JP2001244298A - Flip chip connection method - Google Patents

Abstract

(57) [Problem] To provide a flip chip connection method capable of sufficiently securing the bonding strength of a bare chip and improving the reliability of bonding by suppressing the generation of voids. SOLUTION: A flip-chip connecting method includes a first step of applying a thermosetting resin adhesive 11 to a surface 9 of a wiring board 3; and holding a bare chip 2 with a heating tool 12. By directing the element surface 5 of the bare chip toward the surface of the wiring board, the bumps 7 of the bare chip and the pads 10 on the wiring board are aligned with each other, and the bare chip is heated via a heating tool.
A second step of heating the chip; and pressing the heated bare chip toward the wiring board, thereby abutting the bumps on the pads and bonding the bare chip and the wiring board to each other via an adhesive. And a third step of heating and curing the adhesive by heat conduction from the bare chip;
It has.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip connection method for directly connecting a bare chip called a bare chip to a mounting surface of a wiring board.

2. Description of the Related Art In recent years, the performance of portable electronic devices represented by portable computers has been remarkably improved, and accordingly, the functions of semiconductor packages mounted on electronic devices have been enhanced. As the functionality of semiconductor packages increases, the number of input / output pins increases.Therefore, if a large number of pins are taken out from the periphery of the semiconductor package, the pin arrangement is necessarily narrow, resulting in manufacturing constraints. And restrictions on mounting on the wiring board. In order to avoid this restriction, a so-called flip-chip connection in which a bare chip called a bare chip is directly connected to a wiring board is conventionally known. The bare chip used for the flip-chip connection has a flat element surface, and a large number of bumps are arranged in a row at a predetermined pitch on the element surface. The wiring board on which the bare chip is mounted has a number of pads corresponding to the bumps in a region where the chip is to be mounted, and the bumps are connected to these pads. By the way, as a method for fixing the bare chip to the wiring board, a solder bonding method and a resin bonding method are known. In particular, the resin bonding method can be operated at room temperature and is inexpensive in terms of material. Therefore, it is most frequently used at present. This resin bonding method is a method in which a bare chip and a wiring board are bonded using a thermosetting resin adhesive (paste), and then the adhesive is heated and cured, and includes the following steps. are doing. That is, in the conventional resin bonding method, first, an adhesive of a thermosetting resin is applied to a region of the wiring board where the bare chip is to be mounted. Next, the bare chip is attracted to the heating tool, the element surface of the bare chip is directed to the wiring board, and the bumps of the bare chip are aligned with the pads on the wiring board. In this state, the heating tool is lowered, and the bare chip is pressed against the wiring board so that the bumps of the bare chip contact the pads on the wiring board. By this pressure, the adhesive previously applied to the wiring board is filled between the wiring board and the bare chip,
The bare chip and the wiring board are bonded by this adhesive. Thereafter, the heating tool is energized to heat the bare chip to a predetermined temperature, and the adhesive is thermally cured by heat conduction from the bare chip to the adhesive. Thus, the bare chip and the wiring board are immovably coupled to each other, and the contact state between the bump and the pad is maintained.

In the conventional resin bonding method, first, a bare chip is pressed against a wiring board, an adhesive is filled in a gap between the two, and heating of the adhesive is started. ing. However, according to this conventional process, when the adhesive flows into the gap between the bare chip and the wiring board, the temperature of the adhesive itself is low, and the fluidity of the adhesive is poor. For this reason, when the adhesive previously applied to the wiring substrate is pressed by the bare chip, air may be trapped or trapped in the adhesive. The trapped air remains as bubbles in the adhesive as bubbles even after thermosetting, which causes voids. If a void exists inside the adhesive as described above, stress concentrates on the void, and a crack may occur at the void, which may cause breakage or loss of the adhesive. For this reason, the bonding strength of the bare chip is reduced, the bare chip may be peeled off from the wiring board in a subsequent subsequent process, or the contact state between the bump and the pad may become unstable, and the reliability of the bonding may be reduced. Is reduced. The present invention has been made in view of such circumstances, and it is possible to minimize the occurrence of voids, sufficiently secure the bonding strength of bare chips, and improve the reliability of bonding. The purpose is to provide a chip connection method.

In order to achieve the above object, a flip chip connection method according to the present invention provides a method of applying a thermosetting resin adhesive to a mounting surface of a wiring board on which a number of pads are arranged. (1) holding the bare chip with a heating tool and turning the element surface of the bare chip on which a number of bumps are arranged toward the mounting surface of the wiring board, thereby aligning the bumps and pads with each other; A second step of heating the bare chip via the heating tool; and pressing the heated bare chip toward the wiring board so that the bump abuts on the pad, A third step of bonding the bare chip and the wiring board to each other via the adhesive and heating and curing the adhesive by heat conduction from the bare chip. It is set to. According to such a method, generally, the adhesive of the thermosetting resin temporarily lowers the viscosity when heated, and the fluidity increases, so that the heating of the adhesive is started prior to the pressing of the bare chip. In addition, the wettability of the adhesive is improved, and the adhesive easily flows between the bare chip and the wiring board and between adjacent pads and bumps. As a result, in the process of pressing the adhesive between the bare chip and the wiring board, the probability of entraining air or trapping air bubbles in the adhesive is greatly reduced, and voids are minimized. It can be kept low. Also, since the flowability of the adhesive increases,
The adhesive flows evenly into the gap between the chip and the wiring board, and even if the pitch of the bumps and pads is narrow, the contact portions between these bumps and pads can be covered with the adhesive. Therefore, the bonding strength of the bare chip can be sufficiently ensured, and the contact state between the bump and the pad is stabilized.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows a semiconductor module 1 mounted on an electronic device such as a portable computer. The semiconductor module 1 includes a bare chip 2 and a wiring board 3 on which the bare chip 2 is mounted. The bare chip 2 is a bare chip that is not resin-molded and includes a rectangular silicon base 4. The silicon base 4 has a flat element surface 5, and a large number of pads 6 are arranged in rows around the element surface 5 at intervals. The pitch between these adjacent pads 6 becomes finer as the bare chip 2 becomes more sophisticated. A bump 7 is provided on each pad 6. The bump 7 is made of, for example, a metal material containing gold as a main component.
It is formed on each pad 6 using a bonding tool (not shown) for bonding. Therefore, FIG.
As shown in FIG. 3, each bump 7 has a tip 7a that tapers toward the wiring board 3 to be mounted. Also,
The silicon base 4 has a protective film 8 made of polyimide. This protective film 8 covers the element surface 5 of the silicon base 4 so as to avoid many bumps 7. The wiring board 3 has a flat surface 9 as a mounting surface.
A large number of pads 10 are arranged on the surface 9. The pad 10 is electrically connected to a wiring pattern (not shown) of the wiring board 3. These pads 10
Adjacent pads 10 are arranged in a row at intervals so as to correspond to the bumps 7 of the bare chip 2.
Are miniaturized to match the pitch of the bumps 7. Incidentally, the bare chip 2 is mounted on the front surface 9 of the wiring board 3 by the flip chip connection method according to the present invention, and the connection procedure will be described below. First, as shown in FIG. 1, a wiring board 3 on which a number of pads 10 are arranged is held horizontally.
A thermosetting resin adhesive 11 is applied to the surface 9 of the substrate. The adhesive 11 is generally called a paste, and is applied to a region surrounded by the pad 10 by using, for example, a dispense method. Next, the bare chip 2 is sucked using the heating tool 12, and the bare chip 2 is positioned above the wiring board 3. At this time, the bare chip 2 is held in a posture in which the element surface 5 on which a large number of bumps 7 are formed faces the front surface 9 of the wiring board 3.
And the pad 10 are aligned. When the alignment is completed, the bare chip 2 is lowered toward the wiring board 3 via the heating tool 12, and when the bare chip 2 reaches several μm just before the wiring board 3, the bare chip 2 Stop descent of 2. Next, the heating tool 12 is slowly lowered again, and the tip 7 a of the bump 7 is brought into contact with the pad 10. Then, at time t1 when the tip 7a of the bump 7 contacts the pad 10, the heating tool 12 is energized, and the bare chip 2 is heated via the heating tool 12. Since the heating tool 12 continues to descend even after the tip 7a of the bump 7 contacts the pad 10, as shown in FIG. 4, a pressing force F1 is applied to the bump 7 so as to press the bump 7 against the pad 10. 7 pointed tip 7
a succumbs to the pressing force F1 and collapses. As a result, since the bump 7 is firmly sandwiched between the silicon base 4 and the wiring board 3, the pressing force F1 acting on the bump 7 rises rapidly, and the bump 7 is pressed against the pad 10. The pressing force F1 is set to about 20 to 150 gf per one bump 7. The pressing force F1 reaches a desired value when a predetermined time has elapsed since the start of heating the bare chip 2, and the lowering of the heating tool 12 is stopped. When the bumps 7 are pressed against the pads 10, the adhesive 11 previously applied to the wiring board 3 is applied to the bare chip 2.
Are crushed so as to spread over the gap between the wiring board 3 and the bare chip 2. Therefore, the adhesive 11 adheres the bare chip 2 and the wiring board 3 with a part of the surface thereof in contact with the protective film 8 covering the element surface 5 of the silicon base 4. As shown in FIG. 4, the temperature T of the bare chip 2 heated by the heating tool 12 is controlled in multiple stages so as to change in three stages while the bare chip 2 is being pressed. That is, the bare chip 2 is kept at a temperature of about 140 to 160 ° C. at which at least the surface of the adhesive 11 is thermally cured during a period A1 from the start of heating to the time point t2.
During a period A2 from time t2 to time t3, the adhesive 11 is maintained at a temperature of about 200 to 240 ° C. at which the inside of the adhesive 11 is thermally cured for 5 to 30 seconds. Then, at the time point t3, the power supply to the heating tool 12 is stopped, and the bare tool
The chip 2 is cooled by natural air cooling during a period A3 until a time point t4 when the temperature of the adhesive 11 decreases to about 140 to 160 ° C. The pressurization of the bare chip 2 is performed at the time t4
And only the heating tool 12 rises alone. The heating tool 12 returns to the standby position for sucking the next bare chip 2. Finally, the internal temperature of the wiring board 3 to which the bare chip 2 is bonded is 100 to 150 ° C.
The adhesive 11 is completely cured by being transferred to a drying chamber (not shown) maintained at an appropriate level and left in the drying chamber for about 1 to 2 hours. This results in a series of bare chips 2
Is completed. According to such a flip chip connection method, the adhesive 11 previously applied to the wiring board 3 is heated before the pressure of the bare chip 2 is applied, so that the pitch of the bumps 7 and the pads 10 is narrow. In both cases, high-quality flip-chip connection in which generation of voids is suppressed can be realized. That is, in general, the adhesive 11 made of a thermosetting resin temporarily decreases the viscosity when heated, and the fluidity is increased, so that the wettability to the bare chip 2 is improved, and the adhesive 11 is pressed by the bare chip 2. When the bonding is performed, the adhesive 11 easily flows into the gap between the bare chip 2 and the wiring board 3 and the gap between the adjacent bumps 7 and pads 10. For this reason, when the adhesive 11 is pressurized, air is drawn into the adhesive 11 or
Adhesive 1 greatly reduces the probability of trapping air bubbles
Voids are less likely to be generated in the inside of the first. The adhesive 11
Therefore, even if the pitch between the bumps 7 and the pads 10 is narrow, the connection portions between the bumps 7 and the pads 10 can be evenly wrapped by the adhesive 11. Accordingly, the bonding strength of the bare chip 2 can be sufficiently ensured, and not only can the peeling of the bare chip 2 be prevented, but also the contact state between the bumps 7 and the pads 10 is stabilized, and the electrical connection is made. Reliability is improved. Further, in the present embodiment, since the heating temperature of the bare chip 2 is changed in three steps, the time required for curing the adhesive 11 can be reduced while minimizing the generation of voids. The reason for this is as follows. In general, as the heating temperature of the adhesive 11 of a thermosetting resin increases, the curing speed increases. However, the adhesive 11 is in contact with the polyimide protective film 8 covering the element surface 5 of the silicon base 4, and this protective film 8 releases moisture and gas when heated to a temperature around 160 ° C. Has characteristics.
For this reason, the bare chip 2
Is heated to a high temperature exceeding 200 ° C., moisture and gas released from the protective film 8 are caught in the adhesive 11 and remain as voids in the adhesive 11. However, according to the connection method according to the present embodiment, in the first half of the heating step, the heating temperature of bare chip 2 is suppressed to about 140 to 150 ° C., and the temperature at which moisture or gas is not released from protective film 8 is set. Glue under conditions 11
Is thermally cured, so that the release of moisture and gas from the protective film 8 is suppressed, and the surface of the adhesive 11 in contact with the protective layer 8 is cured before the release of the moisture and gas. be able to. Therefore, in a period A2 following the period A1, the heating temperature of the bare chip 2 is set to 200 ° C.
Even if the temperature is raised to a value higher than the above, moisture and gas released from the protective film 8 will not be taken into the adhesive 11, and the generation of voids can be prevented. Further, in the period A2, the adhesive 11 is heated to a high temperature exceeding 200 ° C. by heat conduction from the bare chip 2, so that the temperature inside the adhesive 11 is accelerated and the curing speed is increased. . Therefore, the adhesive 11 can be cured to a state where a desired adhesive strength can be obtained in a short time, and the posture of the bare chip 2 is stabilized, and the contact state between the pad 10 and the bump 7 is fixed. It can be determined in a specific way. Therefore, it is possible to reduce the mounting time required for fixing the bare chip 2 while suppressing the generation of voids that cause the adhesive 11 to crack, and it is possible to efficiently perform the flip chip connection operation. In addition, according to the above method,
The pressure release of the bare chip 2 is performed after the temperature of the bare chip 2 is 140 to 160 ° C. after the adhesive 11 is thermally cured.
Since the process is performed after waiting for the temperature to drop to the extent, the adhesive 11 has already been cured to a state where the adhesive 11 can exhibit effective adhesive strength at this point. For this reason, even if the pressure of the bare chip 2 is released, the bumps 7 are kept pressed against the pads 10, so that the contact state between the bumps 10 and the pads 7 is stabilized, and the occurrence of poor connection is caused. And high quality flip-chip connection without wires. In addition, bare chip 2
Before the pressure is applied to the wiring board 3, the tip 7 a of the bump 7 is tapered and sharpened.
Even if the fluid flows so as to cover the pad 10, the bump 7
The pointed tip 7a penetrates the adhesive 11 and the pad 1
0 surface is reached. For this reason, if pressure is applied so that the bare chip 2 is pressed against the wiring board 3, the sharp tip 7 a of the bump 7 is gradually deformed while scraping the adhesive 11, and finally is pressed by contact with the pad 10. Crushed.
Therefore, the adhesive 11 does not need to be interposed between the pad 10 and the bump 7 and the pad 10 and the bump 7
A sufficient contact area can be secured, and in this regard, the reliability of the electrical connection can be improved. Note that the heating temperature and heating time of the adhesive are appropriately determined according to the material of the adhesive, and are not limited to the numerical values described in the above-described embodiment.

According to the present invention described in detail above, the heating of the adhesive is started prior to the pressing of the bare chip, so that the wettability of the adhesive to the bare chip is improved. When the adhesive is pressed, the adhesive easily flows into the gap between the bare chip and the wiring board and the gap between adjacent bumps and pads.
For this reason, when the adhesive is pressurized, the probability of entraining air or trapping air bubbles in the adhesive is greatly reduced, and voids are less likely to be generated inside the adhesive. Further, since the fluidity of the adhesive is increased, even if the bumps and pads are arranged at a narrow pitch, the connection portions between the bumps and the pads can be uniformly wrapped by the adhesive. Therefore, the bonding strength of the bare chip can be sufficiently ensured, and the peeling of the bare chip can be prevented. High quality flip chip connection can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a bare chip held by a heating tool is opposed to a wiring board on which an adhesive is applied.

FIG. 2 is a sectional view showing a state in which a bare chip is pressed against a wiring board by a heating tool.

FIG. 3 is a cross-sectional view showing a state in which a bare chip is fixed to a wiring board.

FIG. 4 is a characteristic diagram showing the timing of pressing the bare chip, the timing of starting the heating of the adhesive, and the transition of the heating temperature of the adhesive.

[Explanation of symbols]

 2 ... Bear chip 3 ... Wiring board 5 ... Element surface 7 ... Bump 9 ... Mounting surface (surface) 10 ... Pad 11 ... Adhesive 12 ... Heating tool

Continuing from the front page (72) Inventor Ichi Murakami 2-9-9 Suehirocho, Ome City, Tokyo Inside the Toshiba Ome Plant (72) Inventor Kuniyasu Hosoda 3-3-1 Shinmachi, Ome City, Tokyo 1 Toshiba Compu- TA Engineering Co., Ltd. F-term (reference) 5E319 AA03 AB05 BB20 CC01 CC61 CD04 5F044 KK02 LL11 LL15 QQ04 RR19

Claims (4)

[Claims] A bare chip having an element surface on which a large number of bumps are arranged; and a wiring board having a mounting surface on which a large number of pads corresponding to the bumps are arranged. A flip-chip connection method for directly connecting to a mounting surface of a wiring board, a first step of applying a thermosetting resin adhesive to the mounting surface of the wiring board; and holding the bare chip with a heating tool. A second step of aligning the bumps and pads with each other by directing the element surface of the bare chip toward the mounting surface of the wiring board, and heating the bare chip via the heating tool; By pressing the bare chip toward the wiring board, the bumps are brought into contact with the pads, and the bare chip and the wiring board are mutually contacted via the adhesive. Flip-chip connection method characterized by comprising; joined, the adhesive and the third step of heat curing by heat conduction from the bare chip. 2. The flip-chip connection method according to claim 1, wherein the bumps are tapered toward the pads. 3. The element surface of the bare chip according to claim 1, wherein the element surface of the bare chip is covered with a protective film of polyimide, and the adhesive is provided between the protective film and the mounting surface of the wiring board. A flip chip connection method characterized by being filled with?. 4. The flip chip connection method according to claim 3, wherein, when heating the adhesive, the heating temperature of the adhesive is increased stepwise as the heating time elapses.