JP2001350269A - Method for producing mask for solder printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a mask for solder printing which ensures good releasability of solder and can accurately transfer creamy solder even to the top of an ultrafine circuit pattern having several μm line width. SOLUTION: The method for producing the mask has a step for forming an electrically conductive film 22 on the surface of a resin film 14, a step for coating the surface of the film 22 with a photoresist 24, a step for exposing the photoresist 24 by irradiation with light through a photomaak with a prescribed mask pattern, a step for removing the photoresist 24b except parts 24a cured by the exposure to form a resist 26, a step for forming a nickel layer 28 by electroforming on the surface of the electrically conductive film 22, a step for removing the resist 26 to form openings 30 in the nickel layer 28 and a step for irradiating the surface of the nickel layer 28 with laser light to form openings 32 which communicate with the openings 30 in the nickel layer 28 in the resin film 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0101]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder printing mask, and more particularly to a high-definition solder printing mask suitable for directly transferring cream solder onto a fine circuit pattern formed on the surface of a silicon wafer. It relates to a manufacturing method.

[0092]

2. Description of the Related Art When transferring cream solder onto a substrate on which a circuit pattern has been formed, a solder printing mask having openings formed at necessary locations is brought into close contact with the substrate surface, and the surface of the solder printing mask is exposed. After the cream solder is rolled with a squeegee and pushed into the opening, a step of separating the solder printing mask from the substrate is performed. For this reason,
The transfer accuracy of the cream solder largely depends on the accuracy of the opening formed in the mask and the removability of the solder when the mask is separated.

At present, various materials and manufacturing methods of the mask for solder printing are in practical use. For example, in Japanese Patent Laid-Open No. 7-81027 (hereinafter referred to as "first prior art"),
Using a plastic plate such as polyimide as a mask material,
A technique of irradiating an excimer laser to this plastic plate to form an opening is disclosed. Also, JP-A-11-10
In 5233 (hereinafter referred to as "the second prior art"), after laminating a metal plate having a through hole formed in advance by laser irradiation and a plastic plate, a laser is irradiated from the through hole of the metal plate. There is disclosed a technique of forming a through hole communicating with a through hole of a metal plate on a plastic plate side.

[0093]

In the first prior art, the compatibility between the excimer laser and the polyimide is good, and the inner wall surface of the opening can be formed smoothly. Although a certain evaluation can be given in that it can achieve high adhesion to the substrate surface, the characteristics of the plastic plate are that the shape (position) of the opening easily shifts due to the influence of temperature and external force, and that it has abrasion resistance. There is a problem in lacking. On the other hand, in the case of the second conventional example, the structure is such that the plastic plate is reinforced by the metal plate, so that the advantage of the plastic plate that the adhesion to the substrate surface is high is maintained, and the shape of the opening is stabilized. And improved wear resistance.

However, in the case of the second conventional example, when a hole is formed in a metal plate with a laser, fine irregularities are inevitably left on the inner wall surface of the opening, which adversely affects the removability of solder. is there. Of course, by providing a polishing process such as a sandblasting process after drilling with a laser, irregularities can be improved to some extent, but it is undeniable that extra work is required. In addition, in the above conventional examples, the accuracy of laser processing directly affects the accuracy of the opening of the mask for solder printing in any case, and is used only for soldering a chip-type element on a printed circuit board. Although it can respond satisfactorily, even though the accuracy of laser drilling has been improved, it can be applied along extremely fine patterns, such as when solder is directly transferred onto a circuit pattern formed on the surface of a silicon wafer. However, there is a limit that it cannot be used for the purpose of placing cream solder.

The present invention has been devised in view of the above-mentioned limitations of the prior art. The high smoothness of the inner wall surface of the opening results in extremely good solder removability, and the line width is small. μm
It is an object of the present invention to establish a method of manufacturing a solder printing mask capable of accurately transferring cream solder onto an ultra-fine circuit pattern of an order.

007

In order to achieve the above object, a method of manufacturing a mask for solder printing according to the present invention comprises a step of forming a conductive film on the surface of a resin film, and a method of forming a photoconductive film on the surface of the conductive film. A step of applying a resist, a step of irradiating the photoresist with light that has passed through a photomask having a predetermined mask pattern formed thereon, and performing an exposure process, and a step of exposing the photoresist other than the portion exposed in the above step. Removing and forming a resist; forming a metal layer on the surface of the conductive film by electroforming; removing unnecessary portions in the photoresist to form a resist; Irradiating a laser to the surface of the layer to form an opening communicating with the opening of the metal layer in the resin film.

Another manufacturing method according to the present invention includes a step of applying a photoresist to a surface of a substrate having conductivity, and a step of transmitting a photoresist having a predetermined mask pattern through the photoresist. Irradiating the substrate with light, exposing the photoresist, removing unnecessary portions in the photoresist to form a resist, and forming a metal layer on the surface of the conductive substrate by electroforming. Removing the resist to form an opening in the metal layer; removing the metal layer from the conductive substrate; bonding the metal layer to a resin film; and applying a laser to the surface of the metal layer. And forming an opening communicating with the opening of the metal layer in the resin film.

The resin film is preferably made of polyimide, and the metal layer is preferably made of nickel. Further, as the laser, an excimer laser or a UV-YAG laser is preferable. This UV
The third harmonic (wavelength 355 nm) or the fourth harmonic (wavelength 266 nm) of the -YAG laser is particularly suitable.

[0010] In the mask for solder printing obtained by the above-described manufacturing method, high adhesiveness with the transfer surface can be ensured by turning the resin film side downward. Further, since the metal layer is arranged on the surface of the resin film, high wear resistance and shape stability of the opening can be realized. Since the opening of the metal layer is formed by an electroforming method (photoelectroforming) using a photoengraving technique, it has extremely high positional accuracy and shape / dimensional accuracy. When the surface of the metal layer is irradiated with a laser, the metal layer functions as a mask, so that an opening with extremely high precision is also formed on the resin film side. In addition, compared to the case where the opening is formed in the metal layer by laser irradiation, the inner wall surface of the opening of the metal layer is finished in a smooth surface state with extremely few irregularities, and a sufficiently high solder removal property can be realized as it is. Originally, the combination of the resin film and the laser processing has good compatibility. In particular, when an excimer laser is used for a polyimide film, the processed surface is finished smoothly, so that the opening of the resin film can secure a high level of removability.

[0011]

FIG. 1 is a plan view showing a solder printing mask 10 obtained by a manufacturing method according to the present invention. The solder printing mask 10 is stretched over an aluminum frame 12 and an inner surface of the frame 12. A resin film 14 and a mask portion 16 formed near the center of the resin film 14 are provided. In the mask section 16, a large number of fine openings 18 are formed along a predetermined pattern.

A method of manufacturing the mask section 16 will be described with reference to FIGS. First, the thickness made of polyimide
After a conductive material such as nickel, copper, or graphite is deposited or sprayed on the surface of the resin film 14 having a thickness of 20 μm to form a conductive film 22, a photoresist 24 is uniformly applied to the surface of the conductive film 22. (FIG. 2). The thickness of this photoresist 24 is set to 27 μm.

Next, the surface of the photoresist 24 is irradiated with ultraviolet rays in a predetermined pattern to partially expose the photoresist 24 (FIG. 3). In this exposure processing, a reduced projection exposure method is used. That is, a reticle (mask) in which a mask pattern is drawn by a light-shielding material such as chrome on the surface of a light-transmitting plate made of quartz glass or the like (not shown) is used to transmit ultraviolet light emitted from a light source through the reticle. Then, it is reduced to about 1/5 using a projection lens and guided to the surface of the photoresist 24. Therefore, on the surface of the photoresist 24, an exposure pattern (exposed portion 24a and unexposed portion having a density five times as fine as the mask pattern drawn on the reticle) is provided.
24b) is formed.

Next, a strongly alkaline developer is sprayed on the surface of the photoresist 24 to elute the portions 24b which have not been cured by exposure in the previous step. As a result, the resist pattern 26 is left on the surface of the resin film 14 (FIG. 4). Note that, as described above, instead of using a so-called negative type that is cured by ultraviolet irradiation as the photoresist 24, a positive type that is softened by ultraviolet irradiation is adopted, and ultraviolet light is applied to portions other than the portion that is desired to be left as the resist pattern 26. It can also be used.

Next, a nickel layer 28 is formed on the surface of the resin film 14 by electroforming (FIG. 5). That is, the resin film 14 is immersed in an electrolytic solution (NiSO ₄ ) containing nickel ions together with a nickel plate (not shown)
By applying a voltage using the conductive film 22 of the resin film 14 as a cathode and the nickel plate as an anode, nickel atoms are deposited and electrodeposited on a portion of the surface of the conductive film 22 which is not covered by the resist pattern 26. When the nickel layer 28 has grown to a required thickness, that is, 27 μm, the nickel layer 28 is pulled out of the electrolytic solution and the surface is subjected to a cleaning treatment.

Next, by removing the resist pattern 26 using a special chemical, a nickel layer 28 having fine openings 30 is formed on the surface of the resin film 14 (FIG. 6). Next, as shown in FIG. 7, an excimer laser is irradiated from above the nickel layer. The laser light incident on the surface of the nickel layer 28 is reflected as it is, but the laser light incident on the opening 30 reaches the surface of the resin film 14 and evaporates the resin film 14. As a result, as shown in FIG. 8, an opening 32 is formed in the resin film 14 with the same positional accuracy and shape accuracy as the opening 30 of the nickel layer 28. The opening 18 of the mask 16 is formed by the communication between the opening 30 of the nickel layer 28 and the opening 32 of the resin film 14. Note that instead of suddenly irradiating the excimer laser, a rough processing is performed by irradiating a TEA-CO ₂ laser in advance, and then finishing is performed by irradiating the excimer laser, thereby shortening the processing time. Alternatively, a UV-YAG laser, especially the third harmonic (wavelength
355 nm) or the fourth harmonic (wavelength 266 nm).
Can also be formed.

FIG. 9 shows an example of use of the solder printing mask 10 formed as described above. The solder printing mask 10 is formed on the surface of a silicon wafer 34 on which fine circuit patterns and semiconductor elements are formed. A state in which the cream solder 36 is placed on the surface of the nickel layer 28 in a state in which the resin film 14 of the mask 10 is in close contact, and is rolled in a certain direction with a squeegee 38, so that the cream solder is filled in the opening 18. Is drawn. After all the openings 18 are filled with the cream solder, the cream solder is transferred onto the silicon wafer 34 by lifting the frame 12 upward. Although the size of the opening 18 is exaggerated for the sake of illustration, cream solder is actually transferred with a line width of 10 μm or less, so that a fine circuit pattern formed on the surface of the silicon wafer 34 is soldered. Can be used.

In the above description, an example is shown in which the nickel layer 28 is formed directly on the surface of the resin film 14 via the conductive film 22. As shown in FIG. 10, the nickel layer 28 having the opening 30 is formed. It is also possible to form an opening corresponding to the opening 30 of the nickel layer 28 in the resin film 14 by laser irradiation after bonding this to the surface of the resin film 14 via the adhesive 40 in advance. it can. In forming the nickel layer 28, although not shown, after applying a photoresist on the surface of the conductive substrate, the surface is irradiated with ultraviolet rays along a predetermined pattern to partially expose the photoresist, After removing the unexposed portion to form a resist, a nickel layer is grown on the surface of the conductive substrate by electroforming, and finally, the resist is removed to form an opening 30 in the nickel layer 28.

[0019]

According to the solder printing mask of the present invention, a resin film having good adhesion to the transfer surface is provided, and a metal layer having high wear resistance is provided on the side to be rubbed by the squeegee. Have. Further, since the opening of the metal layer is formed by an electroforming method using a photoengraving technique, it is possible to finish the opening with extremely high definition and high precision. When the surface of the metal layer is irradiated with a laser, the metal layer functions as a mask, so that an opening having the same level of precision as the opening on the metal layer is also formed on the resin film side. . As a result, the solder can be directly transferred to the circuit pattern formed on the surface of the silicon wafer. Moreover, the inner wall surface of the opening of the metal layer is finished to have a smooth surface with very few irregularities, compared to the case where the opening is formed in the metal layer by laser irradiation. Due to the good compatibility, it is formed in a smooth surface shape, and a sufficiently high solder removal property can be realized as it is.

[Brief description of the drawings]

FIG. 1 is a plan view showing an overall image of a solder printing mask according to the present invention.

FIG. 2 is a sectional view showing a manufacturing process of the solder printing mask.

FIG. 3 is a sectional view showing a manufacturing process of the solder printing mask.

FIG. 4 is a cross-sectional view showing a manufacturing process of the solder printing mask.

FIG. 5 is a sectional view showing a manufacturing process of the solder printing mask.

FIG. 6 is a sectional view showing a manufacturing process of the solder printing mask.

FIG. 7 is a cross-sectional view showing a manufacturing process of the solder printing mask.

FIG. 8 is a sectional view showing a manufacturing process of the solder printing mask.

FIG. 9 is a cross-sectional view showing an example of use of the solder printing mask.

FIG. 10 is a sectional view showing another manufacturing step of the solder printing mask.

[Explanation of symbols]

 10 Mask for solder printing 14 Resin film 16 Mask part 18 Opening 24 Photoresist 26 Resist pattern 28 Nickel layer 30 Opening of nickel layer 32 Opening of resin film 36 Cream solder

Claims (3)

[Claims] 1. A step of forming a conductive film on a surface of a resin film, a step of applying a photoresist on a surface of the conductive film, and a step of transmitting a photomask having a predetermined mask pattern formed on the photoresist. Irradiating the exposed light, exposing the photoresist, removing unnecessary portions in the photoresist to form a resist, forming a metal layer on the surface of the conductive film by electroforming, Removing the resist to form an opening in the metal layer; and irradiating the surface of the metal layer with a laser to form an opening in the resin film that communicates with the opening in the metal layer. A method for manufacturing a solder printing mask, which is a feature of the present invention. A step of applying a photoresist on the surface of the conductive substrate; and a step of irradiating the photoresist with light transmitted through a photomask having a predetermined mask pattern formed thereon, and performing an exposure process. Removing unnecessary portions in the photoresist to form a resist, forming a metal layer on the surface of the conductive substrate by electroforming, and removing the resist to form an opening in the metal layer. Forming, removing the metal layer from the conductive substrate, bonding the metal layer to a resin film, irradiating a laser on the surface of the metal layer, and opening the metal layer in the resin film. A method for manufacturing a mask for solder printing, comprising a step of forming a communicating opening. 3. The method according to claim 1, wherein the resin film is made of polyimide, the metal layer is made of nickel, and the laser is an excimer laser or a UV-YAG laser. Manufacturing method of mask for solder printing.