JP2006175700A - Mask for stencil printing and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems such as the development of a bleeding in cream solder and of defects such as cracks, omissions, chippings or the like in solder terminals due to the worsening of the snapping-off properties of a printing plate and of clearing-out properties of a cream solder as the density of a printing pattern becomes higher at the formation of the solder terminal for mounting electronic parts through the printing of the cream solder by stencil printing. <P>SOLUTION: In order to manufacture a mask for stencil printing, a mask base material layer is formed by plating metal on a supporting board so as to provide through opening parts in the mask base material layer by irradiating laser beam from a mask base material layer side and then electropolish the layer and finally peel the layer off the supporting board. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask for stencil printing used for forming solder terminals for connection for mounting electronic components and semiconductor chips at high density by printing a conductive paste such as cream solder, and a method for producing the same. In particular, the handling of the thin film mask and the control of the thickness of the mask are easy, the wall surface of the opening through which the cream solder is extruded by the squeegee is smooth, and the mask surface around the opening is raised. The present invention relates to a mask that is free from generation and adhesion of dross, and as a result, does not generate cream solder bleeding, has excellent plate releasability, and excellent cream solder transferability, and a method for easily manufacturing the mask.

  In order to mount electronic components on a printed wiring board with high density, in order to mount electronic components on a printed wiring board at high density, starting with cellular phones, high-definition wiring patterns of solder terminals are used. The electronic component and the semiconductor chip are mounted on the solder terminal, and the electronic component and the semiconductor chip are mounted through a solder reflow furnace.

  In particular, in recent years, solder bump electrodes are formed by stencil printing on IC, LSI, and other chips mounted on a substrate, BGA, CSP, etc. in which the chips are molded, connectors, and other components, and through the bump electrodes By mounting components, the electronic circuit is becoming smaller and lighter. At this time, high-definition, high-density, and bump-type electrode formation with no change in the amount of solder is required. Particularly, a stencil having an opening with a smooth wall surface and sharp edges and excellent adhesion to the printing surface. There is a need for a mask for printing, and a method for manufacturing a mask for stencil printing, which makes it easy to control the thickness of the mask and to manufacture a thin film mask.

As a method for manufacturing a mask for a stencil printing plate, for example, a mask (laser method) in which an opening in a wiring pattern is formed by irradiating a mask substrate made of metal or resin with laser light, and a support substrate is made of a resist film A mask (electroforming method) formed by metal plating in which a portion corresponding to the opening is formed is known and widely used.
JP 62-90241 A JP 54-10004

In the above-described method for manufacturing a mask for stencil printing, the opening of the laser method is easy. However, the thinner the mask is, the more complicated and difficult it is to handle the mask substrate. Moreover, it is difficult to arbitrarily control the thickness of the mask.

Further, in the laser method, the mask substrate is melted or ablated, the edge of the opening is sagged, a protrusion (tear mark) remains on the wall surface of the opening on the laser beam emission side, and the substrate in the opening is scattered. For this purpose, the mask surface around the opening is raised or so-called dross adheres. Furthermore, thermal distortion occurs around the opening, and as a result, deformation occurs in the opening. As a result, the adhesion between the mask and the substrate is reduced, and the cream solder is smeared. In addition, unevenness is generated on the wall surface of the opening, so that the cream solder is not easily removed and the transferability is lowered.

As a method for solving the above problems, a method of sandblasting a mask and a method of electrolytic polishing have been proposed.
JP-A-6-39988 However, in the mask made by the above-described method, the edge of the opening is further increased, and the rising of the mask surface around the opening and the dross adhesion can be sufficiently eliminated. In addition, the smoothness of the opening wall surface is insufficient.

On the other hand, in the electroforming method, it is easy to control the thickness of the mask, and it is easy to manufacture a thin film mask. However, a complicated process such as a lithographic method is required for forming the opening. Time was required for production, yield was poor, and it was economically disadvantageous.

  Furthermore, in recent years, so-called lead-free solder that does not contain lead has come to be used for environmental considerations. However, the lead-free cream solder has the ability to release cream solder compared to conventional cream solder. The transferability is poor, the formed solder bumps have defects such as chipping, cracking, and disconnection, and the amount of solder tends to vary.

  The object of the present invention is to form a solder bump for high-density mounting on a wafer, a printed wiring board or the like, and when the cream solder is printed by stencil printing, the adhesiveness to the printing surface, the release property, and the removal of the cream solder. Stencil mask capable of preventing the occurrence of defects such as cream solder bleeding, solder terminal chipping, disconnection, cracking and the like, and capable of increasing the printing speed, and the mask are easily manufactured. It is an object of the present invention to provide a method and a manufacturing method in which the thickness of a mask can be easily controlled.

  In the laser method, the inventors of the present invention can form an opening having a sharp edge and a smooth wall surface, prevent swell and dross from occurring around the opening, and can freely control the film thickness of the mask. The method was examined and the present invention was completed.

That is, the present invention
A mask for stencil printing, in which a mask base material layer is laminated on a support substrate, and a laser beam is irradiated from the mask base material layer side to form a through-opening portion of a printing pattern in at least the mask base material layer, and support A mask for stencil printing by peeling off a substrate, and the mask for stencil printing as described above, wherein the mask base material layer is a metal film layer laminated by a metal plating method, and a through-opening portion. After forming, performing electropolishing and peeling the support substrate, the mask for stencil printing described above, and

A method for producing a mask for stencil printing, comprising a step of laminating a mask base material layer on a support substrate, irradiating a laser beam from the mask base material layer side so that a through-opening portion of a printing pattern is at least formed on the mask base material layer In the method of manufacturing a mask for stencil printing comprising the step of forming, the step of peeling off the support substrate, and the method of manufacturing the mask, the step of laminating the mask base layer is the stencil printing described above by a metal plating method And a mask manufacturing method for stencil printing as described in the above, wherein a step of performing electropolishing is added after the step of forming the through opening in the mask manufacturing method, and

In the stencil mask and mask manufacturing method, the mask base material layer is nickel or a nickel alloy, the stencil mask as described above, the mask manufacturing method, and the electrolytic polishing, and then the fluororesin fine particles The mask for stencil printing of the said description formed by carrying out the metal co-plating containing this, and peeling a support substrate, and the manufacturing method of this mask.

  The mask for stencil printing of the present invention has an opening having a smooth wall surface and sharp edges, and there is no swell or dross adhesion around the opening. Therefore, when cream solder is printed, the cream solder does not bleed, and the cream solder can be removed and the release property of the solder is improved. Defects such as cracks, disconnections, and chips can be prevented, and the productivity and yield of the solder terminal forming process are greatly improved. Further, in the method for producing a mask for stencil printing according to the present invention, not only can the mask having the opening described above be easily produced, but also the thickness of the mask can be freely controlled and a thin film mask can be produced. Easy to handle and easy to manufacture.

  Hereinafter, the mask for stencil printing of this invention and its manufacturing method are demonstrated in detail using figures. FIG. 1A shows a cross section in which the mask base layers 2 and 3 are formed on the support substrate 1. The material of the supporting substrate is not particularly limited as long as it can reinforce the mask base material when manufacturing a thin film mask, can be easily peeled off from the mask base material, and does not adversely affect the formation of openings with laser light. There are various metals and resins. The thickness of the support substrate is about 5 to 300 μm, although it depends on the strength of the substrate material, the thickness of the mask base material layer, and the ability of the laser processing machine used for forming the opening.

On the other hand, the mask base material layer has high strength such as nickel, nickel alloy, copper, copper alloy, iron, aluminum, stainless steel, thermosetting resin such as polyimide resin, PPS, PES, PEEK, liquid crystal resin, etc. And a thermoplastic resin excellent in heat resistance, and a laminate of the metal and the resin. In order to laminate the mask base material layer on the support substrate, a method of laminating the thin film of the mask base material by an adhesive or heat fusion, a method of laminating the above metal by plating, sputtering, vapor deposition, etc., polyimide Examples thereof include a method of applying and heat-curing a resin precursor, a method of melting and laminating the above-described thermoplastic resin, and the like.

Among the methods of laminating the mask base material layer described above, it is easy to manufacture a thin film mask and control the film thickness of the mask, and there is no gap between the support substrate and appropriate adhesion. From the viewpoint of having appropriate peelability, a method of plating and laminating a metal on a support substrate is preferable. In this case, the mask base material is preferably nickel or a nickel alloy in consideration of mechanical characteristics and the like. In addition, when the mask base material layer is laminated by plating, the support substrate is preferably a conductive substrate, and examples thereof include metals such as nickel, copper, aluminum, iron, their alloys, and stainless steel, which are economical and easy to use. Stainless steel is more preferable because of its goodness and ease of peeling from the mask substrate.

In FIG. 1 (a), the mask base material layer is laminated on both sides of the support substrate. However, the mask base material layer is laminated only on one side, and the other side may not be laminated. A film layer, a different metal film layer, or the like may be laminated. In the case of laminating the mask base material layer by plating, it is preferable to laminate the mask base material layer on both surfaces of the support substrate in order to prevent curling and to avoid complicated manufacturing processes. The thickness of the mask base material layer is usually about 5 to 300 μm, although it depends on the specifications of the solder terminals to be formed.

  Next, as shown in FIG.1 (b), the laser beam 4 is irradiated from the mask base-material layer side, and an opening part is formed in a desired printing pattern shape. Examples of the laser light to be irradiated include a solid laser, a gas laser, and a semiconductor laser. Specifically, a YAG laser is preferable. The YAG laser can use a fundamental wave, a harmonic wave, and a mixed wave thereof.

  In FIG. 1B, the opening is formed so as to penetrate the mask base material layers and the support substrate on both sides, but only the mask base material layer on the light incident surface side may penetrate. However, when the opening is formed with laser light, protrusions (tear marks) are likely to occur near the laser light emission side of the wall surface of the opening. Therefore, in order to prevent the protrusions from occurring, the opening penetrates the support substrate, and if a mask base material layer is laminated on the light emitting side, the mask base is formed as shown in FIG. It is preferable to form through the material layer. In order to prevent the protrusions from occurring, when the mask substrate layer on the light incident surface side is used as the mask of the present invention, the film thickness of the support substrate and the mask substrate layer on the light emitting surface (not laminated) In this case, the total film thickness is preferably 20 μm or more, more preferably 30 μm or more. Further, the total film thickness is preferably set so as not to exceed the processing limit of the laser processing machine.

  Next, as shown in FIG. 1C, when both mask base material layers are peeled from the support substrate, the mask 2 'of the present invention is completed. The mask can be peeled from the support substrate by a physical method or a chemical method. As a chemical method, it can be easily peeled off by using a liquid that easily erodes either the mask substrate or the support substrate. For example, when nickel is used as the mask base layer and stainless steel is used as the support substrate, a strong alkaline solution may be used.

In the mask 2 'of the present invention, no swell occurred in the periphery of the opening, and no dross was observed. The edge of the opening was very sharp and the wall surface of the opening was smooth. On the other hand, the mask 3 'on the laser beam emitting side in FIG. 2C can also be used as a mask for stencil printing depending on the application, the manufacturing conditions of the mask, and the like. That is, in the present invention, it is possible to make different masks while having the same print pattern by laminating mask base materials of different materials on both sides of the support substrate or changing the film thickness of the mask base material. It can be used for trial production.

  In the present invention, it is preferable to perform electrolytic polishing treatment, particularly intermittent electrolytic polishing, after forming the opening, since the surface of the mask and the wall surface of the opening are further smoothed and the printing characteristics are further improved. Further, it is more preferable to perform co-plating of a metal containing fluororesin fine particles after the electrolytic polishing treatment because the cream solder can be more easily removed and the plate can be separated. Co-plating of the metal containing the fluororesin fine particles can also be performed after peeling the mask from the support substrate.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to this embodiment.

Both surfaces of a SUS304 substrate having a thickness of 550 × 650 mm and a thickness of 100 μm were buffed to prepare a surface. The substrate was placed in a nickel sulfamate plating bath and electroplated at a bath temperature of 45 ° C. and a current density of 2 A / dm 2, and a 40 μm nickel film was laminated on both sides of the SUS304 substrate as a mask base material layer. Next, using a YAG laser processing machine (HPS362B / P, manufactured by Hyper Photon System Co., Ltd.), four basic patterns of 50 × 50 (2500) basic patterns with 50 μm diameter openings were repeated at a pitch of 100 μm. After the opening of the printed pattern was formed, the mask 2 'on the light incident surface side was peeled from the support substrate, and the mask of the present invention was manufactured.
In the mask of the present invention, it swelled around the periphery of the opening, and no adhesion of dross was observed. The wall surface of the opening was also almost smooth. The edge of the opening was very sharp.

Next, the obtained mask was cut into 400 × 480 mm, and bonded to an aluminum frame via a 180 mesh polyester crease to produce a stencil printing plate. The printing plate was printed on a screen printing machine (SP28P-DH, The product was set on Panasonic Factory Solution Co., Ltd., and lead-free cream solder (LF-71S-3, manufactured by Tamura Kaken Co., Ltd.) was printed on the printed wiring board to form solder terminals. The adhesion of the printing plate mask to the surface to be printed was good, and no bleeding of cream solder occurred. Further, the printing plate was excellent in releasability, and the cream solder was easily removed. As a result, the formed solder terminals were almost free from defects such as cracks, disconnections, and chips.

In order to further improve the printing characteristics of the mask, after forming an opening in Example 1, an SUS substrate on which a nickel plating film is laminated at 45 ° C. using an electrolyte solution of phosphoric acid 600 ml / l and sulfuric acid 180 ml / l As an anode, the following conditions were set to one cycle, and 20 cycles of electropolishing were performed.
Current density Energizing time ・ Energizing: 15 A / dm2 15 seconds ・ Reverse energizing: −0.5 A / dm2 3 seconds ・ Non-energizing: 0 A / dm2 20 seconds

  Next, the mask 2 ′ was peeled from the support substrate to produce the mask of the present invention. In the same manner as in Example 1, the mask was bonded to an aluminum frame via a polyester rivet to produce a stencil printing plate, and lead-free cream solder was printed on a printed wiring board to form solder terminals. . The adhesion of the printing plate mask to the surface to be printed was very good, and no blurring of cream solder occurred. On the other hand, the detachability of the printing plate and the detachability of the cream solder were even better than in Example 1. As a result, the formed solder terminals did not have any defects such as cracks, omissions, and chipping, and the variation in the amount of solder was very small.

  The mask for stencil printing of the present invention can be used as a cream solder printing mask when forming solder terminals for mounting electronic components at high density. When cream solder is printed using the mask of the present invention, the cream solder can be printed at high speed and with excellent transferability, and can be used for forming solder bump terminals for high-density mounting of electronic components.

The manufacturing process of the mask for stencil printing of this invention is represented.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Mask base material layer 2 'Mask for stencil printing 3 Mask base material layer 3' (Mask for stencil printing)
4 Laser light 5 Opening

Claims (8)

A mask for stencil printing, in which a mask base material layer is laminated on at least one surface of a support substrate, and a laser beam is irradiated from the mask base material layer side so that a through opening of a printing pattern is at least provided to the mask base material A mask for stencil printing, which is formed in a layer and peeled off from a support substrate. 2. The mask for stencil printing according to claim 1, wherein the mask base material layer is a metal film layer laminated by a metal plating method. The mask for stencil printing according to claim 2, wherein the support substrate is peeled off by electrolytic polishing after forming the through opening. A method for producing a mask for stencil printing, comprising a step of laminating a mask base material layer on a support substrate, irradiating a laser beam from the mask base material layer side so that a through-opening portion of a printing pattern is at least formed on the mask base material layer A method for producing a mask for stencil printing, comprising a step of forming and a step of peeling the support substrate. The method for producing a mask for stencil printing according to claim 4, wherein the step of laminating the mask base material layer is a metal plating method. 6. The method for producing a mask for stencil printing according to claim 5, wherein a step of performing electropolishing is added after the step of forming the through opening. The stencil printing mask according to claim 2 or 3, and the method for producing a stencil printing mask according to claim 5 or 6, wherein the mask base material layer is nickel or a nickel alloy. 8. The stencil mask and the stencil mask manufacturing method according to claim 7, wherein after electropolishing, metal co-plating containing fluororesin fine particles is performed and the support substrate is peeled off.

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