JP2002299501A - Monolithic millimeter wave integrated circuit and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monolithic millimeter wave integrated circuit together with a manufacturing method thereof for improved reliability related to a bump. SOLUTION: On an MMIC substrate 21 of a monolithic millimeter wave integrated circuit 20, a signal line 22 of a coplanar waveguide and ground electrodes 23 and 24 of the coplanar waveguide are formed. The unit area bumps 26a, 26b, 27a, and 27b formed on the ground electrodes 23 and 24 is larger than that of bumps 25a and 25b formed on the signal line 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip-chip mounted monolithic millimeter wave integrated circuit (MMIC).

[0002]

2. Description of the Related Art Millimeter-wave systems such as millimeter-wave radar and millimeter-wave wireless LAN are used for transmitting and receiving millimeter waves.
C (MMIC) is required, but in order to realize these systems, a low-loss mounting technology of the MMIC is required. Conventionally, after mounting this MMIC in a millimeter wave module, wire bonding has been used for connection with wiring on a mounting board. However, there is a problem in that the connection by wire has a problem that the length is not sufficiently small with respect to the wavelength of the millimeter wave, and the variation in the length is large, so that the loss at the connection portion becomes large.

In recent years, flip chip connection has been researched and developed as an MMIC connection method. M
In flip-chip mounting of the MIC, the chip and the wiring on the substrate are connected via bumps. The height of the bumps can be as short as 100 μm or less, which is several hundred μm of the wire length. it can. Further, since the height variation of the bump can be made smaller than the variation of the wire length, the loss due to the impedance deviation of the connection portion can also be reduced.

As described above, flip-chip mounting technology using bumps can reduce the loss of a millimeter-wave module on which an MMIC is mounted. For example, IEEE MTT-S Digest 1997
P. At 731, Au of the same shape is formed by plating.
The MMIC on which the bumps are formed is bonded to an electrode pad having Sn formed on the outermost surface on the alumina substrate (hereinafter, referred to as a first flip-chip mounting structure). Also, I
EEE MTT-S Digest 1998P. 10
In 95, an MMIC on which stud bumps having the same shape are formed is flip-chip mounted on a wiring portion on an alumina substrate (hereinafter, referred to as a second flip-chip mounting structure).

Certainly, in these structures, flip-chip mounting using bumps is performed, thereby realizing low-loss connection in a millimeter wave band such as 77 GHz. However, looking at these structures, the bumps all have the same shape, and the diameter is very fine, about 50 μm. Therefore, the area where the chip and the mounting board are joined is smaller than the area of the chip, and compared to the face-up connection using wire bonding in which the entire back surface is die-bonded to the mounting board with a conductive adhesive or the like. There is a problem that the bonding strength of the chip is reduced.

As a method for improving this, it is conceivable to increase the number of bumps as much as possible. In particular, when stud bumps are used as in the above-mentioned second flip chip mounting structure, the number of bumps increases. There is a new problem that leads to an increase in man-hours. In the first flip-chip mounting structure, the bumps are formed by plating. Therefore, it is possible to increase the number of bumps only by changing the mask. However, if the distance between adjacent bumps is too short, the patterning time is reduced. In this case, the shape of the resist cannot be controlled, and the bump cannot be formed as desired.

Due to these problems, development of a new bump structure and manufacturing method for MMIC flip chip mounting is a key to realizing a millimeter wave system.

[0008]

SUMMARY OF THE INVENTION The present invention has been made under such a background, and an object of the present invention is to provide a monolithic millimeter-wave integrated circuit capable of improving the reliability of bumps and a method of manufacturing the same. Is to provide.

[0009]

According to the present invention, the number of bumps formed on the ground electrode of the coplanar waveguide is smaller than that of bumps formed on the signal line of the coplanar waveguide. When the area of the MMIC is increased, the MM
The bonding area between the IC substrate (chip) and the mounting substrate can be increased. Therefore, the joining strength can be easily improved.

If the material of the bumps is Au (gold), a low-loss connection can be obtained, and a change with time such as oxidation does not easily occur. When the bonding material is formed on the bump as described in claim 3, there is no need to provide the bonding material on the mounting substrate, and a general-purpose mounting substrate can be adopted, which contributes to cost reduction. .

[0011] When the material of the bonding material is SnPb, flip-chip mounting can be easily performed. If the material of the bonding material is Sn, the bump material is Au (gold), so that eutectic AuSn is formed by heating to facilitate flip-lip mounting. It becomes possible.

According to a sixth aspect of the present invention, when the bump formed on the ground electrode of the coplanar waveguide formed across the signal line of the coplanar waveguide extends along the signal line of the coplanar waveguide, Since the ground electrode on the MMIC and the ground electrode on the mounting board have the same potential, leakage of the millimeter wave signal in the parallel plate mode, which is a transmission mode other than the coplanar waveguide mode (CPW mode), can be prevented.

A signal line having a T-shaped or cross-shaped branch as a bump formed on a ground electrode of a coplanar waveguide formed with a signal line of the coplanar waveguide interposed therebetween. When the ground electrode bump is formed so as to be located in the vicinity of the branch portion, the ground electrode of the MMIC and the ground electrode of the mounting board have the same potential in the vicinity of the branch portion. Can be reduced.

According to the present invention, the bump formed on the ground electrode has a larger area per bump than the bump formed on the signal line.
In addition to the functions and effects of the invention described in 7, the bonding strength between the MMIC and the mounting board can be improved.

According to a ninth aspect of the present invention, the cross section of the bump in a direction parallel to the surface of the MMIC substrate is shaped to extend in a direction in which the signal line of the coplanar waveguide extends. In addition to the functions and effects of the present invention, since the shape of the bump can be adjusted to the shape of the ground electrode, the bonding area can be effectively increased, and the bonding strength can be further improved.

According to a tenth aspect, when the material of the bump is Au (gold), in addition to the functions and effects of the inventions according to the sixth to ninth aspects, a low-loss connection can be obtained and oxidation can be achieved. Changes over time are small.

According to the eleventh aspect, when a bonding material is formed on the bump, in addition to the functions and effects of the inventions according to the sixth to tenth aspects, a general-purpose mounting board can be adopted.
Contribute to cost reduction.

According to a twelfth aspect of the present invention, when the material of the joining material is SnPb,
In addition to the effect, flip-chip mounting can be easily performed. As described in claim 13, when the material of the bonding material is Sn,
In addition to the functions and effects of the invention described in claim 11, since the bump material is Au (gold), eutectic AuSn is formed by heating, and flip-chip mounting can be easily performed.

As a method for manufacturing a monolithic millimeter-wave integrated circuit, a plating method is used,
If the bump formed on the ground electrode is formed to have a larger area per bump than the bump formed on the signal line of the coplanar waveguide, the bonding area can be increased and the bonding strength can be improved. Further, since the plating method is adopted as the forming method, the number of steps is not increased.

According to a fifteenth aspect, the plating method is to form an Au bump by an electroplating method.
A low-loss connection is obtained, and changes with time such as oxidation are small.

According to a sixteenth aspect, when a bonding material is formed by a plating method using the same resist mask after forming an Au bump by a plating method, a general-purpose mounting substrate can be adopted, and Contribute to cost reduction. Furthermore, since the resist mask for bump formation is used as it is, an increase in the number of steps can be minimized.

According to a seventeenth aspect, when the material of the bonding material is SnPb, flip-chip mounting can be easily performed. As described in claim 18, when the material of the bonding material is Sn, the bump material is Au (gold), so that the eutectic AuSn is formed by heating and the flip chip mounting can be easily performed. It becomes possible.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a monolithic millimeter-wave integrated circuit (MMIC) 20 and a mounting substrate 10 after mounting. FIG. 2 shows a perspective view of the mounting board 10, and FIG. 3 shows the MMIC 20 with its front and back reversed. Further, FIG. 4 shows the MMIC 20 and the mounting substrate 1 from the direction A in FIG.
FIG. 5 shows the MMIC 20 and the mounting board 10 viewed from the direction B in FIG.

As shown in FIGS. 1 and 2, a coplanar waveguide is formed on the mounting board 10. That is, on the upper surface of the board 11 of the mounting board 10, the ground electrode (ground conductor) 13 is provided on both sides of the signal line (center conductor) 12a.
a, 14a are formed, and ground electrodes (ground conductors) 13b, 14b are formed on both sides of the signal line (center conductor) 12b at positions separated from them.

On the other hand, as shown in FIG. 3, a coplanar waveguide is formed on the back surface of the MMIC substrate 21 in the MMIC 20. That is, on the upper surface of the substrate 21, ground electrodes (ground conductors) 23 and 24 are formed on both sides of the signal line (center conductor) 22. MMIC2
On the signal line 22 at 0, bumps 25a and 25b
On the ground electrodes 23 and 24, bumps 26a,
26b, 27a and 27b are formed. Bump 25
The material of a, 25b, 26a, 26b, 27a, 27b is Au (gold). Also, in the MMIC 20, the MMI
Although not shown, an active element, a matching circuit, a bias line, and the like are formed on the C substrate 21.

Then, as shown in FIG.
The MMIC 20 is placed on top of the
The bump on the MIC 20 side and the line conductor on the mounting substrate 10 are joined. That is, the bumps 25a of the MMIC 20,
25b are joined to the signal lines 12a and 12b of the mounting substrate 10, and the bumps 26a and 26
b, 27a and 27b are the ground electrodes 13 of the mounting board 10.
a, 13b, 14a, and 14b. As shown in FIG. 4, the signal flowing on the mounting substrate 10 side flows through the MMIC 20 via the bumps, and is amplified by the active element through the bumps. Further, the signal flows on the mounting substrate 10 side again via the bumps. Flows.

Here, in the present embodiment, as shown in FIG. 3, bumps 26a, 26b, 27a formed on ground electrodes 23, 24 rather than bumps 25a, 25b formed on signal line 22 of MMIC 20. , 27b have a larger area per one. Specifically, as shown in FIG. 3, if the diameter of the cylindrical bumps 25a and 25b is R1, the diameter of the cylindrical bumps 26a and 26b is R2, and the diameter of the cylindrical bumps 27a and 27b is R3, R1 <
R2 = R3.

That is, in the comparative examples shown in FIGS. 14 and 15, in the relationship among the diameter R1 of the cylindrical bump 100, the diameter R2 of the cylindrical bump 101, and the diameter R3 of the cylindrical bump 102, R1 = R2 = R3. In the embodiment of FIG. 3, R1 <R2 = R3, and the ground electrode 2 is smaller than the bumps 25a and 25b on the signal line 22.
The area per one bump 26a, 26b, 27a, 27b on 3, 3 is large.

The bumps 25a, 25b, 26a, 26
As shown in FIG. 6, b, 27 a, and 27 b are formed by forming a signal line 22 and ground electrodes 23 and 24 on an MMIC substrate 21 in the manufacturing process of the MMIC 20 and then coating and plating a resist mask 28. Form. In other words, the ground electrodes 23, 24 are smaller than the bumps 25a, 25b formed on the signal line 22 using the plating method.
The bumps 26a, 26b, 27a, 27b formed thereon are formed such that the area per one bump is large. In particular,
Au bumps 25a, 25b, 26 by electroplating
a, 26b, 27a and 27b are formed.

When the MMIC 20 is flip-chip mounted, a coplanar waveguide is usually applied to the line of the MMIC 20, but the width of the signal line cannot be made too large due to the characteristics of the millimeter wave and the miniaturization of the chip. On the other hand, since the ground electrode occupies most of the area of the chip, the bump can be enlarged. The bumps 25a formed on the signal line 22 in this manner,
By increasing the area per bump 26a, 26b, 27a, 27b formed on the ground electrodes 23, 24 compared to 25b, the MMIC substrate 21 (chip) can be connected to the MMIC flip-chip. The bonding area of the mounting substrate 10 can be increased. Thus, the joining strength can be easily improved.

The bumps 25a, 25b, 26a, 2
Since the material of 6b, 27a, 27b was Au (gold),
In addition to the effect of increasing the bonding strength, the resistance of the bumps can be reduced, and the change with time such as oxidation does not easily occur, so that the millimeter wave can be transmitted stably with low loss (a low-loss connection can be obtained).

Further, the bumps 25a, 25b, 26a,
By using a plating method as a method for forming 26b, 27a, and 27b, it is possible to freely set the shape of the mask at the time of patterning without causing an increase in man-hours only by changing the mask pattern. In particular, since the Au bumps are formed by the electroplating method, a low-loss connection can be obtained as described above, and changes with time such as oxidation are small.

Here, as shown in FIG.
Au bumps (25a, 25b, 26a, 26b, 27
a, 27b) may be formed on the bonding material 29, and SnPb or Sn is used as the material. As a result, the bonding strength can be increased, and stable low-loss bonding can be achieved. Also, by forming the bonding material 29 on the bumps, it is not necessary to form a bonding material on the electrode pad side of the mounting substrate 10, and a general-purpose mounting substrate can be used, which contributes to cost reduction. In particular, if the material of the bonding material 29 is SnPb, flip-chip mounting can be easily performed, and if the material of the bonding material 29 is Sn, the bump material is Au (gold).
Therefore, when heated, the eutectic AuS
By forming n, flip-lip mounting can be easily performed.

Further, as shown in FIG. 8, at the time of plating in the bump formation step, the Au bump (2
5a, 25b, 26a, 26b, 27a, 27b), a bonding material 29 is formed by plating using the same resist mask. As a result, a bonding material such as SnPb or Sn can be continuously formed on the bumps. Therefore, as described above, a general-purpose mounting board can be adopted, which contributes to cost reduction. further,
Since the resist mask 28 for bump formation is used as it is, an increase in man-hours can be minimized. In particular, as described above, when the material of the bonding material 29 is SnPb, flip-chip mounting can be easily performed.
If the material of No. 9 is Sn, the bump material is Au (gold), so that eutectic AuSn can be formed by heating and flip chip mounting can be easily performed.

In FIG. 3, the bumps 25a, 25b, 2
Although the shapes of 6a, 26b, 27a, and 27b were cylindrical,
The bump shape is not a cylinder, and reference numerals 30, 31, 3 in FIG.
As shown by 2, it may be another shape such as a square pole. (Second Embodiment) Next, the second embodiment will be described in the first embodiment.
The following description focuses on differences from the third embodiment.

FIG. 10 shows a bump structure of the MMIC according to the present embodiment, which replaces FIG. FIG. 11 shows the mounting substrate 1.
0 shows a perspective view. In this MMIC, as shown in FIG. 10, bumps 41 and 42 formed on the ground electrodes 23 and 24 of the coplanar waveguide formed with the signal line 22 of the coplanar waveguide therebetween are connected to the signal line of the coplanar waveguide. It extends along 22. In the mounting substrate 10, the ground electrodes 43 and 44 extend in a connected state as shown in FIG.

In this case, since the ground electrode on the MMIC and the ground electrode on the mounting board have the same potential,
It is possible to prevent the leakage of the millimeter wave signal in the parallel plate mode which is a transmission mode other than the coplanar waveguide mode (CPW mode).

In FIG. 10, columnar pumps are used as the bumps 40a and 40b formed on the signal line 22. (Third Embodiment) Next, a third embodiment will be described with reference to the first embodiment.
The following description focuses on differences from the third embodiment.

FIG. 12 shows a circuit configuration in this embodiment. As shown in part B of FIG. 12, SP3T (Single-po
le three-throw) The signal line has a cross-shaped branch (or T-shaped branch) like a switch, and the bump configuration connected to this coplanar waveguide is as shown in FIG. . FIG. 13 shows the MMI in this embodiment.
It is a top view which shows the bump structure of C.

In FIG. 13, ground electrodes 51 are formed separately along signal lines 50,
A bump 52 formed thereon extends along the signal line 50. In particular, a bump 52 formed on the ground electrode 51
Are formed so as to be located near the branch portion of the signal line 50. That is, as the bump formed on the ground electrode formed with the signal line interposed therebetween, the bump for the ground electrode is positioned near the branch in the signal line 50 having the cross-shaped (or T-shaped) branch. 52 are formed.

For this reason, the ground electrode on the chip side and the ground electrode on the mounting substrate side have the same potential inside the chip, particularly near (around) the branch portion. Therefore, it is possible to reduce unnecessary transmission of millimeter waves in the parallel plate mode generated in the chip and the mounting board. Therefore, it is possible to prevent signal leakage between the lines after branching, and to reduce crosstalk between the lines.

Further, the cross section of the bump 52 in a direction parallel to the surface of the MMIC substrate is extended in the direction in which the signal line 50 of the coplanar waveguide extends. Therefore, the bonding area can be effectively increased, and the bonding strength can be further improved.

Also in the second and third embodiments, if the area per bump of the bump formed on the ground electrode is larger than that of the bump formed on the signal line, the MMI
The bonding strength between C and the mounting board can be improved. When the material of the bump is Au (gold), a low-loss connection can be obtained, and a change with time such as oxidation is small. Further, when a bonding material is formed on the bumps, a general-purpose mounting substrate can be adopted, which contributes to cost reduction. In particular, when the material of the bonding material is SnPb, flip-chip mounting can be easily performed, and when the material of the bonding material is Sn, the bump material is Au (gold). By forming a certain AuSn, flip-chip mounting can be easily performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure according to a first embodiment.

FIG. 2 is a perspective view of a mounting board.

FIG. 3 is a perspective view of an MMIC.

FIG. 4 is a view taken in the direction of the arrow A in FIG. 1;

FIG. 5 is a view taken in the direction of arrow B in FIG. 1;

FIG. 6 is a conceptual diagram for explaining a bump forming process.

FIG. 7 is a longitudinal sectional view for explaining another example.

FIG. 8 is a conceptual diagram for explaining a bump forming process.

FIG. 9 is a partial plan view of an MMIC for explaining another example.

FIG. 10 is a perspective view showing a structure according to a second embodiment.

FIG. 11 is a perspective view of a mounting board.

FIG. 12 is a circuit diagram according to a third embodiment.

FIG. 13 is a plan view showing the structure of a portion B in FIG. 12;

FIG. 14 is a longitudinal sectional view for explaining a comparative example.

FIG. 15 is a transverse sectional view taken along line CC of FIG. 14;

[Explanation of symbols]

10 mounting board, 20 monolithic millimeter-wave integrated circuit (MMIC), 21 MMIC board, 22 signal line,
23, 24: ground electrode, 25a, 25b: bump,
26a, 26b: bump, 27a, 27b: bump, 2
8 resist mask, 29 bonding material, 40a, 40b
Bump, 41, 42 ... bump, 50 ... signal line, 51 ...
Ground electrode, 52 ... bump.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naosuke Uda 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi F1 term in Toyota Central R & D Labs., Inc. 5J012 BA04

Claims (18)

[Claims] 1. A monolithic millimeter-wave integrated circuit (20) having flip-chip mounting bumps formed on an MMIC substrate (21), wherein bumps (25a, 25a) are formed on a signal line (22) of a coplanar waveguide. The bumps (26a, 26b, 27a, 27b) formed on the ground electrodes (23, 24) of the coplanar waveguide are more likely to be 1
A monolithic millimeter-wave integrated circuit having an increased area per unit. 2. The monolithic millimeter-wave integrated circuit according to claim 1, wherein said bumps (25a, 25b, 26a, 26b, 27).
a, 27b) is a monolithic millimeter-wave integrated circuit, wherein the material is Au. 3. The monolithic millimeter-wave integrated circuit according to claim 1, wherein said bumps (25a, 25b, 26a, 26b, 27).
A monolithic millimeter-wave integrated circuit characterized in that a bonding material (29) is formed on (a, 27b). 4. The monolithic millimeter-wave integrated circuit according to claim 3, wherein the material of the bonding material (29) is SnPb. 5. The monolithic millimeter-wave integrated circuit according to claim 3, wherein the material of the bonding material is Sn. 6. A monolithic millimeter-wave integrated circuit in which bumps for flip-chip mounting are formed on an MMIC substrate, wherein a ground electrode (23) of a coplanar waveguide formed with a signal line (22) of the coplanar waveguide interposed therebetween. , 24) are formed on the bumps (41, 42).
A monolithic millimeter-wave integrated circuit extending along a signal line (22) of a coplanar waveguide. 7. A monolithic millimeter-wave integrated circuit in which a bump for flip-chip mounting is formed on an MMIC substrate, wherein the bump is formed on a ground electrode of the coplanar waveguide formed with a signal line of the coplanar waveguide interposed therebetween. A monolithic millimeter-wave integrated circuit, wherein a ground electrode bump (52) is formed so as to be located near the branch in a signal line (50) having a T-shaped or cross-shaped branch. 8. The monolithic millimeter-wave integrated circuit according to claim 6, wherein the bumps (40a, 4) formed on the signal line (22).
A monolithic millimeter-wave integrated circuit, wherein the area per bump (41, 42) formed on the ground electrode (23, 24) is larger than that of the monolithic millimeter wave integrated circuit (0b). 9. The monolithic millimeter-wave integrated circuit according to claim 7, wherein the bump (5) extends in a direction parallel to a surface of the MMIC substrate.
A monolithic millimeter-wave integrated circuit, wherein the cross-sectional shape of (2) is formed to extend in the direction in which the signal line (50) of the coplanar waveguide extends. 10. The monolithic millimeter wave integrated circuit according to claim 6, wherein a material of said bumps (40a, 40b, 41, 42, 52) is Au. Integrated circuit. 11. The monolithic millimeter-wave integrated circuit according to claim 6, wherein a bonding material is formed on said bumps (40a, 40b, 41, 42, 52). Millimeter wave integrated circuit. 12. The monolithic millimeter-wave integrated circuit according to claim 11, wherein the material of the bonding material is SnPb. 13. The monolithic millimeter-wave integrated circuit according to claim 11, wherein the material of the bonding material is Sn. 14. A method of manufacturing a monolithic millimeter-wave integrated circuit (20) in which bumps for flip-chip mounting are formed on an MMIC substrate (21), wherein a signal line (22) of a coplanar waveguide is formed by plating. ), The bumps (2) formed on the ground electrodes (23, 24) rather than the bumps (25a, 25b) formed thereon.
6a, 26b, 27a, and 27b) are formed so as to have a large area per one. 15. The method for manufacturing a monolithic millimeter-wave integrated circuit according to claim 14, wherein the plating is performed by Au plating (25) by electroplating.
a, 25b, 26a, 26b, 27a, 27b) for manufacturing a monolithic millimeter-wave integrated circuit. 16. The method for manufacturing a monolithic millimeter wave integrated circuit according to claim 14, wherein the Au bumps (25a, 25b, 26) are formed by the plating method.
a, 26b, 27a, 27b), and a bonding material (29) is formed by plating using the same resist mask (28). . 17. The method for manufacturing a monolithic millimeter wave integrated circuit according to claim 16, wherein the material of the bonding material (29) is SnPb. 18. The method for manufacturing a monolithic millimeter-wave integrated circuit according to claim 16, wherein the material of said bonding material (29) is Sn.