JPH1187902A - Method for forming bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To omit an exclusive use carrier jig and a cutting step by transferring mounting of solder balls, then once winding a base plate on a reel, increasing an adhesive force of fixing liquid to a degree larger than a product of various accelerations received by the balls, and inserting a spacer between base plates, thereby preventing a mechanical contact. SOLUTION: A placing head 5 for vacuum-sucking a solder ball 1 is urged to a flexible base plate 3 connected to a semiconductor chip 11 for placing the ball 1 on a pad 4 on the plate 3 by an adhesive force of flux 2. The force of the flux 2 is larger than the product of mass and the acceleration of the ball 1, so that the ball 1 does not drop due to impact during conveyance thereafter or to an operator's handling fault. The plate 3 mounted with the ball is wound on a base plate winding reel. In this case, a spacer is wound between the pad 4 and the plate 3, so that the ball 1 is not brought into contact with other members for causing the ball 1 to be displaced or dropped to prevent it from being brought into mechanical contact with the ball 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BGA (Ball Grid Array) in a semiconductor package.
y) Package, CSP (Chip Size Pac)
kage or Chip Scale Package
e) A conductive ball typified by a solder ball or a gold ball is mounted on a package (hereinafter simply referred to as a package) using a solder ball as a connecting material with a mounting board,
The present invention relates to a method for forming a connection projection called a bump.

[0002]

2. Description of the Related Art In recent years, a semiconductor package substrate or the like used for an LSI having many input / output terminals is provided with a plurality of terminal electrodes arranged in a lattice or a staggered lattice on the lower surface thereof, and a circuit board corresponding to the terminal electrodes is provided. A structure in which electrodes are connected by bumps is adopted.

[0003] As a method of forming a solder bump, Japanese Patent Application Laid-Open No. Hei 8-115916 and Japanese Patent Application Laid-Open No. 9-063737 are disclosed.
There are those disclosed in Japanese Patent Publication No. In this known example,
The flux is supplied to the solder ball by immersing the solder ball sucked in vacuum by the suction jig in a flux liquid tank, and the solder ball is transferred onto a pad (connection terminal) formed on the semiconductor package substrate, and the flux is transferred to the solder ball. A technique for forming a solder bump by heating (reflowing) an electronic circuit board on which a solder ball is adhesively held (temporarily fixed) by an adhesive force and an apparatus for transferring and mounting a solder ball on a semiconductor package substrate are disclosed. Further, for heating, a reflow furnace that is very commonly distributed in the market may be used.

[0004]

However, the above conventional method has the following problems.

Recently, tape-shaped flexible substrates have been widely used for semiconductor package substrates. FIG. 12 shows an example of a semiconductor package using such a flexible substrate. In FIG. 12, 3 is a flexible substrate, 15 is a solder bump, 4 is a pad on which the solder bump 15 is formed, 11 is a semiconductor chip, and 19 is a lead connecting the pad 4 and the semiconductor chip 11. Reference numeral 18 denotes a sealing resin, which fixes the semiconductor chip 11 and the flexible substrate 3. Reference numeral 17 denotes a reinforcing plate having a square shape.

In the case of a semiconductor package using such a flexible substrate, in order to use a conventional manufacturing apparatus for a non-flexible substrate when forming bumps, the semiconductor package substrate must be shaped like a strip. Pre-cut into small units. Then, in order to cut the semiconductor package substrate into the minimum unit in the final step of assembling the semiconductor package after the formation of the bumps, two cutting steps are required. For this reason, there is a problem that the cost of bump formation is high.

Further, in order to put the semiconductor package substrate cut into strips into a solder ball mounter, which is a device for transferring and mounting solder balls, or a reflow furnace for heating,
It is necessary to facilitate handling by fixing the package substrate having low rigidity and difficult handling to a dedicated carrier jig having high rigidity. High dimensional accuracy is required for the dedicated carrier jig, and fixing work to the dedicated carrier jig is mainly performed manually. As described above, conventionally, a number of expensive dedicated carrier jigs corresponding to the production volume of the product were prepared, and the work of fixing the semiconductor package substrate cut into strips to the dedicated carrier jig was performed. There was a problem that the cost was high.

In order to solve such a problem, the solder ball mounter and the reflow furnace are modified so as to continuously supply a tape-shaped semiconductor package substrate, and then the solder ball mounter and the reflow furnace are integrated. It is conceivable that the semiconductor package substrate on which the transfer mounting of the solder balls is completed is directly put into a reflow furnace, so that a dedicated carrier jig and a substrate cutting step for forming bumps are not required.

However, according to this method, when a trouble occurs in the solder ball mounter for transferring and mounting the solder ball and the apparatus is stopped, the semiconductor package substrate which is being mounted in the reflow furnace and exposed to high temperature is rescued. It is difficult. In general, the time required for transferring and mounting the solder ball varies depending on whether or not a retry operation is performed. However, the variation in the heating time depends on the thermal energy applied to the solder ball and the semiconductor connected to the semiconductor package substrate. , Which leads to a change in the total amount of bumps, which causes defective bump formation. For this reason, fluctuations in the heating time during bump formation are not allowed, and integration of the solder ball mounter and the reflow furnace is impossible due to the nature of both devices, and has not been realized at present.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide a bump forming method for a tape-shaped semiconductor package substrate that does not use a dedicated carrier jig and does not require a substrate cutting step for forming a bump.

[0011]

In order to achieve the above-mentioned object, a tape-shaped semiconductor package substrate is supplied to a solder ball mounter by a reel, and after the solder ball is transferred and mounted, the substrate is once wound on a reel. I decided that. To prevent the solder balls that are transferred and temporarily fixed from falling, the adhesive force of the fixing liquid such as flux used when transferring and mounting the solder balls is determined by the product of the mass of the solder balls and the various accelerations that the solder balls receive during transport. I made it bigger.
Furthermore, when the tape-shaped semiconductor package substrate is wound on a reel, a spacer is inserted between the substrates so that the solder balls in the temporarily mounted state, which are transferred and temporarily fixed, do not shift due to mechanical contact. Contact was prevented.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the same reference numerals in the drawings denote the same parts, and thus repeated description may be omitted. Also, a bump forming method using a solder ball as an example of a conductive ball and a flux as an example of a fixing solution will be described. However, the present bump forming method is not limited to this combination. A metal ball other than the ball, or a ball covered with a conductor may be used. Further, as a fixing liquid instead of the flux, an adhesive containing a conductive paste and a solder paste may be used.

FIG. 1 is a diagram showing a basic flow of the bump forming method of the present invention. In FIG. 1, reference numeral 6 denotes a substrate take-up reel on which a flexible substrate which becomes a semiconductor package after cutting in a final step is wound, and 16 denotes a semiconductor package. First, at a, a semiconductor chip is connected to a flexible substrate, and this is sealed with a resin. Subsequently, the flexible substrate is wound on the substrate take-up reel 6 as shown in FIG. Next, at c, the flexible substrate is unwound from the substrate take-up reel 6 and solder balls are mounted. The flexible substrate on which the solder balls are mounted is wound on the substrate take-up reel 6 as shown at d. Next, in e, the flexible substrate on which the solder balls have been mounted is paid out from the substrate take-up reel 6 and heated. A bump is formed on the flexible substrate by heating and cooling, and the bump is wound on a substrate take-up reel 6 as shown by f. Thereafter, the semiconductor substrate 16 is completed by washing and cutting the flexible substrate. In the cleaning, it is possible to perform the cleaning while being wound on the substrate take-up reel 6, or the flexible substrate may be taken out from the substrate take-up reel 6 and cleaned. Further, depending on the customer's request, the product may be shipped in a state of being wound on the substrate take-up reel 6 without being cut, and may be cut by the customer if necessary.

In the following, the flow shown in FIG. 1 will be described in more detail. 2 to 4 show the solder ball mounting method shown in FIG. 1c. In each figure, 1 is a solder ball, 2 is a flux, 3 is a flexible substrate, 4 is a pad formed on the flexible substrate, 5 is a mounting head, and 11 is a semiconductor chip.

FIG. 2 shows a method for supplying the solder balls 1 to the mounting head 5. The solder ball 1 is placed in a ball container whose bottom surface is a mesh sheet, and is blown up by an upward air flow through the mesh sheet. A mounting head 5 is located above the ball container, and vacuum sucks the solder balls 1 into a number of ball suction ports by vacuum suction.

FIG. 3 shows a method of supplying a flux to the solder ball 1 vacuum-adsorbed. The flux 2 is spread on a flux plate in advance. Solder ball 1
Is brought into close contact with the flux surface on the flux plate. Thereby, the flux 2 is supplied to each solder ball 1.

FIG. 4 shows a method for mounting the solder balls 1 on the flexible substrate 3. The mounting head 5 that vacuum-adsorbs the solder balls 1 approaches the flexible substrate 3 to which the semiconductor chip 11 is connected, and presses each solder ball 1.
By interrupting the vacuum suction and opening the atmosphere or applying a positive pressure, the solder ball 1 is mounted on the pad 4 on the flexible substrate 3 by the adhesive force of the flux 2. When the solder ball 1 is not correctly mounted on the pad 4, a pin for projecting each solder ball 1 and a mechanism for pushing out the pin are provided inside the mounting head 5, and by using this, a reliable solder ball 1 is formed. Mounting can be realized.

The flux 2 can be supplied to the pad 4 by a general screen printing method, a pin transfer method, or dispensing before the solder ball 1 is mounted. The adhesive strength of the flux 2 is such that the solder ball 1 does not drop due to a shock during subsequent transportation or poor handling of an operator.
Must be larger than the product of the mass of the solder ball 1 and the acceleration that can be received after the solder ball 1 is mounted on the flexible substrate 3. The required flux adhesion value varies depending on the equipment used and the solder ball size.
By selecting 00 gf or more, it is possible to completely prevent the solder balls from falling under a general environment. In addition,
At this time, the adhesive strength of the flux 2 may be measured by a paste adhesive tester manufactured by Malcolm Co., Ltd.

Here, the flexible substrate 3 in the present embodiment is shown in FIG. 10 and FIG. The flexible substrate 3 is made of a material having excellent heat resistance and electrical insulation such as a polyimide material, and metal wirings and pads 4 are formed thereon. Reference numeral 12 denotes a semiconductor chip connection portion, and reference numeral 13 denotes a perforation used for feeding the flexible substrate 3. The flexible substrate 3 shown in FIG. 10 is an example in which one semiconductor chip connecting portion 12 is arranged in the width direction, and the flexible substrate 3 shown in FIG. This is an example in which two are arranged. The periphery of the pad 4 forming portion on the flexible substrate 3 in FIGS. 10 and 11 is an outer edge portion to be finally cut and removed.

In FIG. 1C, the flexible substrate 3 on which the solder balls 1 are mounted is continuously wound on a substrate take-up reel 6 as shown in FIGS. 1D and 5. At this time, the solder ball 1 is brought into contact with another member, so that the position is shifted from above the pad 4 or the solder ball 1 is
In order to prevent the solder ball 1 from falling off, the spacer tape 7 is wound between the flexible substrates 3 to prevent mechanical contact with the solder balls 1. The spacer tape 7 is wound around a spacer tape reel 8, and sends out the spacer tape 7 in synchronization with the rotation of the substrate take-up reel 6. FIG. 6 is a perspective view showing a part of the spacer tape 7. Also, FIG. 7 is a partial cross-sectional view taken along AB of FIG. 5 showing a state in which the flexible substrate 3 on which the solder balls 1 are mounted and the spacer tape 7 are alternately wound on the substrate take-up reel 6. Shown in As described above, the spacer tape 7 has a width substantially equal to that of the flexible substrate 3, and is positioned on the flexible substrate 3 at the outer edge portion of the flexible substrate 3, avoiding the solder balls 1. The spacer tape 7 has a large number of protrusions 9 on both sides thereof, and has an "H" -shaped cross section. The height of the protrusion 9 is determined by the height of the solder ball 1 or the flexible substrate 3 of the semiconductor chip 11 connected to the opposite surface of the flexible substrate 3.
It is higher than the amount of protrusion from the surface. Therefore, the solder balls 1 on the flexible substrate 3 of the spacer tape 7 do not come into contact with other members, and the solder balls 1
It is possible to prevent the pad 4 from slipping or falling off.
It should be noted that the material of the spacer tape 7 may be an inexpensive plastic or the like and is not exposed to a high temperature, so that it can be used repeatedly. If the generation of static electricity is a concern, conductive plastic can be used as the material.

In FIG. 1d, the flexible substrate 3 wound on the substrate take-up reel 6 is continuously heated. In the heating step shown in FIG. 9, after the solder balls 1 are mounted, the flexible substrate 3 is unwound from the substrate take-up reel 6 on which the flexible substrate 3 and the spacer tape 7 have been wound, and a heating furnace such as a reflow furnace is used. Then, the solder ball 1 is melted by heating. Then, the solder ball 1 melted by being allowed to cool is solidified, and a bump is formed. FIG.
As shown in FIG.
The spacer tape 7 that has been wound up together with the flexible substrate 3 when being unwound from the reel is wound up by a spacer tape reel 8. The flexible substrate 3 on which bumps have been formed and which has come out of the heating furnace 10 may be taken up again on a substrate take-up reel or cut at regular intervals in accordance with the convenience of the subsequent step. In the embodiment, as shown in FIGS. 1F and 9, another substrate take-up reel 6 b
The example which wound up was shown. If the formed bumps or the scratches on the flexible substrate 3 pose a problem, it is effective to use the spacer tape 7b also when winding the substrate tape on the substrate take-up reel 6b. FIG. 8 is a partial cross-sectional view of the flexible substrate 3 on which the bumps 15 have been formed wound onto another substrate take-up reel 6b after the bumps are formed, which is cut by CD in FIG.
Shown in This spacer tape 7b is basically the same as that used after mounting the solder balls 1 on the flexible substrate 3, but the height of the projections 9 is greater than the height of the bumps 15 formed. Need to be.

The wound flexible substrate 3 is loaded into a batch-type washing machine while being wound on the substrate take-up reel 6b, if necessary, to remove residuals such as flux.

In addition, since the flexible substrate 3 is cleaned immediately after the bumps are formed by heating, a commercially available continuous cleaning device can be inserted immediately after the heating furnace 10 shown in FIG. . Further, as shown in FIGS. 1f, g and h, it is also possible to pay out the flexible substrate 3 from the substrate take-up reel 6, continuously wash it, and then take it up again to the substrate take-up reel 6. . In these cases,
In any case, the flexible substrate 3 is cut into small units after cleaning. By this cutting, the outer edge of the flexible substrate 3 with which the protrusion 9 of the spacer tape has contacted is cut and removed.

Conversely, it is also conceivable that the flexible substrate after the completion of the bump formation is cut into small units, and then the residue such as flux is washed by a batch type washing apparatus.

According to the present embodiment, the problems in the conventional bump formation are solved, and a tape-shaped semiconductor package substrate does not require a dedicated carrier jig and requires a substrate cutting step for bump formation. A bump forming method can be realized.

[0026]

According to the present invention, bump formation on a tape-shaped flexible substrate widely used as a semiconductor package substrate can be performed at a low cost without using a cutting step for bump formation or using a dedicated carrier jig. Can be realized. Moreover, modification of a general-purpose solder ball mounter or reflow furnace can be minimized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a bump formation flow of the present invention.

FIG. 2 is a partial cross-sectional view showing a method of vacuum-adsorbing a solder ball to a mounting head.

FIG. 3 is a partial cross-sectional view illustrating a method of supplying a flux to a solder ball vacuum-adsorbed to a mounting head.

FIG. 4 is a partial cross-sectional view illustrating a method of mounting a solder ball on a flexible substrate.

FIG. 5 is a diagram illustrating a method of winding a flexible substrate after mounting a solder ball;

FIG. 6 is a perspective view showing a part of the spacer tape.

FIG. 7 is a cross-sectional view showing a state where the flexible substrate after mounting the solder balls is wound on a substrate winding reel together with a spacer tape.

FIG. 8 is a cross-sectional view showing a state where a flexible substrate on which bumps have been formed and a spacer tape have been wound on a substrate take-up reel.

FIG. 9 is a diagram illustrating a method of forming a bump by heating a flexible substrate on which solder balls are mounted.

FIG. 10 is a diagram showing an example of a flexible substrate.

FIG. 11 is a diagram showing another example of a flexible substrate.

FIG. 12 is a diagram illustrating an example of a semiconductor package using a flexible substrate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solder ball, 2 ... Flux, 3 ... Flexible board, 4 ... Pad, 5 ... Mounting head, 6 ... Board take-up reel, 7 ... Spacer tape, 8 ... Spacer tape reel, 9 ... Projection, 10 ... Heating Furnace, 11 semiconductor chip, 1
2 ... Semiconductor chip connection, 13 ... Perforation,
14 solder ball mounter, 15 bump, 16 semiconductor package, 17 reinforcing plate, 18 sealing resin, 19
... lead.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kosuke Inoue 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside of Hitachi, Ltd. No. 1 In the Semiconductor Division, Hitachi, Ltd. 5-22-1, Hitachi Co., Ltd. SII Systems Co., Ltd. (72) Inventor Junichi Suzuki 3-3-3, Fujibashi, Ome-shi, Tokyo 2 Within Hitachi Tokyo Electronics Co., Ltd.

Claims (12)

[Claims] 1. A bump forming method comprising: temporarily fixing a conductive ball on a substrate with a fixing liquid such as a flux, a solder paste or an adhesive containing conductive particles, and then adding a heating step. A method for forming a bump, comprising: winding a substrate on which conductive balls are temporarily fixed after a step of temporarily fixing balls on a reel. 2. The bump forming method according to claim 1, wherein
A method of forming a bump, comprising: inserting a spacer between substrates when winding the substrate on which the conductive balls are temporarily fixed onto a reel. 3. The bump forming method according to claim 2, wherein
A method for forming a bump, comprising separating the substrate and the spacer from the wound reel and supplying the substrate to a heating step. 4. The bump forming method according to claim 3, wherein
A method of forming a bump, comprising winding the substrate around a reel after a heating step. 5. The bump forming method according to claim 4, wherein
After the heating step, a spacer is inserted between the substrates when the substrate is taken up on a reel. 6. The bump forming method according to claim 4, wherein
After the heating step and before winding the substrate on a reel,
A method for forming a bump, comprising cleaning the substrate. 7. The bump forming method according to claim 4, wherein
A method for forming a bump, comprising washing the substrate wound on a reel after the heating step. 8. The bump forming method according to claim 3, wherein
A method of forming a bump, comprising cutting the substrate into small units after a heating step. 9. The bump forming method according to claim 8, wherein
A method of forming a bump, comprising washing the substrate after cutting it. 10. The bump forming method according to claim 2, wherein the cross-sectional shape of the spacer is substantially "H", and the depth of the concave portion facing the conductive particles is not less than the diameter of the conductive ball. Bump forming method. 11. The bump forming method according to claim 5, wherein the cross-sectional shape of the spacer is substantially "H", and the depth of the concave portion facing the bump formed in the heating step is not less than the height of the bump. A method for forming a bump, comprising: 12. A flexible substrate having a semiconductor chip, a lead for connecting to the semiconductor chip, an outer edge for abutting a projection of a spacer tape, and finally removing and cutting the semiconductor chip; and the semiconductor chip and the lead. And a bump formed on a pad at an end of the lead of the flexible substrate, and a reinforcing plate for reinforcing the flexible substrate. Characteristic semiconductor device.