Patent Application
20120306063
The present disclosure relates to a method for manufacturing a high-frequency module in which an electronic component mounted on a resin substrate is covered by a resin, and a circuit formed of the electronic component is shielded.
A conventional high-frequency module will be described with reference to the drawings.
Printed circuit board 2 is made of a thermosetting resin. Electronic component 3 is mounted on an upper surface of printed circuit board 2. Here, electronic component 3 is a semiconductor device or the like, and the semiconductor device and printed circuit board 2 are connected to each other by wire bonding. Components other than electronic component 3 may be mounted on the upper surface of printed circuit board 2. Electronic component 3 forms a high-frequency circuit. Resin portion 4 is formed on the upper surface of printed circuit board 2, and electronic component 3 is buried in resin portion 4. Connection pattern 5 connected to the ground of the high-frequency circuit is formed in a peripheral end portion of the upper surface of printed circuit board 2.
Shield film 6 is a thick film conductor. Shield film 6 is formed to cover an upper surface and side surfaces of resin portion 4 and a part of a side surface of printed circuit board 2. An end portion of connection pattern 5 is arranged to be exposed from a side surface of resin portion 4, and the connection pattern 5 is electrically connected to shield film 6 in this exposing portion.
Next, a method for manufacturing conventional high-frequency module 1 will be described with reference to
In step S13 subsequent to step S12, a recess portion is formed in a position where printed circuit boards 2 are coupled together, and connection pattern 5 is exposed from the side surface of resin portion 4. In step S14 subsequent to step S13, conductive paste 6A is coated on the upper surface of resin portion 4 and is cured. At the same time, conductive paste 6A is also buried in the recess portion.
In step S15 subsequent to step S14, the coupling portion between printed circuit boards 2 is cut off. With this arrangement, high-frequency module 1 is completed.
In recent years, incorporating such high-frequency module 1 into mobile equipment has been progressing. Accordingly, a demand for a low-profile type of high-frequency module 1 has been increasing. Specifically, a thickness less than 1 mm including a thickness of printed circuit board 2 is demanded. An idea to meet such a demand includes reducing thicknesses of printed circuit board 2, resin portion 4, and electronic component 3, and mounting electronic component 3 with a face thereof placed downward.
However, since conventional high-frequency module 1 is formed by transfer molding, an internal stress (residual stress) tends to be caused in resin portion 4. When thickness of printed circuit board 2, resin portion 4, or electronic component 3 is reduced, deformation tends to be caused by the internal stress to printed circuit board 2, resin portion 4, electronic component 3, or the high-frequency module in its entirety. The internal stress is caused by various conditions such as flowability or ununiformity in the flow of resin 4A during transfer molding. The ununiformity becomes particularly noticeable when resin portions 4 are formed in a plurality of high-frequency modules 1 at one time, and different internal stresses are caused in individual high-frequency modules 1. In this way, since conventional high-frequency module 1 has a high-frequency circuit that is covered by resin portion 4, printed circuit board 2, resin portion 4, or electronic component 3 deforms, and sometimes deforms in a different degree. As a result, this may increase a variation in the characteristics of the high-frequency circuit. Particularly, when the high-frequency circuit is formed on printed circuit board 2, the influence exerted on the high-frequency module by the variation in the characteristics of the high-frequency circuit is very noticeable.
One example of the present disclosure relates to a method for manufacturing a high-frequency module.
The method for manufacturing a high-frequency module may includes the following steps:
placing a resin, which is in a non-flowable state, in a resin bath having an upper opening;
softening the resin in the resin bath until the resin becomes flowable;
placing, above the resin bath so as to close the upper opening, a substrate having a first surface on which an electronic component is mounted, with the electronic facing downward, and sucking air in a space formed between the substrate and the resin in the resin bath;
immersing the electronic component into the softened resin after the softening the resin and the sucking air in the space, and bringing the first surface of the softened resin;
pressurizing the softened resin and allowing the softened resin to flow into a gap between the resin substrate and the electronic component after the electronic component is immersed into the softened resin; and
curing the resin formed on the substrate and forming a resin portion on the substrate after the resin is allowed to flow into the gap.
The method may further include forming a metal film on a surface of the resin portion after the resin portion is formed. According to this method, an internal stress in the resin portion can be reduced, and a high-frequency module having a small variation in circuit characteristics can be realized.
Hereinafter, a description will be given of high-frequency module 21 according to this exemplary embodiment.
Resin substrate 22 is a multilayer substrate made of a glass epoxy material. Resin substrate 22 is, for example, a four-layer substrate having a thickness of 0.2 mm. Electronic component 24 such as a semiconductor device or a chip part is mounted on resin substrate 22 by means of solder 23. The semiconductor device which is electronic component 24 is a chip-size package having a thickness of 0.35 mm, and is mounted with a face thereof placed downward on resin substrate 22 by flip-chip bonding through solder bumps. A pitch between the bumps is, for example, about 0.25 mm, a distance between the bumps is about 0.12 mm, and a gap between electronic component 24 and resin substrate 22 is about 0.12 mm. Further, a gap between the chip part and resin substrate 22 is about 0.08 mm if the chip part is mounted.
Electronic component 24 forms a high-frequency circuit 111 When electronic component 24 is mounted on resin substrate 22, a high-frequency circuit 111 (for example, Electronic tuner for TV, Electronic tuner for receiving FM broadcast, Transmitting and receiving module for cell phone, Bluetooth, WiFi, WILAN, or the like) is formed on resin substrate 22. a high-frequency circuit 111 transmits signals which range from, for example, 30 MHz to 6 GHz. Electronic component 24 according to this exemplary embodiment is connected to resin substrate 22 through solder bumps. However, electronic component 24 may be mounted on resin substrate 22 by forming stud bumps in electronic component 24 and using an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), a non-conductive film (NCF), a non-conductive paste (NCP), or the like.
Resin portion 25 is formed on the upper surface of resin substrate 22 and buries therein electronic component 24. Resin portion 25 is a thermosetting resin. Shield metal film 26 is formed to cover surfaces (upper surface and all four side surfaces) of resin portion 25.
Shield metal film 26 is a thin film formed by sputtering and having a thickness of, for example, about 1 μm, and is a very thin and dense film with little pinholes. Shield metal film 26 may be formed by plating or apply conductive paste. Shield metal film 26 formed by sputtering is durum and suitable for dumping high frequency signals. Shield metal film 26 is made of, for example, copper having excellent conductivity. Accordingly, shield metal film 26 has excellent shield performance, and therefore high-frequency module 21 is resistant to interference or the like.
Ground wiring pattern 27 is formed in resin substrate 22. Ground wiring pattern 27 is extended as far as to a peripheral portion of resin substrate 22, and an exposing portion of ground wiring pattern 27 is formed on a side surface of resin substrate 22. Ground wiring pattern 27 and shield metal film 26 are connected to each other at the exposing portion.
Referring to
Ground wiring pattern 27 is connected to mounting pad 30A disposed on a bottom surface of resin substrate 22 through connection conductor 29A. Then, when high-frequency module 21 is mounted on a parent substrate (not illustrated), mounting pad 30A is connected to a ground wiring of the parent substrate. With this arrangement, the high-frequency circuit 111 formed on resin substrate 22 is surrounded by shield metal film 26 in upper and transverse directions thereof. Accordingly, it is possible to prevent a high-frequency signal that is processed (or generated) by the high-frequency circuit 111 from leaking outside, or to reduce a possibility in which a high-frequency noise generated outside jumps into the high-frequency circuit 111 in high-frequency module 21. As a result, it is possible to realize high-frequency module 21 resistant to electric interference.
Further, according to this exemplary embodiment, referring to
Ground wiring pattern 27 is preferably not connected to the ground (not illustrated) of the high-frequency circuit 111. This means that the ground of the high-frequency circuit 111 is connected to ground terminal 28 on the surface of resin substrate 22, and is led to mounting pad 30B on the bottom surface of resin substrate 22 through connection conductor 29B that brings the upper and bottom surfaces of resin substrate 22 into conduction. In this way, the ground of the high-frequency circuit 111 and shield metal film 26 are separated in terms of high frequency (electrically). As a result, it is hardly possible that a high-frequency signal of the high-frequency circuit 111 is radiated outside from shield metal film 26, or a high-frequency noise that hops onto shield metal film 26 infiltrates into the high-frequency circuit 111.
Next, a method for manufacturing high-frequency module 21 will be described with reference to the drawings.
In mounting step S51, electronic component 24 is mounted on resin substrate 22 while a plurality of resin substrates 22 is coupled together (as a main substrate), and the high-frequency circuit 111 is formed on resin substrate 22. Specifically, cream-based solder 23 is printed on the upper surface of resin substrate 22, and electronic component 24 is mounted thereon and soldered to resin substrate 22 by reflow soldering. The high-frequency circuit 111 is formed on a bottom surface side of electronic component 24, and electronic component 24 is mounted by flip-chip bonding in a direction in which a surface where the high-frequency circuit 111 is formed faces resin substrate 22 (in a face-down direction).
In mounting step S51, after mounting of electronic component 24 is completed, characteristics of the high-frequency circuit 111 are tested. In this test, a correction work may be performed on the circuit having characteristics outside a predetermined range. This correction may work involves replacing the part with another chip part having a different constant, trimming of a pattern inductor, or the like.
In resin portion forming step S52 subsequent to mounting step S51, resin portion 25 is formed on the upper surface of resin substrate 22. Resin 25A of a thermosetting type is used for resin portion 25 according to this exemplary embodiment.
In separation step S53 subsequent to resin portion forming step S52, coupled resin substrates 22 are separated into individual pieces using a rotating dicing blade. As a result, resin portion 25 formed on a coupling portion of resin substrate 22 and the coupling portion of resin substrate 22 are removed so that coupled resin substrates 22 are separated into individual resin substrates 22. Also, as a result of the cutting, the exposing portion of ground wiring pattern 27 is formed on a side surface of resin substrate 22.
In shield metal film forming step S54, a metal sputtered thin film is formed by metal sputtering as shield metal film 26 on a surface (upper and side surfaces) of resin portion 25 and side surfaces of resin substrate 22. As a result, shield metal film 26 is connected to ground wiring pattern 27 at the exposing portion of ground wiring pattern 27 provided on a side surface of resin substrate 22. Subsequent to shield metal film forming step S54, a final characteristic test may be performed on high-frequency module 21 so that high-frequency module 21 is completed.
According to the above-mentioned manufacturing method, shield metal film 26 is formed after separation step S53. For this reason, flaws are hardly caused by dicing in shield metal film 26. This is particularly effective when the film thickness of shield metal film 26 is small.
Next, resin portion forming step S52 will be described with reference to the drawings. First, resin portion forming apparatus 61 for forming resin portion 25 on resin substrate 22 will be described.
Resin bath 63 having space in which resin 25A is thrown is provided below resin substrate mounting portion 62. Resin bath 63 may be movable in a vertical direction. In addition, bottom portion 63A of resin bath 63 may be independent from a movement of entire resin bath 63 and may be movable in a vertical direction (direction of an arrow 100 in
Heating portions (not illustrated) are individually provided in resin substrate mounting portion 62 and resin bath 63, and these heating portions individually heat resin substrate 22 and resin 25A. Further, resin portion forming apparatus 61 is provided with a compressor or the like. The compressor sucks air in resin bath 63 or between resin bath 63 and resin substrate mounting portion 62 so that formation of resin portion 25 can be performed substantially under vacuum.
Here, the process of sucking the air in space 64 may be performed either before or after the process of softening resin 25A to a flowable state. However, it is possible to shorten the time by performing these two processes in parallel with each other.
Resin 25A before being thrown into resin bath 63 is granular, and a predetermined amount of resin 25A measured by a measuring container is thrown into resin bath 63. Here, resin 25A is a thermosetting resin that does not exhibit fluidity at a temperature lower than a first temperature, exhibits fluidity in a range of temperature equal to or higher than the first temperature and lower than a second temperature, and is cured at a third temperature which is equal to or higher than the second temperature. Since resin 25A is granular when resin 25A is thrown into resin bath 63, it is possible to accurately measure an amount of resin 25A. It is also easy to automate the measurement and throwing.
Softening step S71 is performed according to the following procedure. Resin substrate mounting portion 62 and resin bath 63 are heated by the heating portions in advance so that a temperature of resin substrate mounting portion 62 and resin bath 63 becomes a temperature (first temperature) or higher at which resin 25A melts (exhibits fluidity) but a temperature lower than a temperature (second temperature) at which resin 25A cures. Resin 25A according to this exemplary embodiment is a thermosetting epoxy resin that exhibits smaller fluidity at a temperature lower than 140° C., is softened the most and exhibits fluidity at a temperature equal to or higher than 140° C. but lower than 175° C., and is cured at a third temperature equal to or higher than 175° C. Accordingly, the temperature of resin substrate mounting portion 62 and resin bath 63 is set to a temperature equal to or higher than 140° C. but lower than 175° C.
Resin substrate mounting portion 62 may be structured to slide in a horizontal direction in
In addition, since resin substrate mounting portion 62 opens an area therebelow by being slid, resin substrate 22 is absorbed onto a bottom surface of resin substrate mounting portion 62 while electronic component 24 is directed downward. Then, resin substrate mounting portion 62 slides again and stops at a position above resin bath 63. When throwing of resin 25A and mounting of resin substrate 22 are completed in this way, sucking air in space 64 is started to be sucked. Then, after resin 25A melts to become a complete flowable state, the suction is stopped, and the vacuum state at this moment is maintained.
In resin portion forming apparatus 61 according to this exemplary embodiment, resin substrate mounting portion 62 horizontally slides. However, resin bath 63 may slide instead. Further, at least one of resin substrate mounting portion 62 and resin bath 63 may be moved in a vertical direction. However, in this case, a distance between resin bath 63 and resin substrate mounting portion 62 is adjusted to be opened to such a degree that allows throwing operation of resin 25A and mounting operation of resin substrate 22.
Specifically, while resin bath 63 and bottom portion 63A are moved upward (direction of an arrow 101 in
Then, after resin bath 63 ascends to a specified position (a position at which resin bath 63 makes contact with resin substrate 22), resin bath 63 is stopped. In this state, the liquid surface of resin 25A is arranged not to make contact with the bottom surface of resin substrate 22 yet. With this arrangement, a chance of resin 25A overflowing from resin bath 63 can be made smaller. However, at the same time, it is preferable that electronic component 24 be kept in contact with the liquid surface of resin 25A. By an action of surface tension of resin 25A, resin 25A creeps up along a side face of electronic component 24, or resin 25A infiltrates into a gap between electronic component 24 and resin substrate 22. As a result, in subsequent pressurized inflow step S73, resin 25A tends to be filled into a very narrow gap between electronic component 24 and resin substrate 22. In addition, bottom portion 63A continues its ascending even after the movement of resin portion 25 is stopped. As a result, the liquid surface of resin 25A makes contact with the bottom surface of resin substrate 22.
To cope with this, pressurized inflow step S73 is performed after immersion step S72. In pressurized inflow step S73, resin 25A is pressurized (in a direction of an arrow 102 in
In this exemplary embodiment, solder 23 is tin and silver based lead-free solder, and melting point thereof is about 200° C. Since the melting point of solder 23 is set to a temperature equal to or higher than the second temperature, solder 23 does not melt in pressurized inflow step S73. Accordingly, an electric link between electronic component 24 and resin substrate 22 is hardly disconnected.
In curing step S74 subsequent to pressurized inflow step S73, resin 25A is further heated until the temperature thereof reaches the third temperature equal to or higher than the second temperature so that resin 25A cures. As a result, resin portion 25 is formed on resin substrate 22. In curing step S74, it is preferable to maintain the pressure that is applied in pressurized inflow step S73 at least during a period until the fluidity of resin 25A ceases to exist. With this arrangement, voids or the like are hardly left in the gap between electronic component 24 and resin substrate 22.
According to the manufacturing method described above, since a pressure is applied in pressurized inflow step S73, resin 25A is reliably filled into a very narrow gap between electronic component 24 and resin substrate 22. In addition, since a pressure is applied to electronic component 24 only in pressurized inflow step S73, this can reduce a stress exerted on electronic component 24. Therefore, deformation of electronic component 24 or resin substrate 22 becomes smaller. As a result of this, variations in a distance between the high-frequency circuit 111 and shield metal film 26, a distance between the high-frequency circuit 111 and resin substrate 22, further, a distance between resin substrate 22 and shield metal film 26, or the like can be made smaller. Consequently, variations in stray capacitance values therebetween can be made smaller, and therefore high-frequency module 21 having small variations can be realized.
In addition, electronic component 24 is merely immersed in immersion step S72, and resin 25A is caused to flow in pressurized inflow step S73. Therefore, a distance in which resin 25A flows is very small as compared with that of the transfer molding. Accordingly, the internal stress caused by ununiformity in the flow of resin 25A or the like after resin 25A cures can be also made smaller. This makes it possible to reduce a strain (deformation) of electronic component 24, resin substrate 22, and resin portion 25 themselves. Accordingly, variations in the stray capacitance values can be made smaller. As a result, it is possible to realize high-frequency module 21 having a small variation in the characteristics of the high-frequency circuit 111.
According to this exemplary embodiment, in particular, since electronic component 24 is mounted with a face thereof placed downward by flip-chip bonding, a clearance between electronic component 24 and resin substrate 22 is very small. This causes a large stray capacitance between the high-frequency circuit 111 formed in electronic component 24 and ground wiring pattern 27. A variation in this stray capacitance exerts a great influence on the characteristics of the high-frequency circuit 111 of electronic component 24. This is a very important issue in burying the high-frequency circuit 111 in resin 25A. To state it differently, even the high-frequency circuit 111 that has passed the test of high-frequency characteristics in mounting step S51 may fail a test conducted after resin portion 25 is formed, if the strain of electronic component 24, resin substrate 22, or resin portion 25 itself is large. However, once the resin portion 25 is formed, a repairing work is very difficult, and there is no other way but to discard the product, which may greatly worsen the yield. To cope with this, a distance in which resin 25A flows is made smaller by using the manufacturing method according to this exemplary embodiment to thereby reduce the residual stress remaining in resin 25A, and reduce the stress exerted on electronic component 24, resin substrate 22, or resin portion 25 itself. With this arrangement, it is possible to reduce a variation in the high-frequency characteristics after resin portion 25 is formed, and realize high-frequency module 21 with high yield.
Further, reducing the residual stress exerts a great influence on reliability of the characteristics of high-frequency module 21 over a long period. It is considered that expansion and contraction are caused in resin portion 25 or resin substrate 22 by a change in temperature or the like, and this may change an internal stress distribution inside resin portion 25. For this reason, an amount of strain of electronic component 24, resin substrate 22, resin portion 25, or the like changes. As a result, values of the stray capacitances between electronic component 24, and resin substrate 22, ground wiring pattern 27, and shield metal film 26 may change from the values during manufacturing. To cope with this, by reducing the internal stress by the above-mentioned manufacturing method, it is possible to realize high-frequency module 21 that can maintain the stable characteristics over a long period of time also against a change in temperature or the like.
Since resin 25A is forcibly filled into the gap in pressurized inflow step S73, it is also possible to reliably fill resin 25A into the gap between electronic component 24 and resin substrate 22 as compared with a printing method or a method by potting. Accordingly, it is possible to realize high-frequency module 21 extremely excellent in reliability.
As described above, according to the exemplary embodiment, since it is possible to reduce a chance of destroying electronic component 24 or the chip part by a compression pressure and reduce deformation of electronic component 24, the thickness of electronic component 24 can be made smaller. For this reason, even if the thickness of resin portion 25 that is formed above electronic component 24 or the chip part is small, resin portion 25 can be reliably formed above electronic component 24 or the chip part as compared with the case of conventional transfer molding. This is because resin portion 25 above electronic component 24 is formed by immersion in immersion step S72. With this arrangement, a low-profile high-frequency module 21 can be realized. According to this exemplary embodiment, high-frequency module 21 having a thickness of 0.8 mm is produced.
High-frequency module 21 having a thickness of 0.5 mm can also be produced in addition to the foregoing. In this high-frequency module 21, resin substrate 22 has a thickness of 0.1 mm, and electronic component 24 has a thickness of 0.25 mm. Although the thicknesses are very small, deformation is also small, and the variation in the characteristics is also small. Further, although a gap between electronic component 24 and resin substrate 22 is 0.08 mm which is very narrow, resin 25A is reliably filled into this gap. Moreover, although the thickness of resin portion 25 above electronic component 24 is 0.07 mm which is very thin, resin portion 25 having a stable thickness is formed.
Next, another high-frequency module according to this exemplary embodiment is described with reference to the drawings.
According to high-frequency module 21 illustrated in
Next, a method for manufacturing high-frequency module 81 will be described with reference to the drawings.
After groove forming step S91, shield metal forming step S54 is performed. Shield metal film 26 is formed in the groove formed on a periphery (upper and side surfaces) of resin portion 25 and resin substrate 22 (upper surface of the step portion 82 and side surface of resin substrate 22). Then, after shield metal film forming step S54, separation step S92 is performed. In separation step S92, the coupling portion of resin substrates 22 is cut so as to be smaller than a width of the groove by a rotating dicing blade or the like having a blade thickness smaller than the width of the groove. With this arrangement, flaws are hardly caused in shield metal film 26 in separation step S92. As a result an excellent shield can be realized. According to this exemplary embodiment, shield metal film forming step S54 can be performed while resin substrates 22 are coupled together. In addition, if a step of the characteristic test is conducted between shield metal film forming step S54 and separation step S92, the test can also be conducted while resin substrates 22 are coupled together, and therefore the productivity becomes excellent. Further, as the shield metal film forming method, a vacuum deposition method, an ion plating method, a physical vapor deposition method, a CVD (Chemical Vapor Deposition) method, or the like may be used other than the sputtering method.
The high-frequency module according to the present disclosure provides an effect of smaller variation in characteristics thereof when the module is reduced in thickness, and is useful as a high-frequency module to be incorporated in portable electronic equipment or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-034461 | Feb 2010 | JP | national |
This application is a Continuation of International Application No. PCT/JP11/000,719, filed on Feb. 9, 2011, claiming priority of Japanese Patent Application No. 2010-034461, filed on Feb. 19, 2010, the entire contents of each of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2011/000719 | Feb 2011 | US |
| Child | 13587297 | US |
