JP3810335B2 - Wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wiring board for mounting electronic components such as semiconductor elements and piezoelectric vibrators.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, wiring boards for mounting electronic components such as semiconductor elements and piezoelectric vibrators are generally made of a substantially square plate-like ceramic material and have an electronic component mounting portion on the upper surface, and the electronic of the insulating substrate. A plurality of wiring layers led out from the component mounting portion to the side surface through the inside of the insulating base, and a frame-shaped metal layer formed on the upper surface of the insulating base so as to surround the electronic component mounting portion; A plurality of connection pads formed on the outer peripheral portion of the lower surface of the insulating base, and a plurality of castellation conductors formed on the side surface of the insulating base and electrically connecting each wiring layer and each connection pad. The electronic component is mounted on the electronic component mounting portion of the insulating base, and each electrode for signal and grounding of the electronic component is electrically connected to each wiring layer via a conductive connecting member such as a bonding wire. After that, a metal lid made of iron-nickel-cobalt alloy or iron-nickel alloy is joined to the frame-like metal layer on the upper surface of the insulating base with a brazing material or the like so as to cover the electronic component. By sealing the electronic component, an electronic device is obtained.
[0003]
Such an electronic device is mounted on an external electric circuit board by connecting a connection pad formed on the outer peripheral portion of the lower surface of the insulating base to a wiring conductor of the external electric circuit board via solder such as tin-lead solder, and at the same time an electronic component These electrodes are electrically connected to an external electric circuit through the wiring layer, the castellation conductor and the connection pad.
[0004]
Among the castellation conductors, at least a grounding electrode of an electronic component is connected (usually about 20 to 50% of all connection pads), a part of which is formed on the upper surface of the insulating base. The metal layer is led out so that the frame-like metal layer can be grounded.
[0005]
Each of the castellation conductors is formed in a direction perpendicular to the side surface of the insulating base, and the castellation conductor connected to the frame-like metal layer is formed from the bottom surface to the top surface on the side surface of the insulating base.
[0006]
[Problems to be solved by the invention]
However, recently, various electronic devices contain lead such as tin-silver-bismuth, tin-silver-copper-bismuth, etc. in place of tin-lead solder which is conventionally used to prevent adverse effects on the environment and human body. The so-called lead-free solder is used to connect to an external electric circuit board, and such a lead-free solder is easier to flow at the time of melting than a conventional tin-lead solder. When mounting on the board, the solder crawls up to the frame-like metal layer on the upper surface of the insulating base or the metal lid attached to the frame-like metal layer through the castellation conductor, and as a result, the connection pad of the insulating base. In addition, the amount of solder interposed between the wiring conductors of the external electric circuit is extremely small, and the electronic device cannot be firmly mounted on the external circuit board.
[0007]
In addition, lead-free solders such as tin-silver-bismuth-based solders tend to have lower bonding strength to connection pads due to segregation of components such as bismuth compared to conventional tin-lead solders, and connection pads due to downsizing of the wiring board The connection area of the electronic device is tinned to the wiring conductor of the external electric circuit board. -After the electronic device is mounted on the external electric circuit board after being connected via a lead-free solder such as silver-bismuth, when the electronic device and the external electric circuit board are heated, the insulating base of the electronic device and the external electric circuit board And thermal stress (horizontal shear stress) due to the difference in thermal expansion coefficient between them occurs along with the lead-free solder and the joint interface between the lead-free solder and the connection pad. Acts in the horizontal direction, resulting in mechanical damage such as cracks along the bonding interface with the lead-free solder connection pads, thereby reducing the connection reliability of the electronic device to the external electric circuit board. It also had the disadvantage of.
[0008]
The present invention has been devised in view of the above disadvantages, and its purpose is to firmly connect the connection pad to the wiring conductor of the external electric circuit board via lead-free solder, thereby firmly connecting to the external electric circuit board. Another object of the present invention is to provide a wiring board that can be mounted with high reliability.
[0009]
[Means for Solving the Problems]
The wiring board of the present invention has an electronic component mounting portion on the upper surface and a frame-shaped metal layer surrounding the mounting portion, an insulating base having a connection pad on the outer periphery of the lower surface, and formed on the side surface of the insulating base, A wiring board including a castellation conductor for connecting the connection pad and a frame-shaped metal layer, wherein the castellation conductor is a first region derived from the connection pad and a first region derived from the frame-shaped metal layer. The first region and the second region are displaced in the width direction of the side surface of the insulating base and are connected via an internal wiring layer formed inside the insulating base, and the connection A convex portion or a concave portion is formed on the surface of the pad.
[0010]
The wiring board of the present invention is characterized in that the convex portion or the concave portion is formed over a region of 20% or more of the surface of the connection pad.
[0011]
According to the wiring board of the present invention, the castellation conductor that electrically connects the frame-shaped metal layer formed on the upper surface of the insulating base and the connection pad formed on the lower surface of the insulating base is led out from the connection pad. 1 region and a second region derived from the metal layer, and since the first region and the second region are shifted in the width direction of the side surface of the insulating base, the connection pad and the wiring conductor of the external electric circuit Even if they are joined using lead-free solder, lead-free solder does not crawl up to the frame-like metal layer or metal lid through the castellation conductor. A sufficient amount of solder can be interposed between the wiring conductors and the wiring board (electronic device) can be bonded to the external electric circuit board very firmly.
[0012]
At the same time, according to the wiring board of the present invention, since the convex portion or the concave portion is formed on the surface of the connection pad, it is caused by the difference in thermal expansion coefficient between the insulating base and the external electric circuit board. Even if thermal stress is generated and this acts in the horizontal direction near the joint interface between lead-free solder and lead-free solder and connection pads, this stress is distributed along the convex or concave surfaces of the connection pads. It can be mitigated, and it is possible to effectively prevent the occurrence of cracks and the like along the joint interface with the lead-free solder connection pad. Further, since the convex portion or the concave portion is formed, the bonding area between the connection pad and the solder can be increased. As a result, the wiring board can be mounted on the external electric circuit board firmly and with high reliability.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail with reference to the accompanying drawings.
FIGS. 1A to 1C show an embodiment in which the wiring board of the present invention is applied to a package for housing a semiconductor element for housing a semiconductor element, wherein 1 is an insulating substrate, 2 is a wiring layer, 3 is A frame-shaped metal layer, 4 is a connection pad, and 5 is a castellation conductor. The insulating substrate 1, the wiring layer 2, the frame-shaped metal layer 3, the connection pad 4 and the castellation conductor 5 form a wiring substrate 7 for mounting the semiconductor element 6.
[0014]
The insulating substrate 1 is made of an electrically insulating material such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, or a glass ceramic sintered body, and a mounting portion on which a semiconductor element 6 is mounted. The semiconductor element 6 is bonded and fixed to the mounting portion via an adhesive such as glass, resin, or brazing material.
[0015]
When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, a suitable organic binder and solvent are added to and mixed with raw material powders such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide to form a mud-like shape. Next, the ceramic slurry is formed into a sheet shape by a sheet forming technique such as a conventionally known doctor blade method or calendar roll method to obtain a ceramic green sheet (ceramic raw sheet) having a predetermined shape. It is manufactured by laminating a plurality of green sheets and firing them at a temperature of about 1600 ° C. in a reducing atmosphere.
[0016]
The insulating base 1 is formed with a plurality of wiring layers 2 from the periphery of the mounting portion on which the semiconductor element 6 on the upper surface is mounted to the side surface through the inside of the insulating base 1. The signal and ground electrodes act as conductive paths for connecting to the connection pads 4, and the signal and ground electrodes of the semiconductor element 6 are electrically connected via bonding wires 8 at one end on the mounting portion side. Connected.
[0017]
The wiring layer 2 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium, etc., and a metal paste obtained by adding and mixing an appropriate organic binder or solvent to the metal powder such as tungsten is used as the insulating substrate 1. The ceramic green sheet to be formed is preliminarily printed and applied in a predetermined pattern by a well-known screen printing method so that the ceramic green sheet is deposited from the upper surface of the insulating substrate 1 to the side surface through the inside of the insulating substrate 1.
[0018]
The insulating base 1 is covered with a frame-shaped metal layer 3 so as to surround the mounting portion on which the semiconductor element 6 is mounted on the upper surface of the insulating substrate 1, and the frame-shaped metal layer 3 is a metal lid described later. It acts as a base metal layer when the body 9 is attached to the insulating substrate 1, and is formed of metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium.
[0019]
A metal lid 9 is brazed and attached to the frame-shaped metal layer 3 via a brazing material, whereby the semiconductor element 6 mounted on the semiconductor element mounting portion of the insulating base 1 is hermetically sealed from the atmosphere. Will be.
[0020]
The frame-shaped metal layer 3 is formed on the upper surface of the insulating substrate 1 so as to surround the semiconductor element mounting portion by the same method as the wiring layer 2 described above.
[0021]
Further, a plurality of connection pads 4 are formed on the outer peripheral portion of the lower surface of the insulating base 1, and the connection pads 4 are connected to the wiring conductor of the external electric circuit board via lead-free solder, and the signal of the semiconductor element 6 Each electrode for grounding and grounding is electrically connected to an external electric circuit.
[0022]
The connection pad 4 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, or palladium, and is formed in a predetermined shape on the outer periphery of the lower surface of the insulating substrate 1 by the same method as that for the wiring layer 2 described above. .
[0023]
Furthermore, the insulating base 1 is coated with a plurality of castoration conductors 5 (conductors provided with a semicircular recess in the side face of the insulating base 1 and formed in the recess) on the side surface, The castellation conductor 5 serves to electrically connect the wiring layer 2 and the connection pad 4.
[0024]
The castellation conductor 5 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium, etc., and a semicircular recess is formed on the side surface of the ceramic green sheet serving as the insulating substrate 1 by a punching method. A metal paste obtained by adding and mixing a suitable organic binder or solvent to a metal powder such as tungsten in the recess is preliminarily printed in a predetermined pattern by a well-known screen printing method, and then predetermined on the side surface of the insulating substrate 1. It is formed into a shape.
[0025]
A part of the castellation conductor 5 connected to the wiring layer 2 electrically connected to the grounding electrode of the semiconductor element 6 is led out to the frame-like metal layer 3 on the upper surface of the insulating base 1. The metal layer 3 is grounded.
[0026]
The wiring layer 2, the frame-shaped metal layer 3, the connection pad 4, and the castoration conductor 5 have corrosion resistance such as nickel and gold, bonding property of the bonding wire 8, solder wettability, etc. on the exposed surface. If a plating layer made of a good metal is applied, the oxidative corrosion of the wiring layer 2 and the frame-shaped metal layer 3 can be effectively prevented and the metal lid 9 on the frame-shaped metal layer 3 can be prevented. And the connection of the connection pad 4 to the external electric circuit board is ensured and strong. Therefore, the wiring layer 2, the frame-shaped metal layer 3, the connection pad 4, and the castellation conductor 5 are made of a metal having good corrosion resistance such as nickel and gold, bonding properties, solder wettability, etc. on the exposed surface. It is preferable to deposit by a plating method. In particular, it is preferable to sequentially deposit, for example, a nickel plating layer having a thickness of 1 to 10 μm and a gold plating layer having a thickness of 0.05 to 3 μm.
[0027]
In this case, the thickness of the gold plating layer may be different depending on the part to be deposited, the crystal orientation of the gold plating layer, etc. For example, the crystal orientation in the X-ray diffraction of the gold plating layer is as much as possible to the (111) plane. In addition, the entire region including the region to which the bonding wire 8 is connected may be about 0.3 to 1 μm, and only the region for soldering should be as thin as about 0.3 μm or less. -Generation | occurrence | production of the gold brittle intermetallic compound may be suppressed, and you may make it improve the reliability of soldering further.
[0028]
Thus, according to the wiring substrate 7 of the present invention, the semiconductor element 6 is mounted on the mounting portion on the upper surface of the insulating base 1 and the signal and ground electrodes of the semiconductor element 6 are connected to the wiring layer 2 via the bonding wires 8. Thereafter, a metal lid body 9 made of iron-nickel-cobalt alloy, iron-nickel alloy, or the like is joined to the frame-like metal layer 3 on the upper surface of the insulating base 1 via a brazing material or the like. Thus, the semiconductor device 6 is hermetically sealed to complete an electronic device (semiconductor device) as a product.
[0029]
The semiconductor device is mounted on the external electric circuit board by joining the connection pads 4 on the outer periphery of the lower surface of the insulating base 1 to the wiring conductor of the external electric circuit board via lead-free solder, and simultaneously the signal of the semiconductor element 6 The electrodes for grounding and grounding are electrically connected to the wiring conductor of the external electric circuit board.
[0030]
In the wiring board 7 of the present invention, the caster conductor 5a connecting the frame-like metal layer 3 and the connection pad 4 out of the caster conductor 5 is led out from the connection pad 4 as shown in FIG. And the second region 5c derived from the frame-shaped metal layer 3, and the first region 5b and the second region 5c are displaced in the width direction of the side surface of the insulating base 1 and are internally formed inside the insulating base 1. It is important to be electrically connected via the wiring layer 10.
[0031]
The castellation conductor 5a connecting the frame-shaped metal layer 3 and the connection pad 4 is divided into a first region 5b derived from the connection pad 4 and a second region 5c derived from the frame-shaped metal layer 3, Is shifted in the width direction of the side surface of the insulating base 1, even if the connection pad 4 and the wiring conductor of the external electric circuit are joined using lead-free solder, the lead-free solder is transmitted through the castellation conductor 5a. As a result, a sufficient amount of solder can be interposed between the connection pad 4 and the wiring conductor of the external electric circuit board. The (electronic device) can be bonded to the external electric circuit board very firmly.
[0032]
The dividing position of the first region 5b and the second region 5c of the castellation conductor 5a that connects the frame-shaped metal layer 3 and the connection pad 4 depends on the type of solder used and the thickness of the insulating substrate 1. The wiring layer 2 may be appropriately determined according to the design convenience of the wiring layer 2. For example, the castellation conductor 5 a has a semicircular shape with a diameter of 0.3 mm to 0.7 mm, and tin-silver solder as the solder. In the case of using the first region 5b, the length of the first region 5b may be in the range of 0.3 mm to 1 mm.
[0033]
In the wiring board 7 of the present invention, it is important to form a convex portion or a concave portion on the surface of the connection pad 4. For example, as shown in FIGS. A convex portion 4 a is formed so as to rise from the surface of the pad 4 with an arcuate cross section.
[0034]
If the protrusion 4a is formed on the surface of the connection pad 4, when solder such as lead-free solder is bonded to the connection pad 4, at least a part of the bonding interface between the connection pad 4 and the solder is stress-reduced. It can be bent and inclined with respect to the horizontal direction in which it acts, heat acts on the wiring board 7 and the external electric circuit board, and thermal stress is generated between them due to the difference in thermal expansion coefficient between them. Even if this acts in the horizontal direction near the joint interface with the solder, particularly the lead-free solder that joins both, especially the connection pad 4, this thermal stress is effectively dispersed and relaxed along the curved surface of the convex portion 4a. It is possible to effectively prevent the occurrence of mechanical breakage such as cracks along the vicinity of the joint interface between the lead-free solder and the connection pad 4. Further, the formation of the protrusion 4a can increase the bonding area between the connection pad 4 and the solder. As a result, the connection pad 4 can be connected to the wiring conductor of the external electric circuit board firmly and with high reliability.
[0035]
In this case, if the height difference (h) of the convex portion 4a from the surface of the connection pad 4 becomes smaller than 15 μm, it becomes difficult to effectively disperse and relax the thermal stress. Accordingly, it is preferable that the height difference (h) of the convex portion 4a of the connection pad 4 with respect to the surface of the connection pad 4 is 15 μm or more, taking into consideration the securing of the mechanical strength, adhesion strength, etc. of the convex portion 4a. Then, it is much more preferable to set it as the range of 15 micrometers-100 micrometers. Even when the recess is formed on the surface of the connection pad, the height difference between the bottom surface of the recess and the surface of the connection pad 4 is preferably 15 μm or more, and the upper limit of the height difference is the thickness of the connection pad. Become.
[0036]
Further, if the region where the convex portion 4a is formed is less than 20% with respect to the surface of the connection pad 4, it becomes difficult to effectively disperse and relieve the thermal stress, and the connection reliability of the connection pad 4 decreases. There is a fear. Therefore, it is preferable that the convex portion 4a is formed over a region of 20% or more of the surface of the connection pad 4.
[0037]
In addition, in FIGS. 3A and 3B, the convex portion 4a is shown as an example having an arc-shaped cross section extending over almost the entire width of a part of the connection pad 4, but FIGS. As shown in the figure, it may be provided in the center of the connection pad 4 in a band shape, or a part of the connection pad 4 may be further projected in a step shape. Also good. In this case, the protruding and stepped portions are joined so as to bite into the solder, and the bonding strength of the connection pads 4 to the external electric circuit board can be further strengthened.
[0038]
In order to form the convex portion 4a on the surface of the connection pad 4 in this way, for example, a similar metal paste is further formed on the surface of the metal paste to be the connection pad 4 printed and applied to the ceramic green sheet, such as a band shape or a circular shape. A method of printing and applying in a predetermined pattern, a method of adjusting the viscosity of the metal paste, and printing and applying so that a part of the surface of the metal paste that becomes the connection pad 4 swells in an arc shape can be used. .
[0039]
In the above-described embodiment, the example in which the convex portion 4a is formed on the surface of the connection pad 4 has been described. However, a concave portion may be formed instead of the convex portion 4a or in combination with the convex portion 4a. . In the case where the concave portion is formed in this way, like the convex portion 4a, the concave portion may be formed in an arc-shaped cross section extending over the entire width of the connection pad 4. Or may be formed. Such concave portions are printed on a ceramic green sheet by using a plate making having the same opening shape as the connection pad 4 and a plate making having a non-printing portion to be a concave portion and printing a metal paste in multiple times. The formed metal paste is formed by a method of pressing a mold having the same shape as the recess to be formed.
[0040]
Further, as shown in FIG. 6, the first region 5b led out from the connection pad 4 of the castellation conductor 5a is provided with a protruding portion 11 protruding inside thereof, so that the connection pad 4 is wired to the external electric circuit board. When joining to a conductor via solder, the said protrusion part 11 is joined so that it may bite into solder, and joining strength will become still stronger. Therefore, it is preferable that the first region 5b led out from the connection pad 4 of the castellation conductor 5a is formed with a protruding portion 11 protruding inward as shown in FIG.
[0041]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiments, the wiring board of the present invention is a semiconductor. Although the present invention is applied to a package for housing a semiconductor element that houses elements, it may be applied to other uses such as a hybrid integrated circuit board.
[0042]
【The invention's effect】
According to the wiring board of the present invention, the castellation conductor that electrically connects the frame-shaped metal layer formed on the upper surface of the insulating base and the connection pad formed on the lower surface of the insulating base is led out from the connection pad. 1 region and a second region derived from the metal layer, and since the first region and the second region are shifted in the width direction of the side surface of the insulating base, the connection pad and the wiring conductor of the external electric circuit Even if they are joined using lead-free solder, lead-free solder does not crawl up to the frame-like metal layer or metal lid through the castellation conductor. A sufficient amount of solder can be interposed between the wiring conductors and the wiring board (electronic device) can be bonded to the external electric circuit board very firmly.
[0043]
At the same time, according to the wiring board of the present invention, since the convex portion or the concave portion is formed on the surface of the connection pad, it is caused by the difference in thermal expansion coefficient between the insulating base and the external electric circuit board. Even if thermal stress is generated and this acts horizontally in the vicinity of the lead-free solder and the joint interface between the lead-free solder and the connection pad, this stress is distributed along the convex surface of the connection pad surface or the curved surface of the recess. It can be mitigated, and it is possible to effectively prevent the occurrence of cracks and the like along the joint interface with the lead-free solder connection pad. Further, since the convex portion or the concave portion is formed, the bonding area between the connection pad and the solder can be increased. As a result, the wiring board can be mounted on the external electric circuit board firmly and with high reliability.
[Brief description of the drawings]
1A, 1B and 1C are a side view, a plan view and a bottom view showing an embodiment of a wiring board according to the present invention.
FIG. 2 is an enlarged perspective view of a main part of a wiring board according to the present invention.
3A is an enlarged bottom view of the main part of the wiring board of the present invention, and FIG. 3B is a cross-sectional view taken along the line AA ′ of FIG.
4A is an enlarged view of a main part of another embodiment of the wiring board of the present invention, and FIG. 4B is a sectional view taken along line BB ′ of FIG.
5A is an enlarged view of a main part of another embodiment of the wiring board of the present invention, and FIG. 5B is a cross-sectional view taken along the line CC ′ of FIG. 5A.
FIG. 6 is an enlarged view of a main part of another embodiment of the wiring board of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Wiring layer 3 ... Frame-shaped metal layer 4 ... Connection pad 4a ... Projection part 5 ... Castellation Conductor 5a... Castoration conductor 5b connecting connection pad and frame-shaped metal layer... First region 5c... Second region 6. .... Wiring board 8 ... Bonding wire 9 ... Lid 10 ... Internal wiring layer 11 ... Projection

Claims (2)

An insulating base having an electronic component mounting portion on the upper surface and a frame-shaped metal layer surrounding the mounting portion, and having a connection pad on the outer peripheral portion of the lower surface; formed on the side surface of the insulating base; A wiring board comprising a castellation conductor for connecting to a metal layer, wherein the castellation conductor comprises a first region derived from a connection pad and a second region derived from a frame-shaped metal layer, The first region and the second region are displaced in the width direction of the side surface of the insulating base and are connected via an internal wiring layer formed inside the insulating base, and a convex portion or a surface is formed on the surface of the connection pad. A wiring board having a recess. The wiring board according to claim 1, wherein the convex portion or the concave portion is formed over a region of 20% or more of the surface of the connection pad.

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