JP2003142817A - Mask for solder printing and manufacturing method for wiring board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mask for solder printing which can precisely form solder bumps on solder joining pads of a wiring board, and a manufacturing method for a wiring board which is superior in the reliability of connection between terminals of electronic components and the solder joining pads through the solder bumps. SOLUTION: The mask 5 for solder printing has through holes 6 for supplying solder paste 7 to the solder joining pads 2 exposed in opening parts 4 of a solder-resistant resin layer 3 covering an insulating substrate 1. The through holes 6 have their opening area 1.3 to 1.8 time as large as the area of the exposed solder joining pads 2, and also have the openings divided by 100 to 200 μm×100 to 200 μm for the exposed solder joining pads 2 having 200 μm×200 μm area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder printing mask for forming solder bumps on solder joint pads of a wiring board for mounting electronic components such as semiconductor elements and resistors, and a wiring board using the same. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, wiring boards used for mounting electronic parts such as semiconductor elements and resistors have an insulating plate made of a glass base material and a thermosetting resin and a wiring conductor layer made of a copper foil. A printed circuit board made by alternately stacking multiple
2. Description of the Related Art Build-up boards have been used in which a plurality of insulating layers made of a thermosetting resin and a filler and wiring conductor layers made of a copper plating layer are laminated on an insulating plate. Then, solder bonding bumps for connecting electrodes of electronic components such as semiconductor elements are formed on the surface of such a printed board or build-up board.

An electronic device in which electronic parts are mounted on such a wiring board is small, thin, high-performance, high-function, and high-performance.
High reliability is required, and it is becoming important to mount small and highly precise electronic components on a wiring board with high density. For this reason, the method of high-density mounting of electronic components on a wiring board is shifting from through-hole mounting of lead insertion mounting components to flip-chip mounting of surface mounting components.

In such a flip-chip mounted wiring board, a large area and a small number of solder joint pads having an area of 200 μm × 200 μm or more are formed in the mounting region of electronic parts having a small number of electrodes such as resistors and capacitors. However,
In a mounting region of an electronic component such as a semiconductor element having a large number of electrodes, a small area with an area of less than 200 μm × 200 μm and a large number of solder joint pads are formed densely. Further, usually, a solder bonding pad having a large area and a solder bonding pad having a small area are mixed in the mounting area of the wiring board. And
On such a solder joint pad, a solder bump for electrically connecting the solder joint pad and an electrode of an electronic component is formed by printing a solder paste and melting the paste.

The solder printing mask used when printing the solder paste on the surface of the wiring substrate is a metal mask, and the solder joint pad exposed from the opening of the solder-resistant resin layer covering the insulating substrate. Is provided with a through hole for supplying the solder paste, and the opening of the through hole is formed in a circle or a quadrangle having a size substantially equal to or larger than the opening of the solder-resistant resin layer.

In the method of manufacturing a wiring board using the solder printing mask, a step of applying a solder-resistant resin layer having an opening exposing the central portion of the solder joint pad to the outermost layer of the wiring board. And a solder printing mask provided with through holes for supplying the solder paste is placed on the surface of the wiring board so that the openings of the corresponding solder-resistant resin layer and the through holes of the solder printing mask overlap. After that, place the solder paste on the solder printing mask, supply the solder paste from the through hole of the solder printing mask with a squeegee, and print on the exposed solder joint pad, and heat it above the melting point of the solder. And melting the solder paste on the solder joint pads to form solder bumps. The solder paste is made by mixing and kneading solder particles / flux and organic solvent, and the solder particle size is 1 to 10 μm from the viewpoint of printability and filling property.
It has become m.

[0007]

However, in the above wiring board, the solder paste printed on the solder joint pad having a small area of less than 200 μm × 200 μm has a raised shape due to surface tension. 200 μm x 200 μm
The solder paste printed on the above-mentioned large area solder joint pad has a dented shape in the center, which causes a shortage of the amount of solder and uneven height of the solder bumps, which causes a problem that electronic components cannot be joined well. Was.

Further, in the above-mentioned method for manufacturing a wiring board, the solder paste is heated above its melting point to form the solder bumps on the solder joint pads. However, when the solder paste is heated, Flux cannot be completely removed from the solder bumps, resulting in voids in the solder bumps.
In a heat resistance test such as a temperature cycle test (TCT) after mounting an electronic component, there is a problem that cracks due to voids occur and disconnection occurs.

Further, in the above-described method of manufacturing a wiring board, since the solder bumps are substantially hemispherical, the contact area between the tops of the solder bumps and the electrodes of the electronic component is small. However, there is a problem in that the electrodes of the electronic component and the solder bumps are displaced and mounted.

The present invention has been completed in view of the problems of the prior art, and an object thereof is to provide a solder bump on a solder bonding pad of a wiring board for mounting an electronic component such as a semiconductor element or a resistor. Provided is a solder printing mask which can be formed with high accuracy, and a method of manufacturing a wiring board which is excellent in connection reliability between an electrode of an electronic component and a solder joint pad via a solder bump.

[0011]

In the solder printing mask of the present invention, a through hole for supplying a solder paste is provided to a solder joint pad exposed from an opening of a solder resistant resin layer covering an insulating substrate. In the solder printing mask, the through-hole has an area of 1.3 to 1.8 times the area of the exposed solder joint pad and is 200 μm.
For the exposed solder bonding pad having an area of × 200 μm or more, the opening is 100 to 200 μm × 100 to 200 μm
It is characterized by being divided by the area of.

The method of manufacturing a wiring board according to the present invention further comprises the step of depositing a solder-resistant resin layer having an opening exposing at least the central portion of the solder bonding pad on an insulating substrate on which the solder bonding pad is formed. , Minimum solder particle size is 10μm
And a step of printing the solder paste on the solder joint pads exposed by the solder printing mask according to claim 1, using a solder paste having a maximum grain diameter of 40% of the exposed solder joint pads. The step of heating the solder particles to a temperature equal to or higher than the melting point of the solder particles to melt the solder paste on the solder joint pads to form solder bumps is sequentially performed.

Further, the method for manufacturing a wiring board of the present invention is
In the step of forming the solder bump, the solder bump whose top is flat is formed by pressing the top of the solder bump so that the height of the solder bump is uniform.

According to the solder printing mask of the present invention, the area of the opening of the through hole of the solder printing mask is set to 1.3 to 1.8 times the area of the exposed solder joint pad, and
For exposed solder joint pads with an area of 200 μm × 200 μm or more, open the through holes with 100 to 200 μm × 100 to 200
Since the area is divided by μm, the amount of solder paste on the solder bonding pad can be controlled regardless of the size of the solder bonding pad area on the wiring board. As a result,
A solder printing mask capable of forming solder bumps of uniform height can be provided.

Further, according to the method of manufacturing a wiring board of the present invention, a step of applying a solder-resistant resin layer having an opening exposing at least a central portion of the solder bonding pad to the insulating substrate on which the solder bonding pad is formed. And the minimum particle size of solder particles is 10μ
The step of printing the solder paste on the solder joint pad exposed by the above-mentioned solder printing mask using the solder paste whose m is m and the maximum grain diameter is 40% of the solder joint pad diameter, and the melting point of the solder grain Since the steps of heating and melting the solder paste on the solder bond pads to form the solder bumps are sequentially performed, the amount of gas when the solder paste is melted decreases and the gap between the solder particles increases. This makes it easier for flux to escape from the solder paste when heating the solder paste, and as a result, it is possible to reduce voids in the solder bumps, and even when electronic components are mounted and a temperature cycle test is performed, cracks occur. It is possible to provide a wiring board having excellent connection reliability.

Further, according to the method for manufacturing a wiring board of the present invention, in the step of forming the solder bumps, the tops of the solder bumps are pressed so that their heights are aligned to form the solder bumps having flat tops. Therefore, the height of the solder bumps can be made constant, and the contact area between the electrodes of the electronic component and the tops of the solder bumps increases, so that a wiring board having excellent connection reliability can be provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a solder printing mask of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1A is a cross-sectional view showing an example of an embodiment of a solder printing mask and a wiring substrate on which solder bumps are formed using the solder printing mask.
(B) is a plan view of the solder printing mask when viewed from the solder printing mask side when the solder printing mask is overlaid on the wiring board. In FIG. 1, 1 is an insulating substrate, 2 is a solder joint pad, 3 is a solder-resistant resin layer, 4 is an opening, and 5 is a solder printing mask.

The solder printing mask 5 is provided with through holes 6 for supplying solder paste to the solder joint pads 2 exposed from the openings 4 of the solder resistant resin layer 3 covering the insulating substrate 1. The solder printing mask 5 is made of a metal material such as a nickel alloy or a nickel-cobalt alloy, and the through holes 6 are formed by adopting an etching method or a laser processing method.

The thickness of the solder printing mask 5 is preferably 20 to 60 μm from the viewpoint of the ease of removing the solder paste from the through hole 6 and the filling property of the opening 4, and the thickness of the solder printing mask 5 is less than 20 μm. If it is more than 60 μm, it tends to be damaged, and if it exceeds 60 μm, the detachability of the solder paste is deteriorated and the solder paste remains in the through holes 6 to fill the openings 4 with the solder paste. There is a tendency that the height of the solder bump becomes insufficient and the height of the solder bump becomes uneven. Therefore, the thickness of the solder printing mask 5 is preferably 20 to 60 μm.

In the solder printing mask 5 of the present invention, the area of the opening of the through hole 6 is 1.3 to 1.8 times the area of the exposed solder joint pad 2, and 200 μm × 200.
With respect to the exposed solder bonding pad 2 having an area of μm or more, the opening is divided into an area of 100 to 200 μm × 100 to 200 μm. This is also important.

In the solder printing mask 5, the area of the opening of the through hole 6 is 1.3 times the area of the exposed solder joint pad 2.
If it is less than double, the solder paste amount tends to be insufficient and the height of the solder bump tends to be lower than a predetermined value. If it is more than 1.8 times, the contact between the solder bumps when the adjacent solder joint pads 2 are narrow is made. Then, it tends to be short-circuited. Therefore, it is preferable to set the area of the opening of the through hole 6 to be 1.3 to 1.8 times the area of the exposed solder joint pad 2. .

Further, the exposed solder joint pad having an area of 200 μm × 200 μm or more has an opening of 100 to 200 μm.
It is important to divide into an area of m × 100 to 200 μm.
If the opening is divided into smaller areas than 100 μm × 100 μm, the solder paste will tend to be less removable and the solder bump height will become uneven.
If the area is larger than the area of the solder joint pad 2,
The center portion of the solder paste printed on the printed circuit board has a hollow shape, and the solder amount tends to be insufficient and the height of the solder bump tends to be uneven. Therefore, it is preferable to divide the opening into areas of 100 to 200 μm × 100 to 200 μm for the exposed solder bonding pad 2 having an area of 200 μm × 200 μm or more.

Thus, according to the solder printing mask 5 of the present invention, the area of the opening of the through hole 6 of the solder printing mask 5 is in the range of 1.3 to 1.8 times the area of the exposed solder joint pad 2. At the same time, the through hole 6 is formed for the exposed solder joint pad 2 having an area of 200 μm × 200 μm or more.
Since the area is divided into 100 to 200 μm × 100 to 200 μm, the amount of solder paste on the solder joint pad 2 can be controlled regardless of the size of the solder joint pad 2 on the wiring board. Thus, the solder printing mask 5 capable of forming solder bumps of uniform height can be provided.

Next, a method of manufacturing a wiring board using the solder printing mask of the present invention will be described with reference to FIG. Figure 2
(A)-(d) is sectional drawing in each process of the manufacturing method of the wiring board using the said solder printing mask, respectively. In this figure, 7 is a solder paste, 8 is a solder bump, and others are denoted by the same reference numerals as those in FIG.

The wiring substrate is formed by forming the solder joint pads 2 on the insulating substrate 1 and by depositing the solder resistant resin layer 3 having the openings 4 formed on the solder joint pads 2, the insulating substrate 1 being an electronic component. It serves as a support plate for mounting (not shown), and the electrodes of electronic parts (not shown) are electrically connected to the outside by the wiring conductor layer (not shown) inside the insulating substrate 1 and the solder bonding pads 2 on the surface. It has a function of electrically connecting to a circuit (not shown).

The wiring board manufactured by the manufacturing method of the present invention comprises a wiring board made of resin as an insulating layer such as a printed board or a build-up board. For example, when the wiring board is a printed board, copper is provided on both upper and lower surfaces. A plurality of insulating plates with wiring conductor layers made of plating or copper foil are laminated with an adhesive resin, and after heating and pressurizing and curing, a through hole is formed with a drill and copper plating is applied to the inner wall of the through hole. The insulating wiring board is electrically connected to produce the insulating substrate 1, and then the solder bonding pad 2 is formed on the surface of the insulating substrate 1. Further, the solder resistant resin layer 3 is exposed at the central portion of the solder bonding pad 2. It is manufactured by depositing.
When the wiring board is a build-up board, the insulating layers are laminated on the upper and lower surfaces of the insulating plate, and then through holes are formed in the insulating layer with a laser. An insulating substrate 1 is manufactured by forming a wiring conductor layer and then repeating stacking of an insulating layer and a wiring conductor layer, forming a solder joint pad 2 on the surface of the insulating substrate 1, and further solder-bonding a solder resistant resin layer 3 thereto. It is manufactured by applying the pad 2 so that the central portion of the pad 2 is exposed.

After the solder paste 7 is printed on the exposed solder joint pads 2 on the surface of the wiring board, the solder paste 7 is overheated and melted through a reflow furnace to form a hemispherical conductor having a height of about 10 to 100 μm. The bump 8 is formed. These conductor bumps 8 have a function of electrically connecting the wiring conductor layer of the wiring board and each electrode (not shown) of the electronic component. In the above example, the conductor bump 8 is formed by using the solder paste.
As the material of, a tin-lead alloy, a tin-lead-antimony alloy, a lead-zinc alloy, a tin-silver-bismuth alloy, etc. are also used. Further, the exposed surface of the solder joint pad 2 made of copper plating or copper foil is coated with nickel and gold in order to prevent oxidation and corrosion of the solder joint pad 2 and to ensure good joint with the conductor bump 8. It has been subjected.

On the other hand, on the surface of the wiring board opposite to the surface on which the conductor bumps 8 are formed, solder joint pads 2 for connecting to electrodes of an external electric circuit board (not shown) via solder.
(Not shown) is formed.

Next, a method of manufacturing a wiring board according to the present invention will be described with reference to the drawings. First, as shown in the cross-sectional view of FIG. 2A, after laminating insulating layers on both sides of the insulating plate, a through hole is formed in the insulating layer by laser, and then the surface of the insulating layer and the inside of the through hole are plated with copper. An insulating substrate 1 is manufactured by forming a wiring conductor layer and then repeating stacking of the insulating layer and the wiring conductor layer. Next, by a conventionally known semi-additive copper plating method on the surface of the insulating substrate 1, a solder bonding pad 2 for bonding to a semiconductor element electrode having a diameter of 30 to 100 μm and a thickness of 5 to 30 μm, and an area of 200 to 2000 μm × 200-2000μm,
A solder joint pad 2 having a thickness of 5 to 30 μm for joining with a resistor or a capacitor electrode is formed. Further, a solder resistant resin layer 3 made of a photosensitive resin and a filler is applied on the insulating substrate 1 and the solder bonding pad 2 to a thickness of 10 to 50 μm, and then exposed and developed to form a solder resistant resin layer 3. Opening 4 that exposes at least the center of the solder joint pad 2
To form.

Next, as shown in the sectional view of FIG.
The minimum particle diameter of the solder particles is 10 μm and the maximum particle diameter is 40% of the exposed diameter of the solder bonding pad 2, for example, tin: lead = 9: 1 to 4: 6 of the solder paste 7 is used, and the through holes 6 are formed. The area of the opening is 1.3 to 1.8 times the area of the exposed solder joint pad 2, and the area is 200 μm × 200 μ.
The exposed solder joint pad 2 having an area of m or more is soldered on the exposed solder joint pad 2 by using the solder printing mask 5 whose opening is divided by an area of 100 to 200 μm × 100 to 200 μm. Print paste 7.

As the solder paste 7, it is preferable to use the solder paste 7 in which the minimum particle size of the solder particles is 10 μm and the maximum particle size is 40% of the diameter of the solder bonding pad 2 in which the exposed maximum particle size is exposed. If the minimum particle size of the solder particles is less than 10 μm, it becomes difficult for the flux in the solder paste to completely escape from the solder bumps when the solder paste is heated, and voids may tend to occur in the solder bumps. ,
If the maximum grain size is larger than 40% of the exposed diameter of the solder bonding pad 2, the solder paste 7 is not sufficiently filled in the openings 4 of the solder resistant resin layer 3, and the solder bumps tend to be uneven in height. Therefore, it is preferable that the minimum particle diameter of the solder particles is 10 μm and the maximum particle diameter is 40% of the exposed diameter of the solder bonding pad 2. The viscosity of the solder paste is preferably 150-250 PaS.

Next, as shown in the sectional view of FIG.
The wiring board on which the solder paste 7 is printed is passed through a reflow oven and heated to 230 to 280 ° C., which is higher than the melting point of the solder particles, and the solder paste 7 is melted on the solder joint pads 2 to form hemispherical solder bumps 8. To do.

According to the method of manufacturing a wiring board of the present invention, since the wiring board is manufactured by the above steps, the amount of gas when the solder paste 7 is melted is reduced and the gap between the solder particles is increased, When the solder paste 7 is heated, flux easily escapes from the solder paste 7, and as a result, voids in the solder bumps 8 can be reduced, and cracks are generated even when an electronic component is mounted and a temperature cycle test is performed. It is possible to provide a wiring board having excellent connection reliability.

In the wiring board manufacturing method of the present invention, as shown in the sectional view of FIG. 2 (d), a ceramic press jig is used so that the tops of the solder bumps 8 are aligned. Pressed to solder bumps 8 with flat tops
Is preferably formed.

According to the method for manufacturing a wiring board of the present invention, in the step of forming the solder bumps 8, the tops of the solder bumps 8 are pressed so that their heights are aligned to form the solder bumps 8 having a flat top. Therefore, the height of the solder bump 8 can be made constant, and the electrode of the electronic component and the solder bump 8 can be formed.
Since the contact area with the top of the wiring board increases, a wiring board having excellent connection reliability can be provided. By controlling the press pressure, the solder bump height is 5 to 50 μm, and the top surface area of the solder bonding pad 2 is approximately equal to the exposed area of the solder bonding pad 2 to provide excellent connection reliability with electronic components. A wiring board can be provided.

Thus, according to the method of manufacturing a wiring board of the present invention, the opening 4 exposing at least the central portion of the solder bonding pad 2 is formed on the insulating substrate 1 on which the solder bonding pad 2 is formed.
And a solder printing mask having a minimum solder particle size of 10 μm and a solder paste having a maximum particle size of 40% of the diameter of the solder bonding pad 2 with the maximum particle size exposed. A step of printing the solder paste 7 on the solder joint pad 2 exposed by 5; and a step of heating the solder paste 7 above the melting point of the solder particles to melt the solder paste 7 on the solder joint pad 2 to form the solder bumps 8. Since the solder paste 7 is melted, the amount of gas is reduced and the gap between the solder particles is increased, so that the gas can easily escape. As a result, the solder bump 8
The voids can be reduced, and even if an electronic component is mounted and a temperature cycle test is performed, cracks do not occur, and a method for manufacturing a wiring board having excellent connection reliability can be provided.

Further, in the step of forming the solder bumps 8, the tops of the solder bumps 8 are pressed so that their heights are aligned to form the solder bumps 8 having flat tops.
Since the height of the solder bumps 8 can be made constant and the contact area between the electrodes of the electronic component and the tops of the solder bumps 8 increases, a method of manufacturing a wiring board with excellent connection reliability can be obtained.

The method for manufacturing a wiring board of the present invention is not limited to the above-described example of the embodiment, and various modifications and improvements may be made without departing from the scope of the present invention. No problem.

[0040]

According to the solder printing mask of the present invention, the area of the opening of the through hole of the solder printing mask is set to 1.3 to 1.8 times the area of the exposed solder joint pad, and 200 μm × For exposed solder joint pads with an area of 200 μm or more, the through-hole opening is 100 to 200 μm × 100.
Since it is divided by the area of ~ 200μm, it is possible to control the amount of solder paste on the solder bond pad regardless of the size of the solder bond pad on the wiring board, and as a result, the solder with uniform height can be used. The mask can be a solder printing mask on which bumps can be formed.

Further, according to the method for manufacturing a wiring board of the present invention, a step of applying a solder-resistant resin layer having an opening exposing at least a central portion of the solder bonding pad to the insulating substrate on which the solder bonding pad is formed. And the minimum particle size of solder particles is 10μ
The step of printing the solder paste on the solder joint pad exposed by the above-mentioned solder printing mask using the solder paste whose m is m and the maximum grain diameter is 40% of the solder joint pad diameter, and the melting point of the solder grain Since the steps of heating and melting the solder paste on the solder bond pads to form the solder bumps are sequentially performed, the amount of gas when the solder paste is melted decreases and the gap between the solder particles increases. This makes it easier for flux to escape from the solder paste when heating the solder paste, and as a result, it is possible to reduce voids in the solder bumps, and even when electronic components are mounted and a temperature cycle test is performed, cracks occur. It is possible to provide a wiring board having excellent connection reliability.

Further, according to the method of manufacturing a wiring board of the present invention, in the step of forming the solder bumps, the tops of the solder bumps are pressed so that their heights are aligned to form solder bumps having flat tops. Therefore, the height of the solder bumps can be made constant, and the contact area between the electrodes of the electronic component and the tops of the solder bumps increases, so that a wiring board having excellent connection reliability can be provided.

[Brief description of drawings]

1A and 1B are a cross-sectional view and a top view of an example of an embodiment of a solder printing mask and a wiring board of the present invention, respectively.

2 (a) to 2 (d) are cross-sectional views for each step for explaining the method for manufacturing a wiring board of the present invention.

[Explanation of symbols]

1 ... Insulating substrate 2 ... Solder joint pad 3 ... Solder resistant resin layer 4 ... Opening 5 ... Solder printing mask 6 ... through holes 7 ... Solder paste 8 ... Solder bump

Claims (3)

[Claims] 1. A solder printing mask provided with a through hole for supplying a solder paste to a solder bonding pad exposed from an opening of a solder-resistant resin layer covering an insulating substrate,
The area of the opening of the through hole is 1.3 to 1.8 times the area of the exposed solder joint pad, and the exposed solder joint pad has an area of 200 μm × 200 μm or more. On the other hand, the opening is 100 to
A solder printing mask characterized by being divided into areas of 200 μm × 100 to 200 μm. 2. A step of depositing a solder-resistant resin layer having an opening exposing at least a central portion of the solder bonding pad on an insulating substrate on which the solder bonding pad is formed, and a minimum particle diameter of solder particles is 10 μm. Printing the solder paste on the solder joint pad exposed by the solder printing mask according to claim 1, using a solder paste having a maximum grain size of 40% of the diameter of the solder joint pad exposed. A method of manufacturing a wiring board, which comprises sequentially performing a step of heating above the melting point of the solder particles and melting the solder paste on the solder joint pads to form solder bumps. 3. The step of forming the solder bumps, wherein the tops of the solder bumps are pressed so that the heights thereof are even, to form the solder bumps having flat tops. A method for manufacturing a wiring board as described above.