JPH09298357A - Fusing method for soldering to printed-wiring board and printed-wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fusing method in which the costs of a raw material for a base film are reduced, whose working costs are suppressed to be equal to those of a soldering operation in conventional cases and whose costs can be lowered sharply as a whole, by a method wherein solder can be fused to a wiring pattern on a printed-wiring board formed of the synthetic resin base film whose solder heat resistance is low. SOLUTION: A base film 2 at a printed-wiring board 1 is provided with an infrared transmitting property. When solder pieces 8 are positioned in land parts 5 so as to be irradiated with an infrared beam B, only the solder pieces 8 absorb infrared heat so as to be heated, and the solder pieces are fused to the land parts 5, the infrared beam B which is leaked from parts around the land parts 5 is transmitted through the base film 2 without convecting or conducting, heat is not generated, and the base film 2 is not fused/softened. Consequently, by a soldering operation whose working costs are low, an electronic component 4 can be mounted on, and attached to the printed-wiring board 1 on which the base film 2 is formed of a material whose solder heat resistance is low, and a solder coating operation can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder welding method for a printed wiring board, in which solder is welded to a land portion when an electronic component is mounted on the printed wiring board.
It is a printed wiring board used therefor, and is particularly suitable for welding solder on a base substrate or base film made of a synthetic resin having low solder heat resistance that melts or softens at a soldering temperature.

[0002]

2. Description of the Related Art In recent years, high-density mounting in electronic equipment
Miniaturization, weight reduction, thinning, and high performance are remarkable
Since the number of electronic components such as ICs and LSIs has increased dramatically,
Printed wiring boards are widely used for mounting these at high density. In addition, recently, a film-shaped flexible wiring board has been used to three-dimensionally and densely mount a large number of electronic components in a narrow wiring space of a small electronic device.

FIG. 4 is a sectional view showing the basic structure of such a flexible wiring board 31. A wiring pattern 33 based on electrical design is formed on the surface of a thin base film 32 having both insulation and flexibility. The wiring pattern 33 is formed of a conductive material such as copper foil, and the wiring pattern 33 is covered with a cover lay 34 made of a flexible insulating resin layer except for the land portions 33a for soldering electronic components. .

The base film 32 of the flexible wiring board 31 is required to have sufficient mechanical strength such as solder heat resistance and bending resistance to withstand high temperatures for soldering, and therefore a polyimide resin film is used. It is used. The wiring pattern 33 is generally formed by a subtractive method in which unnecessary copper foil other than the wiring pattern 33 is dissolved and removed with a chemical from a flexible copper clad plate in which a copper foil is bonded to the base film 32.

By the way, in recent years, the price of electronic devices has become more and more constant, and the cost of printed wiring boards including the electronic parts constituting the electronic devices has been sought to be reduced. Since the cost of the raw material of the polyimide used as the base film 32 occupies 70 to 80% of the total, the low-priced base film material to replace this is being tried. In this case, if electronic parts can be mounted by a method other than soldering, they will not be exposed to high temperatures, so low-cost materials such as polyethylene terephthalate (PET) and polycarbonate (PC), which have low soldering heat resistance, can be used. The base film can be formed by using it, and the raw material cost of the base film 32 can be suppressed to about 10% of that of polyimide.

FIG. 5 shows a method of mounting an electronic component on a PET film or a PC film having low solder heat resistance. A conductive adhesive 41 is applied to the land portion 33a of the wiring pattern 33.
The electronic component 42 is mounted via the. If you install it in this way, you do not need to solder it,
The wiring pattern 33 can be easily formed by printing the silver paste on the base film 32, which is not only required to have the solder heat resistance for the base film 32 but also uses a silver paste which is inferior to the solder welding property as compared with the copper foil. You can
Therefore, the cost of forming the wiring pattern 33 can be reduced.

[0007]

However, even though the cost for forming the wiring pattern 33 can be reduced, the conductive adhesive is very expensive as compared with solder, and therefore the inexpensive PET as the base film 32 is used. Even if a film or a PC film is used, it is not possible to significantly reduce the cost as a whole. In addition, the conductive adhesive 41 is mainly used to secure electrical continuity between the terminals of the electronic component 42 and the land portion 33a, and the adhesive strength enough to fix the electronic component 42 to the base film 32 is sufficient. Therefore, the following troublesome mounting process must be performed to obtain the adhesive strength.

That is, after the electronic component 42 is temporarily fixed to the base film 32 by the temporary adhesive 43, the conductive adhesive 41 is injection-coated on the land portion 33a in a required amount by using a dispenser or the like, and further, the electronic In order to securely fix the component 42 on the base film 32, the land portion 33a or the entire electronic component 42 is coated with a reinforcing adhesive 44 such as an epoxy resin. As described above, since the number of steps is larger than that of soldering, the processing cost is high, and the cost cannot be reduced as a whole. Further, after the temporary fixing adhesive 43, the conductive adhesive 41, and the reinforcing adhesive 44 cannot be easily peeled off after drying, repair cannot be performed after the product inspection, and therefore the yield is reduced. Unfortunately, this was also a factor that prevented cost reduction.

In view of the above, the present invention enables mounting of electronic components by soldering or land coating on a base substrate or base film made of a synthetic resin having low solder heat resistance so that the base substrate or base can be coated. The technical challenge is to significantly reduce the raw material cost of the film, to suppress the processing cost to the same level as the conventional soldering, and to significantly reduce the overall cost.

[0010]

In order to solve this problem, the present invention provides a solder for a printed wiring board in which a solder is welded to a land portion on a base substrate or a base film made of a synthetic resin having low solder heat resistance. In the welding method, the base substrate or the base film transmits infrared rays to such an extent that the base substrate or the base film is not heated to the melting point or the softening point when the base substrate or the base film is irradiated with the infrared beam for solder melting for the same time as the time until the solder melts. And the solder is heated and melted by irradiating the land portion with an infrared beam in a state where the solder is positioned on the land portion.

According to the method of the present invention, for example, when mounting an electronic component on a printed wiring board, the electronic component is positioned at a predetermined mounting position, and the land portion of the wiring pattern is coated with, for example, cream solder. When the land portion is irradiated with the infrared beam, the solder is heated by the infrared rays, and the electronic component is fixed at a predetermined mounting position with its terminals electrically connected to the land portion.

At this time, as a material of a base substrate or a base film on which electronic parts are mounted, an infrared beam for solder melting is not heated to a melting point or a softening point when it is irradiated for the same time as the time until the solder melts. Since a synthetic resin having infrared transmissivity is used, when the land part is irradiated with the infrared beam, the infrared beam leaking from the surroundings passes through the base substrate or the base film as it is. Therefore, the base substrate or the base film is not directly heated by the infrared beam, and the heat of the molten solder is only transmitted to the base substrate or the base film.

Since the solder is not melted by the heat supplied from a heat source having a large heat capacity such as a soldering iron, but by the heat generated when the infrared beam is absorbed, the solder is melted through the land portion and the base substrate or the base film. The heat that is transmitted to the land is only the heat of the solder itself that adheres to the land portion, and not all of that heat is transmitted, only a portion of which is dispersed and transmitted to the base substrate or base film. Is. Also, when heating with an infrared beam, the heat resistance is small and minute temperature control is possible, the time until the solder melts is extremely short (for example, about 1 to 2 seconds), and the heat of the melted solder is transferred through the land portion. Since it is not continuously supplied to the base substrate or the base film for a long time, the soldering work is completed before a large amount of heat is transferred to the base substrate or the base film so that the base substrate or the base film is melted or softened. Therefore, the processing cost of electronic parts can be reduced with respect to a low-priced printed wiring board in which a base substrate or a base film is formed of a synthetic resin having a low solder heat resistance such as PET or PC whose melting point is lower than that of solder. It can be mounted or solder-coated by various soldering methods, which greatly reduces the cost as a whole.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a sectional view showing a printed wiring board according to the present invention, FIG. 2 is a sectional view showing a state in which an electronic component is mounted by the method of the present invention, and FIG. 3 is a sectional view showing another printed wiring board according to the present invention. It is sectional drawing which shows the state which mounted the electronic component by the method.

The printed wiring board 1 of this example is a flexible type which can be bent, and its base film 2 is
Solder heat resistance is low, and it is made of a synthetic resin that has infrared transparency that does not heat the melting point or softening point when the solder is irradiated with an infrared beam for melting for the same time as the time until the solder melts. Specifically, for example, a flexible film of polyethylene terephthalate (PET) having a thickness of about 100 to 125 μm, which is annealed by heating at 150 to 160 ° C. for 30 minutes, is used.

A wiring pattern 3 made of a conductive material is formed on the base film 2, and the terminals 4 of the electronic component 4 are formed.
A cover lay 6 is insulatingly coated except for the land portion 5 and the like which are electrically connected to a. This cover lay 6 also has an infrared ray transmissivity similar to that of the base film 2, and the base film 2 on which the wiring pattern 3 is already formed.
It is formed by thermocompression bonding an insulating resin film to be the cover lay 6 or by applying / drying a resist ink.

The wiring pattern 3 is formed, for example, by an additive method in which a conductive ink is printed on the base film 2. As the conductive ink, silver powder is dispersed in a vehicle of synthetic resin (eg acrylic resin). Is used. Although this silver paste has slightly higher electric resistance than copper foil, it has excellent printing characteristics, so that the wiring pattern 3 can be easily formed by printing, and thus the cost of forming the wiring pattern 3 can be reduced. .

The land portion 5 is formed by dispersing copper powder coated with silver in a vehicle of thermosetting synthetic resin (for example, phenol resin) on the wiring pattern 3 formed of silver paste. A solder welding layer 7 of silver-copper paste is formed. The silver paste for forming the wiring pattern 3 was originally used as a conductor of a printed wiring board on the premise that the electronic component 4 is not mounted by soldering, and since it has poor solderability, it remains as it is. So you can't solder. Therefore, the solder weldability to the land portion 5 is improved through the solder weld layer 7 of the silver-copper paste, which is excellent in solder weldability and also in adhesiveness to the silver paste.

Since the silver-copper paste forming the solder-welding layer 7 has better adhesion to the wiring pattern 3 than to the solder-bonding property with the solder 8, the electronic component 4 is forced to be forced. Even if it is peeled off, it peels off at the interface between the silver-copper paste and the solder 8, and the land portion 5 remains on the base film 2 as it is. Therefore, for example, a contact failure of the electronic component 4 mounted on the base film 2 may occur. When it occurs, the electronic component 4 can be once replaced or remounted by reheating the solder 8.

The above is the configuration example of the printed wiring board according to the present invention. Next, the electronic component mounting method according to the present invention will be described with reference to FIG. First, wiring pattern 3
After a predetermined amount of cream solder 8 is applied on the solder welding layer 7 of the land portion 5, the electronic component 4 is positioned at a predetermined position. In this state, when the land portion 5 is irradiated with an infrared beam B emitted from an infrared lamp such as a xenon lamp or an infrared laser light source (neither is shown), the cream solder 8 absorbs infrared rays and is heated and melted. The electronic component 4 is fixed to the mounting position on the base film 2 in a state where the terminal 4a thereof is electrically joined to the solder welding layer 7 of the land portion 5.

The base film 2 and the coverlay 6
As a material for the above, a synthetic resin (for example, PET or PC) having an infrared ray transmissive property such that the infrared ray B used for melting the solder is not heated to the melting point or the softening point even when the solder is irradiated for the same time as the melting time Since the infrared beam B leaking around the land portion 5 is transmitted through the base film 2 as it is, the base film 2 is not directly heated by the infrared beam B, and at most the molten solder 8 is melted. Only heat is transmitted.

In this case, the solder 8 is not melted by the heat supplied from a heat source having a large heat capacity such as a soldering iron, but is melted by the heat of the absorbed infrared rays. The heat transferred to the base film 2 through the pattern 3 is only the heat of the small amount of the solder 8 itself adhering to the land portion 5,
Moreover, not all of the heat is transmitted, but only part of the heat is dispersed and transmitted to the base film 2. further,
The time until the solder 8 is melted by the infrared beam B is 1 to 2
The heat of the molten solder 8 is extremely short in seconds and the land portion 5
Since it is not continuously supplied to the base film 2 for a long time through, the soldering work is completed before a large amount of heat is transferred so that the base film 2 is melted or softened.
Therefore, by doing so, the electronic component 4 can be soldered at a low processing cost to the low-priced printed wiring board 1 on which the base film 2 is formed of a synthetic resin having low solder heat resistance such as PET or PC. The printed circuit board 1 can be mounted, and the manufacturing cost of the printed wiring board 1 including the mounting of the electronic component 4 can be significantly reduced.

FIG. 3 is a sectional view showing a state in which an electronic component is mounted by the method of the present invention using another printed wiring board according to the present invention. Printed wiring board 11 according to this example
Is a synthetic resin (for example, PET) having an infrared ray transmissive property such that the base film 12 is not heated to the melting point or the softening point when the infrared beam B used for melting the solder is irradiated for the same time as the time until the solder melts. And P
C). A wiring pattern 13 is printed and formed on the base film 12 with a conductive ink, and the cover layer 1 is removed except for a land portion 15 which is a contact electrically connected to the terminal 4a of the electronic component 4.
Insulated by 6. This cover lay 16 also has the same infrared transparency as the base film 12. As the conductive ink for forming the wiring pattern 13, in this example, a silver-copper paste in which silver-coated copper powder is dispersed in a thermosetting resin vehicle (for example, a phenol-based vehicle) is used. Since this silver-copper paste originally has good solder-welding properties, it is not necessary to separately form a solder-welding layer.

Then, the cream solder 8 is applied on the wiring pattern 13 formed of the silver-copper paste of the land portion 15 to position the electronic component 4, and the land portion 15 is positioned.
When the infrared beam B is irradiated onto the solder, the solder 8 of the land portion 15 is heated and melted, and the electronic component 4 is mounted, as in the above-described embodiment. At this time, the infrared beam B leaking around the land portion 15 passes through the cover lay 16 and the base film 12 as it is, so the base film 12 and the cover lay 16 are not directly heated by the infrared beam B. In addition, the heat of the solder 8 is only partly dispersed and transmitted to the base film 12, and the time until the solder 8 is melted by the infrared beam B is extremely short as 1 to 2 seconds. Since it is not continuously supplied to the base film 12 through the land portion 15 for a long time, the soldering work is completed before a large amount of heat is transferred to the base film 12 so that the base film 12 is melted or softened. As described above, according to this example, not only the electronic component 4 can be mounted on the base film 12 made of synthetic resin having low solder heat resistance by soldering, but especially, the land portion 15
Since there is no need to separately form a solder welding layer, the processing cost can be reduced accordingly.

In the above description, as the printed wiring boards 1 and 11, the flexible type in which the wiring patterns 3 and 13 are formed on the base films 2 and 12 has been described as an example, but the present invention is of course flexible. Even if it is a rigid type with a wiring pattern formed on a non-flexible base substrate, the electronic component mounting part is rigidly formed on the base substrate and the bent part is flexibly formed on the base film. -Applicable to rigid wiring boards. Moreover, although the case where the electronic component 4 is mounted on the printed wiring boards 1 and 11 by soldering has been described, the present invention is not limited to this, and the land portions 5 and 15 are preliminarily solder-coated before mounting the electronic component 4 or the like. It can also be applied when soldering. further,
As the printed wiring board used in the method of the present invention, the one in which the wiring patterns 3 and 13 are formed by printing with the silver paste and the silver-copper paste has been described, but the printed wiring board used in the method of the present invention is not limited to this, and the base substrate or The base films 2 and 12 are made of a synthetic resin having an infrared ray transmissive property such that the infrared ray B used for melting the solder is not heated to the melting point or softening when the solder is irradiated for the same time as the melting time. The wiring patterns 3 and 13 may be formed by any method using any conductive material as long as they are provided. Furthermore, the solder is not limited to the case of using the cream solder 8, but may be the case of using any solid solder in the form of threads or pellets.

[0026]

As described above, according to the present invention, P
Solder such as ET or PC Solder electronic parts to low-priced printed wiring boards on which a base substrate or base film is made of a synthetic resin with low heat resistance, or soldering land parts at low processing costs. Since it can be coated, it has a very excellent effect that the cost of the entire printed wiring board, including the processing cost until the electronic component is mounted, can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a printed wiring board according to the present invention.

FIG. 2 is an explanatory diagram showing a method of mounting an electronic component according to the method of the present invention.

FIG. 3 is a sectional view showing a state in which an electronic component is mounted by the method of the present invention using another printed wiring board according to the present invention.

FIG. 4 is a sectional view of a printed wiring board on which electronic components are mounted by a conventional method.

FIG. 5 is a sectional view of a printed wiring board on which electronic components are mounted by a conventional method.

[Explanation of symbols]

 1, 11 --- Printed wiring board 2, 12 --- Base film 3, 13 --- Wiring pattern 4 ... --- Electronic component 4a ...・ ・ ・ ・ ・ Terminals 5,15 ・ ・ ・ ・ ・ ・ Land portion 6,16 ・ ・ ・ ・ ・ ・ Coverlay 7 ・ ・ ・ ・ ・ ・ ・ Solder welding layer 8 ・ ・ ・ ・ ・ ・・ Cream solder B ・ ・ ・ ・ ・ ・ Infrared beam

Claims (3)

[Claims] 1. A solder welding method for a printed wiring board, wherein solder is welded to a land portion (5, 15) on a base substrate or base film (2, 12) made of synthetic resin, wherein the base substrate or base film ( 2, 12) is not heated to the melting point or the softening point when the base substrate or the base film (2, 12) is irradiated with the infrared ray (B) for solder melting for the same time as the time until the solder melts. The land (5, 15) is made of a synthetic resin having infrared transparency, and the land (5, 15) is irradiated with an infrared beam (B) while the solder (8) is positioned on the land (5, 15). (8) A method for solder welding to a printed wiring board, which comprises heating and melting. 2. A land (5) of a wiring pattern (3) formed on a synthetic resin base substrate or base film (2) is irradiated with an infrared beam (B) to weld a solder (8). In the printed wiring board, the base substrate or base film (2) is the same as the time until the solder melts the infrared beam (B) for solder melting.
Is formed of a synthetic resin having infrared transmissivity that is not heated to the melting point or softening point when irradiated with, and the wiring pattern (3) is formed of a silver paste in which silver powder is dispersed in a vehicle. In the land portion (5) of the wiring pattern (3), a silver-copper paste formed by dispersing copper powder coated with silver in a vehicle on the wiring pattern (3) formed of the silver paste is used. A printed wiring board having a solder welding layer (7) formed thereon. 3. The infrared beam (B) is applied to the land portion (15) of the wiring pattern (13) formed on the base substrate or base film (12) made of synthetic resin to weld the solder (8). In a printed wiring board, the base substrate or base film (12) is the same as the time until the solder melts the infrared beam (B) for solder melting.
The wiring pattern (13) is formed of a synthetic resin having an infrared ray transmissive property such that it is not heated to the melting point or the softening point when it is irradiated with silver, and the wiring pattern (13) is formed by dispersing copper powder coated with silver in a vehicle. A printed wiring board, which is formed of a copper paste.