JP3795644B2 - Joining method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an electronic device in which electronic components such as surface acoustic wave elements and semiconductor elements are mounted on a substrate, and more particularly to a method for manufacturing an electronic device in which chip-type electronic components are mounted on a substrate by a flip chip method.
[0002]
[Prior art]
One technique for mounting various chip-shaped electronic components such as semiconductor elements on a substrate, a package, or the like is a flip chip method. This is a mounting method in which a connection terminal provided on an electronic component and a connection terminal provided on a substrate or the like are connected by conductive bumps.
[0003]
For the mounting of electronic components such as surface acoustic wave devices (SAW devices) such as surface acoustic wave filters and surface acoustic wave resonators, wire bonding has been the mainstream in the past, but in recent years, ultrasonic waves, heating, and pressing are used together. The flip chip method has been introduced. For example, “Flip-chip type GHz band SAW filter” (Science Technical Report, May 7, 1995, published by The Institute of Electronics, Information and Communication Engineers) has a technology regarding flip-chip type SAW devices using face-down bonding. Are listed.
Here, effective conditions of ultrasonic wave and load when performing face-down bonding are described. According to this, a method of performing face-down bonding twice for one chip is used, and the first time, bumps are flattened (level adjustment) by using weak ultrasonic waves with a constant load, and the second time. In this method, the bumps and the connection terminals are joined by using the same constant load as the first time and using ultrasonic waves stronger than the first time. There is a description that according to this method, face-down bonding with a shear strength of about 40 gf / bump is possible.
[0004]
The shear strength of the bump connection varies depending on the application and usage conditions of the semiconductor device and the electronic device equipped with the surface acoustic wave device. The bonding strength obtained by the above-described method is considered to be sufficient shear strength when sufficient bonding strength is not required and sufficient bonding reliability is not required.
[0005]
However, when the use conditions are severe or a high degree of reliability is required, it is necessary to ensure a larger bonding strength.
For example, if there is a large difference in the coefficient of thermal expansion between a chip such as a semiconductor element or surface acoustic wave element and the substrate on which this chip is mounted, it is caused by the thermal load applied depending on the manufacturing process or actual usage environment. Thus, there is a great risk of connection failure such as bump peeling.
In addition, when the chip face-down bonded on the substrate is sealed with a mold resin or the like, that is, when the curing shrinkage stress or thermal expansion stress of the sealing resin directly acts on the chip, The share strength is insufficient.
[0006]
In addition, since mounting of such electronic components is often performed in large quantities, how to reduce the cost and tact time required for mounting is a major issue in increasing productivity. Thus, establishment of the technique which mounts an electronic component with high productivity is ensured, ensuring sufficient joint strength.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve such problems.
That is, an object of the present invention is to provide a highly reliable manufacturing method of an electronic device that can improve the shear strength of bump connection. It is another object of the present invention to provide a method for manufacturing an electronic device that can improve connection reliability and productivity.
It is another object of the present invention to provide a method for manufacturing an electronic device capable of improving the bonding strength between an electronic component and a substrate and reducing contact resistance.
[0008]
[Means for Solving the Problems]
In order to solve such problems, the present invention employs the following configuration.
[0009]
In the bonding method of the present invention, the first electrode and the second electrode are set to be large in a multistage manner in the bonding method for bonding the bump disposed on the first electrode and the second electrode . In addition to pressing with a load, the method includes a step of joining the bump and the second electrode by applying ultrasonic waves with an output set in a multistage manner corresponding to the load . The ratio of the set value between the ultrasonic output and the load that are set to be large in multiple stages may be adjusted to be greater than about 0.001 W / gf per bump.
[0010]
The bonding method of the present invention is a bonding method for bonding a bump disposed on a first electrode and a second electrode, wherein the first electrode and the second electrode are connected to a height of the bump. Pressing with a second load larger than the first load required for leveling, and applying an ultrasonic wave with a first output to join the bump and the second electrode; The first electrode and the second electrode are pressed with a third load larger than the second load, and the ultrasonic wave is applied with a second output larger than the first output. and having a second junction step of joining the second connecting terminal and the conductive bump.
[0011]
The ratio between the first output and the second load and the ratio between the second output and the third load are adjusted to be greater than about 0.001 W / gf per bump. It may be.
Further, the second joining step may be performed in multiple stages while increasing the second output and the third load.
[0012]
That is, the bonding method of the present invention is a method of heating, pressing, and mounting electronic components such as a surface acoustic wave element and a semiconductor element on a host side (simply referred to as a substrate) such as a package substrate or mother substrate by so-called face-down bonding. Solid-phase diffusion connection between bumps and electrodes (connection terminals) is performed by a plurality of bonding steps combined with ultrasonic application. Then, an ultrasonic wave is applied while applying a load that is larger than the load required for level adjustment from the first stage and substantially contributes to the solid phase diffusion connection between the bump and the electrode. By performing such bonding, it is possible to obtain higher bonding strength than before and to improve connection reliability. Further, according to the present invention, not only the bonding strength can be improved, but also the time required for bonding can be greatly shortened. Therefore, the productivity of the electronic component mounting process can be greatly improved, and the product cost can be reduced.
[0013]
Furthermore, by optimizing the ratio between the load applied in each stage of the bonding process and the ultrasonic output, the occurrence rate of bonding failure can be greatly reduced without increasing the overall tact time.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in further detail below.
[0015]
(Embodiment 1)
FIG. 1 is a time chart showing an example of bonding conditions in the ultrasonic thermocompression bonding method of the present invention. For comparison, an example of a time chart showing bonding conditions in a conventional ultrasonic thermocompression bonding method is shown in FIG.
As shown in FIG. 2, in the conventional ultrasonic thermocompression bonding method, the first stage bonding is performed by applying a weak ultrasonic output while applying a load necessary to make the bump height uniform, and then bumping. In order to perform thermocompression bonding between the electrode and the electrode, the second stage bonding is performed by applying an ultrasonic output stronger than the first stage while applying the same load as the first stage. That is, two-stage bonding is performed by changing the ultrasonic output while applying substantially the same load.
[0016]
On the other hand, the bonding method of the present invention performs bonding in a plurality of stages while increasing both the applied load and the ultrasonic output in multiple stages. Further, the load applied at the time of the first stage bonding is larger than the load necessary for leveling the bump height, and a load that contributes to the solid phase diffusion connection between the bump and the electrode is applied.
[0017]
By performing such bonding, it is possible to obtain a bonding strength greater than that of the conventional bonding method, and to improve the reliability of the electronic device.
[0018]
FIG. 3 is a view for explaining a state of a joint portion when performing flip chip bonding according to the present invention. By performing bonding while increasing the load and the ultrasonic output in a multistage manner, as shown in FIG. 3, the contact portion 1 2 x between the connection terminal 1 2 a and the bump 14 on the surface acoustic wave element, and The bonding strength between the bump 14 and the contact portion 1 1 x between the connection terminal 11a disposed on the substrate 11 is shown in FIGS. 3 (a), 3 (b), 3 (c), and 3 (d). It turns out that it becomes almost continuously large in order. For this reason, not only the bonding strength is improved, but also a strong bonding can be obtained with a lower ultrasonic output. Therefore, it is possible to stabilize and improve the bonding strength after bonding as a whole.
[0019]
FIG. 4 is a diagram schematically showing an example of the structure of an electronic device manufactured by applying the present invention. This electronic device is a semiconductor package in which a semiconductor element 12 is mounted on a substrate 11 in a face-down manner and is further sealed with a mold resin 13.
A connection terminal 12 a made of, for example, Al is disposed on the surface of the semiconductor element 12 facing the substrate 11. On the other hand, a connection terminal 11a made of, for example, Au, Ni, Cr, Cu, or an alloy thereof is disposed on the surface of the substrate 11 on which the semiconductor element 12 is mounted. The semiconductor element 12 and the substrate 11 are joined by solid phase diffusion connection with bumps 14 made of, for example, Au sandwiched between the connection terminal 12a of the semiconductor element 12 and the connection terminal 11a of the substrate 11. The bumps 14 may be disposed on the semiconductor element 12 or may be disposed on the substrate 11. Such a bump 14 may be formed, for example, by bringing a bonding wire of Au into contact with the connection terminal with a bonding tool and applying a voltage.
According to the bonding method of the present invention, the bonding strength can be improved as compared with the conventional bonding method. Therefore, for example, when the mold resin 13 is cured and contracted, the stress acting between the substrate 11 and the semiconductor element 12 due to the difference in thermal expansion coefficient between the substrate 11 and the semiconductor element 12, and such a semiconductor package Due to the thermal load that is cyclically applied to the actual use of electronic components, etc., the substrate 11 and the semiconductor element 12 can be bonded with sufficient strength to resist stress, and the bonding state can be stabilized. Can be held. Therefore, a highly reliable electronic device can be provided by applying the present invention (Embodiment 2).
Next, the result of the experiment conducted in order to confirm the effect of the joining method of this invention is demonstrated.
Au bumps were formed on a connection terminal mainly made of Al, such as a semiconductor element and a surface acoustic wave element, using a bonding tool, for example. On the other hand, a connection terminal made of Au was formed on a wiring board on which this element was mounted. Then, the connection terminals of the wiring board and the bumps of the element are arranged so as to face each other, and while the whole is heated to about 200 ° C., the back surface of the element is pressed with a bonding head and ultrasonic waves are applied to the bumps. And the connection terminal were connected by solid phase diffusion.
[0020]
In this example, the first stage bonding is performed with a load of about 150 gf / bump and an ultrasonic output of about 0.07 W / bump, and the second stage bonding is performed with a load of about 250 gf / bump and an ultrasonic output of about 0.29 W / bump. Set and went.
As a result, a shear strength of about 150 gf / bump corresponding to about three times or more of the bonding strength obtained by the conventional bonding method could be obtained.
[0021]
The conventional example employs an ultrasonic thermocompression bonding method in which the ultrasonic output is increased in two stages, but the ultrasonic output applied in the first bonding process is a process for leveling the bumps to the same level. In addition, since the ultrasonic wave is weak with respect to the applied load, it is not possible to obtain the effect of increasing the joint area between the bump and the electrode and improving the shear strength.
In contrast, in the present invention, by applying ultrasonic waves in multiple stages with an output optimized for the load, the bonding strength can be significantly improved and highly reliable mounting can be performed.
[0022]
(Embodiment 3)
Bonding was performed by an ultrasonic thermocompression bonding method under conditions different from those of the example described in Embodiment 2, and the effect of the bonding method of the present invention was confirmed.
[0023]
In this example, the first stage bonding is set to a load of about 50 gf / bump and the ultrasonic output is about 0.03 W / bump, and the second stage bonding is set to a load of about 150 gf / bump and the ultrasonic output is about 0.07 W / bump. The bonding of the third stage was set to a load of about 250 gf / bump and an ultrasonic output of about 0.29 W / bump, and ultrasonic thermocompression bonding between the electrode and the bump was performed. By such a three-stage bonding process, a shear strength of about 150 gf / bump equivalent to the two-stage bonding process described above was obtained.
Furthermore, the processing time required for ultrasonic oscillation and load application could be reduced to about ½ per bonding step. Therefore, the time required for the process can be reduced to about 2/3 as compared with the conventional bonding method and the bonding method of the second embodiment.
As described above, according to the present invention, not only the bonding strength between the electrode and the bump can be improved, but also the productivity can be greatly improved.
[0024]
(Embodiment 4)
As described above, the bonding method of the present invention performs bonding while increasing the load and ultrasonic output in multiple stages, and applies a load larger than the load required for bump leveling from the beginning. Furthermore, by appropriately adjusting the value of the ultrasonic output with respect to the load applied throughout the entire bonding process, diffusion bonding can always proceed.
[0025]
The inventors of the present invention further improved by adjusting the load applied to the electrode and the bump and the value of the ultrasonic output in each stage of bonding so as to be larger than about 0.001 W / gf per bump. It has been found that an excellent bonding state can be obtained. Another experimental result performed to confirm the effect of the present invention will be described. First, a case where connection is performed in a single bonding process will be described.
The load applied at the time of bonding was set to 250 gf / bump, and the ultrasonic output was set to 0.29 W. The (ultrasonic output / load) at this time is about 0.0012 W / gf. In the conventional bonding method, the ultrasonic power applied at the first stage is much weaker than this because it is intended for leveling, and contributes to the formation of a substantial electrode-bump solid phase diffusion bonding. Not. In the conventional bonding method, the load applied at the first stage is about 40 gf / bump because the purpose is to level a plurality of bumps. On the other hand, in the present invention, a load and an ultrasonic output that substantially contribute to the formation of the solid phase diffusion bonding between the electrode and the bump are applied from the first bonding step. By such a joining method of the present invention, a shear strength of 150 gf / bump, which is more than three times the shear strength of 40 gf / bump obtained in the conventional two-step bonding process, could be obtained.
The process time in this experiment was 0.5 seconds, which could be shortened to 1/3 or less compared with 1.6 seconds of the conventional example. However, when the peeled portion at the time of the shear test which was carried out by extracting a part of the sample was examined, bonding failure was found in about 30% of the bumps.
[0026]
(Embodiment 5)
An example in which two-stage bonding is performed will be described.
The load applied during the first stage bonding is set to about 121 gf / bump and the ultrasonic output is set to 0.14 W. The load applied during the second stage bonding is set to about 250 gf / bump and the ultrasonic output is set to about 0.29 W. Set. The value of (ultrasonic output W / load gf) at this time is about 0.0012 W / gf in both the first and second stages.
[0027]
When the joining state of the sample was examined after completion of joining, the obtained shear strength was about 150 gf / bump equivalent to the strength obtained by one-step bonding, but the joint failure bump was reduced to about 10% of the whole. Could be reduced to. The process time for this bonding was 0.25 seconds for each stage, and the total process time was 0.5 seconds.
Thus, by performing the bonding at each stage with the ratio of the ultrasonic output W and the load gf set to about 0.0012 W / gf or more, the bonding strength can be improved and the productivity can be improved.
[0028]
(Embodiment 6)
Further, an example in which three-stage bonding is performed will be described.
The load applied during the first stage bonding is set to about 64 gf / bump and the ultrasonic output is set to 0.07 W, the load applied during the second stage bonding is set to about 121 gf / bump and the ultrasonic output is set to 0.14 W. Bonding was continuously performed by setting the load applied at the time of the third stage bonding to about 250 gf / bump and the ultrasonic output to 0.29 W.
The value of (ultrasonic output W / load gf) at this time is about 0.0011 W / gf for the first stage, about 0.0012 W / g for the second stage, and about 0.0012 W for the third stage. / Gf.
[0029]
After the three-stage joining was extracted and the joining state was examined, the shear strength obtained was about 150 gf / bump equivalent to that obtained when joining in one stage and joining in two stages. It was possible to reduce the generation rate of the above to about 3% of the entire bump. The process time in this experiment was 0.17 seconds for each stage, and the total time was 0.5 seconds.
[0030]
(Embodiment 7)
Further, an example in which four-stage bonding is performed will be described.
The load applied during the first stage bonding is set to about 64 gf / bump and the ultrasonic output is set to 0.07 W, the load applied during the second stage bonding is set to about 121 gf / bump and the ultrasonic output is set to 0.14 W. The load applied during the third stage bonding is set to about 188 gf / bump and the ultrasonic output is set to 0.21 W, the load applied during the fourth stage bonding is set to about 250 gf / bump and the ultrasonic output is 0.29 W. Bonding was carried out continuously with setting.
The value of (ultrasonic output W / load gf) at this time is about 0.0011 W / gf for the first stage, about 0.0012 W / g for the second stage, and about 0.0011 W for the third stage. / Gf, and the fourth stage is about 0.0012 W / gf.
[0031]
When the bonding state when the four-stage bonding was finished was examined, the obtained shear strength was about 150 gf / bump equivalent to that obtained when bonding was performed in one stage, bonding in two stages, and bonding in three stages. However, it was possible to reduce the incidence of bonding failure to 1% of all the bumps. The process time in this experiment was 0.13 seconds for each stage, and the total time was 0.5 seconds.
[0032]
As can be seen from the above experiments, the optimization of the load and ultrasonic output is effective in greatly improving the shear strength. Furthermore, by appropriately adjusting the load and ultrasonic output as described above and performing multi-step bonding, it is possible to dramatically improve the bondability between the bump and the electrode without extending the process time. . Note that the present invention can be applied to materials of electrodes and bumps other than the above-described examples.
[0033]
【The invention's effect】
As described above, according to the present invention, the bonding strength between the bump and the electrode can be improved. Accordingly, it is possible to greatly improve the reliability of an electronic device in which electronic parts such as a surface acoustic wave element and a semiconductor element are mounted.
Further, according to the present invention, not only the bonding strength can be improved, but also the time required for bonding can be greatly shortened. Therefore, the productivity of the electronic component mounting process can be greatly improved, and the product cost can be reduced.
[0034]
Furthermore, by optimizing the ratio between the load applied in each stage of the bonding process and the ultrasonic output, the occurrence rate of bonding failure can be greatly reduced without increasing the overall tact time.
As described above, according to the present invention, the bonding strength between the bump and the electrode can be improved, the tact time can be shortened, and the yield can be improved.
[Brief description of the drawings]
FIG. 1 is a time chart showing application conditions of a load and ultrasonic output in a bonding method of the present invention.
FIG. 2 is a time chart showing application conditions of load and ultrasonic output in a conventional joining method.
FIG. 3 is a view for explaining the joining action of the present invention, and schematically showing the structure of a joining portion.
FIG. 4 is a diagram schematically showing an example of the structure of a semiconductor package mounted according to the present invention.
[Explanation of symbols]
11 ………… Substrate 11a ………… Connection terminal (first electrode)
12 ………… Electronic component 12a ………… Connection terminal (second electrode)
13 ………… Mold resin

Claims (5)

In the bonding method of bonding the bump disposed on the first electrode and the second electrode,
And said first electrode and said second electrode while pressed with a load that is set in multiple stages large, the said bumps so as to correspond to the load applying ultrasound output set multiple stages large first A joining method comprising the step of joining two electrodes. 2. The ratio of the set value of the ultrasonic power and the load that are set to be large in a multistage manner is adjusted to be larger than about 0.001 W / gf per one bump. Joining method. In the bonding method of bonding the bump disposed on the first electrode and the second electrode,
The first electrode and the second electrode are pressed with a second load larger than the first load required for leveling the bump height, and an ultrasonic wave is applied with a first output to A first joining step for joining the bump and the second electrode;
The first electrode and the second electrode are pressed with a third load larger than the second load, and the ultrasonic wave is applied with a second output larger than the first output. joining method characterized by having a second junction step of joining the second connecting terminal and the conductive bump.   The ratio between the first output and the second load and the ratio between the second output and the third load are adjusted to be greater than about 0.001 W / gf per bump. The bonding method according to claim 3.   The joining method according to any one of claims 3 to 4, wherein the second joining step is performed in multiple stages while increasing the second output and the third load.

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