JPH07183646A - Wiring board and mounting method using it - Google Patents

Abstract

PURPOSE:To obtain a circuit device of high reliability at low cost by covering with an unhardened insulating resin layer at least part of a surface of a wiring board for mounting equipped with a group of conductive bumps, which has a connection pad group, each equipped with a conductive bump. CONSTITUTION:A chip mounter is used for a conductive bump 4 of a wiring board 5 for mounting to match, position and arrange electrodes 6a and 6b of a chip-shape resistant element. For this positioning arrangement, a weight is applied instantaneously to the chip mounter to make the tip of the conductive bump 4 in a crushed shape, thus reducing the conductive bump 4 height. Next, this is left in room temperature to harden a room-temperature hardening type silicone resin as an unhardened-shape insulating resin layer 3. This enables the unhardened insulating resin layer 3 to isolate and insulate each connecting part. On the other hand, once it is hardened, its connecting parts are protected from the outer surface and making packaged electronic parts and the wiring board into one unit and fixing it are promoted, thus obtaining the packaged circuit device of high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting wiring board suitable for surface mounting of electronic components and a mounting method using this mounting wiring board.

[0002]

2. Description of the Related Art For the purpose of making electronic devices lighter or more compact, circuit structures have been made smaller.
That is, a mounting circuit device (mounting circuit unit) in which required electronic components are mounted on a surface of a wiring board having pads for surface mounting is being widely put to practical use in various electronic devices. A mounting method using soldering is often used for mounting the electronic components. Specifically, after printing a solder paste in a cream shape on a predetermined position of the conductor turn of the mounting wiring board, that is, on each connection pad surface provided corresponding to the electrode of the electronic component to be mounted, the electronic component Generally, the method of mounting and arranging the electrode groups on the corresponding connection pad surface, passing through a Lilofu furnace to melt the solder paste, cooling and solidifying, and fixing the electronic components on the wiring board is generally adopted. ing. In this step, metal bumps may be provided on each connection pad on the wiring board surface or on the electrode surface of the electronic component.

[0003]

As described above, the mounting of electronic components on the wiring board surface is performed by soldering (solder connection).
Although the method is common, the soldering method has various problems. Specifically, (a) a temperature of 200 ° C to 300 ° C is required to melt the solder, and therefore, a wiring board for mounting is required to have heat resistance that can withstand the above temperature, and also to be mounted. Electronic parts also need to be preliminarily subjected to heat protection so as to withstand the above temperature. To meet these requirements, it is necessary to use relatively expensive materials,
There is a problem that heat protection more than necessary is required.

(B) Also, at the solder melting temperature of 200 ° C. to 300 ° C., stress-free soldered electronic components are cooled at a normal temperature due to a difference in thermal expansion coefficient between the electronic components and the wiring board. It will be a great deal of stress.
For this reason, the connection fixing part,
In particular, the soldered portion where stress is concentrated may cause metal fatigue, resulting in disconnection.

(C) Further, flux is required for soldering, and in the case of cream solder, it is preliminarily mixed in the solder paste. And this flux is
When the solder melts, it decomposes and exhibits acidity or alkalinity to remove the oxide of the conductor pattern surface (for example, copper foil surface) of the wiring board or the electrode of the electronic component to promote soldering. However, on the other hand, since the decomposed product of the flux has a harmful effect of lowering the insulating property of the electric circuit, it is necessary to remove it by washing treatment after soldering. This removal generally requires the use of CFCs or other organic solvents, and because of the adverse effects of the waste liquid on the global environment, alternative measures are required. (d) As the wiring pitch of wiring boards becomes finer with the development of high-density mounting circuits, the problem that molten solder bridges adjacent wiring patterns is also increasing.

It is an object of the present invention to solve (avoid) the problems in soldering and to provide a mounting wiring board and a mounting method suitable for the construction of a mounting circuit device which is low in cost and high in reliability.

[0007]

A mounting wiring board according to the present invention is a mounting wiring board having a connection pad group corresponding to an electrode group of an electronic component to be mounted on at least one main surface,
The connection pad group on the surface of the mounting wiring board has conductive bumps, and at least a part of the surface having the conductive bump group is covered with an uncured insulating resin layer, and In the mounting method according to the present invention, a connection pad group having a conductive bump is formed on at least one main surface, and at least a part of the surface having the conductive bump group is covered with an uncured insulating resin layer. On the surface of the wiring board
A step of aligning and mounting an electronic component having an electrode group corresponding to the conductive bump group, and a stress acts between the conductive bump group and the electrode group of the electronic component of the aligned wiring board. And a step of hardening the insulating resin layer on the surface of the wiring board.

The present invention is based on the following knowledge. That is, the surface of an ordinary metal is contaminated with an oxide or an organic substance, and even if a conductive liquid such as a conductive paste is contacted or applied and fixed,
There is a fairly large interfacial resistance at that interface. Moreover,
The interface resistance easily fluctuates greatly in environments such as temperature and humidity and could not be applied to electronic circuits, but the conductive bumps of appropriate hardness were pressed against the metal forming the electrodes of electronic parts. When applying and further applying stress, it was found that the dirt on the metal surface is mechanically removed to expose the new surface, and the new surface of the metal and the new surface of the conductive bump easily form a bond with zero interface resistance. The present invention has been completed by utilizing this phenomenon.

In the present invention, the mounting wiring board is formed with conductive bump groups at predetermined positions on the outer layer circuit pattern before the solder resist is printed and finished, for example, while the conductive bump groups are formed. It is configured by integrally providing an uncured insulating resin with a thickness that is almost filled. The uncured insulating resin layer does not have to be provided on the entire surface on which the conductive bump group is formed, and may be formed in an island shape such as a peripheral portion of each conductive bump.

Here, since the surface of the copper pattern forming the outer layer circuit of the printed wiring board is contaminated in various process histories, the surface of the copper pattern is mechanically or chemically polished to be a clean surface, and then the conductive bumps are formed. It is desirable to form a group, and by making the surface clean, it is possible to promote the prevention of the occurrence of the interface resistance between the copper pattern and the conductive bump group. Also,
The conductive bumps are made of conductive powder such as silver, gold, copper or solder powder, alloy powder of these or composite metal powder, and polycarbonate resin, polysulfone resin, polyester resin, phenoxy resin, epoxy resin, phenol resin, for example. , A conductive composition prepared by mixing a binder component such as a polyimide resin, or a conductive metal, a conductive organic semiconductor, or the like. When the conductive composition is formed, a conductive bump having a high aspect ratio can be formed by, for example, a printing method using a relatively thick metal mask, and the height of the conductive bump is generally 10 to 10. It can be formed in a wide range of about 400 μm.

On the other hand, as means for forming bumps of conductive metal, (a) when copper foil is used as an outer layer circuit pattern,
Printing and patterning plating resist, copper, tin,
After plating gold, silver, solder, etc. to selectively form minute metal pillars (bumps), or (b) applying and patterning a solder resist on the outer layer circuit pattern surface,
For example, it may be immersed in a solder bath to selectively form minute metal columns (bumps). Here, the minute metal particles or minute metal columns corresponding to the conductive bumps may have a multilayer structure or a multilayer shell structure formed by combining different metals.

In the present invention, when the conductive bumps are formed of a conductive composition, the process can be further simplified as compared with the case where the conductive bumps are formed by a plating method or the like, which is effective in terms of cost reduction. Is. In addition, conductive bumps with appropriate hardness are used to mechanically remove the contaminant layer such as oxides and organic substances on the metal surface forming the electrodes of electronic parts to be mounted and mounted from the contact surface by pressing force. When a stress is applied to the surface of the newly formed metal, the hardness of the electrode of the electronic component should not be deformed or destroyed, and a durometer hardness of 70 to 120 is generally preferable.

The size of the conductive bumps corresponds to the size of the electrodes of the electronic parts to be mounted and mounted, but the conductive bumps can be arbitrarily formed to have a diameter of about 10 to 400 μm. The shape of the bump is preferably such that the bottom surface is large and becomes narrower toward the tip, and may be a mountain shape or a hemispherical shape.

The uncured insulating resin layer that is integrally formed and formed on the surface of the wiring board to a thickness to fill the conductive bumps may be formed and formed on the entire surface of the wiring board. , May be selectively formed only in a necessary portion,
Further, the uncured insulating resin layer may be applied and formed immediately before mounting the electronic component. The insulating resin layer has a role of fixing the mounted electronic component, a role of protecting the circuit portion of the wiring board, and a role of protecting the connection portion. It is preferable that the insulating resin layer is formed of a thermosetting resin, an ultraviolet curable resin, an anaerobic curable resin, or a mixed type thereof, and is cured by ultraviolet rays or heating after mounting the electronic component. A resin that is commercially available as a solder resist is suitable.

Further, in the mounting method of the present invention, when the electrodes of the electronic component and the conductive bumps of the wiring board are mounted by forming a connection having an interface resistance of substantially zero by the action of stress,
The application of the stress may be a force of about 0.5 to 20 N / bump, or the curing shrinkage of the uncured resin depending on the shape and material of the conductive bump. In other words, the electronic components to be mounted and mounted are usually a collection of products from different manufacturers, so the storage period is not constant and the types of electrode materials are different, so the types of oxide layers and organic substances that stain the surface are different. The thickness of the contaminated layer is generally on the order of submicrons, although the thickness thereof is various. With respect to the contaminated layer having such a thickness, the contaminated layer can be removed at the abutting surface of the conductive bump by pressing the conductive bump having the appropriate hardness and having the sharp tip. As a concrete means for this, when the individual electronic components are mounted or after all the electronic components are mounted, they are collectively applied by using a jig plate or the like, and a force is applied from above the electrode portions.

In the present invention, the electronic components to be mounted are chip type resistors and capacitors made of ceramic materials, or IC packages having various lead types such as flat leads, galling type leads and J leads, and connectors. Examples include electronic components such as, and bare IC chips that are rarely used for high-density mounting. The electrodes of these electronic components may be made of noble metal, and are made of a general material such as tin-lead solder material, tin-plated finish, nickel-plated finish, copper, aluminum thin film, etc. Good.

[0017]

In the mounting wiring board according to the present invention described above, the conductive bumps corresponding to the electrodes of the electronic component to be mounted / mounted are installed in such a manner that they are embedded in the uncured insulating resin layer. The conductive bump has a function of breaking a thin oxide layer or the like to expose a new metal surface by the action of stress. Therefore, after the alignment, by applying a stress, the electrode of the electronic component to be mounted / mounted is electrically connected to the conductive bump in a state where the interface resistance is zero. Moreover, while the uncured insulating resin layer insulates and separates the respective connection portions from each other, while hardening the connection portions and the like from the outside world, it promotes the integration and fixing of the mounted electronic components and the wiring board. It is possible to provide a highly reliable mounted circuit device.

[0018]

EXAMPLES Examples 1 (a), 1 (b), 1 (c), 2 (a),
An embodiment of the present invention will be described with reference to (b), (c), and FIGS. 3 (a), (b), (c).

Example 1 FIG. 1 (a) is a sectional view showing an example of a mounting wiring board according to the present invention.
Further, FIG. 1B is a sectional view schematically showing a mode of mounting electronic components on the mounting wiring board shown in FIG. 1A, and FIG. 1C is the mounting shown in FIG. 1B. It is sectional drawing which shows typically the state after mounting an electronic component by applying a stress in a mode.

First, in FIG. 1 (a), 1 is a double-sided mounting wiring board body, 2a is a copper pattern forming a connection pad of the double-sided mounting wiring board body 1, 2b is a circuit pattern, and 3 is the connection. An uncured insulating resin layer 4 integrally laminated on the pad 2 formation surface is a conductive bump formed and arranged on the connection pad 2 surface. More specifically, the double-sided mounting wiring board main body 1 is made of epoxy resin containing glass cloth as a base material, and the thickness of the connection pads 2a and the circuit patterns 2b is 35.
μm, the shape of the connection pad 2a is 0.9 × 1.2 mm, the conductive bumps 4 are 60 μm in height, and the uncured insulating resin layer 3 is a room temperature curing type silicone resin layer with a thickness of 40 μm. The total thickness is 1.0 mm, which enables mounting and mounting of elements.
This is the mounting wiring board 5.

The mounting wiring board 5 having the above structure can be manufactured as follows. That is, the double-sided mounting wiring board main body 1 manufactured by a general means was first prepared, the surface on which the connection pads 2a were formed was polished with a rotary brush, then washed with water and air-cooled and dried. Then, quickly, using a metal mask with a hole of 0.3 mm diameter drilled at a predetermined location on an aluminum plate with a plate thickness of 300 μm, make a hole for the metal mask on the surface of the connection pad 2a of the double-sided mounting wiring board body 1. Position, place a polymer type silver-based conductive paste on it, and
A m-shaped chevron-shaped conductive bump 4 was formed (formed). After that, it is heat-cured at 120 ° C for 30 minutes and 40 μm of room-temperature curing type silicone resin (trade name, RTV rubber, KF3498 manufactured by Shin-Etsu Chemical KK) is used as an adhesive insulating resin layer (uncured insulating resin layer) 3.
Manufactured by applying m thickness.

The mounting of the electronic component 6 on the mounting wiring board 5 having the above-described structure, for example, the mounting of the chip type resistance element is performed as follows. That is, a chip mounter is used for the conductive bumps 4 of the mounting wiring board 5 as shown in FIG.
As shown in, the electrodes 6a and 6b of the chip-shaped resistance element 6 are
Position and arrange in accordance with. In this positioning arrangement, when a load of 5.0 N was momentarily applied to the chip mounter, the tip of the conductive bump 4 was crushed as shown in FIG. Height was reduced to 30 μm. Then, this was left at room temperature for 24 hours to cure the silicone resin 3.

In the mounted circuit mounted above, the chip-shaped resistance element 6 has an electrically sufficient function as a resistance element, and has a thermal shock test (-65 ° C. to 125 ° C., 1000 hours) and a heating test (125 ° C.). , 1000h), humidity resistance test (80 ° C, 85% total humidity resistance, 1000h) and other accelerated reliability tests did not cause any problems.

Embodiment 2 FIG. 2 (a) is a cross-sectional view of another mounting wiring board example according to the present invention, and FIG. 2 (b) is an electronic circuit diagram of the mounting wiring board shown in FIG. 2 (a). FIG. 2 is a cross-sectional view schematically showing an aspect of mounting components.
2C is a cross-sectional view schematically showing a state after mounting the electronic component by applying stress in the mounting mode shown in FIG. 2B.

In accordance with the case of the first embodiment, a conductive bump 4 capable of mounting a galling type FP package type IC memory 6 having a 28-pin lead as shown in a sectional view in FIG. A mounting wiring board 5 having a configuration was prepared. The shape of the connection pads 2a of the mounting wiring board 5 was 0.8 × 1.6 mm square with a minimum pitch of 1.25 mm, and the conductive bumps 4 were mountain-shaped with a height of about 50 μm. Then, on the surface of the mounting wiring board 5, the leads of the IC memory 6 are
Align 6a with the corresponding conductive bump 4 and place it on the flat surface of the leads 6a and 6b as shown in cross section in FIG. 2 (b).
Applying a force of 20 N, the height of the conductive bump 4 is approximately 35 μm.
The mounting was carried out by pressing so as to achieve a certain degree.

The thus constructed IC memory mounted circuit device as shown in cross section in FIG. 2 (c) exhibits an electrically sufficient function, and is subjected to a thermal shock test (-65 ° C. to 125 ° C., 1000 h).
There were no problems in accelerated reliability tests such as heating tests (125 ° C, 1000h) and humidity resistance tests (80 ° C, 85% total humidity resistance, 1000h).

Example 3 First, the base material made of epoxy resin containing glass cloth was manufactured by a conventional method to have a thickness of 1.0 mm, and a copper pattern had a thickness of 18 mm.
The wiring board is 100 μm square, the minimum pitch is 150 μm, the surface is thin nickel, and the connection pads 2a group coated with gold plating are used.
According to the first embodiment, the height is about 30 through the metal mask.
A wiring board 5 for mounting was prepared in which a conductive bump 4 having a mountain shape of μm was provided, and an uncured insulating resin layer 3 was provided on the conductive bump 4 installation surface. On the other hand, an IC memory chip (chip size, 15 × 10 mm square) having 100 µm square, I / O terminals made of aluminum thin film with a thickness of about 1 µm and a minimum pitch of 150 µm was prepared as an electronic component. here,
The conductive bumps 4 of the mounting wiring board 5 have an average particle size of 0.5 μm.
Insulating resin layer 3 which is uncured by printing a conductive paste consisting of scaly silver powder and bisphenol type epoxy resin and heat curing at 120 ° C for 30 minutes
Is a solder resist (trade name. UVR-150R, Taiyo Ink
KK) to a thickness of about 30 μm.

The IC memory chip 6 is mounted on the surface of the mounting wiring board 5 by aligning the conductive bumps 4 and the I / O terminals 6a and 6b with each other as shown in a sectional view in FIG. 3 (b).
After arranging, a weight of 20 N was applied so that the weight was evenly applied from above the IC memory chip 6, and the height of the conductive bump 4 was reduced to 15 μm, and this was placed in an ultraviolet irradiation furnace. The uncured insulating resin layer 3 was hardened and further heated at 120 ° C. for 30 minutes to be completely hardened to form a mounted circuit device as shown in a sectional view in FIG. 3C. The above-configured mounted circuit device has an electrically sufficient function, and has a thermal shock test (-65 ° C to 125 ° C, 1000h), a heating test (125 ° C, 1000h), and a humidity resistance test (80 ° C, 85%). Total humidity resistance,
There was no problem in the accelerated reliability test such as 1000h).

[0029]

According to the mounting wiring board of the present invention, it is possible to easily avoid the problem due to the solder connection, which has been posed in the conventional mounting of electronic components. Specifically, (1) electronic components can be mounted and connected at room temperature to 100 ° C process temperature, and high-grade heat-resistant materials do not have to be used for wiring boards and electronic components. (2) Since it is possible to connect at low temperature as described above, the stress due to the difference in the coefficient of thermal expansion between the wiring board and the electronic component can be suppressed to a small level, and the occurrence of peeling of the connection part can be suppressed for long-term use. Will endure. (3) Since it is not necessary to use electrically harmful substances such as flux used for solder connection, environmental problems do not occur. (Four)
Even if the pitch of the wiring becomes fine, by forming the conductive bumps finely, reliable electrical connection with electronic components is achieved, and there is a problem that the pattern of adjacent connection parts bridges. Absent. Thus, it can be said that the mounting wiring board and the mounting method using the mounting wiring board according to the present invention bring many practical advantages.

[Brief description of drawings]

FIG. 1 illustrates a mounting wiring board and a mounting method according to the present invention. (A) is a cross-sectional view of the mounting wiring board, and (b) is a schematic view showing a state in which a chip-type electronic component is mounted. 2C is a cross-sectional view of a mounted circuit device formed by mounting electronic components.

FIG. 2 shows another example of a mounting wiring board and a mounting method according to the present invention, in which (a) is a cross-sectional view of the mounting wiring board,
FIG. 2B is a cross-sectional view schematically showing a state in which an IC with leads is mounted, and FIG. 6C is a cross-sectional view of a mounted circuit device formed by mounting electronic components.

3A and 3B show still another example of a mounting wiring board and a mounting method according to the present invention, in which FIG. 3A is a sectional view of the mounting wiring board, and FIG. 3B is a state in which a bare chip IC is mounted. FIG. 3C is a schematic cross-sectional view of the mounting circuit device formed by mounting the electronic component.

[Explanation of symbols]

1 ... Wiring board body for double-sided mounting 2a ... Connection pad 2b
... Circuit pattern 3 ... Unhardened insulating resin layer 4 ... Conductive bump 5
… Mounting wiring board 6… Mounting / mounting electronic components 6a, 6b
… Electrodes (terminals) 7… Crushed conductive bumps

Claims (2)

[Claims] 1. A mounting wiring board having a connection pad group corresponding to an electrode group of an electronic component to be mounted on at least one main surface, wherein each connection pad group on the mounting wiring board surface includes a conductive bump. And a mounting wiring board characterized in that at least a part of the surface provided with the conductive bump group is covered with an uncured insulating resin layer. 2. A surface of a wiring board in which a connection pad group having conductive bumps is formed on at least one main surface, and at least the surface having conductive bump groups is covered with an uncured insulating resin layer. Above, a step of aligning and mounting an electronic component having an electrode group corresponding to the conductive bump group, and between the conductive bump group of the aligned wiring board and the electrode group of the electronic component respectively. A mounting method comprising a step of mounting an electronic component so that a stress acts, and a step of curing an insulating resin layer on the surface of the wiring board.