JPH0661624A - Printed circuit board and method for mounting electronic component thereon - Google Patents

Abstract

PURPOSE:To produce a printed circuit board provided with a solder layer having high solderability without requiring a step for cleaning flux, and to provide a method for mounting electronic components thereon. CONSTITUTION:The printed board 1 comprises a first solder layer 5 formed, mainly of tin and lead, on a predetermined wiring pattern 2 which is formed on a basic material, and a second solder layer or a tin layer 6 laminated on the first solder layer 5 while containing more tin than the first solder layer 5. An electronic component is mounted directly on the printed board 1 and then heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board,
In particular, the present invention relates to a printed board having a solder layer having good solderability and a method for mounting electronic components on the printed board.

[0002]

2. Description of the Related Art In order to mount electronic parts on a printed circuit board, a circuit pattern having a predetermined shape is provided on a base material, and then a protective layer is provided on the surface of a wiring pattern.
After processing the protective layer, electronic components are mounted. As this printed circuit board, a copper through-board type with pre-flux applied to prevent the oxidation of copper in the wiring pattern and a solder layer by the hot air leveler method on the circuit pattern are used to prevent oxidation of the wiring pattern and solderability. Improved solder coated substrate types have been used conventionally.

FIG. 3 shows a schematic flow of mounting a surface mounting type electronic component on a printed circuit board by using a copper through substrate. In this method, a preflux film as a protective film is washed with chlorofluorocarbon or the like. After the solder paste is applied to necessary portions, electronic components are bonded with an adhesive or the like, and then the components are soldered by heating, and then unnecessary flux is washed.

FIG. 4 shows a schematic flow of mounting an electronic component on a printed circuit board by using a solder coated substrate. This method is applied on a circuit pattern of the printed circuit board by a gas leveler method. After applying a solder paste on the solder layer, the electronic components are bonded with an adhesive or the like, and then the electronic components are soldered by heating, and then unnecessary flux is washed.

[0005]

When soldering an electronic component using a copper through board, a pre-flux applied as an anti-oxidation film of a circuit pattern and a solder paste applied after cleaning the pre-flux are used. It is necessary to clean the contained flux with a cleaning liquid such as CFC, but the CFC used for this will cause environmental damage such as destruction of the ozone layer in the atmosphere and will be prohibited from use in the future. An implementation method that does not require is required. Also, when using a solder-coated substrate, unevenness occurs on the surface of the solder layer on the circuit pattern formed by the hot air leveler method, and the thickness becomes uneven, so applying solder paste eliminates unevenness and makes it uniform. The solder paste used for this purpose has a problem that the flux contained therein is washed with chlorofluorocarbon, which causes environmental damage and cannot be used in the future.

The present invention has been made in order to solve the above problems, and does not require a flux cleaning step, and a printed circuit board provided with a solder layer having good solderability and the printed board. An object is to provide a method for mounting electronic components on a board.

[0007]

A printed circuit board according to a first aspect of the present invention is a first solder layer containing tin and lead as main components on a wiring pattern of a base material having a wiring pattern of a predetermined shape. And a second solder layer or tin layer having a tin content higher than that of the first solder layer laminated on the first solder layer.

The printed circuit board according to the second aspect of the present invention is characterized in that the total thickness of the first solder layer and the second solder layer or tin layer is 2 μm or more.

Furthermore, the printed circuit board according to the third aspect of the present invention is characterized in that the first solder layer and the second solder layer or the tin layer contain silver and / or bismuth in addition to tin and lead. To do.

Furthermore, the method of mounting an electronic component on a printed circuit board according to the present invention is such that the electronic component is directly mounted on the second solder layer or tin layer of the printed circuit board of the first invention or the second invention and heated. It is characterized by doing.

The method for mounting electronic components on a printed circuit board according to the present invention is a board having a wiring pattern having a predetermined shape, and a solder layer or a tin layer having a tin content higher than that of the solder eutectic composition on the pattern. Then, a solder paste having a tin content lower than that of the solder layer or the tin layer is applied onto the solder layer or the tin layer, and then an electronic component is mounted and heated.

Further, according to the method of mounting an electronic component on a printed circuit board according to the present invention, a solder layer or tin having a tin content higher than that of a solder eutectic composition is formed on the wiring pattern of a board having a wiring pattern of a predetermined shape. Forming a layer, and then having a tin content lower than that of the solder layer or the tin layer on the solder layer or the tin layer, and after heating, forms a solder eutectic composition layer mixed with the solder layer or the tin layer. After the solder paste is applied, the electronic component is mounted and heated.

The method for mounting electronic components on a printed circuit board according to the present invention includes a flux containing no flux or a non-cleaning type flux as a solder paste, and
It is characterized by using a material containing silver, bismuth, etc. in addition to tin and lead.

Furthermore, the method for mounting electronic components on a printed circuit board according to the present invention uses tin as a solder layer or a tin layer,
It is characterized by using an alloy composition containing silver and / or bismuth in addition to lead.

[0015]

The printed circuit board according to the first aspect of the present invention is provided with a first solder layer containing tin and lead as main components on a wiring pattern and a first solder layer laminated on the first solder layer. Since it is configured to include a second solder layer or tin layer having a tin content higher than that of the layer, the second solder layer or tin layer has a higher tin content and therefore has a higher oxidation resistance than normal solder. It is possible to provide a printed circuit board which has improved solderability on the printed circuit board, is less likely to deteriorate in solderability due to surface oxidation, and has good wettability without flux. Therefore, it is not necessary to apply pre-flux to prevent the wiring pattern from being oxidized, and it is not necessary to use CFC or the like to clean it.

Further, by setting the total thickness of the first solder layer and the second solder layer or tin layer of the printed circuit board to 2 μm or more, a potential component is formed on the second solder layer or tin layer of the printed circuit board. The electronic component can be mounted on the printed circuit board more simply by directly mounting and heating.

Further, according to the method for mounting electronic components on a printed circuit board of the present invention, a solder layer or tin having a tin content higher than that of the solder eutectic composition is formed on the wiring pattern of a base material having a wiring pattern of a predetermined shape. After forming a layer and applying a solder paste having a tin content lower than that of the solder layer or the tin layer to the solder layer or the tin layer, for example, a solder paste containing no flux or no cleaning type flux, electronic components are mounted. By heating, electronic components can be easily mounted, and by forming a solder layer or tin layer on the wiring pattern, the wiring pattern can be prevented from being oxidized, and thus no flux or no cleaning type flux can be used. Electronic components can be easily mounted on a printed circuit board by using a solder paste containing

Further, according to the method of mounting an electronic component on a printed circuit board of the present invention, a solder layer or a tin layer having a tin content higher than that of a solder eutectic composition is formed on the wiring pattern of a substrate having a wiring pattern of a predetermined shape. A solder paste having a tin content lower than that of the solder layer or tin layer on the solder layer or tin layer, and after heating, forms a solder eutectic composition layer mixed with the solder layer or tin layer. Since the composition is applied, the heating temperature at the time of mounting the electronic component on the printed circuit board can be lowered, and the influence of heat on the electronic component can be reduced.

[0019]

EXAMPLES Example 1. Hereinafter, a printed circuit board according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view showing a mounted state of electronic components, and in FIG.
Is a substrate for printed circuit boards such as glass and epoxy resin, (2)
Is a wiring pattern provided on the base material (1), which is formed by forming a copper foil into a predetermined shape by etching or the like. Here, in a tin-lead alloy, Sn: Pb = 6
The melting point is the lowest at the eutectic point of 1.9: 38.1, so it is possible to solder at low temperatures. Therefore, as shown in FIG. 1, first, a first solder layer (5) having a thickness of 1 μm and a tin-lead ratio of 6: 4 is formed on the wiring pattern by electroless plating. Next, on the first solder layer (5), a second solder layer or tin layer (6) with a thickness of 1 μm of tin and lead of 9: 1 or 100% tin is formed by electroless plating. To do. By forming this second solder layer or tin layer (6) with a high tin content, oxidation of the solder layer surface can be prevented and it can be stored for a long time before using it in the next step. Is.

The total thickness of the first solder layer and the second solder layer or tin layer can be appropriately changed according to the wiring pattern pitch and width. If the total thickness is 2 μm, the solder paste and the flux can be changed. Good solderability can be obtained without treatment. The first solder layer is further thickly formed by electroless plating of 9 μm, and the total thickness of the first solder layer and the second solder layer or tin layer is 10 μm.
Good solderability can be obtained even with a printed circuit board having a thickness of μm or more without solder paste or flux treatment.

The printed circuit board used for mounting the electronic component shown in Example 1 is constructed as described above, and the lead frame (4) of the IC is fixed with an adhesive (not shown) to directly form the second solder layer. Or, by mounting the lead frame on the printed circuit board with good characteristics even if the time from the completion of the printed circuit board to the mounting of electronic parts has elapsed, by mounting by heating while keeping it in contact with the tin layer. You can In addition, when the total thickness of the first solder layer and the second solder layer or tin layer is relatively thin, the solder paste does not contain flux on the second solder layer or tin layer or contains a non-cleaning type flux. Applied, and then the lead frame
It is also possible to mount (4) by fixing it with an adhesive and heating it. In this case, it is not necessary to wash with fluorocarbon or the like after mounting the electronic component.

Example 2. Hereinafter, examples of mounting electronic components on a printed circuit board according to another embodiment of the present invention will be described with reference to the drawings. 2 is a partial cross-sectional view showing a mounted state of electronic parts. In FIG. 2, (1) is a substrate of a printed circuit board such as glass or epoxy resin, and (2) is provided on the substrate (1). The wiring pattern is formed by forming a copper foil into a predetermined shape by etching or the like. (3) is this wiring pattern
(2) In the solder layer formed above, an electroless plating solution containing tin and lead in a ratio of 7: 3 and organic sulfonic acid as a main component is used, and the plating temperature is 70 ° C. and the plating time is 3 minutes. 2 is a solder layer (alloy coating layer) having a dimension (A) of 1 μm or a tin layer of 100% tin obtained by electroless plating under the conditions. (4) is a lead frame such as an IC fixed to the solder layer or the tin layer (3).

The printed circuit board used in the method for mounting electronic components shown in Example 2 is constructed as described above, and the ratio of tin to lead is 5: 5 to 6: 4 on this solder layer or tin layer (3).
Of cream solder (7) with a thickness of about 100 μm is applied,
Base material (1) for the lead frame (4) with an adhesive (not shown), etc.
When it is mounted in a predetermined position and heated, the solder layer or tin layer (3) and the cream solder (7) are fused and the lead frame can be mounted on a printed circuit board. At this time, since the solder layer or the tin layer (3) contains a relatively large amount of tin or is made of 100% tin, the surface is less oxidized, so it is necessary to apply an anti-pre-flux to prevent oxidation. There is therefore no need to use CFCs to clean the preflux. Further, since the solder layer or tin layer (3) formed by electroless plating is a film formed by the reaction at the interface between the metal copper that is the wiring pattern and the plating solution, the flatness similar to that of the wiring pattern (2) is obtained. Obtained,
It is not necessary to apply a paste containing flux for correcting irregularities.

Example 3. In the second embodiment, the lead frame (4) is mounted after forming the electroless plating layer having a tin to lead ratio of 9: 1 or tin 100% and a thickness of 1 to 2 μm as the solder layer or the tin layer (3). When applying 100% thick cream solder (7) with a tin to lead ratio of 6: 4 and heating after mounting electronic components, the solder layer and cream solder (7) fuse together, resulting in a eutectic crystal as a whole. A eutectic composition layer close to the composition of the solder is formed, and the soldering can be performed at a relatively low temperature near 183 ° C.

Example 4. In the printed boards obtained in Examples 2 to 3, when the solder layer or the tin layer (3) is relatively thin, no flux is contained on the solder layer or the tin layer (3), or a non-cleaning type solder paste. Then, the lead frame (4) is fixed with an adhesive (not shown),
If the mounting is performed by heating, it is not necessary to wash with a fluorocarbon or the like after mounting the electronic component.

Example 5. Other than tin and lead as the alloy composition constituting the first solder layer (5) and the second solder layer or tin layer (6) or the solder layer or tin layer (3) described in Examples 1 to 4 above. By adding 0.5 to 2.0% by weight of silver and / or bismuth, the soldering temperature at the time of joining can be controlled to be increased or decreased, and the lead frame (4) and the wiring pattern (2) can be adjusted. There is an effect that the solder heat resistance strength can be improved. Further, the same effect as described above can be expected by using a solder paste containing silver and / or bismuth in addition to tin and lead.

Example 6. Furthermore, in the above Examples 1 to 5, when the lead frame (4) is heated during mounting, the first solder layer (5) and the second solder layer or tin layer (6), or the solder layer or tin layer (3 ) And the cream solder layer (7) are combined to form a copper-tin compound having a thickness of about 1.5 μm at the interface between the wiring pattern and the solder layer, but the total thickness of the solder layer is large. If the thickness is 2 μm or more, it is possible to perform good soldering without being affected by the influence.

[0028]

The printed circuit board according to the present invention has a first solder layer having a normal solder composition and a second solder layer or tin layer having a tin content higher than that of the first solder layer on the wiring pattern. Therefore, the second solder layer or tin layer with a high tin content has an excellent anti-oxidation effect and can be stored for a long time.Furthermore, even when mounting electronic parts, no flux is used or no cleaning type is used. By using a solder paste containing a flux, for example, cream solder, or mounting without using a solder paste or the like, there is an effect that a mounting method of an electronic component that does not require cleaning with chlorofluorocarbon can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a printed board according to a first embodiment of the present invention and a mounting state of electronic components on the printed board.

FIG. 2 is a cross-sectional view showing a printed circuit board and a mounting state of electronic components on the printed circuit board according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a mounting process using a printed circuit board according to a conventional example.

FIG. 4 is a flowchart showing a mounting process using a printed circuit board according to a conventional example.

[Explanation of symbols]

 1 Base Material 2 Wiring Pattern 3 Solder Layer or Tin Layer 4 Lead Frame 5 First Solder Layer 6 Second Solder Layer or Tin Layer 7 Cream Solder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiko Watanabe 1-57 Miyashita, Sagamihara City Sagami Works (Mitsubishi Electric Corporation) (72) Hiroyuki Sawamura 1-57 Miyashita, Sagamihara Mitsubishi Electric Machinery Company Sagami Factory

Claims (8)

[Claims] 1. A first solder layer containing tin and lead as a main component on a wiring pattern of a base material having a wiring pattern of a predetermined shape, and a first solder layer laminated on the first solder layer. A printed circuit board comprising a second solder layer or a tin layer having a tin content higher than that of the solder layer. 2. The printed circuit board according to claim 1, wherein:
A printed circuit board, wherein the total thickness of the first solder layer and the second solder layer or tin layer is 2 μm or more. 3. The printed circuit board according to claim 1, wherein the first solder layer, the second solder layer or the tin layer contains silver and / or bismuth in addition to tin and lead. Printed circuit board. 4. An electronic device for a printed circuit board according to claim 1, wherein an electronic component is directly mounted on the second solder layer or tin layer of the printed circuit board and heated. How to mount parts. 5. A solder layer or tin layer having a tin content higher than that of a solder eutectic composition is formed on the wiring pattern of a base material having a wiring pattern of a predetermined shape, and then the solder layer or tin layer. A method for mounting an electronic component on a printed circuit board, comprising: applying a solder paste having a tin content lower than that of the solder layer or tin layer onto the electronic component; 6. A solder layer or tin layer having a tin content higher than that of a solder eutectic composition is formed on the wiring pattern of a base material having a wiring pattern of a predetermined shape, and then the solder layer or tin layer. The content of tin is lower than that of the solder layer or tin layer, and after heating, a solder paste mixed with the solder layer or tin layer to form a solder eutectic composition layer is applied, and then electronic components are mounted and heated. A method for mounting an electronic component on a printed circuit board, comprising: 7. A method for mounting electronic components on a printed circuit board according to claim 5, wherein the solder paste contains a flux of no flux or no cleaning type, silver and / or bismuth in addition to tin and lead. A method for mounting an electronic component on a printed circuit board, characterized in that the electronic component containing the material is used. 8. A method for mounting an electronic component on a printed circuit board according to claim 5, wherein the solder layer or the tin layer contains tin and lead, and silver and / or bismuth. A method for mounting an electronic component on a printed circuit board, characterized by using an alloy composition having the following composition.