JP2004119442A - Method for manufacturing wiring board with solder bump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a wiring board with a solder bump in which a void is hardly formed in the solder bump and which can rigidly connect an electrode of an electronic component to a solder connecting pad via the solder bump. <P>SOLUTION: The method for manufacturing the wiring board with the solder bump includes the steps of forming a solder resistant resin layer 4 having a plurality of solder connecting pads 3 and openings 4a for exposing a centers of the pads 3 on a surface of an insulating board 2, then coating the pads 3 with a solder plating layer 21, then coating the layer 21 with a solder paste 22, and then heating to melt the solder in the paste 2 and the layer 21 to form the solder bumps 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board with solder bumps for mounting electronic components such as semiconductor elements and resistors, and a method of manufacturing the same.
[0002]
[Prior art]
In recent years, wiring boards used for mounting electronic components such as semiconductor elements and resistors have been alternately laminated with an insulating plate made of a glass base material and a thermosetting resin and a wiring conductor layer made of a copper foil or the like. And a build-up board in which a plurality of insulating layers made of a thermosetting resin and a filler and a wiring conductor layer made of a copper plating layer are laminated on an insulating plate. On the upper surface of a wiring board such as a printed board or a build-up board, a solder bonding pad for connecting an electrode of an electronic component such as a semiconductor element and a solder-resistant resin for exposing a central portion of the solder bonding pad are provided. A layer is formed, and a solder bump for joining the electronic component and the solder joint pad is formed on the solder joint pad exposed from the solder resistant resin layer.
[0003]
In such a wiring board with solder bumps, the electronic component is placed on the upper surface of the wiring board such that each electrode thereof comes into contact with the corresponding solder bump, and these are heated by, for example, an electric furnace. The electronic component is mounted on the wiring board by heating the device to melt the solder bump and joining the solder bump and the electrode of the electronic component.
[0004]
Note that such a wiring board with solder bumps has a plurality of substantially circular solder bonding pads connected to the wiring conductors and the solder bonding pads on the surface of an insulating substrate having a plurality of wiring conductors inside and / or on the surface. A solder-resistant resin layer having an opening for exposing the central portion of the solder bump is applied, and a solder paste made of flux and solder powder is applied to the solder bumps on the solder bonding pad by using a conventionally known screen printing method. It is manufactured by printing and applying a single amount at a time and heating it to vaporize and remove the flux in the solder paste and melt the solder powder in the solder paste to form solder bumps on the solder joint pads. (Patent Document 1).
[0005]
[Patent Document 1]
JP-A-6-122090
[Problems to be solved by the invention]
However, according to the conventional wiring board with solder bumps, the flux in the solder paste printed and applied on the solder bonding pads is vaporized and removed, and the solder powder in the solder paste is melted to form solder bumps on the solder bonding pads. When soldering, a part of the flux contained in the solder paste applied at a time is likely to be left in the molten solder and voids are likely to be generated in the solder bumps. When bonding occurs between the electrodes of the electronic component and the solder bonding pad via the solder bumps, the bonding between the electrode of the electronic component and the solder bonding pad may be hindered by voids or the strength of the solder bump may be weak. As a result, it becomes impossible to firmly join the electrodes of the electronic component and the solder joint pads via the solder bumps. It was.
[0007]
The present invention has been devised in view of such a conventional problem, and an object of the present invention is to prevent a void from being formed in a solder bump formed on a solder bonding pad, and to form an electrode of an electronic component and a solder bonding pad. Is to provide a method for manufacturing a wiring board with solder bumps, which can firmly join the wiring boards via solder bumps.
[0008]
[Means for Solving the Problems]
The method for manufacturing a wiring board with solder bumps according to the present invention includes, on a surface of an insulating substrate having a wiring conductor, a plurality of solder bonding pads connected to the wiring conductor and an opening exposing a central portion of the solder bonding pad. A step of forming a solder-resistant resin layer, a step of applying a solder plating layer on the solder bonding pad exposed in the opening, a step of applying a solder paste on the solder plating layer, Forming a solder bump on the solder joint pad by heating and melting the solder and the solder plating layer.
[0009]
According to the method for manufacturing a wiring board with solder bumps of the present invention, a step of applying a solder plating layer on a solder bonding pad exposed in an opening of a solder resistant resin layer, and applying a solder paste on the solder plating layer Since the step and the step of heating and melting the solder and the solder plating layer in the solder paste to form a solder bump on the solder joint pad are performed, the solder plating layer applied on the solder joint pad melts. As a result, the solder bonding pad and the solder bump are satisfactorily bonded, and the solder paste applied thereon can form a solder bump having a sufficient height with few voids.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, 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 with solder bumps manufactured by the manufacturing method of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part in each step for explaining a method of manufacturing a wiring board with solder bumps according to the present invention.
[0011]
In FIG. 1, reference numeral 1 denotes an insulating substrate, 2 denotes a wiring conductor, 3 denotes a solder joint pad, 4 denotes a solder-resistant resin layer, 5 denotes a solder bump, and 6 denotes an external lead pin. A substrate is configured. In this example, the example having the external lead pins 6 is shown. However, the external lead pins 6 are not always necessary, and instead of the external lead pins 6, an external connection terminal made of, for example, solder may be provided.
[0012]
The insulating substrate 1 is formed by impregnating a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin into a glass fabric in which glass fibers are woven vertically and horizontally. A plurality of insulating layers 1b each made of a thermosetting resin such as a resin, and a plurality of wiring conductors formed of a conductive layer such as a copper foil or a copper plating film on the surface of the core body 1a or each insulating layer 1b; 2 are formed.
[0013]
The core 1a constituting the insulating substrate 1 has a thickness of about 0.3 to 1.5 mm and has a plurality of through holes 7 with a diameter of about 0.1 to 1.0 mm from the upper surface to the lower surface. . A part of the wiring conductor 2 is attached to the inner wall of each through hole 7, and the wiring conductors 2 formed on the upper and lower surfaces of the core 1 a are electrically connected to each other through the wiring conductor 2 in the through hole 7. Connected.
[0014]
Such a core 1a is manufactured by thermally curing a sheet in which a glass fabric is impregnated with an uncured thermosetting resin, and then performing drilling for the through holes 7 from the upper surface to the lower surface. . The wiring conductors 2 on the upper and lower surfaces of the core 1a are attached with copper foil having a thickness of about 3 to 50 μm on the entire upper and lower surfaces of the sheet for the core 1a, and the copper foil is etched after the sheet is cured. By processing, a predetermined pattern is formed on the upper and lower surfaces of the core 1a. The wiring conductor 2 in the through-hole 7 is formed by forming a through-hole 7 in the core 1a and then forming a copper plating film having a thickness of about 3 to 50 μm on the inner wall of the through-hole 7 by electroless plating and electrolytic plating. Is deposited on the inner wall of the through-hole 7.
[0015]
Further, the core 1a is filled with a resin column 8 made of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin inside the through hole 7. The resin pillar 8 is for enabling the insulating layer 1b to be formed directly above and directly below the through hole 7 by closing the through hole 7, and the uncured paste-like thermosetting resin is placed in the through hole 7. It is formed by filling by a screen printing method, thermally curing the material, and then polishing the upper and lower surfaces thereof to be substantially flat. An insulating layer 1b is laminated on the upper and lower surfaces of the core 1a including the resin columns 8.
[0016]
The insulating layer 1b laminated on the upper and lower surfaces of the core 1a has a thickness of about 20 to 60 μm, and has a plurality of through holes 9 having a diameter of about 30 to 100 μm from the upper surface to the lower surface of each layer. A part of the wiring conductor 2 is formed in these through holes 9. These insulating layers 1b are for providing an insulating interval for wiring the wiring conductors 2 at high density. By electrically connecting the upper layer wiring conductor 2 and the lower layer wiring conductor 2 via the wiring conductor 2 in the through-hole 9, high-density wiring can be formed three-dimensionally.
[0017]
Such an insulating layer 1b is formed by attaching an uncured thermosetting resin film having a thickness of about 20 to 60 μm to the upper and lower surfaces of the core body 1a, thermosetting the same, and forming the through holes 9 by laser processing. The insulating layer 1b is formed by successively stacking the next insulating layers 1b in a similar manner. The wiring conductor 2 attached to the surface of each insulating layer 1b and the inside of the through-hole has a thickness of about 5 to 50 μm on the surface of each insulating layer 1b and inside the through-hole 9 every time the insulating layer 1b is formed. It is formed by applying a plating film to a predetermined pattern by a known pattern forming method such as a semi-additive method or a subtractive method.
[0018]
Further, a solder-resistant resin layer 4 is provided on the outermost insulating layer 1b. The solder-resistant resin layer 4 is made of, for example, an insulating material in which an inorganic powder filler such as silica or talc is dispersed in an acrylic-modified epoxy resin by about 30 to 70% by mass, and improves the electrical insulation reliability between the surface wiring conductors 2. At the same time, it acts to increase the bonding strength of the solder bonding pad 3 and the pin bonding pad 10 to be described later to the insulating substrate 1.
[0019]
Such a solder-resistant resin layer 4 has a thickness of about 10 to 50 μm. The uncured resin paste for the solder-resistant resin layer 4 having photosensitivity is formed on the outermost layer by using a roll coater method or a screen printing method. After coating on the insulating layer 1b and drying it, exposure and development treatments are performed to form openings 4a and 4b for exposing the central portions of the solder bonding pads 3 and the pin bonding pads 10, and then, heat is applied. It is formed by curing. Alternatively, after an uncured resin film for the solder-resistant resin layer 4 is adhered on the uppermost insulating layer 1b, this is thermally cured, and then the position corresponding to the solder bonding pad 3 or the pin bonding pad 10 is set. Is formed so as to have openings 4a and 4b for exposing the solder bonding pads 3 and the pin bonding pads 10 by irradiating a laser beam to the resin film and partially removing the cured resin film.
[0020]
The wiring conductor 2 formed from the upper surface to the lower surface of the insulating substrate 1 functions as a conductive path for connecting each electrode of the electronic component to an external electric circuit board, and is provided in a mounting area on the upper surface of the insulating substrate 1. A part of the exposed part is connected to each electrode of the electronic component via a solder bump 5 made of, for example, a lead-tin alloy. A pin bonding pad 10 for bonding the external lead pins 6 connected to the substrate is formed. Such a solder bonding pad 3 or a pin bonding pad 10 is formed by covering an outer peripheral portion of a substantially circular pattern formed of a conductor layer connected to the wiring conductor 2 with a solder resin layer 4 to a width of about 15 to 35 μm. By defining the outer peripheral edge, the diameter is about 70 to 200 μm for the solder bonding pad 3 and about 0.5 to 2.5 mm for the pin bonding pad 10. By covering the outer peripheral portions of the solder bonding pads 3 and the pin bonding pads 10 with the solder-resistant resin layer 4, an electrical short circuit between the solder bonding pads 3 and between the pin bonding pads 10 is effectively prevented. In addition, the bonding strength of the solder bonding pad 3 and the pin bonding pad 10 to the insulating substrate 1 is high.
[0021]
Normally, on the exposed surfaces of the solder bonding pads 3 and the pin bonding pads 10, the prevention of oxidation corrosion of the solder bonding pads 3 and the pin bonding pads 10 and the good connection with the solder bumps 5 and the external lead pins 6 are provided. In this case, it is preferable to apply a metal having good conductivity and excellent corrosion resistance, such as nickel or gold, to a thickness of 1 to 20 μm by plating.
[0022]
The solder bumps 5 are fixedly formed on the solder bonding pads 3. The solder bump 5 is made of a solder material such as a lead-tin alloy, and functions as a terminal for electrically and mechanically connecting the solder joint pad 3 to the electronic component. The electronic components are mounted on the insulating substrate 1 so as to be in contact with the bumps 5, and are heated by a heating device such as an electric furnace to melt the solder bumps 5 so that the solder bumps 5 and the electrodes of the electronic components are melted. And are connected.
[0023]
The pin bonding pad 10 has external lead pins 6 made of a metal such as copper or an iron-nickel-cobalt alloy bonded via solder having a higher melting point than the solder bumps 5. The external lead pin 6 functions as a terminal member for electrically connecting an electronic component mounted on the insulating substrate 1 to an external electric circuit board, and connects the external lead pin 6 to a wiring conductor of the external electric circuit board via solder or a socket. In this case, the electronic component is electrically connected to the external electric circuit.
[0024]
Next, a method for forming the solder bumps 5 on the solder bonding pads 3 by the method for manufacturing a wiring board with solder bumps of the present invention will be described.
[0025]
First, as shown in FIG. 2A, on an upper surface of an insulating substrate 1 having a wiring conductor 2, a solder bonding pad 3 connected to the wiring conductor 2 and an opening 4 a exposing a central portion of the solder bonding pad 3. Is formed. The solder connection pad 3 is formed by forming a copper plating film having a thickness of about 5 to 20 μm on the uppermost insulating layer 1b constituting the insulating substrate 1 into a predetermined pattern by a pattern forming method such as a known semi-additive method or a subtractive method. It is formed by applying. The solder-resistant resin layer 4 is formed by applying an uncured resin paste for the solder-resistant resin layer 4 having photosensitivity to the uppermost insulating layer 1b by using a roll coater method or a screen printing method, and drying the paste. After that, an opening 4a for exposing the central portion of the solder bonding pad 3 is formed by performing exposure and development treatments, and is formed by heat curing. Alternatively, after an uncured resin film for the solder-resistant resin layer 4 is adhered on the uppermost insulating layer 1b, it is thermally cured, and then a laser beam is irradiated to a position corresponding to the solder bonding pad 3. Then, the cured resin film is partially removed to form an opening 4a for exposing the solder bonding pad 3. The surface of the solder bonding pad 3 exposed from the opening 4a of the solder-resistant resin layer 4 has a thickness of 2 to 5 μm in order to prevent its oxidation and corrosion and to make the bonding with the solder bump 5 strong. A nickel plating layer and a gold plating layer having a thickness of 0.01 to 0.03 μm are sequentially deposited by an electrolytic plating method or an electroless plating method.
[0026]
Next, as shown in FIG. 2B, a solder plating layer 21 made of, for example, a lead-tin alloy is applied on the solder bonding pad 3 exposed from the opening 4a of the solder-resistant resin layer 4. In order to apply the solder plating layer 21 on the solder bonding pad 3, the insulating substrate 1 on which the solder connection pad and the solder-resistant resin layer are formed may be formed, for example, by using stannous borofluoride 130 g / l and lead borofluoride. What is necessary is just to immerse for about 1 to 5 minutes in a solder plating solution having a temperature of 20 to 30 ° C., which is composed of 50 g / l, 125 g / l of borofluoric acid, and 25 g / l of boron borofluoride.
[0027]
At this time, it is preferable that the height of the solder plating layer 21 be in a range of −5 μm to +15 μm with respect to the height of the solder-resistant resin layer 4. When the height of the solder plating layer 21 is lower than −5 μm with respect to the height of the solder-resistant resin layer 4, a second solder paste 22 described below is printed and applied on the solder plating layer 21 and heated. When the solder bump 5 is formed, a flux is left inside the solder bump 5 due to a step formed between the solder plating layer 21 and the solder-resistant resin layer 4, and a void tends to be generated. On the other hand, if it is higher than +15 μm, a gap is formed between the print mask and the insulating substrate 1 when the solder paste 22 is applied by printing, and the amount of applied solder tends to vary.
[0028]
Next, as shown in FIG. 2C, a solder paste 22 is applied on the solder plating layer 21 to a thickness of 30 to 50 μm by using, for example, a conventionally known screen printing method. As the solder powder, for example, a spherical powder made of solder such as a lead-tin alloy having a particle size of about 5 to 25 μm is used. When the amount of flux in the solder paste 22 is less than 5% by mass, the solder paste 22 cannot be provided with an appropriate viscosity as a paste, and the solder paste 22 should be applied well on the solder plating layer 21. On the other hand, if it exceeds 15% by mass, the solder paste 22 and the solder plating layer 21 are heated to vaporize and remove the flux in the solder paste 22 and the solder in the solder paste 22 as described later. When the powder and the solder plating layer 21 are melted to form the solder bumps 5, the amount of flux in the solder paste 22 is large, so that the vaporized flux tends to be left in the solder bumps 5 and a large amount of voids are easily generated. is there. Therefore, the flux amount in the solder paste 22 is preferably in the range of 5 to 15% by mass.
[0029]
Next, as shown in FIG. 2D, the solder paste 22 and the solder plating layer 21 are heated to vaporize and remove the flux in the solder paste 22, and the solder powder and the solder plating layer 21 in the solder paste 22 are melted. Thus, the solder bumps 5 are formed on the solder bonding pads 3. At this time, since the solder plating layer 21 is previously applied on the solder bonding pad 3, the solder plating layer 21 is melted, so that the solder bonding pad 3 and the solder bump 5 are satisfactorily bonded. Further, since the solder bonding pad 3 and the solder bump 5 are satisfactorily bonded by the solder plating layer 21, it is not necessary to include a large amount of flux in the solder paste 22, and the solder paste 22 and the solder plating layer 21 are heated. The flux in the solder paste 22 is vaporized and removed, and the solder powder and the solder plating layer 21 in the solder paste 22 are melted to form the solder bump 5. It is possible to form the solder bumps 5 with a small amount.
[0030]
Thus, according to the wiring board with the solder bumps provided by the present invention, the electronic component is placed on the upper surface of the wiring board 1 such that its electrodes are in contact with the solder bumps 5 and the solder bumps 5 are melted. An electronic device as a product is obtained by joining the electrode of the component and the solder joint pad 3.
[0031]
It should be noted that the present invention is not limited to the example of the above-described embodiment, and various changes can be made without departing from the scope of the present invention.
[0032]
【The invention's effect】
According to the method for manufacturing a wiring board with solder bumps of the present invention, a solder plating layer is applied on a solder bonding pad exposed in an opening of a solder resistant resin layer, and then a solder paste is printed on the solder plating layer. Since the solder and the solder plating layer in the solder paste are melted and the solder bumps are formed on the solder bonding pads, the solder plating layer deposited on the solder bonding pads is melted and the solder bonding pads and the solder are melted. The solder bumps are satisfactorily bonded to each other, and the solder paste applied thereon can form a solder bump having a sufficient height with few voids. Therefore, it is possible to provide a wiring board with solder bumps that can firmly join the electrodes of the electronic component and the solder joining pads via the solder bumps.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an embodiment of a wiring board with solder bumps manufactured by a manufacturing method of the present invention.
FIGS. 2A to 2D are enlarged cross-sectional views of a main part in each step for explaining a method of manufacturing a wiring board with solder bumps according to the present invention.
[Explanation of symbols]
1, an insulating substrate 2, a wiring conductor 3, a solder bonding pad 4, a solder-resistant resin layer 4a, an opening 5 in the solder-resistant resin layer, etc. ... Solder bump 21 ... Solder plating layer 22 ... Solder paste

Claims (1)

Forming, on a surface of an insulating substrate having a wiring conductor, a solder-resistant resin layer having a plurality of solder bonding pads connected to the wiring conductor and an opening exposing a central portion of the solder bonding pad; A step of applying a solder plating layer on the solder bonding pad exposed to the step, a step of applying a solder paste on the solder plating layer, and heating and melting the solder in the solder paste and the solder plating layer, Forming a solder bump on the solder bonding pad.

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