JP2005007706A - Squeegee made of plastic and cream solder printing apparatus equipped with squeegee - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a squeegee made of a plastic which can suppress an influence caused by wear to a minimum, and a cream solder printing apparatus equipped with the squeegee. <P>SOLUTION: A belt-like squeegee 2 which slides on a screen 18 with an opening part 17 and squeezes a printing agent 19 placed on the screen 18 to fill the printing agent 19 into the opening part 17 is formed of a plastic material, and the thickness of the plate is made approximately 0.3-0.8 mm, preferably approximately 0.5 mm. The plastic material can be selected from a group comprising polyamideimide, polyimide, polyamide, polyetheretherketone, polyacetal and ultrahigh molecular weight polyethylene. The squeegee 2 can be used by laminating at least one back-up material 3, and it is preferable that an extending space with approximately 1-5 mm is provided between the back-up material 3 and the squeegee 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention slides on a screen having an opening covering a substrate to be printed, and squeezes (spreads) the printing agent placed on the screen to fill the opening with a predetermined amount of printing agent. The present invention relates to a squeegee and a cream solder printing apparatus including the squeegee.
[0002]
[Prior art]
Generally, a printed circuit board in an electronic device is printed with solder paste on electrodes, lands, etc. before mounting the electronic component, and the electronic component is placed on the printed circuit board. It is joined to.
[0003]
FIG. 6 shows an overall outline of the cream solder printing apparatus. In the figure, a cream solder printing apparatus 10 includes a board carry-in holding section 11 for carrying a printed board into the apparatus and holding it, a head section 12 for printing cream solder on the printed board by moving a mounted squeegee, a head It is mainly composed of a robot 13 that conveys the unit 12 in the Y direction in the figure. A squeegee assembly 14 is attached to the head unit 12, and the squeegee assembly 14 reciprocates in the Y direction in the figure on a screen on which a printed board (not shown) carried from the board carry-in holding unit 11 is positioned and fixed. Then, transfer the solder paste onto the printed circuit board and print it.
[0004]
FIG. 7 shows an outline of the relationship between the squeegee assembly 14 attached to the head unit 12, the printed circuit board 16, and the screen 18. In the figure, a printed circuit board 16 on which a circuit network has already been formed is carried into the cream solder printing apparatus 10 and is formed on the lower surface of a screen 18 having openings 17 corresponding to electrodes, lands, etc. of electronic components constituting the circuit. Positioning is fixed. After the cream solder 19 is placed on the screen 18, the squeegee assembly 14 is pressed against the surface of the screen 18 with a predetermined pressure and moved in the Y direction in the figure to squeeze the cream solder 19. The cream solder 19 is supplied from the part 17 onto the printed circuit board 16, and a solder layer having a required thickness is formed at a predetermined position. Thereafter, a terminal of an electronic component (not shown) is joined to the printed solder layer, and the solder layer is melted by heating in a reflow furnace, and then cooled to cure the solder, thereby bonding the terminal of the electronic component to the printed circuit board 16. .
[0005]
FIG. 8 shows a cross section of the squeegee assembly 14 taken along its longitudinal central portion. As shown in the figure, the squeegee assembly 14 mainly includes a squeegee 21, a holder 22, and a holder cover 23. The squeegee 21 is sandwiched between the holder 22 and the holder cover 23 and fixed. Yes. The squeegee 21 has a strip shape in which the illustrated shape extends a predetermined length in a direction perpendicular to the drawing, and one edge portion 24 thereof is in line contact with the surface of the screen 18 (the contact portion extends in a direction perpendicular to the drawing). .
[0006]
During operation of the squeegee assembly 14 configured as described above, the squeegee assembly 14 in a state in which the edge portion 24 is in line contact with the screen 18 is applied with a predetermined pressure downward in the drawing, and the head As the portion 12 moves, the edge portion 24 slides on the screen 18 in the direction indicated by the arrow 25, thereby squeezing the cream solder 19 placed on the screen 18 and filling the opening portion 17. Since the printed circuit board 16 is positioned and fixed on the lower surface of the screen 18, the cream solder 19 filled in the opening 17 is transferred onto the printed circuit board 16 and printed.
[0007]
In order to facilitate the filling of the cream solder 19, the squeegee 21 is attached with a slight inclination with respect to the screen 18 as shown in the figure (for example, with an inclination of about 60 ° with respect to the screen surface). The squeegee 21 that has moved in the direction indicated by the arrow 25 and finished printing is pulled upward, and then the same or another squeegee assembly 14 inclined downward is lowered to bring the edge 24 of the squeegee 21 onto the screen 18. The cream solder 19 is printed on the next printed circuit board 16 by bringing it into contact and moving it in the direction opposite to the arrow 25.
[0008]
By the way, the material of the squeegee 21 is required to have appropriate hardness and flexibility in addition to abrasion resistance sufficient to slide on the screen 18 and solvent resistance to printing agents such as cream solder. Is done. If the material is too hard, the edge portion 24 in contact with the screen 18 does not follow the curvature and undulation of the surface of the screen 18 and causes squeezing leakage of the cream solder, and if too soft, the filling pressure of the cream solder 19 is increased. The squeegee 21 loses and squeezing leakage occurs. For this reason, as a material of the squeegee 21, use of urethane rubber, steel, or the like has been conventionally known (see, for example, Patent Document 1 and Patent Document 2).
[0009]
Among these, in the case of the squeegee 21 made of urethane rubber, hard urethane rubber having a hardness of about 90 °, which is the highest in practical use, is usually used. However, even if the urethane rubber has such hardness, depending on the shape and size of the opening 17 of the screen 18, the edge of the squeegee 21 is placed in the opening 17 due to the elasticity of the urethane rubber as shown in FIG. 9. 24 may bend and enter, and a part of the cream solder 19 to be filled in the opening 17 is scraped off, so that a predetermined amount of cream solder cannot be transferred.
[0010]
On the other hand, an example of a squeegee assembly 14a having a steel metal squeegee is shown in FIG. In the figure, a metal squeegee 27 made of a thin plate is fixed between a holder 22 and a holder cover 23 together with a urethane rubber backup material 28, and only the edge portion 24 a of the metal squeegee 27 is attached to the screen 18. It is configured to touch. With such a configuration, a longitudinal elastic modulus to 8N / mm ² of (urethane rubber from much larger than the urethane rubber squeegee 21, metal squeegee 210 of metal squeegee 27, 000 N / mm ² ), the edge 24 a of the metal squeegee 27 is hardly elastically deformed and enters the opening 17. Therefore, scraping of the cream solder 19 from the opening 17 can be minimized, and the problems of the urethane rubber can be solved.
[0011]
However, when such a metal squeegee 27 is used, the counterpart screen 18 on which the metal squeegee 27 slides is usually formed of stainless steel. Metals slide between each other, and a new problem that the screen 18 is seriously damaged occurs. If the screen 18 is damaged, the printing quality is lowered, and this replacement causes a reduction in production efficiency, resulting in a cost disadvantage.
[0012]
As a technique for solving the problems inherent in the conventional urethane rubber and steel squeegees as described above, a plastic squeegee can be used. The term “plastic” as used in the present specification does not include a substance (elastomer) having rubber-like elasticity such as urethane rubber. Rubber generally has the property of extending its length twice at room temperature (18-29 ° C), holding it for 1 minute, releasing it, and shrinking it to 1.5 times or less of its original length within 1 minute Such plastics are not included in the plastic here.
[0013]
When a plastic squeegee is used, due to the unique hardness and flexibility of the plastic material, the printing agent (cream solder) filled in the opening of the screen is not scraped off, and the screen or substrate to be printed is not bent. There is an advantage that it is possible to realize a squeegee that can sufficiently follow undulations and can avoid severe damage to the screen.
[0014]
[Patent Document 1]
JP 10-86327 A [Publication 2]
JP 2001-88271 PR [0015]
[Problems to be solved by the invention]
However, when a plastic squeegee is used, it must have sufficient durability to withstand use as a squeegee that repeatedly slides on a screen provided with openings. In particular, the plastic material does not have the same abrasion resistance as that of a metal material such as steel, and depending on the mode of use, it may be considered that the print quality is deteriorated due to wear. Further, for example, when the plate thickness of a plastic squeegee is extremely thin, deformation is likely to occur, which may also cause squeezing leakage.
[0016]
Therefore, the present invention clarifies the dimensions of the squeegee that can minimize the influence of wear and deformation when using a plastic squeegee, thereby improving the durability of the squeegee and reducing the manufacturing cost. It is an object of the present invention to provide a plastic squeegee capable of maintaining and improving quality, and a cream solder printing apparatus provided with the squeegee.
[0017]
[Means for Solving the Problems]
In the present invention, the squeegee is formed of a plastic material, and the thickness of the squeegee is about 0.8 mm to about 0.3 mm so that the characteristics of the plastic can be fully utilized without impairing the durability. Specifically, the following contents are included.
[0018]
That is, one aspect of the present invention is a belt-like squeegee that slides on a screen having an opening, squeezes the printing agent placed on the screen, and fills the opening with the printing agent. The squeegee is made of a plastic material, and the thickness of the squeegee is between about 0.3 mm and about 0.8 mm. The plate thickness of the squeegee is more preferably about 0.5 mm.
[0019]
The plastic material can be selected from the group consisting of polyamideimide, polyimide, polyamide, polyetheretherketone, polyacetal, and ultra high molecular weight polyethylene.
[0020]
The squeegee is used in an overlapped manner with at least one backup material, and the edge of the backup material facing the screen is provided with an outlet that retracts from the tip of the squeegee by about 1 mm to about 5 mm with respect to the screen. This is preferable for maintaining the flexibility of the squeegee.
[0021]
The printing agent can be cream solder.
[0022]
Another aspect of the present invention includes a board carry-in holding unit that carries a printed board and positions and fixes the head, a head unit that holds a squeegee, and a robot that moves the head unit, and has an opening. The cream solder placed on the screen is squeezed by the squeegee sliding on the screen to fill the opening, and the solder paste is transferred onto the printed circuit board positioned and fixed on the lower surface of the screen for printing. The present invention relates to a cream solder printing apparatus using any one of the squeegees described above.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a plastic squeegee and a cream solder printing apparatus including the squeegee according to the present invention will be described below with reference to the drawings. The same components as those described in the related art are denoted by the same reference numerals. FIG. 1 shows an example of a squeegee assembly 1 having a plastic squeegee 2. In the figure, a squeegee assembly 1 includes a plastic squeegee 2, a backup material 3 superimposed on the squeegee 2 to reinforce the squeegee 2, and a holder 22 and a holder And a cover 23. The squeegee 2 has a strip shape extending a predetermined length in a direction perpendicular to the drawing, and one edge portion 4 thereof is in line contact with the screen 18 (the contact portion extends in the vertical direction in the drawing). In this state, the squeegee 2 slides on the screen 18, squeezes the cream solder 19 placed on the screen 18, fills the openings 17 of the screen 18, and is positioned and fixed on the lower surface of the screen 18. The filled cream solder 19 is transferred to the printed board 16 and printed.
[0024]
The plastic material constituting the squeegee 2 is preferably excellent in wear resistance and solvent resistance, does not damage the material of the screen 18 (generally stainless steel), and has a higher longitudinal elastic modulus than urethane rubber. . In the examples of the present embodiment, a polyamide-imide plate material is processed and used as a squeegee. Polyamideimide satisfies all the above-mentioned conditions and is easy to process. For example, a commercially available polyamideimide thin plate is cut or punched, and if necessary, an edge portion that becomes a contact surface with the screen 18 4 can be easily obtained by forming by machining such as grinding.
[0025]
However, the squeegee 2 made of the plastic material according to the present embodiment is not limited to the one using the polyamide imide plate material, and other plastic materials may be used as long as the above conditions are satisfied. . As an alternative material, for example, polyimide, polyamide, polyetheretherketone, polyacetal, ultra high molecular weight polyethylene and the like can be used.
[0026]
Next, as the material of the backup material 3, a material having sufficient strength capable of reinforcing the plastic squeegee 2 and excellent in solvent resistance is preferable. Specifically, polyamide is used. Since the squeegee 2 is generally pressed against the surface of the screen 18 with a pressure of about 0.5 N / mm, the thin plastic squeegee 2 alone may not have sufficient strength. If the printing operation is performed in a state where the strength is insufficient, the squeegee 2 loses the filling pressure of the cream solder 19 and squeezing leakage of the cream solder 19 occurs. Therefore, the backup material 3 is used to reinforce this. . That is, the backup material 3 is for reinforcing the squeegee 2 and does not directly contact the screen 18. Therefore, the wear resistance as high as that of the squeegee 2 is not required for the backup material 3, and a cheaper material can be selected for the squeegee 2.
[0027]
In FIG. 1, the front end portion of the backup material 3 facing the screen 18 is retracted from the front end of the squeegee 2 with respect to the screen 18, whereby the backup material 3 is not covered with the squeegee 2. This is referred to as “Take out A”). This is to provide flexibility so that the squeegee 2 can satisfactorily follow the curvature and undulation of the screen 18 and the printed circuit board 16, and the user appropriately selects the margin A according to the printing conditions. be able to. For example, when a polyamideimide squeegee 2 having a thickness of 0.5 mm is used, it is preferable that the take-off A is set to about 1 mm to about 5 mm.
[0028]
The backup material 3 has an inclined portion B in which the plate thickness sequentially increases in a direction away from the screen 18 after providing the feeding allowance A, and a thick plate portion C in which the plate thickness becomes constant. The length of the inclined portion B (that is, the gradient of the inclined portion) can be set to an arbitrary size from 0 (no inclined portion) depending on the use conditions. Thus, the characteristic that the followability to the screen 18 can be adjusted while using the same squeegee 2 according to the printing conditions can be said to be an effect peculiar to the present invention that cannot be obtained with a conventional urethane rubber integrated squeegee.
[0029]
Further, as shown in FIG. 2, the backup material 3 is composed of a plurality of elements 3a and 3b, and the materials of the respective backup materials are appropriately combined with, for example, plastic, metal, etc. A flexible reinforcement can also be provided. The length of the take-out A and the stepped portion B can also be appropriately selected. In FIG. 2, the backup material is composed of two elements 3a and 3b, but it is also possible to use three or more numbers.
[0030]
The inventors of the present application have examined whether the thickness of the squeegee 2 in the squeegee assembly 1 configured as shown in FIG. 1 can be reduced in wear and deformation and increase the durability of the squeegee. FIG. 3 shows the results, and shows the effect of wear on the edge portion 4 of the squeegee 2 and deformation of the squeegee 2 when the plate thickness of the squeegee 2 is variously changed. The horizontal axis shows the three types of plate thickness (0.8 mm, 0.5 mm, 0.3 mm) of the squeegee 2, and the vertical axis in the figure shows the degree of influence due to wear (left side) and the degree of influence due to deformation (right side). The number of squeezing shots that can be used (thousands of shots) is shown. Of the two line graphs, a rising line (1) rising to the right indicates a change in the number of shots due to wear, and a falling line (2) decreasing to the right indicates a change in the number of shots due to deformation.
[0031]
As is apparent from the figure, when the plate thickness is increased to 0.8 mm, the effect of deformation is slight and it can withstand squeezing use up to about 110,000 shots, but the effect of wear is large, about 2 After 500 shots, the cream solder has been scraped off (squeezing leakage) on the screen. This scraping is a phenomenon observed in some mask pattern portions (openings on the screen). On the other hand, when the plate thickness is reduced to 0.3 mm, the influence of wear is improved until it can be used for about 30,000 shots. However, the effect of deformation due to the reduction of the plate thickness is large, and the phenomenon of the cream solder remaining due to the deformation appears after about 10,000 shots.
[0032]
The cause of wear and deformation in accordance with the change in plate thickness as described above is determined as follows. In FIG. 4A, when the plate thickness is as large as 0.8 mm, the flexibility (degree of freedom) of the edge portion 4 of the squeegee 2 is slightly reduced due to the high rigidity due to the plate thickness, as indicated by the symbol F in the figure. When the edge portion 4 of the squeegee 2 and the edge of the opening portion 17 of the screen 18 made of stainless steel hit each other, the edge portion 4 is rubbed due to the high rigidity of the squeegee 2, and this is repeated to the edge portion 4. Wear occurs. As a result, the scraped residue of the cream solder can be seen at the opening on the screen, and it can be seen that wear is caused by the contact between the edge of the opening 17 and the edge 4 of the squeegee 2.
[0033]
On the other hand, when the plate thickness is reduced to, for example, 0.3 mm, the rigidity of the squeegee 2 is reduced by the change in the plate thickness. Therefore, as shown by the symbol F in FIG. Even when the edge of the opening 17 hits, the edge portion 4 of the squeegee 2 has sufficient flexibility to escape from the contact, and wear is easily avoided. This improves the durability against wear. However, since the rigidity is lowered by reducing the plate pressure, it is easily affected by, for example, solvent infiltration, and deformation is likely to occur even when slight squeezing shots are repeated.
[0034]
On the other hand, in the squeegee having a plate thickness of 0.5 mm shown in the center of FIG. 3, by providing appropriate rigidity and flexibility, it is comparable to the plate having a plate thickness of 0.3 mm for wear. It can withstand use up to over 10000 shots, and can withstand deformation up to about 110,000 shots equivalent to those with a plate thickness of 0.8 mm. That is, by setting the thickness of the plastic squeegee to about 0.5 mm, the useful life as a squeegee can be enhanced from both the wear and deformation sides.
[0035]
Note that the determination of the influence of wear and deformation in FIG. 3 is based on the point at which cream solder with a width of approximately 0.1 mm is left on the screen. In particular, in the case of the influence of deformation, this criterion corresponds to the case where the straightness of the edge portion 4 of the squeegee 2 exceeds ± 0.5 mm. If the straightness is smaller than this, it is possible to avoid the above-mentioned scraping residue due to the elasticity of the plastic. Further, in the experiment of FIG. 3, the take-out A (see FIG. 1) of the backup material 3 is 5 mm, and the conveying speed of the squeegee 2 is 40 mm / second.
[0036]
Judging from FIG. 3, when the plate thickness of the squeegee 2 is larger than 0.8 mm or smaller than 0.3 mm, the problem of wear and the problem of deformation become more serious, respectively. It turns out that it becomes low. On the other hand, if the plate thickness is between about 0.8 mm and about 0.3 mm, although there is a difference in durability, the use as the squeegee 2 is sufficiently possible as shown below.
[0037]
FIG. 5 shows the plate thickness of the plastic squeegee 2 for the openings 17 of various sizes provided in the screen 18 (9 types of squares from 1.5 mm square to 6 mm square as shown on the right side of the figure). Represents the rate of solder transfer to each opening 17 when the thickness is 0.8 mm, 0.5 mm, and 0.3 mm. Solder transfer rate is:
Filling mass / (screen opening volume x cream solder density) x 100
Is represented by That is, the higher the solder transfer rate, the smaller the amount of solder scraped from the opening 17. When the solder transfer rate is 100%, the opening 17 is just filled with the cream solder 19. .
[0038]
The average transfer rate for each squeegee plate thickness calculated based on the graph is 101.9% at 0.8 mm thickness, 98.4% at 0.5 mm thickness, and 104.9% at 0.3 mm thickness. Although a slight variation is seen, it cannot be said that the difference is significant, and it can be determined that the function as the squeegee is sufficiently performed at any of these plate thicknesses.
[0039]
As mentioned above, although the embodiment of the plastic squeegee according to the present invention has been described, the present embodiment also includes a cream solder printing apparatus including the plastic squeegee configured as described above. The cream solder printing apparatus can be configured similarly to the conventional cream solder printing apparatus shown in FIG. 6 except for the squeegee portion.
[0040]
【The invention's effect】
According to the plastic squeegee according to the present invention, it is possible to avoid a scraping phenomenon of a printing agent such as cream solder at the time of screen printing, and to provide a squeegee that follows the curvature and undulation of the screen and has excellent durability. Can do.
[0041]
Moreover, according to the cream solder printing apparatus equipped with the plastic squeegee according to the present invention, high-quality printing with a high transfer rate is possible, and the production efficiency is improved by the excellent durability of the squeegee and the avoidance of screen damage. A printing device can be provided.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a squeegee assembly provided with a plastic squeegee according to an embodiment of the present invention.
FIG. 2 is a side sectional view showing another aspect of the squeegee assembly including the plastic squeegee according to the embodiment of the present invention.
FIG. 3 is a chart showing the degree of influence of wear and deformation when the thickness of a plastic squeegee is changed.
FIG. 4 is an explanatory diagram showing the flexibility (degree of freedom) of the edge portion when the plate thickness of the plastic squeegee is changed.
FIG. 5 is a chart showing the solder transfer rate when the thickness of the plastic squeegee is changed.
FIG. 6 is a perspective view showing an overview of a cream solder printing apparatus.
FIG. 7 is a partial perspective view showing main components of the cream solder printing apparatus.
FIG. 8 is a side sectional view showing a squeegee according to the prior art.
9 is a side partial cross-sectional view showing the phenomenon of cream solder scraping by the squeegee shown in FIG. 8;
FIG. 10 is a side sectional view showing another squeegee according to the prior art.
[Explanation of symbols]
1, 1a. 1. Squeegee assembly, Squeegee, 3, 3a, 3b. Backup material, 4. Edge part, 10. 15. solder printing device; Printed circuit board, 17. Opening, 18. Screen, 19. Cream solder, 22. holder,
23. Holder cover A. Take out

Claims (6)

A belt-like squeegee that slides on a screen having an opening, squeezes the printing agent placed on the screen, and fills the opening with the printing agent,
The squeegee is formed of a plastic material;
A squeegee having a thickness of about 0.3 mm to about 0.8 mm. A belt-like squeegee that slides on a screen having an opening, squeezes the printing agent placed on the screen, and fills the opening with the printing agent,
The squeegee is formed of a plastic material;
A squeegee having a thickness of about 0.5 mm. The squeegee according to claim 1 or 2, wherein the plastic material is selected from the group consisting of polyamideimide, polyimide, polyamide, polyetheretherketone, polyacetal, and ultrahigh molecular weight polyethylene. The squeegee is used in an overlapping manner with at least one backup material, and the edge of the at least one backup material facing the screen is retracted from the tip of the squeegee by about 1 mm to about 5 mm with respect to the screen. The squeegee according to claim 1 or 2, wherein the squeegee is provided. The squeegee according to any one of claims 1 to 4, wherein the printing agent is cream solder. A board carry-in holding section for carrying in and fixing the printed board;
A head portion for holding a squeegee;
A robot that moves the head unit,
Cream solder placed on a screen having an opening is squeezed by the squeegee sliding on the screen to fill the opening, and the cream is placed on the printed circuit board positioned and fixed on the lower surface of the screen. In cream solder printing equipment that transfers and prints solder,
The cream squeegee printing apparatus, wherein the squeegee is the squeegee according to any one of claims 1 to 5.

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