Array mask

Abstract

We provide a mask for soldering that can prevent solder ball placement defects. [Solution] This is an array mask that places solder balls 2 at predetermined positions on a workpiece 3 by loading solder balls 2 into through holes 12 corresponding to a predetermined array pattern. It comprises a mask body 10 in which through holes 12 are formed. A coating layer is provided on both the inner surface of the through holes 12 and the surface of the mask body 10. A projection 15 is provided on the lower side of the mask body 10, that is, the side facing the workpiece 3. A coating layer is provided on the surface of the projection 15, and the thickness of the coating layer on the surface of the mask body 10 and the thickness of the coating layer on the surface of the projection 15 are set to be the same.

Description

Technical Field

[0001] The present invention relates to an alignment mask used for forming, for example, solder bumps.

Background Art

[0002] As a method for forming solder bumps, bumps are formed through a printing step of applying flux to electrodes on a workpiece such as a wafer, a flexible substrate, or a rigid substrate, an alignment step of arranging solder balls on the flux, and a heating step of heating and melting the solder balls. In the aforementioned alignment step, as a method for arranging solder balls on the workpiece, there is a transfer method using a mask. In the transfer method, an alignment mask (hereinafter appropriately simply referred to as "mask") having positioning through holes through which solder balls can pass corresponding to the arrangement pattern of the electrodes of the workpiece is used to mount the solder balls on the electrodes of the workpiece. Specifically, after aligning the mask with respect to the workpiece so that the through holes and the electrodes coincide with each other, the solder balls supplied onto the mask are swept with a squeegee, a brush or the like to feed one solder ball into each through hole. Then, by fixing the solder balls to the flux, the solder balls are temporarily mounted at predetermined positions on the workpiece.

[0003] As such a mask, there is one disclosed in Patent Document 1. The mask described in Patent Document 1 is provided with a large number of supporting protrusions on the lower surface of a mask body having through holes, and the projection dimensions of the protrusions are set to the same dimension. Thereby, when the mask is placed on the workpiece, the lower ends of all the supporting protrusions are brought into contact with the upper surface of the workpiece, and a facing gap between the mask body having the through holes and the workpiece is secured.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, in recent years, with the miniaturization of electronic devices, bumps have become smaller. In other words, as bumps become smaller, the spacing between through-holes and pattern areas in the mask becomes narrower, and the external dimensions of the protrusions themselves, which are placed between through-holes and pattern areas (outer periphery of the pattern area), also tend to become smaller. As a result, the distance between the mask and the workpiece becomes narrower, and flux placed on the electrodes of the workpiece is more likely to adhere to the mask. If flux adheres to the surface of the mask, solder ball mounting defects are likely to occur. The object of the present invention is to provide an array mask that can prevent solder ball mounting defects. [Means for solving the problem]

[0006] The present invention provides an array mask that places solder balls 2 at predetermined positions on a workpiece 3 by loading them into through holes 12 corresponding to a predetermined array pattern, and comprises a mask body 10 with through holes 12 formed therein, and a coating layer is provided on both the inner surface of the through holes 12 and the surface of the mask body 10. A projection 15 is provided on the lower side of the mask body 10, that is, the side facing the workpiece 3. A coating layer is provided on the surface of the projection 15, and the thickness of the coating layer on the surface of the mask body 10 and the thickness of the coating layer on the surface of the projection 15 are set to be the same dimension. It is characterized by the following:

[0007] When T1 is the thickness of the coating layer on the inner surface of the through-hole 12, and T2 is the thickness of the coating layer on the lower surface of the mask body 10, i.e., the surface facing the workpiece 3, then T1 > T2. When the thickness of the coating layer on the inner surface of the through hole 12 is T1, and the thickness of the coating layer on the lower surface of the mask body 10, i.e., the surface facing the workpiece 3, is T1 <T2である。 When T1 is the thickness of the coating layer on the inner surface of the through-hole 12, and T2 is the thickness of the coating layer on the squeegee surface, which is the upper surface of the mask body 10, then T1 > T2. When the thickness of the coating layer on the inner surface of the through-hole 12 is T1, and the thickness of the coating layer on the squeegee surface, which is the upper surface of the mask body 10, is T1 <T2である。 [Effects of the Invention]

[0008] According to the array mask of the present invention, a coating layer is formed on the underside of the mask body, which prevents flux from remaining attached to the underside of the mask body. Furthermore, by forming the coating layer so as to cover the underside of the mask body and the surface of the protrusions, the coating layer functions as a protective layer for the protrusions, preventing them from falling off, deforming, or being damaged. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing the overall configuration of the array mask and workpiece of the present invention. [Figure 2] This is a longitudinal cross-sectional side view of an array mask according to the first embodiment of the present invention. [Figure 3] This is a plan view of an array mask according to the first embodiment of the present invention. [Figure 4] This is a longitudinal cross-sectional side view of another embodiment of the array mask according to the first embodiment of the present invention. [Figure 5] This is a plan view of another embodiment of the array mask according to the first embodiment of the present invention. [Figure 6] This is a longitudinal cross-sectional side view of another embodiment of the array mask according to the first embodiment of the present invention. [Figure 7] This is an explanatory diagram of a method for manufacturing an array mask according to the first embodiment of the present invention. [Figure 8] This is an explanatory diagram of a method for manufacturing an array mask according to the first embodiment of the present invention. [Figure 9] This is a longitudinal cross-sectional side view of an array mask according to a second embodiment of the present invention. [Figure 10] This is an explanatory diagram of a method for manufacturing an array mask according to a second embodiment of the present invention. [Figure 11] This is an explanatory diagram of a method for manufacturing an array mask according to a second embodiment of the present invention. [Figure 12] This is a partially enlarged plan view of an array mask according to another embodiment of the present invention. [Figure 13]This is a partially enlarged longitudinal cross-sectional side view of another embodiment of the array mask according to the second embodiment of the present invention. [Figure 14] This is an explanatory diagram of a manufacturing method for another embodiment of the array mask according to the second embodiment of the present invention. [Modes for carrying out the invention]

[0010] (First Embodiment) Figures 1 to 3 show a solder ball arrangement mask according to the first embodiment of the present invention. This arrangement mask (hereinafter simply referred to as the mask) 1 is used in the arrangement process of solder balls 2 in solder bump formation. In Figure 2, reference numeral 3 indicates a workpiece on which the solder balls 2 will be mounted by the mask 1. This workpiece 3 is, for example, made by mounting a plurality of semiconductor chips 5 on a glass epoxy substrate base 4, wiring them with wire bonds, and then sealing them with transfer mold. Electrodes 6, which are input / output terminals, are formed in a predetermined pattern on the upper surface of the workpiece 3, surrounding the semiconductor chips 5. The workpiece 3 is cut into individual pieces after bump formation to form individual LSI chips.

[0011] As shown in Figure 1, the mask 1 consists of a mask body 10 made from nickel, nickel-cobalt or other nickel alloys, copper or other metals, and a frame 11 can be attached to this mask body 10 so as to surround it. In the center of the surface of the mask body 10, numerous pattern areas consisting of numerous independent through holes 12 for inserting solder balls 2 are formed, corresponding to each semiconductor chip 5. As shown in Figure 2, the through holes 12 correspond to the arrangement patterns corresponding to the arrangement positions of the electrodes 6 of each semiconductor chip 5 on the workpiece 3. The solder balls 2 have a radius dimension of 50 μm or less, and accordingly, each through hole 12 is formed in a circular shape in plan view with an inner diameter dimension slightly larger than the radius dimension of the ball 2.

[0012] The frame body 11 is a flat plate body made of a material such as aluminum, 42 alloy, Invar material, SUS430, etc., and is provided with one quadrangular opening corresponding to the mask main body 10 at the center of its plate surface. In the present embodiment, one mask main body 10 is held by one frame body 11. The frame body 11 is a molded product thicker than the mask main body 10, and is joined inseparably and integrally to the outer peripheral edge of the mask main body 10. Here, the thickness dimension of the frame body 11 is, for example, approximately 0.05 to 1.0 mm, and is set to 0.5 mm in the present embodiment. Further, the thickness of the mask main body 10 is preferably 10 μm or more, and is set to 200 μm in the present embodiment.

[0013] On the lower surface side of the mask main body 10 (mask 1), that is, on the side facing the workpiece 3, a protruding portion 15 protruding downward can be provided. Specifically, as shown in FIGS. 2 and 3, the protruding portion 15 (crosspiece 15a) can be provided between the pattern regions (on the outer periphery of the pattern region) so as to surround the pattern region. This protruding portion 15 (crosspiece 15a) does not need to be provided continuously as shown in FIG. 3, and may be provided fragmentarily. Further, as shown in FIG. 4, the protruding portion 15 (support post 15b) can be provided at a position in the pattern region where the through-holes 12 are not formed. Further, the shape of the protruding portion 15 provided between adjacent pattern regions (on the outer periphery of the pattern region) so as to surround the pattern region is not limited to the crosspiece 15a, and may be a support post 15c as shown in FIG. 5. If such protruding portions 15 are provided, they come into contact with the upper surface of the workpiece 3 during alignment operation, so that the facing gap between the mask main body 10 and the workpiece 3 can be secured. As shown in FIGS. 2 and 4, each of the protruding portions 15 (crosspiece 15a, support post 15b) is preferably formed so as to taper from the lower surface of the mask main body 10 toward the tip of the protruding portion 15, and has a truncated cone shape.

[0014] As for the shape of the protruding portion 15, other than the above, as shown in FIG. 6, it may be a flared shape in which the root dimension of the protruding portion 15 increases toward the lower surface of the mask main body 10 (a tapered shape that narrows from the root of the protruding portion 15 toward the tip), with the side surface formed in an arc shape. This can prevent damage caused by stress concentration particularly at the root portion 15'' of the protruding portion 15, and even if flux 17 adheres to the protruding portion 15 when the mask 1 is placed on the workpiece 3, the arced side surface of the protruding portion 17 can prevent the flux 17 from creeping into the through hole 12, thus eliminating the risk of defective mounting of the solder ball 2 caused by flux 17 adhering to the through hole 12. The terminal position of the root portion 15'' of the protruding portion 15 is preferably located near the through hole 12 on the lower surface of the mask main body 10, and embodiments where it is located at the intersection of the mask main body lower surface 10a and the through hole inner surface 12a, or at a position spaced apart from the through hole 12 on the mask main body lower surface 10a are conceivable. In addition, the side surface of the protruding portion 15 may be either a convex arc or a concave arc; a convex arc provides good strength, while a concave arc ensures that there is no portion on the side surface of the protruding portion 15 that approaches the electrode 6 to which the flux 17 is adhered, that is, a state where a constant distance from the flux-adhered electrode 6 is maintained. Furthermore, the tip portion 15' and / or the root portion 15'' of the protruding portion 15 may be formed in an arc shape, whereby the risk of flux 17 adhering to the protruding portion 15 is reduced as much as possible.

[0015] In this mask 1, it is preferable that the ratio of the height of the projection 15 to the thickness of the mask body 10 be 2:1 or more, and it is more preferable that the thickness of the mask body 10 is within the range of 10 to 300 μm. Furthermore, it is preferable that the projection 15 has a large aspect ratio (ratio of the height of the projection 15 to the tip dimension), and in this embodiment, the aspect ratio is 3. Furthermore, it is preferable that the base dimension L2 of the projection 15 be 1.0 to 1.5 times the tip dimension L1 of the projection 15, and in this embodiment, it is set to 1.2 times. In addition, it is preferable that the ratio of the tip dimension L1 of the projection 15, the base dimension L2, and the width dimension L3 between the through hole 12 be 1:1.2:1.4 or more. Furthermore, it is preferable that the dimension L4 from the pattern area to the base of the projection 15 (bar 15a, support column 15c) be set to 0.01 mm or more, and in this embodiment, it is set to 0.02 mm. By these conditions, flux adhesion can be prevented as much as possible. At this time, by satisfying the relationship between the ratio of the tip dimension L1 and the base dimension L2 of the projection 15 as described above, and the relationship between the dimension L4 from the pattern area to the base of the projection 15, it is possible to prevent damage to the projection 15 and prevent flux adhesion at the same time. Furthermore, when the dimension from the pattern area to the center of the tip of the projection 15 (bar 15a, support column 15c) is L5, the above-mentioned effect of achieving both can be maximized by making the ratio of L1, L2, and L5 1:3:2.5 or more.

[0016] Here, the mask 1 is described as having a mask body 10 and a projection 15 integrated into one piece, but the mask body 10 and the projection 15 may also be formed integrally from separate components. This is because, in the above mask 1, if the mask body 10 is made of a magnetic material and the projection 15 is made of a non-magnetic material, when the mask 1 is fixed to the workpiece 3 by magnetic attraction of a magnet, the magnetic force can be applied uniformly to the mask 1, so there is no risk of the mask 1 bending unintentionally, it can be made to adhere well to the workpiece, and the alignment accuracy of the through-hole 12 with respect to the electrode 6 can be improved. Furthermore, when removing the mask 1, the workpiece 3 and the projection 15 do not directly magnetically couple, so the plate can be easily removed. Such a mask 1 can be obtained, for example, by making the mask body 10 from a magnetic metal (nickel, iron, etc.) and the projection 15 from a non-magnetic metal (copper, aluminum, etc.).

[0017] Furthermore, in cases where the protrusions 15 are formed from a non-magnetic material, they may be formed from resin or resist, not just the metal mentioned above. This allows for a cushioning effect derived from the elasticity of the resin, reducing the risk of damage to the workpiece 3 when the protrusions 15 come into contact with it. To significantly achieve this effect, it is preferable to form not only the protrusions 15 but all parts of the mask 1 that come into contact with the workpiece 3 from resin. Also, when forming the protrusions 15 from resin, using the same resist used when forming the mask body 10 by electroforming allows for efficient production.

[0018] Furthermore, in this mask 1, as shown in Figures 2, 4, and 6, a coating layer 50 is provided on the lower surface of the mask body 10 and the inner surface of the through-holes 12. The coating layer 50 is preferably water-repellent, and its material may be fluororesin, silicone resin, emulsion, or resist (liquid). By providing such a coating layer 50, even if flux adheres to the lower surface of the mask body 10 or the inner surface of the through-holes 12, the flux can be repelled, preventing the flux from remaining adhered to the lower surface of the mask body 10 or the inner surface of the through-holes 12. Note that the coating layer 50 may be formed on the upper surface of the mask body 10, and it does not need to be formed on the lower surface of the mask body 10 between pattern regions and between the protrusions 15 (bars 15a, support columns 15c). In short, it is desirable to form it in areas where solder ball mounting defects are likely to occur if flux adheres, and it is desirable to form it on the surface of the mask body 10 and protrusions 15 that face the flux 17 applied on the electrode 6 when the mask 1 is placed on the workpiece.

[0019] Note that each drawing does not depict the actual appearance of the mask 1, but rather shows it schematically. Also, the opening dimensions of the through-hole 12 and the thickness dimensions of the mask body 10, etc., in each drawing are shown as such for the convenience of drawing creation. Furthermore, in Figures 3 and 5, the part indicated by reference numeral 15 is the lower end surface (tip surface) of the projection 15, and the base of the projection 15 is not shown. Also, the coating layer 50 is not shown in Figures 3 and 5.

[0020] The arrangement of solder balls 2 using the mask 1 is carried out in the following procedure. This arrangement is performed using a dedicated arrangement device (see Figures 1 and 5 of Patent Document 1, etc.). First, flux 17 (see Figure 2) is printed onto the electrodes 6 of the workpiece 3. Next, the mask 1 is positioned on the workpiece 3 so that the through holes 12 and electrodes 6 coincide, and then the mask 1 is fixed in place. This positioning is actually performed by aligning the outer edges of the frame 11 and the workpiece 3. Once the positioning is complete, in this fixed state, the lower end surface of the projection 15 contacts the surface of the workpiece 3, and the mask body 10 is held in a separated position with a gap between it and the workpiece 3, as shown in Figures 2, 4, and 6. At this time, a magnet can be placed below the workpiece 3, and the mask 1 can be attracted to the workpiece 3 by the magnetic force of this magnet.

[0021] Next, a large number of solder balls 2 are supplied onto the mask 1, and the solder balls 2 are dispersed on the mask 1 using a squeegee brush, and then one by one, the solder balls 2 are fed into the through holes 12. In this way, the solder balls 2 are temporarily held in place on the electrodes 6 by the flux 17. In this solder ball feeding operation using a squeegee brush, even if a large amount of pressure is applied to the mask 1 by the squeegee brush, the protrusions 15 prevent the mask 1 from bending, allowing the feeding operation to proceed smoothly and efficiently.

[0022] As described above, the mask 1 according to this embodiment is equipped with a projection 15 that forms a gap between the mask body 10 and the workpiece 3. Therefore, the projection 15 can reliably secure a gap between the mask and the workpiece 3, making it possible to efficiently and completely insert the solder balls 2 into the through hole 12.

[0023] A reinforcing frame 11 can be provided on the outer edge of the mask body 10. If the mask body 10 is formed under tension such that a stress acts on it in the direction of inward contraction, the expansion of the mask body 10 due to changes in ambient temperature can be absorbed by the tension in the contraction direction. This prevents misalignment of the mask body 10 relative to the workpiece 3. Furthermore, since uniform tension can be applied to the entire mask body 10, the solder balls 2 can be mounted on the workpiece 3 with high positional accuracy.

[0024] Next, Figures 7 and 8 show the manufacturing method of the array mask 1 with the above configuration. First, a photoresist layer 31 is formed on the surface of a matrix 30 made of, for example, conductive stainless steel or brass. This photoresist layer 31 is formed by laminating one or more negative-type photosensitive dry photoresists to a predetermined height and then heat-pressing them together. Next, as shown in Figure 7(a), a pattern film (glass mask) 32 having light-transmitting holes 32a corresponding to the protrusions 15 is placed in close contact with the photoresist layer 31, and then exposed by irradiating with ultraviolet light from an ultraviolet light lamp 33, followed by development and drying processes to dissolve and remove the unexposed portions, thereby forming a primary pattern resist 34 having resist bodies 34a corresponding to the tapered protrusions 15 on the matrix 30, as shown in Figure 7(b). At this time, it is preferable to use a photoresist that does not easily transmit ultraviolet light or to reduce the exposure amount to create a taper in the resist body 34a. Next, the master mold 30 was placed in an electroforming bath prepared under predetermined conditions, and as shown in Figure 7(c), an electrodeposited metal such as nickel or copper was electroformed onto the surface of the master mold 30 that was not covered by the resist body 34a, within the height range of the resist body 34a, to form a primary electroformed layer 35. Here, the primary electroformed layer 35 was formed over almost the entire surface of the master mold 30 (first electroforming step). Next, as shown in Figure 7(d), the primary pattern resist 34 was removed. At this point, it is advisable to polish the surface of the primary electroformed layer 35.

[0025] Next, as shown in Figure 8(a), a photoresist layer 36 was formed on the entire surface of the primary electroformed layer 35 and the matrix 30. Then, a pattern film (glass mask) 37 having light-transmitting holes 37a corresponding to the through-holes 12 was placed in close contact with the surface of the photoresist layer 36. After exposure by irradiating with ultraviolet light from an ultraviolet lamp 33, development and drying processes were performed to dissolve and remove the unexposed areas, thereby forming a secondary pattern resist 38 having a resist body 38a corresponding to the mask body 10 on the surface of the primary electroformed layer 35, as shown in Figure 8(b). Subsequently, the material was placed in an electroforming bath prepared under predetermined conditions, and as shown in Figure 8(c), an electrodeposited metal such as nickel or copper was electroformed onto the matrix 30 and the surface of the primary electroformed layer 35 that was not covered by the resist body 38a, within the height range of the resist body 38a, to form a secondary electroformed layer 39 (second electroforming step). Next, the secondary pattern resist 38 is dissolved and removed, and the secondary electroformed layer 39 is peeled off from the matrix 30 and the primary electroformed layer 35. Finally, a coating layer 50 is formed on the matrix surface side of the secondary electroformed layer 39 corresponding to the lower surface of the mask body 10 and on the surface of the secondary electroformed layer 39 facing the secondary pattern resist 38 corresponding to the inner surface of the through-hole 12, thereby obtaining the mask 1 shown in Figures 8(e) and 2.

[0026] By attaching the frame 11 to the mask 1 thus obtained, an array mask 1 as shown in Figure 1 can be obtained. The mask 1 (secondary electroformed layer 39) can be held in the frame 11 under tension such that a stress acts on it in the direction of inward contraction. This stress can be applied, for example, by utilizing the difference in thermal expansion coefficients between the frame 11 and the mask 1, by attaching the frame 11 to the outer edge of the mask 1 in a high-temperature environment, causing the mask 1 to contract inward at room temperature.

[0027] According to the manufacturing method of the mask 1 described above, a high-precision array mask can be manufactured using electroforming, so that solder balls 2 can be mounted on the workpiece 3 with good positional accuracy. Furthermore, if the mask 1 having the projection 15 is formed by forming the mask body 10 and the projection 15 inseparably as a single unit in a single electroforming process (second electroforming step), there is less risk of problems such as damage to the projection 15 compared to a mask body 10 and projection 15 formed separately, and it is superior in that a highly reliable mask 1 can be obtained with high precision. In addition, if the projection 15 is formed in a tapering shape so that it becomes larger as it approaches the lower surface of the mask body 10, stress concentration, especially at the base of the projection 15, is avoided, so the strength of the projection 15 can be firmly reinforced, and the projection 15 can contact the electrodes 6 while being separated from the electrodes 6 to which flux 17 is applied, so that solder ball 2 mounting defects caused by flux 17 applied to the electrodes 6 adhering to the mask body 10 can be prevented. At this time, it is more effective to make the ratio of the dimension of the tip portion 15' of the projection 15 to the dimension of the base portion 15" 1:3 or more, and to make the aspect ratio of the projection 15 3 or more. The fabrication of a projection 15 having such desired dimensions and aspect ratio can be easily obtained by adjusting the shape of the resist pattern 35.

[0028] In the mask 1 with the above configuration, the shape of the through-hole 12 and the projection 15 may be straight or tapered. Specifically, when the through-hole 12 and projection 15 are tapered, in the case of the through-hole 12, by providing a tapered shape that narrows toward the side of the mask body 10 facing the workpiece 3, it becomes easier to guide the solder balls 2 into the through-hole 12, and by providing a tapered shape that widens toward the side of the mask body 10 facing the workpiece 3, it is possible to prevent flux from adhering to the periphery of the through-hole 12 on the side of the mask body 10 facing the workpiece 3. In the case of the projection 15, by providing a tapered shape that narrows toward the side of the mask body 10 facing the workpiece 3, the mask can be firmly placed on the workpiece 3, and by providing a tapered shape that widens toward the side of the mask body 10 facing the workpiece 3, even when the electrodes 6 of the workpiece 3 are arranged at a narrow pitch, the strength of the projection 15 can be ensured and the projection 15 can firmly contact the workpiece 3. Such shapes can be easily obtained by changing the photosensitivity and exposure conditions of the photoresist layers 31 and 36.

[0029] (Second Embodiment) Next, a mask for arrays according to the second embodiment will be described. In this embodiment, as shown in Figure 9, the coating layer 50 is formed not only on the lower surface of the mask body 10 but also on the surface of the protrusions 15.

[0030] In this embodiment of the array mask, a coating layer 50 is also formed on the surface of the protrusions 15, thus preventing flux from adhering to the protrusions 15. Furthermore, by forming the coating layer 50 on the lower surface of the mask body 10, the inner surface of the through-holes 12, and the surface of the protrusions 15, even if flux adheres to the inner surface of the through-holes 12, the coating layer 50 repels the flux and allows it to flow onto the workpiece via the lower surface of the mask body 10 and the surface of the protrusions 15. In addition, it is possible to more reliably prevent flux 17 from flowing into the through-holes 12.

[0031] Furthermore, by forming a coating layer 50 so as to cover the entire surface of the lower surface of the mask body 10 and the surface of the protrusions 15, for example, if the mask body 10 and the protrusions 15 are formed from separate components, the bonding strength between them will be weak (this is because, as the bumps become finer, the spacing between through holes and between pattern areas becomes narrower, and the external dimensions of the protrusions 15 themselves, which are placed between through holes and between pattern areas (outer periphery of the pattern area), tend to become smaller, resulting in a smaller bonding area between the protrusions 15 and the mask body 10). This may cause the protrusions 15 to detach, deform, or break unintentionally when the mask 1 is used. However, with this configuration, the coating layer 50 functions as a protective layer for the protrusions 15, thus contributing to the prevention of the protrusions 15 detaching, deforming, or breaking. Furthermore, if the goal is to specifically prevent the detachment, deformation, or damage of the protrusion 15, a coating layer 50 can be provided by forming a metal layer (such as Ni or Cu) on the lower surface of the mask body 10 and the surface of the protrusion 15 using sputtering or electroless plating.

[0032] Figures 10 and 11 show the manufacturing method of the array mask according to this embodiment. First, a master mold 40 is prepared as shown in Figure 10(a). The master mold 40 can be made of any conductive material, and in this embodiment, stainless steel was used. Next, a photoresist layer is formed on the surface of the master mold 40, and exposure, development, and drying processes are performed in a well-known manner to dissolve and remove the unexposed portions, thereby forming a primary pattern resist 41 having a resist body 41a on the master mold 40 as shown in Figure 10(b). The above photoresist layer was formed by laminating one or more negative-type photosensitive dry film resists to a predetermined height. Next, the master mold 40 is placed in an electroforming bath prepared under predetermined conditions, and as shown in Figure 10(c), an electrodeposited metal is electroformed onto the surface of the master mold 40 that is not covered by the resist body 41a to a height approximately the same as the height of the resist body 41a, thereby forming a primary electrodeposited layer 42. In this embodiment, the primary electrodeposited layer 42 was formed by Ni-Co electroforming. Furthermore, it is preferable to mechanically polish the surface of the primary electrodeposited layer 42, such as by belt polishing, and / or electropolish it after forming the primary electrodeposited layer 42. Next, as shown in Figure 10(d), the resist body 41a (resist pattern 41) was dissolved and removed.

[0033] Next, as shown in Figure 11(a), a solder resist layer 43 was formed on the surface of the primary electrodeposited layer 42. This solder resist layer 43 was formed by laminating one or more layers to a predetermined height. Then, exposure, development, and drying processes were performed to dissolve and remove the unexposed portions, thereby integrally forming a secondary pattern resist 44 having a resist body 44a on the primary electrodeposited layer 42, as shown in Figure 11(b). It is preferable to perform a delamination prevention treatment such as baking after forming the secondary pattern resist 44. This makes the adhesion between the secondary pattern resist 44 having a resist body 44a and the primary electrodeposited layer 42 stronger. Next, as shown in Figure 11(c), the primary electrodeposited layer 42 and the secondary pattern resist 44 formed on its surface were peeled off from the mold 40. Finally, by forming a coating layer 50 on the surface of the primary electrodeposited layer 42 that has the secondary pattern resist 44 and on the surface of the secondary pattern resist 44, the array mask 1 shown in Figures 11(d) and 9 can be obtained. The coating layer 50 may be formed before peeling the primary electrodeposition layer 42 and the secondary pattern resist 44 from the mold 40. Furthermore, the coating layer 50 may be formed not only on the surface of the primary electrodeposition layer 42 that has the secondary pattern resist 44, but also on the entire surface of the primary electrodeposition layer 42. Of course, the coating layer 50 may also be formed on the inner surface of the through-hole 12.

[0034] Next, another embodiment of the array mask according to the second embodiment will be described. Here, as shown in Figure 13(a), the projection 15 is made of resin, and a coating layer 70 is formed on the surface of the projection 15, and the material of the coating layer 70 is different from the material of the projection 15.

[0035] As described above, this mask is used to mount solder balls onto the electrodes of a workpiece. However, dirt and other contaminants may adhere to the mask during the solder ball arrangement process (swiping), so the mask is cleaned as needed to remove them. When cleaning the mask, a solvent is used, which may cause adverse effects such as stickiness on the surface of the material constituting the protrusions. However, a coating layer on the surface of the protrusions protects against such adverse effects.

[0036] Therefore, in order to protect the projections 15 formed of resin from adverse effects, the mask of this embodiment has a coating layer 70 formed on the surface of the projections 15, and the coating layer 70 is made of a different material from the material (resin) that makes up the projections 15. In addition to the above material, the coating layer 70 can also be made of a photosensitive material mainly composed of acrylic resin, for example.

[0037] The method for manufacturing the array mask is the same as the previously described process (see Figure 10) from the preparation of the mold to the formation of the primary electrodeposition layer and removal of the resist. Next, a solder resist layer is formed on the surface of the primary electrodeposition layer 42, and by performing exposure, development, and drying processes, a secondary pattern resist 60 having a resist 60a is integrally formed on the primary electrodeposition layer 42, as shown in Figure 14(a). Next, as shown in Figure 14(b), a coating layer 70 is formed on the surface of the secondary pattern resist 60. The coating layer 70 is an alkali-developable photosensitive material, and its main components are acrylic resin (55-65%), barium sulfate (15-25%), and silicon dioxide (15-25%). Finally, the primary electrodeposition layer 42 is peeled off from the mold 40 together with the secondary pattern resist 60 and coating layer 70 formed on its surface, thereby obtaining the array mask 1 shown in Figures 14(c) and 13. The coating layer 70 may also be formed on the surface of the primary electrodeposited layer 42 on the side having the secondary pattern resist 60. Alternatively, the coating layer 70 may be formed after the secondary pattern resist 60 has been formed on the primary electrodeposited layer 42 and then peeled off from the mold 40. This allows for easy formation of the coating layer 70 not only on the surface of the primary electrodeposited layer 42 on the side having the secondary pattern resist 60, but also on the entire surface of the primary electrodeposited layer 42. The coating layer 70 may also be formed on the inner wall of the through-hole 12. Furthermore, it is preferable to perform a delamination prevention treatment, such as baking, after forming the secondary pattern resist 60 and the coating layer 70. This strengthens the adhesion between the primary electrodeposited layer 42 and the secondary pattern resist 60, and between the secondary pattern resist 60 and the coating layer 70. This delamination prevention treatment may be performed each time the secondary pattern resist 60 and the coating layer 70 are formed, or it may be performed after the coating layer 70 has been formed on the surface of the secondary pattern resist 60.

[0038] The mask 1 obtained by this manufacturing method is resistant to cleaning (solvents), and the occurrence of stickiness on the protrusions 15 can be prevented as much as possible. Furthermore, as shown in Figure 13(b), if the coating layer 70 is formed to cover the entire surface of the protrusions 15, damage or loss of the protrusions 15 can be prevented.

[0039] Here, since the protrusions 15 and the coating layer 70 are made of the same resin, the adhesion between the protrusions 15 and the coating layer 70 is strong. However, by washing the protrusions 15 after forming them on the mask body 10 (before forming the coating layer 70 on the surface of the protrusions 15) to intentionally create a sticky surface on the protrusions 15, and then forming the coating layer 70 on that surface, the adhesion between the protrusions 15 and the coating layer 70 can be made even stronger.

[0040] Furthermore, as shown in Figure 13(c), the protrusions 15 can also be formed using only the material that forms the coating layer 70. The material that forms the coating layer 70 is one that does not easily adhere to flux, and specifically, a resin mixture containing barium sulfate and / or silicon dioxide in an acrylic resin is an example. This resin mixture has excellent solvent resistance. To explain this in more detail, masks made of this resin mixture with protrusions of width dimensions of 0.2 to 3.0 mm (a total of 7 products: 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 2.0 mm, and 3.0 mm) attached to a mask body made of a nickel-cobalt alloy were immersed in a cleaning agent (manufactured by Kaken Tech Co., Ltd.) for 6 to 24 hours (a total of 3 times: 6 hours, 12 hours, and 24 hours), and it was confirmed that there was no peeling of the protrusions on any of the masks. Moreover, this resin mixture has good compatibility with the mask body 10 and good adhesion, so it is possible to narrow the width dimension of the protrusions 15. Furthermore, since the resin mixture in question has hardness (5H to 6H in the JIS standard scratch hardness test), if the thickness of the mask body is 100 μm or less, and the width of the protrusion is made larger than 5 mm, there is a risk of the mask warping, so it is preferable to keep the width of the protrusion 5 mm or less. Thus, the coating layer 70 is formed mainly from materials such as fluororesin, silicone resin, and acrylic resin. And it is possible to construct the protrusion 15 using these materials as the main components.

[0041] The main component of the resin mixture forming the above-mentioned protrusions 15 is acrylic resin, but is not limited to this. Examples include polyethylene, polypropylene, polystyrene, polyurethane, polyvinyl chloride, polyvinyl acetate, ABS resin, AS resin, PET resin, EVA resin, fluororesin, polyamide, polyacetal, polycarbonate, polyphenylene ether, polyester, polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyethersulfone, amorphous polyarylate, liquid crystal polymer, polyetheretherketone, polyimide, polyamideimide, etc. (so-called thermoplastic resins). In addition, phenolic resin, epoxy resin, melamine resin, urea resin, alkyd resin, polyurethane, etc. (so-called thermosetting resins) may also be used.

[0042] In each of the above embodiments, the arrangement of the projection 15 (support column 15b) and the through hole 12 may be such that the projection 15 (support column 15b) surrounds one through hole 12, or that one projection 15 is surrounded by the through hole 12. When the projection 15 is arranged to surround one through hole 12, the shape of the projection 15 is not limited to a partially provided structure like a support column, but may also be provided in an endless frame shape. Furthermore, the shape of the projection 15 is not limited to a slat 15a or a cylinder, but may also be a polygon such as a rhombus or hexagon, or an ellipse. Moreover, in these shapes, as shown in Figure 12, an elongated shape and / or a shape with rounded corners are preferred. By aligning the longitudinal direction and major axis direction of these shapes in a certain direction, for example, when washing the back surface of the mask 1, the risk of damage to the washing means (cloth, sponge, etc.) or the projection 15 due to the washing means getting caught on the projection 15 can be minimized, and washing can be performed smoothly. Therefore, it is desirable to align the longitudinal and major axis directions of all projections 15 in one direction. Note that the elongated shape is only applied to the lower end surface (tip surface) of the projection 15; the base surface 15b of the projection 15 does not necessarily need to be elongated in terms of strength, etc.

[0043] Furthermore, in each of the above embodiments, the thickness of the coating layers 50 and 70 may be varied between the inner surface of the through-hole 12 and the surfaces of the mask body 10 and the protrusion 15. Specifically, when the thickness of the coating layer 50 on the inner surface of the through-hole 12 is defined as T1, and the thickness of the coating layer 50 on the surfaces of the mask body 10 and the protrusion 15 is defined as T2 (see FIG. 9), by setting T1>T2, it is possible to more reliably prevent flux from adhering to the inner surface of the through-hole 12, which would cause defective mounting of solder balls. In addition, if the coating layer 50 is formed of a material that is slippery (low friction), a slippery region corresponding to the thickness T1 will appear at the boundary between the upper surface of the mask body 10 and the inner surface of the through-hole 12. The greater the thickness T1, the larger this region becomes, so that when the solder balls 2 are swept with a squeegee brush, the squeegee brush and the solder balls 2 can be moved smoothly, and improvements in productivity and work efficiency can be expected. By setting T1<T2, when the protrusion 15 is formed separately on the lower surface of the mask body 10, falling off, deformation, and breakage of the protrusion 15 can be more reliably prevented. Note that there are various methods for forming the coating layer 50, such as a dipping method and a spray method. When forming the coating layer 50, it is preferable to cover portions other than the desired formation positions with a protective sheet. Further, when it is desired to form the coating layer 50 thickly, this can be achieved by locally spraying the portion to be thickened, or by changing the direction in which the mask 1 is dipped (for example, when it is desired to thicken the lower surface of the mask body 10, dipping is preferably performed with the lower surface of the mask body 10 parallel to the dipping surface, and when it is desired to thicken the inner surface of the through-hole 12, dipping is preferably performed with the lower surface of the mask body 10 perpendicular to the dipping surface).

Description of Reference Signs

[0044] 1 Mask 2 Solder ball 3 Workpiece 6 Electrode 10 Mask body 12 Through-hole 15 Protrusion 15a Crosspiece 15b Support post 15c Support post 15' Tip portion 15" base 30, 40 Maternal blood type 31, 36, 43 Photoresist layer (solder resist layer) 34, 41 Primary pattern resist 34a, 41a Resist material 35, 42 Primary electrodeposition layer 38, 44, 60 Secondary pattern resist 38a, 44a Resist 39 Secondary electrodeposition layer 50, 70 coating layers

Claims

1. An array mask for mounting solder balls (2) at predetermined positions on a workpiece (3) by loading solder balls (2) into through holes (12) corresponding to a predetermined array pattern, The mask body (10) comprises the aforementioned through hole (12), A coating layer is provided on the inner surface of the through-hole (12) and on the surface of the mask body (10). A projection (15) is provided on the lower side of the mask body (10), that is, on the side facing the workpiece (3), and a coating layer is provided on the surface of the projection (15). A mask for arrays, characterized in that the thickness of the coating layer provided on the surface of the mask body (10) and the thickness of the coating layer provided on the surface of the protrusion (15) are set to the same dimension.

2. The array mask according to claim 1, wherein the thickness of the coating layer provided on the inner surface of the through-hole (12) is different from the thickness of the coating layer provided on the surface of the mask body (10).

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