JP3150068B2 - Manufacturing method of printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board for supplying preliminary solder onto narrow pitch pads.

[0002]

2. Description of the Related Art Conventionally, when soldering various mounted components of a printed wiring board, as shown in FIGS. 2A to 2H, the method of mounting surface mounted components is based on the lead portion of the mounted components. A mask 3 having a portion corresponding to
After overlaying the mask 3 on the printed wiring board with the pad 2 on which the component is mounted on the printed wiring board so that their positions overlap, the squeegee is used from above the mask screen 3 to be perpendicular or parallel to the direction of the pad 2. The solder paste 5 is printed on the pad 2 through the opening 4 by printing the solder paste 5 on the pad 2. Thereafter, the mounted components are placed on the printed wiring board to which the solder paste 5 has been supplied, and the solder paste 5 is heated and melted by a reflow device, thereby completing the mounting of the components by soldering to the printed wiring board. However, the pad pitch of the printed wiring board and the lead pitch of each component have been narrowed with the mounting density. Therefore, when the components are mounted by the above-described method using a solder paste 5 that is generally used for a narrow pitch, the openings 4 of the mask screen 3 become very fine, so that each part of the mask screen 3 becomes Since the solder paste 5 is not completely transferred onto the substrate 1 from the individual openings 4 corresponding to the components and the component leads 6, and the solder paste 5 is not supplied onto the pads 2 of the printed wiring board from the openings 4. Since a shortage of the solder occurs or a gap between the individual openings 4 is narrowed, a bridge occurs in the supplied solder paste 5. Also, it is difficult to accurately align each opening 4 with a target pad of the printed wiring board, so that printing displacement of the solder paste 5 occurs, resulting in a shortage of the solder 7 and a defect such as a bridge.

As a method for solving these problems and corresponding to a narrow pitch, a printing method using a one-character type mask in which each lead portion is integrated into one opening has been proposed (Japanese Patent Publication No. 60-58600). . Certainly, this method improved the supply of solder paste and improved the accuracy of alignment between the printed wiring board and the mask. However, bridges may be formed when components are mounted and heated and melted. . Further, if the amount of solder is controlled so as not to cause bridging, a shortage of solder occurs.

As a further solution, there has been proposed a method of controlling the heating and melting behavior of a solder paste by mixing and using solder pastes having different solder compositions (Japanese Patent Application Laid-Open No. 03-44996). Gazette). However, even if the single letter printing method and the mixed solder paste method are used in combination, the 0.5 m
The mounting of parts of about m pitch is the limit.

As a method of supplying solder to pads having a narrow pitch, a method of performing preliminary soldering on a printed wiring board has been proposed (Japanese Patent Application Laid-Open Nos. 04-174593 and 06-152120). Although the pre-soldering method makes it possible to mount components at a pitch of 0.30 mm, these methods involve a special chemical reaction, which causes a problem in terms of expensive capital investment. In the case of a narrow pitch of 0.3 mm or less, there remains a problem in solder film formability (film thickness, uniformity, etc.) due to the reaction.

[0006]

As described above, when a component is mounted on a narrow pitch with a lead gap of 0.5 mm or less, even when a single-character printing method is used, the solder paste printed on one character is used for mounting the component. Bridges were sometimes formed without being divided into individual pads. In addition, the problem was solved to some extent by the mixed solder paste (Japanese Patent Laid-Open No. 03-4499).
No. 6), the defect rate due to the occurrence of bridges is extremely high for those having a thickness of 0.5 mm or less. Further, even if the solution is set to 0.5 mmP or less by the preliminary soldering method, expensive capital investment is required.

An object of the present invention is to eliminate the occurrence of bridges,
Another object of the present invention is to provide a method of manufacturing a printed wiring board that can supply a preliminary solder corresponding to a narrow pitch without requiring expensive capital investment.

[0008]

The present invention has openings arranged in the same direction as a plurality of pads of a printed wiring board.
Printing a solder paste on the plurality of pads in a strip shape using a mask screen, heating and melting the solder paste to separate and deposit solder on each of the pads, in the printed wiring board manufacturing method of supplying a preliminary solder on the pad by a step of washing away the paste residue formed on the solder, the step of printing the solder paste on the strip is, as before Symbol solder paste composition and two Sn-Pb solder powder having a different, a mixture of the active rosin flux, the solder powder content using 50～80Wt% of the solder paste,
Arrangement direction of the openings and printing direction of the solder paste
The solder paste is printed at an angle of 20 °
Configured as characterized in that it consists of. In the present invention, as the two kinds of solder powders having different compositions, one is a solder powder of Sn 45 to 55 wt% and the balance Pb, and the other is S 2 when the two kinds of solder powder are heated and melted.
It is a Sn-Pb solder powder having an n: Pb ratio having a eutectic solder composition.

[0009]

Embodiments of the present invention will be described below in detail.

[0010] The method of supplying the preliminary solder is performed by using a mask screen having a band-shaped (one character) opening design to prevent solder bridging and insufficient solder due to misalignment, and to improve solder supply from the mask opening design. Aim for improvement. When a band-shaped (one character) mask screen is used, the solder paste is partially supplied to the pad. However, by providing two or more band-shaped (one character) holes, the solder paste is stably and uniformly formed on the pad. The paste can be supplied by a printing method. In addition, by adjusting the solder composition by mixing individual solder powders of different compositions, it is possible to maintain the molten state of the solder near the eutectic point, while controlling the behavior of the solder paste during melting and By optimizing the content of the flux component of the above, the solder wiping and fluidity were improved, and it was possible to form a film having a uniform film thickness and no bridge. In addition, the preliminary solder supply method according to the embodiment of the present invention enables stronger cleaning compared with cleaning after mounting, so that the amount of the activator enough to ensure solder wet spreadability and the activity containing the additive component are sufficient. Rosin-based flux can be used. Furthermore, the solder paste according to the embodiment of the present invention uses two kinds of solder powders having different compositions and has a melting temperature of 230 ° C. or less, thereby reducing thermal damage to the printed wiring board during preliminary solder formation. can do.
Generally, the solder used for soldering electronic components and printed wiring boards is considered to be 63Sn-37Pb supplied solder or solder near this eutectic point in terms of soldering strength and solderability. However, in the embodiment of the present invention, the mixing ratio of the solder powder was adjusted so that the melting point of the preliminary solder after formation was eutectic or near the eutectic point.

Hereinafter, the present invention will be described with reference to examples. Reference Example 1 FIGS. 1A to 1H are a sectional view and a plan view, respectively, showing a process of forming a preliminary solder according to a first embodiment of the present invention.
1A and 1B show the surface layer of a printed wiring board, in which pads and the like are formed by a subtractive method or the like. In this embodiment, the pad width of the narrow pad for supplying the solder is 0.125 mm, and the pad gap is 0.1.
The pad pitch was 0.250 mm, the pad length was 2.0 mm, and the pad thickness was 37 μm. FIG.
As shown in (c) and (d), a one-character type mask screen is overlaid on the printed wiring board having the narrow pitch, and the opening 4 of the mask screen is aligned with the corresponding mounting pad 2. At this time, the opening 4 of the mask screen
Is designed to provide the required amount of solder during mounting. In order to form a preliminary solder layer evenly on the pad 2, the shape of the opening 4 is two characters, and the angle of the opening 4 is inclined by 45 ° with respect to the printing direction.

In this reference example, the pad group length direction is a pad group plus 0.65 mm on both sides for a group of pad rows, the pad longitudinal thickness is 0.65 mm, the pad longitudinal gap is 0.40 mm, A 70 μm thick metal mask screen having two strip-shaped openings in the pad longitudinal direction was used (FIG. 4).

Next, as shown in FIGS. 1 (e) and 1 (f), the solder paste 5 is placed on a mask screen, and the solder paste 5 is printed on the corresponding pads 2 of the printed wiring board using a squeegee by a printing method. Supply. At this time, the thickness of the supplied solder paste 2 is about 70 μm. At this time, the mounting pad 2 for supplying the solder paste 2
Is a narrow pad portion only, and the other mounting pads 2 supply solder during mounting. Next, as shown in FIGS. 1 (g) and 1 (h), the substrate supplied with the solder paste 5 is preheated 15
The solder paste 5 supplied on the narrow pad 2 is heated and melted by a reflow apparatus using infrared rays and air at a temperature setting of 0 ° C. for 60 seconds and a main heating peak temperature of 230 ° C. Solder paste 5 is made of 50Sn / 10Pb powder and 90Sn / 10P in order to control the behavior during heating and melting.
60 wt% of a powder obtained by mixing the spheres of the b powder and a flux component containing 0.4 wt% of the remaining activator were mixed and adjusted. Thereafter, the solder and the flux components in the paste adhering to portions other than the supply section are washed by an ethylene glycol-based cleaning agent, hot water washing at 30 ° C. or higher, and ultrasonic washing. In this way, an amount of preliminary solder coating that allows component mounting without supplying the solder paste 5 during mounting is formed on the narrow pad 2. At the time of mounting, after performing paste printing by a normal method, the relevant component is placed on a narrow portion where a general component is mounted and a preliminary solder coating is formed, and the solder is melted and mounted.

As a result of using the present reference example, a solder film of 20 to 50 μm was formed on the pad in the narrow portion, and no bridge was formed by forming the preliminary solder. In addition, as a result of mounting using this preliminary solder, no mounting failure occurred in the narrow pitch pad 2 portion.

The conditions of Reference Example 1 are shown in Table 1.

[0016]

[Table 1]

REFERENCE EXAMPLE 2 In this reference example, the pad width of the narrow pad for supplying the solder formed by the subtractive method is 0.075 mm, and the pad gap is 0.075 m.
m, the pad pitch is 0.150 mm, and the pad length is 1.
2 mm and the pad thickness was 32 μm. A one-character type mask screen is overlaid on the printed wiring board having the narrow pitch, and the opening of the mask screen is aligned with the corresponding mounting pad. In order to form a preliminary solder layer uniformly on the pad, the shape is set to three characters, and the angle of the opening is inclined by 45 ° with respect to the printing direction. The solder paste is placed on the mask screen, and the squeegee is used to supply the solder paste on the corresponding pads of the printed wiring board by a printing method. At this time, the thickness of the supplied solder paste is about 100 μm. At this time, the mounting pad for supplying the solder paste is only the narrow pad portion, and the other mounting pads supply the solder at the time of mounting.
The substrate to which the solder paste has been supplied is processed by an infrared / air reflow apparatus, and the solder paste supplied on the narrow pad is heated and melted. Solder paste is 50Sn / 50P to control the behavior during heating and melting.
50 wt% of a powder obtained by mixing the spherical shapes of the b powder and 90Sn / 10Pb powder were mixed with a flux component containing the remaining activator of 0.2 wt%.

After that, the solder adhering to portions other than the supply portion and the flux components in the pace are removed by a solvent-based cleaning agent,
Wash with hot water at ℃ or higher and ultrasonic cleaning. In this way, an amount of preliminary solder coating that allows component mounting without supply of solder paste during mounting is formed on the narrow pad.
At the time of mounting, after performing paste printing by a normal method, the relevant component is placed on a narrow portion where a general component is mounted and a preliminary solder coating is formed, and the solder is melted and mounted.

As a result of using the present reference example, a solder film of 20 to 40 μm was formed on the pad of the narrow portion, and no bridge was formed by forming the preliminary solder. Further, as a result of mounting using the preliminary solder, no mounting failure occurred in the narrow pitch pad portion.

The conditions of Reference Example 2 are shown in Table 2.

[0021]

[Table 2]

[0022] [Example] In the present embodiment, 0.060 mm pad width of narrow pad for supplying a solder formed by the additive method, the pad clearance to 0.060 mm, 0.120 mm pad pitch, pad length 1 0.0mm,
The pad thickness was 15 μm. Overlay a one-character type mask screen on the printed wiring board with this narrow pitch,
Align the opening of the mask screen with the corresponding mounting pad. In order to form a preliminary solder layer evenly on the pad, the shape is set to two characters, and the angle of the opening is inclined by 20 ° with respect to the printing direction. The solder paste is placed on the mask screen, and the squeegee is used to supply the solder paste on the corresponding pads of the printed wiring board by a printing method. At this time, the thickness of the supplied solder paste is about 40 μm. At this time, the mounting pad for supplying the solder paste is only the narrow pad portion, and the other mounting pads supply the solder at the time of mounting. The substrate supplied with the solder paste is processed by a nitrogen reflow device, and the solder paste supplied on the narrow pad is heated and melted. Solder paste consists of 55Sn / 45Pb powder and 95Sn / 5Pb to control the behavior during heating and melting.
80 wt% of the powder obtained by mixing the spheres of the powder and a flux component containing 0.8 wt% of the remaining activator were mixed and adjusted. After that, the solder and the flux components in the pace attached to the parts other than the supply part are removed with an alcohol-based cleaning agent at 60 ° C.
The above hot water washing and ultrasonic washing are performed and the washing is performed. In this way, an amount of preliminary solder coating that allows component mounting without supply of solder paste during mounting is formed on the narrow pad.
At the time of mounting, after performing paste printing by a normal method, the relevant component is placed on a narrow portion where a general component is mounted and a preliminary solder coating is formed, and the solder is melted and mounted.

As a result of using the embodiment of the present invention, a solder film of 15 to 30 μm is formed on the pad of the narrow portion,
No bridge was formed by the pre-solder formation. Further, as a result of mounting using the preliminary solder, no mounting failure occurred in the narrow pitch pad portion.

It should be noted the conditions of the present embodiment shown in Table 3.

[0025]

[Table 3]

[0026]

The method according to the embodiment of the present invention, that is, providing a sufficient amount of preliminary solder for mounting on a printed wiring board by a printing method, and adjusting the composition of a paste component used for solder formation. By making the opening design of the mask screen into a strip shape and providing an angle to the direction at the time of printing, a preliminary solder that can reduce mounting defects can be formed at a pitch of 0.5 mm, and even a narrow pitch of 0.25 mm or less. We can supply printed wiring boards.

Further, in the step of forming the preliminary solder, a sufficient amount of solder for mounting can be easily formed without variation.

Further, by using the conventional printing method as a base, it is possible to supply a spare solder corresponding to a narrow pitch onto a printed wiring board without a large capital investment.

[Brief description of the drawings]

[1] (a) ~ (h) is a process cross-sectional view and a plan view of a pre-solder formation of Reference Example 1 of the present invention.

FIGS. 2A to 2H are a cross-sectional view and a plan view of an example of a preliminary solder forming process in a conventional method for manufacturing a printed wiring board.

3 (a) and 3 (b) are plan views of a mask screen of the present invention, and FIGS. 3 (c) and 3 (d) are plan views of a conventional mask screen.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base material 2 Pad 3 Mask 4 Opening 5 Solder paste 6 Components and component leads 7 Solder

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H05K 3/26 H05K 3/26 A (72) Inventor Takanori Tsunoda 560 Irizen-cho, Shimoshinagawa-gun, Toyama Prefecture Toyama Nippon Electric Co., Ltd. (56) Reference Document JP-A-63-124496 (JP, A) JP-A-2-22889 (JP, A) JP-A-6-122090 (JP, A) JP-A-8-186367 (JP, A) 50219 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/34 H05K 3/26

Claims (5)

(57) [Claims] 1. The same one as a plurality of pads of a printed wiring board
Using a mask screen having openings arranged in different directions
Printing the solder paste on the plurality of pads in a strip shape, heating and melting the solder paste to separate and deposit the solder on each of the pads, and washing and removing the paste residue formed on the solder. in the printed wiring board manufacturing method of supplying a preliminary solder on the pad by a step of the step of printing the solder paste on the strip is, as before Symbol solder paste, different compositions 2
A mixture of different types of Sn-Pb solder powder and active rosin-based flux , and the content of the solder powder is 50 to 80 wt%
Using the solder paste, the arrangement direction of the openings and the front
When the angle of the printing direction of the solder paste is 20 ° and the solder
A method for manufacturing a printed wiring board, comprising printing a solder paste . 2. The two kinds of solder powders having different compositions, one of which is a solder powder of 45 to 55 wt% Sn and the balance Pb, and the other has the same Sn: Pb ratio when the two kinds of solder powder are heated and melted. Sn-
2. The method for manufacturing a printed wiring board according to claim 1, wherein the method is a Pb solder powder. 3. The printed wiring board according to claim 1 , wherein a screen or a metal mask in which the openings are arranged in at least two rows per pad is used as the mask screen. Method. 4. A cleaning agent and 20 to 80 in the step of cleaning and removing the paste residue formed on the solder.
2. The method for manufacturing a printed wiring board according to claim 1, wherein ultrasonic cleaning or normal spray cleaning using city water at a temperature of ° C. is performed. 5. The active rosin-based flux includes a resin of 40 to 60 wt%, an activator of 0.8 wt%, and an additive of 15 %.
The method for manufacturing a printed wiring board according to claim 1, wherein a flux composed of wt% and a balance of a solvent is used.