JP2005305725A - Metal mask and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a defect such as a crack, an omission or a chip of a solder terminal due to a fault of bleeding or snap-off of cream solder or a fault of slip-off properties of the cream solder from an opening part, and to make the solder terminal free from the defect due to repeated printing, even when a high-precision pattern is printed with a high density and at a high speed on the occasion when the solder terminal for mounting electronic components in a high density is formed of the cream solder by screen printing. <P>SOLUTION: Intermittent electropolishing is applied to an original sheet of a metal mask wherein the opening part for transfer of an electroconductive paste is formed, so as to form the metal mask. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask for printing a conductive paste such as cream solder used when forming solder terminals for connection for mounting electronic components and semiconductor chips at high density.

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, a conductive paste such as cream solder is printed on the printed wiring board to form a high-definition wiring pattern of the solder terminal, and the solder terminal The electronic parts and semiconductor chips are mounted on the electronic parts and the electronic parts 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, metal masks with resin pattern openings, resin masks, metal-resin laminated masks, etc., for high-definition printability, durability of printing accuracy, ease of making printing plates, etc. Widely used. As a method of forming a wiring pattern-shaped opening in a mask for printing (mask manufacturing method), an etching method or pattern formed by etching a metal or resin on a metal or resin film or plate using a photolithographic method A laser method that directly irradiates a metal or resin film or plate with a laser beam to open a 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. In particular, a metal mask made by a laser method or an additive method can cope with a high-definition pattern, and its use is expanding for high-density mounting.

  When cream solder is printed on a printed wiring board using a high-definition printing mask made by the method as described above, and solder terminals for mounting electronic components are formed, the higher the pattern becomes, the higher the pattern becomes. , The release of the cream solder from the plate becomes worse, the separation of the printing plate becomes worse, and the transfer property of the cream solder is deteriorated. 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.

Although there are various causes for causing the above-mentioned printing problems, the major cause is the smoothness of the wall surface of the opening. Therefore, a method of chemically and physically treating the wall surface of the opening has been proposed. inside that
JP-A-4-9059 JP-A-6-91839 Japanese Patent Laid-Open No. 7-32759 proposes a method of electrolytic polishing treatment for smoothing the wall surface of the opening of the metal mask.

  However, even when using a metal mask subjected to the above-described electropolishing treatment, the printability is not necessarily sufficient for the recent increase in the density of electronic components, and further improvements are required. Yes. In recent years, so-called lead-free solder that does not contain lead has been used for environmental reasons. However, the lead-free cream solder is inferior in transferability as compared with the conventional cream solder. Defects are likely to occur.

  The purpose 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 conductive paste such as cream solder is printed, bleeding of the cream solder described above, chipping or disconnection of the solder terminal, An object of the present invention is to provide a printing metal mask that can prevent the occurrence of defects such as cracks and can increase the printing speed.

  In order to solve the various problems described above when printing cream solder using a metal mask, the present inventors have studied an electrolytic polishing treatment method and completed the present invention.

That is, the present invention
The above description is a metal mask obtained by subjecting a metal mask original plate provided with an opening for transferring conductive paste to an intermittent electrolytic polishing treatment, and a metal mask original plate provided with an opening by laser light irradiation on a metal substrate. A metal mask of the above, and a metal mask original plate made by an additive method, and a step of irradiating the metal substrate with a laser beam to form an opening for transferring the conductive paste, an intermittent electrolytic polishing process A metal mask manufacturing method comprising steps, and a screen printing plate having a tension of 0.8 to 1.2 mm, which is formed by attaching the metal mask described above to a metal frame via a scissors.

  The metal mask for cream solder printing of the present invention has a smoothed wall surface of the opening and a sharp edge, so that the bleeding of the cream solder when the cream solder is printed, the ability to pull out from the plate is improved, Even if the printing speed is increased, defects such as cracking, disconnection, and chipping of the solder terminal due to the poor transferability of the cream solder can be prevented, and the productivity and yield of the solder terminal forming process are greatly improved.

  The material used for the metal mask for cream solder printing in the present invention is preferably a metal or alloy mainly composed of nickel, copper, chromium, zinc, iron or the like. The metal mask has a thickness of 30 to 150 μm, and may be a single layer or a laminate of the metal or alloy.

  The metal mask of the present invention has a cream solder transfer opening, but the shape thereof is not particularly limited. And other irregular shapes such as a bowl shape and a dumbbell shape. And the size is 40-200 micrometers for the largest opening part of various shapes mentioned above for high-density mounting, and a repetition pitch is 70-400 micrometers. The opening may have a taper.

  As a method for producing a metal mask original plate of the present invention, an etching method in which an opening is dissolved in a metal or alloy plate as described above with a chemical solution, a laser method in which a hole is formed with a laser beam, an additive method manufactured by electroforming, etc. are put into practical use. However, in the present invention, the laser method or the additive method is preferable.

In the laser method, a metal plate such as stainless steel or nickel is directly irradiated with laser light to form an opening.
In the additive method, a convex portion corresponding to the opening is formed with a photosensitive resin by a photolithographic method on a conductive substrate, and a metal layer is formed by electroplating on the surface where the convex portion is formed. The conductive substrate is removed.

In the metal mask of the present invention, an intermittent electrolytic polishing treatment is performed on the metal mask original plate in which the opening is formed by the above-described method.
Intermittent electropolishing is a method in which electropolishing is intermittently performed. A metal mask original plate is immersed in a polishing solution and energized for a certain period of time, and then not energized for a certain period of time. This energization and non-energization cycle is repeated. At this time, it is more preferable to perform reverse energization for a short time between the energization process and the non-energization process. Specifically, the energization process has a current density of 5 to 35 A / dm 2, preferably 10 to 30 A / dm 2, an energization time of 5 to 30 seconds, and the reverse energization process has a current density of −3 to −0.3 A / dm 2, The energization time is 0.5 to 5 seconds, and the non-energization process takes about 10 to 60 seconds.
Needless to say, an electrolytic solution suitable for the material to be polished is used as the polishing liquid.

As for the difference between the conventional electropolishing and the metal mask subjected to the intermittent polishing process, the smoothness of the wall surface of the opening is greatly different from the result of observing the opening. Also, the edge shape of the opening is different. That is, in the case of conventional electrolytic polishing, the edge of the opening is also polished and rounded. On the other hand, the edge is sharp in the case of intermittent electropolishing. As a result, it seems that bleeding was improved when cream solder was printed.

  The metal mask of the present invention is attached to a metal frame made of aluminum, stainless steel, copper or the like via a ridge to form a screen printing plate. Specifically, after attaching a ridge to the above-described metal frame, and attaching the outer peripheral portion of the metal mask smaller than the size of the metal frame to the heel using an adhesive, Cut the firewood. In this way, a screen printing plate in which the outer peripheral portion of the metal mask is attached to the metal frame via the ridge is completed. The metal mask is pulled by the heel tension. This tension is also largely related to the printing characteristics of the cream solder as described above. For high-density mounting and printing of lead-free cream solder, the tension is preferably 0.8 to 1.2 mm, 0.9 to 1 More preferably, it is 1 mm. In this case, the tension is measured by the amount of deflection of the printing plate when a certain amount of weight is applied to the center of the screen printing plate, and the value measured with a tension gauge STG-75B (Protech Co., Ltd.). .

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

  As a solder pattern for mounting electronic components on a stainless steel plate having a thickness of 50 μm, a basic pattern is a square of about 10 mm × 10 mm consisting of 68 openings (total 4624 in total) with a pitch of 150 μm and openings of 70 μm in diameter. An opening was formed with a YAG laser so as to form a pattern in which 3 × 5 (total 15) patterns were repeatedly arranged at a pitch of 15 mm, and a 400 × 480 mm metal mask original plate was manufactured.

Using the above-mentioned metal mask original plate, an electrolytic solution having a phosphoric acid concentration of 600 ml / l and a sulfuric acid concentration of 180 ml / l, and at 45 ° C., with the metal mask original plate as an anode, the following electropolishing conditions are set to one cycle, 20 cycles of electropolishing were performed to produce a metal mask.
Current density Energization time energization: 15 A / dm2 15 seconds Reverse energization: -0.5 A / dm2 3 seconds Non-energization: 0 A / dm2 20 seconds

  Next, the outer periphery of the metal mask is attached to the center of a screen having an outer shape of 550 × 650 mm aluminum frame and a 180-mesh polyester wrinkle stretched using an epoxy adhesive. A screen printing plate was made by cutting off the wrinkles within 10 mm from the outer periphery. The tension of the plate measured with a tension gauge STG-75B (Protech Co., Ltd.) was 0.9 mm.

  Set the above screen printing plate on a screen printing machine (SP28P-DH, Panasonic Factory Solution Co., Ltd.), print lead-free cream solder (LF-71S-3, Tamura Kaken Co., Ltd.) on the printed circuit board, The formed cream solder terminal was observed. Even when printing was repeated 5000 times, defects such as cream solder bleeding, solder terminal chipping, disconnection, and cracking were not observed.

As Comparative Example 1, a metal mask and a screen printing plate were prepared in the same manner as in Example 1 except that in Example 1, the electropolishing conditions were a current density of 18 A / dm2 and an energization time of 300 seconds. The cream solder was printed. When printing was repeated 100 times, bleeding of cream solder began to occur, and chipping also occurred on the solder terminals.
As Comparative Examples 2 and 3, the metal mask manufactured in Example 1 was attached to a screen with a different tension of the heel, and the tensions were 1.3 mm (Comparative Example 2) and 0.7 mm (Comparative Example 3), respectively. A screen printing plate was made and cream solder was printed. The plate of Comparative Example 2 had poor plate separation at the time of printing, and had defects such as chipping and cracking in the solder terminals. Further, in the plate of Comparative Example 3, the printing plate was suddenly separated, and the solder terminals were chipped.

  The surface of a SUS304 substrate having a plate thickness of 1 mm and 550 × 650 mm was leveled (buffed), and a dry film resist (FP240, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was laminated on both sides. Next, as a solder terminal pattern for mounting electronic components, using a glass mask having the same pattern as in Example 1, double-sided exposure with a mirror reflection type parallel light exposure machine, aging for 15 minutes, and then 1.0% carbonic acid Development with a sodium aqueous solution and washing with water were carried out to form a solder terminal pattern of a dry film resist film on both surfaces of the SUS304 substrate.

Next, it was placed in a nickel sulfamate plating bath, and a nickel film having a thickness of 60 μm was formed on the substrate at 2 A / dm 2 and a bath temperature of 45 ° C. The obtained nickel film-coated substrate is immersed in a 1.0% sodium hydroxide aqueous solution at 50 ° C. to remove the resist film, and then the nickel film is peeled off from the substrate to obtain a 400 × 480 mm nickel metal mask original plate. Produced.

Using the above metal mask original plate, an intermittent electropolishing treatment was performed in the same manner as in Example 1 except for the following electropolishing conditions to produce a metal mask.
Current density Energization time energization: 25 A / dm2 10 seconds Reverse energization: -1.5 A / dm2 1 second Non-energization: 0 A / dm2 40 seconds

  Using the above metal mask, a screen printing plate having a tension of 1.0 mm was prepared in the same manner as in Example 1, and printing evaluation of cream solder was performed. The result was the same as in Example 1. Further, as comparative examples, a screen printing plate using a metal mask subjected to electropolishing only for continuous energization (Comparative Example 4) and Example 2 using a metal mask, the plate tension was 1.3 mm (Comparative Example 5). A screen printing plate having a thickness of 0.7 mm (Comparative Example 6) was prepared and evaluated. As a result, in Comparative Example 4, bleeding of cream solder began to occur, and chipping also occurred in the solder terminals. In Comparative Example 5, the plate separation at the time of printing was poor, and defects such as chipping and cracking occurred in the solder terminal. In Comparative Example 6, the plate separation of the printing plate occurred rapidly and chipping occurred in the solder terminal.

The metal mask of the present invention can print lead-free cream solder with high transferability even when high-definition patterns are printed at high density and high speed, and is a solder terminal for high-density mounting of electronic components. Can be used to create

Claims (5)

A metal mask obtained by subjecting a metal mask original plate provided with an opening for transferring a conductive paste to an intermittent electrolytic polishing treatment. The metal mask according to claim 1, which is a metal mask original plate in which an opening is provided on a metal substrate by laser light irradiation. 2. The metal mask according to claim 1, wherein the metal mask is an original metal mask made by an additive method. A method for producing a metal mask comprising a step of irradiating a metal substrate with laser light to form an opening for transferring a conductive paste, and an intermittent electrolytic polishing treatment step. A screen printing plate having a plate tension of 0.8 to 1.2 mm, wherein the metal mask according to claim 2 or 3 is attached to a metal frame through a ridge.