JP2005144973A - Perforated printing mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perforated printing mask for forming high density, high precisely forming a solder terminal for high density mounting of an electronic part to a wafer, a print wiring substrate or the like, a fine and a smooth opening part on a wall surface is in a high density provided, a through property or a plate separating property from the opening part of the cream solder is excellent, though cream solder of lead free is printed at a high speed, the cream solder is not bled generated solder terminals are free from generation of defects such as chip, extraction, crack or the like and has an excellent printing durability. <P>SOLUTION: An aromatic polyimide resin opened with ultraviolet laser or a mask of the metallized aromatic polyimide resin opened with the ultraviolet laser is further filmed by a diamond like carbon coating. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a mask for stencil printing used for printing cream solder or the like used for forming connection terminals for mounting electronic components and semiconductor chips at high density.

From the demand for miniaturization and weight reduction of electronic circuits, such as mobile phones and digital cameras, etc., high integration of LSI circuits, ultra miniaturization of electronic components, high-density mounting of electronic components on printed circuit boards, especially on both sides, etc. Is widely practiced. In this high integration of LSI circuits and high density mounting of electronic components on a printed wiring board, in order to mount electronic components on the LSI or printed wiring board surface, cream solder is printed on the wafer or printed wiring board, It is widely practiced to form a high-definition and high-density wiring pattern of solder terminals, mount electronic components and semiconductor chips on the solder terminals, and mount the electronic components and semiconductor chips through a solder reflow furnace.
At this time, various stencil printing plates have been proposed and put into practical use for printing the wiring patterns of solder terminals without defects and with high definition and high density.

  For example, metal masks with resin pattern openings, resin masks, metal-resin laminated masks, etc., have high-definition / high-density printability, durability of printing accuracy, ease of making printing plates, etc. Widely used. As a method for forming an opening of a wiring pattern in the stencil printing mask described above (mask manufacturing method), an etching method or laser beam produced by etching a metal or resin on a metal or resin film using a photolithography method. A laser method that directly irradiates a metal or resin film in the form of an opening pattern to make an opening hole, and another method for manufacturing a metal mask is to form a wiring pattern with a resist film on the surface of a conductive metal and manufacture it by electroforming There are additive methods, etc., which are used properly from the viewpoints of mounting density and economical efficiency of electronic components.

  When cream solder is printed on a wafer or printed wiring board using a mask for stencil printing made as described above to form solder terminals for mounting electronic components, the pattern becomes highly precise and dense. The longer the cream solder is removed from the plate, the lower the transferability of the cream solder and the worse the plate release of the printing plate. 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. In particular, when the printing speed is increased, the above-described defects are more likely to occur, and the printing speed cannot be increased. In addition, due to the creep characteristics of the mask material, deformation and misalignment of the opening occurs due to squeegee stress during printing, so that cream solder oozes out and the solder terminal position accuracy decreases, so the printing durability of the mask Decreased.

  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.

In order to improve the printing problem of the cream solder described above,
Japanese Laid-Open Patent Publication No. 2002-67267 proposes a stencil printing mask in which a diamond-like carbon film treatment is performed on a stencil printing mask provided with an opening. Japanese Patent No. 3279761 proposes a printing mask made of plastic in which an opening for cream solder printing is formed, in which the opening is formed by ablation with a short wavelength laser such as an excimer laser. .

  However, since the diamond-like carbon coating is smooth and the coefficient of friction is small, the mask opening of the above-mentioned Patent Document 1 is not detached from the opening of the cream solder as compared with the case where the coating treatment is not performed. However, when the opening is formed by electric discharge machining, the wall surface of the opening is not smooth, and the opening cannot be formed with high density and high definition. On the other hand, in the mask of Patent Document 2, a fine opening can be formed in a predetermined shape, but due to the problem of the creep characteristics of the mask material, the mask opening is deformed during printing, or the positional accuracy is lowered. . Accordingly, none of the stencil masks described above is necessarily sufficient for high-density and high-definition printing, and further improvements are required.

  An object of the present invention is a stencil mask for forming high-density, high-definition solder terminals for high-density mounting of electronic components on a wafer, a printed wiring board, etc. As a result, even if cream solder is printed, the cream solder can be easily removed from the openings and the plate can be removed, even if lead-free cream solder is printed at high speed. An object of the present invention is to provide a mask for stencil printing that does not bleed, does not cause defects such as chipping, detachment, and cracking in the formed solder terminal and has excellent printing durability.

  In order to print cream solder with high definition and high density, the present inventors have intensively studied the mask material for stencil printing, the processing method of the opening, the surface treatment method of the mask, etc. completed.

That is, the present invention
A stencil mask having a printed pattern opening on a substrate, the substrate having an aromatic polyimide resin layer and having a diamond-like carbon film on a surface thereof The mask for stencil printing, the opening of the aromatic polyimide resin layer is formed by irradiating ultraviolet laser light, and the mask for stencil printing as described above, wherein the substrate also has a metal layer, The stencil mask described above, and the stencil mask as described above, wherein the metal layer is made of copper, chrome, nickel, an alloy of these metals, or stainless steel, and the aromatic polyimide resin surface. A mask for stencil printing as described above, which has a diamond-like carbon film, and a diamond layer on the surface having a metal layer. The mask for stencil printing described in the above, characterized in that it has a carbon film, and the mask for stencil printing described in the above, which has a diamond-like carbon film on both sides of the substrate, and a plurality of chamfers In the mask of the printing plate of the mold, the repeated basic pattern part including the printing opening area constituting the chamfer of the printing plate is not provided with a metal layer, and the metal is formed only in the area other than the repeated basic pattern part constituting the chamfer. A mask for stencil printing as described above, wherein a layer is provided.

  Since the mask for stencil printing of the present invention has excellent creep characteristics, the openings do not deform or shift due to stress during printing, and have high-definition and smooth-walled openings with high density. Also, the cream solder can be easily removed from the opening and the release of the plate, so even if the printing speed is increased, the cream solder does not bleed, and the solder terminal cracks and falls due to poor transfer of the cream solder. Further, the occurrence of defects such as chipping can be prevented, and the productivity and yield of the solder terminal forming process are greatly improved.

Hereinafter, the mask for stencil printing of the present invention will be described in detail.
Examples of the mask substrate for stencil printing include a mesh screen, a plastic film, a metal plate, a laminated plate of plastic and metal, etc., but the mask substrate in the present invention is easy to process a high-definition opening, Aromatic polyimide resin is preferable from the viewpoint of the ability of the cream solder to be removed from the opening, strength, and the like, and the thickness is about 40 to 250 μm although it depends on the amount of cream solder printed.

  The opening of the mask for stencil printing can be formed by various methods such as chemical etching and machining, but in the present invention, it is possible to easily form a high-definition opening having a smooth opening wall surface. Is preferably formed by irradiating an aromatic polyimide resin substrate with laser light, particularly ultraviolet laser light. Examples of the ultraviolet laser beam include an excimer laser, a third harmonic of a YAG laser, and a semiconductor laser.

  The shape of the opening of the mask for stencil printing of the present invention is not particularly limited, for example, a circle, an oval, an ellipse, a square such as a square, a rectangle, a rhombus, a trapezoid, a polygon such as a hexagon and an octagon, Other examples include an irregular shape such as a saddle shape and a dumbbell shape, and the size is 50 to 500 μm for the maximum opening of various shapes described above for high-density mounting.

In the mask for stencil printing of the present invention, a diamond-like carbon (hereinafter abbreviated as DLC) film is further provided on the aromatic polyimide resin substrate having the opening.
Various methods for forming a DLC film are already known and put into practical use. For example, methane, propane, ethylene, ethyl alcohol, benzene, naphthalene, or the like is used as a carbon source, and the film is formed by thermal CVD, plasma CVD, RF plasma CVD, plasma spraying, ionization using a hot filament, or the like. can do. Usually, when the DLC film is formed, the substrate temperature rises, and the degree of the rise varies depending on the film forming method. In the present invention, since an aromatic polyimide resin is used as a substrate, a film forming method and conditions suitable for the heat resistance of the aromatic polyimide resin used may be used. The film thickness of the DLC film is preferably 10 nm or more, and more preferably 20 nm or more, in order to exhibit the effects of the present invention. On the other hand, the upper limit of the film thickness of the DLC film is about 5 μm from the viewpoint of the temperature rise of the substrate and economic efficiency, more preferably 2 μm or less, and most preferably 900 nm or less. The DLC film may be provided on one side or both sides of the substrate. Further, when forming the DLC film, the surface of the substrate to be formed may be treated by a known chemical or mechanical method.

  Furthermore, in the mask for stencil printing of the present invention, in order to further improve the creep characteristics and wear resistance of the mask, the substrate is preferably composed of an aromatic polyimide resin layer and a metal layer. The metal is preferably a conductive metal such as copper, chromium, nickel, an alloy of these metals, or stainless steel. In order to laminate a metal layer on an aromatic polyimide resin, there are a method of laminating the above-described metal thin film, a method of forming a film by sputtering or vapor deposition, and a method of laminating by electroless plating or electroplating. In this case, the metal layer may be a single layer or two or more layers. The metal layer may be laminated only on one side of the aromatic polyimide resin layer or on both sides.

  In order to bond the metal thin film to the aromatic polyimide resin, the metal thin film can be bonded using a polyimide or epoxy adhesive, or when the aromatic polyimide resin is thermoplastic, it can be bonded by thermal fusion. At that time, the openings may be bonded to each other after being provided, or the openings may be formed after the bonding. The method for forming the opening in the aromatic polyimide resin is based on the ultraviolet laser as described above, but the method for providing the opening in the metal layer is not particularly limited, and a known chemical etching method, laser method, or the like can be used.

  On the other hand, in order to laminate a metal layer by electroplating, a thin film of conductive metal such as copper, nickel, silver, or chromium is formed on an aromatic polyimide resin by electroless plating or sputtering or vapor deposition. A film can be formed by electroplating nickel or an alloy of these metals by a known method.

In the case of a substrate in which a metal layer is laminated by electroplating as described above, there are various methods for forming the opening.
For example, after forming an opening in an aromatic polyimide resin with an ultraviolet laser, when forming a conductive metal thin film, the portion corresponding to the opening is covered with a mask, or the entire surface is electrically conductive After the metal thin film is formed, the portion of the conductive metal thin film corresponding to the opening is removed by chemical etching or the like, or the portion corresponding to the opening is covered with a resist film, and then electroplating is performed. An opening can be easily formed in the metal layer.

As another method of forming the opening, after forming a conductive metal thin film on the aromatic polyimide resin, the opening is simultaneously formed on both the aromatic polyimide resin layer and the conductive metal thin film layer with an ultraviolet laser. A method of performing metal plating after forming,
As another method, an opening is first formed on a substrate in which a metal layer is laminated on an aromatic polyimide resin by a chemical etching method, and then an opening is formed on the aromatic polyimide resin layer by an ultraviolet laser. Etc.

  As described above, the metal layer in the mask for stencil printing of the present invention plays a role of improving the creep characteristics and wear resistance of the mask and preventing the deformation and misalignment of the opening due to stress during printing. The creep characteristics of the mask can be improved by the DLC film. However, in order to obtain the desired creep characteristics with the DLC film, it is necessary to increase the film thickness of the DLC film. Therefore, in the present invention, it is preferable to separately laminate a metal layer. The thickness of the metal layer is about 40% or less of the total thickness of the mask, preferably 5 to 50 μm, more preferably 10 to 40 μm.

  On the other hand, the metal layer does not necessarily give good results for the printability of cream solder. That is, the wall surface of the opening of the metal layer is difficult to be smoothed by any method, and the solder solder is inferior in terms of wettability due to cream solder. , Omissions, cracks, etc. occur, or cream solder oozes out. Therefore, for example, in a plurality of chamfering type masks for printing, a repetitive basic pattern portion including a printing opening region constituting the chamfering of the mask is not provided with a metal layer, but a repetitive basic pattern portion constituting chamfering It is preferable to provide a metal layer only in the region.

  In the mask for stencil printing of the present invention, when the substrate is composed of an aromatic polyimide resin layer and a metal layer, the DLC film may be formed before the metal layer is laminated or after the metal layer is laminated. However, it is preferable to form the DLC film after forming the opening because the inner wall of the opening is covered with the DLC film. Of course, the DLC film may be formed on the metal layer, or conversely, the metal layer may be laminated on the DLC film. In the present invention, it is preferable that the printed material side of the mask is an aromatic polyimide resin layer and the squeegee side is a DLC film layer on the surface. At this time, the metal layer is preferably provided between the aromatic polyimide resin and the DLC film.

  The mask for stencil printing of the present invention may be provided with a mark (opening) or the like for positioning when printing the mask or printing.

  The mask for stencil printing of the present invention is directly attached to a metal frame made of aluminum, stainless steel, copper or the like with an adhesive, or is attached through a ridge to form a screen printing plate. A specific method of attaching the mask through the heel is to attach the heel to the metal frame with an adhesive, and to place the outer periphery of the mask for printing of the present invention smaller than the size of the metal frame at the center of the heel. Affix to the heel using an adhesive. Next, cut off the inner wrinkles other than the bonded part. In this manner, a printing plate is completed in which the outer peripheral portion of the mask is attached to the metal frame through the ridge.

  The printing plate created as described above is mounted on a screen printing machine, set on a printed wiring board, put cream solder on the plate, move the squeegee and fill the cream solder into the opening of the mask, When the printing plate is separated from the printed wiring board, the cream solder filled in the opening is transferred onto the printed wiring board to form solder terminals. The shape of the formed solder terminal is usually about 50 to 500 μm in diameter.

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

  A UV-YAG laser processing machine having a beam diameter of 25 μm with a wavelength of 355 nm after a copper film is deposited by sputtering on a 125 μm thick aromatic polyimide resin film, trade name Kapton 500V (manufactured by Toray DuPont Co., Ltd.) Set a square of 30 mm x 30 mm as a repetitive basic pattern portion constituting a chamfer, and arrange a total of 15 basic patterns of 3 x 5 with a repetitive pitch of 43 mm, and within all the basic pattern portions, a beam Irradiate laser light from the side of the aromatic polyimide resin in the manner of one-stroke writing in consideration of the diameter, and make a circle with a diameter of 100 μm and make 68 (total 4624) penetrating processes at a pitch of 150 μm each in length and width. Formed.

  On the copper surface side of the substrate in which the opening is formed, a DLC film is formed to a thickness of 500 nm by using an ionized DLC film forming apparatus using a hot filament, and is cut so that the outer shape becomes 400 mm × 480 mm. The mask for was made.

  After pasting the portion 1 cm inside from the outer periphery of the mask created as described above to an aluminum frame having an outer shape of 550 × 650 mm with a 180-mesh polyester wrinkle stretched, using an epoxy-based adhesive, A screen printing plate was prepared by cutting off the wrinkles 1 cm inside from the outer periphery of the printing mask.

  The printing plate made as described above is mounted on a screen printing machine (SP28P-DH, manufactured by Panasonic Factory Solution Co., Ltd.), and lead-free cream solder (LF-71S-3, Tamra Chemical Research ( Manufactured by Co., Ltd.) and dried to form solder terminals having a diameter of approximately 100 μm. The formed solder terminals were observed, but no defects such as cream solder bleeding, solder terminal cracks, omissions, and chipping occurred. Further, even if cream solder was repeatedly printed 5000 times, no abnormality occurred in the formed solder terminals.

[Comparative Example 1]
A mask and a printing plate were produced in exactly the same manner as in Example 1 except that no DLC film was formed, and printing evaluation of cream solder was performed. Chipping due to poor transferability of cream solder occurred in about half of the formed solder terminals. Further, when cream solder was repeatedly printed, bleeding of cream solder, which seems to be due to the deformation of the opening, occurred about every 100 times. Further, a positional deviation exceeding the allowable range occurred at the position of the opening from the 200th time.

    Using a nickel sulfamate plating bath on a copper of the trade name Metaroyal manufactured by Toyo Metallizing Co., Ltd., in which an aromatic polyimide film having a thickness of 50 μm and copper of 10 μm are laminated on one side of the trade name Kapton, 2A / A nickel film having a thickness of 15 μm was laminated by electroplating at dm 2 and a bath temperature of 45 ° C. The planar size of this material was 500 × 500 mm.

  A dry film (trade name 371Y of Nichigo Morton Co., Ltd.) with a thickness of 25 μm was bonded to the nickel surface of this material using a laminator. Next, using a 30mm x 30mm square with 5mm R at the four corners as the basic pattern part that constitutes the chamfer, this pattern is arranged in a total of 15 patterns of 3x5 with a repeat pitch of 43mm. The exposed part was made into the part which does not permeate | transmit an ultraviolet-ray, and the film mask which made the other part transparent was piled up, and ultraviolet exposure was performed.

  After completion of exposure, development is performed, and after removing the dry film corresponding to the repetitive basic pattern portion constituting the chamfer, etching is performed in a ferric chloride solution, and the repetitive basic pattern portion constituting the chamfer is formed. The corresponding portions of the nickel and copper layers were removed, and finally the dry film was peeled off.

  Using the UV-YAG laser processing machine used in Example 1, the above materials are set so that the laser can be irradiated from the aromatic polyimide resin surface side, and the center of the repeated basic pattern constituting the chamfer and the basic pattern While making the center of the circumscribed quadrangle of the inner opening group coincide with each other, the aromatic polyimide material is irradiated with a laser beam in the manner of one stroke in consideration of the beam diameter, and the diameter is in all the basic pattern portions. A 100 μm circle was subjected to 68 penetrating processes in the vertical and horizontal directions at a pitch of 150 μm to form 4624 openings. Next, it cut | disconnected so that a magnitude | size might become 400x480mm, and manufactured the mask.

  A DLC film having a thickness of 500 nm was formed on the nickel surface side of the mask thus prepared in the same manner as in Example 1 to produce a mask for stencil printing according to the present invention.

  Next, using the above-described mask of the present invention, a screen printing plate was produced in the same manner as in Example 1 so that the DLC film surface side was a squeegee surface, and printing evaluation of cream solder was performed. As a result of printing, no defects such as bleeding, chipping, cracking and omission occurred in all the solder terminals formed. In addition, no abnormality occurred even when printing was repeated 7000 times.

[Comparative Example 2]
In Example 2, a mask and a screen printing plate were produced by the same method as in Example 2 except that no DLC film was formed, and cream solder was printed. The formed solder terminals all had chipping and omission defects that seem to be due to poor transferability. Further, when cream solder was repeatedly printed, bleeding of cream solder, which seems to be due to deformation of the opening, occurred from around 1200 times.

  A mask for stencil printing in the same manner as in Example 1 except that an aromatic polyimide film having a thickness of 75 μm, a trade name of Kapton 300V (manufactured by Toray DuPont Co., Ltd.) and a DLC film thickness of 900 nm are used. A screen printing plate was produced and the printing evaluation of cream solder was performed. The evaluation results were substantially the same as in Example 1.

  A 100 nm copper film was formed by sputtering on a 75 μm thick aromatic polyimide film, trade name Kapton 300V (manufactured by Toray DuPont). At this time, a shape of 30 mm × 30 mm square with 5 mm R at the four corners is used as a repeated basic pattern constituting the chamfer, and the basic pattern is a portion in which a total of 15 pieces of 3 × 5 are arranged at a repeated pitch of 43 mm. The copper was not deposited on the portion of the repeated basic pattern constituting the chamfer.

  Nickel electroplating was performed on the processed material under the same conditions as in Example 2, and a 15 μm nickel layer was laminated in a region other than the portion corresponding to the repeated basic pattern portion constituting chamfering.

  Next, in all the repetitive basic pattern portions (the portions where the aromatic polyimide resin surface is exposed), using the same UV-YAG laser processing machine as in Example 1, a circle with a diameter of 50 μm is vertically and horizontally at a pitch of 100 μm. Each of 68 penetrating processes was performed to form 4624 openings. At this time, control was performed so that the center of the repeated basic pattern coincided with the center of the circumscribed quadrangle of the opening group in the basic pattern. Next, it cut | disconnected to the magnitude | size of 400x480mm, and created the mask.

  A DLC film having a thickness of 300 nm was formed on the nickel surface side of the mask prepared in the same manner as in Example 1 to produce a mask for stencil printing according to the present invention. A screen printing plate was prepared by the same method as in Example 2 using the mask, and the printing evaluation of cream solder was performed. The result was substantially the same as in Example 2, and the formed solder terminal had no defects. Moreover, no abnormality occurred even when printing was repeated.

  The surface of a SUS304 substrate having a plate thickness of 0.2 mm and 550 × 650 mm was leveled (buffed), and a dry film resist (FP240, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was laminated. Next, as a solder terminal pattern for mounting electronic components, a glass mask having a chamfered pattern of four basic patterns of 2500 (50 × 50) pieces with a pitch of 130 μm and a circle that transmits ultraviolet light having a diameter of 70 μm is used. Then, after exposure with a mirror reflection type parallel light exposure machine (EXM-1201, manufactured by Oak Co., Ltd.) and aging for 15 minutes, development with 1.0% sodium carbonate aqueous solution, washing with water, and 70 μm on a SUS304 substrate. A solder terminal pattern group of a circular dry film resist film was formed (excluding the portion corresponding to the solder terminal, the surface of the SUS304 substrate was exposed).

  The SUS304 substrate was placed in a nickel sulfamate plating bath, and a nickel film having a thickness of 20 μm was formed on the substrate at 2 A / dm 2 and a bath temperature of 45 ° C. The surface of the formed nickel film is buffed to remove the resist film and the like protruding from the nickel film surface, and then a 75 μm thick aromatic polyimide resin film (Kapton 300V, manufactured by Toray DuPont Co., Ltd.) is used. Bonded with an epoxy adhesive. Next, the board | substrate which peeled from the SUS304 board | substrate and laminated | stacked the aromatic polyimide resin film on the nickel plate which has an opening part was created.

  With the UV-YAG laser processing machine used in Example 1, the substrate was irradiated with laser light from the aromatic polyimide surface side to the opening provided on the nickel surface side, and through-processing was performed. Then, an opening was formed, and a mask was manufactured by cutting into a size of 400 mm × 480 mm.

  A DLC film having a thickness of 200 nm was formed on the nickel surface side of the mask prepared in the same manner as in Example 1 to produce a mask for stencil printing according to the present invention. A screen printing plate was prepared by the same method as in Example 2 using the mask, and the printing evaluation of cream solder was performed. The result was substantially the same as in Example 2, and the formed solder terminal had no defects. Moreover, no abnormality occurred even when printing was repeated.

The mask for stencil printing of the present invention can be printed with cream solder and with excellent transferability even when high-definition patterns are printed at high density and at high speed. Can be used for creation.

Claims (8)

A stencil mask having a printed pattern opening on a substrate, the substrate having an aromatic polyimide resin layer and having a diamond-like carbon film on a surface thereof Mask. 2. The stencil printing mask according to claim 1, wherein the opening of the aromatic polyimide resin layer is provided by irradiating with ultraviolet laser light. The mask for stencil printing according to claim 1 or 2, wherein the substrate also has a metal layer. 4. The mask for stencil printing according to claim 3, wherein the metal layer is made of copper, chrome, nickel, an alloy of these metals, or stainless steel. The mask for stencil printing according to any one of claims 1 to 4, further comprising a diamond-like carbon film on the surface of the aromatic polyimide resin. The mask for stencil printing according to any one of claims 3 to 4, further comprising a diamond-like carbon film on the surface having the metal layer. The mask for stencil printing according to any one of claims 1 to 4, further comprising a diamond-like carbon film on both surfaces of the substrate. In a mask for multi-chamfer type stencil printing, the repeated basic pattern part including the printing opening area constituting the chamfer of the mask is not provided with a metal layer, and only the area part other than the repeated basic pattern part constituting the chamfering is provided. A mask for stencil printing according to any one of claims 3 to 7, wherein a metal layer is provided on the mask.