JP2006199027A - Mask and its manufacturing process for stencil printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that printing solder paste (cream solder) by stencil printing and forming solder terminals for mounting of electronic components causes deterioration in snap off of a printing plate and worsening of the solder paste omission as the printing pattern density becomes higher and results in bleeding of solder paste (cream solder) and splits, and in failures such as omissions or chipping of solder terminals. <P>SOLUTION: Metal top coat 2 is formed by plating on the mask substrate 1 and the openings 4 are created by laser beam irradiation. Additionally, the metal coat 2 for masks is formed on the conductive substrate 1 by plating and the openings 4 are created by laser beam irradiation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask for conductive paste printing such as cream solder used when forming conductive terminals for connection for mounting electronic components and semiconductor chips at high density by stencil printing. The mask surface around the opening pushed out by the squeegee has no swell and no foreign matter attached, and has a smooth wall surface and sharp edge opening. The present invention relates to a mask having excellent properties and a method for manufacturing the mask.

With the demand for miniaturization and weight reduction of electronic circuits, such as mobile phones, electronic components are mounted on a printed wiring board with high density, and particularly electronic components are mounted on both sides of the printed wiring board with high density. In this high-density mounting, in order to mount an electronic component on the surface of the printed wiring board, cream solder is printed on the printed wiring board to form a high-definition wiring pattern of the solder terminal, and the electronic component or semiconductor is formed on the solder terminal. A chip is mounted, and electronic components and semiconductor chips are mounted through a solder reflow furnace.
At this time, various printing plates for printing the wiring patterns of the solder terminals without defects and with high definition have been proposed and put into practical use.

For example, a mask is known in which a metal or resin plate is irradiated with laser light to form a wiring pattern-shaped opening. In particular, metal masks using stainless steel plates are widely used.
However, in the above-described stainless steel mask, when the opening is formed with a laser beam, the mask base material is melted, ablated, etc. Protrusions (tear marks) remain in the vicinity of the laser beam emission side, or the mask surface around the opening is raised or so-called dross adheres due to scattering of the base material in the opening. Further, thermal distortion occurs around the opening. As a result, the adhesion between the mask and the substrate is reduced, and the cream solder is smeared. In addition, due to the protrusions and irregularities on the wall surface of the opening, the ability to remove the cream solder is deteriorated and the transferability is lowered. Further, when the mask is thin, it is not easy to handle the mask base material at the time of manufacture, which is very complicated.

As a method for improving the above problem, there has been proposed a method of polishing a mask by sandblasting after forming an opening.
However, this method does not improve the edge of the opening, and some dross can be ground, but it is not sufficient. Moreover, the sandblasting operation was complicated. On the other hand, a method for smoothing the wall surface of the opening by electrolytic polishing instead of sandblasting has also been proposed. JP-A-6-918396

  Even if a mask made by the above-described method is used, the dripping of the edge of the opening, the rising of the mask surface around the opening, and the dross adhesion are not sufficiently eliminated, and the smoothness of the wall of the opening is also eliminated. As the terminal pattern becomes higher in definition, the separation of the printing plate becomes worse and the cream solder does not come off from the plate, resulting in deterioration of transferability of the cream solder. As a result, the transferred cream solder oozes out, and defects such as chipping, cracking, and disconnection occur in the formed solder terminal, which is a major cause of yield reduction. Further, when the printing speed is increased, the aforementioned defects are more likely to occur, and the printing speed cannot be increased.

  Furthermore, in recent years, so-called lead-free solder that does not contain lead has been used for environmental considerations, but the lead-free cream solder is inferior in transferability as compared with conventional cream solder, and has been described above. Defects are likely to occur.

  The object of the present invention is to form a solder terminal for high-density mounting on a printed wiring board or the like, and when the cream solder is printed by stencil printing, it is excellent in stencil release and cream solder detachment. An object of the present invention is to provide a mask for stencil printing which can prevent the occurrence of defects such as solder bleeding, chipping of solder terminals, disconnection and cracking, and increase the printing speed, and a method for manufacturing the mask.

  The inventors of the present invention have studied a method for sharpening the edge of the opening, preventing the swell and dross from occurring around the opening, and smoothing the wall of the opening when forming the opening with a laser. The present invention has been completed.

That is, the present invention
It is a mask for stencil printing, and a protective film layer is laminated on both sides of the mask substrate, and a laser beam is irradiated from above the protective film layer to form a through-opening portion of the printing pattern on the mask substrate, thereby protecting it. A mask for stencil printing formed by peeling a film layer, and the mask for stencil printing described above, wherein the protective film layer is a metal layer or a thermosetting resin layer, and

The mask for stencil printing described above, which is formed by laminating a metal protective film layer on the mask substrate by plating, and the mask for stencil printing described above, wherein the mask substrate is made of stainless steel, and a through opening. Then, the mask for stencil printing described above, wherein the protective film layer is peeled off after electrolytic polishing, and

A method of manufacturing a mask for stencil printing, a process of laminating protective film layers on both sides of a mask substrate, and irradiating a laser beam on the protective film layer to form a through opening portion of a printing pattern on the mask substrate A process for removing the protective film layer from the mask substrate, a method for producing a mask for stencil printing, and the protective film layer as described above, wherein the protective film layer is a metal layer or a thermosetting resin layer. Mask manufacturing method, and

In the step of laminating the protective film layer on the mask substrate, the method for producing a mask for stencil printing as described above by a metal plating method, and the method for producing a mask for stencil printing as described above, wherein the mask substrate is made of stainless steel, And the manufacturing method of the mask for stencil printing of the said description formed by adding an electropolishing process after the process of forming a through-opening part.

  The mask for stencil printing of the present invention has a sharp edge and a smooth opening on the wall surface, and there is no swell or adhesion of dross around the opening. Therefore, when the cream solder is printed, the cream solder does not bleed, and the cream solder is easily removed and the plate is peeled off. Defects such as omission and chipping can be prevented, cream solder bleeding does not occur, and the productivity and yield of the solder terminal forming process are greatly improved. Even if the mask substrate is thin, the mask substrate can be easily handled in the manufacturing process.

Hereinafter, the mask for stencil printing of this invention and its manufacturing method are demonstrated in detail using figures.
FIG. 1 shows an example of the manufacturing process of the mask of the present invention. FIG. 1A shows a cross section in which a protective film layer 2 is formed on a mask substrate 1. Examples of the mask substrate include various metals, resins, and laminates of metals and resins that are easy to process with laser light and have excellent properties as printing plates. Specifically, nickel, nickel alloys, copper, copper Alloys, metals such as iron, aluminum, and stainless steel, thermosetting resins such as polyimide resins, thermoplastic resins with high strength and excellent heat resistance such as PPS, PES, PEEK, and liquid crystal resins, and lamination of the above metals and resins Such as the body. The thickness of the mask substrate is usually about 5 to 300 μm, although it depends on the specifications of the solder terminals to be formed.

As a protective film layer to be laminated on the mask substrate, the mask substrate can be reinforced when manufacturing a thin film mask, it is easy to peel off from the mask substrate, and adversely affects when forming an opening with a laser beam. Is not particularly limited, and various metal layers and resin layers can be mentioned. In particular, from the viewpoint of thermal characteristics, a metal layer containing one or more metals selected from nickel, iron, and copper, and a thermosetting resin layer such as polyimide are preferable. In order to laminate the above protective film layer on the mask substrate, a method of laminating the thin film of the protective film to the mask substrate by an adhesive or heat fusion, and laminating the above protective film metal by plating, sputtering, vapor deposition or the like. The method, the method of apply | coating and heat-curing the precursor of a polyimide resin, the method of melt-laminating the above-mentioned thermoplastic resin, etc. are mentioned.

Furthermore, as the protective film layer of the present invention, no gap is generated between the mask substrate, moderate adhesion and moderate peelability, and control and management of the thickness of the protective film. A layer in which the metal is laminated by a plating method is particularly preferable from the viewpoint of easily performing the process. When the protective film layer is a plating method, the protective film layer is formed by an ordinary known electroplating method. In this case, the substrate for mask is preferably a conductive substrate, and examples thereof include the metals described above. In the case of a resin such as polyimide resin, PPS, PES, PEEK, or liquid crystal resin, a conductive metal is sputtered, electroless plated, or a thin film is laminated to make the resin surface conductive. When laminating by a plating method, stainless steel is most preferable as a mask substrate, and nickel or a nickel alloy is most preferable as a protective film layer from the viewpoint of appropriate adhesion and peelability with a protective film layer, mechanical strength, and economy. .

The role of the protective film layer is to prevent swell and dross adhesion around the opening, and ease of handling of the thin film mask substrate. The film thickness of the protective film layer is the thickness of the mask substrate used. In addition, it may be determined in consideration of the releasability from the mask substrate, etc., preferably 10 to 200 μm, more preferably 20 to 150 μm. When the protective film layer is laminated by a metal plating method, if the protective film layer is thick, plating takes a long time. In this case, a thin metal protective film layer is preferably laminated by a plating method, and a metal foil or a resin film is laminated thereon. Moreover, when the metal protective film layer is thick, it is not preferable because the wall surface of the opening is burned or the generation of burrs is increased. From these points, it is more preferable to laminate a thin metal protective film layer by a plating method and to laminate a resin film thereon. When the protective film layer is made of metal and resin, the metal protective film layer preferably has a thickness of 5 to 40 μm, and the resin protective film layer preferably has a thickness of 15 to 140 μm. The protective film layer of the resin is laminated by laminating a resin film or applying a resin liquid.

There is no restriction | limiting in particular as resin used as a protective film layer, A normal thermoplastic resin and a thermosetting resin are mentioned. Specific examples of the resin include polyethylene resin, polypropylene resin, polyester resin, polyamide resin, acrylic resin, polycarbonate resin, polystyrene resin, PPS, PES, PEEK, polyimide resin, and epoxy resin. Furthermore, a photosensitive resin such as a dry film resist is preferable because it can improve releasability by irradiating light when it is peeled off. The type, configuration, and thickness of the protective film layer on both sides of the mask substrate may be the same or different, but the same film configuration and film thickness are preferred from the viewpoint of curl of the mask substrate.

Next, as shown in FIG. 1B, a laser beam 3 is irradiated from above the protective film layer to form a through-opening 4 having a desired print pattern on the mask substrate. In order to form the opening, the converged laser beam is irradiated while scanning along the outer periphery of the opening, and the outer periphery is cut. Examples of the laser beam to be irradiated include a solid laser, a gas laser, and a semiconductor laser. Specifically, a YAG laser is preferable, and a fundamental wave, a harmonic wave, and a mixed wave of the YAG laser can be used.
When forming the through opening, the protective film layer on the laser beam incident side is naturally formed with the through opening, but the protective film layer on the laser beam emission surface side does not necessarily pass through.

  When forming the opening with laser light, there are a method of holding the mask substrate on which the protective film layer is laminated, a method of floating in the air to fix the peripheral portion of the mask substrate, and a method of closely mounting on the pedestal. In view of the uniformity of the shape of the opening to be formed, a method of closely mounting on the pedestal is preferable. When placed in close contact with the pedestal, when the opening is provided through the protective film layer on the laser light emission side, the cut waste of the cut opening is scattered on the surface of the protective film layer on the upper surface of the mask substrate, This is not preferable because it obstructs the formation of the opening. In order to prevent the scattering of the cutting waste, an opening is formed partway through the protective film layer on the lower surface (laser beam emission side).

  Next, as shown in FIG. 1C, when both protective film layers are peeled from the mask substrate, the mask 1 'of the present invention is completed. The protective film layer can be removed 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 protective layer film or the mask substrate. For example, when stainless steel is used as the mask substrate and copper is used as the protective film layer, an alkaline etching solution may be used, and when nickel is used as the protective film layer, a strong alkaline solution may be used.

In the present invention, it is more preferable to perform electropolishing treatment on the wall surface of the opening of the mask because the printing characteristics are further improved. Further, after electrolytic polishing, eutectoid plating containing fluororesin fine particles may be performed. The above-described electropolishing treatment may be performed after the protective film layer is peeled off, but the protective film layer is peeled from the viewpoint of preventing dripping of the edge of the mask opening, change in mask thickness, damage to the mask surface, and the like. It is preferable to perform electropolishing before performing. However, as described above, when the opening does not penetrate the protective film layer on the laser light emission side, the inflow of the electrolytic polishing liquid to the wall surface of the opening is hindered, and as a result, the electropolishing is not sufficiently performed. Absent. Also in this case, the protective film layer has a laminated structure of metal and resin, and the opening is processed near the interface between the metal protective film and the resin protective film, or through the protective film layer of the metal, to the middle of the resin protective film layer, It is preferable to peel the resin protective film layer and perform electropolishing before performing electropolishing.

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

A SUS304 substrate having a thickness of 550 × 650 mm and a thickness of 60 μm is placed in a nickel sulfamate plating bath, and electroplating is performed at a bath temperature of 45 ° C. and a current density of 2 A / dm 2. Was deposited. 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. A printed pattern opening was formed.

In the state in which the nickel protective film layer immediately after forming the opening is not peeled off, it was swelled around the opening peripheral part of the protective film surface, and adhesion of dross was observed, but after the nickel protective film layer was peeled off, In the mask 1 ′, no swell occurred in the periphery of the opening, and no adhesion of dross was observed. Moreover, the edge of the opening was very sharp and the wall surface of the opening was substantially smooth.

Next, the obtained mask was cut into 400 × 480 mm, and bonded to an aluminum frame through a 180 mesh polyester crease to produce a stencil printing plate, and the stencil printing plate was printed on a screen printing machine (SP28P-DH). , Manufactured by Panasonic Factory Solution Co., Ltd.) and lead-free cream solder (LF-71S-3, manufactured by Tamura Kaken Co., Ltd.) was printed on the printed circuit board to form solder terminals. The adhesion of the printing plate mask to the surface to be printed was good, and no blurring of cream solder occurred. On the other hand, the printing plate was excellent in the release property, and the cream solder was easily removed. As a result, the formed solder terminals were almost free from defects such as cracks, omissions, and chipping, and the variation in the amount of solder was small.

In order to further improve the printing characteristics of the mask, after forming the opening of Example 1, an electrolytic solution consisting of 600 ml / l phosphoric acid and 180 ml / l sulfuric acid was used at 45 ° C. without peeling off the nickel protective film layer. Then, using the mask as an anode, the following conditions were set to 1 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, after performing an electropolishing treatment, the protective film layer was peeled off to produce a 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.

  A SUS304 substrate having a thickness of 550 × 650 mm and a thickness of 20 μm is placed in a nickel sulfamate plating bath, and electroplating is performed at a bath temperature of 45 ° C. and a current density of 2 A / dm 2. Was deposited. Further, a negative dry film of 50 μm was laminated on both sides as a resin protective film on the nickel film. Next, using a YAG laser processing machine (Model 5300 esi), openings of a printed pattern are formed by chamfering four basic patterns consisting of 50 × 50 (2500) openings with a diameter of 40 μm and openings with a diameter of 40 μm. did. However, the opening was formed partway through the dry film film layer through the nickel film layer of the protective film layer made of the nickel film and dry film film on the laser light emission side.

  Next, the dry film on both sides was irradiated with ultraviolet rays to cure the film, and then immersed in a stripping solution and peeled off. The opening of the mask substrate having the nickel protective film laminated on both sides completely penetrated from the upper surface to the lower surface. The same electrolytic solution as in Example 2 was used for the metal mask substrate, and a current of 15 A / dm 2 was applied for 90 seconds to perform an electropolishing treatment. Finally, the nickel protective film on both sides was peeled off to produce the mask of the present invention. There was no dross on the surface of the mask, and there was no rise around the opening. Further, the wall surface of the opening of the mask was completely free of burrs, and the laser irradiation traces (fine ridges) disappeared and were very smooth.

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 stencil printing mask of the present invention can be used as a cream solder printing mask in the formation of solder terminals when electronic components are mounted. When cream solder is printed using the mask of the present invention, the cream solder can be printed at high speed, high density, and excellent transferability, and can be used to form solder terminals for high density mounting of electronic components. Available.

1 represents an embodiment of a process for producing a mask for stencil printing according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mask substrate 1 'Mask for stencil printing 2 Protective film layer 3 Laser beam 4 Opening

Claims (10)

A mask for stencil printing, in which a protective film layer is laminated on both sides of the mask substrate, and a laser beam is irradiated on the protective film layer to form a through-opening portion of the printing pattern on the mask substrate. A mask for stencil printing, comprising a protective film layer peeled off from a substrate. 2. The mask for stencil printing according to claim 1, wherein the protective film layer is a metal layer or a thermosetting resin layer. 2. A mask for stencil printing according to claim 1, wherein a protective film layer of metal is laminated on the mask substrate by plating. 4. A mask for stencil printing according to claim 3, wherein the mask substrate is made of stainless steel. The mask for stencil printing according to claim 4, wherein the protective film layer is peeled off after electrolytic polishing is performed after the through opening is formed. A method of manufacturing a mask for stencil printing, a process of laminating protective film layers on both sides of a mask substrate, and irradiating a laser beam on the protective film layer to form a through opening portion of a printing pattern on the mask substrate A method for producing a mask for stencil printing, comprising: a step of removing a protective film layer from a mask substrate. The method for producing a mask for stencil printing according to claim 6, wherein the protective film layer is a metal layer or a thermosetting resin layer. 7. The method for producing a mask for stencil printing according to claim 6, wherein the step of laminating the protective film layer on the mask substrate comprises a metal plating method. 9. The method for producing a mask for stencil printing according to claim 8, wherein the mask substrate is made of stainless steel. The method for producing a mask for stencil printing according to claim 9, wherein an electropolishing step is added after the step of forming the through opening.