portion due to stress concentration.

In the surface mount electronic device according to the present invention, the length of the vertical side of the bottom surface of the package is set to L.
1, the length of the horizontal side is L2, and the width of the side along the vertical side of the two orthogonal sides of the right-angled triangular cut portion of the mounting electrode arranged along the vertical side is It is characterized by L2 / L1 = w1 / w2 where w1 is the length of the other side and w2.
There is no limitation on the shape of the excised part when the mounting electrode is excised into a right triangle, but for example, if the above relationship is satisfied, only the mounting electrode part corresponding to the stress concentration part can be effectively excised. it can.

Further, the surface-mount type electronic device according to the present invention has a length L1 of a vertical side of the bottom surface of the package.
, And the length L2 of the lateral side and the widths w1 and w2 of each side of the cut portion are expressed as L2 / L1 = w
1 / w2 = 1/1.

The surface mount electronic device according to the present invention is characterized in that two or more of the mounting electrodes are arranged along one end side of the bottom surface of the package.

Further, the present invention is characterized in that the surface mount electronic device is a piezoelectric device.
The surface-mounted electronic device of the present invention can be widely applied as a mounting electrode structure in a package of a piezoelectric device such as a piezoelectric vibrator, a piezoelectric oscillator, or a SAW device.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
In the following embodiments, a surface-mount type piezoelectric device, particularly a crystal resonator (piezoelectric resonator) will be described as an example of a surface-mount type electronic device.
1A, 1B, and 1C are a front view, a bottom view, and an enlarged view of a mounting electrode showing a configuration of a surface-mount type crystal resonator according to an embodiment of the present invention.

This crystal resonator 1 includes a crystal resonator element (an element in which an excitation electrode is formed on a crystal substrate) 10 in an upper surface recess 3 of an insulating container 2 formed by laminating sheet-like insulating materials such as ceramic sheets. While accommodating, the structure which sealed the recessed part 3 of the insulating container 2 with the metal cover 4 is provided.
Two vertical sides 2 constituting the substantially rectangular bottom surface (package bottom surface) of the insulating container (package) 2
a and two lateral sides 2b, which are opposite to each other, in this example, are provided with mounting electrodes 5 at positions along the central portion of each vertical side 2a, and the crystal resonator element 10 is provided inside the recess 3. The two internal pads 6 are electrically connected to each other, and each internal pad 6 is electrically connected to the corresponding mounting electrode 5. The outer side of each mounting electrode 5 may be in contact with each corresponding vertical side 2a as shown, or may be spaced apart.

When this crystal resonator 1 is surface-mounted on a circuit board or other printed circuit board 15,
The mounting electrodes 5 are made to correspond to the lands 16 of the printed circuit board (circuit board) 15 in a one-to-one relationship and then connected by solder 17.
At this time, in order to prevent the solder connection portion located farthest from the center point C on the bottom surface of the insulating container 2 from being damaged by stress due to heat cycle or the like, in the present invention, the outside of each mounting electrode 5 is The corners are chamfered in a straight line.

That is, as shown in FIG. 1B and FIG. 1C, each corner portion of each corner portion of each of the substantially rectangular mounting electrodes 5 has two corner portions on the side close to the vertical side 2a of the package bottom surface. Is cut into a right triangle (isosceles triangle) to provide a linear chamfered portion (chamfered side) 5a. In this way, the angle formed between each chamfered portion 5a provided at each of the two corners of the mounting electrode 5 and the corresponding vertical side 2a by forming the cutout portion 20 having a right triangular shape with the chamfered portion 5a as the hypotenuse. θ is set to be equal.

The shape of the cut portion 20 or the value of the angle θ may be in any range,
For example, the length of the vertical side 2a of the bottom surface of the package is L1, the length of the horizontal side 2b is L2, and two orthogonal sides of the right-angled triangular cutout 20 of the mounting electrode arranged along the vertical side. When the width of the side (first side) along the vertical side 2a is w1, and the width of the side (second side) along the horizontal side 2b is w2, "L2 / L1 = w1 / W2 "is preferably satisfied.

The shape of each side of the cutout 20 in the mounting electrode of FIG. 1 is L2 / L1 = w1 / w2 =
1/1.
For example, the length L1 of the vertical side 2a of the bottom surface of the package is 2.5 mm, and the length L2 of the horizontal side 2b
Is 3.2 mm, the width w1 of the first side and the width w2 of the second side of the cut portion 20 are:
Both are preferably about 0.3 mm.

Further, as shown in another embodiment of FIG. 2, when L2 / L1 = w1 / w2 = 1/1 is not satisfied, for example, the length L1 of the vertical side 2a of the package bottom surface is 2.5 mm, and the horizontal side 2b Length L2
Is 3.2 mm, the width w1 of the first side and the width w2 of the second side of the cut portion 20 are:
A range of 1 to 0.3 mm is preferable.

Next, FIG. 3 is a package bottom view showing the structure of a mounting electrode according to a modified embodiment of the present invention. The mounting electrode in this embodiment includes two mounting electrodes 5 along each opposing vertical side 2a. The juxtaposed configuration is characteristic. Three or more mounting electrodes may be disposed along each vertical side 2a, or two mounting electrodes may be disposed on one end side and one on the other end side.

Since a terminal structure having four or more mounting electrodes can be realized in this way, the package including the mounting electrodes can be applied to a piezoelectric oscillator such as a crystal oscillator.
That is, the surface mount type piezoelectric oscillator is realized by mounting an oscillation circuit component inside or outside the package of the piezoelectric vibrator, but the piezoelectric oscillator requires four or more mounting electrodes. . Therefore, by realizing the arrangement of the mounting electrodes as shown in FIG. 3, it is possible to construct a surface mount package for the piezoelectric oscillator.

FIG. 4 shows the chamfered dimensions w1, w of the cut portion 20 in the mounting electrode according to the embodiment of FIG.
It is the graph which showed the relationship between the value of 2 and the distortion amplitude of the stress which generate | occur | produces in the solder joint part on a mounting electrode. According to this graph, it is clear that when the chamfered dimensions w1 and w3 are both 0.3 mm, the distortion amplitude is 2/3 as compared with the rectangular mounting electrode in which the cut portion 20 does not exist, As a result, cracks are less likely to occur in the solder joint.

As described above, according to the present invention, a straight chamfered portion (right triangle) is formed by cutting out two corners along the edge of the bottom surface of the package out of corners of each of the substantially rectangular mounting electrodes. 5a (corresponding to the hypotenuse of the cut portion of the shape). The cut portion 20 is a position farthest from the center point C on the bottom surface of the package and corresponds to a place where various stresses are likely to concentrate. By adopting a configuration in which the corners of the mounting substrate corresponding to locations where stress is likely to concentrate are cut in advance, FIG.
When each mounting electrode 5 is soldered onto the land 16 of the printed circuit board 15 as shown in FIG.
It is possible to disperse the stress that has been easily concentrated in one place (the portion corresponding to the cut portion 20) in the past, and the connection portion farthest from the center point C of the container bottom is damaged by the stress generated by heat cycle, impact, etc. No cracks occur.

Further, the shape of the land on the circuit board side for joining the mounting electrode 5 having the linear chamfered portion 5a may be a conventional rectangle, or a linear shape corresponding to the shape of the chamfered portion 5a. It is good also as a structure provided with the chamfering part. In any case, it is not necessary to adopt a configuration having a curved portion or an arc-shaped portion as the shape of the land on the circuit board side, thereby preventing an increase in the number of wiring pattern formation steps on the circuit board side and increasing the degree of design freedom. Can be planned.

Further, the shape and area of the mounting electrode 5 provided on the bottom surface of the package are the same as the land 16 on the circuit board 15.
By remarkably different from this shape, it is possible to eliminate a problem that a solder ball formed by excess solder on the land moves out of the land and short-circuits between the separated patterns, or causes other problems. Furthermore, the fillet shape is easily formed stably when the solder is solidified.

The mounting electrode structure of the present invention can be applied to mounting electrodes of all types of surface mount electronic devices, not limited to surface mount piezoelectric devices such as crystal resonators, crystal filters, and crystal oscillators.

(A), (b) and (c) are the front view, bottom view, and enlarged view of a mounting electrode which show the structure of the surface mount-type crystal resonator based on one Embodiment of this invention. It is a bottom view which shows the mounting electrode structure which concerns on other embodiment of this invention. It is a package bottom view which shows the structure of the mounting electrode which concerns on the deformation | transformation embodiment of this invention. FIG. 2 is a graph showing the relationship between the value of the chamfered dimension of the cut portion in the mounting electrode according to the embodiment of FIG. 1 and the strain amplitude of stress generated at the solder joint on the mounting electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface mount type electronic device (piezoelectric vibrator), 2 ... Package, 2a ... Vertical side, 2b ... Horizontal side, 3 ... Recessed part, 4 ... Cover member, 5 ... Mounting electrode, 5a ... Chamfer part, 15 ... Circuit Substrate, 16 ... land, 17 ... solder, 20 ... excision.

Claims (5)

In a surface mount electronic device comprising a package having a substantially rectangular bottom shape, and a substantially rectangular mounting electrode formed along at least one end side of the bottom surface of the package,
A straight chamfered portion formed by cutting the corner corner into a right triangle shape is provided at two corner corners on the side close to one end side of the package bottom surface of each corner corner of the mounting electrode. A surface-mount type electronic device characterized by that. The length of the vertical side of the bottom surface of the package is L1, and the length of the horizontal side is L2.
Of the two orthogonal sides of the right-angled triangular cut portion of the mounting electrode arranged along the vertical side, the width of the side along the vertical side is w1, and the length of the other side is w2. When
2. The surface mount electronic device according to claim 1, wherein L2 / L1 = w1 / w2. The relationship between the length L1 of the vertical side and the length L2 of the horizontal side of the bottom surface of the package, and the widths w1 and w2 of each side of the cut portion,
3. The surface mount electronic device according to claim 2, wherein L2 / L1 = w1 / w2 = 1/1. The surface-mount type electronic device according to claim 1, 2 or 3, wherein two or more of the mounting electrodes are arranged along one end side of the bottom surface of the package. The surface-mount type electronic device according to claim 1, wherein the surface-mount type electronic device is a piezoelectric device.

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