JP2006237298A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board in which mechanical destruction of a bonding face between a connection pad and a conductor bump and of the conductor bump itself can securely be prevented for long time, even if the connection pad becomes small and the conductor bump is formed of lead-free solder, and which is superior in reliability of mechanical and electric connection with respect to an external electric circuit board. <P>SOLUTION: In the wiring board 9, a loading part where an electronic component is loaded on one main face of an insulating substrate 1 having a wiring conductor and a plurality of connection pads 3 which are electrically connected to the wiring conductors 2 are loaded on the other face. A plurality of convex parts corresponding to the connection pads 3 by one to one are arranged on the other face of the insulating substrate 1, and the connection pads 3 are covered from top faces of the convex parts to sides. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to semiconductor integrated circuit elements such as IC and LSI, LD (semiconductor laser), LED (light emitting diode), PD (photodiode), CCD, line sensor, image semiconductor and other optical semiconductor elements, piezoelectric vibrator, crystal The present invention relates to a wiring board used for mounting a vibrator such as a vibrator and other various electronic components.

  Semiconductor integrated circuit elements such as IC and LSI, LD (semiconductor laser), LED (light emitting diode), PD (photodiode), CCD, line sensor, optical semiconductor element such as image sensor, piezoelectric vibrator, crystal vibrator, etc. Wiring boards on which vibrators and other various electronic components are mounted generally include an insulating base made of an insulating material such as an aluminum oxide sintered body, a glass ceramic sintered body, an aluminum nitride sintered body, and an insulating base. And a plurality of connection pads formed on the main surface of the insulating base.

  Electronic components are usually mounted on the main surface of the insulating base other than the main surface on which the connection pads are formed, and are electrically connected to the wiring conductor via solder or bonding wires. The printed wiring board is completed as an electronic device by sealing electronic components with a resin or a cap as necessary.

  Thereafter, the plurality of connection pads formed on the main surface of the insulating base are connected to the circuit wiring of the corresponding external electric circuit board via solder or the like, whereby the electronic device is mounted on the external electric circuit board.

  In recent wiring boards, the space between adjacent connection pads is reduced according to the demand for miniaturization, and when solder is connected to the circuit wiring of an external electric circuit board, the solder flows out and a solder bridge is used between adjacent connection pads. Short circuit (electrical short circuit) is likely to occur.

  To solve such a problem caused by a short due to the solder bridge, a technique of adjusting the solder volume by a prior test is known.

  In addition, thermal stress is generated due to a difference in thermal expansion coefficient between the insulating base and the substrate of the external electric circuit (hereinafter abbreviated as thermal expansion difference), and this thermal stress causes the joint surface between the solder and the connection pad to There is a problem that mechanical destruction such as a crack is likely to occur in the solder itself, and the reliability of external connection of the wiring board is likely to be lowered.

  For the problem caused by such a difference in thermal expansion coefficient, a through conductor is provided so as to protrude from the inside of the insulating base to the outside of the main surface at the portion where the connection pad is formed. A land conductor is formed so as to cover the connection pad, and solder is bonded to the land conductor, so that a solder bridge between adjacent connection pads is prevented and a sufficient volume of solder is applied to each connection pad. A method is known in which even if a stress due to a difference in thermal expansion is generated, mechanical stress is prevented by absorbing the stress with a solder having a large volume.

In addition, a conductive pad (dummy pad) is formed in a portion of the lower surface of the insulating substrate where the connection pad is not formed, and this conductive pad is connected to the external electric circuit board, and the connection pad and the circuit wiring of the external electric circuit board are connected. The bonding between the electronic component storage package and the external electric circuit board is reinforced by bonding through the same solder as the solder forming the conductive bump, and the mechanical bump such as the conductive bump due to the thermal stress as described above A technique for preventing destruction is known.
JP 2003-100802 A JP 2003-100811 A

  However, in order to prevent a short circuit due to a solder bridge, when adjusting the solder volume by a prior test, there are problems such as a decrease in productivity and a defective product.

  Also, in order to prevent mechanical destruction due to the difference in thermal expansion coefficient, when penetrating conductors are projected on the surface and land conductors are formed so as to cover the penetrating conductors, the penetrating conductors are not projected on the surface. Compared to this method, mechanical destruction can be prevented, but it is difficult to suppress variations in the amount of protrusion of the through conductor. It is easy to induce problems such as difficulty in connecting to the land conductor.

  Furthermore, when a conductive pad is formed at the center of the lower surface of the insulating substrate and bonded to the external electric circuit board, the overall bonding between the electronic component storage package and the external electric circuit board is effectively reinforced. Therefore, although it is possible to suppress mechanical damage on the joint surface between the connection pad and the solder and on the solder itself, a large thermal stress is concentrated along the peripheral edge of the conductive pad. Starting from the peripheral edge of the metal, cracks occur in the joint surface between the conductive pad and the insulating base, the joint surface between the conductive pad and solder, etc., and the effect of reinforcement by the conductive pad is insufficient during long-term use Therefore, there is a risk that mechanical damage is likely to occur on the joint surface between the connection pad and the solder and the solder itself, and the connection reliability to the external electric circuit board tends to be insufficient.

  In particular, with the recent miniaturization of the wiring board (the length of one side is about 2 mm or less), the area of the connection pad is further reduced, the softening temperature is high, and the tin-silver system, tin which is not easily deformed -Since lead-free solder such as silver-copper has been used frequently, the thermal stress acting on the joint part of the conductive pad is increased, and the joint surface between the conductive pad and the solder is cracked. This is likely to occur, and the deterioration of the connection reliability with respect to the external electric circuit board is becoming more remarkable.

  In addition, when lead-free solder or the like is used as the solder, the soldering temperature is high and the thermal stress is larger, so it is effective to cause mechanical damage to the joint surface between the connection pad and the solder or to the solder itself. It was difficult to prevent.

  The present invention has been devised in view of the above-described problems, and the purpose thereof is to reduce the connection pad, even if lead-free solder is used as the solder, the bonding surface between the connection pad and the solder, An object of the present invention is to provide a wiring board excellent in connection reliability with respect to an external electric circuit board capable of effectively preventing mechanical destruction of solder itself or the like.

  The wiring board of the present invention is provided with a mounting portion on which an electronic component is mounted on one main surface of an insulating substrate having a wiring conductor, and a plurality of connection pads electrically connected to the wiring conductor on the other main surface. A plurality of convex portions corresponding to the connection pads on the other main surface of the insulating base, and the connection pads are attached from the top surface to the side surfaces of the convex portions. It is characterized by having made it.

  In the wiring board of the present invention, the plurality of convex portions are arranged from the central region to the outer peripheral region of the insulating base, and the area where the connection pad is attached to the side surface of the convex portion in the outer peripheral region is convex in the central region. It is characterized in that it is larger than the area where the connection pad is attached to the side surface of the part.

  Furthermore, in the wiring board of the present invention, the plurality of protrusions are arranged in a matrix in plan view, and the height of the protrusions gradually increases from the central region to the outer peripheral region of the insulating base. It is characterized by that.

  Still further, in the wiring board according to the present invention, the insulating base has a quadrangular shape, and the plurality of convex portions are arranged in a matrix in plan view, and the shape of the top surface of the convex portion is the insulating base. In the outer peripheral region of the insulating base, an elliptical shape with the diagonal direction of the insulating base as the major axis direction is formed.

  According to the wiring board of the present invention, the mounting portion on which the electronic component is mounted on one main surface of the insulating base having the wiring conductor, and the plurality of connection pads electrically connected to the wiring conductor on the other main surface. The wiring board is provided with a plurality of protrusions corresponding to the connection pads on the other main surface of the insulating base, and the connection pads are attached from the top surface to the side surfaces of the protrusions. Therefore, since the connection pad is attached to the side surface of the convex portion, a large connection area between the connection pad and the solder can be secured, and the connection reliability with the external electric circuit board is increased. Even if the solder volume is increased, the solder with a large volume can be reliably connected with the connection pad applied from the top surface to the side surface of the convex portion, and the solder can be connected between the adjacent convex portions (connection pads). Flowing out is suppressed. Thereby, it is possible to effectively prevent a short-circuit between the connection pads due to a solder bridge or the like.

  In addition, according to the wiring board of the present invention, the plurality of convex portions are arranged from the central region to the outer peripheral region of the insulating base, and the area where the connection pad is attached to the convex side surface of the outer peripheral region is Even if it is connected using more solder in the outer peripheral area where a large thermal stress due to the difference in thermal expansion tends to act, Since the solder wets well on the side of the convex part with a large area, the solder hardly flows out between the adjacent convex parts, effectively preventing the short circuit between the adjacent connection pads and externally connecting the wiring board. It is possible to firmly connect to the electric circuit board, and at the same time, it is possible to more reliably prevent mechanical breakdown due to thermal stress.

  Furthermore, according to the wiring board of the present invention, the plurality of convex portions are arranged in a matrix in plan view, and the height of the convex portions is gradually increased from the central region to the outer peripheral region of the insulating base, Even if more solder is used in the outer peripheral area where a large thermal stress due to the difference in thermal expansion tends to act on the connecting pads arranged in a shape, the area of the convex side surface is wide. Therefore, the connection pads can be deposited in a sufficiently large area. Therefore, the wiring board can be firmly solder-bonded to the external electric circuit board, and mechanical destruction due to thermal stress can be more reliably prevented.

  Still further, according to the wiring board of the present invention, the insulating base is square-shaped, and the plurality of convex portions are arranged in a matrix in plan view, and the shape of the top surface of the convex portion is arranged in the outer peripheral area of the insulating base. Thus, by forming an elliptical shape in which the diagonal direction of the insulating substrate is the major axis direction, the area of the top surface of the convex portion is increased in the outer peripheral area where a large thermal stress due to the difference in thermal expansion tends to act. Can be sufficiently spread and firmly connected, and this can also effectively prevent mechanical breakage due to thermal stress.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a sectional view showing an example of an embodiment of a wiring board according to the present invention, and FIG. 2 is a plan view of the wiring board shown in FIG. In these drawings, 1 is an insulating substrate, 2 is a wiring conductor, and 3 is a connection pad. The insulating substrate 1, the wiring conductor 2 and the connection pad 3 mainly constitute the wiring board 9 of the present invention.

  The insulating substrate 1 is made of an electrically insulating material such as a glass ceramic sintered body, an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, a silicon nitride sintered body, or a silicon carbide sintered body. Become.

  If the insulating substrate 1 is made of, for example, a glass ceramic sintered body, a suitable organic binder and solvent are added to and mixed with glass ceramic raw material powder such as silicon oxide and aluminum oxide to form a slurry, and a doctor blade method. Is used to obtain a plurality of ceramic green sheets. After that, the ceramic green sheets are formed into an appropriate shape by cutting or punching, and a plurality of them are laminated, and finally this lamination is performed. The ceramic green sheet is produced by firing at a temperature of about 1000 ° C. in a reducing atmosphere.

  The insulating substrate 1 is a semiconductor integrated circuit element such as an IC or LSI, an LD (semiconductor laser), an LED (light emitting diode), a PD (photodiode), a CCD, a line sensor, an optical semiconductor element such as an image sensor, a piezoelectric vibrator, It functions as a base for mounting and supporting a resonator such as a crystal resonator and other various electronic components (not shown), and has a mounting portion on which an electronic component (not shown) is mounted. ing.

  In the example of FIGS. 1 and 2, the insulating base 1 has a flat plate shape. However, a concave portion for accommodating an electronic component is formed on the top surface, and the bottom surface of the concave portion is used as a mounting portion. Good.

  The insulating base 1 has a wiring conductor 2 inside or on the surface. One end of the wiring conductor 2 is exposed to the mounting portion, and the other end is led out to the lower surface of the insulating base 1.

  A plurality of connection pads 3 electrically connected to the wiring conductor 2 are formed on the lower surface of the insulating base 1.

  The wiring conductor 2 and the connection pad 3 function as a conductive path for connecting an electronic component mounted on the mounting portion to an external electric circuit. Of the wiring conductor 2, an electrode of an electronic component is electrically connected to a portion exposed to the mounting portion via a bonding wire, solder, or the like, and the connection pad 3 is a conductor made of solder or the like to an external electric circuit (not shown). By connecting via a bump (not shown), the electrode of the electronic component is electrically connected to an external electric circuit.

  The wiring conductor 2 and the connection pad 3 are made of a metal material such as copper, silver, palladium, gold, tungsten, molybdenum, or manganese. For example, when made of copper, copper powder is kneaded with an organic solvent and a binder. It is formed by printing the produced metal paste on a ceramic green sheet to be the insulating substrate 1.

  The connection pad 3 on the lower surface of the insulating base 1 is formed by subjecting the ceramic green sheet to be the insulating base 1 to a process such as punching using a mold.

  In other words, the convex connection pad 3 is formed by laminating the green sheet for the convex portion punched into the shape of the convex portion to be formed on the lower surface of the ceramic green sheet (laminated body) to be the insulating substrate 1. Is done.

  And while mounting an electronic component on the upper surface of the insulation base | substrate 1, the electrode of an electronic component is electrically connected to the exposed part of the wiring conductor 2 via conductive connection materials, such as a solder and a bonding wire, and as needed An electronic device is completed by sealing the electronic component with a lid or a sealing resin.

  In this electronic device, the connection pad 3 is electrically and mechanically connected to the circuit wiring of the external electric circuit board via a conductor bump made of solder or the like, so that the electrode of the electronic component is connected to the wiring conductor 2 and the connection pad 3. And electrically connected to an external electric circuit through the conductor bump.

  In the wiring board 9 of the present invention, the connection pad 3 is convex, and the connection pad itself (metallized layer) is not convex, but has a convex part, to which the connection pad 3 is attached. .

  That is, since the connection pad 3 is deposited from the top surface to the side surface of the convex portion, a large connection area between the connection pad 3 and the solder can be ensured by the amount deposited on the side surface of the convex portion. In order to increase the connection reliability between the wiring board 9 and the external electric circuit board, even if the solder volume is increased, the connection pad 3 in which a large volume of solder is applied from the top surface to the side surface of the convex portion is used. Since it can connect reliably, it can suppress that a solder flows out between adjacent convex parts (connection pad 3), and can prevent the short circuit between connection pads 3 etc. resulting from a solder bridge etc. effectively. .

  In addition, since the deposition area of the connection pad 3 on the convex side surface of the outer peripheral area is larger than the deposition area of the connection pad 3 on the convex side surface of the central area, a large thermal stress due to a difference in thermal expansion acts. Even in the outer peripheral area where there is a tendency to solder, even if more solder is used for connection, the solder will wet well to the side of the convex part with a large deposition area, so that the solder will flow out between the adjacent convex parts The wiring board can be firmly connected to the external electric circuit board while effectively preventing the short circuit between the adjacent connection pads 3, and at the same time, the mechanical breakdown caused by the thermal stress is further reduced. It can be surely prevented.

  Furthermore, since the height of the convex portion of the connection pad 3 is gradually increased from the central region of the insulating substrate 1 to the outer peripheral region, it is caused by the difference in thermal expansion with respect to the connection pads 3 arranged in a matrix. Even if the connection is made using more solder in the outer peripheral region where a large thermal stress tends to act, since the area of the side surface of the convex portion is wide, the connection pad 3 is also deposited in a sufficiently large area. be able to. Therefore, the wiring board can be firmly solder-bonded to the external electric circuit board, and mechanical destruction due to thermal stress can be more reliably prevented.

  Furthermore, by making the shape of the top surface of the convex portion into an elliptical shape with the diagonal direction of the insulating substrate 1 as the major axis direction in the outer peripheral region of the insulating substrate 1, a large thermal stress due to the difference in thermal expansion acts. Since the area of the top surface of the convex portion becomes large in the outer peripheral area where solder tends to spread, the solder can be sufficiently spread and firmly connected, and this also effectively prevents mechanical breakage due to thermal stress. Can do.

  According to the wiring substrate 9 of the present invention as described above, it is possible to effectively reinforce the bonding by solder between the connection pad 3 and the wiring conductor of the external electric circuit substrate. As a result, the bonding between the connection pad 3 and the wiring conductor of the external electric circuit board, the bonding between the connection pad 3 and the solder is maintained for a long time, and the connection between the wiring board 9 and the external electric circuit board is maintained. Can be reinforced. Therefore, it is possible to reliably prevent mechanical damage on the joint surface between the connection pad 3 and the conductor bump, the conductor bump itself, and the like over a long period of time. It is possible to provide the wiring substrate 9 having excellent connection reliability.

  Moreover, it is preferable that the convex part of the connection pad 3 is an ellipse shape by planar view, and is formed in multiple numbers by the matrix form. As a result, thermal stress does not concentrate on a part of the convex portion of the connection pad 3, and mechanical damage occurs on the joint surface between the connection pad 3 and the conductor bump, the conductor bump itself, and the like. Therefore, it is possible to provide a wiring board excellent in connection reliability with respect to an external electric circuit board, which can be reliably prevented over the entire area.

  Note that the height of the side surface of the convex portion of the connection pad 3 is preferably 0.2 mm or more. If it is less than 0.2 mm, the effect of reinforcing the bonding of solder or the like to the connection pad 3 may be insufficient, and the electrical and mechanical connection between the connection pad 3 and the circuit wiring can be effectively performed over a long period of time. This is because it becomes difficult to reinforce.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

It is a top view which shows an example of embodiment of the wiring board of this invention. It is sectional drawing of the wiring board of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Wiring conductor 3 ... Connection pad 9 ... Wiring board

Claims (4)

A wiring board comprising a mounting portion on which an electronic component is mounted on one main surface of an insulating substrate having a wiring conductor, and a plurality of connection pads electrically connected to the wiring conductor on the other main surface. A plurality of convex portions corresponding to the connection pads on the other main surface of the insulating base are provided, and the connection pads are attached from the top surface to the side surfaces of the convex portions. Wiring board. The plurality of convex portions are arranged from the central region to the outer peripheral region of the insulating base, and the area of the connection pad attached to the convex side surface of the outer peripheral region is the area of the connection pad attached to the convex side surface of the central region The wiring board according to claim 1, wherein the wiring board is larger than the wiring board. The plurality of convex portions are arranged in a matrix in plan view, and the height of the convex portions gradually increases from the central region to the outer peripheral region of the insulating base. 2. The wiring board according to 2. The insulating base has a quadrangular shape, and the plurality of convex portions are arranged in a matrix in a plan view, and the shape of the top surface of the convex portion is formed in the outer peripheral area of the insulating base. 4. The wiring board according to claim 1, wherein the wiring board has an elliptical shape with a diagonal direction as a major axis direction.

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