Patent Application
20120211764
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-36273, filed on Feb. 22, 2011, the entire contents of which are incorporated herein by reference.
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In recent years, the development of electronic devices (compound semiconductor devices) in which a GaN layer and an AlGaN layer are sequentially formed on a substrate, and the GaN layer is used as an electron transit layer has been actively performed. As one of such compound semiconductor devices, a GaN-based high electron mobility transistor (HEMT) is mentioned. In the GaN-based HEMT, a high-concentration two-dimensional electron gas (2DEG) formed at a hetero-junction interface of AlGaN and GaN is utilized.
The band gap of GaN is 3.4 eV and is larger than the band gap of Si (1.1 eV) or the band gap of GaAs (1.4 eV). More specifically, GaN has a high breakdown field strength. Moreover, GaN also has a high saturated electron speed. Therefore, GaN is very promising as a material of compound semiconductor devices which allow high-voltage operation and high output. Then, the GaN-based HEMT has been expected as high efficiency switching elements and high breakdown voltage power devices for use in electric vehicles and the like.
In recent years, with respect to not only such GaN-based HEMT but also various semiconductor elements, a reduction in size and a reduction in thickness of semiconductor devices containing semiconductor elements have progressed. In such semiconductor devices, a semiconductor element is bonded onto a lead frame by a solder material or a die bond material, such as a nano Ag paste.
However, it is difficult to obtain sufficient heat dissipation properties with the structure in which the semiconductor element is bonded to the lead frame by the solder material. Moreover, since the junction with the solder material is strong, the thermal stress generated in the junction portion and the vicinity thereof in the operation of the semiconductor element cannot be sufficiently relieved. Therefore, it is hard to say that the junction reliability is good. Moreover, a considerable mechanical stress may work on the semiconductor element in connection with the thermal stress, which may cause malfunction of the semiconductor element. For example, a threshold value voltage of a transistor varies in some cases. Furthermore, when a solder material is melted in order to mount the semiconductor element on the lead frame, a position shift of the semiconductor element is also caused in some cases.
In contrast, in the structure in which the semiconductor element is bonded to the lead frame by the nano Ag paste, stress is relieved and the influence of a position shift of the semiconductor element is smaller than that in the structure in which the semiconductor element is bonded to the lead frame by the solder material. Moreover, high heat dissipation properties can also be obtained. However, it is difficult to secure sufficient junction strength.
In addition to the above, various proposals have been made. However, it has been difficult heretofore to achieve heat dissipation properties, stress relieving properties, and junction strength at the same time.
Japanese Laid-open Patent Publication No. 2001-230351 and Japanese Laid-open Patent Publication No. 2007-201314 are examples of related arts.
According to one aspect of the present invention, a semiconductor device includes: a support base material, and a semiconductor element bonded to the support base material with a binder, the binder including: a porous metal material that contacts the support base material and the semiconductor element, and a solder that is filled in at least one part of pores of the porous metal material.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explaneatory and are not restrictive of the invention, as claimed.
Hereinafter, the embodiments are specifically described with reference to the attached drawings.
First, a first embodiment is described.
In the first embodiment, a semiconductor element 15 is bonded to a lead frame 11 through a composite material 16 as illustrated in
In the first embodiment, the composite material 16 contains a film-like porous metal material 16a as illustrated in
In the first embodiment, the heat generated in the semiconductor element 15 can be sufficiently transmitted to the lead frame 11 through the porous metal material 16a contained in the composite material 16. Even when stress is generated with the generation of heat, the stress is relieved by the porous metal material 16a. Furthermore, since at least one part of the pores 16b of the porous metal material 16a is filled with the solder 16c, it is also possible to secure sufficient junction strength between the lead frame 11 and the semiconductor element 15.
Since the stress can be sufficiently relieved, even when a transistor, such as a GaN-based HEMT transistor, is contained in the semiconductor element, a variation in the threshold value voltage thereof can be suppressed. For example, even when a high temperature storage test and a temperature cycle test are performed, damages to the semiconductor element 15 can be remarkably reduced.
Next, a method for manufacturing the semiconductor device according to the first embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
As the solder sheet 13, materials are not particularly limited insofar as the materials have a melting point which is higher than the temperature at which the Ag particles contained in the nano Ag pastes 12 and 14 are sintered and a melting point which is lower than the melting point of the Ag particles. For example, a SnAgCu-based solder sheet can be used.
Subsequently, as illustrated in
Then, at least the nano Ag paste 12, the solder sheet 13, and the nano Ag paste 14 are heated to melt the solder sheet 13. Thereafter, the molten solder is solidified by cooling. In this process, since the melting point of the solder sheet 13 is higher than the temperature at which the Ag particles contained in the nano Ag pastes 12 and 14 are sintered, the Ag particles contained in the nano Ag pastes 12 and 14 are sintered before the solder sheet 13 melts, to thereby form a film-like porous metal material 16a. When the solder sheet 13 melts, the molten solder flows into the pores 16b of the porous metal material 16a. When the solder is solidified with the subsequent cooling process, the composite material 16 is formed which contains the porous metal material 16a and the solder charged in at least one part of the pores 16b as illustrated in
Thereafter, as illustrated in
Subsequently, as illustrated in
Thereafter, the resin-sealed assembly is removed from the die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
According to such a method, there is no necessity of using expensive materials as compared with former cases. Therefore, a semiconductor device which can achieve heat dissipation properties, stress relieving properties, and junction strength can be obtained while suppressing an increase in cost.
The materials of the porous metal material 16a are not particularly limited. For example, a substance (a metal simple substance, an alloy, or a mixture) containing at least one selected from the group consisting of Ag, Au, Ni, Cu, Pt, Pd, and Sn can be used. The same substance is applied to the following embodiments.
Moreover, the material of the solder sheet 13 is not particularly limited insofar as the melting point thereof is higher than the temperature at which the material of the porous metal material 16a is sintered. For example, a substance (a metal simple substance, an alloy, or a mixture) containing at least one selected from the group consisting of Sn, Ni, Cu, Zn, Al, Bi, Ag, In, Sb, Ga, Au, Si, Ge, Co, W, Ta, Ti, Pt, Mg, Mn, Mo, Cr, and P can be used. The same substance is applied to the following embodiments.
It is preferable that a metal film 15a is formed on the rear surface of the semiconductor element 15 as illustrated in
According to the semiconductor device and the like described above, good heat dissipation properties and stress relieving properties can be obtained by the porous metal material, and good junction strength can be obtained by the solder.
Next, a second embodiment is described.
In the second embodiment, the semiconductor element 15 is bonded to the lead frame 11 through a composite material 26 and a solder layer 23a as illustrated in
According to the second embodiment, higher junction strength can be obtained as compared with the first embodiment. In particular, when the outer region of the semiconductor element 15 contacts the composite materials 26 and the inner region contacts the solder layer 23a, high junction strength can be obtained at the central portion on which stress hardly acts while effectively relieving the stress at the outer region on which relatively high stress acts.
Next, a method for manufacturing the semiconductor device according to the second embodiment is described.
First, as illustrated in
Subsequently, a nano Ag paste 22 is applied to the circumference of the solder sheet 23 in a region of the lead frame 11 where the semiconductor element 15 is to be mounted as illustrated in
Thereafter, the semiconductor element 15 is mounted in a face-up manner on the solder sheet 23 and the nano Ag paste 22 as illustrated in
Subsequently, at least the nano Ag paste 22 and the solder sheet 23 are heated to mold the solder sheet 23. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag paste 22 are sintered before the solder sheet 23 melts, to thereby form a film-like porous metal material. Then, when the solder sheet 23 melts, the molten solder partially flows into the pores of the porous metal material, and the remaining molten solder remains at the central portion. When the solder is solidified with the subsequent cooling process, the composite material 26 is formed and the solder layer 23a is formed inside the composite material 26 as illustrated in
Thereafter, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
Next, a third embodiment is described.
In the third embodiment, as illustrated in
According to the third embodiment, high junction strength can be obtained at the central portion on which stress hardly acts while effectively relieving stress at the outer region on which relatively high stress acts.
Next, a method for manufacturing the semiconductor device according to the third embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
Subsequently, as illustrated in
Then, at least the nano Ag paste 32, the solder sheet 33, and the nano Ag paste 34 are heated to solidify the solder sheet 33. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag pastes 32 and 34 before the solder sheet 33 melts, to thereby form a film-like porous metal material. Then, when the solder sheet 33 melts, the molten solder flows into the pores of the porous metal material. When the solder is solidified with the subsequent cooling process, the composite material 36 is formed so that the solder ratio decreases from the central portion to the outer region as illustrated in
Thereafter, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
Next, a fourth embodiment is described.
As illustrated in
According to the fourth embodiment, at the outer region on which relatively high stress acts, the stress can be effectively relieved by the resin material 49.
Next, a method for manufacturing the semiconductor device according to the third embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
Subsequently, as illustrated in
Subsequently, as illustrated in
Thereafter, at least the nano Ag paste 42, the solder sheet 43, and the nano Ag paste 44 are heated to molt the solder sheet 43. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag pastes 42 and 44 are sintered before the solder sheet 43 melts, to thereby form a film-like porous metal material. Then, when the solder sheet 43 melts, the molten solder flows into the pores of the porous metal material. When the solder is solidified with the subsequent cooling process, the composite material 46 is formed which contains the porous metal material and the solder charged in at least one part of the pores as illustrated in
Subsequently, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
Next, a fifth embodiment is described.
In the fifth embodiment, a resin material 59 is interposed between the semiconductor element 15 and the lead frame 11 at the outer region of the semiconductor element 15 and the semiconductor element 15 is bonded to the lead frame 11 inside the resin material 59 through a composite material 56 and a solder layer 53a as illustrated in
According to the fifth embodiment, the effects of the second embodiment and the fourth embodiment can be obtained. More specifically, higher junction strength can be obtained at the central portion on which stress hardly acts as compared with the fourth embodiment.
Next, a method for manufacturing the semiconductor device according to the fifth embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
Then, as illustrated in
Subsequently, at least the nano Ag paste 52 and the solder sheet 53 are heated to molt the solder sheet 53. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag paste 52 are sintered before the solder sheet 53 melts, to thereby form a film- like porous metal material. Then, when the solder sheet 53 melts, the molten solder partially flows into the pores of the porous metal material and the remaining molten solder remains at the central portion. When the solder is solidified with the subsequent cooling process, the composite material 56 is formed as illustrated in
Thereafter, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
Next, a sixth embodiment is described.
In the sixth embodiment, the semiconductor element 15 is bonded to the lead frame 11 through a composite material 66 and a porous metal material 62a not containing a solder as illustrated in
According to the sixth embodiment, at the outer region on which relatively high stress acts, the stress can be more effectively relieved.
Next, a method for manufacturing the semiconductor device according to the sixth embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
Subsequently, at least the nano Ag paste 62 and the solder sheet 63 are heated to molt the solder sheet 63. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag paste 62 are sintered before the solder sheet 63 melts, to thereby form a film- like porous metal material. Then, when the solder sheet 63 melts, the molten solder partially flows into the pores of the porous metal material. In this case, the amount of the solder sheet 63 is small in the sixth embodiment, and therefore, the entire solder flows into the pores of the porous metal material. In contrast, the solder does not flow into the outer region of the porous metal material. When the solder is solidified with the subsequent cooling process, a porous metal material 62a is formed at the outer region and a composite material 66 is formed inside the porous metal material.
Subsequently, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
Next, a seventh embodiment is described.
In the seventh embodiment, as illustrated in
According to the seventh embodiment, the effects of the fourth embodiment and the sixth embodiment can be obtained. More specifically, at the outer region on which relatively high stress acts, the stress can be more effectively relieved as compared with the fourth embodiment.
Next, a method for manufacturing the semiconductor device according to the seventh embodiment is described.
First, as illustrated in
Subsequently, as illustrated in
Thereafter, as illustrated in
Then, as illustrated in
Subsequently, at least the nano Ag paste 72 and the solder sheet 73 are heated to molt the solder sheet 73. Thereafter, the molten solder is solidified by cooling. In this process, the Ag particles contained in the nano Ag paste 72 are sintered before the solder sheet 73 melts, to thereby form a film- like porous metal material. Then, when the solder sheet 73 melts, the molten solder partially flows into the pores of the porous metal material. In this case, the amount of the solder sheet 73 is small in the seventh embodiment, and therefore, the entire solder flows into the pores of the porous metal material. In contrast, the solder does not flow into the outer region of the porous metal material. When the solder is solidified with the subsequent cooling process, a porous metal material 72a is formed at the outer region and a composite material 76 is formed inside the porous material 72a. The side surfaces of the porous metal material 72a are covered with the resin material 79. More specifically, the resin material 79 remains in a state where the resin material 79 contacts the undersurface of the semiconductor element 15 and the upper surface of the lead frame 11.
Subsequently, as illustrated in
Thereafter, a resin-sealed assembly is removed from a die, and then the outer leads of the lead frame 11 are cut to divide the same into semiconductor devices. Thus, a discrete package containing the GaN-based HEMT semiconductor element 15, for example, is obtained.
In all the embodiments, it is preferable to use one containing Sn—Bi-based solder particles and Cu particles as the solder paste. In this case, a layer containing the Cu and the Sn is formed on the surface of the Cu particles in melting the solder paste by heating. Since the melting point of the layer is higher than the melting point (about 240° C.) of the Sn—Bi-based solder, junction strength at higher temperatures can be sufficiently secured.
When the semiconductor element is the GaN-based HEMT, the semiconductor devices according to these embodiments can be used as a high power amplifier of a discrete package, for example.
The GaN-based HEMT can also be used for a power supply device, for example.
As illustrated in
As illustrated in
A power supply device which is similar to such a server power supply 100 and which allows higher speed operation can also be built. A switch element similar to the switch element 94 can be used for a switch power supply or an electronic device. Furthermore, these semiconductor devices can also be used as parts for a full bridge power circuit, such as a power circuit of a server.
The present inventors manufactured a discrete-packaged semiconductor device containing the GaN-based HEMT according to the second embodiment, and then measured the heat resistance of the entire package during the operation of the semiconductor element. Thus, the heat resistance was 0.5° C./W or lower. When a temperature cycle test (3000 cycles) was performed between −65° C. and +150° C., the rate of change in the heat resistance was +5% or lower. Furthermore, a cross-sectional SEM analysis of the junction portion of the semiconductor element and the lead frame was performed after the respective tests. Then, cracks or fractured portions were not observed at the junction portion, and it was confirmed that the early junction state was favorably maintained. When manufacturing the semiconductor device, one containing SnBi solder particles and Cu particles was used as the solder paste.
For comparison, the present inventors manufactured a discrete-packaged semiconductor device containing the GaN-based HEMT according to the second embodiment, except bonding the semiconductor element to the lead frame only using a SnBi solder paste without using the nano Ag paste. Then, the same tests as above were performed. As a result, the heat resistance of 0.7° C./W was 1.4 times or more comparing that in the above results. The rate of change in the heat resistance accompanied with the temperature cycle test was about 10 times comparing with that in the above results. Furthermore, when a cross-sectional SEM analysis of the junction portion was performed, cracks were observed at the junction portion near the outer region of the semiconductor element.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-036273 | Feb 2011 | JP | national |
