JPH10214839A - Formation of solder bumps - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable easy and reliable formation of solder bumps at low costs. SOLUTION: A printing screen mask 2 having openings 2a, 2a,... arranged in the form of a lattice is applied onto a semiconductor chip 1 having pad area 11a, 11a,... exposed thereon, and then flux 3 is printingly applied on the chip 1 containing a predetermined zone of the pad areas 11a. Then respective openings of a punching die and punches are positioned above the respective pad areas 11a, a solder tape is inserted between the punching die and punches, the punches are moved down to punch out many solder pieces from the solder tape, and then these solder pieces are set on the respective pad areas 11a having the flux 3 printingly coated thereon. And the chip 1 having the solder pieces temporarily set thereon by the adhesive force of the flux 3 is heated at 220 to 230 deg.C to reflow the solder pieces, and thereafter the flux 3 is removed and cleaned to obtain solder bumps arranged in the form of a lattice.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder bump, and more particularly, to a method for forming a solder bump required in a post-process of manufacturing a semiconductor device such as an LSI.

[0002]

2. Description of the Related Art As electronic devices become smaller and have higher performance, the density of semiconductor devices on a plane is increased by increasing the number of terminals and increasing the fine pitch. Along with this, for example, a CSP (Chip Chip) that can be connected to the wiring of the mounting board using solder bumps while maintaining the dimensions of the semiconductor chip substantially.
A semiconductor device having a (ize package) structure has been proposed. Also, for example, an FPBGA (Fine Pitch) is formed on a pad on the surface of a semiconductor chip by forming ball-shaped solder bumps in a grid pattern at a fine pitch to serve as external connection electrodes.
Ball Grid Array) is often adopted. To form a solder bump on a pad on the surface of a semiconductor chip, a solder tape punching method, a solder ball mounting method, or the like has been conventionally used.

[0003] Solder tape punching is a method of punching a solder piece from a thin solder tape using a fine punch and a die, and placing the solder piece on a pad of a semiconductor chip to which flux has been applied in advance. In this method, a semiconductor bump is formed by heating a semiconductor chip to a temperature equal to or higher than the melting point of solder. In the solder ball mounting method, after a large number of solder balls are collectively placed on a pad of a semiconductor chip to which flux has been applied in advance, using a special jig for temporarily sucking the large number of solder balls, This is a method of forming a solder bump by heating a semiconductor chip to a temperature equal to or higher than the melting point of solder.

[0005] In the above two methods, as shown in FIG. 5, the flux 101 is applied to the semiconductor chip 1 including the respective pads 102 a by screen printing or spin coating.
02 is applied over the entire surface. However, when the flux is applied to the entire surface, especially at a fine pitch,
When trying to form a large number of small solder bumps, the amount of flux increases more than necessary, and the flux flows during reflow heating, so that solder pieces (solder balls) also move and the pad There is a problem that the product is deviated from the position, or is absorbed by an adjacent solder bump, thereby causing a defective product. Therefore, a method as described in JP-A-6-124954 has been proposed. In this method, as shown in FIG. 6, a screen having a number of openings corresponding to each pad 102a of the semiconductor chip 102 is prepared, and each opening of the screen is made to correspond to each pad 102a.
After the alignment, the flux 101 is applied by printing using a screen.

[0005]

However, in the method described in the above-mentioned publication, since it is necessary to perform screen alignment with high accuracy, complicated operations are required, and the number of steps is increased and the cost is increased. There is.

The present invention has been made in view of the above circumstances, and has as its object to provide a low-cost, easy and reliable method for forming solder bumps.

[0007]

According to a first aspect of the present invention, there is provided a semiconductor device manufacturing method comprising the steps of: providing an external connection on an electrode pad provided on a semiconductor substrate in a subsequent step; A method for forming solder bumps as electrodes, wherein a flux is applied to the electrode pads by using a screen mask having a large number of openings scattered regularly or irregularly and two-dimensionally. A flux application step of printing and applying, and a solder temporary attachment step of temporarily attaching a flaky or spherical solder on the electrode pad by the adhesive force of the flux printed and applied to the electrode pad in the flux application step, The semiconductor substrate on which the solder is temporarily attached in the solder temporary attachment step is heated above the melting point of the solder, so that the It is characterized in that it consists of a reflow process to fix the I.

According to a second aspect of the present invention, there is provided the method of forming a solder bump according to the first aspect, wherein in the solder temporary attaching step, a tape-shaped solder is punched into a shape corresponding to the electrode pad. The punched-out solder is landed on the electrode pad on which the flux is printed and applied, so that the solder is temporarily attached by the adhesive force of the flux.

Further, the invention according to claim 3 is the method for forming a solder bump according to claim 1 or 2, wherein the arrangement pitch of the plurality of openings is a diameter or a predetermined length of the electrode pad. It is characterized in that it is set smaller than the dimensions.

[0010]

According to the structure of the present invention, in the flux applying step, the flux is printed and applied on the semiconductor substrate provided with the electrode pads using a screen mask having a large number of scattered openings. Since the flux is not applied to the entire surface on the semiconductor substrate, the amount of the flux becomes larger than necessary, and the flux moves during heating in the reflow process, causing the solder to move out of the position of the electrode pad. In addition, there is no possibility of being absorbed by the adjacent solder bumps. Therefore,
Since the solder bumps can be reliably formed on the electrode pads, the yield can be improved and a highly reliable semiconductor device can be manufactured. In addition, the flux can be applied to a predetermined area on each electrode pad by applying the screen mask to the semiconductor substrate without precise alignment, so that the solder bumps can be formed easily and reliably at low cost. Can be formed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The description will be specifically made using an embodiment. First Embodiment FIGS. 1 to 3 are process diagrams for explaining a method of forming a solder bump according to a first embodiment of the present invention. In the method of forming a solder bump in this example, for example, a solder bump as an external connection electrode used when connecting a semiconductor device having a CSP structure to a wiring of a mounting board is formed at a fine pitch on a pad on the surface of a semiconductor chip. This is the preferred method for use in such cases. In the semiconductor device of this example, as shown in FIG. 3 (i), substantially circular pads 11a, 11a,... Formed on the surface of a semiconductor chip 1 on which an integrated circuit such as an LSI having a CMOS structure is formed. Solder bumps 8b, 8b, ...
Are joined together. FIG. 1 (a),
As shown in (b), the semiconductor chip 1 is covered with an insulating layer 12 except for each pad portion 11a on the surface of the conductor layer 11. The solder bumps 8b are arranged in a grid at a pitch of about 500 μm.

First, as shown in FIG.
Prepare Here, the diameters of the pad portions 11a, 11a,... Are approximately 180 μm, and are arranged in a grid at a pitch of approximately 500 μm. Next, as shown in FIG. 1C, a printing screen mask 2 having substantially rectangular openings 2a, 2a,. here,
The openings 2a, 2a,... Have a size of about 120 μm square and are arranged in a lattice at a pitch of about 200 μm.
The screen mask 2 is, for example, a stainless steel mesh member covered with a lacquer or the like except for the openings 2a.

Next, as shown in FIG. 1D, the squeegee 4 is moved from above the screen mask 2 so as to press the flux 3 so that the flux is applied to a position directly below each opening 2 a on the semiconductor chip 1. 3 is applied. As a result, as shown in FIGS. 2E and 2F, each of the pad portions 11a has a flux 3 of 10 to 3 in a substantially 1/4 region.
It is applied with a thickness of 0 μm. Next, screen mask 2
After the removal of the openings 5a, 5a, 5a, 5a, 5a,
, And the openings 5a, 5a,
, Respectively, are inserted into fine projections 6a, 6a,.
And a punch 6 having the above-mentioned configuration are arranged on the semiconductor chip 1 on which the flux 3 is applied. At this time, the punching die 5
Each punch 5a is positioned so as to be directly above each pad 11a of the semiconductor chip 1, and the punch 6 is arranged such that each protrusion 6a is disposed directly above each opening 5a. Positioning is performed using the guide 7. Here, each protrusion 6a
Has a circular tip with a diameter of approximately 250 μm.

Then, a solder tape 8 is inserted between the punching die 5 and the punching punch 6, the punching punch 6 is lowered, and each projection 6a is pierced into the soldering tape 8, and each opening of the punching die 5 is opened. 5a, the solder pieces 8a, 8a,... Are punched out of the solder tape 8 and landed on the pads 11a, 11a,. Here, the solder tape 8 is a eutectic alloy of tin and lead, and has a thickness of about 100 μm. As a result, as shown in FIG. 3H, a solder piece 8a having a thickness of about 100 μm and a diameter of about 250 μm and having a circular cross section is temporarily attached to each pad portion 11a by the adhesive force of the flux 3. You.

Next, the semiconductor chips 1 to which the solder pieces 8a, 8a,... Are temporarily attached are heated at 220 to 230 ° C. to reflow the solder pieces 8a, 8a,.
Using a washing solution that dissolves flux 3, flux 3
Is removed and, as shown in FIG. 1 (i), a diameter of about 200 μm fixed to the pads 11a, 11a,.
Of the solder bumps 8b, 8b,. Thus,
Arranged in a grid at a pitch of about 500 μm, for example,
A semiconductor device having 200 solder bumps 8b, 8b,... Is obtained. These solder bumps 8b are used as external connection electrodes for connecting the semiconductor device to the wiring of the mounting board.

The semiconductor devices on which the solder bumps 8b, 8b,... Are formed are manufactured in three lots in a lot size of 300 pieces, and are inspected. As a result, during heating for reflow, the solder becomes the pad portions 11a, 11a,. , And the number of defects absorbed by adjacent solder bumps is 1/10
It was found that it was reduced to.

According to the above configuration, the openings 2a, 2a,.
Pad portion 11 using screen mask 2 having
Since the flux 3 is printed and applied on the semiconductor chip 1 provided with the a, 11a,..., the flux 3 is not applied on the entire surface of the semiconductor chip 1;
Of the solder pieces 8a, 8a,.
Flux during heating for reflow after temporary attachment of 3
Due to the flow of the solder, the solder moves and the pad portions 11a, 1
1a,... And are not absorbed by adjacent solder bumps. Therefore,
Since the solder bumps 8b can be reliably formed on the pad portions 11a, the yield can be improved and a highly reliable semiconductor device can be manufactured. Further, the flux 3 can be applied to a predetermined area on each pad portion 11a by applying the screen mask 2 to the semiconductor chip 1 without performing precise alignment, so that the cost can be reduced easily and reliably. , A solder bump can be formed.

Second Embodiment FIG. 4 is a plan view for explaining a method of forming solder bumps according to a second embodiment of the present invention. The second embodiment is largely different from the first embodiment in that, as shown in FIG. 4, a screen mask in which circular openings 9a, 9a,. 9
This is the point that is used. Also, the area of each opening 9a is
Due to the adhesive force of the flux 3 applied through the opening 9a, each solder piece 8a is temporarily attached, and each pad 1
The minimum size required to be able to be joined to 1a. Except for this, the configuration is substantially the same as that of the first embodiment, and the description thereof is omitted.

According to the above configuration, the flux 3 during heating is
By this flow, the movement of the solder to be displaced from the position of each pad portion 11a or being absorbed by an adjacent solder bump, and the resulting semiconductor device can be more reliably prevented from becoming defective.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like that do not depart from the gist of the present invention. Is also included in the present invention. For example, in the above-described embodiment, a case has been described in which a screen through which flux can pass through only a necessary portion is used as a screen mask. However, a metal mask having openings in a metal foil may be used. Also, to temporarily attach solder to the pad,
The method is not limited to a method in which a solder piece is punched out from a solder tape and landing is performed, but a method in which a solder ball is mounted on a pad using a dedicated jig may be used. The shape of the opening of the screen mask is not limited to a square or a circle, but may be another polygon or an arbitrary shape. Also, the shapes of the individual openings need not necessarily be the same.

[0021]

As described above, according to the structure of the present invention, in the flux application step, a screen mask having a large number of scattered openings is used to cover a semiconductor substrate provided with electrode pads. Because the flux is applied by printing, the flux is not applied to the entire upper surface of the semiconductor substrate, so that the amount of the flux becomes larger than necessary, and the flux moves at the time of heating in the reflow process, so that the solder moves and the electrode moves. It does not come off the pad position or be absorbed by the adjacent solder bump. Therefore, since the solder bumps can be reliably formed on the electrode pads, the yield can be improved and a highly reliable semiconductor device can be manufactured. In addition, the flux can be applied to a predetermined area on each electrode pad by applying the screen mask to the semiconductor substrate without precise alignment, so that the solder bumps can be formed easily and reliably at low cost. Can be formed.

[Brief description of the drawings]

FIG. 1 is a process chart for explaining a method of forming a solder bump according to a first embodiment of the present invention.

FIG. 2 is a process chart for explaining a method of forming the solder bump.

FIG. 3 is a process chart for explaining a method of forming the solder bump.

FIG. 4 is a plan view for explaining a method of forming solder bumps according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining a conventional technique.

FIG. 6 is an explanatory diagram for explaining a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor chip (semiconductor substrate) 11a Pad part (electrode pad) 2 Screen mask 2a Opening part 3 Flux 7 Solder tape 7a Solder piece 7b Solder bump

Claims (3)

[Claims] 1. A method for forming a solder bump as an electrode for external connection on an electrode pad provided in advance on a semiconductor substrate in a later step of a semiconductor device manufacturing process, the method comprising: A flux application step of printing and applying a flux to the electrode pad using a screen mask having a large number of openings scattered regularly and two-dimensionally; and in the flux application step, a flux is applied to the electrode pad by printing. A solder temporary attaching step of temporarily attaching a flaky or spherical solder on the electrode pad by the adhesive force of the flux, and the semiconductor substrate on which the solder is temporarily attached in the solder temporary attaching step is provided by the solder A reflow step of fixing the solder on the electrode pad by heating to a temperature equal to or higher than the melting point of the solder pad. The method of forming the pump. 2. In the solder temporary attaching step, a tape-shaped solder is punched into a shape corresponding to the electrode pad, and the punched solder is landed on the electrode pad on which the flux is printed and applied. 2. The method according to claim 1, wherein the flux is temporarily attached by an adhesive force.
The method for forming a solder bump according to the above. 3. The method according to claim 1, wherein an arrangement pitch of the plurality of openings is set smaller than a diameter or a predetermined length of the electrode pad. .