JPH02246236A - Flip-chip bonding method - Google Patents

Abstract

PURPOSE:To alleviate stress acting on the junction interface between a brittle semiconductor element and solder bumps by forming the central part of each solder bump in a constricted shape, and buffering the stress due to thermal strain by the entire solder bumps. CONSTITUTION:Semispherical solder bumps 12 are formed. A silicon plate 13 having the same size is placed on the solder bumps 12. Flat parts are formed on the tops of all the solder bumps 12 by heating again. A semiconductor ele ment 11 is turned over and mounted on a circuit wiring board 14 on which flux is applied. The top parts of the solder bumps 12 are brought into contact with electrode parts 15 of the circuit wiring board 14. After a spacer 16 compris ing one-liquid type room-temperature hardening silicone rubber filled with a dispenser is hardened, the solder bumps 12 is made to reflow. Since the top part of the solder bump is wider than the area of the electrode part 5, the central part of the solder bump is constricted at the time of reflow. Therefore, stress due to thermal strain is not concentrated in the vicinities of both interfaces of the junction parts.

Description

[Detailed Description of the Invention] [Summary] Flip-chip bonding method, especially large-scale integrated circuit (LSI)
) Regarding the flip-chip bonding method of devices onto circuit wiring boards, the purpose of this is to provide a flip-chip bonding method that can alleviate stress caused by thermal distortion in the solder joints, and all solder bumps formed on semiconductor devices. The top of the solder bump is brought into contact with the electrode part of the circuit wiring board, and the liquid, which is initially viscous, is applied to the gap between the semiconductor element and the circuit wiring board for a certain period of time. The present invention includes a flip-chip bonding method characterized by including a step of arranging a spacer that hardens after a period of time, and a step of reflowing the solder bump by heating for bonding.

[Industrial application field]

The present invention relates to a flip-chip bonding method, and more particularly to a flip-chip bonding method for large-scale integrated circuit (LSI) devices onto a circuit wiring board.

[Prior art] With the recent demand for faster computer systems, L
There is a need to reduce delay in signal propagation between SI elements. For this reason, a flip-chip bonding method has been proposed in which surface electrodes on a semiconductor chip are directly soldered to wiring electrodes on a circuit wiring board. Strain (thermal strain) will be added due to the difference in linear expansion coefficient. Furthermore, since solder joints are minute, in order to obtain solder joints with high reliability, it is necessary to carefully consider the solder material to be used and the shape of the solder joints to be formed.

FIGS. 5(a) to 5(d) are process diagrams showing a conventional flip-chip bonding method.

As shown in FIG. 2(a), solder bumps 2 are formed on a semiconductor element 1 by, for example, depositing solder such as indium (In) on the element electrode through a metal mask 3, and then
As shown in FIG. 5B, flux was applied and then heated to a temperature above the melting point of the solder to form a hemispherical shape.

Next, as shown in the figure (C), the tops of the solder bumps 2 of the semiconductor element 1 are brought into contact with the electrode parts 5 of the circuit wiring board 4, and as shown in the figure (d), they are heated again. They were joined by reflowing the solder bumps 2.

Therefore, the solder bumps 2 on the semiconductor element 1 become hemispherical before coming into contact with the circuit wiring board 4, and if the amount of solder vapor deposited on each electrode varies (the holes in the metal mask 3 (caused by variations in diameter), the heights of the solder bumps 2 become non-uniform, as shown in FIG. In addition, the solder bump 2 when bonded is shown in the same figure (
As shown in d), the solder bumps 2, the semiconductor elements 1, and the solder bumps 2 were crushed by the weight of the semiconductor element 1 and were formed in a bulging shape at the center, and the solder joints had a spherical shape. Stress due to thermal strain will be concentrated at the interface between the circuit wiring board 4 and the circuit wiring board 4.

[Problem to be solved by the invention]

Therefore, in the conventional flip-chip bonding method, the thermal strain buffering effect, which is an important role of the solder bump 2 itself, is insufficient.
Alternatively, there was a problem in that cranking occurred near the interface with the circuit wiring board 4, eventually leading to breakage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a flip-chip bonding method that can alleviate stress caused by thermal strain in solder joints.

[Means to solve the problem]

The above problem involves a step of forming the tops of all solder bumps formed on a semiconductor element into a flat surface, and a step of bringing the tops of the solder bumps into contact with electrode parts of a circuit wiring board, and filling the gaps between the semiconductor element and the circuit wiring board. , by a flip-chip bonding method characterized by including a step of arranging a spacer that is a viscous liquid in an initial state and hardens after a certain period of time, and a step of reflowing the solder bump by heating for bonding. achieved.

[Effect]

According to the present invention, since the spacer is inserted into the gap between the semiconductor element and the circuit wiring board, the gap between the two does not change during reflow. On the other hand, since the top of the solder bump is wider than the area of the electrode portion of the circuit wiring board, the center portion of the solder bump becomes constricted during reflow as the solder bump wets the electrode portion. Therefore, stress due to thermal strain is no longer concentrated near both interfaces of the joint,
Relaxed across the solder bump.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to an illustrated embodiment.

FIGS. 1(a) to 1(f) are process diagrams showing a flip-chip bonding method according to an embodiment of the present invention.

First, as shown in FIG. 2A, solder bumps 12 are formed on the electrodes of the semiconductor element 11 by a conventional method. For example, as the semiconductor element 11, a 10 mm opening is used.
, In (melting point: 156°C) is applied onto the electrode of a silicon element with a thickness of about 3a+m through a metal mask (not shown).
After depositing the materials, flux (Alpha Metals, RM-5776) is applied and heated to a temperature higher than the solder melting point to form hemispherical solder bumps 12.

Then, solder the silicon plate 13 of the same size to the solder bump 1.
Place it on 2.

Next, as shown in FIGS. 9 and 9C, heating is performed again to form one flat portion on the tops of all the solder bumps 12.

Next, as shown in FIG. 2D, the semiconductor element 11 is turned over and placed on the circuit wiring board 14 coated with flux, and the tops of the solder bumps 12 are brought into contact with the electrode portions 15 of the circuit wiring board 14. . The circuit wiring board 14 is formed of, for example, an alumina substrate with a diameter of 35 mm and a thickness of about 0.6 mm.

Next, as shown in FIG. 6(e), before the heating process for bonding, molded room-temperature curing silicone rubber (manufactured by Shin-Etsu Silicone, KE347 A dispenser (not shown) is used to fill the spacer 16 made of .348> or the like.

Next, as shown in Figure 1), after confirming that the spacer 16 made of molded room temperature curing silicone rubber has hardened (
After 10 hours), the solder bumps 12 were reflowed by heating to about 210° C. using a conveyor type reflow oven (not shown).

FIG. 2 is a perspective view of the embodiment of the present invention in the step of FIG. 1(f). Note that parts corresponding to those in FIG. 1 are denoted by the same reference numerals.

In the flip-chip bonding method described above, since the spacer 16 is inserted into the gap between the semiconductor element 11 and the circuit wiring board 14, the gap between the two does not change during reflow. on the other hand,
Since the top of the solder bump 12 is wider than the area of the electrode part 15 of the circuit wiring board 14, the center part of the solder bump 12 becomes constricted in the process of getting wet with the electrode part 15 during reflow. . Therefore, stress due to thermal strain is no longer concentrated near both interfaces of the joint, and is relaxed throughout the solder bump 12. In the present invention, it is essential that the solder bumps 12 are in contact with all the electrode parts, so it is necessary to make all the tops of the solder bumps 12 into one plane. For this reason, for example, flux is applied on the solder bumps 12 formed by the conventional method, and a silicon plate 13 is used as a plate that does not get wet with solder.
is heated to the melting point of the solder. Furthermore, since the spacer 16 is a viscous liquid in its initial state, variations in the height of the solder bump 12 after flattening do not pose a problem.

FIG. 3 is a schematic diagram based on a photograph of a solder joint according to an embodiment of the present invention, and the solder bump 12 in the gap between the semiconductor element 11 and the circuit wiring board 14 is formed in a constricted shape at the center. . Note that parts corresponding to those in FIG. 1 are denoted by the same reference numerals.

FIG. 4 is a schematic diagram based on a photograph of a conventional solder joint, in which the solder bump 2 in the gap between the semiconductor element 1 and the circuit wiring board 4 is crushed by the weight of the semiconductor element 1, and its central part is It is formed in a bulged shape. Note that parts corresponding to those in FIG. 5 are denoted by the same reference numerals.

In the above embodiment, one-component room temperature curing silicone rubber is used as the spacer 16, but the scope of the present invention is not limited to this.In the initial state, it is a viscous liquid, and after a certain period of time, Any material that hardens may be used. Also,
The solder bumps 12 are not limited to those formed by vapor depositing In.

〔Effect of the invention〕

As explained above, according to the present invention, by making the central part of the solder bump constricted, stress caused by thermal strain can be buffered throughout the solder bump, and the bonding interface between the fragile semiconductor element and the solder bump is It can relieve the stress that is applied,
This greatly contributes to improving the reliability of the flip-flop assembly.

[Brief explanation of drawings]

Figures 1 (a) to (a) are process diagrams showing the flip-chip bonding method according to the embodiment of the present invention, Figure 2 is a perspective view of the embodiment of the present invention, and Figure 3 is a photograph of the solder joint according to the embodiment of the present invention. FIG. 4 is a schematic diagram based on a photograph of a conventional solder joint, and FIGS. 5(a) to 5(b) are process diagrams showing a conventional flip-chip bonding method. In the figure, 11 is a semiconductor element, 12 is a solder bump, 13 is a silicon plate, 14 is a circuit wiring board, 15 is an electrode portion, and 16 is a spacer. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney Akimoto Kuki Hajime Osuga Yoshiyuki Hanson Ihon Soryo 11 Book Expression] Punihoden Muikyu's Examination Book Sanskrit Kinubunike 4? IIt:Jru1;nfc'' joint photo l9 schematic diagram Fig. 3 Conventional 11n fc joint photo l: Diagram of the underlying membrane 7 Reno-Frotsuf/Joining Method Diagram

Claims (1)

[Claims] All solder bumps (
forming the top of the solder bump (12) into a flat surface;
), and the semiconductor element (11
) and the circuit wiring board (14), there is a spacer (14) that is a viscous liquid in its initial state and hardens after a certain period of time.
6); and a step of reflowing the solder bump (12) by heating for bonding.