JP2763470B2 - Wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board on which electronic components such as semiconductor elements are mounted.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which electronic components such as semiconductor elements are mounted is made of an electrically insulating material such as alumina ceramics and has a square shape having a mounting portion for mounting electronic components such as semiconductor elements on the upper surface. An insulating base, a plurality of metallized wiring layers made of a high melting point metal powder such as tungsten, molybdenum, or manganese which are led out from an electronic component mounting portion of the insulating base to a lower surface; A plurality of metallized pads electrically connected to the wiring layer, and an electronic component such as a semiconductor element is mounted on an electronic component mounting portion of the insulating base.
Attaching by joining each electrode of the electronic component and the metallized wiring layer via a brazing material such as solder,
By connecting the metallized pad on the lower surface of the insulating base to the wiring conductor of the external electric circuit board made of epoxy resin or the like via a brazing material such as solder, the electronic components such as semiconductor elements mounted on the wiring board are connected to the external electric circuit. Will be done.

In the above-mentioned conventional wiring board, an insulating base made of an electrically insulating material such as alumina ceramic is formed into a slurry by adding an appropriate organic solvent and a solvent to ceramic raw material powder and mixing it with a conventionally known doctor. A ceramic green sheet (ceramic green sheet) is obtained by forming the sheet into a sheet shape by employing a blade method, a calendar roll method, or the like. Thereafter, the ceramic green sheet is subjected to an appropriate punching process and a plurality of sheets are laminated. (About 1600 ° C.).

The metallized wiring layer and the metallized pad are preliminarily screened on a ceramic green sheet as an insulating substrate by adding a metal paste obtained by adding a suitable organic solvent and a solvent to a refractory metal powder such as tungsten, molybdenum, manganese or the like. By printing and applying a predetermined pattern by a thick film technique such as a printing method, a predetermined shape is formed at a predetermined position on the insulating substrate.

However, in this conventional wiring board, the thermal expansion coefficient of the alumina ceramics constituting the insulating base is 6.0 to 7.5 × 10 ^-6 / ° C., and the thermal expansion of the external electric circuit board made of epoxy resin. Coefficient (23 to 75 × 10
⁻⁶ / ° C.) and the coefficient of thermal expansion of the solder (24 × 10 ⁻⁶ / ° C.), so that the metallized pad adhered to the lower surface of the insulating base is soldered to the wiring conductor of the external electric circuit board. When they are joined via a material, a large thermal stress is generated between the insulating base and the external electric circuit board and between the insulating base and the solder, and near the corner of the insulating base having a large difference in expansion and contraction. , Which are present at the interface between the metallized pad and the insulating base located near the corner of the substrate, causing the following defects.

That is, an electronic component such as a semiconductor element mounted on a wiring board generates heat during operation, and when the heat is repeatedly applied to the insulating base of the wiring board, the external electric circuit board, and the solder for joining them, the insulation is generated. Thermal expansion occurs in the substrate, etc., causing a change in the magnitude of the stress existing at the interface between the insulating base and the metallized pad. If this stress change occurs repeatedly, the bond between the metallized pad and the insulating base is broken, and the metallized pad is broken. Have been separated from the insulating base, and as a result, there has been a drawback that electronic components such as semiconductor elements cannot be reliably and firmly electrically connected to an external electric circuit.

Therefore, in order to solve the above-mentioned drawback, a ceramic green sheet having a metal paste printed and applied in a predetermined pattern is baked to produce an insulating substrate having a metallized pad adhered to the lower surface. It has been proposed that an insulating paste made of ceramic mud is printed and applied to the entire surface of the ceramic green sheet including the outer peripheral portion of the pattern, and the outer peripheral portion of the metallized pad is covered with an annular projection sintered and integrated with the insulating base. (See Japanese Utility Model Laid-Open No. 57-78651).

[0008]

However, an insulating paste is printed and applied over the entire surface of the ceramic green sheet including the outer peripheral portion of the metal paste pattern to be a metallized pad, and the outer peripheral portion of the metallized pad is manufactured by firing. The insulating substrate covered with an annular projection has a large difference in firing shrinkage between the ceramic green sheet and the insulating paste, and the insulating substrate is greatly warped. This makes it impossible to accurately join the wiring conductor to the wiring conductor, which causes a drawback that an electronic component such as a semiconductor element cannot be accurately electrically connected to an external electric circuit.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and has as its object to effectively prevent metallized pads on a wiring board from peeling off from an insulating substrate, and to securely connect the wiring board to an external electric circuit board. To provide a wiring board that can be firmly connected.

[0010]

SUMMARY OF THE INVENTION The present invention has a plurality of metallized wiring layers, and has a quadrangular insulating base on a lower surface thereof.
A wiring board comprising a plurality of metallization pads electrically connected to the metallization wiring layer, wherein an outer peripheral portion of the metallized pad located near a corner of the insulating base has an insulation around the outer peripheral portion. The annular projection extending from the lower surface of the base and the lower surface of the insulating base are sandwiched.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a cross-sectional view showing an embodiment of a wiring board according to the present invention, FIG. 2 is a bottom view, and FIG. 3 is an enlarged view of a main part, wherein 1 is an insulating base, 2 is a metallized wiring layer, 3 is a metallization pad.

The insulating substrate 1 has a rectangular shape and has a mounting portion on which an electronic component 4 such as a semiconductor element is mounted on its upper surface.

[0014] The insulating substrate 1 is made of an electrically insulating material such as alumina ceramics, such as alumina (Al ₂ O
₃ ) Raw materials such as silica (SiO ₂ ), calcia (CaO), and magnesia (MgO) are mixed with an appropriate organic solvent and a solvent to form a slurry, which is then formed into a slurry, which is conventionally known by a doctor blade method or a calender roll. By forming a ceramic green sheet (ceramic green sheet) by employing a method or the like, a suitable punching process is then performed on the ceramic green sheet, a plurality of the sheets are laminated, and fired at a high temperature (about 1600 ° C.). Be produced.

The insulating substrate 1 has a plurality of metallized wiring layers 2 extending from the electronic component mounting portion to the lower surface.
Are formed, and each electrode of the electronic component 4 is bonded to the electronic component mounting portion of the metallized wiring layer 2 via a brazing material such as solder, so that each electrode of the electronic component 4 is connected to the metallized wiring layer 2. Electrically connected.

The metallized wiring layer 2 is made of tungsten,
Molybdenum, made of high melting point metal powder such as manganese, a suitable organic solvent to the high melting point metal powder, a metal paste obtained by adding and mixing a solvent, employing a conventionally known thick film forming technology such as screen printing method, The ceramic green sheet serving as the insulating base 1 is printed and applied in a predetermined pattern in advance, so that the ceramic green sheet is adhered and formed from the electronic component mounting portion of the insulating base 1 to the lower surface.

The insulating substrate 1 further has a plurality of metallized pads 3 attached to the lower surface thereof. Each of the metallized pads 3 has a plurality of metallized wiring layers 2 led out to the lower surface of the insulating substrate 1. One ends are each electrically connected.

The metallized pad 3 functions to electrically connect the metallized wiring layer 2 to which each electrode of the electronic component 4 is connected to an external electric circuit.
To the wiring conductor 7 via a brazing material 8 such as solder.

The metallized pad 3 is made of a high melting point metal powder such as tungsten, molybdenum, manganese or the like. A metal paste obtained by adding a suitable organic solvent and a solvent to the high melting point metal powder is mixed with the insulating base 1. The ceramic green sheet is formed on the lower surface of the insulating substrate 1 by printing and applying the same in advance by a conventionally known screen printing method or the like.

On the exposed surfaces of the metallized wiring layer 2 and the metallized pad 3, a metal such as nickel or gold having good conductivity and excellent corrosion resistance and a metal having good wettability with a brazing material is used in a range of 0.1 to 0.1. If it is layered to a thickness of 20.0 μm, the metallized wiring layer 2 and the metallized pad 3
Of the electronic component 4 via solder to the metallized wiring layer 2 and the brazing material 8 between the metallized pad 3 and the wiring conductor 7 of the external electric circuit board 6. Can be firmly joined. Therefore, the metallized wiring layer 2 and the metallized pad 3 are coated with nickel, gold or the like on the exposed surfaces of 0.1 to 2 mm.
It is preferable that the layer is deposited to a thickness of 0.0 μm.

Of the plurality of metallized pads 3 attached to the lower surface of the insulating substrate 1, the outer peripheral portion of the metallized pad 3 located near the corner A of the insulating substrate 1 further extends from the lower surface of the insulating substrate 1. It is covered with the annular projection 5 and is sandwiched between the lower surface of the insulating base 1 and the annular projection 5.

The metallized pad 3 located near the corner A of the insulating base 1 has its outer peripheral portion sandwiched between the lower surface of the insulating base 1 and the annular projection 5 so that the adhesion strength of the metallized pad 3 is reinforced. A large thermal stress generated when joining the metallized pad 3 of the insulating base 1 to the wiring conductor 7 of the external electric circuit board 6 via the brazing material 8 such as solder is generated in the metallized pad located near the corner A of the insulating base 1. The metallized pad 3 is not present at the interface between the metallized pad 3 and the insulating substrate 1, and the metallized pad 3 is not separated from the insulating substrate 1 even if the magnitude of the internal stress changes.

The annular projection 5 is made of an electrically insulating material such as alumina ceramics. An insulating paste obtained by adding a suitable organic solvent and a solvent to a ceramic raw material powder such as alumina is mixed with a ceramic green sheet to be used as an insulating substrate 1. The outer peripheral portion of the metal paste pattern to be the metallized pad 3 printed on the surface in the vicinity of the corner and the ceramic green sheet around the outer peripheral portion are coated in advance with a predetermined thickness, so that the outer peripheral portion of the metallized pad 3 and the outer periphery are formed. It is joined to the insulating base 1 around the part. In this case, since the insulating paste for forming the annular projections 5 is applied to a part of the surface of the ceramic green sheet serving as the insulating substrate 1 near the corners, the insulating paste is fired together with the ceramic green sheet and sintered and integrated. To form the insulating base 1
Does not cause a large warp, and as a result, the metallized pads 3 on the lower surface of the insulating base 1 are removed from the external electric circuit board 6.
It is also possible to join the wiring conductor 7 accurately.

When the width X of the annular projection 5 to be bonded to the metallized pad 3 is set to 50 to 100 μm, the adhesion strength between the metallized pad 3 and the insulating base 1 can be greatly enhanced, and the insulation of the metallized pad 3 can be improved. Peeling from the substrate 1 can be effectively prevented. Therefore, the width X of the annular projection 5 and the metallized pad 3 are set to 50
It is preferable to set the thickness to 100 μm.

When the annular projection 5 has a bonding width Y of 50 to 100 μm with the insulating substrate 1, the stress applied to the insulating substrate 1 at the time of firing becomes extremely small, and the insulating substrate does not warp. In addition, the bonding strength with the insulating base 1 can be increased. Accordingly, it is preferable that the width Y of the annular protrusion 5 to be bonded to the insulating base 1 is set to 50 to 100 μm.

The annular projection 5 has a thickness Z of 20.
When the thickness is set to 40 μm, the adhesion strength between the metallized pad 3 and the insulating base 1 can be greatly enhanced, and the bonding between the metallized pad 3 and the wiring conductor 7 of the external electric circuit board 6 via the brazing material 8 is strengthened. Can be made. Therefore, it is preferable that the thickness Z of the annular projection 5 is set to 20 to 40 μm.

When the annular projection 5 is formed with the same composition as the insulating base 1, the bonding strength between the annular projection 5 and the insulating base 1 can be further improved. Therefore, it is preferable to form the annular projection 5 with the same composition as the insulating base 1.

Thus, according to the wiring board of the present invention, the electronic component 4 such as a semiconductor element is mounted on the electronic component mounting portion of the insulating base 1.
The electrodes of the electronic component 4 and the metallized wiring layer 2 are attached by joining them via a brazing material such as solder, and the metallized pads 3 on the lower surface of the insulating base 1 are connected to the external electric circuit board 6 made of epoxy resin or the like. By connecting to the wiring conductor 7 via a brazing material 8 such as solder, the electronic component 4 such as a semiconductor element mounted on the wiring board is connected to an external electric circuit.

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

In the above embodiment, the case where the insulating substrate 1 is formed only of an inorganic material such as alumina ceramics has been described as an example. However, an organic polymer material such as a polyimide resin is formed on the upper surface of the substrate made of an inorganic material such as alumina ceramics. It may be a thin film multilayer wiring portion in which an insulating film to be formed and a wiring conductor formed by a thin film forming technique such as vapor deposition or sputtering are laminated in multiple layers.

[0031]

According to the wiring board of the present invention, the outer peripheral portion of the metallized pad adhered to the lower surface of the insulating base is held between the insulating substrate and the annular projection extending from the lower surface of the insulating substrate around the outer peripheral portion. In addition, since the metallized pad has been reinforced to adhere to the insulating substrate, the metallized pad can be effectively prevented from peeling off from the insulating substrate. As a result, the wiring board is firmly joined to the external electric circuit board, and the electronic component is connected. It is possible to reliably and firmly make an electrical connection to an external electric circuit.

Further, since the annular projection for clamping the outer peripheral portion of the metallized pad is provided only around the outer peripheral portion of the metallized pad located near the corner of the insulating base, the insulating member is insulated when the annular projection is joined to the insulating base. The stress applied to the substrate is extremely small, and as a result, the occurrence of warpage in the insulating substrate is eliminated, and the metallized pad can be accurately and reliably bonded to the predetermined wiring conductor of the external electric circuit board.

[Brief description of the drawings]

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

FIG. 2 is a bottom view of the wiring board shown in FIG.

FIG. 3 is an enlarged view of a main part of the wiring board shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 2 ... Metallized wiring layer 3 ... Metallized pad 4 ... Electronic component 5 ... Annular protrusion 6 ... External electric circuit board

Claims (1)

(57) [Claims] 1. A wiring board comprising a plurality of metallized wiring layers, wherein a plurality of metallized pads electrically connected to the metallized wiring layers are adhered to a lower surface of a quadrangular insulating base. The metallized pad located near the corner of the insulating substrate has its outer peripheral portion
Independent from each other extending from the lower surface of the insulating base around the part
Is covered with the annular projections,
A wiring board, wherein each outer peripheral portion is sandwiched between each of the annular protrusions and the lower surface of the insulating base.