JP3015470B2 - Solder bump forming method and mask fixing magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder bump forming method and a mask fixing magnet, and more particularly to a solder bump forming method and a mask fixing magnet for forming a solder bump while fixing a mask to a semiconductor substrate or the like using a magnet. About.

2. Description of the Related Art Large-scale integrated circuit (LSI) devices are required to have higher circuit densities and higher processing speeds, and high-performance LSI devices meeting such needs have been developed. In the case of such an LSI element, the number of signal input / output terminals tends to increase inevitably.

As a method of mounting such a high-performance LSI element on a circuit board, flip-chip bonding in which the LSI element is directly bonded to the circuit board via solder is promising. In order to perform this flip chip bonding, it is necessary to form solder bumps on the LSI element and the electrode portion of the circuit board in advance.

In particular, when the number of signal input / output terminals increases as described above, it is necessary to form solder bumps with high density. Therefore, it is desired to form solder bumps with high accuracy.

[0005]

2. Description of the Related Art Generally, a solder bump is formed on an electrode portion of an LSI element or the like by the following procedure. First, a metal mask on which a pattern corresponding to an electrode formed on an LSI element is formed is prepared.
Placing a metal mask on the solder bump formation side of the I element,
On the side different from the side on which the solder bumps are formed, a magnet and a cooling copper plate used to cool the wafer in a vapor deposition process performed later are arranged. Then, the metal mask is held at a predetermined position of the LSI element by attracting the metal mask by the magnetic force of the magnet. This holding state is shown in FIG. In FIG. 1, reference numeral 1 denotes a magnet, 2 denotes a metal mask, 3 denotes an LSI device wafer, and 4 denotes a cooling copper plate. Conventionally, the magnetization direction of the magnet 1 is such that one surface of the magnet 1 is an N pole and the other surface is an S pole (in FIG. 6, the upper surface is an N pole and the lower surface is an S pole).

Subsequently, solder is deposited in the state shown in FIG. 1 to form solder bumps on the electrodes of the LSI element. Through the above procedure, the solder bump was formed on the electrode portion of the LSI element or the like.

[0007]

Since the metal mask 2 is as thin as several tens to several hundreds of micrometers, the attractive force of the magnet 1 is poor.
Good holding by the magnet 1 becomes impossible. As shown in FIG. 6, when the size of the magnet 1 is larger than the size of the wafer 3, the lines of magnetic force of the magnet 1 flow through the metal mask 2. As is well known, when a magnet is attracted by a magnet, the attraction force is stronger when the magnet is incorporated in a magnetic circuit formed by the magnet. However, in the configuration shown in FIG.
Are not incorporated in the magnetic circuit that constitutes the device. Accordingly, the attraction force of the metal mask 2 by the magnet 1 is also reduced by this.

Thus, the metal mask 2 by the magnet 1
When the suction force of the metal mask 2 is small,
Is warped by its own weight, and a gap is formed between the outer peripheral portion and the wafer 3. If a gap is formed between the metal mask 2 and the wafer 3, the solder is also deposited on the gap in the deposition step, causing a short circuit between the electrodes of the wafer 3, There is a problem that the formed electronic element may be damaged.

On the other hand, the magnetic field lines on the outer side of the magnet 1 are not perpendicular, and draw a circular locus including an oblique component from the N pole to the S pole. As shown in FIG. 7 (the configuration corresponding to that of FIG.
Approaching the wafer 3, the lines of magnetic force from the N pole to the S pole affect the metal mask 2. More specifically, since the magnetic resistance of the metal mask 2 is smaller in the surface direction, a part of the magnetic field lines from the N pole to the S pole travels inside the metal mask 2. As described above, when a part of the line of magnetic force advances inside the metal mask 2, a force acts on the metal mask 2 in a plane direction, and the metal mask 2 is displaced from a predetermined position due to the force. If the metal mask 2 is displaced from a predetermined position, there is a possibility that a short circuit may occur between the respective electrodes or the electronic elements on the wafer 3 may be damaged.

The present invention has been made in view of the above points, and an object of the present invention is to provide a solder bump forming method and a mask fixing magnet capable of accurately forming a solder bump by holding a mask in a good state. Aim.

[0011]

According to the present invention, in order to solve the above-mentioned problems, a mask formed of a magnetic material and having a predetermined pattern formed thereon is arranged on a surface of a substrate on which solder bumps are to be formed. a magnet disposed on a surface different from the surface where the solder bumps are formed in the substrate, the magnetic force of the magnet
Accordingly, in a solder bump forming method of depositing solder on the mask while holding the mask and forming a solder bump, the magnet is configured to have a plurality of magnetic poles on a surface that adsorbs the mask, and the plurality of magnets are formed. The mask is attracted by a magnet having a magnetic pole.

Further, disposed on the other side of the substrate mask having a predetermined pattern is composed is formed of a magnetic material on one surface is placed, the mask in the mask fixing magnet that attracted by the magnetic force, the magnetic poles Are different from each other
Different magnetic poles are alternately arranged on the surface where the mask is sucked.
It is characterized in that it has a simple configuration .

Further, the plurality of magnetic poles may be configured such that different magnetic poles are alternately formed in stripes.

[0014]

A plurality of magnetic circuits are formed between the magnet and the mask by providing the magnet for attracting the mask with a plurality of magnetic poles. 1 and 2 are diagrams for explaining the principle of the present invention. FIG. 2 is a plan view of the magnet 10 in which a plurality of magnetic poles are formed. As shown in FIG. 1, the magnet 10 has an aggregate structure of a plurality of magnets having alternately different polarities.

FIG. 1 shows a state in which the mask 11 is attracted by the magnet 10. As described above, since the magnet 10 has an aggregate structure of magnets having different magnetic poles alternately, the lines of magnetic force emitted from one magnetic pole pass through the mask 11 made of a magnetic material and have a polarity different from that of one adjacent magnetic pole. Get into the magnetic pole.
That is, each magnetic pole and the mask 11 form a magnetic circuit, and a plurality of magnetic circuits are formed corresponding to the number of magnetic poles.

Therefore, the mask 11 constituting a part of the magnetic circuit is firmly fixed by the magnetic force of the magnet 10, and the magnetic circuit is formed at various places of the magnet. The mask 11 is held, and is firmly fixed to the wafer 12.

[0017]

Next, an embodiment of the present invention will be described with reference to the drawings. 3 to 5 show a solder bump forming method according to an embodiment of the present invention along a forming procedure. Note that components corresponding to those shown in FIGS. 1 and 2 are denoted by the same reference numerals and described.

FIG. 3 shows a state where the metal mask 11 is fixed on the wafer 12 using the magnet 10. Wafer 1
Reference numeral 2 denotes a silicon wafer having a diameter of 3 inches, and the metal mask 11 is made of copearl having a thickness of 50 μm and a diameter of 3 inches. This metal mask 11 has a 150 μm diameter hole having a diameter of
About 150,000 pieces are formed at a pitch of μm. In addition, 1 in the figure
Reference numeral 3 denotes a cooling copper plate, which has a function of cooling the wafer 12 in a vapor deposition step performed later.

The magnet 10 is a ferrite magnet having a thickness of 5 mm and a diameter of 4 inches, and as shown in FIG.
The surface for adsorbing 1 has a configuration in which a plurality of magnetic poles are formed. That is, the surface on which the metal mask 11 is adsorbed has a configuration in which N poles and S poles are alternately arranged in stripes. As described above, since the magnet 10 has an aggregate structure of magnets having different magnetic poles alternately, the magnetic lines of force coming out of the N pole enter the metal mask 11 which is a magnetic substance, pass through the metal mask 11 to the adjacent S pole. Form a magnetic circuit that penetrates. A plurality of such magnetic circuits are formed on the magnet 11 corresponding to the number of magnetic poles.

Therefore, the metal mask 11 is sucked at a plurality of positions where the magnetic circuit is formed.
Therefore, the metal mask 11 is firmly held on the wafer 12. Therefore, it is possible to prevent the metal mask 11 from warping due to its own weight, which has occurred conventionally, and to prevent solder from adhering to unnecessary portions.

Further, since the magnet 10 has an aggregate structure of magnets having different magnetic poles as described above, the lines of magnetic force that draw an arc-shaped locus on the outer portion of the magnet 10 like the conventional magnet 1 (see FIG. 6) not exist. Therefore, even if the size of the magnet 10 is made close to the size of the metal mask 11, the metal mask 11 does not shift due to the magnetic force of the magnet 10, and the metal mask 11 can be positioned with high accuracy.

FIG. 4 shows a state where the wafer 12 on which the metal mask 11 is mounted as described above is mounted on a solder vapor deposition device (not shown). In the figure, reference numeral 15 denotes a holder. The members of the magnet 10, the metal mask 11, the wafer 12, and the cooling copper plate 13 which are unitized by the attractive force of the magnet 10 are collectively attached to the holder 15. At this time, the cooling copper plate 13 is configured to be in contact with the holder 15,
The holder 15 is provided with a cooling pipe 16. Therefore, during the vapor deposition process, the wafer 12 holds the cooling copper plate 13 and the holder 1.
5, Cooled by the cooling pipe 16 and the like.

When the wafer 12 and the like are mounted on the solder vapor deposition apparatus, the apparatus is started up and vapor deposition of indium (In) solder is performed to a height of 40 μm. FIG. 5 shows the wafer 12 after the vapor deposition processing. According to the experiment of the present inventor, by using the magnet 10 having a plurality of magnetic poles formed thereon, the solder bumps 17 are formed at the same pitch of 80 μm and 150 μm in diameter as the simulation pattern formed on the metal mask 11. I was able to. At this time, the magnet 10
As a result, the metal mask 11 is firmly and accurately held on the wafer 12, so that no solder is deposited on unnecessary portions, and the solder bumps 17 can be formed accurately at predetermined positions on the wafer 12. .

In the above-described embodiment, the configuration in which the magnetic poles are arranged in stripes as shown in FIG. 2 is shown as the magnetization pattern of the magnet 10, but the magnetization pattern is not limited to this. Alternatively, another configuration may be used as long as a plurality of magnetic circuits are formed on the suction side surface of the metal mask 11.
For example, a magnetized pattern having a configuration in which a plurality of magnetic poles different from each other are arranged radially may be used, or a magnetized pattern having a spiral shape may be used.

[0025]

As described above, according to the present invention, since the magnet has an aggregate structure of magnets having different magnetic poles alternately, the lines of magnetic force coming out of one magnetic pole pass through the mask made of the magnetic substance and are adjacent to each other. Enter another magnetic pole. That is, since each magnetic pole and the mask form a magnetizing circuit, the mask can be firmly held on the wafer by the magnetic force of the magnet.

Also, since a plurality of magnetic circuits are formed corresponding to the number of magnetic poles and formed at various locations on the magnet, a mask can be held at various locations where the magnetic circuit is formed.
This also allows the mask to be held firmly on the wafer.

Further, even if the size of the magnet is made close to the size of the mask, the metal mask does not shift due to the magnetic force of the magnet, and the metal mask can be positioned with high accuracy.

[Brief description of the drawings]

FIG. 1 is a view for explaining the structure and operation of a mask fixing magnet according to one embodiment of the present invention.

FIG. 2 is a plan view of the mask fixing magnet shown in FIG.

FIG. 3 is a view for explaining a step of fixing a metal mask to a wafer in the solder bump forming method according to one embodiment of the present invention.

FIG. 4 is a view for explaining a step of performing solder vapor deposition in the solder bump forming method according to one embodiment of the present invention.

FIG. 5 is a view showing a solder bump formed by a solder bump forming method according to one embodiment of the present invention.

FIG. 6 is a view showing an example of a conventional method for fixing a metal mask to a wafer.

FIG. 7 is a view showing an example of a conventional method of fixing a metal mask to a wafer.

[Explanation of symbols]

 10 Magnet 11 Metal mask 12 Wafer 17 Solder bump

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-69936 (JP, A) JP-A-63-156343 (JP, A) JP-A-4-4742 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H01L 21/60

Claims (3)

(57) [Claims] 1. A mask formed of a magnetic material and having a predetermined pattern formed thereon is disposed on a surface of a substrate on which solder bumps are formed, and a magnet is formed on a surface of the substrate different from the surface on which solder bumps are formed. In a solder bump forming method of disposing and vapor-depositing solder on the mask in a state where the mask is held by the magnetic force of the magnet, and forming a solder bump, a plurality of magnetic poles are provided on a surface on which the mask is adsorbed. Wherein the mask is attracted by the magnet having the plurality of magnetic poles. Wherein disposed on the other side of the substrate mask having a predetermined pattern is composed is formed of a magnetic material on one surface is placed, the mask in the mask fixing magnet that attracted by the magnetic force, the magnetic poles Are different from each other, and the mask is
Characterized in that different magnetic poles are alternately arranged on the surface to be masked. 3. The magnet for fixing a mask according to claim 2, wherein the plurality of magnetic poles are formed by alternately forming magnetic poles different in a stripe shape.