JPH0699568A - Cream solder printing method of printed wiring board - Google Patents

Abstract

PURPOSE:To obtain a cream solder printing method not generating a non- soldered part or printing blur even when the method is adapted to a fine pitch IC mixed loading type printed wiring board whose lead pitch is a specific value or less. CONSTITUTION:A metal mask having aperture parts 5B, 5F with a printing width of 0.8mm or less and aperture parts with a printing width of 8.8mm or more is superposed on the surface of a fine pitch surface mounting type printed wiring board 1. Cream solder 10 is transferred through the aperture parts by the squeeze 9 sliding on the metal mask in the printing width direction under predetermined pressure to be printed on the printed wirings 3 of the printed wiring board 1. In this method, the transfer printing of cream solder is performed using a metal mask 15 having divided aperture parts 15A, 15B formed by dividing the aperture parts with a printing width of above 0.8mm in the width direction thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a printed wiring of a printed wiring board for fine pitch surface mounting.
Clear for soldering active and passive components
Printing method for transfer soldering, especially printing width is 0.
The present invention relates to a method for preventing print blur caused by a squeegee biting into an opening of a metal mask exceeding 8 mm.

[0002]

2. Description of the Related Art In a fine-pitch surface-mounting type printed / printed wiring board, the printed wiring formed on the surface of the printed-wiring board is relieved at the mounting portion of active elements such as fine-pitch ICs.
The fine pitch is 0.5 mm or less and the resistance,
The printed width of the passive parts such as capacitors, reactors and diodes is as large as 0.8 to 2.7 mm. Correspondingly, the width of the cream solder printed portion for conductively coupling the active component and the passive component on the printed wiring is also widened from 0.5 mm or less to about 2.7 mm. Therefore, in order to securely electrically and mechanically solder active components and passive components to a printed wiring in a fine pitch surface mount compatible printed printed wiring board, transfer printing is performed using a metal mask on the printed wiring. The cream solder printed part maintains a uniform print thickness determined by the thickness of the metal mask regardless of the print width determined by the opening width of the metal mask, and does not include a thin print portion, so-called print blur. Is required.

FIG. 5 is a schematic sectional view for explaining a conventional cream solder printing method of a printed wiring board for fine pitch surface mounting, and FIG. 6 is a fine pitch surface printed by cream solder. It is a cross-sectional view schematically showing a mounting-compatible printed / printed wiring board. In the figure,
The fine printed circuit board 1 of the fine pitch surface mounting type, in which the printed wiring 3 is formed on the surface of the substrate 1 made of a fiber reinforced plastic material by a predetermined pattern, the printed wiring 3 has a lead pitch p = 0. Fine pitch of 65mm (wiring width w is 0.35mm), wiring width w = 0.8mm
Or a passive element mounting wiring part such as 1.4 mm,
It includes many types of wiring portions having different wiring widths. The metal mask 5 for transferring and printing the cream solder 9 on the printed wiring 3 is a metal plate having a thickness of 0.2 mm, and a fine pitch having an opening width of 0.35 mm at a position corresponding to the wiring. Starting from opening 5F, opening width 0.8mm
5B, and an opening 5A having an opening width of 1.4 mm.

The transfer printing method of cream solder is as follows:
The metal mask 5 is placed on a predetermined position on the printed / printed wiring board 1 and set on the table of the printing machine. Then, with the squeegee 9 made of a soft urethane rubber having a tip pressed against the metal mask with a predetermined pressure, slide the squeegee 9 from the right to the left in the figure to place an appropriate amount on the metal mask. Transfer printing is performed by rubbing the dropped cream solder 10 into the respective openings of the metal mask 5, and as shown in FIG. Printing units (hereinafter abbreviated as printing units) 6, 7, and 8 are formed. Further, the terminal fitting 11A of the IC module 11 is mounted on the printing section 6, the terminal fitting 12A of the capacitor 12 is mounted on the printing section 7, and the terminal fitting 13A of the resistor 13 is mounted on the printing section 8. By heating the printed / printed wiring board 1 to a predetermined temperature, the respective components are solder-bonded to predetermined positions of the printed / printed wiring 3 to form a surface-mounted printed wiring circuit.

[0005]

In the above-described cream solder printing method, a skim inclined at a certain angle in the sliding direction.
The pressure applied to the dice 9 is determined by the pressure required to rub a sufficient amount of the cream solder 10 into the opening 5F having the narrowest printing width to prevent insufficient cremation of the cream solder, and a lead pitch of 0.5 mm. Including the fine-pitch IC of 4 to 5 kg is usually required. However, when printing is performed while maintaining this pressure, the corners of the tips of the squeegees 9 fall into the openings at the openings 5A, 5B having a wide printing width, and the cream solder is scraped off (skipping). Called shaving)
Occurs, which causes depressions on the surfaces of the printing portions 7 and 8, and the transfer rate of the cream solder (assuming the thickness of the metal mask is 100%) is 50% or less in the printing portion 7.
In this case, so-called print fading occurs, which is reduced to about 80%. In this way, if insufficient rub-in of the cream solder or print fading is present in the printed parts, unsoldered defects, or unsoldered defects, may occur when components are soldered to these printed parts to form a high density surface mount type integrated circuit. There is a problem that insufficient soldering occurs and a highly reliable high-density surface mount type integrated circuit cannot be obtained.

Therefore, in order to avoid the occurrence of these defects, measures are taken to keep the squeegee at a high angle close to the vertical of the metal mask surface and to lower the printing pressure to 4 kg or less. Therefore, in the fine pitch area where the lead pitch is 0.5 mm or less, insufficient rubbing of solder and non-solder failure due to this may occur.
The solder solder printing method is limited to application to 0.65mm pitch IC mixed-type printed printed wiring boards, and is applicable to 0.5mm pitch IC mixed-mounted printed printed wiring boards.
Development of a solderless printing method is required.

The object of the present invention is to provide a lead pitch of 0.5 mm.
Another object of the present invention is to obtain a cream solder printing method that does not cause unsoldering or print blur even when applied to the following fine pitch IC mixed type printed printed wiring board.

[0008]

In order to solve the above problems, according to the present invention, a printing width is provided on the surface of a fine pitch surface mounting type printed printed wiring board on which printed wiring is formed. By stacking metal masks each having an opening and holding a predetermined load and sliding on the metal mask in the printing width direction, a cream solder is formed on the printed wiring board through the openings. In the method of transfer printing on a predetermined position of a printed wiring, an opening having a print width exceeding a predetermined value is divided into a plurality of parts in the width direction to form a divided opening having a width equal to or smaller than a predetermined value, and a clear mask is used. Transfer printing of solder is to be performed.

When the printing width exceeds 0.8 mm and is 1.8 mm or less, the opening of the metal mask is divided into two divided openings. Further, when the print width is more than 1.8 mm and 2.7 mm or less, the opening of the metal mask is divided into three divided openings. Furthermore,
The prescribed load applied to the squeegee shall be 4 kg or more.

[0010]

In the structure of the present invention, the transfer printing of the cream solder is performed by using the metal mask having the divided opening in which the opening having the printing width exceeding the predetermined value, for example, 0.8 mm is divided in the width direction. With this configuration, the opening width of the metal mask is reduced to 0.8 mm or less and the
Since the difference in the print width from the portion with a lead pitch of 0.5 mm or less is reduced, the function of suppressing the squeegee bite into the opening and avoiding print blur can be obtained. Even if it is applied to a pitch IC mixed print printed wiring board, a cream solder printing method that hardly causes defects such as unsolder and insufficient solder can be obtained.

When the print width is more than 0.8 mm and 1.8 mm or less, the opening of the metal mask is divided into two divided openings, and the print width is more than 1.8 mm and 2.7 mm.
In the following cases, if the opening of the metal mask is configured to be divided into three divided openings, the distance between the divided openings is set to 0.3 mm, and the divided opening width is 0.8 mm.
By reducing the pressure to the following and maintaining the printing pressure at 4 kg or more, preferably about 5 kg, a cream solder printed portion free from insufficient solder defects and unsoldered defects in the fine pitch printed portion can be obtained.

[0012]

EXAMPLES The present invention will be described below based on examples. FIG. 1 is a schematic cross-sectional view for explaining a cream solder printing method of a fine-pitch surface-mounting type printed printed wiring board according to an embodiment of the present invention, and FIG.
FIG. 2 is a schematic cross-sectional view of a fine-pitch surface-mounting type printed printed wiring board that has been solder-printed, and the same components as those of the prior art are designated by the same reference numerals, and a duplicate description will be omitted. In the figure, the metal mask 15 has an opening 5F having a print width W of about 0.3 mm, an opening 5B having an opening width W of 0.8 mm, and a wiring width W corresponding to a fine pitch IC having a lead pitch of 0.5 mm. From the right side of the drawing, a squeegee 9 including divided opening portions 15A and 15B divided into two parts having an opening width w of 0.6 mm corresponding to the printed wiring 3 of 1.5 mm and having a printing pressure of 5 kg is held. By sliding toward the left side and rubbing the cream solder 10 into each opening, the transfer printing of the cream solder is performed.

As a result, as shown in FIG. 2, the obtained cream solder printing portion has a transfer rate of 90% or more, a printing portion 18 having a printing width of 0.8 mm, and a printing width of 0 in the fine pitch printing portion 16. A transfer rate of 80% or more is shown in the 6 mm division printing sections 17A and 17B, and the opening of the metal mask corresponding to the printing section exceeding the printing width of 0.8 mm is divided into two and the opening width is set to 0.8 mm or less. It has been demonstrated that the exemplary printing method can prevent squeegee shaving and prevent print smearing.

FIG. 3 is a plan view showing a state in which passive components are soldered to the divided printing portions obtained by the embodiment method, and a pair of divided printing portions 17A and 17B are printed on the terminals 3A and 3B of the printed wiring. It has been confirmed that the terminal metal fitting 12A of the capacitor 12 soldered to the above has good solderability and exhibits a good electrical and mechanical coupling state without causing excessive solder defects. Further, in the fine pitch printing portion 16 as well, no unsoldered defect was observed between the lead wire and the lead wire.

FIG. 4 is a plan view of a divided printing section showing a different embodiment of the present invention, in which the width of the printed wiring 3 is 1.8 mm.
If it exceeds 2.7 mm and is less than 2.7 mm, the opening of the metal mask is 3
Three divided print portions 27 having a print width of 0.4 to 0.7 mm are formed by division, and the print width is reduced in the same manner as in the above-mentioned embodiment to prevent print blur due to shaving. be able to.

[0016]

As described above, according to the present invention, the printing width is 0.
It was configured to perform the transfer printing of the cream solder by using a metal mask having a divided opening in which the opening exceeding 8 mm is divided in the width direction. As a result, for example, when the print width is more than 0.8 mm and 1.8 mm or less, the opening of the metal mask is divided into two divided openings, and the print width is more than 1.8 mm and 2.7 mm or less. At one time, if the opening of the metal mask is divided into three divided openings, the maximum width of the divided opening becomes 0.8 mm or less, and the printing width with the fine pitch printing portion with a lead pitch of 0.5 mm or less. Therefore, the problem of the prior art that a print blur occurs due to a squeegee biting into an opening having a print width exceeding 0.8 mm can be eliminated. Therefore, by maintaining the printing pressure at 4 kg or more, even when applied to a fine pitch IC mixed printed printed wiring board with a lead pitch of 0.5 mm or less, unsoldered defects and insufficient soldering defects occur when soldering circuit components. It is possible to provide a cream solder printing method capable of forming a difficult and highly reliable surface mount type integrated circuit.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a cream solder printing method for a fine-pitch surface-mounting type printed printed wiring board according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a fine-pitch surface-mounting type printed printed wiring board which is cream solder printed by the example method.

FIG. 3 is a plan view showing a state in which passive components are soldered to the divided printing section obtained by the method of the embodiment.

FIG. 4 is a plan view of a division printing unit showing a different embodiment of the present invention.

FIG. 5 is a schematic sectional view for explaining a conventional cream solder printing method for a fine-pitch surface-mounting type printed printed wiring board.

FIG. 6 is a schematic cross-sectional view showing a fine-pitch surface-mounting type printed printed wiring board printed with cream solder.

[Explanation of symbols]

 1 Printed Printed Wiring Board 2 Board 3 Printed Wiring 5 Metal Mask 5A Opening 5B Opening 5F Opening (Fine Pitch) 6 Cream Solder Printing (Fine Pitch) 7 Cream Solder Printing 8 Cream Soldering Part 9 Squeegee 10 Cream solder 11 IC module 12 Capacitor 13 Resistor 15 Metal mask 15A Divided opening 15B Divided opening 16 Cream solder printed part (fine pitch) 17A Cream solder divided printed part 17B Cream solder division printing section 18 Cream solder division printing section 27 Cream solder division printing section (3 divisions)

Claims (4)

[Claims] 1. A metal mask having an opening corresponding to a printing width is superposed on the surface of a fine-pitch surface-mounting type printed / printed wiring board on which printed wiring is formed, and a predetermined load is held to hold the metal. In the method of transferring and printing the cream solder to a predetermined position of the printed wiring of the printed wiring board through the opening by a squeegee sliding on the mask in the printing width direction, the printing width has a predetermined value. The openings that exceed the width are divided into a plurality of parts in the width direction, and the transfer printing of the cream solder is performed by using a metal mask as divided openings having a width of a predetermined value or less. -Mussolder printing method. 2. The printed-wiring board according to claim 1, wherein the opening of the metal mask is divided into two divided openings when the printing width is more than 0.8 mm and 1.8 mm or less. Cream solder printing method. 3. The printed wiring board according to claim 1, wherein the opening of the metal mask is divided into three divided openings when the printing width is more than 1.8 mm and not more than 2.7 mm. Cream solder printing method. 4. The method for cream solder printing of a printed wiring board according to claim 1, wherein the predetermined load applied to the squeegee is 4 kg or more.