Array Mask

Abstract

To obtain a mask for arrangement of solder balls which is unlikely to be damaged even when tension is applied while ensuring an excellent solder ball mounting rate.SOLUTION: In a mask for arrangement for mounting a solder ball 2 at a predetermined position on a workpiece 3, the opening edge of a ball insertion hole 12 is formed into a rounded polygon in a plan view. The mask is provided with a partially arc-shaped rounded portion 17 located at each corner of the rounded polygon, and a straight portion 16 that forms the side of the rounded polygon and is connected to the rounded portion 17. An inclined portion is provided that slopes downward from the rounded portion 17 to the straight portion 16.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a mask for arranging solder balls, which is used, for example, in creating solder bumps for a BGA (Ball Grid Array) system. [Background technology]

[0002] In general, solder bumps are formed through a process of applying solder paste or flux to electrodes, a process of mounting solder balls on the electrodes, and a process of melting the mounted solder balls. In the above-mentioned process of mounting solder balls on electrodes, it is known to use an array mask having an opening pattern corresponding to the array pattern of the electrodes. For example, Patent Documents 1 and 2 disclose array masks having circular ball insertion holes, and Patent Documents 3 and 4 disclose array masks having polygonal ball insertion holes such as square openings and triangular openings. Patent Documents 1, 4, etc. disclose providing a frame body for supporting a mask body having ball insertion holes on the outer periphery of the mask body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-287215 A [Patent Document 2] JP 2006-324618 A [Patent Document 3] JP 2012-227466 A [Patent Document 4] JP 2014-107282 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the arrangement masks of Patent Documents 1 and 2, in which the ball insertion holes are formed in a circular shape, the spherical outer surface of the solder ball and the arc-shaped opening edge of the insertion hole come into line contact, and the solder ball is easily damaged. In addition, since the outer surface of the solder ball and the opening edge of the insertion hole come into contact with each other in a large area, the contact resistance increases, and the solder ball cannot be smoothly dropped into the insertion hole, which is disadvantageous in that the mounting rate decreases. In contrast, in the arrangement masks of Patent Documents 3 and 4, in which the ball insertion holes are polygonal, such as a square opening or a triangular opening, the opportunity for the opening edge and the solder ball to come into contact with each other can be reduced compared to a circular insertion hole, so that the solder ball can be effectively prevented from being damaged. In addition, the solder ball can be smoothly dropped into the insertion hole to improve the mounting rate. However, in the arrangement masks of Patent Documents 3 and 4, when the mask body is attached to the frame, the stress resulting from the tension is likely to concentrate on the minor-angle corners of the polygonal insertion holes, which may cause cracks in the corners and damage the arrangement mask.

[0005] The present invention has been made to solve the problems associated with conventional array masks as described above, and has an object to provide a solder ball array mask that is less likely to break even when tension is applied while ensuring an excellent solder ball mounting rate. [Means for solving the problem]

[0006] The present invention is an array mask that has ball insertion holes 12 corresponding to a predetermined array pattern, and places the solder balls 2 at predetermined positions on a workpiece 3 by dropping the solder balls 2 into the ball insertion holes 12. The opening edge of the ball insertion holes 12 is formed into a rounded regular polygon in a plan view, and each corner of the rounded regular polygon has a partially arcuate rounded portion 17, and at least one of the rounded portions 17 at each corner has a different radius r.

[0007] Here, the concept of a "partial arc" includes a partial regular circular arc and a partial elliptical arc. In addition, there are rounded regular polygons with even corners (rounded regular quadrilaterals, rounded regular hexagons, rounded regular octagons, etc.) and rounded regular odd corners (rounded regular triangles, rounded regular pentagons, rounded regular heptagons, etc.).

[0008] In the movement direction of the squeegee 25 for dropping the solder ball 2 into the ball insertion hole 12, the radius r of the rounded portion 17 is different between the corner portion located on the upstream side of the squeegee movement direction and the corner portion located on the downstream side of the squeegee movement direction.

[0009] The opening edge of the ball insertion hole 12 is formed into a rounded regular even polygon, which has rounded portions 17 located at the corners of the rounded regular even polygon and straight portions 16 that form sides of the rounded regular even polygon and are connected to the rounded portions 17, a virtual regular even polygon 18 is defined by extending the straight portions 16, and a corner straight portion 20 is defined by connecting a vertex 19 of the virtual regular even polygon 18 and an end of the straight portion 16 facing the vertex 19, the movement direction of the squeegee 25 and the extension direction of the two straight portions 16, which are a pair of opposing sides of the rounded regular even polygon of the ball insertion hole 12, coincide with each other, and a radius ra of the rounded portion 17a located upstream in the movement direction of the squeegee 25 is different from a radius rb of the rounded portion 17b located downstream in the movement direction of the squeegee 25.

[0010] In addition, in the movement direction of the squeegee 25 for dropping the solder ball 2 into the ball insertion hole 12, the radius r of the curved portion 17 is different between the ball insertion hole 12 formed on the upstream side of the squeegee movement direction and the ball insertion hole 12 formed on the downstream side of the squeegee movement direction.

[0011] A feature of this embodiment is that the radius r of the rounded portion 17 is gradually changed from the upstream side to the downstream side in the squeegee movement direction.

[0012] The opening edge of the ball insertion hole 12 is formed into a rounded regular even polygon, which has rounded portions 17 located at the corners of the rounded regular even polygon and straight portions 16 that form sides of the rounded regular even polygon and are connected to the rounded portions 17, a virtual regular even polygon 18 is defined by extending the straight portions 16, and a corner straight portion 20 is defined by connecting a vertex 19 of the virtual regular even polygon 18 and an end of the straight portion 16 facing the vertex 19, the movement direction of the squeegee 25 and the extension direction of the two straight portions 16, 16 that are a pair of opposing sides of the rounded regular even polygon of the ball insertion hole 12 coincide with each other, and the radius r of the rounded portions 17 gradually changes from the upstream side to the downstream side in the movement direction of the squeegee 25.

[0013] Also, the radius (r) of the rounded portion (17) is made different at each corner of the ball insertion hole (12). Effect of the Invention

[0014] In general, stress applied during the manufacturing process of the array mask and acting on the opening edge of the ball insertion hole 12 is concentrated at a location where the opening edge shape of the ball insertion hole 12 changes suddenly (for example, at a corner). For this reason, when the ball insertion hole 12 is formed as a regular polygon with rounded corners as in the present invention, the sudden change in the opening edge shape at the corners can be suppressed compared to the opening edge of a regular polygon ball insertion hole with the same number of corners, and the stress can be distributed and applied to the rounded corners. Therefore, according to the present invention, an array mask that is less likely to break even when tension is applied can be obtained compared to a mask having a polygonal ball insertion hole. In addition, since the distortion of the array mask caused by the deformation of the ball insertion hole 12 due to stress concentration can be suppressed, there is also the advantage that the flatness of the array mask can be maintained.

[0015] In addition, the rounded regular polygon has a partially arcuate rounded portion 17 at each corner of the rounded regular polygon, and at least one of the rounded portions 17 at each corner can be set to have a different radius r. For example, if the positions of the rounded portions 17 with different radii r are aligned with the corners of each ball insertion hole 12, the front-rear and left-right directions of the array mask can be confirmed by checking the ball insertion hole 12. In addition, by setting the radius r of the rounded portion 17 to be different between the corner located upstream of the squeegee movement direction and the corner located downstream of the squeegee movement direction in the movement direction of the squeegee 25 for dropping the solder balls 2 into the ball insertion hole 12, the upstream side and downstream side of the squeegee movement direction (left-right direction of the array mask) can be confirmed. Furthermore, by forming the opening edge of the ball insertion hole 12 into a rounded regular even polygon, which has rounded portions 17 located at the corners of the rounded regular even polygon and straight portions 16 that form the sides of the rounded regular even polygon and are connected to the rounded portions 17, the opening edge of the ball insertion hole 12 can be configured so that the rounded portions 17 and the straight portions 16 are smoothly connected, thereby eliminating the formation of minor angled bent portions that are prone to stress concentration at the opening edge of the ball insertion hole 12. Moreover, by aligning the movement direction of the squeegee 25 with the extension direction of the two straight portions 16, 16 that are a pair of opposing sides of the rounded regular even polygon of the ball insertion hole 12, the operation of inserting solder balls with the squeegee can be performed after more reliably grasping the positions of the upstream and downstream sides of the squeegee movement direction in the ball insertion hole 12 that is a rounded regular even polygon.

[0016] In the movement direction of the squeegee 25 for dropping the solder balls 2 into the ball insertion holes 12, the radius r of the rounded portions 17 is set to be different between the ball insertion holes 12 formed on the upstream side of the squeegee movement direction and the ball insertion holes 12 formed on the downstream side of the squeegee movement direction, so that it is possible to confirm the upstream and downstream positions of the squeegee movement direction on the array mask by checking the ball insertion holes 12 (corner portions). Also, the radius r of the rounded portions 17 can be set to gradually differ from the upstream side to the downstream side of the squeegee movement direction. For example, by setting the radius r of the curved portion 17 in the ball insertion hole 12 to gradually decrease from the upstream side (one side) to the downstream side (the other side) of the movement direction of the squeegee brush 25, the movement direction of the squeegee can be visually grasped, and the opening area of ​​the ball insertion hole 12 increases from the upstream side to the downstream side of the squeegee movement direction, thereby creating an arrangement that corresponds to the solder balls 2 that are inserted into each ball insertion hole 12 as the squeegee brush 25 moves and gradually decrease from above the mask body 10, ensuring an excellent mounting rate of solder balls 2 even on the downstream side of the squeegee movement direction. Furthermore, by forming the opening edge of the ball insertion hole 12 into a rounded regular even polygon, which has rounded portions 17 located at the corners of the rounded regular even polygon and straight portions 16 that form the sides of the rounded regular even polygon and are connected to the rounded portions 17, the opening edge of the ball insertion hole 12 can be configured so that the rounded portions 17 and the straight portions 16 are smoothly connected, thereby eliminating the formation of minor-angled bent portions that are prone to stress concentration at the opening edge of the ball insertion hole 12. Moreover, by aligning the movement direction of the squeegee 25 with the extension direction of the two straight portions 16, 16 that are a pair of opposing sides of the rounded regular even polygon of the ball insertion hole 12, the operation of inserting solder balls with the squeegee can be performed after more reliably grasping the positions of the upstream and downstream sides of the squeegee movement direction in the ball insertion hole 12 that is a rounded regular even polygon.

[0017] By setting the radius r of the rounded portion 17 to be different at each corner of the ball insertion hole 12, the ball insertion hole 12 will have various radii r of the rounded portion 17 according to the number of corners. Therefore, when the squeegee 25 is moved in various directions to deposit solder balls into the ball insertion hole, it is possible to mount the solder ball 2 in a manner specialized for the radius r of each rounded portion 17; for example, near the corners where the radius of the rounded portion 17 is small, the solder ball 2 can be more easily guided into the ball insertion hole 12, and near the corners where the radius of the rounded portion 17 is large, the solder ball 2 can be more easily dropped into the ball insertion hole 12. [Brief description of the drawings]

[0018] [Figure 1] 1 is a plan view of a main part of an array mask according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing an entire array mask. [Diagram 3] FIG. 2 is a vertical sectional front view of a main part of the array mask. [Figure 4] 5(a) to 5(d) are explanatory views showing a method for manufacturing an array mask. [Diagram 5] 5(a) to 5(d) are explanatory views showing a method for manufacturing an array mask. [Figure 6] FIG. 11 is a plan view of a main part of an array mask according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a plan view of a main part of an array mask according to a third embodiment of the present invention. [Figure 8] FIG. 11 is a plan view of a main part of an array mask according to a fourth embodiment of the present invention. [Figure 9] 6(a) to 6(c) are plan views showing modified examples of ball insertion holes in the array mask according to the present invention. [Figure 10] FIG. 11 is a plan view of a main part of an array mask according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Example 1) Figures 1 to 5 show Example 1 of a solder ball array mask according to the present invention. In this example, front, back, left, right, and top and bottom refer to the crossed arrows shown in Figures 1, 2, and 3, and the notations for front, back, left, right, and top and bottom in the vicinity of the crossed arrows. Note that the dimensions such as thickness and width in each figure of this example are shown diagrammatically, not as they actually appear. The same applies to the figures of the following examples.

[0020] This array mask (hereinafter referred to as "mask") 1 is used, for example, in the process of mounting solder balls 2 in creating solder bumps for the BGA system. In Figures 2 and 3, reference numeral 3 indicates a workpiece on which the solder balls 2 are to be mounted using the mask 1. This workpiece 3 is, for example, a glass epoxy substrate base 4 on which multiple semiconductor chips 5 are mounted, wired with wire bonds, and then sealed with transfer molding. Electrodes 6, which are input / output terminals, are formed in a predetermined pattern on the top surface of the workpiece 3 so as to surround the semiconductor chips 5. After the solder bumps are created, the workpiece 3 is cut into individual pieces to become individual LSI chips.

[0021] 2, the mask 1 is composed of a mask body 10 made of nickel, nickel alloys such as nickel-cobalt, copper, or other metals, and a frame 11 joined to surround the mask body 10. In the center of the surface of the mask body 10, a number of pattern areas 13 are formed, each having a number of independent ball insertion holes (hereinafter referred to as "insertion holes") 12 for inserting solder balls 2, corresponding to each semiconductor chip 5.

[0022] The insertion holes 12 correspond to an arrangement pattern that corresponds to the arrangement positions of the electrodes 6 of each semiconductor chip 5 in the work 3. The solder balls 2 have a diameter dimension of 100 μm or less, and accordingly, the front-to-back and left-to-right dimensions of each insertion hole 12 are slightly larger than the diameter dimension of the balls 2.

[0023] As shown in FIG. 1, the opening edge of the insertion hole 12 is formed in a square shape with rounded corners (regular polygon with rounded corners) in a plan view. More specifically, the opening edge of the insertion hole 12 has a total of four straight portions 16 running in the front-rear and left-right directions, and quarter-circular (partial circular arc) rounded portions 17 formed at the four corner portions, and is formed in a square shape with rounded corners in a plan view. In the mask 1 according to the present embodiment, the radius dimensions of the four rounded portions 17 are set to the same dimension. Also, for each rounded portion 17, two adjacent straight portions 16·16 are tangentially connected. That is, for the rounded portion 17 formed in a quarter-circular arc shape, the adjacent straight portions 16·16 are configured to be tangentially connected, and the rounded portion 17 and the straight portion 16 are smoothly connected. The insertion hole 12 is preferably arranged in the mask body 10 such that the extending directions of the two straight portions 16·16, which are the front and rear sides of the square with rounded corners, coincide with the moving direction (left-right direction) of a squeegee brush (squeegee) 25 described later.

[0024] The ratio occupied by the rounded portion 17 in the side dimension of the square shape, that is, the ratio occupied by the non-linear portion in each side of the square shape, is preferably less than 1 / 2, and more preferably 1 / 4 to 1 / 3 (1 / 4 or more and 1 / 3 or less). More specifically, in FIG. 1, reference numeral 18 indicates a virtual square (virtual regular polygon) formed by extending the straight portion 16. Let the side dimension of the virtual square 18 be D. A corner straight portion 20 is defined by connecting the vertex portion 19 of the virtual square 18 and the end portion of the straight portion 16 facing the vertex portion 19, and the length dimension of the corner straight portion 20 is defined as d1. At this time, the length dimension d1 of the corner straight portion 20 preferably satisfies the inequality (d1 < D / 2), and more preferably optimally satisfies the inequality (D / 4 ≤ d1 ≤ D / 3). The length dimension d1 of this corner straight portion 20 becomes the radius dimension r of the rounded portion 17. In the present embodiment, the length dimension d1 of the corner straight portion 20 is set to D / 4. The side dimension D of the virtual square 18 is preferably set to 1.05 to 1.15 times the diameter dimension of the solder ball 2.

[0025] As shown in FIG. 2, a frame 11 that supports the mask body 10 is joined to the mask body 10. Specifically, the frame 11 may be directly attached to the mask body 10 with an adhesive or the like, or the frame 11 and the mask body 10 may be joined via a gauze such as Tetron (registered trademark). The frame 11 also serves as a reinforcing member for the mask body 10. The frame 11 is a horizontally long flat plate made of a material with a low thermal expansion coefficient such as aluminum, stainless steel, 42 alloy, Invar material, Super Invar material, or SUS430, and a horizontally long rectangular opening corresponding to the mask body 10 is formed in the center of the plate surface. The frame 11 is a molded product that is thicker than the mask body 10, and is joined inseparably to the outer periphery of the mask body 10. The thickness of the frame 11 is, for example, about 0.05 to 3 mm. The overall thickness of the mask 1 can be designed to match the diameter of the solder balls 2 to be used, and in particular, it is preferable that the thickness of the mask body 10 (including the thickness of the support protrusions 23 if they are provided as described below) be approximately the same as the diameter of the solder balls 2.

[0026] On the lower surface side of the mask body 10, that is, on the surface side facing the workpiece 3, a support protrusion 23 for securing a facing distance with the workpiece 3 is provided so as to protrude downward. The support protrusion 23 has an inverted truncated cone shape, and during the arrangement work of the solder balls 2, the lower end face of the support protrusion 23 is brought into contact with the surface of the workpiece 3 to secure a facing distance between the mask 1 and the workpiece 3. The support protrusion 23 can be provided in a lattice frame shape so as to surround the pattern region 13. In this case, the support protrusion 23 may be provided continuously or intermittently. The support protrusion 23 can be provided so as to be scattered inside and outside the pattern region 13. Although the support protrusion 23 is integrally formed with the mask body 10, it is also possible to integrally join a separate body (e.g., resin) to the mask body 10.

[0027] The arrangement of the solder balls 2 using the mask 1 is performed in the following procedure. First, the flux 24 is printed and applied onto the electrodes 6 of the workpiece 3 (see FIG. 3). Next, the mask 1 is aligned on the workpiece 3 so that the ball insertion holes 12 and the electrodes 6 coincide with each other, and then the mask 1 is fixed. This alignment is actually performed by aligning the outer peripheries of the frame 11 and the workpiece 3. It is possible to place a magnet below the workpiece 3, and after the alignment is completed, the mask 1 can be fixed to the workpiece 3 in an inseparable manner by the magnetic attraction force of the magnet. In this fixed state, the lower end surface of the support protrusion 23 abuts against the surface of the workpiece 3, so that the mask 1 is held in a separated position in which a facing distance from the workpiece 3 is secured as shown in FIG. 3.

[0028] Next, a large number of solder balls 2 are supplied to the opening of the frame 11, i.e., on the mask body 10, and the solder balls 2 are dispersed on the mask body 10 using a squeegee brush 25 with a brush-shaped tip, and the solder balls 2 are inserted into the insertion holes 12 one by one. In this embodiment, the left direction is the upstream side and the right direction is the downstream side, and the squeegee brush 25 is moved from left to right once or multiple times (in some cases, the squeegee brush 25 is then moved from right to left, and reciprocated once or multiple times) to insert the solder balls 2 into the insertion holes 12, and the solder balls 2 are mounted on the electrodes 6. The solder balls 2 inserted into the insertion holes 12 are adhesively held in a temporary state by the flux 24. Finally, the remaining solder balls 2 are removed from the upper surface of the mask 1, and then the mask 1 is removed, and the solder balls 2 are melted, thereby forming solder bumps on the electrodes 6 of the workpiece 3.

[0029] 4 and 5 show a method for manufacturing the array mask 1 according to this embodiment. First, as shown in FIG. 4(a), a photoresist layer 28 is formed on the surface of a matrix 27 made of, for example, stainless steel or brass, which has electrical conductivity. This photoresist layer 28 can be formed by laminating one or several negative-type photosensitive dry photoresists to a predetermined height and then thermocompressing them. Next, a pattern film 29 (glass mask) having light-transmitting holes 29a corresponding to the inverted truncated cone-shaped support protrusions 23 is adhered to the photoresist layer 28, and then the unexposed portions are dissolved and removed by irradiating ultraviolet light from an ultraviolet lamp 30 to perform exposure, development, and drying processes, and a primary pattern resist 31 having resist bodies 31a corresponding to the support protrusions 23 is formed on the matrix 27 as shown in FIG. 4(b).

[0030] Next, the above-mentioned mother mold 27 was placed in an electroforming tank prepared under specified conditions, and nickel, copper, or other electrodeposited metal was electroformed on the surface of the mother mold 27 not covered by the resist body 31a within the range of the height of the resist body 31a as shown in Fig. 4(c) to form a primary electroformed layer 32. Here, the primary electroformed layer 32 was formed over almost the entire surface of the mother mold 27. Next, as shown in Fig. 4(d), the primary pattern resist 31 is removed. In order to improve the workability of the subsequent peeling step, it is desirable to subject the surface of the primary electroformed layer 32 to a polishing treatment or a peeling treatment after removing the primary pattern resist 31.

[0031] Next, as shown in Figure 5(a), a photoresist layer 35 was formed on the entire surface of the primary electroforming layer 32 and the mold 27, and a pattern film 36 (glass mask) having light-transmitting holes 36a corresponding to the insertion holes 12 was adhered to the surface of the photoresist layer 35.Then, ultraviolet light was irradiated from an ultraviolet lamp 30 to perform exposure, development, and drying processes, thereby dissolving and removing the unexposed portions, and a secondary pattern resist 37 having resist bodies 37a corresponding to the insertion holes 12 as shown in Figure 5(b) was formed on the surface of the primary electroforming layer 32.

[0032] Next, the matrix 27 was placed in an electroforming tank prepared under specified conditions, and nickel, copper, or other electrodeposited metals were electroformed on the matrix 27 and the surface of the primary electroformed layer 32 not covered by the resist body 37a within the range of the height of the resist body 37a to form a secondary electroformed layer 38. Next, the secondary pattern resist 37 was dissolved and removed, and the matrix 27 and the primary electroformed layer 32 were peeled (removed) from the secondary electroformed layer 38 to obtain a mask body 10 as shown in Figures 5(d) and 3. Then, a frame 11 was joined to the mask body 10 to obtain a mask 1 as shown in Figure 2.

[0033] The secondary electroformed layer 38, i.e., the mask body 10, can be supported by the frame 11 in a state where a tension is applied to the mask body 10 in a direction that causes the mask body 10 to shrink inward. In other words, the mask body 10 is supported by the frame 11 in a state where tension is applied to the mask body 10, and such a state can be realized by joining the secondary electroformed layer 38 (mask body 10) to the frame 11 before peeling the secondary electroformed layer 38 from the matrix 27. This makes it possible to absorb the expansion of the mask body 10 caused by changes in the ambient temperature by the tension in the shrinking direction, thereby preventing the mask body 10 from shifting in position relative to the workpiece 3. In addition, since a uniform tension can be applied to the entire mask body 10, the solder balls 2 can be mounted on the workpiece 3 with good positional accuracy.

[0034] As described above, in the array mask 1 according to the present embodiment, the opening edge of the insertion hole 12 into which the solder ball 2 is inserted is formed into a rounded regular square (rounded regular polygon) in a plan view, so that even when tension is applied to the mask body 10 during bonding to the frame body 11, the mask body 10 can be effectively prevented from being damaged. That is, the stress acting on the opening edge of the insertion hole 12 due to the tension of the mask body 10 generally tends to concentrate on the portion where the opening edge shape of the insertion hole 12 changes suddenly, and for example, when the insertion hole is formed into a regular square shape, stress is concentrated on the right-angled corners, and the insertion hole is likely to be damaged from the corners. In contrast, when the insertion hole 12 is formed into a regular square with rounded corners, as in the present embodiment, the sudden change in the opening edge shape at the corners can be suppressed compared to the opening edge of a conventional square-shaped insertion hole, and the stress can be distributed and applied to the rounded corners. Therefore, according to this embodiment, it is possible to obtain an array mask 1 that is less likely to break even when tension is applied, compared to a mask with a square-shaped ball insertion hole. In addition, there is an advantage that the distortion of the mask body 10 (mask 1) caused by the deformation of the ball insertion hole 12 due to stress concentration can be suppressed, and the flatness of the array mask 1 can be maintained. In addition, compared to a mask with a circular ball insertion hole, it is possible to reduce the chance of the opening edge coming into contact with the solder ball, so it is possible to drop the solder ball 2 more smoothly into the insertion hole 12, and it is also possible to improve the mounting rate of the solder balls 2 using the array mask 1.

[0035] Furthermore, in this embodiment, the opening edge of ball insertion hole 12 is formed by quadrant arc-shaped (partial arc-shaped) rounded portions 17 located at the corners of the rounded regular rectangle, and straight portions 16 that form the sides of the rounded regular rectangle and are tangentially connected to said rounded portions 17, so that the opening edge of ball insertion hole 12 can be configured so that rounded portions 17 and straight portions 16 are smoothly connected. This makes it possible to eliminate the formation of minor angled bends that are prone to stress concentration at the opening edge of ball insertion hole 12, and therefore makes it possible to more effectively prevent damage and deformation of the mask for arranging solder balls 2 due to stress concentration.

[0036] When the relationship between the side dimension D of the virtual square (virtual regular polygon) 18 and the length dimension d1 of the corner straight portion 20 is configured to satisfy the inequality (d1 < D / 2), the curvature of the rounded portion 17 is made as small as possible within the range where the opening edge of the ball insertion hole 12 does not become circular, and stress can be sufficiently dispersed at the corner portion. In each of the above embodiments, the relationship between the side dimension D of the virtual square 18 and the length dimension d1 of the corner straight portion 20 is configured to satisfy the inequality (D / 4 ≤ d1 ≤ D / 3). This is based on the fact that when the length dimension d1 is less than D / 4, it is difficult to sufficiently disperse stress at the corner portion because the curvature of the rounded portion 17 is large. Also, when the length dimension d1 exceeds D / 3, the straight portion 16 is not sufficiently secured, the solder ball 2 is likely to be damaged, and the mounting rate of the solder ball 2 also deteriorates.

[0037] (Embodiment 2) FIG. 6 shows Embodiment 2 of the mask for arranging solder balls according to the present invention. In this embodiment, the length dimension d1a (d1) (radius ra of the rounded portion 17a) of the corner straight portion 20 of the two rounded portions 17a (17) located on the upstream side (left side) in the moving direction of the squeegee brush 25 is different from the previous Embodiment 1 in that it is set smaller than the length dimension d1b (d1) (radius rb of the rounded portion 17b) of the corner straight portion 20 of the two rounded portions 17b (17) located on the downstream side (right side) in the moving direction of the squeegee brush 25. The length dimension d1a of the rounded portion 17a is set to D / 4, and the length dimension d1b of the rounded portion 17b is set to D / 3. Since the rest is the same as in Embodiment 1, the same members are denoted by the same reference numerals and their description is omitted. The same applies to the following embodiments.

[0038] According to the insertion hole 12 as described above, the length dimension of the straight portion 16 on the left side located on the upstream side in the moving direction of the squeegee brush 25 can be increased. According to this, when the center of gravity position of the solder ball 2 is located on the ball insertion hole 12 in a plan view, the solder ball 2 tries to fall into the ball insertion hole 12. Therefore, by increasing the length dimension of the straight portion 16 on the upstream side (left side) in the moving direction of the squeegee brush 25, it is possible to easily attract the solder ball 2 into the ball insertion hole 12 and improve the mounting rate of the solder ball 2.

[0039] Furthermore, according to the insertion hole 12 as described above, the two rounded portions 17a (17) located on the upstream side in the movement direction of the squeegee brush 25 are disposed close to the vertex 19 of the virtual regular square (virtual regular polygon) 18, which makes it possible to increase the opening area of ​​the ball insertion hole 12 on the upstream side in the movement direction of the squeegee brush 25, thereby contributing to improved induction of the solder ball 2. Also, since the length dimension d1b of the two rounded portions 17b located on the downstream side in the movement direction of the squeegee brush 25 is large, it is possible to prevent the squeegee brush 25 from getting caught on the right side located downstream in the movement direction, allowing the squeegee brush 25 to pass smoothly over the ball insertion hole 12.

[0040] (Example 3) FIG. 7 shows Example 3 of the solder ball array mask according to the present invention. In this example, contrary to Example 2, the length dimension d1a (d1) (radius ra of the rounded portion 17a) of the corner straight portion 20 of the two rounded portions 17a (17) located on the upstream side (left side) of the moving direction of the squeegee brush 25 is set to be larger than the length dimension d1b (d1) (radius rb of the rounded portion 17b) of the corner straight portion 20 of the two rounded portions 17b (17) located on the downstream side (right side) of the moving direction of the squeegee brush 25. The length dimension d1a of the rounded portion 17a is set to D / 3, and the length dimension d1b of the rounded portion 17b is set to D / 4. With such an insertion hole 12, the solder ball 2 can be quickly dropped into the insertion hole 12. In detail, the outer surface of the solder ball 2 falling into the insertion hole 12 falls while contacting the inner surface of the insertion hole 12 downstream of the moving direction of the squeegee brush 25. Therefore, by increasing the length dimension of the straight portion 16 on the downstream side in the moving direction of the squeegee brush 25, the contact area between the outer surface of the solder ball 2 in the middle of falling and the inner surface of the insertion hole 12 can be reduced, and the falling action of the solder ball 2 can be prevented from being braked by friction between the two when the solder ball 2 falls, and the solder ball 2 can be quickly dropped into the ball insertion hole 12. This makes it possible to prevent the solder ball 2 in the middle of falling from being scraped out of the ball insertion hole 12 by the squeegee brush 25.

[0041] Furthermore, by ensuring a large inner area (length of the opening outer edge) of the right half of ball insertion hole 12 in a planar view, that is, the downstream side in the movement direction of squeegee brush 25, the solder ball 2 that falls into ball insertion hole 12 from the upstream side in the movement direction of squeegee brush 25 can be received by the inner surface of ball insertion hole 12, which is formed over a wide area on the downstream side in the movement direction of squeegee brush 25, and the solder ball 2 can be dropped into ball insertion hole 12, contributing to an improvement in the mounting rate of solder ball 2.

[0042] (Example 4) Fig. 8 shows Example 4 of the solder ball array mask according to the present invention. In this example, the radius of the rounded portion 17 is formed to gradually change from the upstream side to the downstream side in the moving direction of the squeegee brush 25. Specifically, the radius r of the rounded portion 17 in the ball insertion hole 12 (the length dimension d1 of the corner straight portion 20) is set to gradually decrease from the upstream side (one side) to the downstream side (the other side) in the moving direction of the squeegee brush 25. By arranging the ball insertion holes 12 in this way, the opening area of ​​the ball insertion hole 12 can be increased from the upstream side to the downstream side in the moving direction of the squeegee brush 25, and an array according to the state of the solder balls 2 on the mask body 10 that changes with the movement of the squeegee brush 25, that is, an array corresponding to the solder balls 2 on the mask body 10 that are input into each ball insertion hole 12 and are reduced by moving the squeegee brush 25 from the upstream side to the downstream side, and the mounting rate of the solder balls 2 can be maintained even on the downstream side of the moving direction of the squeegee brush 25 on the mask body 10. When the radius r of the rounded portion 17 (the length dimension d1 of the corner straight portion 20) is set so as to gradually decrease from the upstream side to the downstream side in the moving direction of the squeegee brush 25, it may be set so as to gradually decrease for each adjacent ball insertion hole 12 in the moving direction of the squeegee brush 25, but this is not limiting. For example, the radius r of the rounded portion 17 (the length dimension d1 of the corner straight portion 20) may be set so as to gradually decrease for each group of multiple rows of the ball insertion holes 12 arranged in the moving direction of the squeegee brush 25 with the front-rear direction of the mask body 10 as rows. Of course, it is also possible to set the radius r of the rounded portion 17 (the length dimension d1 of the corner straight portion 20) to gradually decrease for each group of multiple rows of the pattern regions 13 arranged in the moving direction of the squeegee brush 25 with the front-rear direction of the mask body 10 as rows.

[0043] In the above-mentioned embodiments, the connection between the straight portion 16 and the rounded portion 17 is configured to be tangentially connected, but a slightly less-angled corner may be formed at the connection between the two. In this case, it is preferable that the angle of the corner is close to 180 degrees to avoid stress concentration. Although each rounded portion 17 is configured as a quadrant arc, the rounded portion 17 may be configured as a quarter elliptical arc. Even in this case, it is preferable that the adjacent straight portions 16 are configured to be tangentially connected to the rounded portion 17, so that the rounded portion 17 and the straight portion 16 are smoothly connected. Even in this case, it is preferable that the length dimension d1 of the corner straight portion 20 satisfies the inequality (D / 4≦d1≦D / 3). In addition, the length dimension d1 of the corner straight portion 20 can be changed between one side (front side) and the other side (rear side) in the direction perpendicular to the moving direction of the squeegee brush 25. In addition, the length dimension d1 may be different at each corner of the insertion hole 12.

[0044] In each of the above embodiments, the radius r of the rounded portion 17 in the ball insertion hole 12 (the length dimension d1 of the corner straight portion 20) is set so as to gradually decrease from the upstream side (one side) to the downstream side (the other side) in the moving direction of the squeegee brush 25, but it may be set so as to gradually increase. Also, it may be set so as to gradually decrease (increase) in the direction perpendicular to the moving direction of the squeegee brush 25 (front-rear direction). In addition, the radius r (length dimension d1 of the corner straight portion 20) of the rounded portions 17 in the ball insertion hole 12 is set to gradually decrease (increase) for all of the rounded portions 17 in the ball insertion hole 12 which is a rounded rectangle (rounded regular polygon). However, in a ball insertion hole 12 which is a rounded rectangle (rounded regular polygon), the radius r of at least one of the rounded portions 17 may be set to gradually decrease (increase), or the radius r of two of the rounded portions 17 (two rounded portions 17a located upstream in the direction of movement of the squeegee brush 25, two rounded portions 17b located downstream in the direction of movement of the squeegee brush 25, two rounded portions located in opposing positions, etc.), or three or more of the rounded portions 17 may be set to gradually decrease (increase). The radius r of the rounded portion 17 in the ball insertion hole 12 (the length dimension d1 of the corner straight portion 20) may be different between one end (the upper end side in the moving direction of the squeegee brush 25) and the other end (the lower end side in the moving direction of the squeegee brush 25) of the ball insertion hole 12. The radius r of the rounded portion 17 in the ball insertion hole 12 of a rounded regular rectangle (rounded regular polygon) may be different at each corner. In this case, since the ball insertion hole 12 has various radii r (curvatures) of the rounded portion 17 according to the number of corners, even if the squeegee 25 is moved from an unspecified direction, for example, the solder ball 2 can be easily guided into the ball insertion hole 12 at (or near) a corner where the radius r of the rounded portion 17 is small, and the solder ball 2 can be easily dropped into the ball insertion hole 12 at (or near) a corner where the radius r of the rounded portion 17 is large. Moreover, the ball insertion hole 12 having a rounded quadrangle (rounded regular polygon) may not have the straight line portion 16, that is, may be configured with only the rounded portion 17.

[0045] FIG. 9 shows a modified example of the insertion hole 12. As for the rounded regular polygon, there are a rounded regular even polygon and a rounded regular odd polygon. FIG. 9(a) shows that the opening edge of the insertion hole 12 is a rounded equilateral triangle (rounded regular polygon, rounded regular odd polygon) in a plan view. FIG. 9(b) shows that the opening edge of the insertion hole 12 is a rounded regular pentagon (rounded regular polygon, rounded regular odd polygon) in a plan view. FIG. 9(c) shows that the opening edge of the insertion hole 12 is a rounded regular hexagon (rounded regular polygon, rounded regular even polygon) in a plan view. Also in these modified examples, the adjacent straight portions 16·16 are configured to be tangentially connected to the rounded portion 17 formed in a partial arc shape, and the rounded portion 17 and the straight portion 16 are smoothly connected. Thus, the rounded regular polygon forming the insertion hole 12 is not limited to the rounded square shown in each of the above embodiments.

[0046] (Example 5) FIG. 10 shows an example of a mask for arranging solder balls according to the present invention. In this example, the opening edge of the insertion hole 12 is formed into an irregular regular square (irregular regular polygon) having a straight portion 41 constituting a side of a square (regular polygon) and a partial arc portion 43 bulging outward at each vertex portion 42 constituting the square. The radius dimension R of the partial arc portion 43 is set to 1 / 8 of the length dimension L of the side of the square formed by the opening edge of the insertion hole 12, and the connection portion between the straight portion 41 and the partial arc portion 43 is rounded with a radius dimension smaller than the radius dimension R of the partial arc portion 43. The insertion holes 12 are arranged in a staggered pattern such that the extending directions of the two straight portions 41·41 which are the front and rear sides of the square are the same as the moving direction (left-right direction) of the squeegee brush 25, and the extending directions of the two opposite straight portions 41·41 of the square are inclined by 45 degrees with respect to the moving direction (left-right direction) of the squeegee brush 25. Note that the regular polygon forming the opening edge of the insertion hole 12 is not limited to a square, and may be, for example, an equilateral triangle, a regular pentagon, or the like. Also, the radius dimension R of the partial arc portion 43 is preferably configured to satisfy the inequality (L / 8 < R ≦ L / 2).

[0047] According to the insertion hole 12 as described above, the influence of the formation of the opening edge of the minor angle, which is likely to concentrate stress, at the corner of the ball insertion hole 12 can be eliminated. Therefore, according to the present invention, compared with the opening edge of the polygonal ball insertion hole with the same number of corners, the sudden change of the opening edge shape at the corner can be suppressed, so that the stress can be distributed and applied to the rounded corner, and compared with the mask having the polygonal ball insertion hole, an array mask that is less likely to be broken even when tension is applied can be obtained. Compared with the mask having the circular ball insertion hole, the opening edge and the solder ball can be less likely to come into contact with each other, so that the solder ball 2 can be more smoothly dropped into the insertion hole 12, and the mounting rate of the solder ball 2 can be improved. In addition, the partial arc portion 43 serves as a guide portion for the solder ball 2, and the solder ball 2 that has reached the partial arc portion 43 can be guided to the insertion hole 12. At this time, if an inclined surface that slopes downward from the partial arc portion 43 to the straight portion 41 is provided, the guide function of the partial arc portion 43 to the insertion hole 12 can be more effectively exhibited. Such a configuration can be adopted in each of the above-described embodiments, that is, a sloping surface that slopes downward from the rounded portion 17 to the straight portion 16 may be provided. Note that at least the area surrounded by the partial arc portion 43 may be formed to have a bottom (not penetrating).

[0048] (Reference Example) In each of the above embodiments, the insertion hole 12 has a regular polygon as the reference shape of the opening edge, but the reference shape of the opening edge can be a rectangle. It can also be a convex polygon, a concave polygon, a star-shaped polygon, or the like. It can also be a combination of a circle, a polygon, and a polygon with rounded corners (arcs, straight lines, vertices). In these cases, the opening edge of the insertion hole 12 is set to a size that allows at least one solder ball 2 to be dropped into it. [Explanation of symbols]

[0049] 1 Array mask 2 Solder balls 3 Work 12 Ball insertion hole 16 Straight section 17 R Section 17a: The curved portion located upstream of the squeegee movement direction 17b: A curved portion located downstream in the direction of squeegee movement 18 Virtual regular polygon (virtual regular quadrilateral) 19 Apex 20 Straight corner section 25 Squeegee (Squeegee Brush) 41 Straight section 42 Apex 43 Partial arc D Side dimensions of imaginary regular polygon d1 Length of the straight corner section d1a Length of the straight corner part of the rounded part 17a d1b Length of the straight corner part of the rounded part 17b r Radius of the curved part

Claims

[Claim 1] An array mask having ball insertion holes (12) corresponding to a predetermined array pattern, and for mounting solder balls (2) at predetermined positions on a workpiece (3) by inserting solder balls (2) into the ball insertion holes (12), The opening edge of the ball insertion hole (12) is formed into a rounded polygon in a plan view, and includes a partially arcuate R portion (17) located at a corner of the rounded polygon, and a straight portion (16) that constitutes a side of the rounded polygon and is connected to the R portion (17), An arraying mask characterized in that a slope portion is provided that slopes downward from a curved portion (17) to a straight portion (16).

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