Semiconductor device having a heat sink with bumpers for protecting outer leads

A QFP adapted to lowering the heat resistance and increasing the number of pins includes a heat-radiating metal plate having bumpers formed at the four corners thereof as a unitary structure, a semiconductor chip mounted on the heat-radiating metal plate, leads provided on the heat-radiating metal plate and surrounding the peripheries of the semiconductor chip, bonding wires for connecting the leads to the semiconductor chip, and a sealing resin member for sealing part of the semiconductor chip, inner leads of the leads, bonding wires and part of the heat-radiating metal plate. The tips of the bumpers integrally formed with the heat-radiating metal plate are positioned outside the tips of the outer leads that are protruding from the sealing resin member. In the QFP producing method, the heat-radiating metal plate having the bumpers and the lead frame having the leads are secured outside the sealing resin member.

BACKGROUND OF THE INVENTION 
The present invention relates to a technology for producing semiconductor 
devices and, particularly, to a semiconductor device equipped with a 
resin-sealed package of surface mount type, such as one which has many 
pins and a small heat resistance, and is small in size and is produced at 
a decreased cost. 
As ICs are now produced having many functions, and are highly densely 
fabricated and operate at high speeds, it has been desired to develop a 
surface mount resin-sealed package having many lead pins with a good 
heat-emitting property or a small heat resistance. A surface mount type 
resin-sealed package which is constituted as described below has been 
proposed in, for example, Japanese Patent Laid-Open No. 286558/1991. 
In such a package, the tabs to which a semiconductor pellet is bonded and 
heat-radiating fin leads are integrally formed together, and the 
heat-radiating fin leads and heat-radiating fins outwardly protruding from 
a sealing resin member of the package are integrally formed together. 
Moreover, a heat sink is buried in the package on the side of the back 
surface of the tabs, and is mechanically coupled to the heat-radiating fin 
leads inside the package. 
A QFP (quad flat package) which has a good heat-radiating property and 
whose outer leads are prevented from deforming has been disclosed in 
Japanese Patent Laid-Open No. 218262/1993. 
This QFP employs a lead frame, and tabs to which a semiconductor pellet is 
bonded and heat-radiating fin leads are formed integrally. The 
heat-radiating fin leads and heat-radiating fins outwardly protruding from 
the sealing resin member of the package are integrally formed, the tips of 
the heat-radiating fins being outwardly protruded beyond the tips of the 
outer leads. 
SUMMARY OF THE INVENTION 
In the former device in which the heat sink and the heat-radiating fin 
leads are mechanically coupled together inside the sealing resin, however, 
the coupling portions impose a limitation upon the arrangement of leads 
and upon the number of pins. Besides, the pellet must be bonded, wires 
must be bonded and sealing with resin must be executed after a plurality 
of heat sinks are coupled to a series of lead frames, deteriorating the 
throughput of production. 
In the latter device in which the leads and the heat-radiating fins are 
constituted by a lead frame, a problem arises in that it is impossible to 
design a package having a sufficiently high heat-radiating performance. 
The object of the present invention is to provide a semiconductor device 
whose outer leads can be prevented from being deformed, yet with a high 
heat-radiating performance. 
Another object of the present invention is to provide a method of producing 
semiconductor devices at a low cost. 
The above and other objects as well as novel features of the present 
invention will become obvious from the description of the specification 
and the accompanying drawings. 
Among the inventions disclosed in this application, representative 
embodiments will be briefly described below. 
That is, the semiconductor device has a feature that the semiconductor 
pellet is bonded to a main surface of the heat sink which is partly buried 
in a sealing resin member of a square shape, and the heat sink has a 
plurality of bumpers formed integrally therewith, the bumpers protruding 
from the corners of the sealing resin member and having tips which are 
arranged on the outer sides of the row of tips of the outer leads which 
are led out from the four sides of the sealing resin member. 
A method of producing semiconductor devices comprises: 
a step of preparing a series of lead frames having unit lead frames which 
are arranged in a row and in each of which the outer leads and inner leads 
are radially arranged from the region where a semiconductor pellet is 
provided; 
a step of preparing a series of heat sinks having unit heat sinks which are 
arranged in a row, and having main surfaces to which the semiconductor 
pellets are to be bonded and a plurality of bumpers that are integrally 
formed together therewith; 
a step of coupling the series of lead frames and the series of heat sinks 
together outside at least a pair of bumpers of the unit heat sinks; 
a step of bonding the semiconductor pellets onto main surfaces of the unit 
heat sinks; 
a step for electrically connecting the electrodes of the semiconductor 
pellets to the inner leads with bonding wires thereto; 
a step of sealing the semiconductor pellets, inner leads, and at least the 
main surfaces of the unit heat sinks on the semiconductor pellet side with 
a resin; 
a step of cutting the series of lead frames to form the unit lead frames; 
and 
a step of cutting off the unit heat sinks from the series of heat sinks. 
According to the above-mentioned semiconductor device, the heat generated 
by the semiconductor pellet is conducted to the heat sink; i.e., the 
semiconductor pellet is cooled quite efficiently. 
Moreover, since the tips of bumpers arranged at the corners of the sealing 
resin member protrude outwardly beyond the tips of the outer leads, in 
case an external force is unexpectedly given to the package during the 
steps of production, during the shipment to the user, or while it is being 
mounted by the user, the bumpers absorb the external force, preventing the 
outer leads from being deformed. 
According to the above-mentioned method of producing semiconductor devices 
in which the coupling portion between the heat sink and the lead frame is 
not buried in the sealing resin member, no limitation is put on the layout 
of the inner leads by the coupling portion in the sealing resin member. 
Additionally, an increase in the degree of freedom of laying out the 
wirings permits the bumpers to be arranged, making it possible to produce 
even semiconductor devices that do not have leads for the heat-radiating 
fins. 
Since the heat sink is coupled to the lead frame, furthermore, the devices 
for fabricating the semiconductor pellets and inner leads of the prior art 
may be employed. Before being coupled, moreover, the heat sink is separate 
from the lead frame. Therefore, the thickness of only the heat sink can be 
easily increased, contributing to further enhancing the heat-radiating 
performance with ease.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment of the FIGS 1(a)-(c) semiconductor device of the 
invention is constituted as a resin-sealed QFP 29 having a good 
heat-radiating property, which is a semiconductor integrated circuit 
device that realizes a low heat resistance. 
The QFP 29 includes a silicon semiconductor pellet (hereinafter referred to 
as a pellet) 23, which has the shape of a square small plate and on the 
main surface of which is formed a semiconductor element, a heat sink 15 on 
which the pellet 23 is mounted, a plurality of inner leads 9 radially 
arranged along the four sides of the pellet 23, bonding wires 25 that 
electrically connect the inner leads 9 to electrode pads 23a which are 
external terminals formed on the main surface of the pellet 23, outer 
leads 8 integrally coupled to the inner leads 9, respectively, and a 
sealing resin member 27 which seals the pellet 23, part of the heat sink 
15, inner leads 9 and wires 25. The sealing resin member 27 is made of an 
epoxy resin having an insulating property and has a shape of a square flat 
board which is sufficiently larger than the pellet 23. The heat sink 15 is 
made of a material having a good heat conducting property, and has the 
shape of a square flat plate which is smaller than the sealing resin 
member 27 but is larger than the pellet 23. Bumpers 18 are integrally 
formed together with the heat sink 15 and protrude from the four corners 
thereof, the bumpers 18 outwardly protruding from the four corners of the 
sealing resin member 27 along the diagonal lines. The tips of the bumpers 
18 protrude from the sides of the sealing resin member 27, and are 
disposed on the outer sides beyond the tips of the outer leads 8 that are 
bent like gull wings. 
A method of producing QFPs according to the present embodiment of the 
present invention will be described. 
In this embodiment, a series of lead frames 1 shown in FIG. 2(a)-2(c) are 
used for producing QFPs. The series of lead frames 1 are made of a thin 
plate of a copper-containing material (copper or copper alloy) which is 
integrally formed by a suitable means such as punching or etching. On the 
surfaces of the series of lead frames 1 is deposited a film (not shown) 
for properly effecting the wire bonding that will be described later, by 
electroplating with silver (Ag) or the like. The series of lead frames 1 
are constituted by a plurality of unit lead frames 2 which are arranged in 
a row in the lateral direction. The series of lead frames 1 are 
constituted by a repetition of the same pattern with a region demarcated 
by dash-and-dot lines C--C, C'--C' of FIG. 2(a) as a unit lead frame. 
Basically, hereinafter, a unit lead frame will be described and shown. 
The unit lead frame 2 includes a first outer frame (top rail) 3, a second 
outer frame (bottom rail) 4, a third outer frame (side rail) 5, and a 
fourth outer frame (side rail) 6, these outer frames 3, 4, 5 and 6 forming 
a square shape. The first outer frame 3 and the second outer frame 4 have 
pilot holes 3a and 4a, respectively, and the third outer frame 5 and the 
fourth outer frame 6 have small holes 5a and 6a for mechanical coupling, 
and small holes 5b and 6b for positioning in a pair of diagonally opposite 
positions. A notch 3b for arranging a sub-runner is formed in a position 
connecting the first outer frame 3 and the third outer frame 5 together, 
and the first outer frame 3 is cantilevered at the notch 3b. 
The lead frame 2 having four outer frames 3, 4, 5 and 6 is so formed as to 
surround a square region 7 for arranging a semiconductor pellet, the 
region 7 having a size corresponding to that of the pellet. A plurality of 
outer leads 8 are formed in parallel at regular intervals along the 
peripheries of the inner sides of the four outer frames 3, 4, 5 and 6, and 
the inner leads 9 are integrally coupled to the outer leads 8, 
respectively. The inner leads 9 are so arranged as to surround the region 
7, and the tips on the inner side thereof are arranged nearly in a 
straight line along the sides of the region 7. Dam bars 10 are formed 
among the neighboring outer leads 8. 
In this embodiment, the QFPs are produced using a series of heat sink 
assemblies 11 shown FIGS. 3(a) through 3(c). The series of heat sink 
assemblies 11 are made of a plate made of a copper-containing material 
(copper or copper alloy) having a thickness which is about four times as 
large as the thickness of the series of lead frames 1, and are integrally 
formed by punching. The series of heat sink assemblies 11 are constituted 
by a plurality of unit heat sink assemblies 12 which are arranged in a row 
in the lateral direction, each heat sink assembly 12 being arranged to 
mate with the respective unit lead frame 2 of the series of lead frames 1. 
The series of heat sink assemblies 11 are constituted by a repetition of 
the same pattern with a region demarcated by dash-and-dot lines D--D, 
D'--D' of FIG. 3(a) as a unit heat sink 12. Basically, hereinafter, the 
unit heat sink 12 will be described and shown. 
The heat sink assembly 12 has a first outer frame (top rail) 13 and a 
second outer frame (bottom rail) 14, the two outer frames 13 and 14 being 
arranged in parallel. In the first outer frame 13 and in the second outer 
frame 14 is formed a heat sink 15 of nearly a square shape as a unitary 
structure, the heat sink 15 being smaller than the sealing resin member 
but larger than the pellet. On the main surface of the heat sink 15 on the 
bonding side of the pellet is deposited a film (not shown) for adequately 
bonding the pellet by electroplating with silver (Ag) as will be described 
later. 
A trapezoidal notch 16A is formed in a central portion of each of the four 
sides of the heat sink 15. Furthermore, a stepped portion 16B is formed on 
the side of the heat sink 15 in a manner that the upper surface protrudes. 
A bumper-hanging bar 17 is formed at each of the four corners of the heat 
sink 15. On the outer side of each bumper-hanging bar 17 is provided a 
bumper 18 which is formed in a shape of a square plate having a 
predetermined thickness. The bumpers 18 have such a size that the tips 
thereof are located on the outer sides of the tips of the outer leads that 
are bent in the form of a gull wing. The four bumpers 18 are integrally 
coupled to the first outer frame 13 and to the second outer frame 14, 
respectively, and the first outer frame 13 and the second outer frame 14 
are integrally formed together with the bumpers 18, bumper-hanging bars 17 
and the heat sink 15. 
In the first outer frame 13 and in the second outer frame 14 are arranged 
stepped portions 19 for floating the inner leads from the heat sink on the 
outer bumper of the bumpers 18 at three places except one side of the 
first outer frame 13, the stepped portions 19 being so formed by pressing 
that the upper surfaces thereof are in flush. The height of the stepped 
portion 19 is set to a minimum value at which an insulation gap between 
the inner leads and the heat sink 15 can be ensured. On the upper surfaces 
of the three stepped portions 19 of the first outer frame 13 and the 
second outer frame 14 are formed a pair of protuberances 13a and 14a for 
mechanical coupling and a protuberance 14b for positioning by pressing. At 
a place of the first outer frame 13 where no stepped portion 19 is formed, 
a protuberance 13b that forms a pair together with the positioning 
protrusion 14b of the second outer frame 14 along a diagonal line with 
respect to the center of the heat sink 15. These protuberances are so 
formed as to correspond to the above-mentioned coupling holes 5a, 6a and 
the positioning holes 5b, 6b. 
A protruded portion 20 for arranging a sub-runner is outwardly formed near 
the positioning protuberance 13b of the first outer frame 13, the 
protruded portion 20 corresponding to the notch 3b for arranging a 
sub-runner in the above-mentioned lead frame 2. The length of the 
protruded portion 20 in a direction where it separates away from the first 
outer frame 13 corresponds to the length of the sub-runner that will be 
described later, and the lateral width in the direction perpendicular to 
the longitudinal direction is larger than the width of the sub-runner. 
The series of lead frames 1 and the series of heat sink assemblies 11 are 
integrally fabricated in a step of integration so that the individual 
units are superposed as shown in FIGS. 4(a) through 4(c). That is, the 
lead frames 2 and the heat sink assemblies 12 are arranged and superposed 
vertically in such a way that the regions 7 for disposing the pellets are 
concentric with the heat sinks 15. In this case, coupling protuberances 
13a, 14a and positioning protuberances 13b, 14b on the heat sink assembly 
12 side are inserted in the coupling holes 5a, 6a and in the positioning 
holes 5b, 6b on the lead frame 2 side, relative. Thus, the lead frame 2 
and the heat sink assembly 12 are accurately positioned relatively to each 
other. Then, the upper ends of the two coupling protuberances 13a, 14a are 
caulked (mechanically deformed) thereby to form coupling portions 21 in 
the shape of a rivet head which is greater than the two coupling holes 5a, 
6a. Peripheries of the two coupling holes 5a, 6a in the lead frame 2 are 
sandwiched between the two stepped portions 19 of the two coupling 
portions 21, whereby the lead frame 2 and the heat sink assembly 12 are 
secured together, superposed one upon the other. 
The superposing work, insertion work and caulking work can be 
simultaneously executed for a plurality of lead frames 2 and heat sink 
assemblies 12. Therefore, these operations are executed very efficiently. 
In a coupled member 22 in which the lead frame 2 and the heat sink assembly 
12 are superposed vertically as described above, the tips on the inner 
side of a group of inner leads 9 of the upper lead frame 2 are overlapped 
on the inside with the outer peripheral edges of the heat sink 15 of the 
lower heat sink assembly 12 by a predetermined length when viewed from 
above, and are floated above the upper surface of the heat sink 15 by the 
height of the stepped portion 19. 
In a pellet-bonding step, as shown in FIGS. 5(a) and 5(b) the pellet 
bonding is executed for each of the heat sinks 15 of the coupled members 
22 in which the series of lead frames 1 and the series of heat sink 
assemblies 11 are coupled together as mentioned above. Then, in a 
wire-bonding step, the wires are bonded for each of the pellets and lead 
frames 2. Here, since the coupled members 22 are constituted in series, 
these bondings are executed for each of the units as the coupled members 
22 are fed pitch by pitch in the longitudinal direction. The thickness and 
shape of the series of lead frames are the same as those of the 
conventional series of lead frames and, hence, the above-mentioned works 
are carried out using the conventional pellet-bonding device and the 
wire-bonding device. 
Referring to FIG. 5(b), the pellet 23 is formed in the shape of a square 
plate smaller than the heat sink 15. The pellet 23 is disposed on the 
upper surface of the heat sink 15, and is fastened by a bonding layer 24 
formed between the heat sink 15 and the pellet 23. In this embodiment, the 
bonding layer 24 is formed of a solder layer. That is, the pellet 23 is 
bonded to the heat sink 15 through the bonding layer 24 on which the 
pellet 23 is placed in a state that the solder foil is placed on the upper 
surface of the heat sink 15 and heated. 
The bonding layer may be composed of a gold-silicon eutectic layer or a 
silver paste adhesive layer other than the solder layer. Here, it is 
desirable that the bonding layer formed does not hinder the conduction of 
heat from the pellet 23 to the heat sink 15. The bonding layer 24 of 
solder not only has a high heat conductivity but also is rich in softness, 
and absorbs mechanical stress that acts between the pellet 23 and the heat 
sink 15. 
After an integrated circuit made up of a group of semiconductor elements 
and wiring circuits is fabricated through an ordinary wafer processing 
step in the process of producing semiconductor devices, the pellet 23 is 
cut into a predetermined shape in the dicing step, thus producing a 
semiconductor device. 
The wires 25 are bonded at their both ends to electrode pads 23a of the 
pellet 23 and to the tips of the inner leads 9 to thereby electrically 
connect the pellet 23 and the inner leads 9 together. Here, since the 
inner tips of the inner leads 9 are overlapped on the peripheral portions 
of the heat sink 15, the reaction force against the press of the wires 25 
can be obtained from the heat sink 15 during the bonding of wires to the 
inner leads. Accordingly, the wires are bonded using a conventional 
thermocompression type wire-bonding device, ultrasonic thermocompression 
type wire-bonding device or ultrasonic wire-bonding device. 
Using a transfer-molding device 30 in the step of sealing with the resin 
shown in FIGS. 6(a) to 8(c) sealing resin members 27 shown in FIGS. 
9(a)-9(c) are simultaneously molded for each of the assemblies of the 
coupled member 22 to which the pellet 23 and the wires 25 have been bonded 
as shown in FIGS. 5(a) and 5(b). 
The transfer-molding device 30 shown in FIGS. 6(a) to 8(c) is equipped with 
a pair of upper force plates 31 and lower force 32 that are clamped to 
each other by a cylinder device or the like (not shown). In the mating 
surfaces of the upper force plate 31 and the lower force plate 32 are 
formed upper cavity recessed portions 33a and lower cavity recessed 
portions 33b in plural pairs to form cavities 33. Here, however, the 
drawings and the description deal with only one unit like the series of 
lead frames and the series of heat sink assemblies. The shape of the 
cavity 33 corresponds to the square shape defined by dam bars 10 of the 
lead frame 2 in the assembly 26. The height of the cavity 33 is greater 
than the height of the assembly 26. The depth of the upper cavity recessed 
portion 33a is greater than the height of the loop of the wire 25 in the 
assembly 26. The depth of the lower cavity recessed portion 33b is equal 
to the height from the lower surface of the heat sink 15 to the upper 
surface of the stepped portion 19 in the assembly 26. 
In the mating surface of the lower force plate 32 is formed a pot 34 into 
which is inserted a plunger 35 that is moved back and forth by being 
driven by the cylinder device (not shown) so as to feed a resin which is a 
molding material. In the mating surface of the upper force plate 31 is 
formed a cull 36 opposed to the pot 34, and there are further formed a 
main runner 37 and a sub-runner 38 which communicate with each other. The 
end of the sub-runner 38 is connected to the gate 39 formed at a 
predetermined corner portion that will be described later in the upper 
cavity recessed portion 33a, and the gate 39 is so formed as to inject the 
resin into the cavity 33. 
In this embodiment, four holes 40 for containing bumper-hanging bars are 
formed in the mating surface of the lower force plate 32 at four corners 
of the lower force cavity recessed portions 33b integrally with the cavity 
recessed portions 33b. Therefore, the corners of the lower cavity recessed 
portion 33b are open because their corner portions are cut away. The hole 
40 for containing the bumper-hanging bar has a horizontal outline which 
corresponds to the horizontal outline of a bumper-hanging bar 17 of the 
heat sink assembly 12 and, hence, the hole 40 for containing the 
bumper-hanging bar contains the bumper-hanging bar 17. In the mating 
surface of the lower force plate 32 are formed holes 41 for containing 
bumpers at positions on the outer side of the holes 40 for containing 
bumper-hanging bars, the holes 41 being continuous to the holes 40 for 
containing bumper-hanging bars. A hole 41 for containing a bumper has a 
horizontal outline that corresponds to the horizontal outline of the 
bumper 18 of the heat sink assembly 12. Therefore, the holes 41 contain 
the bumpers 18, respectively. 
In the mating surface of the lower force plate 32 are further formed holes 
42 for containing protruded portions on the outer side of the holes 41 for 
containing bumpers that correspond to the gates 39 of the upper force 
plate 31, the holes 42 being so provided as to be partly overlapped with 
the holes 41 for containing bumpers. The holes 42 for containing protruded 
portions correspond to the horizontal outlines of the protruded portions 
20 of the heat sink assembly 12 and, hence, serve to contain the protruded 
portions 20. In the mating surface of the lower force plate 32 are further 
formed a pair of escape grooves 43 at both side suitably away both sides 
of the cavity recessed portion 33b. 
On the other hand, in the mating surface of the upper force plate 31 are 
formed four protuberances 44 for filling the holes that contain 
bumper-hanging bars at four corners of the upper force cavity recessed 
portion 33a. The horizontal outline of each protuberance 44 corresponds to 
the horizontal outline of the hole 40 for containing a bumper-hanging bar, 
and the height of each protuberance 44 is set to a value obtained by 
subtracting the thickness of the bumper-hanging bar 17 from the depth of 
the hole 40. Therefore, the hole 40 is filled with the protuberance 44 and 
with the bumper-hanging bar 17. That is, the notches formed at corners of 
the lower force cavity recessed portion 33b and opened by the hole 40 are 
closed by the protuberances 44. 
Protuberances 45 for filling the bumper-containing holes are formed on the 
outer sides of the protuberances 44 that fill the holes for containing 
bumper-hanging bars in the mating surface of the upper force plate 31, the 
protuberances 45 being formed integrally with the protuberances 44 that 
fill the holes for containing bumper-hanging bars. The horizontal outline 
of the protuberance 45 corresponds to the horizontal outline of the bumper 
18 of the heat sink assembly 12 and, hence, the protuberance 45 serves, in 
cooperation with the bumper 18, to fill the hole 41. 
Moreover, protuberances 46 for filling the holes that contain protuberances 
are formed on the outer sides of the protuberances 45 for filling the 
holes that contain bumpers at positions corresponding to the gates 39 on 
the mating surface of the upper force plate 31, the protuberances 46 being 
formed continuously to the protuberances 45 for filling the holes that 
contain bumpers. The horizontal outline of the protuberance 46 corresponds 
to the horizontal outline of the protruded portion 20 of the heat sink 
assembly 12. Therefore, the protuberance 46 and the protruded portion 20 
fill the hole 42. The sub-runner 38 is formed in the surface of the 
protrusion 46 mating with the protruded portion 20, and a gate 39 is 
formed in the surfaces of the protuberances 45, 44 continuous to the 
protuberance 46, which mate with the bumper 18 and the bumper-hanging bar 
17. In the mating surface of the upper force plate 31 are further formed a 
pair of escape grooves 47 suitably away from both sides of the cavity 
recessed portion 33a. 
Next, described below is a method of sealing the assembly 26 with the resin 
using the transfer-molding device 30. 
First, the assembly 26 is placed on the lower force plate 32. In this case, 
the heat sink 15 is contained in the lower force cavity recessed portion 
33b, and the bumper-hanging bar 17, bumper 18 and protruded portion 20 at 
each corner are contained in the holes 40, 41 and 42, respectively. In 
this state, the lower surfaces of the heat sink 15, bumper-hanging bar 17, 
bumper 18 and protruded portion 20 are in contact with the bottom surfaces 
of the cavity recessed portion 33b and of the holes 40, 41 and 42. The 
lower surface of the lead frame 2 is in contact with the mating surface of 
the lower force plate 32. 
Then, the upper force plate 31 and the lower force plate 32 are clamped 
together. When they are clamped together, the periphery of the dam bar 10 
of the lead frame 2 is sandwiched from the upper and lower directions 
between the mating surfaces of the upper force plate 31 and the lower 
force plate 32. Moreover, the protuberances 44, 45 and 46 formed on the 
mating surface of the upper force plate 31 are fitted into the holes 40, 
41 and 42 formed in the mating surface of the lower force plate 32, and 
the lower surfaces of the protuberances 44, 45 and 46 press the upper 
surfaces of the bumper-hanging bar 17, bumper 18 and protruded portion 20 
that are contained in the holes 40, 41 and 42. In this state, the notches 
formed at the corners of the lower force cavity recessed portion 33b and 
opened by the hole 40 are closed by the protuberances 44. Accordingly, the 
cavity 33 formed by the upper force cavity recessed portion 33a and the 
lower force cavity recessed portion 33b is sealed substantially 
completely. 
Then, a resin 48 which is to be molded is injected into the cavity 33 from 
a pot 34 by a plunger 35 via the main runner 37, sub-runner 38 and gate 
39. The resin 48 flows through the sub-runner 38, flows along the upper 
surface of the protruded portion 20 of the heat sink assembly 12, and is 
injected into the cavity 33 through a passage surrounded by the protruded 
portion 20 and the gate 39 formed in the lower force plate 32. 
The cavity 33 is filled with the resin 48, which is then thermally set, and 
the sealing resin member 27 is formed. After the sealing resin member 27 
is formed, the upper force plate 31 and the lower force plate 32 are 
opened. As the mold is opened, the sealing resin member 27 is pushed up by 
the ejector pins (not shown) and is parted from the upper force plate 31 
and the lower force plate 32. During this parting, it is desirable that 
the ejector pins also push up portions of the heat sink 15 of the assembly 
26. 
In such a way, the assembly 26 is molded, and parted, completing a molded 
article 28. The pellet 23, the inner leads 9, the wires 25, part of the 
heat sink 15, and part of the four bumper-hanging bars 17 of the molded 
article 28 are sealed inside the sealing resin member 27. That is, the 
main surface of each of the heat sink 15 and the bumper-hanging bars 17 is 
exposed from one main surface of the sealing resin member 27, and the 
other main surface and the side surfaces are buried inside the sealing 
resin member 27. Furthermore, four bumpers 18 are outwardly and radially 
protruded from the four corners of the sealing resin member 27. 
The flash of the runner and culls appearing during the transfer molding are 
removed in the removing step. Then, in the step of solder plating, the 
molded article 28 is plated with solder over all surfaces that are exposed 
from the sealing resin member 27. Since the series of lead frames 1 and 
the series of heat sink assemblies 11 in the molded article 28 are all 
electrically connected, the electroplating with solder is executed at one 
time. 
The molded article 28 is transferred to a step of cutting the leads. In 
this step, the dam bars 10 are cut off among the neighboring outer leads 
8. The outer leads 8 are cut off from the outer frames 3, 4, 5 and 6, and 
are then bent in the form of a gull wing. The bumpers 18 are cut off from 
the outer frames 13 and 14. Here, it is desirable that the bumpers 18 and 
the outer frames 13, 14 are cut at right angles to the diagonal lines of 
the sealing member 27. By this cutting method, the shape of the bumpers 18 
can be easily adjusted, and the edges of the bumpers 18 in parallel with 
the sides of the sealing resin member 27 can be always positioned on the 
outer sides of the tips of the outer leads 8, and maintained in position. 
Thus, the QFP 29 that is shown in FIGS. 1(a)-1(c) is prepared. The QFP 29 
is mounted on a printed wiring board as shown in, for example, FIGS. 10(a) 
and FIG. 10(b). 
The printed wiring board 50 shown in FIGS. 10(a) and 10(b) has a main body 
51 of an insulating plate member made of, for example, glass, epoxy or the 
like. On one main surface of the main body 51 are formed a plurality of 
mounting pads 52 of an elongated shape corresponding to flat portions of 
the outer leads 8, the mounting pads 52 being arranged correspondingly to 
the rows of the outer leads 8. On the upper surface of the main body 51 
are further formed lands 53 for radiating heat at a central portion and at 
four corners of the square constituted by the rows of mounting pads 52. 
These lands 53 correspond to the heat sink 15 of the QFP 29 and to the 
bumpers 18. 
To mount the QFP 29 on the surface of the printed wiring board 50, 
soldering material (not shown) such as cream solder is applied to the 
mounting pads 52 and to the lands 53 by screen printing, or the like. In 
this case, the soldering material is applied to the lands 53 partly. 
Then, the flat portions of the outer leads 8 of the QFP 29, heat sink 15 
and bumpers 18 are adhered to the mounting pads 52 and lands 53 to which 
the soldering material is applied. In this state, the soldering material 
is melted by a reflow solder processing, and then solidified. Due to this 
processing, soldered portions 54 and 55 are formed between the outer leads 
8 and the mounting pads 52, between the heat sink 15 and the lands 53, and 
between the bumpers 18 and the lands 53. Thus, the QFP 29 is mounted on 
the surface, electrically and mechanically connected to the printed wiring 
board 50. 
As the pellet 23 becomes hot due to the heat of solder reflow, the heat is 
conducted to the heat sink 15 since the pellet 23 is directly bonded to 
the heat sink 15. The heat sink 15 is thicker than the lead frame and has 
a large area and, hence, has a very low heat resistance. Therefore, the 
heat of the pellet 23 is conducted to the heat sink 15 highly efficiently, 
and the heat is dissipated from the heat sink 15 to the mounting board 50 
and radiated to the air; i.e., the pellet 23 is efficiently cooled. The 
heat directly transferred to the heat sink 15 diffuses from the heat sink 
15 to the four bumpers 18, and is further radiated into the air. The heat 
diffused into the heat sink 15 and to the bumpers 18, is then conducted to 
the lands 53 from the heat sink 15 and the four bumpers 18, and is 
transferred to the printed wiring board 50. Moreover, the heat of the 
pellet 23 is directly conducted to the heat sink 15 and is diffused to the 
whole sealing resin member 27 from the wide surface area of the heat sink 
15. 
As described above, the QFP 29 of the present invention well radiates the 
heat and prevents the occurrence of reflow cracks. 
The above-mentioned embodiment has the following effects. 
(1) Since the pellet 23 is directly bonded to the heat sink 15, the heat of 
the pellet 23 is conducted to the heat sink 15, making it possible to 
improve the thermal stability. 
(2) Part of the heat sink 15 and the bumpers 18 integrally coupled to the 
corners of the heat sink 15 are outwardly exposed from the sealing resin 
member 27. Therefore, the heat absorbed by the heat sink 15 is emitted 
into the open air, making it possible to further enhance the effect 
mentioned in item (1). 
(3) The tips of the bumpers 18 disposed at four corners of the sealing 
resin member 27 outwardly protrude beyond the tips of the outer leads 8. 
Therefore, in case an external force is unexpectedly exerted on the 
package while the product is being assembled, being shipped to the user, 
or being mounted by the user, the bumpers 18 absorb the external force to 
prevent the outer leads 8 from deforming. 
(4) In the step of producing the QFP 29, the mechanical coupling portion 21 
between the lead frame 2 and the heat sink assembly 12 is not buried 
inside the sealing resin member 27, and the layout of the inner leads 9 
inside the sealing resin member 27 is not limited by the mechanically 
coupling portion 21. 
(5) Owing to the effect mentioned in item (4), the invention can be adapted 
even to a QFP that has neither heat-radiating fins nor heat-radiating fin 
leads for coupling the heat-radiating fins to the tabs. 
(6) The coupling between the lead frame 2 and the heat sink assembly 12 is 
accomplished by the mechanical coupling portion 21. Therefore, no gas 
generates during the coupling, and the pellet is prevented from being 
contaminated by the gas. 
(7) Since the heat sink assembly 12 is coupled to the lead frame 2, the 
assembling devices that execute the works of the pellet 23 and the inner 
leads 9 may be those used in the prior art. Moreover, since the lead 
frames 2 and the heat sink assemblies 12 are formed in series structures 
the productivity is raised. 
(8) Before being coupled, the heat sink assembly 12 is separate from the 
lead frame 2 and, hence, it is possible to fabricate a heat sink 15 and 
bumpers 18 having thicknesses larger than that of the lead frame 2. 
Accordingly, the heat-radiating performance can be further increased with 
ease. Since the lead frame 2 can be thinly formed, furthermore, the wiring 
density can be increased. 
In the foregoing was concretely described an embodiment of the present 
invention accomplished by the present inventors. It should, however, be 
noted that the invention is in no way limited to the above-mentioned 
embodiment only but can be modified in a variety of other ways without 
departing from the gist and scope of the invention. 
For instance, the shapes of the sealing resin member and the heat sink are 
not limited to squares only but may be tetragonal (for example, 
rectangular), rectangular. In particular, the heat sink needs not be 
limited to a regular tetragon but may be circular or polygonal. 
The heat sink assemblies are not limited to the series structures but may 
be constituted in a single unit which may then be assembled on a series of 
lead frames. 
The mechanical coupling between the heat sink and the lead frame is not 
limited to caulking, but may be a weld using the soldering material. In 
this case, the coupling holes can be omitted. 
The heat sink is not limited to the structure in which it is partly buried 
in the sealing resin member but may have a structure that the heat sink is 
entirely buried in it. When the heat sink is partly exposed through the 
main surface of the sealing resin member, the external heat-radiating fins 
may be attached thereto. In such a case, the outer leads may be bent in 
the direction of the main surface on the side opposite to the heat sink. 
In the bumpers may be formed bolt-insertion holes and internal threads. 
The material for forming the heat sink assembly is not limited to the 
copper-type material but may be any other metal material having a good 
heat conductivity, such an aluminum-type material (aluminum or alloy 
thereof) or the like. In particular, it is desirable to use a material 
having an excellent heat conductivity, such as silicon carbide (SiC), and 
having a coefficient of thermal expansion which is nearly equal to that of 
silicon which is a material of the pellet. 
In the foregoing embodiment, the heat sink and the bumpers are soldered to 
the lands of the printed wiring board. However, a sufficiently high 
heat-radiating performance is exhibited even when the heat sink and the 
bumpers are not soldered. 
Moreover, the heat sink may be used to serve as an electrically conducting 
member for the ground terminal and the feeder terminal. 
The foregoing description was made about the case where the invention 
accomplished by the present inventors was adapted to the QFP IC in the 
field of art which is the background of the invention. The invention, 
however, is in no way limited thereto only but can be adapted to 
surface-mount resin-sealed packages such as QFJ, QFI, etc., as well as to 
packages for power transistors and other electronic devices in general. In 
particular, the invention produces excellent effects when it is utilized 
for semiconductor devices which are required to be small in size, have 
many pins, be inexpensive, and have a high heat-radiating performance.