JP2005252120A - Printed wiring board and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board in which the generation of troubles such as packaging defects can be prevented even in the case of packaging an electronic component by lead-free solder. <P>SOLUTION: In the printed wiring board on which the electronic component is packaged by lead-free solder, the water content of the printed wiring board is set to ≤0.2 wt%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a printed wiring board that can prevent defects such as mounting defects of electronic components and delamination that occur due to high-temperature processing such as lead-free solder processing, and a manufacturing method thereof.

  Problems that occur during high-temperature processing such as soldering of electronic components include poor mounting of electronic components (pad floating, etc.) due to expansion of moisture contained in the insulating layer of the printed wiring board, and the interface between the conductor and the insulating layer. In particular, in a build-up multilayer printed wiring board or a flexible substrate (including a rigid flexible substrate) that easily absorbs moisture, the dehumidifying means is an important factor.

  As means for solving such a problem, a mesh-shaped opening is provided in a power source and ground layer having a large conductor area, and moisture expanded during high-temperature processing such as soldering is discharged to the outside through the opening, thereby A method of preventing the occurrence of interface peeling between a power supply or ground layer and an adjacent insulating layer is already known (for example, see Patent Document 1).

  In addition, in the above-described build-up multilayer printed wiring board or flexible board that easily absorbs moisture, the electronic circuit board is baked before mounting, and the moisture content of the printed wiring board (the moisture content here is the printed wiring). It is also known to reduce the ratio of the water content to the weight of the plate.

  However, in recent years, lead-free solder has been used for mounting electronic components, and the lead-free solder has a higher mounting temperature than conventional tin-lead solder (for example, about 245 to 245). 260 ° C.), the following problems have occurred.

  First of all, when the tin-lead solder was used, the above problem could be avoided by setting the moisture content of the printed wiring board to about 0.3% by weight. Dehumidification treatment was performed only on build-up multilayer printed wiring boards and flexible boards that easily absorb moisture. However, when lead-free solder was used, the above-mentioned problems could not be avoided with the moisture content.

Secondly, as for the surface treatment of the printed wiring board, the surface of the mounting pad etc. does not oxidize for those that are subjected to gold plating or soldering, so dehumidification treatment by baking is possible. With respect to what is applied, the surface of the mounting pad or the like is oxidized, so that dehumidification by baking is impossible.
Japanese Patent Application Laid-Open No. 3-108397

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to provide a printed wiring board that does not cause problems such as mounting defects even when mounting electronic components with lead-free solder, and its An object is to provide a manufacturing method.

  In order to achieve the above object, the present invention according to claim 1 is a printed wiring board on which electronic components are mounted with lead-free solder, and the moisture content of the printed wiring board is 0.2% by weight or less. It is the printed wiring board characterized.

  Thereby, even when component mounting is performed with lead-free solder, a printed wiring board can be obtained in which defects such as mounting failure of electronic components and delamination do not occur.

  The present invention according to claim 2 is a method of manufacturing a printed wiring board in which electronic components are mounted with lead-free solder, and the moisture content is reduced by dehumidifying the printed wiring board before mounting the electronic components. A printed wiring board characterized by being 0.2% by weight or less.

  Thereby, even when components are mounted using lead-free solder, it is possible to easily obtain a printed wiring board in which defects such as mounting defects of electronic components and delamination do not occur.

  According to a third aspect of the present invention, there is provided a printed wiring board characterized in that the dehumidifying treatment according to the second aspect is performed by performing a baking treatment after forming a surface treatment film on the surface of the wiring pattern. It is a manufacturing method.

  Thereby, dehumidification can be easily performed without oxidizing the surface of the mounting pad or the like.

  According to a fourth aspect of the present invention, there is provided a method for producing a printed wiring board, wherein the dehumidifying process according to the second aspect is performed by a vacuum drying process at room temperature.

  Thereby, even in a printed wiring board that has been subjected to a preflux treatment as a surface treatment, it is possible to easily perform a dehumidification treatment without oxidizing the surface of a mounting pad or the like.

  According to a fifth aspect of the present invention, there is provided a printed wiring board manufacturing method, wherein the room temperature vacuum drying process of the fourth aspect of the invention is performed in a reducing gas atmosphere.

  Accordingly, it is possible to perform the dehumidification process and the removal of the oxide film at the same time on the printed wiring board in which the oxide film is formed on the surface of the mounting pad or the like by leaving it for a long time.

  If electronic components are mounted on the printed wiring board of the present invention using lead-free solder, it is possible to easily prevent the occurrence of defects such as defective mounting of electronic components and delamination, which have occurred in the past. According to the manufacturing method of the invention, it is possible to easily obtain a printed wiring board capable of preventing the occurrence of the above-mentioned problems.

  An embodiment of the present invention will be briefly described with reference to FIGS.

  FIG. 1 is a schematic process explanatory view showing a manufacturing example of the printed wiring board of the present invention to be dehumidified by baking treatment in the first embodiment. First, as shown in FIG. A surface treatment film of a gold plating film or a solder film is formed on the surface of the wiring pattern (mounting pad or the like) exposed from the solder resist of the printed wiring board on which the solder resist or the like is formed.

  Next, as shown in FIG. 1 (b), after the outer shape of the printed wiring board on which the gold plating or the like is formed, the baking is performed using an oven or the like as shown in FIG. 1 (c). By the treatment, the printed wiring board is subjected to dehumidification treatment (temperature: 120 to 150 ° C., time: 1.5 to 2.5 h) to obtain a printed wiring board having a moisture content of 0.2% by weight or less.

  And as shown in FIG.1 (d), the reflow process (preheating: 175-180 degreeC, 120) which used lead-free solder (For example, mounting temperature is 245-260 degreeC) to this obtained printed wiring board. Component mounting is performed by ± 10 seconds, main heating: 230 ° C. or higher (peak temperature 260 ° C., 60 ± 5 seconds).

  In this way, there is no fear of oxidation due to baking for printed wiring boards whose surface of the wiring pattern (mounting pads, etc.) is protected by a gold plating film or solder film. Can be made 0.2 wt% or less.

  Next, FIG. 2 is a schematic process explanatory view showing a manufacturing example of the printed wiring board of the present invention to be dehumidified by vacuum drying at room temperature in the second embodiment. First, as shown in FIG. Further, after the outer shape of the printed wiring board on which the wiring pattern, solder resist, etc. are formed, the pre-flux treatment is performed on the printed wiring board as shown in FIG.

  Next, as shown in FIG. 2 (c), a vacuum drying treatment at normal temperature (vacuum degree: 0.1 MPa or less, treatment time: 0.5 to 16 hours) is performed, and the water content is 0.2% by weight. The following printed wiring board is obtained.

  And as shown in FIG.2 (d), the reflow process (preheating: 175-180 degreeC, 120) which used the lead-free solder (For example, mounting temperature is 245-260 degreeC) to this obtained printed wiring board. Component mounting is performed by ± 10 seconds, main heating: 230 ° C. or higher (peak temperature 260 ° C., 60 ± 5 seconds).

  As described above, the printed wiring board subjected to the preflux treatment is easily subjected to a moisture content of 0. 0% without oxidizing the surface of the mounting pad or the like by using a vacuum drying treatment at room temperature as the dehumidification treatment. It can be 2% by weight or less.

  FIG. 3 is a schematic process explanatory view showing a manufacturing example of the printed wiring board of the present invention when the vacuum drying process at room temperature is performed in a reducing gas atmosphere. As shown in FIG. This is basically the same as FIG. 2 except that the treatment is performed in a reducing gas atmosphere.

  Thus, by performing vacuum drying at room temperature in a reducing gas atmosphere, the oxide film can be removed at the same time as the dehumidification treatment. This is particularly advantageous when the surface of the mounting pad or the like has been oxidized.

Test example 1
A four-layer printed wiring board (hereinafter referred to as sample 1) having an insulating layer of FR-4, and a double-sided (two-layer) printed wiring board (hereinafter referred to as sample 2) made of SEM-3. The occurrence of defects due to moisture content was tested and observed.

  First, the samples 1 and 2 are baked (temperature: 120 ° C., treatment time: 2 hours) to obtain an absolute dry state (water content 0% by weight), and then the humidified treatment ( By performing a temperature of 40 ° C. and a humidity of 90%, each sample has a moisture content of 0.2% by weight (7 days of humidification) and 0.3% by weight (30 days of humidification). Prepared.

  Next, reflow treatment (preheating: 180 ° C., 125 seconds) was performed on samples 1 and 2 having respective moisture contents that were allowed to stand at room temperature (temperature: 25 ° C., humidity: 60%) for 0 hours, 24 hours, 48 hours, and 96 hours. Main heating: 230 ° C. or higher (peak temperature 260 ° C., 60 seconds) was performed, and the occurrence of defects such as delamination and measling was observed. The results are shown in Table 1.

  As can be seen from the results in Table 1, in both samples 1 and 2, no trouble occurred when the moisture content was 0.2% by weight, and in any sample when the moisture content was 0.3% by weight, It was confirmed that the problem occurred. Therefore, it was confirmed that when the high-temperature treatment such as lead-free soldering is performed, the occurrence of the above-described problems can be prevented by setting the moisture content of the printed wiring board to at least 0.2% by weight or less.

Test example 2
After the preflux treatment, the same humidification treatment as in Test Example 1 is performed to set the moisture content to 0.3% by weight, and then the reflow treatment as in Test Example 1 is performed to forcibly oxidize the mounting pad. A vacuum drying treatment (vacuum degree) at room temperature in a reducing gas atmosphere (gas type: Ar—H ₂ gas (Ar: 95%, H ₂ : 5%), gas pressure: 1 L / min) : 0.1 MPa, treatment time: 16 hours). As a result, it was confirmed that the moisture content was 0.18% by weight and the eutectic solder wettability on the mounting pad was good. Therefore, it was confirmed that the oxide film was removed simultaneously with the dehumidifying process.

Schematic process explanatory drawing which shows the manufacture example of this invention printed wiring board which performs a dehumidification process by baking process. Schematic process explanatory drawing which shows the manufacture example of this invention printed wiring board which performs a dehumidification process by the vacuum drying process of normal temperature. Schematic process explanatory drawing which shows the manufacture example of this invention printed wiring board which performs the vacuum drying process at normal temperature in a reducing gas atmosphere.

Claims (5)

  A printed wiring board on which electronic components are mounted with lead-free solder, wherein the printed wiring board has a moisture content of 0.2% by weight or less.   A printed wiring board manufacturing method for mounting an electronic component with lead-free solder, wherein the moisture content of the printed wiring board is reduced to 0.2 wt% or less by dehumidifying the printed wiring board before mounting the electronic component. A method for manufacturing a printed wiring board.   3. The method of manufacturing a printed wiring board according to claim 2, wherein the dehumidifying treatment is performed by baking after forming a surface treatment film on the surface of the wiring pattern.   The method for manufacturing a printed wiring board according to claim 2, wherein the dehumidifying treatment is a vacuum drying treatment at room temperature.   The method for producing a printed wiring board according to claim 4, wherein the vacuum drying treatment at room temperature is performed in a reducing gas atmosphere.

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