JP4214127B2 - Flip chip mounting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flipchip mounting method having high connection reliability. <P>SOLUTION: This flipchip mounting method is provided with (a) a process of forming an electrode on a wiring board; (b) process of forming a gold bump on the electrode of a semiconductor chip; (c) process of forming a tin film of a previously decided film thickness on a transfer plate; (d) process of processing the tin film formed in the process c into a previously decided size with the position of the gold bump formed in the process b; (e) process of transferring the processed tin film acquired in the process d on the gold bump acquired in the process b, and formed on the electrode of the semiconductor chip; and process (f) of joining the gold bump of the semiconductor chip acquired in the process e on which the tin film is transferred, on the electrode of the wiring board formed in the process a. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

The present invention relates to a flip chip mounting method of a semiconductor chip using a thermocompression bonding eutectic bonding method, and more particularly to a technique for forming a tin film and transferring the formed tin film to a gold bump of a semiconductor chip.

As one of flip chip mounting methods for semiconductor chips, a technique is known in which gold bumps formed on electrodes of a semiconductor chip and electrodes of a wiring board on which the semiconductor chip is mounted are subjected to tin plating and eutectic bonding. (See Patent Document 1 and Patent Document 2).

A conventional semiconductor chip flip-chip mounting method will be described with reference to FIG.
FIGS. 8A, 8B, 8C, and 8D are diagrams schematically showing an example of a conventional flip chip mounting method for a semiconductor chip in the order of steps.
In FIG. 8, 61 is a wiring substrate such as a glass-impregnated epoxy resin substrate or a ceramic substrate on which an electrode pad 62 for mounting a semiconductor chip is formed, and 63 is a tin plating layer formed on the electrode pad. Reference numeral 71 denotes a semiconductor chip, and gold bumps 72 are formed on the electrode pads.

A method of flip-chip mounting such a semiconductor chip 71 on the wiring board 61 will be described in the order of steps based on FIG.
First, a wiring board is prepared, and electrode pads 62 are formed at positions corresponding to positions where a predetermined circuit pattern (not shown) and the semiconductor chip 71 are mounted.
Is manufactured (FIG. 8A).
Next, tin plating is performed on the surface of the wiring board 61 on which the electrode pads 62 are formed, and a tin plating layer 63 is formed on the electrode pads 62 (FIG. 8B). At this time, a plating resist treatment is performed on the portion not subjected to tin plating, and the plating resist is removed after the plating treatment is completed.

Next, the semiconductor chip 71 is aligned with the mounting position of the wiring board 61 (FIG. 8 (
c)).
Then, the semiconductor chip 71 is mounted on the wiring board 61, and the wiring board 61 and the semiconductor chip 71 are heated while pressing the semiconductor chip 71 against the wiring board 61 in this state. By doing so, the tin plating layer 63 formed on the electrode pad 62 of the wiring substrate 61 and the gold bump 72 formed on the electrode pad of the semiconductor chip 71 are alloyed, and a gold-tin alloy layer is formed at the contact portion between them. 67 is formed, and the semiconductor chip 71 is bonded onto the wiring board 61 (FIG. 8D). Thus, flip chip mounting of the semiconductor chip is completed.
JP 2002-368038 A JP 2002-217232 A

According to these conventional semiconductor chip flip-chip mounting methods, the thickness of the tin plating layer formed on the electrode pads of the circuit board is about 1 μm.
However, in a tin plating layer having a thickness of about 1 μm, the amount of gold-tin alloy formed is small, and it is difficult to ensure sufficient bonding reliability.
Therefore, it is necessary to supply tin by some method in order to obtain an amount of gold-tin alloy that can ensure sufficient bonding reliability.

Therefore, a method has been proposed in which tin or an alloy thereof (for example, solder such as SnAg or SnCu) is supplied in advance by known printing, vapor deposition, an implant method, or the like on the electrode pads of the wiring board or the gold bumps of the semiconductor chip. .
However, with these methods, technical issues such as printability, complicated masking jigs,
There was a problem that cost increases such as the production of mold jigs were unavoidable.

The present invention has been made to solve the above-mentioned problems, and tin is deposited on a transfer plate such as a glass plate by vacuum vapor deposition or the like to form a tin film with a predetermined thickness. Easily bonding reliability by etching to the position and size according to the size, bonding the tin film formed in the predetermined shape onto the gold bump and peeling it from the transfer plate to transfer it to the gold bump side An object of the present invention is to provide a flip-chip mounting method of a semiconductor chip capable of supplying a tin-eutectic amount of gold-tin eutectic.

A flip-chip mounting method according to the present invention is a flip-chip mounting method for mounting a semiconductor chip having gold bumps formed on electrodes on a wiring board, and includes the following steps.
a) A step of forming a tin film having a thickness of 1 to 5 μm on a transfer plate having a thermal expansion coefficient of 15 ppm / ° C. or more by a vacuum deposition method or a sputtering method.
b) A step of processing the tin film formed in step a into small pieces of a tin film having a predetermined size in accordance with the position of the gold bump.
c) The tin film piece processed in step b and the gold bump are aligned, the semiconductor chip and the transfer plate are superposed and pressed, heated to a temperature at which tin does not melt, and ultrasonic vibration is applied. While joining the small pieces of tin film processed into the gold bumps.
d) Tin film pieces processed into the gold bumps by pulling the semiconductor chip away from the transfer plate when the temperature of the transfer plate drops after a predetermined time has elapsed after the application of heating and ultrasonic vibrations has stopped. The process of transferring.
e) A step of bonding the gold bumps of the semiconductor chip onto which the tin film pieces have been transferred in step d to the electrodes of the wiring board.

By using the flip chip mounting method according to the present invention, tin is deposited on a transfer plate of 15 ppm / ° C or higher such as a glass plate by vacuum deposition or the like to form a tin film with a predetermined thickness. Etching to a position and size according to the arrangement of the film , the tin film pieces formed into a predetermined shape are bonded onto the gold bumps by the thermal ultrasonic method , cooled, and then peeled off from the transfer plate. It was decided to transfer to the bump side. That is, the tin film piece is easily transferred to the transfer plate by the residual stress caused by the temperature change based on the difference in thermal expansion coefficient and the ultrasonic vibration between the tin film piece and the transfer plate which occurs almost simultaneously with the joining by the thermal ultrasonic vibration. Therefore, it is possible to supply tin necessary for the gold-tin alloy layer formed at the time of flip chip mounting. Therefore, it is possible to provide a flip chip mounting method of a semiconductor chip with high bonding reliability.

In addition, if a glass plate is used as the transfer plate, it can be used repeatedly as the transfer plate, so that a flip chip mounting method with low manufacturing cost can be provided.

Next, the flip chip mounting method according to the present invention will be described in detail with reference to the drawings.
1 to 7 are diagrams schematically showing an embodiment of a flip chip mounting method according to the present invention.
FIG. 1 schematically shows a process of forming gold bumps on the electrodes of a semiconductor chip, FIG. 2 schematically shows a state in which a tin film is formed on a glass plate, and FIG. It is a figure which shows typically the tin film after the process shape | molded by the predetermined | prescribed magnitude | size at the position corresponding to the gold bump formed on the electrode pad of the semiconductor chip which mounts a tin film.

FIG. 4 is a diagram showing a process of transferring the tin film formed in FIG. 3 to the gold bump formed on the electrode of the semiconductor chip, and FIG. 5 is a diagram showing the process of transferring the tin film formed in FIG. FIG. 6 is a diagram schematically showing a state in which a semiconductor chip is positioned and mounted on a wiring board, and FIG. 7 is a diagram schematically showing the semiconductor chip transferred to a gold bump formed thereon. It is a figure which expands and shows the mode of the joined part after flip chip mounting to a wiring board typically.

Next, the flip chip mounting method according to the present invention will be described with reference to FIGS. In this embodiment, a case where a semiconductor chip in which gold bumps are formed using a gold wire having a diameter of 25 μm is flip-chip mounted on a gold-plated alumina ceramic substrate by a thermocompression eutectic bonding method will be described as an example.

First, the formation of gold bumps will be described with reference to FIG.
As shown in FIG. 1A, a gold wire 10 as a material of a gold bump 18 is a capillary 1 in a thermobonding or ultrasonic thermocompression type wire bonding apparatus (not shown).
1, and the tip portion of the capillary 11 protrudes from the tip of the capillary 11. The length of the protruding portion is a predetermined length.

When thermal energy from a discharge torch (not shown) in the wire bonding apparatus is urged to the protruding end portion of the gold wire 30, the protruding end portion of the gold wire 30 is heated and melted to form the ball 13 by surface tension. Then, as shown in FIG.
As the amount of heating and melting increases, the amount of heat increases and gradually rises in the direction of the tip surface 11a of the capillary 11.

Then, the capillary 11 is lowered in the direction of the electrode pads 17, as shown in FIG. 1 (c), contacting the ball 13 on the electrode pads 17, the spherical distorted spherical slight upper ball 13 .
Here, the ball 13 is pressed by the tip surface 11 a of the capillary 11. By this pressing, as shown in FIG. 1 (d), the ball 13 is formed on the electrode 17 in a substantially hemispherical shape following the shape of the tip end surface 11 a of the capillary 17. Further, when the electrode pad 17 is heated or ultrasonic energy is applied to the capillary 11, the ball 13 is pressed and fixed to the electrode pad 17.

When the ball 13 is fixed to the electrode pad 17, as shown in FIG. 1 (e), the capillary 11 is raised in a direction away from the electrode pad 17 in a state where the gold wire 10 to free the ball 13 electrode pads 17 The gold wire 10 fixed to is relatively fed out from the capillary 11. At this time, the length of the protruding portion of the gold wire 10 from the capillary 11 is controlled to be a predetermined length from the surface of the electrode pad 13.

When the gold wire 10 is protruded by a predetermined length, the capillary 11 is raised with a clamper (not shown) attached to the capillary 11 holding the gold wire 10. With the increase of the capillary -11 gold wire 10 is torn off as shown in FIG. 1 (f). Then, gold bumps 18 are formed by the balls 13 that remain fixed on the electrode pads 17. The above gold bump forming method is repeated, and gold bumps 18 are sequentially formed on a predetermined number of electrode pads 13. The gold bump 18 has a bowl shape with a bump diameter of 80 to 90 μm and a bump height of 80 to 90 μm.

Next, formation of a tin film will be described.
First, a transfer plate 21 for forming a tin film is prepared. This transfer plate is made of glass or inorganic material having a coefficient of thermal expansion of 15 ppm / ° C. or more so that the tin film formed on the transfer plate is easily peeled off when transferred to a gold bump formed on an electrode of a semiconductor chip to be described later. Use a base plate of metal or organic resin. For example, glass that can be mirror polished (thermal expansion coefficient of 15 ppm / ° C or more), stainless steel (SUS30
4, thermal expansion coefficient 17ppm / ° C) and copper alloys (thermal expansion coefficient 15ppm / ° C or more)
A copper foil is pasted on a metal such as, and an organic resin or adhesive whose adhesiveness is lowered at 150 ° C. or higher. Here, the coefficient of thermal expansion is set to 15 ppm / ° C. or higher when a semiconductor chip, which will be described later, is lifted and separated from the transfer plate, a small piece of tin film formed on the transfer plate is cooled at room temperature. This is because it can be easily peeled off from the transfer plate by thermal stress.

Here, a glass substrate is used as the transfer plate. At this time, a metal film as a base for forming a tin film is not formed on the transfer plate. This is for facilitating peeling when the formed tin film is transferred to a gold bump formed on an electrode of a semiconductor chip to be described later.
A tin film 22 is formed on the transfer plate 21 by a known vacuum deposition method or sputtering method (FIG. 2). The film thickness of this tin film shall be 1-5 micrometers. This is a sufficient amount when a semiconductor chip and a wiring substrate are eutectic bonded to a gold-tin eutectic in flip-chip mounting, which will be described later, so that the supply amount of tin and the time for forming a tin film do not become too long. .

Next, processing of the above-described tin film 22 into small pieces having a predetermined position and size according to the position of the gold bump on the electrode of the semiconductor chip will be described. The small piece of the tin film has a circular shape with a diameter of 50 to 80 μm. This is because it matches the size of the gold bump formed on the electrode of the semiconductor chip and makes it possible to supply a required amount of tin.

Since it is a process to a small piece by a known photoetching method, a completed state is schematically shown in FIG. In FIG. 3, 22a and 22a are small pieces of tin film to be transferred to gold bumps on the electrodes of the processed semiconductor chip.

This process will be briefly described.
First, a photoresist is applied on the tin film 22 formed on the transfer plate 21. Then, the applied photoresist is dried. Next, the photoresist dried through a positive or negative film formed so as to be shielded from the tin film 22 except for the portions left as small pieces 22a and 22a of the tin film is exposed to ultraviolet rays, and the small pieces 22 are exposed.
The photoresist corresponding to the upper part of a and 22a is cured. Then, the uncured photoresist is removed.

By doing so, only the photoresist on the tin film pieces 22a, 22a remains, and the portions are masked. Here, the portion of the tin film that is not masked is removed by etching. Finally, by removing the photoresist used for masking, tin film pieces 22a and 22a are completed (FIG. 3).

Next, the electrodes 17 of the semiconductor chip 16 are placed on the small pieces 22a and 22a of the tin film.
The joining of the gold bumps 18 and 18 formed above will be described.
This joining is performed using a thermal ultrasonic joining apparatus (not shown). That is, the semiconductor chip 16 is lowered and mounted on the tin film pieces 22a and 22a formed on the transfer plate 21, and bonded by applying pressure, heating, and applying ultrasonic vibration ( FIG. 4). When the joining is completed, heating and ultrasonic vibration are stopped.

The mounting conditions by this thermal ultrasonic bonding method will be described.
First, the pressing force of the semiconductor chip 16 on the transfer plate 21 will be described. The pressing force is such that the saddle-shaped tips of the gold bumps 18, 18 are crushed to a diameter of 25 to 30 μm,
In addition, the height of the gold bumps 18 and 18 is also set to 0.1 to 0.2 N per bump, which is a degree of compression deformation to 40 to 50 μm. Gold bumps 18, 18 and tin film pieces 22a,
It is because the contact of 22a can be performed satisfactorily.

Next, the ultrasonic amplitude is about 3 μm. Tin film pieces 22a, 2
Since 2a is only weakly adhered to the glass forming the transfer plate 21,
This is because the small pieces 22 a and 22 a of the tin film are peeled off from the transfer plate 21 by a slight ultrasonic vibration in the horizontal direction.

Next, although it is heating temperature, 150-230 degreeC is suitable.
When a high temperature is applied to melt the small pieces 22a, 22a of the tin film, the small pieces 22a
, 22a is peeled off from the transfer plate 21, but the oxidation progresses when heated at a high temperature, and an oxide film is formed on the surface. Thus, the semiconductor chip 16 which is the final purpose described later is flip-chip mounted on the wiring substrate 31. Because it becomes an obstacle.
In addition, this heating causes a temperature rise for both the semiconductor chip 17 and the transfer plate 21. In this case as well, both are set to the same temperature, or the transfer plate 21 having a large coefficient of thermal expansion is set to a higher temperature. It is good. Tin film piece 22
This is to facilitate peeling of a and 22a.

As described above, the small pieces 22a of the tin film are formed on the gold bumps 18 and 18 of the semiconductor chip 16.
, 22a are joined, and heating and ultrasonic vibration are stopped.
Then, after a predetermined time has elapsed, the semiconductor chip 16 is raised. At this time, the small pieces 22a and 22a of the tin film are peeled off from the transfer plate 21 together with the gold bumps 18 and 18 of the semiconductor chip 16 (FIG. 5). This is because a transfer plate having a coefficient of thermal expansion of 15 ppm / ° C. or more is used, so that when the heating is stopped, the thermal stress when returning to normal temperature is large, and thus the film is easily peeled.

Finally, the flip chip mounting of the semiconductor chip 16 to which the small pieces 22a and 22a of the tin film are bonded to the wiring substrate 31 on which the corresponding electrode pads 32 and 32 are formed will be described.
This flip chip mounting is also performed using a thermocompression bonding apparatus or a thermal ultrasonic bonding apparatus (not shown). That is, the electrode pad 3 formed on the wiring substrate 31.
2 and 32 (FIG. 6), the semiconductor chip 16 is lowered and mounted, and bonded by applying pressure, heating, or applying ultrasonic vibration together. When the joining is completed, heating and ultrasonic vibration are stopped.

The mounting conditions by this flip chip mounting method will be described.
First, the pressing force of the semiconductor chip 16 on the wiring board 31 will be described. The pressing force needs to be sufficient to compress and deform at least 10 μm from 30 to 40 μm from 40 to 50 μm where the height of the gold bumps 18 and 18 is the original height. This is because the wiring board 31 has a lower surface flatness than the transfer plate 21. This is because even when the wiring substrate 31 has a maximum of 10 μm unevenness, it is necessary to make sure that all the gold bumps 18 and 18 are in contact with the electrode pads 32 and 32 of the wiring substrate 31.

Next, regarding the heating temperature, a temperature of 280 to 350 ° C. is appropriate for the joint portion.
If the temperature is too high, the bonding reliability decreases due to the residual stress in the cooling process to room temperature after flip chip mounting, so this effect is minimized as much as possible.
This is to produce a gold-tin eutectic in flip chip mounting.

After bonding the semiconductor chip 17 to the wiring board 31 as described above, the pressurization and heating are stopped.
And the pressurization to the semiconductor chip 16 is released after a predetermined time elapses. Thus, the semiconductor chip 16 is flip-chip mounted on the wiring board 31 (FIG. 7). In FIG. 7, 23 and 23 are gold tin eutectic layers.

By the flip-chip mounting method under such conditions, a gold-tin eutectic layer that can ensure bonding reliability can be generated.

It is a figure which shows typically the process in which a gold bump is formed on the electrode of the semiconductor chip which shows a part of one embodiment of the flip chip mounting method according to the present invention. It is a figure which shows typically the state by which the tin film is formed on the glass plate which shows a part of one Embodiment of the flip chip mounting method which becomes this invention. A part of one embodiment of the flip chip mounting method according to the present invention is formed in a predetermined size at a position corresponding to the gold bump formed on the electrode pad of the semiconductor chip on which the tin film of FIG. 2 is mounted. It is a figure which shows typically the tin film after processing. The figure which shows one process of the process which transcribe | transfers the tin film formed in FIG. 3 which shows a part of one Embodiment of the flip chip mounting method which becomes this invention to the gold bump formed on the electrode of a semiconductor chip. is there. The figure which shows typically the state which transcribe | transferred the tin film shape | molded in FIG. 3 which shows a part of one Embodiment of the flip chip mounting method which becomes this invention to the gold bump formed on the electrode of a semiconductor chip It is. It is a figure which shows typically the place which is going to position and mount a semiconductor chip on the wiring board which shows a part of one Embodiment of the flip chip mounting method which becomes this invention. It is a figure which expands and shows typically the mode of the joined part after flip chip mounting to the wiring board the semiconductor chip which shows a part of one embodiment of the flip chip mounting method concerning the present invention. It is the figure which showed typically the flip chip mounting method of the conventional semiconductor chip in order of the process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 16 Semiconductor chip 17 Electrode pad of semiconductor chip 18 Gold bump on electrode 17 Transfer plate 22 Tin film 22a Tin piece of processed tin film 31 Wiring board 32 Electrode pad on wiring board

Claims (1)

A flip chip mounting method for mounting a semiconductor chip having gold bumps formed on an electrode on a wiring board, comprising the following steps.
a) A step of forming a tin film having a thickness of 1 to 5 μm on a transfer plate having a thermal expansion coefficient of 15 ppm / ° C. or more by a vacuum deposition method or a sputtering method.
b) A step of processing the tin film formed in step a into small pieces of a tin film having a predetermined size in accordance with the position of the gold bump.
c) The tin film piece processed in step b and the gold bump are aligned, the semiconductor chip and the transfer plate are superposed and pressed, heated to a temperature at which tin does not melt, and ultrasonic vibration is applied. While joining the small pieces of tin film processed into the gold bumps.
d) Tin film pieces processed into the gold bumps by pulling the semiconductor chip away from the transfer plate when the temperature of the transfer plate drops after a predetermined time has elapsed after the application of heating and ultrasonic vibrations has stopped. The process of transferring.
e) A step of bonding the gold bumps of the semiconductor chip onto which the tin film pieces have been transferred in step d to the electrodes of the wiring board.

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