Packaged semiconductor device incorporating heat sink plate

A packaged semiconductor device is provided which comprises a die pad, a semiconductor chip mounted on the die pad, a plurality of leads electrically connected to the semiconductor chip, a heat sink plate bonded to the die pad opposite to the semiconductor chip, and a resin package enclosing at least the semiconductor chip together with the die pad and a part of each lead. The heat sink plate has a peripheral portion partially overlapping each lead but electrically insulated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a packaged semiconductor device of the type which 
incorporates a heat sink plate for effectively dissipating the heat 
generated by a semiconductor chip. The present invention also relates to a 
method for making such a semiconductor device. The present invention 
further relates to supersonic bonding which can be advantageously used in 
making such a semiconductor device. 
2. Description of the Related Art 
As is well known, certain types of semiconductor devices generate a lot of 
heat during operation. For example, power ICs for motor drive, certain 
gate array devices and ultra LSIs are known to generate much heat. 
Therefore, these semiconductor devices equally need to incorporate a heat 
sink plate within the resin package for effectively dissipating the 
generated heat, as shown in FIG. 36 of the accompanying drawings. 
Specifically, as shown in FIG. 36, a prior art packaged semiconductor 
device of this type comprises a semiconductor chip 5 mounted on a heat 
sink plate 4 within a resin package 1. The chip 5 is electrically 
connected to a plurality of leads 2 via respective bondwires 6. An inner 
portion of each lead 2 is attached to the heat sink plate a via an 
adhesive layer 3, whereas an outer portion of the lead 2 is extended out 
of the package 1. In operation, the heat sink plate 4 serves to dissipate 
heat which is generated by the semiconductor chip. 
However, the prior art semiconductor device has been found to have the 
following disadvantages. 
First, before molding the resin package 1 in manufacturing the prior art 
semiconductor device, the heat sink plate 4 need be supported solely by 
the tip ends of the respective leads 2 via the adhesive layer 3. Since the 
leads 2 need be extremely slenderized for enabling a dense arrangement in 
a limited size, they cannot provide a sufficiently rigid support if the 
heat sink plate 4 is rendered relatively heavy. Therefore, it is difficult 
to increase the heat dissipating ability of the heat sink plate 4 beyond a 
certain limit. 
Secondly, in bonding the bondwires 6 to the respective leads 2 before 
molding the resin package 1, the heat sink plate 4 need be placed on a 
heater block (not shown) to supply heat required for performing a 
thermo-compression bonding method. However, since the adhesive layer 3 
blocks heat transmission from the heat sink plate 4 to each lead 2, it is 
difficult to properly and efficiently bond the wire 6 to the lead 2. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a packaged 
semiconductor device which is capable of incorporating a relatively heavy 
heat sink plate for providing an improved heat dissipating ability while 
preventing unexpected deformation of leads. 
Another object of the present invention is to provide a method of making 
such a semiconductor device. 
A further object of the present invention is to provide a supersonic 
bonding method which can be advantageously used for making such a 
semiconductor device. 
Still another object of the present invention is to provide a supersonic 
bonding apparatus which can be advantageously used for making such a 
semiconductor device. 
According to a first aspect of the present invention, there is provided a 
packaged semiconductor device comprising: 
a die pad; 
a semiconductor chip mounted on the die pad; 
a plurality of leads electrically connected to the semiconductor chip; 
a heat sink plate bonded to the die pad opposite to the semiconductor chip, 
the heat sink plate have a peripheral portion partially overlapping each 
of the leads but electrically insulated therefrom; and 
a resin package enclosing at least the semiconductor chip together with the 
die pad and a part of each said lead. 
According to the arrangement described above, the die pad and the leads may 
originate from a common leadframe, and the heat sink plate need not be 
bonded to the die pad. Thus, the leads will not be deformed under the 
weight of the heat sink plate even if the heat sink plate is enlarged in 
size (namely, area and thickness) for providing an increased heat 
dissipating ability. 
On the other hand, when the heat sink plate is placed on a heater block for 
performing wire bonding with respect to the leads, each of the leads may 
be elastically deformed into direct contact with the heat sink plate 
because there is no need to provide an intervening bonding layer between 
the heat sink plate and the lead. Thus, the heat from the heater block can 
be effectively transmitted to the lead for facilitating the wire bonding 
process. 
The heat sink plate may be directly bonded to the die pad without 
intervention of a separate bonding layer. Such an arrangement improves 
heat transmission between the die pad and the heat sink plate. In this 
case, the heat sink plate may be bonded to the die pad only in a limited 
central region while holding the entirety of the die pad in direct contact 
with the heat sink plate. 
Each of the leads may be electrically insulated from the heat sink plate by 
a spacing therebetween. Alternatively, each of the leads may be 
electrically insulated from the heat sink plate by an insulating adhesive 
tape attached to the lead. Further, each of the leads may be electrically 
insulated from the heat sink plate by a spacing therebetween as well as by 
an insulating adhesive tape attached to the lead. 
The heat sink plate may have a surface exposed outside the resin package to 
promote heat dissipation. In this case, the exposed surface of the heat 
sink plate may be formed with depressions for providing an increased heat 
dissipating area. 
Alternatively, the heat sink plate may be fully enclosed in the resin 
package to improve sealing for the semiconductor chip. In this case, 
again, the heat sink plate may have a non-exposed surface formed with 
depressions for improving anchorage within the resin package. 
For additionally improving heat dissipation of the semiconductor device, 
the die pad may be integrally formed with at least one heat dissipating 
fin located outside the resin package. 
According to a second aspect of the present invention, there is provided a 
method for making a packaged semiconductor device comprising the steps of: 
preparing a leadframe which has at least one die pad and a plurality of 
leads associated with the die pad; 
bonding the die pad to a heat sink plate in such a manner that a peripheral 
portion of the heat sink plate partially overlaps while being electrically 
insulated from each of the leads; 
bonding a semiconductor chip on the die pad opposite to the heat sink 
plate; 
electrically connecting the semiconductor chip to each said lead by 
bondwires; and 
molding a resin package which encloses at least the semiconductor chip 
together with the die pad and a part of each said lead. 
According to a preferred embodiment of the method, the step of bonding the 
die pad to the heat sink plate comprises placing the heat sink plate on a 
support base, placing the die pad on the heat sink plate, pressing a 
presser tool against the die pad, and supersonically vibrating the presser 
tool while the presser tool is held pressed against the die pad. In this 
case, the presser tool may be held pressed against the die pad only in a 
limited central region thereof. Further, the presser tool may have 
engaging teeth for engagement with the die pad, and the support base may 
also have engaging teeth for engagement with the heat sink plate. 
According to another preferred embodiment of the method, an insulating 
adhesive tape may be attached to inner portions of the respective leads 
prior to performing the step of bonding the die pad to the heat sink 
plate. 
According to a third aspect of the present invention, there is provided a 
method for supersonically bonding a first element to a second element 
comprising the steps of: 
bringing a presser tool into contact with the first element for pressing 
the first element against the second element; 
supersonically vibrating the presser tool while the first element is held 
pressed against the second element; 
detecting vibration of the second element; and 
stopping or slowing down the supersonic vibration of the presser tool when 
the vibration of the second element reaches a predetermined state. 
If the supersonic bonding method described above is used for making a 
packaged semiconductor device, the first element may be a die pad of a 
leadframe, whereas the second element may be a metallic heat sink plate. 
Alternatively or additionally, the first element may be a bondwire, 
whereas the second element may be a lead of a leadframe. 
According to a fourth aspect of the present invention, there is provided an 
apparatus for supersonically bonding a first element to a second element 
comprising: 
a presser tool which is brought into contact with the first element for 
pressing the first element against the second element; 
a supersonic generator for supersonically vibrating the presser tool while 
the first element is held pressed against the second element; 
a controller for controlling the supersonic generator; and 
a vibration sensor for detecting vibration of the second element and for 
causing the controller to stop or slow down the supersonic generator when 
the vibration of the second element reaches a predetermined state. 
Other objects, features and advantages of the present invention will be 
fully understood from the following detailed description given with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 of the accompanying drawings illustrate a dual-in-line type 
packaged semiconductor device according to a first embodiment of the 
present invention. The semiconductor device generally designated by 
reference numeral 10 comprises a resin package 11 which encloses a 
semiconductor chip 13 bonded on a die pad or island 12. The package 11 may 
be preferably made of epoxy for example. The chip 13 may be bonded on the 
die pad 12 by means of a silver paste or a low melting point metal such as 
solder. 
The die pad 12 is mounted on a heat sink plate 14 in direct contact 
therewith as a whole. The heat sink plate 14 may be square or rectangular 
and preferably made of copper, aluminum, a copper alloy or an aluminum 
alloy for ensuring good heat dissipation. However, the heat sink plate 14 
may be made of a non-metal material as long as such a material ensures 
good heat dissipation. 
The semiconductor chip 13 is electrically connected to a plurality of leads 
15 via respective bondwires 16. Each of the leads 15 has an inner flat 
portion 15a located within the package 11, and an outer bent portion 15b 
extending out of the package 11. The outer bent portion 15b is bent to 
become substantially flush with the bottom surface of the package 11 for 
conveniently mounting on a circuit board (not shown). 
According to the first embodiment shown in FIGS. 1 and 2, the heat sink 
plate 14 has a bottom surface flush with the bottom surface of the package 
11 for exposure to the exterior. Further, the heat sink plate 14 has 
marginal portions which laterally overlap the inner flat portions 15a of 
the respective leads 15 with a small spacing 17. The resin material of the 
package 11 occupies the spacing 17, so that the respective leads 15 are 
electrically insulated from the heat sink plate 14. 
Further, according to the first embodiment shown in FIGS. 1 and 2, the die 
pad 12 is directly bonded to the heat sink plate 14 in a limited central 
region 18 without the use of a separate bonding layer (e.g. adhesive 
layer). Such localized direct bonding may be preferably performed by a 
supersonic bonding method, as described hereinafter. However, other direct 
bonding method such as spot welding is also applicable. 
With the arrangement described above, the entirety of the die pad 12 is 
held in direct contact with the heat sink plate 14 in spite of localized 
bonding therebetween. Thus, the heat generated by the semiconductor chip 
13 in operation can be effectively transmitted to the heat sink plate 14 
for dissipation from the exposed bottom surface of the heat sink plate 14. 
On the other hand, since the die pad 12 is bonded to the heat sink plate 14 
only in the limited central region 18, these two elements 12, 14 can 
thermally expand and contract substantially independently of each other 
even if they differ in coefficient of thermal expansion. Thus, it is 
possible to prevent or reduce thermal stresses between the die pad 12 and 
the heat sink plate 14, thereby avoiding damages to the interior structure 
which might be caused by such thermal stresses. 
The packaged semiconductor device according to the first embodiment may be 
preferably made in the following manner. 
First, as shown in FIGS. 3 and 4, a suitably configured leadframe 19 is 
prepared. Such a leadframe may be prepared by punching a thin metal sheet 
which may be made of a copper alloy or an iron-nickel alloy for example. 
The leadframe 19 comprises a pair of side bands 21 connected together by a 
plurality of section bars 20. Two adjacent ones of the section bars 20 
define a unit region X which contains a die pad 12 flanked, longitudinally 
of the leadframe 19, by two groups of leads 15. The die pad 12 is 
supported by the respective side bands 21 via support bars 22, whereas the 
leads 15 in each group extend toward the die pad 12 from a corresponding 
section bar 20 and are connected together by a tie bar 23 extending 
transversely of the leadframe 19. Each lead 15 is divided at the tie bar 
23 into an inner portion 15a closer to the die pad 12 and an outer portion 
15b farther from the die pad 12. As shown in FIG. 4, the die pad 12 is 
downwardly offset from the normal plane of the leadframe 19 by a 
predetermined amount Z of 0.2-0.4 mm (200-400 micrometers) for example. 
Then, as shown in FIGS. 5-7, a metallic heat sink plate 14 is bonded to the 
bottom surface of the die pad 12 in such a manner that a peripheral 
portion of the heat sink plate 14 partially overlaps the inner portions 
15a of the respective leads 15. As previously described, the bonding 
between the die pad 12 and the heat sink plate 14 is preferably effected 
only in a limited central region 18. This bonding region may be minimally 
reduced as long as a sufficient bonding or supporting strength between the 
die pad 12 and the heat sink plate 14 is ensured. Because of the downward 
offset of the die pad 12 relative to the normal plane of the leadframe 19, 
a spacing 17 is formed between each lead 15 and the heat sink plate 14. 
As previously described, the heat sink plate 14 may be preferably bonded to 
the die pad 12 by a supersonic bonding method. An example of such 
supersonic bonding is illustrated in FIGS. 8-10. 
As shown in FIGS. 8 and 9, for supersonic bonding, use is made of a 
supersonic bonding apparatus 25 which comprises a supersonic generator 26 
connected to a presser tool 28 through a horn 27. The presser tool 28 
together with the supersonic generator 26 and the horn 27 is vertically 
movable toward and away from a support base 24 on which the heat sink 
plate 14 is placed. The supersonic generator 26 is driven for supersonic 
vibration by a controller 29 (see FIG. 9). A vibration sensor 30 is 
attached to the heat sink plate 14 for detecting the vibration of the heat 
sink plate 14 and for feeding detection signals to the controller 29. It 
should be appreciated that only the die pad 12 of the leadframe 19 is 
shown in FIG. 9 for purposes of better illustration. 
In operation, the presser tool 28 is lowered into pressing contact with a 
central portion of the die pad 12, and the supersonic generator 26 is 
actuated for supersonic vibration. The amplitude of vibration may be in 
the order of 20 micrometers for example. Initially, the die pad 12 
vibrates supersonically with the presser tool 28 relative to the heat sink 
plate 14, so that frictional heat is generated at the interface between 
the die pad 12 and the heat sink plate 14. Combined with the pressure 
applied by the presser tool 28, the frictional heat causes thermal fusion 
between the die pad 12 and the heat sink plate 14 at the limited central 
region where the pressure is applied. 
As the thermal fusion or bonding proceeds, the heat sink plate 14 starts 
vibrating with the die pad 12. When the bonding step is complete, the heat 
sink plate 14 vibrates synchronously with the die pad 12. Such completion 
of the bonding step may be detected by the vibration sensor 30 attached to 
the heat sink plate 12. 
Specifically, the vibration energy (kinetic energy) of the heat sink plate 
14 increases up to a certain limit as the bonding between the die pad 12 
and the heat sink plate 14 proceeds. This is illustrated in FIG. 10 
wherein the abscissa represents time while the ordinate represents the 
vibration energy of the heat sink plate 14. Thus, when the vibration 
energy of the heat sink plate 14 increases to a range A in FIG. 10 which 
is close to a maximum energy value, it is considered that the bonding 
between the die pad 12 and the heat sink plate 14 is almost complete. The 
vibration sensor 30 detects such a state and causes the controller 29 to 
stop or slows down the supersonic generator 26. It is to be understood 
that the supersonic bonding step should be preferably finished in the 
range A (slightly earlier than complete) because it is otherwise feared 
that the die pad 12 and/or the heat sink plate 14 may be thermally 
damaged. 
The vibration sensor 30 may be a contact type pressure sensor which is 
capable of detecting high frequency vibration, as shown in FIG. 9. 
Alternatively, the vibration sensor 30 may be replaced by a non-contact 
type vibration sensor which acoustically or electromagnetically detects 
the vibratory state of the heat sink plate 14 by utilizing the Doppler 
effect. 
After bonding the die pad 12 to the heat sink plate 14, a semiconductor 
chip 13 is bonded on the die pad 12 by soldering or by using a silver 
paste, as shown in FIG. 11. 
Then, as shown in FIGS. 12 and 13, the semiconductor chip 13 is 
electrically connected to the inner portion 15a of each lead 15 through a 
bondwire 16 by using a capillary tool 32. Such wire bonding comprises a 
first bonding step for attaching one end of the bondwire 16 to the 
semiconductor chip 13 and a second bonding step for attaching the other 
end of the bondwire 16 to the lead 15. In each of the first and second 
wire bonding steps, the heat sink plate 14 is supported on a heater block 
31. The first bonding step may be a known ball bonding step wherein a ball 
end of the bondwire 16 is pressed against the semiconductor chip 13 for 
bonding thereto under the heat from the heater block 31. 
On the other hand, the second wire bonding step may be preferably performed 
by utilizing supersonic vibration. For this purpose, the capillary tool 32 
is connected to a supersonic generator 26a via a horn 27a. The supersonic 
generator 26a is driven for supersonic vibration by the controller 29 
which may be commonly used for the supersonic generator 26 of the 
supersonic bonding apparatus 25 shown in FIG. 9. A vibration sensor 30a is 
attached to a suitable portion of the leadframe 19 for detecting the 
vibration of the lead 15. 
In the second wire bonding step, the capillary tool 32 is lowered to 
elastically deform each lead 15 into pressing contact with the heat sink 
plate 14, as shown in FIG. 13. Thus, the heat generated by the heater 
block 31 is effectively transmitted to the lead 15 via the heat sink plate 
14. Initially, the bondwire 16 vibrates supersonically with the capillary 
tool 32 relative to the lead 15, so that the bondwire 16 is rubbed against 
the lead 15 with resultant generation of frictional heat. Combined with 
the pressure applied by the capillary tool 32 as well as the heat from the 
heater block 31, the frictional heat causes thermal fusion between the 
bondwire 16 and the lead 15. As the thermal fusion or bonding proceeds, 
the lead 15 or the leadframe 19 as a whole starts vibrating with the 
bondwire 16. When the bonding step is almost complete, the leadframe 19 
vibrates synchronously with the capillary tool 32, thereby causing the the 
vibration sensor 30a to generate a signal for stopping or slowing down the 
supersonic vibrator 26a (see FIG. 10). 
After finishing the second wire bonding step, the capillary tool 32 is 
raised away from the lead 15. As a result, the lead 15 elastically 
restores to its natural state to form the spacing 17 between the lead 15 
and the heat sink plate 14. 
Then, as shown in FIG. 14, the semiconductor chip 13 together with its 
associated elements is placed in a mold 33 which includes an upper mold 
member 33a and a lower mold member 33b, and a known transfer molding step 
is carried out to form a package 11 of an epoxy resin. 
Thereafter, other necessary steps are performed which include solder 
plating of the leadframe 19, marking the resin package 11, cutting of the 
support bars 22 and tie bars 23 (see FIG. 3), cutting and bending of the 
leads 15, and so on. As a result, the individual semiconductor device 10 
shown in FIGS. 1 and 2 is thus obtained. 
FIG. 15 shows a semiconductor device according to a second embodiment of 
the present invention. The semiconductor device of this embodiment 
generally designated by reference numeral 10' is similar to that of the 
first embodiment (FIGS. 1 and 2), so that the same reference numerals as 
used for the first embodiment are also used with a prime (') for 
corresponding elements of the second embodiment. The only difference 
between the first and second embodiments resides in that the heat sink 
plate 14' of the latter embodiment is completely enclosed in the resin 
package 11' without direct exposure to the exterior. 
FIGS. 16 through 20 show a modified process for making a semiconductor 
device according to a third embodiment of the present invention. In this 
embodiment, the same reference numerals as used for the first embodiment 
are also used with a double prime (") to indicate corresponding elements. 
According to the third embodiment, bonding between the die pad 12" and the 
heat sink plate 14" is performed in the manner shown in FIGS. 16 and 17. 
Specifically, the heat sink plate 14" is supported on a support base 24 
which has a plurality of upwardly directed minute teeth 24a", and the die 
pad 12" is placed on the heat sink plate 14", as shown in FIG. 16. In this 
condition, a presser tool 28" having a plurality of downwardly directed 
minute teeth 28a" is lowered into pressing contact with the die pad 12" 
and supersonically vibrated by a supersonic generator (not shown) via a 
horn 27", as shown in FIG. 17. As a result, the die pad 12" is 
supersonically fused or bonded to the heat sink plate 14", as shown in 
FIG. 18. 
In the die pad bonding step described above, the teeth 28a" of the presser 
tool 28" come into non-sliding engagement with the die pad 12", whereas 
the teeth 24a" of the support base 24" come into non-sliding engagement 
with the heat sink plate 14". Thus, the supersonic energy of the presser 
tool 28" is effectively transmitted to the die pad 12" and converted into 
frictional heat for effectively bonding the die pad 12" to the heat sink 
plate 14". In FIG. 18, the depressions of the heat sink plate 14" and die 
pad 12" formed by the respective teeth 24a", 28a" are indicated by 
reference numerals 12a", 14a", respectively. 
Further, according to the third embodiment, use is made of an annular 
presser member 34" for simultaneously pressing all of the leads 15" 
against the heat sink plate 14" in the second wire bonding step, as shown 
in FIG. 19. Apparently, the annular presser member 34" stabilizes the 
position of the respective leads 15" relative to each other and to the 
heat sink plate 14", thereby facilitating the second wire bonding step. 
Each of the leads 15" will restore to its natural state after removal of 
the annular presser member 34", so that a suitable spacing 17" (see FIGS. 
16-18) is formed between the heat sink plate 14" and the lead 15". 
In addition to the advantages described above, the third embodiment is also 
advantageous for the following reasons. Specifically, as shown in FIG. 20, 
when a resin package 11" is later formed to fully enclose the heat sink 
plate 14", the resin material for the package 11" enters in the respective 
depressions 12a", 14a" of the die pad 12" and heat sink plate 14" to 
increase the contact area. As a result, the bonding of the package 11" 
relative to the die pad 12" and the heat sink plate 14" is greatly 
reinforced to prevent unexpected dislocation of these parts within the 
package 11" and/or cracking of the package 11" due to such dislocation. 
Further, if the package 11" is so formed as to expose the bottom surface 
of the heat sink plate 14", the depressions 14a" will increase the heat 
dissipating area of the heat sink plate 14" to correspondingly enhance 
heat dissipation. 
While, in the third embodiment, the presser tool 28" is shown to come into 
full contact with the die pad 12", the presser tool 28" may be made to 
come into contact with only a limited central portion of the die pad 12", 
as described for the first embodiment (see FIGS. 8 and 9). 
FIG. 21 shows a semiconductor device 10A according to a fourth embodiment 
of the present invention. The device 10A of this embodiment is a 
single-in-line type semiconductor device having a heat dissipation fin 35A 
which extends out of a resin package 11A. The fin 35A is integral with a 
die pad 12A which is mounted on a heat sink plate 14A, and a semiconductor 
chip 13A is mounted on the die pad 12A. A plurality of leads 15A are 
electrically connected to the chip 13A through respective bondwires 16A 
inside the package 11A but extend out of the package 11A from one side 
thereof. The semiconductor device 10A of the fourth embodiment is 
otherwise similar to the semiconductor device 10 of the first embodiment 
(FIGS. 1 and 2) and may be made substantially in the same manner (FIGS. 
3-14 or 16-20). 
FIG. 22 shows a semiconductor device 10B according to a fifth embodiment of 
the present invention. The device 10B of this embodiment is a dual-in-line 
type semiconductor device having a pair of heat dissipation fins 35B each 
of which extends out of a resin package 11B. The respective fins 35B are 
integral with a die pad 12B which is mounted on a heat sink plate 14B, and 
a semiconductor chip 13B is mounted on the die pad 12B. A plurality of 
leads 15B are electrically connected to the chip 13A through respective 
bondwires 16B inside the package 11B but extend out of the package 11B 
from both sides thereof. The semiconductor device 10B of the fifth 
embodiment is otherwise similar to the semiconductor device 10 of the 
first embodiment (FIGS. 1 and 2) and may be made substantially in the same 
manner (FIGS. 3-14 or 16-20). 
FIG. 23 of the accompanying drawings illustrate a squad type packaged 
semiconductor device according to a sixth embodiment of the present 
invention. The semiconductor device generally designated by reference 
numeral 10C comprises a resin package 11C which encloses a semiconductor 
chip 13C bonded on a die pad or island 12C. The die pad 12C is bonded to a 
heat sink plate 14C only in a limited central region 18C but held in 
direct contact therewith as a whole, similarly to the arrangement of the 
first embodiment (FIGS. 1 and 2). The die pad 12C may be rectangular or 
square with each of the four corners connected to a support bar 22C. 
The semiconductor chip 13C is electrically connected to a plurality of 
leads 15C via respective bondwires 16C. Each of the leads 15C has an inner 
flat portion 15Ca located within the package 11C, and an outer bent 
portion 15Cb extending out of the package 11C. The outer bent portion 15Cb 
is bent to become substantially flush with the bottom surface of the 
package 11C for conveniently mounting on a circuit board (not shown). 
The heat sink plate 14C is completely enclosed in the package 11C, so that 
the bottom surface of the heat sink plate 14C is not exposed to the 
exterior. Thus, the heat generated by the semiconductor chip 13C in 
operation is transmitted to the heat sink plate 14C for dissipation 
indirectly through the resin material of the package 11C. 
The heat sink plate 14C has marginal portions which laterally overlap the 
inner flat portions 15Ca of the respective leads 15C with a small spacing 
17C. The resin material of the package 11C occupies the spacing 17C, so 
that the respective leads 15C are electrically insulated from the heat 
sink plate 14C. 
According to the sixth embodiment shown in FIG. 23, the inner flat portions 
15Ca of the respective leads 15C are connected to each other by an annular 
insulating adhesive tape 36C. The use of such an adhesive tape is 
particularly advantageous for preventing the respective leads 15C from 
unexpectedly contacting each other in wire bonding where the leads 15C are 
crowdedly arranged, as more specifically described below. The adhesive 
tape 36C may be made of a polyimide film to which an adhesive material is 
applied. 
The packaged semiconductor device according to the sixth embodiment may be 
preferably made in the following manner. 
First, as shown in FIG. 24, a suitably configured leadframe 19C is 
prepared. Such a leadframe may be prepared by punching a thin metal sheet 
which may be made of a copper alloy or an iron-nickel alloy for example. 
The leadframe 19C comprises a pair of side bands 21C connected together by 
a plurality of section bars 20C. Two adjacent ones of the section bars 20C 
define a unit region which contains a die pad 12C surrounded by four 
groups of leads 15C. The die pad 12C is supported by four support bars 22C 
extending from the four corners of the die pad 12C to a square tie bar 
frame 23C which is in turn supported by suspension bars 37C. The tie bar 
frame 23C divide each lead 15C into an inner portion 15Ca closer to the 
die pad 12C and an outer portion 15Cb farther from the die pad 12C. Each 
group of leads 15C extends from a base bar 39C which is connected to 
connection bars 38C. Further, the leadframe 19C is also formed with a 
resin passage opening 41C having a neck portion 40C at one corner of the 
square tie bar frame 23C. 
Then, as shown in FIGS. 25 and 26, an annular insulating adhesive tape 36C 
is attached to the underside of the respective leads 15C. As a result, the 
adhesive tape 36C holds the respective leads 15C as suitably spaced from 
each other. This is particularly advantageous in view of the fact that the 
leads 15C of the squad type semiconductor device may be crowdedly arranged 
at a minute spacing of about 200 micrometers for example while each lead 
15C with a width of e.g. 80-120 micrometers is easily deformable. The 
adhesive tape 36C may have a thickness of 30-70 micrometers for example. 
It should be appreciated that the die pad 12C is downwardly offset from 
the normal plane of the leadframe 19C by an amount Z of 0.2-0.4 mm 
(200-400 micrometers), as shown in FIG. 26. 
Then, as shown in FIGS. 27 and 28, a metallic heat sink plate 14C is bonded 
to the bottom surface of the die pad 12C in such a manner that a 
peripheral portion of the heat sink plate 14C partially overlaps the inner 
portions 15Ca of the respective leads 15C. As previously described, the 
bonding between the die pad 12C and the heat sink plate 14C is preferably 
effected only in a limited central region 18C. Because of the downward 
offset of the die pad 12C which is greater than the thickness of the 
adhesive tape 36C, a spacing 17C is formed between the heat sink plate 14 
and the adhesive tape 36C. 
As previously described for the first embodiment, the heat sink plate 14C 
may be preferably bonded to the die pad 12C by a supersonic bonding 
method. FIG. 29 corresponding to FIG. 8 shows an example of such 
supersonic bonding. Since the supersonic bonding method has been already 
described in detail, no specific description is made with respect to FIG. 
29 wherein the same reference numerals as used for FIG. 8 are also used 
with a suffix "C" to indicate corresponding parts. 
After bonding between the die pad 12C and the heat sink plate 14C, a 
semiconductor chip 13C is bonded on the die pad 12C by soldering or by 
using a silver paste, as shown in FIGS. 30 and 31. 
Then, as shown in FIGS. 32 through 34, the semiconductor chip 13C is 
electrically connected to the inner portion 15Ca of each lead 15C through 
a bondwire 16C. Such wire bonding may be performed by using a heater block 
31C and a capillary tool 32C substantially in the same manner as already 
described for the first embodiment (see FIGS. 12 and 13). 
Then, as shown in FIG. 35, the semiconductor chip 13C together with its 
associated elements is placed in a mold 33C which includes an upper mold 
member 33Ca and a lower mold member 33Cb, and a known transfer molding 
step is carried out to form a package 11C of an epoxy resin. 
Thereafter, other necessary steps are performed which include solder 
plating of the leadframe 19C, marking the resin package 11C, cutting of 
the leadframe 19C, bending of the leads 15C, and so on. As a result, the 
individual semiconductor device 10C shown in FIG. 23 is thus obtained. 
The sixth embodiment described above may be modified so that the adhesive 
tape 36C rests directly on the heat sink plate 14C. In this case, the 
insulating adhesive tape 36C serves to insulate the respective leads 15C 
from the heat sink plate 14C and from each other. 
The preferred embodiments of the present invention being thus described, it 
is obvious that the same may be varied in many ways. Such variations are 
not to be regarded as a departure from the spirit and scope of the present 
invention, and all such modifications as would be obvious to those skilled 
in the art are intended to be included within the scope of the following 
claims.