JP2009056706A - Metal mask plate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal mask plate, which can prevent the degradation of printing accuracy or the degradation of conductive ball loading position accuracy at the solder paste printing time or the conductive ball loading time caused by the secular deformation of the metal mask plate, can enhance durability, and is composed of chemical fiber screen fabric or stainless steel screen fabric being conventional supporter screens. <P>SOLUTION: The metal mask 2 whose inner stress is tensile stress, formed on a metallic base material 1 is joined on the support screen 4 stretched on a plate frame 3 without peering off the metallic base material 1. In the metal mask plate, the metal mask 2 is joined to the supporter screen 4 at the outer peripheral part of the metal mask 2 on the contact side with a printed matter at the conductive paste printing time, and at the outer peripheral part of the metal mask 2 on the contact side with a loaded matter at the conductive ball loading time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal mask plate used when a solder paste is printed with high accuracy on a silicon wafer, a printed wiring board or the like, or when a conductive ball is mounted, and a method for manufacturing the same.

The connection method between the electrode of the semiconductor element and the external terminal is roughly classified into a bonding wire method using a fine metal wire and a Philip chip method for connection using a solder bump formed on the electrode of the semiconductor element. It is said that the Philip chip method is advantageous for increasing the density and the number of pins. In recent years, in order to improve the mounting density of semiconductor packages, a ball grid array (hereinafter referred to as “BGA”) in which solder bumps are formed on external terminals as a technology that can accommodate a large number of pins while maintaining a wide terminal pitch. Abbreviated) type semiconductor devices are widely used. In a BGA type semiconductor device, a so-called chip scale package (hereinafter abbreviated as CSP), in which the area of the package is approximately equal to the area of the semiconductor chip, has been developed together with the above-described BGA electrode arrangement structure. Greatly contributes to the reduction of size and weight. The CSP cuts a silicon wafer on which a circuit is formed, and individually performs a packaging process on each semiconductor chip to complete a package.
On the other hand, in a manufacturing method generally called “wafer level CSP”, an insulating layer, a rewiring layer, a sealing layer, and the like are formed on this silicon wafer, and solder bumps are formed. As a method for forming solder bumps, solder is supplied by various methods such as electroplating, solder paste printing, and conductive ball mounting and supply methods, and hemispherical bumps are formed by reflowing using flux. Is common. After the solder bumps are formed, the semiconductor chip having the package structure can be obtained by cutting the wafer into a predetermined chip size in the final process. Since these circuits are stacked on the entire surface of the wafer and the wafer is diced in the final process, the size of the cut chip itself becomes a packaged semiconductor chip, which has a minimum projected area with respect to the mounting substrate. Can be obtained.

  As described above, the solder bump forming method includes various methods such as an electroplating method, a solder paste printing method, and a conductive ball mounting supply method. After that, in the solder paste printing method and the conductive ball mounting method, A metal mask plate in which a predetermined pattern opening is formed on a metal plate is used. In the solder paste printing method, a metal mask plate having a desired opening through which the solder paste passes is used, and in the ball mounting method, a metal mask plate having a desired opening through which the conductive ball is sucked and held or used is used. It is done.

  In recent years, the Philip chip system has been increased in density and increased in number of pins, the bump diameter of the solder bump itself has been reduced, and the distance between the solder bumps has become very narrow. Along with this, the metal mask plate used for forming solder bumps has also been required to reduce the opening diameter and the opening interval, and at the same time to improve the position accuracy and the overall length accuracy of the opening of the metal mask plate. . For example, the required accuracy has become within ± 15 μm with respect to the overall length dimension of about 203.200 mm in the overall length dimension accuracy of an 8-inch wafer, and the full length dimension accuracy can be satisfied over time. It is requested.

Therefore, as a conventional technique for improving pattern position accuracy, pattern pitch accuracy, and time-lapse printing accuracy, a metal mask plate manufacturing method that achieves pattern position accuracy of ± 10 μm with a deposition mask of about 50 cm square (for example, Patent Document 1). And a reinforcing frame integrally with the outer peripheral edge on the electroformed surface side of the mask body having a pattern area in which a predetermined pattern is formed and an outer peripheral pattern formed on the outer periphery from the pattern area. In order to maintain the formed metal mask with good pattern pitch accuracy and its manufacturing method (see, for example, Patent Document 2) and printing accuracy over time, the support screen is made of stainless steel fibers instead of chemical fibers. Metal mask using a rigidized screen in which the surface of the braided part of the screen mesh braided is coated with a plating film There is a version (see, for example, Patent Document 3).
JP-A-2005-158319 (paragraphs {0040} to {0061} of {Best Mode for Carrying Out the Invention} in the claims section and the detailed description section, and FIGS. See Japanese Unexamined Patent Publication No. 2007-83411 (paragraphs {0017} to {0051} of {Best Mode for Carrying Out the Invention} in the claims section and the detailed description section, and FIGS. See JP 2007-62225 A (refer to paragraphs {0008} to {0016} of {Examples} in the claims section and detailed description section of the invention, and FIGS. 1 and 2)

However, Patent Document 1 discloses the pattern position accuracy and Patent Document 2 discloses the stability of the initial dimensional accuracy of the pattern and pitch accuracy, but does not disclose anything about the dimensional stability over time. Absent.
In addition, Patent Document 3 discloses dimensional stability over time in addition to the stability of initial dimensional accuracy, but it is not a synthetic fiber or metal cage generally used for a support screen, but stainless steel. The solution is to use a rigidized screen in which the surface of the braided portion of the screen mesh braided fiber is coated with a plating film.
Furthermore, what can be said with respect to any of Patent Documents 1 to 3 is a form usually used as a metal mask plate, that is, a synthetic fiber or a metal cage as a support screen and a metal mask joined to the support screen. It does not take the form of a metal mask version.
The reason is that, for example, when the tension is increased by using the support screen supporting the metal mask as a synthetic fiber, the load applied to the metal mask increases, the metal mask undergoes deformation over time, and the printing position accuracy decreases, that is, the metal This is because a problem of reducing the durability of the mask plate occurs.
In addition, when producing a metal mask plate with an electroformed metal mask, in order to improve the position accuracy of the desired opening of the metal mask plate, a metal mask having no internal stress and having no distortion is applied to the support screen. When the metal mask plate is manufactured, for example, if the support screen has a high tension, the strength of the metal mask itself is reduced, and the metal mask is deformed over time. This is because the problem of reducing the durability of the plate occurs.
That is, in the case of a metal mask plate using a chemical fiber or a metal rod for the support screen, it has been considered extremely difficult to improve the overall length dimensional accuracy.

A first invention of the present invention capable of achieving the above object is a metal mask plate as described in claim 1, and is as follows.
Metal having a metal mask whose internal stress is tensile stress, a support screen bonded so as to overlap an outer peripheral portion of the metal mask whose internal stress is tensile stress, and a plate frame on which the support screen is stretched In the mask plate, the metal mask whose internal stress is tensile stress is the outer peripheral portion of the metal mask that is in contact with the substrate when the conductive paste is printed, and the side that is in contact with the substrate when the conductive ball is mounted. The outer periphery of the metal mask is joined to the support screen.

A second invention of the present invention capable of achieving the above object is a metal mask plate as described in claim 2, and is as follows.
In addition to the invention described in claim 1, a metal mask produced by electroplating using a nickel sulfamate bath containing citric acid and having an internal stress of tensile stress is used.

A third invention of the present invention capable of achieving the above object is a metal mask plate as described in claim 3, which is as follows.
In addition to the invention described in claim 2, the electroplating condition is a current density exceeding 1.0 A / dm ² .

A fourth invention of the present invention capable of achieving the above object is a metal mask plate as described in claim 4, and is as follows.
In addition to the invention described in any one of claims 1 to 3, the surface hardness of the metal mask is in the range of HV200 to 800 in terms of Vickers hardness.

A fifth invention of the present invention capable of achieving the above object is a method for producing a metal mask plate as described in claim 5, and is as follows.
A step of forming a metal mask having an internal stress of tensile stress on a metal base material by electroforming, and a metal mask having a tensile stress of internal stress while being integrated with the metal base material, The support screen stretched on the frame is arranged from the side where the support screen is bonded to the plate frame, and the outer periphery of the metal mask whose internal stress is tensile stress is bonded to the support screen. And a method of cutting and removing the support screen inside the joint with the metal mask whose internal stress is tensile stress, and peeling the metal base material from the metal mask whose internal stress is tensile stress It is the structure provided with a process.

A sixth invention of the present invention capable of achieving the above object is a method for producing a metal mask plate as described in claim 6, and is as follows.
In addition to the invention described in claim 5, a metal mask plate whose internal stress is tensile stress is produced by electroplating using a nickel sulfamate bath containing citric acid.

A seventh invention of the present invention capable of achieving the above object is a method for producing a metal mask plate as described in claim 7, and is as follows.
In addition to the invention of claim 6, the electroplating condition is a current density exceeding 1.0 A / dm ² .

An eighth invention of the present invention capable of achieving the above object is a method for producing a metal mask plate as described in claim 8, and is as follows.
In addition to the invention according to any one of claims 5 to 7, the surface hardness of the metal mask whose internal stress is tensile stress is in the range of HV200 to 800 in terms of Vickers hardness.

Since the metal mask plate and the manufacturing method thereof according to the present invention have the configuration as described above, the following effects can be obtained.
(1) Since the metal mask whose internal stress is tensile stress has the property of shrinking, even when it is joined to the support screen, the tension property to stretch the metal mask of the support screen and the force to counteract each other Therefore, it is possible to obtain a metal mask plate with little dimensional change over time.
(2) When the metal mask whose internal stress is tensile stress is peeled off from the metal base material and then an attempt is made to join the support screen, the metal mask is placed with the plating growth surface inside when the metal mask is peeled off from the metal base material. It will be rounded and it will be difficult to join the support screen. In the present invention, the metal mask can be bonded to the support screen without distortion by bonding the metal mask to the support screen without removing the metal mask from the metal base material.
(3) If the plating growth surface of the metal mask is uneven, that is, if the plating surface is matte plating or semi-gloss plating, the metal mask is not peeled off from the metal base material. By joining to a support body screen in the outer peripheral part of the metal mask of the contact side, a plating growth surface can be joined to a support body screen as a surface which contacts the said to-be-printed body. The unevenness of the plating growth surface plays a role such as air bleeding during printing of the conductive paste, and as a result, the printability of the conductive paste is improved.
(4) As the support screen, generally used synthetic fiber and metal cocoons are used, so there is no particular increase in manufacturing process, and there is no extra capital investment, and metal with little change over time. A mask plate can be produced.
(5) Boron regulation can be avoided by using citric acid as the pH buffering agent.

  As shown in FIG. 1, a process of forming a metal mask 2 whose internal stress is a tensile stress by electroforming on a metal base material 1, and the internal stress in a state of being integrated with the metal base material 1 The metal mask 2 having a tensile stress is arranged from the side of the support screen 4 stretched on the plate frame 3 from the side where the support screen 4 is joined to the plate frame 3, and the internal stress is the tensile stress. A step of bonding the outer periphery of the metal mask 2 and the support screen 4, and a step of cutting and removing the support screen 4 inside the bonding portion of the metal mask 2 where the internal stress is a tensile stress. A metal mask plate manufacturing method and a metal mask plate comprising a step of peeling the metal base material 1 from the metal mask 2 in which the internal stress is a tensile stress.

Hereinafter, the metal mask plate of the present invention will be described in detail.
The metal mask of the present invention is composed of nickel or a nickel alloy made by electroforming, and the nickel alloy is mainly composed of nickel, cobalt, iron, chromium, tungsten, tin, copper, vanadium, phosphorus, boron. And the like.
Of course, the metal mask of the present invention may contain components of various additives such as a brightener, a hardener, a buffering agent and a complexing agent added to the plating bath during electroforming. It is.

Here, the first embodiment of the present invention will be described in detail.
A surface of a SUS material having a plate thickness of 0.25 mm and 500 × 620 mm is prepared by buffing as a metal base material, and a dry film resist having a thickness of 40 μmt is laminated twice on the surface of the metal base material to obtain a thickness of 80 μmt. A dry film resist film was formed.
Next, as a pattern for forming solder bumps on the silicon wafer, a pattern consisting of 648,891 circles having a diameter of 150 μm and a repetition pitch of 200 μm was exposed on the dry film resist film by a direct drawing method using ultraviolet light as a light source. After the exposure, development was performed with a 1.0% sodium carbonate aqueous solution, followed by a water washing step, and a dry film resist film was formed on the metal base material to form a solder bump pattern.

Next, the metal base material in which the solder bump pattern is formed is put in a plating bath composed of nickel sulfamate 450 g / L, citric acid appropriate amount, additive A appropriate amount, additive B appropriate amount, pH 4.2, bath temperature 45 ° C. A nickel film having a thickness of 65 μm was electrodeposited on the metal base material at a current density of 4.0 A / dm ² .
The metal base material on which the nickel film is electrodeposited is immersed in an aqueous sodium hydroxide solution to remove the solder bump pattern of the dry film resist film, and a pattern consisting of 648,891 pieces having a diameter of 150 μm and an opening pitch of 200 μm. As a result, a metal mask with a metal base material was obtained.
The metal mask with the metal base material was confirmed to be warped toward the nickel side due to tensile stress. The internal stress was evaluated by a strip electrodeposition stress measurement method using a strip electrodeposition stress measuring instrument (Specialty Testing And Development Co, Inc.). In this measuring instrument, if the measurement result is a value of “+ (positive)”, it indicates a tensile stress, if it is a value of “− (negative)”, it indicates a compressive stress, and if it is “0”, the stress is zero. Indicates. The measured value of the film stress was +60 Mpa.
Moreover, the Vickers hardness of the metal mask part in the metal mask with a metal base material was HV333 (MXT-30, manufactured by Matsuzawa Seiki Co., Ltd.).

Next, a polyester ridge having a wire diameter of 45 μm and a 230 mesh is used as a support screen, and is stretched on an aluminum frame having an outer diameter of 550 × 650 mm with a tension of 850 μm (STG-75B, manufactured by Protec Co., Ltd.) did.
The metal mask with the metal base material is disposed from the side where the support screen is bonded to the plate frame, and the outer periphery of the metal mask is bonded using an adhesive at the substantially central portion of the tension frame, The support screen inside the joint was cut off, and the metal base material was peeled off from the metal mask to produce a metal mask plate.
The produced metal mask plate was stored in an environment of 23 ± 1 ° C. and 50 ± 10% RH, and from 648,891 with a diameter of 150 μm and a repeated pitch of 200 μm in the period from the day of preparation to 35 days later. The dimension 203.200 mm of the longest part in the X direction and the dimension 203.200 mm of the longest part in the Y direction were repeatedly measured.
As a result, the dimensional change was less than +10 μm in both the X and Y directions even after 35 days.

As a second embodiment, the same method as in the first embodiment except that the diameter of the circle exposed on the dry film resist film is 90 μm, the thickness of the nickel film is 20 μm, and the tension of the tension frame is 1250 μm. A metal mask plate was produced.
As a result, it was confirmed that the metal mask with the metal base material warped toward the nickel side due to the tensile stress. The measured value of the film stress was +60 Mpa. The Vickers hardness of the metal mask was HV325.
When the dimension measurement was performed by the same measurement method under the same environment as the first example, the dimension change was less than +10 μm in both the X direction and the Y direction even after 35 days.

Next, as Comparative Example 1 for comparison with the example of the present invention, a metal mask plate was produced by the same method as in the first example except that the current density was 0.2 A / dm ² .
The metal mask with the metal base material was confirmed to be warped toward the substrate due to the compressive stress. The measured value of the film stress was −80 Mpa. The Vickers hardness of the metal mask was HV560.
When dimensional measurement was performed by the same measurement method under the same environment as in the first example, the change in dimension was about +40 μm in the X direction and about +60 μm in the Y direction after 35 days.

Further, as Comparative Example 2, a metal mask plate was produced by the same method as in the first example except that the current density was 1.0 A / dm ² .
In the metal mask with a metal base material, the distortion warped to the nickel side due to the tensile stress and the distortion warped toward the substrate side due to the compressive stress could not be confirmed. The measured value of the film stress was 0 Mpa. The Vickers hardness of the metal mask was HV437.
When dimensional measurement was performed by the same measurement method in the same environment as in the first example, the change in dimension was about +20 μm in the X direction and about +30 μm in the Y direction after 35 days.

Further, as Comparative Example 3, a metal mask plate was produced in the same manner as in the second example except that the current density was 0.2 A / dm ² .
The metal mask with the metal base material was confirmed to be warped toward the substrate due to the compressive stress. The measured value of the film stress was −80 Mpa. The Vickers hardness of the metal mask was HV560.
When the dimension measurement was performed by the same measurement method in the same environment as the first embodiment, the dimension change was about +40 μm in the X direction and about +50 μm in the Y direction after 30 days.

Next, as Comparative Example 4, a metal mask plate was produced in the same manner as in the second example except that the tension of the tension frame was 850 and the current density was 0.2 A / dm ² .
The metal mask with the metal base material was confirmed to be warped toward the substrate due to the compressive stress. The measured value of the film stress was −80 Mpa. The Vickers hardness of the metal mask was HV560.
When the dimension measurement was performed by the same measurement method under the same environment as the first embodiment, the dimension change was about +60 μm in the X direction and about +70 μm in the Y direction after 35 days.

Table 1 shows the conditions of the first example, the second example, the comparative example 1, the comparative example 2, the comparative example 3, and the comparative example 4 described above, and the time-dependent deformation of the metal mask plate obtained from each condition. The measurement results are shown in Tables 2 to 5.

As is apparent from Tables 1 to 5, Comparative Example 2 having almost no internal stress of the film, Comparative Example 1, and Comparative Example 3 and Comparative Example 4 in which the internal stress of the film is a compressive stress are as follows. In the past, the dimensional change amount is already +20 μm or more, whereas the metal mask plate of the first example and the second example whose tensile stress is the internal stress of the film is the dimensional change amount even after 35 days. Is very small, less than +10 μm.
The current density is preferably more than 1.0 A / dm ² where the internal stress becomes tensile stress, and more preferably 4.0 A / dm ² or more. Moreover, about surface hardness, HV200-800 are preferable at the Vickers hardness which can obtain the durability of a metal mask, and Hv250-500 is more preferable among these.
The work examples in the first and second examples and Comparative Examples 1 to 4 are only one work example and are not limited.
For example, as an exposure method, a pattern may be formed by contact exposure using a photomask, or a pattern may be formed by a direct drawing machine using a semiconductor laser as a light source.

  Based on the above results, the metal mask plate having an internal stress of tensile stress according to the present invention is less likely to be deformed with time, can suppress the printing position accuracy degradation, and can suppress the durability degradation of the metal mask plate. That is, the metal that can prevent the deterioration of printing accuracy and the accuracy of mounting position of the conductive ball due to the temporal deformation of the metal mask plate during solder paste printing or mounting of the conductive ball, and improve the durability. The mask plate can be provided in the form of a metal mask plate using a synthetic fiber or a metal rod on a support screen having a conventional structure.

  It can also be used for metal mask plates used for screen printing plates which are also used in the field of precision pattern formation processes related to electronics.

It is sectional drawing of the metal mask plate which concerns on this invention.

Explanation of symbols

1 .... Metal base material 2 .... Metal mask 3 .... Plate frame 4 .... Support screen

Claims (8)

Metal having a metal mask whose internal stress is tensile stress, a support screen bonded so as to overlap an outer peripheral portion of the metal mask whose internal stress is tensile stress, and a plate frame on which the support screen is stretched In the mask plate, the metal mask whose internal stress is tensile stress is the outer peripheral portion of the metal mask that is in contact with the substrate when the conductive paste is printed, and the side that is in contact with the substrate when the conductive ball is mounted. A metal mask plate, wherein the metal mask plate is joined to the support screen at an outer periphery of the metal mask. 2. The metal mask plate according to claim 1, wherein a metal mask produced by electroplating using a nickel sulfamate bath containing citric acid and having an internal stress of tensile stress is used. 3. The metal mask plate according to claim 2, wherein the electroplating condition is a current density exceeding 1.0 A / dm ² . The metal mask plate according to any one of claims 1 to 3, wherein the surface hardness of the metal mask is in the range of HV200 to 800 in terms of Vickers hardness. A step of forming a metal mask having an internal stress of tensile stress on a metal base material by electroforming, and a metal mask having a tensile stress of internal stress while being integrated with the metal base material, The support screen stretched on the frame is arranged from the side where the support screen is bonded to the plate frame, and the outer periphery of the metal mask whose internal stress is tensile stress is bonded to the support screen. And a method of cutting and removing the support screen inside the joint with the metal mask whose internal stress is tensile stress, and peeling the metal base material from the metal mask whose internal stress is tensile stress A method for producing a metal mask plate, comprising a step. 6. The method for producing a metal mask plate according to claim 5, wherein a metal mask plate whose internal stress is tensile stress is produced by electroplating using a nickel sulfamate bath containing citric acid. Method for producing a metal mask plate according to claim 6, wherein the electroplating conditions are current density 1.0A / dm ² greater. The surface hardness of the metal mask whose internal stress is tensile stress is in the range of HV200 to 800 in terms of Vickers hardness, and the metal mask plate according to any one of claims 5 to 7, Production method

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