JP2002110872A - Wiring board and wiring board module - Google Patents

Abstract

(57) Abstract: The present invention reduces tensile residual stress generated in an insulating substrate, suppresses cracking of the insulating substrate during use, maintains a good bonding state between a metal plate and the insulating substrate, and is released from a semiconductor element. Provided is a wiring board and a wiring board module that can efficiently conduct heat to a storage container. A metal plate mainly composed of a low-resistance metal is bonded to one main surface of an insulating substrate made of ceramics by a bonding material for a metal plate.
A metallized layer 39 was formed on the other main surface so that the end face was inside the end face of the joining material 37 for a metal plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for a package for accommodating a semiconductor element in which a semiconductor element is accommodated and mounted, and a hybrid integrated circuit device in which various electronic components such as a capacitor and a resistor are mounted in addition to the semiconductor element. The present invention relates to a simple wiring board and a wiring board module.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices such as ICs and LSIs have become faster and more highly integrated, wiring boards on which the semiconductor devices are mounted have been further miniaturized in pattern, and high-density wiring patterns have been developed. In addition, with the recent increase in power of semiconductor devices, power wirings for transmitting the accompanying large power are formed.

As shown in FIG. 6A, such a wiring board 9 is provided on the upper surface of an insulating substrate 2 made of ceramics.
A metal plate (power wiring) 3 mainly composed of a low resistance metal is joined by a joining material 5 for a metal plate, and a metallized layer 7 is formed on the lower surface of the insulating substrate 2.

[0004] A power semiconductor element 8 such as an IGBT element is bonded and mounted on the metal plate 3.
Is fixed to a storage container 11 made of a high heat conductive material such as aluminum via a board bonding material 13 made of a heat conductive grease, a high heat conductive adhesive, solder, or the like. A module is formed.

In such a wiring board module, the power semiconductor element 8 mounted on the wiring board 9 generates heat when driven, but the heat is generated by the metal plate 3, the insulating substrate 2 of the wiring board 9, heat conductive grease or high heat. Conducted to the storage container 11 via the board bonding material 13 such as a conductive adhesive and solder,
It is transmitted from the storage container 11 to the atmosphere or the like.

At this time, the magnitude of the thermal conductivity of the insulating substrate 2 is important, but the thermal conductive grease or the high thermal conductive adhesive,
The thickness of the board bonding material 13 such as solder greatly affects the heat dissipation.

Further, due to the recent expansion of applications of various electronic devices such as semiconductor devices mounted with semiconductor elements, the usage environment has become more diversified and severer than in the past. When used in an in-vehicle environment with development, the use environment is severe and high reliability is required.

[0008] In various electronic control devices used in the above-mentioned vehicle-mounted environment, what is important for ensuring high reliability is a heat dissipation design including a circuit design and a unit structure, and a structural reliability design. In order to ensure the heat dissipation of the power semiconductor element itself mounted on the wiring board mounted on the electronic control unit, it is necessary to ensure the thermal conductivity of the insulating substrate and to ensure a good bonding state between the power semiconductor element and the insulating substrate. It is important to ensure that the insulating substrate and the storage container have good bonding properties.

Above all, it is important to prevent peeling of the metal plate due to cracking of an insulating substrate provided with a metal plate (power wiring) made of a metal having high thermal conductivity and low resistance. It is needless to say that the heat generation of the power wiring itself to which a large current is applied is reduced.

Therefore, in order to ensure high heat dissipation and low heat generation of the power wiring as described above, and to prevent peeling of the power wiring due to cracking of the insulating substrate, improvement of the wiring material, improvement of the substrate structure, and improvement of the wiring substrate Countermeasures such as improvement of module structure, improvement and improvement of various joints are taken.

[0011]

The low-resistance wiring material of the power wiring for a large current used for the wiring board is basically a low-melting-point metal such as copper (Cu, melting point of about 1085 ° C.). In an electronic circuit board made of an alumina ceramic material or the like, the low-resistance wiring material cannot be formed by simultaneous firing.

Therefore, when a material requiring high-temperature sintering, such as an alumina ceramic material, an aluminum nitride ceramic material, or a silicon nitride ceramic material, is used as the insulating substrate, the power wiring using the low resistance wiring material is replaced with the insulating substrate. Is formed on the insulating substrate after firing.

As the power wiring, a metal plate such as copper or copper-tungsten is used. Such a low-resistance wiring material generally has a larger thermal expansion than an insulating substrate made of a ceramic material. Therefore, when the power wiring is melt-bonded to the insulating substrate with a brazing material, a tensile residual stress is generated in the wiring substrate due to a difference in thermal expansion between the power wiring and the insulating substrate. In particular, the largest residual stress occurs on the insulating substrate located at the end face of the joining material for a metal plate. The distribution of the stress generated on the insulating substrate by joining the power wiring is shown by a solid line in FIG. 6B.

Next, the wiring board is mounted on a container made of a metal material or the like with a bonding material for the substrate such as solder or silver braze to form a wiring board module. Residual stress occurs due to the difference in the coefficient of thermal expansion of the substrate. The broken line in FIG. 6b shows the stress distribution generated on the insulating substrate by joining to the storage container.

As is apparent from FIG. 6B, the stress generated in the insulating substrate when joining the power wiring and the stress generated in the insulating substrate when joining to the storage container are superimposed, and the insulation located at the end face of the joining material for the metal plate is overlapped. The largest stress occurs on the substrate. When a temperature change occurs in the use environment, a stress due to the temperature change occurs in the wiring board module,
In combination with the residual stress described above, cracks occur at the end face of the bonding material for the metal plate of the insulating substrate, the power wiring peels off, heat dissipation from the power semiconductor element is reduced, and a malfunction due to an increase in the temperature of the semiconductor element, etc. May be caused.

On the other hand, by reducing the thickness of the power wiring and the thickness of the storage container to reduce the bending rigidity, the insulation caused by the difference in the coefficient of thermal expansion between the power wiring (metal plate), the storage container, and the insulating substrate is reduced. Although the tensile stress of the substrate can be reduced, for example, reducing the thickness of the power wiring causes new problems such as an increase in resistance, a reduction in heat capacity, and a reduction in heat dissipation. Further, the storage container is not preferable because structural reliability is reduced.

The present invention reduces the tensile residual stress generated in the insulating substrate, suppresses the cracking of the insulating substrate during use, maintains a good joint between the metal plate and the insulating substrate, and reduces the heat released from the semiconductor element. To provide a wiring board and a wiring board module that can efficiently transmit the data to the storage container.

[0018]

A wiring board according to the present invention is formed by joining a metal plate mainly composed of a low-resistance metal to one main surface of an insulating substrate made of ceramics with a metal plate joining material. A metallized layer is formed on the other main surface of the insulating substrate such that the end surface is inside the end surface of the bonding material for a metal plate.

According to the above configuration, the end face of the metallized layer exists inside the end face of the joining material for a metal plate, and the end face portion of the joining material for a metal plate at which the largest residual stress occurs due to joining of the metal plates. The insulating substrate does not generate residual stress due to bonding to the storage container, and is located at an end surface portion of the metal plate bonding material due to a difference in thermal expansion coefficient between the three members of the metal plate, the insulating substrate, and the storage container. Residual stress in the insulating substrate can be reduced, cracking of the wiring substrate during use can be suppressed, and peeling of the metal plate can be prevented.

[0020] This makes it possible to maintain a good joining state of the metal plate to the insulating substrate, and to effectively conduct heat from the power semiconductor mounted on the metal plate to the housing and radiate the heat. As a result, malfunctions such as malfunctions of the power semiconductor element and the like due to the temperature rise above the appropriate operating temperature upper limit do not occur, and high reliability can be maintained.

In the case where a plurality of metal plates are joined to the insulating substrate by a joining material for a metal plate, the other principal surface of the insulating substrate has its end face inside the joining region of the plurality of metal plate groups. Even if a metallized layer is formed, substantially the same functions and effects as described above can be obtained. That is, a single metallized layer is formed in a region including a plurality of metal plates in a range narrower than this region.

Further, the wiring board module of the present invention comprises a wiring board formed by joining a metal plate mainly composed of a low-resistance metal to one main surface of an insulating substrate made of ceramics with a joining material for a metal plate. A wiring board module which is housed in a storage container made of an alloy, and wherein the wiring board is bonded to the storage container by a bonding material for a substrate, wherein an end face of the bonding material for the substrate is formed of the bonding material for the metal plate. It is characterized by being present inside the end face.

As described above, when the wiring board is directly joined to the storage container by the joining material for the substrate, since the end face of the joining material for the substrate exists inside the end face of the joining material for the metal plate, Similar effects can be obtained.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wiring board according to the present invention will be described with reference to FIG. FIG. 1 shows a wiring board of the present invention, and reference numeral 31 denotes a wiring board. This wiring board 31
A metal plate 35 (also referred to as power wiring) mainly composed of a low-resistance metal is bonded to one main surface of an insulating substrate 32 made of ceramics by a metal plate bonding material 37, and the other main surface of the insulating substrate 32 is formed. A metallized layer 39 is formed on the surface.

In the wiring board according to the present invention, as shown in FIGS. 1 and 2, the end face of the metallized layer 39 is located inside the end face of the bonding material 37 for a metal plate. That is,
The relationship between the distance L ₁ from the end face of the bonding material 37 for metal plates provided on the wiring board 31 to the center of the insulating substrate 32 and the distance L ₂ from the end face of the metallized layer 39 to the center of the insulating substrate 32 is L _1. > and has a L _2. In other words, as shown in FIG. 2, the metal plate bonding material 37 and the metallized layer 39 are substantially rectangular, and the area of the metallized layer 39 is smaller than that of the metallized layer 39. L ₂ −L ₁ is desirably ₁ mm or more.

In such a wiring board, as shown in FIG. 3, a power semiconductor element 41 such as an IGBT element is bonded and mounted on a metal plate 35, and a wiring board 31 on which such a semiconductor element 41 is mounted is formed. A wiring board module is formed by joining via a board joining material 45 to a storage container 43 also serving as a heat sink made of a high heat conductive material such as aluminum.

From the lower surface of the semiconductor element 41, the metallized layer 3
Assuming that the distance up to 9 is A and the distance from the end face of the semiconductor element 41 to the end face of the metallization layer 39 is B, it is preferable that A ≦ B from the viewpoint of improving heat dissipation. This is because the heat is diffused at an angle of 45 degrees from the semiconductor element 41, so that the heat dissipation can be improved.

The semiconductor element 41 is connected to the metal plate 35, and the metal plate 35 and the storage container 43 are connected by wires 45.

The insulating substrate 32 is made of alumina, aluminum nitride,
Silicon nitride, sialon (containing Si, Al, O, N),
It is made of a ceramic containing mullite or silicon carbide as a main component.

The metal plate 35 has low resistance, high thermal conductivity,
From the viewpoint of cost, for example, a Cu plate having a thickness of 0.035 to 2.0 mm is used.

The joining material 37 for the metal plate and the joining material 45 for the substrate are made of Ag-Cu braze, heat conductive grease, high heat conductive adhesive, solder or the like. The storage container 43 is made of Cu or Cu-W.

As shown in FIG. 4, when the metallized layer is not formed on the insulating substrate 52, the insulating substrate 52
Although it is directly joined to the storage container 53 by the board joining material 55, in this case, the end face of the board joining material 55 needs to be located inside the end face of the metal plate joining material 57.

Further, as shown in FIG.
In the case where the plurality of metal plates 65 are bonded by the metal plate bonding material 67, respectively, the metallized layer is formed on the other main surface of the insulating substrate 62 such that the end face is inside the bonding region X of the plurality of metal plate groups. 69, ie, a plurality of metal plates 6
Even if a single metallized layer 69 is formed in a region X including the region 5 in a range narrower than the region X, substantially the same operation and effect as described above can be obtained.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the present invention.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, Al ₂ O ₃ , SiO ₂ , MgO, CaO
A suitable organic binder, a plasticizer, and a solvent are added to and mixed with the raw material powder to prepare a slurry, and the slurry is formed into a ceramic green sheet having a thickness of about 300 μm by a tape forming technique such as a well-known doctor blade method or a calendar roll method. Was molded.

Thereafter, a metal paste obtained by adding an appropriate amount of alumina particles to a powder mainly composed of a high melting point metal such as W or Mo, and adding and mixing an appropriate organic binder, a plasticizer and a solvent is mixed with the ceramic paste. Green sheet semiconductor elements,
Screen printing was performed at the position where the metallized layer was formed.

At this time, the value of L ₂ −L ₁ in FIG.
1.0 mm, -2.5 mm, -4.0 mm, and as a comparative example, 2.5 mm, 1.0 mm, and 0 mm.
The metal paste was printed on a ceramic green sheet.

Thereafter, the green sheets on which the pattern is printed and applied are laminated so as to satisfy the desired conditions, and are laminated in a reducing atmosphere comprising a mixed gas of hydrogen (H ₂ ) and nitrogen (N ₂ ) for about 1600. Firing at a temperature of ℃, length 25m
An insulating substrate composed of four layers of m, 15 mm in width and about 1 mm in thickness was produced.

Next, Ni plating and A plating were performed on the metallized pattern for mounting the power wiring (metal plate) and the metallized pattern for mounting the storage container provided on the front and back surfaces of the insulating substrate.
u plating was applied.

Thereafter, using a metal plate made of a low-resistance metal on the insulating substrate, a power wiring for allowing a large current and securing heat radiation was provided. As a metal plate made of a low-resistance metal, from the viewpoint of low resistance, high heat conduction, and cost, a thickness of 1.0
mm copper (Cu) plate was used. The copper plate is 20 mm long,
After cutting to a width of 15 mm, the Au
Bonding was performed on the plating by using a bonding material for a metal plate made of silver brazing, and power wiring was provided to produce a wiring board as shown in FIG.

Thereafter, a length 35 mm and a width 25 made of copper were used.
An insulating substrate provided with the power wiring is joined to a box-shaped container having a thickness of 2 mm and a thickness of 2 mm to the bottom of the container using a bonding material for a substrate made of solder, and a wiring board module as shown in FIG. Produced.

The obtained wiring board module is assumed to be in actual use, and
In two high temperature tanks controlled at each temperature of 65 ° C and 150 ° C,
The cycle of holding the wiring board module for 60 minutes / 60 minutes was defined as one cycle, and the cycle was repeated up to 500 cycles.

The appearance of cracks in the insulating substrate near the end of the power wiring junction was observed by a stereoscopic microscope every 100 cycles, and the results are shown in Table 1.

[0044]

[Table 1]

As is clear from Table 1, the wiring board module Nos. In 1-6, the distance L ₁ from the end face of the metal plate for bonding material to the center of the insulating substrate, the difference between the distance L ₂ from the end surface of the metallized layer to the center of the insulating substrate L ₂
In -L ₁ is 0 or more, and larger, because the stress transmitted from the container to the insulating substrate is increased, early in the temperature cycle, it can be seen that the crack in the insulating substrate has occurred.

On the other hand, the wiring board module No.
In Nos. 7 to 12, no crack was observed on the surface of the insulating substrate up to 500 cycles, and a good bonding state between the power wiring and the insulating substrate could be maintained.

[0047]

As described above in detail, according to the present invention, the end face of the metallized layer exists inside the end face of the joining material for a metal plate, and the largest residual stress is generated by the joining of the metal plate. The residual stress caused by joining to the storage container does not occur on the insulating substrate at the end surface of the joining material for the metal plate, and the metal due to the difference in the coefficient of thermal expansion between the three members of the metal plate, the insulating substrate and the storage container. It is possible to reduce the residual stress in the insulating substrate located at the end face portion of the bonding material for a board, to suppress cracking of the wiring board during use, and to prevent peeling of the metal plate.

As a result, it is possible to maintain a good bonding state of the metal plate to the insulating substrate, and to effectively conduct heat from the power semiconductor mounted on the metal plate to the housing and radiate the heat. As a result, malfunctions such as malfunctions of the power semiconductor element and the like due to the temperature rise above the appropriate operating temperature upper limit do not occur, and high reliability can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a wiring board of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a schematic sectional view showing a wiring board module of the present invention.

FIG. 4 is a schematic cross-sectional view showing another wiring board module of the present invention in which an insulating substrate is directly bonded to a storage container with a bonding material for a substrate without forming a metallized layer.

5A and 5B show another wiring board module of the present invention in which a plurality of metal plates are joined to an insulating substrate, wherein FIG. 5A is a schematic sectional view and FIG. 5B is a plan view.

FIG. 6 is a schematic sectional view showing a conventional wiring board module.

[Explanation of symbols]

 31 ... wiring board 32, 52, 62 ... insulating board 35, 65 ... metal plate 37, 57, 67 ... metal plate bonding material 39, 69 ... metallization layer 43, 53 ...・ Storage containers 45, 55: bonding material for substrate X: bonding region

Claims (6)

[Claims] 1. A metal plate mainly composed of a low-resistance metal is joined to one main surface of an insulating substrate made of ceramics by a joining material for a metal plate, and an end surface is formed on the other main surface of the insulating substrate. A wiring board, wherein a metallized layer is formed so as to be inside an end face of a joining material for a metal plate. 2. A plurality of metal plates mainly composed of a low-resistance metal are bonded to one main surface of an insulating substrate made of ceramics by a bonding material for a metal plate, and the other main surface of the insulating substrate is A wiring board, wherein a metallized layer is formed such that an end face is inside a joint region of the plurality of metal plate groups. 3. The wiring board according to claim 1, wherein a semiconductor element is bonded to a surface of the metal plate. 4. A storage container made of a metal or an alloy, wherein the wiring substrate according to any one of claims 1 to 3 is stored, and a metallized layer of the wiring substrate is formed of a bonding material for the substrate. A wiring board module, wherein the wiring board module is joined to the wiring board module. 5. A wiring board formed by joining a metal plate mainly composed of a low-resistance metal to one main surface of an insulating substrate made of ceramics with a joining material for a metal plate in a storage container made of metal or alloy. And a wiring board module in which the wiring board is bonded to the storage container with a bonding material for a substrate, wherein an end surface of the bonding material for the substrate is present inside an end surface of the bonding material for the metal plate. A wiring board module characterized by the above-mentioned. 6. A storage container made of a metal or an alloy, wherein a wiring board formed by joining a plurality of metal plates mainly composed of a low-resistance metal to one main surface of an insulating substrate made of ceramics by a joining material for a metal plate. A wiring board module in which the other main surface of the insulating substrate is bonded to the storage container by a bonding material for a substrate, wherein an end surface of the bonding material for the substrate is formed of the plurality of metal plate groups. A wiring board module, wherein the wiring board module exists inside a bonding region.