JPH1071696A - Screen for supplying cream solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deformation of a screen and printing inferiority at a part to which an opening part continues and to enable the printing of a fine pitch part by supplying cream solder to the respective electrode parts arranged on a printed circuit board from the opening part divided into a plurality of regions. SOLUTION: Each of opening parts 2 arranged on a printed circuit board in opposed relation to electrode parts at a constant interval is divided into four regions by two partition parts 1 arranged so as to obliquely cross each other with respect to each opening part 2. As a result, when a squeegee is moved in an X-direction, the force acting on a screen 4 acts in an obliquely downward direction A. Cream solder flows to the interior B of the opening part 2 by this force. At this time, the force in the same direction as the moving direction X of the squeegee also acts on the partition part 3 between the adjacent electrodes of the screen 4 by cream solder to be ready to deform the partition part 3. Herein, two partition parts 1 achieve the function of a reinforcing plate to the partition part 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cream solder supply screen for printing cream solder for mounting surface-mounted electronic components on a printed circuit board.

[0002]

2. Description of the Related Art In recent years, due to the demand for high-density mounting of electronic components, surface-mounting types without lead wires have been attracting attention. High-density mounting of components is rapidly progressing. The mounting method of electronic components by reflow soldering includes a printing process of printing cream solder etc. on a printed circuit board, a mounting process of mounting surface-mounted electronic components on a circuit board, and heating the printed circuit board to perform soldering. The reflow process to be performed is included.

With reference to FIGS. 4 and 5, a conventional method for mounting electronic components will be described. In the cream solder printing apparatus shown in FIG. 4A, an opening of a cream solder supply screen 4 having an opening 2 for cream solder printing is formed on a printed board 5 provided with an electrode pattern 7 on the surface. 7 are positioned so as to overlap. The flat squeegee 8 shown in FIG.
Is provided with a contact portion 8a that comes into contact with an appropriate pressure on the surface, and is configured to be movable left and right.

When the flat squeegee 8 moves in the printing direction indicated by X in the figure, the cream solder 6 injected into the space formed by the flat squeegee 8 and the cream solder supply screen 4 is pushed by the slope 8 b of the squeegee 8. While rotating in the direction indicated by R in the drawing, flows into the opening 2 provided in the cream solder supply screen 4. The flow of the cream solder 6 occurs because the internal pressure of the cream solder 6 increases near the tip of the squeegee 8 when the squeegee 8 moves. Furthermore, the cream solder 6 having fluidity behaves in an attempt to release the internal pressure, and flows upward in a direction with less resistance, that is, along a squeegee.

When the movement of the squeegee 8 is completed,
The cream solder 6 applied to the opening 2 comes to a stationary state, and its viscosity increases. Next, when the printed board 5 is separated from the cream solder supply screen 4, the cream solder 6 is printed on the electrode pattern 7, as shown in FIG. In the above printing process, it is known that the moving speed of the squeegee, the inclination angle thereof, and the amount of cream solder injected have a great effect on the printing state, and the internal pressure generated in the cream solder depends on the movement of the squeegee. The larger the speed, and the smaller the inclination angle, the larger. Further, the internal pressure increases as the amount of cream solder injected increases.

When the internal pressure increases, the fluidity of the cream solder increases, and the cream solder can be applied to smaller openings. However, since the resistance applied to the squeegee also increases, it is necessary to increase the force for pressing the squeegee against the cream solder supply screen, that is, the printing pressure. If the printing pressure is insufficient, the squeegee will rise due to the resistance of the cream solder, and not only will the cream solder remain on the cream solder supply screen, but also it will not be possible to generate sufficient internal pressure. Cannot print in print state.

Therefore, in order to obtain a good printing condition,
In accordance with the size of the opening, it is necessary to ensure appropriate fluidity of the cream solder, and in order to realize this, it is necessary to adjust the moving speed, the inclination angle, and the printing pressure of the squeegee. . Hereinafter, a case where an IC package is mounted on a printed circuit board will be described. The IC plays an important role in downsizing the board by high-density mounting, and is currently mounted on most printed boards. As a package form of this IC, one in which leads are arranged at regular intervals in two directions of the package (SO
P) and ones (QFPs) that are regularly arranged in four directions. For example, in the case of QFPs, as shown in FIG.
The electrode patterns 7 on the printed board are arranged at regular intervals according to the intervals between the leads. Further, as shown in FIG. 5B, one electrode pattern 7 is
When soldering is carried out on a substrate, it is necessary to secure the electrode portions before and after the lead 10 in order to secure the bonding strength after soldering, and therefore, it is formed in a rectangular shape. Therefore, the opening of the cream solder supply screen opposed thereto is also formed in a rectangular shape.

In recent years, there has been an increasing demand for smaller and lighter electronic devices, and in order to reduce the mounting area of printed circuit boards,
The lead pitch of the IC is 0.5 mm to 0.4 mm.
The pitch is becoming narrower at 3 mm, and the openings of the cream solder supply screen are also arranged at a narrower pitch.

[0009]

However, in the conventional structure as described above, the narrow pitch IC portion, especially
When soldering an IC part having a pitch of less than mm, not only the shape of the printed cream solder becomes unstable, but also the cream solder comes into contact between adjacent electrode patterns.

When the cream solder contacts between adjacent electrode patterns, the solder remains in contact between the leads in a later reflow process, causing a mounting defect. Hereinafter, the reason why the printing shape becomes unstable will be described with reference to FIG.
As described above, when printing cream solder, it is necessary to adjust the moving speed of the squeegee, the tilt angle, and the like so that an internal pressure of the cream solder suitable for the size of the opening is generated. To meet these conditions,
It is necessary to adjust the printing pressure. Also, the smaller the opening, the higher the internal pressure is required, and the printing pressure also needs to be increased accordingly. In addition, during mass production, the amount of cream solder injected into the squeegee decreases each time printing is performed on a printed circuit board. An injection has been made. For this reason, the required printing pressure becomes larger.

The printing pressure and the internal pressure of the cream solder are:
When the squeegee 8 moves in the direction indicated by X in FIG. 6, the squeegee 8 falls downward on the cream solder supply screen 4 in the direction of travel of the squeegee 8 as shown in FIG. Here, a screen having a thickness of 0.1 mm to 0.2 mm is often used as the cream solder supply screen 4, and particularly a screen having a thickness of 0.15 mm is often used. Further, the material of the cream solder supply screen 4 is often stainless steel or nickel alloy.
For this reason, when rectangular openings like a QFP pattern are continuous, the dimension of the portion 3 serving as a partition of each opening becomes smaller as the pitch of the electrode pattern 7 becomes smaller, and the strength becomes smaller. Become.

For this reason, when the openings 2 are continuous, particularly when the interval between the openings 2 is 0.4 mm or less, as shown in FIG. The partition 3 of the solder supply screen is deformed, and the deformation is particularly large near the center of the opening 2.
Further, a case where the moving direction of the electrode pattern and the moving direction of the squeegee are different will be described with reference to FIG.

When the squeegee moves in the direction indicated by X in the figure with respect to the arrangement of the electrode patterns 7, the force applied to the cream solder supply screen due to the printing pressure and the internal pressure of the cream solder is as shown in FIG. Then, the opening portion 2 acts in a direction of expanding the opening portion, so that the partition portion 3 of the screen is deformed in the direction of travel of the squeegee. In particular, the deformation near the center of the opening 2 is the largest.

Here, since the cream solder is a fluid and has a higher fluidity than a stationary state due to a rise in internal pressure, it is caused by deformation of the opening between the cream solder supply screen and the printed circuit board. In extra space,
The cream solder is filled. As a result, overfill occurs and the printed cream solder comes into contact with the cream solder on the adjacent electrode pattern.

If the thickness of the cream solder supply screen is increased when the pitch is 0.3 mm or less, overfilling due to deformation of the screen occurs frequently, making it impossible to perform printing continuously. Furthermore, the deformation of the screen does not always have a certain tendency, the amount of deformation varies greatly, and the printing shape becomes unstable.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cream solder supply screen which prevents deformation of the screen at a portion where openings are continuous and stabilizes the printed shape of the printed cream solder. Still another object of the present invention is to prevent the occurrence of a printing failure in which the printed cream solder contacts an adjacent electrode pattern. Still another object is to realize printing of a fine pitch portion.

[0017]

According to the present invention, there is provided a cream solder supply screen having an opening for supplying cream solder to a desired position on a printed circuit board. It is characterized in that cream solder is supplied to each of the arranged electrode portions from openings divided into a plurality of regions.

According to the present invention, in the cream solder supply screen, the partitioning portion that divides the opening prevents the deformation of the screen due to the internal pressure and the printing pressure at the time of filling the cream solder, and the printed shape of the printed cream solder. Can be stabilized. Further, it is possible to prevent a printing defect in which the printed cream solder contacts an adjacent electrode pattern. Further, printing of a fine pitch portion can be realized.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An invention according to claim 1 of the present invention is a cream solder supply screen having an opening for supplying cream solder to a desired position on a printed circuit board, the screen being arranged on the printed circuit board. It is characterized in that cream solder is supplied to each of the electrode portions through openings divided into a plurality of regions. It has the effect of improving strength and preventing deformation during printing.

According to the second aspect of the present invention, the partitioning portion is disposed so as to obliquely intersect the opening.
It is characterized by forming an opening divided into a plurality of areas, improving the strength of the cream solder supply screen and preventing deformation during printing compared to the case of forming with a single opening It has the action of: The invention according to claim 3 is characterized in that an opening divided into a plurality of regions is formed by a partition portion arranged so as to be divided in the longitudinal direction with respect to the opening. Compared to the case where the opening is formed, the cream solder supply screen has an effect of improving the strength and preventing deformation during printing.

According to a fourth aspect of the present invention, the interval between the plurality of regions divided in the longitudinal direction is 90% of the thickness of the screen.
% To 110% or less, and has the effect of improving the strength of the cream solder supply screen and preventing deformation during printing, as compared with the case of forming with a single opening. . The cream solder supply screen of the present invention is the same as the conventional cream solder supply screen, except for the openings for the electrode portions arranged at regular intervals on the printed circuit board. The description of is omitted. In the cream solder supply screen in the following embodiment, cream solder in which solder powder having a particle diameter of 25 μm and 9% by weight of flux are mixed is used as a printing material.
Set the squeegee angle to 60 ° and set the printing pressure to 2.5kgf
/ Cm ² and the moving speed of the squeegee is 10 to 30 mm /
Screen printing was performed as s.

[0022]

Embodiment 1 A first embodiment of the present invention will be described with reference to FIG. The cream solder supply screen shown in FIG. 1 has two openings 2 arranged at regular intervals on a printed circuit board facing an electrode portion so as to obliquely intersect the openings. It is divided into four regions by the partition part 1.

In this embodiment, the electrode pattern is
It is intended for a 0.5 mm pitch QFP, the screen has a thickness of 0.18 mm, and the dimensions of the opening 2 and the partition 1 are 0.18 mm in width. The dimensions of the entire opening are 0.24 mm in width and 1.3 mm in length. Next, the operation of the present embodiment will be described with reference to FIG.

The arrangement of the electrode patterns of the IC package is as follows.
Depending on the arrangement of the electronic components on the printed circuit board, they are arranged in a direction parallel to the direction perpendicular to the direction of travel of the squeegee. However, as described above, in the conventional opening shape, cream solder to be filled in the opening is used. Due to the pressure and the printing pressure, a portion corresponding to a partition portion between adjacent electrodes is deformed so as to be expanded.

When the squeegee moves in the direction indicated by X in the figure, the force acting on the screen 4 acts obliquely downward from above the screen 4 as shown by A in the figure. The cream solder flowing in front of the squeegee due to this force flows into the opening 2 as shown in FIG. At this time, not only the direction shown by A in the figure but also the direction of movement of the squeegee shown by X in the figure depends on the flow direction of the cream solder after flowing, in the partition 3 between the adjacent electrodes of the screen. To act to cause the partition portion 3 to deform.

Here, according to the present embodiment, the role of the reinforcing plate for the partition 3 between the adjacent electrodes of the screen is provided by providing two partitions 1 arranged obliquely at the opening 2 in the opening 2. Therefore, the deformation of the partition portion 3 due to the force at the time of filling can be prevented. In addition,
In the above description, an example was described in which the opening was divided into four regions by two partition portions and a cream solder supply portion for one electrode was configured, but any configuration in which the partition portion between adjacent electrodes is reinforced is used. It can be similarly implemented.

[0027]

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. Although the configuration described in the first embodiment of the present invention is effective at a pitch of 0.5 mm or 0.4 mm, an electrode portion having a pitch of 0.3 mm or less is divided by a partition portion. Since the area of the opening is too small, the cream solder may remain on the opening and may not be transferred onto the printed circuit board.

In view of the above, the cream solder supply screen shown in FIG.
Is divided into two. In the present embodiment, a 0.3 mm pitch QFP is targeted as the electrode pattern, the screen has a thickness of 0.15 mm, and the partition part 1 of the opening is provided.
Has a width of 0.15 mm, and the length of the opening 2 divided by the partition 1 is 0.6 mm.
It is. The width of the opening itself is 0.15 mm.

The partition 1 disposed at the center functions as a reinforcing plate for the partition 3 between the adjacent electrodes, and can prevent the deformation of the screen when the cream solder is filled. When the cream solder was printed on the opening in the form of FIG. 3 by the screen printing machine under the above-described setting conditions, a printing failure occurred in which the printed cream solder was in contact with the cream solder printed on the adjacent electrode. After printing 25 sheets in succession.

Printing under the same conditions was performed at a length of 1.35 mm,
When the printing was performed at a conventional opening having a width of 0.15 mm, printing failure in contact with an adjacent electrode occurred continuously for one time.
After printing three sheets, the effect of the present invention was confirmed. In the above description, the opening is set at 1 in the longitudinal direction.
In the example described above, the cream partitioning portion is divided into two regions by the book partitioning portion 1 to form a cream solder supply portion for one electrode.
Regarding the number of divisions of the region, the embodiment can be similarly implemented as long as the partition between adjacent electrodes is reinforced.

The number of divisions and the size of the partition 1 need not be determined in consideration of only the strength of the screen. Since the length of the electrode itself is determined, the larger the number of divisions, the narrower each opening area becomes. As a result, the cream solder stays in the opening and cannot be transferred to the printed circuit board. In the present invention, the configuration in which the partition portion is provided in the central portion and divided into two as described in the second embodiment, and the configuration in which the width of the partition portion is equal and the division is evenly divided into three are most effective.

It is not necessary to divide the single electrode into equal regions for a single electrode. In the case of two divisions, when the position is shifted while keeping the width of the center partition at 0.15 mm, the division is performed. The length of the opening on one side is 0.4 mm,
The same effect was obtained when the length of the opening on the other side was 0.8 mm. It is desirable to increase the size of the partition from the viewpoint of the strength of the screen. However, if the size is increased, the size of the divided openings becomes smaller, so that the amount of cream solder to be printed becomes insufficient. Furthermore, if a large partition is provided at the center of the electrode, when the QFP is mounted after the cream solder printing, the solder under the leads is insufficient, so that soldering having sufficient strength cannot be performed. In other words, the cream solder cannot hold the QFP during mounting and reflow in the post-process.
A state occurs in which the FP is shifted.

With respect to the division in the longitudinal direction, experiments were conducted on various dimensions in the case where the center part was divided into two parts. The width of the partition part at which the effect of the present invention can be effectively obtained varies depending on the thickness of the screen. Good results were obtained when the width was 90% or more and 110% or less of the screen thickness. The same applies to the case of dividing into three. If the width is larger than this, the amount of cream solder to be printed is insufficient, and the bonding strength of the lead is reduced. If the width is smaller than this, the strength of the partition portion itself is insufficient. , The screen is deformed.

[0034]

As described above, according to the present invention, the cream solder is supplied from a plurality of areas to the respective electrodes to the electrode portions arranged at regular intervals on the cream solder supply screen. By providing the configured opening, the deformation of the screen due to the internal pressure and the printing pressure at the time of filling the cream solder can be prevented, and the effect of preventing the printing failure in which the cream solder contacts the adjacent electrode can be obtained.

Further, by providing an opening arranged so as to supply cream solder from a plurality of regions divided in the longitudinal direction, not only printing failure in which the cream solder contacts adjacent electrodes can be prevented, but also 0%. It is possible to obtain a stable print shape in a fine pitch portion of 0.4 mm or less. Furthermore, the effect of the present invention can be further enhanced by setting the interval between the plurality of regions divided in the longitudinal direction to be 90% or more and 110% or less of the thickness of the screen.

[Brief description of the drawings]

FIG. 1 is a top view showing an opening shape of a cream solder supply screen according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing how a force at the time of printing is applied to an opening of the cream solder supply screen according to the first embodiment of the present invention.

FIG. 3 is a top view showing an opening shape of a cream solder supply screen according to a second embodiment of the present invention.

FIG. 4 shows a screen printing situation in a conventional example;
(A) is a conceptual diagram showing a relationship between a squeegee, a printing material, and a screen in a printing process, and (b) is a conceptual diagram showing a state in which the screen is subsequently separated.

FIG. 5 shows an example in which electrode patterns are arranged at regular intervals.
4A and 4B show electrode patterns of a QFP, FIG. 4A is a layout diagram of electrode patterns on a printed circuit board, and FIG.

FIG. 6 is a conceptual diagram showing a direction of a force applied to a screen and a state of deformation during screen printing in a conventional example.

FIG. 7 is a conceptual diagram showing a direction of a force applied to a screen and a state of deformation during screen printing in a conventional example from an upper surface of the screen.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Opening partition part 2 Opening part 3 Partition part between adjacent electrodes 4 Screen 5 Printed circuit board 6 Cream solder 7 Electrode pattern 8 Squeegee 9 QFP main body 10 IC lead

Claims (4)

[Claims] 1. A cream solder supply screen having an opening for supplying cream solder to a desired position on a printed circuit board, wherein each electrode portion arranged on the printed circuit board is divided into a plurality of regions. A cream solder supply screen, characterized in that cream solder is supplied from the opened opening. 2. A cream solder supply screen according to claim 1, wherein an opening divided into a plurality of regions is formed by a partition portion arranged so as to obliquely intersect the opening. . 3. The cream solder supply device according to claim 1, wherein an opening divided into a plurality of regions is formed by a partition portion arranged so as to be divided in the longitudinal direction with respect to the opening. screen. 4. The cream solder supply screen according to claim 3, wherein the interval between the plurality of regions divided in the longitudinal direction is 90% or more and 110% or less of the thickness of the screen.