JP3930327B2 - High frequency circuit board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency circuit board used at a high frequency such as a microwave band or a millimeter wave band.
[0002]
[Prior art]
As a high-frequency circuit board used in a microwave band, a millimeter wave band, or the like, for example, there is a face-up MMIC board (hereinafter referred to as an MMIC board). In the MMIC substrate, circuit elements such as amplifier elements are arranged on the front surface, and the back surface thereof is bonded to a predetermined position on the package by AuSn solder or the like.
[0003]
When joining the MMIC substrate on the package, in order to improve the wetness of the AuSn solder, for example, a method of attaching the MMIC substrate to the transfer collet and moving the MMIC substrate slightly in the X-axis direction or the Y-axis direction is taken. Yes.
[0004]
However, when the MMIC substrate is bonded onto the package using a transfer collet or the like and then the bonded portion is observed with a soft X-ray transmission device, bubbles are often generated at the bonded portion. When the size of such bubbles is increased and the number thereof is increased, the thermal resistance is increased, the heat radiation characteristics of the semiconductor are deteriorated, and the thermal reliability is lowered.
[0005]
Here, a conventional high-frequency circuit board will be described with reference to FIG. 3 taking an MMIC board as an example.
[0006]
FIG. 3A is a top view showing an MMIC substrate 31, an amplifying element 32 such as a field effect transistor and a capacitor 33, an electrode of the amplifying element 32 and a VIA hole 34 for grounding the capacitor 33, a signal terminal 35, a bias terminal 36, and the like. Circuit elements are formed.
[0007]
FIG. 3B is a bottom view. In this case, for example, a portion of a metal PHS (Plate-Heat-Sink) structure 37 provided on the entire back surface of the MMIC substrate 31 is shown. The PHS structure 37 has a function of grounding the back surface of the MMIC substrate 31 or releasing the heat of the substrate, and a plurality of holes 38 for forming VIA holes 34 are formed in the PHS structure 37. FIG. 3C is an enlarged view of a portion of a circle B in FIG.
[0008]
FIG. 3D is a diagram showing a state in which the MMIC substrate 31 is bonded to a predetermined mounting position of the package 39, and the MMIC substrate 31 and the package 39 are bonded by AuSn solder 40 or the like. This soldering is usually performed in an atmosphere of N2 gas or the like. For example, the MMIC substrate 31 is attached to a transfer collet (not shown), and the MMIC substrate 31 is slightly moved, for example, in the X-axis direction or the Y-axis direction while scrubbing while applying an appropriate load to the MMIC substrate 31. Then, the MMIC substrate 31 and the package 39 are joined.
[0009]
At this time, the AuSn solder 40 diffuses into the surface of the PHS structure 37 on the back surface of the MMIC substrate 31, and the MMIC substrate 31 and the package 39 are joined.
[0010]
FIG. 3E is a perspective view of the joint between the MMIC substrate 31 and the package 39 using a soft X-ray transmission device. Reference numeral 41 indicates bubbles remaining inside the joint.
[0011]
[Problems to be solved by the invention]
When bonding a conventional high-frequency circuit board on a package, for example, the high-frequency circuit board is attached to a transfer collet, and the high-frequency circuit board is scrubbed and bonded. However, even if the high-frequency circuit board is moved in the X-axis direction or the Y-axis direction, bubbles often remain in the joint portion. Therefore, when the joint portion between the high-frequency circuit board and the package is seen through with a soft X-ray transmission device or the like, many bubbles are seen inside the joint portion.
[0012]
In this case, the high-frequency circuit board is moved in both the X-axis direction and the Y-axis direction by the transfer collet so as to improve the wetness of the AuSn solder and no bubbles remain, and is scrubbed and joined. However, even when scrubbing, bubbles remain inside the joint, resulting in an increase in thermal resistance and a decrease in the thermal reliability of the semiconductor.
[0013]
Moreover, the conventional high frequency circuit board is provided with a metal PHS structure on the back surface thereof. In this case, for example, GaAs and PHS structure metal constituting the main body portion of the high-frequency circuit board have different thermal expansion coefficients. Therefore, when the temperature rises, as shown in FIG. 4, the MMIC substrate 31 may be warped due to the bimetal effect, and the circuit elements formed on the MMIC substrate 31 may be damaged.
[0014]
An object of the present invention is to provide a high-frequency circuit board in which the above-described drawbacks are solved and the thermal resistance of the joint portion is reduced.
[0015]
[Means for Solving the Problems]
The present invention provides a high frequency circuit board having a PHS structure formed on a back surface, wherein a slit having an intersection is formed in the PHS structure, and the width of the intersection is larger than that of a slit adjacent to the intersection. It is characterized by becoming .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG. 1 by taking an MMIC substrate as an example.
[0017]
FIG. 1A is a top view, and an MMIC substrate 11 includes an amplifying element 12 and a capacitor 13 such as a field effect transistor, a VIA hole 14 for grounding an electrode of the amplifying element 12 and the capacitor 13, a signal terminal 15, and a bias terminal. Circuit elements such as 16 are formed.
[0018]
FIG. 1B is a bottom view, and in this case, a portion of a metal PHS structure 17 provided on the back surface of the MMIC substrate 11 is shown. The PHS structure 17 has a function of grounding the back surface of the MMIC substrate 11 and a function of releasing heat generated by the amplifying element 12 on the MMIC substrate 11, and a plurality of holes constituting the VIA hole 14 in the PHS structure 17 portion. 18 is formed.
[0019]
Further, fine slits S extending in the vertical direction and the horizontal direction, for example, are formed in a lattice shape in the portion of the PHS structure 17. The slit S is provided, for example, so as to pass through the hole 18 of the VIA hole 14 or, for example, is formed so that the intersection of the slit S and the position of the hole 18 of the VIA hole 14 coincide. In this case, the crossing portion of the slit S is larger in dimensions such as the width than the adjacent portion. FIG. 1C is an enlarged view of a circle B portion in FIG.
[0020]
FIG. 1D shows a state in which the MMIC substrate 11 is bonded to a predetermined mounting position of the package 19, and the MMIC substrate 11 and the package 19 are bonded by AuSn solder 20 or the like. This soldering is usually performed in an atmosphere of N2 gas or the like. For example, the MMIC substrate 11 is attached to a transfer collet (not shown), and the MMIC substrate 11 is slightly moved, for example, in the X-axis direction or the Y-axis direction while scrubbing while applying an appropriate load to the MMIC substrate 11. Then, the MMIC substrate 11 is bonded to the package 19.
[0021]
At this time, the AuSn solder 20 is rapidly diffused to the entire surface of the PHS structure 17 through the slit 12 or the like, and the MMIC substrate 11 and the package 19 are joined.
[0022]
FIG. 1E is a perspective view of the joint between the MMIC substrate 11 and the package 19 using a soft X-ray transmission device or the like, and there is almost no trace of bubbles observed in the case of the prior art.
[0023]
According to the configuration described above, the fine slits S are provided in the PHS structure 17. In this case, due to the capillary phenomenon caused by the slit S, the AuSn solder 20 having a large surface tension in a molten state flows through the slit S at a high speed, and the AuSn solder 20 is diffused on the entire surface of the PHS structure 17. In addition, the rapid diffusion of the AuSn solder 20 eliminates the accumulation place of the AuSn solder 20 and reduces bubbles.
[0024]
A slit S is provided in the PHS structure 17. Therefore, as shown in FIG. 2, the warpage of the MMIC substrate 11 due to the bimetal effect is suppressed, and damage and the like occurring in the circuit elements on the MMIC substrate 11 are prevented.
[0025]
In the configuration described above, the dimension of the intersection of the slits S is enlarged. In this case, bubbles are driven out by the AuSn solder gathered at the intersection, and the generation of bubbles is reduced. Moreover, since the hole of the VIA hole is formed in the PHS structure portion, the hole portion can be used as a bubble escape location.
[0026]
For VIA holes such as VIA holes that ground the source electrode of a field effect transistor, for example, if there is no problem even if it penetrates from the back surface to the surface, open the VIA hole. In this case, the bubbles are completely expelled, and the bubbles inside the joint can be reduced.
[0027]
As described above, according to the structure in which the slit is provided in the portion of the PHS structure, the generation of bubbles at the joint portion is reduced, and the thermal reliability of the MMIC substrate is improved. Further, when a slit is provided in the PHS structure portion on the back surface, the bimetal effect of, for example, GaAs constituting the main body portion of the MMIC substrate and, for example, an Au / Pa / Ti film constituting the PHS structure portion is reduced, and the MMIC substrate Warpage can be suppressed.
[0028]
In addition, the wettability of the AuSn solder is improved by the capillary action of the slit. This eliminates the need for an expensive transfer collet for moving the high-frequency circuit board, thereby reducing the manufacturing cost. Further, at the time of joining, scrubbing operation becomes unnecessary only by pressurization. Therefore, for example, AuSn solder can be wetted to the extent that ultrasonic vibration is applied, and automation is facilitated, and reflow in an N2 atmosphere is facilitated.
[0029]
Further, when the dimension of the intersecting portion between the slits is increased, the dimension, shape, position, and the like may be formed so as to coincide with the grounding VIA hole.
[0030]
【The invention's effect】
According to the present invention, an MMIC substrate with reduced thermal resistance can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic structural diagram for explaining an embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining a state of warping of the MMIC substrate in the embodiment of the present invention.
FIG. 3 is a schematic structural diagram for explaining a conventional example.
FIG. 4 is an explanatory diagram for explaining a state of warping of an MMIC substrate in a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... MMIC board 12 ... Amplifying element 13 ... Capacitor 14 ... VIA hole 15 ... Signal terminal 16 ... Bias terminal 17 ... PHS structure 18 ... VIA hole 19 ... Package 20 ... AuSn solder S ... Slit

Claims (7)

In a high-frequency circuit board having a PHS structure formed on the back surface, a slit having an intersection is formed in the PHS structure, and the width of the intersection is larger than that of a portion adjacent to the intersection. High frequency circuit board characterized by High-frequency circuit board of 請 Motomeko 1 wherein that are formed in a lattice shape with a slit extending in longitudinal and transverse directions. High-frequency circuit board according to claim 1 Symbol placement soldered surface of the PHS structure to the package. In a high-frequency circuit board having a PHS structure formed on the back surface, a VIA hole having a hole penetrating from the back surface side to the front surface side is provided in the high- frequency circuit board, and the PHS structure portion passes through the hole portion of the VIA hole. A high frequency circuit board having a slit as described above . In the high frequency circuit board having the PHS structure formed on the back surface, a VIA hole having a hole penetrating from the back surface side to the front surface side is provided in the high frequency circuit board, and the intersection of the PHS structure portion is a hole of the VIA hole. A high-frequency circuit board , wherein a slit is provided so as to coincide with the position of . 6. The high frequency circuit board according to claim 4, wherein the slits are formed in a lattice shape extending in the vertical direction and the horizontal direction . 6. The high-frequency circuit board according to claim 4, wherein the surface of the PHS structure is soldered to the package.

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