Patent Application
20070262409
Embodiment 1 of the present invention will be described below with reference to
As shown in
The inner leads 5 are connected to outer leads 8 through the tie bars 3. At least one trench 9 is formed in a part of each inner lead 5 on the outer lead 8 side while a protrusion 10 is formed at the end of each inner lead 5 on the die pad 2 side.
The trenches 9 are formed in the surface portions of the inner leads 5 in a direction perpendicular to the direction that the inner leads 5 extend by half-etching or the like, and have a depth of, for example, 0.09 mm. Formation of the trench 9 in each inner lead 5 suppresses peeling off of the sealing resin material from the lead frame 1A, which is caused by mechanical stress or thermal stress generated in cut-bending of the outer leads 8, and suppresses development of the pealing off toward bonding areas 11 of the inner leads 5.
The protrusions 10 of the inner leads 5 protrude, for example, 0.2 mm in the in-plane direction perpendicular to the direction that the inner leads 5 extend. Provision of the protrusion 10 of each inner lead 5 increases the contact area between the inner leads 5 and the sealing resin material, increasing adhesiveness of the sealing resin material to the lead frame 1A to enable suppression of pealing off caused by thermal stress.
In the present embodiment, the depth of the trenches 9 is set to 0.09 mm because an effect of suppressing development of peeling off can be obtained sufficiently with a step difference of approximately 0.09 mm, and therefore, the present invention is not limited to this numerical value. Further, the trenches 9 may be formed by pressing rather than half-etching. The protruding length of the protrusions 10 is not limited to 0.2 mm and may be any arbitrary length only if they are out of contact with the respective adjacent inner leads 5.
The first feature of the lead frame 1A according to the present embodiment lies in that an island bonding area 12 of which potential is equal to that of the die pad 2 is formed in a region of one of the radiation plates 4 which is sealed by the sealing resin material. The island bonding area 12 is located at the central part in the width direction of the corresponding radiator plate 4, in detail, at the central part between the respective sides of the radiator plate 4 which face the inner lead leads 5. The island bonding area 12 is in a rectangular shape having a size of approximately 0.3 mm by 0.2 mm in plan in the present embodiment, but may be in any shape of quadrangles including squares, circles, and ellipses, or in a U-shape, a V-shape, or the like only if it has an area wide enough to be wire bonded. Further, the island bonding area 12 may be formed not only at one point, and a second island bonding area 12 may be formed so as to interpose the die pad 2 As shown in
In both side portions of the joint part 13 which are connected to the radiator plate 4 and the island bonding area 12, trenches 9 are formed so as to extend toward the inner leads 5. Herein, the width of the joint part 13 is set to 0.15 mm, which is smaller than the width of the island bonding area 12, 0.3 mm, so that the island bonding area 12 is covered from the four sides thereof with the sealing resin material when a semiconductor chip is sealed to the die pad 2 by the sealing resin material. This increases adhesiveness of the sealing resin material to the island bonding area 12, enabling suppression of development of peeling off toward the island bonding area 12.
In the present embodiment, the width of the slit 14a is set to 0.20 mm because development of peeling off between the sealing resin material and the lead frame 1A is suppressed sufficiently with the width of such an extent. Accordingly, the width of the slit 14a is not necessarily set to 0.20 mm. As well, the slit 14a may be formed by etching rather than pressing.
In the present embodiment, the joint part 13 is connected to the corresponding radiator plate 4 at a part thereof on an opposite side of the island bonding area 12 from the die pad 2. This can set the creepage distance from the die pad 2 to the island bonding area 12 longer than that in the case where the island bonding area 12 is connected at a part nearer the die pad 2, suppressing development of peeling off, which is caused by thermal stress between the lead frame 1A and the sealing resin material from the die pad 2 toward the outside, toward the island bonding area 12.
Further, the longer the length of the joint part 13 is set, the more development of the peeling off is suppressed. In the present embodiment, the length of the joint part 13 is set to 0.6 mm, which enables sufficient suppression of development of the peeling off. It is known by experiments that with the joint part 13 having a length of, for example, 0.3 mm, pealing off reaches the island bonding area 12.
Further, notches extending toward the inner leads 5 arranged on the respective sides of the radiator prates 4 are formed at respective sides of the slit 14a where the joint part 13 is connected to the corresponding radiator plate 4. This further extends the creepage distance from the die pad 2 to the island bonding area 12, further suppressing development of peeling off. Moreover, formation of the notches increases adhesiveness of the sealing resin material to the lead frame 1A, suppressing development of peeling off between the lead frame 1A and the sealing resin material from the edge of the sealing resin material toward the inside, which is caused by mechanical stress in cut-bending of the radiator plates 4, and suppressing lowering of humidity resistance accompanied by the development thereof. Hence, the semiconductor device can be prevented from lowering of breakdown voltage, which is caused due to moisture permeation from the edge of the sealing resin material toward the die pad 2 that holds the semiconductor chip. The lowering of humidity resistance can be suppressed sufficiently with the notches of the slit 14A extending approximately 0.1 mm to 0.2 mm toward the inner leads 5 on the respective sides of the radiator plates 4.
The two trenches 9 having a depth of 0.09 mm are formed in the joint part 13 by half etching. This increases the creepage distance from the edge of the sealing resin material to the island bonding area 12. Accordingly, even if peeling off is caused by mechanical stress between the lead frame 1A and the sealing resin material from the edge of the sealing resin material toward the inside, development of the peeling off can be suppressed by the trenches 9. It is noted that the trenches 9 of the joint part 13 is formed by half etching but may be formed by pressing. Further, the number of the trenches 9 may be set appropriately according to the length of the joint part 13.
As described above, in the present invention, formation of the slit 14a results in the island bonding area 12 covered from four sides thereof with the sealing resin material. Accordingly, even if peeling off is caused by mechanical stress between the sealing resin material and one of the radiator plates 4 from the edge of the sealing resin material toward the inside or peeling of is cause by thermal stress between the lead frame 1A and the sealing resin material from the die pad 2 toward the outside, development of such peeling off toward the island bonding area 12 is suppressed. As a result, peeling off between the wire bond and the bonding area and breakage of the wire bond can be prevented. Hence, reliability in electric connection of the connection parts is prevented from being lowered. Further, provision of the island bonding area 12 in one of the radiator plates 4 increases the number of bonding areas capable of being connected electrically to a semiconductor chip held by the die pad 2, which increases the degree of freedom of layout of the semiconductor chip to be held by the die bad 2.
In Embodiment 1, only a slit 14b is formed in the sealing region 7 of the other radiator plate 4 in which the island bonding area 12 is not formed. Formation of the slit 14b, as well as the formation of the slit 14a surrounding the island bonding area 12, increases adhesiveness of the sealing resin material to the lead frame 1A, suppressing development of peeling off between the lead frame 1A and the sealing resin material from the edge of the sealing resin material toward the inside, which is caused by mechanical stress in cut-bending of the radiator plates 4, and suppressing lowering of humidity resistance accompanied by the development thereof. Hence, lowering of breakdown voltage of the semiconductor device, which is caused due to moisture permeation from the edge of the sealing resin material toward the die pad 2 that holds the semiconductor chip, is prevented. When the width of the slit 14b is set to approximately ⅔ or larger of the width of the radiator plate 4, the lowering of humidity resistance can be suppressed sufficiently.
Referring to the second feature of the lead frame 1A according to Embodiment 1, the GND lead 6 includes two bent portions 15 bent in its plane. This extends the creepage distance from the die pad 2 to the corresponding tie bar 3 when compared with the case where the GND lead 6 with no bent portions 15 is connected to the die pad 2. In the present embodiment, extension of the creepage distance from the die pad 2 to an on-GND-lead bonding area 16 increases adhesiveness of the sealing resin material to the GND lead 6, thereby suppressing development of peeling off caused by thermal stress from the die pad 2 toward the outside. It is noted that the number of bent portions 15 formed in the GND lead 6 is not limited to two.
Moreover, as shown in
Comparatively large potential difference is caused between the outer lead 8 arranged on the outward extension of the GND lead 6 and an outer lead 8 arranged on the outward extension of an inner lead 5 adjacent to the GND lead 6, and therefore, it is necessary to set the distance for insulation between the outer lead 8 connected to the GND lead 6 and the other outer lead 8 adjacent thereto to be large for allowing the lead frame 1A to hold a semiconductor chip including a high breakdown voltage element. Accordingly, in the present embodiment, one of the other outer leads 8 adjacent to the outer lead 8 connected to the GND lead 6 is not connected to any inner leads 5 and is removed after a resin sealing step to present a state in which the pin is lacked.
Accordingly, in Embodiment 1, the GND lead 6, which includes a plurality of bent portions 15 for extending the creepage distance, is connected to the die pad 2 on the extension of the outer lead 8 that is not connected to any inner leads 5 in a space of the adjacent inner lead 5 in the state in which the pin is lacked. In this way, formation of a plurality of bent portions in the GND lead 6 for extending the creepage distance from the die pad 2 needs no additional area, enabling size reduction of a semiconductor device including a high breakdown voltage element. It is noted that the number of bent portions formed in the GND lead 6 is not limited to two. As well, the GND lead 6 may be connected to the die pad 2 on an extension of any one of the outer leads 8 other than the outer lead 8 that is connected to any inner leads 5.
Embodiment 2 of the present invention will be describe below with reference to
As shown in
Formation of the independent slit 14d in addition to the slit 14c formed around the island bonding area 12 increases adhesiveness of the sealing resin material to the lead frame1B, suppressing development of peeling off caused by mechanical stress in cut-bending of the radiator plates 4 between the lead frame 1B and the sealing resin material from the edge of the sealing resin material toward the inside, and suppressing lowering of humidity resistance accompanied by the development thereof.
Further, the semiconductor device is prevented from lowering of breakdown voltage, which is caused due to moisture permeation from the edge of the sealing resin material toward the die pad 2 that holds the semiconductor chip.
In Embodiment 2, the length of the slit 14d is set to 1 mm relative to the width of the die pad 2, 1.5 mm. Though development of peeling off can be suppressed sufficiently with the slit 14d having a length of such an extent, the length is not limited thereto.
Formation of the slit 14d between the island bonding area 12 and the end of the sealing resin material in Embodiment 2 extends the creepage distance from the end of the sealing resin material to the island bonding area 12 and increases adhesiveness of the sealing resin material to the lead frame 1B to suppress development of peeling off, thereby preventing lowering of reliability in electric connection of the connection parts.
Embodiment 3 of the present invention will be described below with reference to
As shown in
Provision of the joint part 13 for connecting the island bonding area 12 near the die pad 2 in this way extends the creepage distance from a part of the corresponding radiator plate 4 which corresponds to the edge of the sealing resin material to the island bonding area 12. Accordingly, peeling off caused by mechanical stress in cut-bending of the radiator plates 4 between the lead frame 1C and the sealing resin material from the edge of the sealing resin material toward the inside hardly reaches the island bonding area 12.
While, because provision of the joint part 13 near the die pad 2 shortens the creepage distance from the die pad 2 to the island bonding area 12, peeling off caused by thermal stress between the lead frame 1C and the sealing resin material from the die pad 2 toward the outside may develop to the island bonding area 12. For tackling this problem, in Embodiment 3, the slit 14f having the same structure as the slit 14d in Embodiment 2 is formed between the island bonding area 12 and the die pad 2 for extending the creepage distance from the die pad 2 to the island bonding area 12, thereby suppressing the development of the peeling off caused by thermal stress.
Embodiment 4 of the present invention will be described below with reference to
As shown in
The electrode pads 18 and the ground electrode pad 19 of the semiconductor chip 17 die bonded on the die pad 2 are wire bonded and connected electrically to bonding areas 20 of the inner leads 5 and the island bonding area 12, respectively, by means of the metal thin lines 21. In the present embodiment, the ground electrode pad 19 of the semiconductor chip 17 is wire bonded to the island bonding area 12, but the ground electrode pad 19 may be wire bonded to the on-GND-lead bonding area 16 by means of the metal thin lines 21, as shown in the modified example in
The sealing region 7 of the lead frame 1A which is connected electrically to the semiconductor chip 17 is sealed by a sealing part 22 made of a sealing resin material, such as epoxy resin or the like by transfer molding. In a resin sealing step, the sealing resin material is filled in the trenches 9 and the slit 14a. In this step, parts of the radiator plates 4, the tie bars 3, and the outer leads 8 connected to the inner leads 5, which are exposed from the sealing part 22, are subjected to resin burr removal. Further, the tie bars 3 are tie-bar cut. An outer lead 8 not connected to an inner lead 5 adjacent to the GND lead 6 is cut out, thereby presenting the state in which the pin is lacked. The parts of the radiator plates 4 and the outer leads 8 are lead-cut and bent to be in gull wing forms.
The thus structured semiconductor device according to Embodiment 4 includes the island bonding area 12 electrically connected to the ground electrode pad 19 of the semiconductor chip 17 by means of the metal thin line 21 in the sealing part 22 on the lead frame 1A. Wherein, the peripheral sides of the island bonding area 12 except the side connected to the joint part 13 is separated from the lead frame 1A by the slit 14a.
Comparison is made below between the semiconductor device using the lead frame 1A for a high breakdown voltage element according to Embodiment 4 and a semiconductor device using a conventional lead frame for a high breakdown voltage element.
Table 1 indicates ratios of occurrence of defects that peeling off from the edge of the sealing part 22 toward the inside reaches the GND connection bonding area (the island bonding area 12 in the present invention) in THB (temperature humidity bias) tests under the conditions of 85° C. temperature value, 85% relative humidity, and 1000-hour source voltage application and ratios of occurrence of defects that peeling off from the die pad that holds the semiconductor chip toward the outside reaches the GND connection bonding area in thermal shock tests of 100 cycle repetition of temperature cycling between −65° C. and 150° C.
As can be understood from Table 1, no defect occurs in the semiconductor according to Embodiment 4 shown in
Table 2 indicates ratios of occurrence of defects that breakdown voltage lowers due to lowering of humidity resistance accompanied by peeling off development in THB tests under the conditions of 85° C. temperature value, 85% relative humidity, and 1000-hour source voltage application.
As can be understood from Table 2, the breakdown voltage does not lower in the semiconductor device according to Embodiment 4 shown in
Further, Table 3 indicates the results of tests equivalent to those in Table 1 performed on a semiconductor device in which the ground electrode pad and the on-GND-lead bonding area 6 are wire bonded.
As can be understood from Table 3, in both the tests, no defect occurs in the semiconductor device according to the modified example of Embodiment 4 shown in
As described above, in the semiconductor devices according to Embodiment 4 and the modified example thereof, the island bonding area 12 of which three sides are surrounded by the slit 14a is covered with the sealing resin material. Accordingly, even if peeling off is caused which would develop from the edge of the sealing part 22 toward the inside or from the die pad 2 toward the outside, peeling off development to the island bonding area 12 can be suppressed. Hence, peeling off of the wire bond from the bonding area and breakage of the wire bond can be prevented, preventing lowering of reliability in electric connection of the connection parts.
In the semiconductor device according the modified example, in which the ground electrode pad 19 of the semiconductor chip 17 and the on-GND-lead bonding area 16 are wire bonded, provision of the bent portions 15 in the GND lead 6 extends the creepage distance from the die pad 2 to the on-GND-lead bonding area 16 and further to the corresponding outer lead 8. In addition, formation of at least one trench 9 in the GND lead 6 further extends the creepage distance from the die pad 2 to the corresponding tie bar 3, increasing adhesiveness of the sealing resin material to the GND lead 6. As a result, peeling off caused by thermal stress from the die pad 2 toward the outside is prevented from developing toward the on-GND-lead bonding area 16.
Hence, peeling off at the interface between the wire bond and the bonding area and breakage of the wire bond can be prevented, preventing lowering of reliability in electric connection of the connection parts.
As described above, with the use of the lead frame and the semiconductor device using it according to the present invention, even if peeling off is caused between the lead frame and the sealing resin material, development of the peeling off is suppressed to prevent lowering of reliability in electric connection of the connection parts. Therefore, the present invention is useful for a lead frame for holding a semiconductor chip which requires the lead frame to have high heat radiation, such as a high breakdown voltage element or the like and a semiconductor device using it.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-130369 | May 2006 | JP | national |
