Note: Descriptions are shown in the official language in which they were submitted.
~4683
This invcntiOn relates to mcthods and app~ratus or
asscmbly of componcnts on circuit board~ and the like.
More particularly, it relates to methods and apparatus for
asscmbly and mounting of semiconductor devices and heat sinks
for semiconductor devices and the like on printed circuit boards
or other mounting substrates.
Many semiconauctor devices generate heat during operatio
which must be dissipated to a~oid aamage to the de~ice. In
some devices the heat generated is dissipated sufficiently by
the enclosure, header or leads. Other devices may be mounted
j on heat sinks comprising bodies of thermally conductive materials
i such as copper, aluminum or the like which dissipate the heat
¦ generated by the devices lnto the surrounding environment. Such
¦ heat sinks may be extruded or sheet metal bodies incluaing heat
! dissipating fins or the like.
! In many applications it is customary to mount a heat
I sink between the semiconductor header or case and ~le substrate
¦ on which the case is mounted, such as a circuit board
¦ or the like, so that the case and heat sink may be held in
I intimate broad-area contact to aid in conduction of thermal
! energy from the case to the heat sin~ and so that the case may
! be electrically connected to the mounting substrate by soldering
! or other means, if desired. Conventionally, a circuit employing
a plurality of components, some of which utilize heat sinks, is
! pre-assembled with the individual components which do not emplov
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heat sinks positioned on the circuit board. Thereafter, the components
are attached to the c;rcuit board by convent~onal wave soldering of the
leads to the circuit pads. After cleaning and tr;mming, the circu~t
board ls inspected and the heat s~nk and semiconductor device are hand
mounted on loose hardware such as bolts or the like wh;ch pass through
the circuit board. The leads from each heat sink mounted component
must then be hand soldered to the c;rcuit board, the mounting hardware
installed, and the clean;ng, tr;mming and ;nspection steps repeated.
In accordance with the present invention all the circuit
components, including those mounted with heat sinks as well as the heat
s;nk ;tself, may be pre-assembled on a circuit board or the like and
soldered to the circu;t board ;n a single solder;ng opérat;on. Ac-
cordingly, the additional steps of hand mounting and solder;ng, etc.,
of heat sink mounted components is el;m;nated, result;ng in a sub-
stantial t;me sav;ng and reliability improvement.
In accordance with one aspect of the present invent;on,
a novel mount;ng stud ;s employed ;n combinat;on with a heat sink.
The stud compr;ses an elongate shaft, preferably threaded at its first
end, hav;ng a radially enlarged port;on, such as a flange, extend;ng
outwardly between its ends. The second or head end of the shaft is
coated w;th a solder-promot;ng material, such as tin. The first end of
the stud extends through a hole in the flat base portion of the heat
sink. The shank of the threaded end of the shaft is preferably knurled
or serrated adjacent the flange so that the stud may be swaged or
force-f;tted ;nto the heat sink mount;ng hole. As a result of this
arrangement, the sem;conductor case may be pre-assembled on the heat
s;nk with the leads extending through holes ;n the heat sink. The pre-
assembled semiconductor device and heat s;nk assembly may then be
46~
1 positioned on the circuit board and the semiconductor device leads
2 and the mounting stud holding the heat sink and case together soldered
3 to the circuit board in a single wave soldering operation along the other
4 components. Accordingly, the conventional subsequent steps of mounting
the heat sink with loose hardware, hand soldering and subsequent cleaning,
6 trimming and inspection are totally eliminated. Pre-assembly of the heat
7 sink and semiconductor case in accordance with the invention thus results
8 in vast time savings in circuit board assembly operations, eliminates
g tedious hand assembly of circuit boards with loose hardware , and eliminates
hand soldering. Thus not only is a vast saving in assembly time realized,
11 bur reliability of solder connections and uniformity of the soldering
12 assembly process is vastly improved.
13 Broadly stated, the invention is a mounting stud, for use
14 in connection with mounting components to a circuit board, comprising: an
elongated cylindrical shaft having a flange extending outwardly and radially
16 therefrom between its ends to define first and second shaft portions; the
7 end of said second shaft portion being adapted to fit in a hole formed in
18 the circuit board and to be soldered to the circuit board; and a coating
13 of solder-promoting material covering the end of said second shaft portion.
Other features and advantages of the invention will become
21 more readily understood from the following detailed description when
22 taken in connection with the appended claims and attached drawings in
23 which:
24 Figure 1 is an exploded view of a heat sin~ mounting assembly
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on a c;rcuit board employing the methods and apparatus of the invention;
Figure 2 is an elevational view of one embodiment of the
novel mounting stud of the invention; and
Figure 3 is an elevational view of an alternative embodi-
ment of the novel mounting stud of the invention.
Assembly of a semiconductor device case and heat sink
on a circuit board or the like in accordance with the principles
of the invention is illustrated in Figure 1. While the invention
is disclosed with particular reference to assembly of a semi-
conductor device encapsulated in a standard TO-3 type header
and employs a single broad-base heat sink, it will be readily
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lZ446E13
apparent that the principles of the inVentiOn are equally
applicable to assembly of circuits employing various othe~
encapsulation cases a~d other forms of heat sinks. 1,
As illustrated in FIGURE 1, a conventional printed
circuit board 10 (shown only in p~rtion) is employed for
mounting and electrically interconnecting a plurality of discrete
semiconductor components to form a circuit. conventioAally,
the printed circuit board 10 is a non-conductive material having
a conductive pattern (not shown) printed on the underside thereof.
Semiconductor devices are positioned on the top surface of the
board with their leads extending through holes 11. In the
assembly operation, the semiconductor devices are positioned on
the top surface of circuit board 10 with the leads 12 extending
l through the holes 11 and the leads electrically connected to the
l printed conductive cir~uit on the underside of the board by
¦conventional wave soldering methods. The design, fabrication
¦ and assembly of circuit boards and circuit co~ponents is well `
¦ known to those skilled in the art and therefore will not be
I described in detail herein.
¦ When the circuit to be fabricated includes components
which generate excess thermal energy, it is frequently necessary
¦ to interpose a heat dissipating device, known as a heat sink,
between the semiconductor case and the circuit board.
Conventionally, the devices which do not employ heat sinks are
first placed on the circuit board ànd their leads solaered to
the circuit board by a first wave soldering operation. Thereafter
the devices employing heat sinks are attached to the heat
sinks by conventional hardware such as screws, bolts or the like
- which pass through the circuit board. This is usually accomplishe 1
by posi`tioning the semiconductor case on the heat sinX with the
1 .
II _5_ I
~244~83
semiconductor leads extending through the heat sink and into the
I printed circ~it board eyelets. The semiconductor component leads
j are then hand soldered to the printed circuit and the heat sink
! and case attached ~o the board with loose hardware. rZrequently,
additional hardware or soldering is used to assure electrical
contact between the case and the circuit ~oard. Obviously, since
the heat sink mounted devices are attached to the heat sink and
¦ the circuit board after the other components have been soldered
¦ thereto, the attachment of heat sink mounted devices is very
! time-consuming and risks damage to the already partially assembled
¦ circuit. Furthermore, since the soldering operation for the
other components has been completed, the leads from the heat
sink mounted component must be hand soldered to the circuit
board. Such hand soldering is not only time-consuming but
results in less reliable electrical connections and possible
damage to the previously soldered components.
As illustrated in FIGIIRE 1, the heat sink and
semiconductor c~ponent may be pre-as~embled employing thè novel
mounting stud illustrated in FIGURE 2. Accordingly, the
pre-assembled heat sink and semiconductor case assembly may be
positioned on the printed circuit board along with the other
components and soldered to the circuit board in a single soldering
i operation which attaches the assembly to the board, solders the
! leadsj and provides electrical contact with the case.
~As illustrated in FIGURES 1 and 2, the mounting stud 20
¦! of the invention compriseslan elongated cylindrical shaft having
I a relatively `thin flange 21 radially extending therefrom,
! preferably near one end thcreof. Ad]acent the flange 21 and
1. ``' ` `
.
! - ` ` .
,. .
,
I!
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lZ~46~33
, . .
on the side thereof adjacent the longer portion of the shaft 20
Iis provided a slightly expanded and knurled or serrated base 22.
¦The remainder of the longer portion of the shaft 20 is threaded
¦with standard threads to accept standard nuts or the like. The
!entixe stud 20, or at least the head stud portion 23r is preferabl! r
tin-plated to aid in forming solder connections thereto.
The stud 20 is force fitted or swaged into a hole 25 in
the flat base portion 26 of a heat sink 27. The heat sink may ,~
¦be of various types such as that illustrated in FIGURE 1.
incluaing heat aissipated fins or various other conventional heat
sink bodies. The tin-plated stud 20 and the heat sink 27 may i
be pre-assembled by suitable machine operations, thus eliminating
tedious hand assembly of screws, bolts and the like. A standard
¦semiconductor case 28 is then mounted on the heat sink with the
studs 20 passing through mounting holes 29 and the semiconductor
device leads 12 extending through holes 30 in the flat base
portion 26 of the heat sink. Nuts 31 and lock washers 32 are
posi~tioned on the studs 20 and the pre-assembled case and heat
slnk is t~en ready for attachment to the circuit board 10.
Since the pre-assem~led heat sink and case is to be
attached to the circuit board by soldering, the pre-assembled
unit may be treated in exactly the same manner as other circuit
components. The components are simply positioned with their
leads extenaing thro~gh the -appropriate holes in the board anA
the pre-assembled unit is positioned with the tin-plated heads 23
extendi tnrough e hole6 35 provided for attaching the heat sinj.
;'~'' ...,.` ,' '' '.
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:IZ~46~33
S;nce the head 23 of the stud 20 ;s pre-tinned, the pre-assembled
unit is soldered to the circuit board in the same soldering
operation used to solder the leads of the other components.
Therefore, the conventional post-assembly and hand soldering
operations are totally elim;nated.
It should be noted that although the heat sink is attached
to the circuit board when the head 23 is soldered, the nuts 31 are
on the top surface. Accordingly the case 28 may be removed for
replacement without removing the heat s;nk. Therefore, servicing
and ma;ntenance of circuit boards using the heat sink mounting
of the invention ;s quite convenient.
Not only does the assembly process of the invention
result in a major time saving; elimination of hand soldering
operations improves reliability of the completed c;rcuit boards.
Any hand soldering operation conducted after partial assembly of
the circuit board may result in accidental damage to the
previously soldered connections. Furthermore, manual handling of
the partially assembled boards to attach heat sinks thereto with
conventional loose hardware also increases the risk o~ accidental
damage. By soldering all the components in a single operation,
the risks of post-soldering hand operations are totally eliminated.
The use of tin-plated studs also aids in permitting
soldering o~ the heat sink mounting hardware to the circuit board.
While the ;nvention is described herein in terms of t;n-plated
components, it will be understood that those skilled in the art that
the terms "tin-plated", "pre-tinned" and the like are used
herein in the broadest sense to include coatings of conventional
solder and solder-aiding or solder-promoting compositions such
1244683
as tin, tin-lead alloys, fluxes and the like, regardless of the
actual composition of the coating or the method by which it is
applied.
It will be observed that employing a mounting stud 20
with a thin flange 21 as shown in Figures 1 and 2 results in
mounting the flat base portion 26 of the heat sink 27 closely
adjacent or even in contact with the circuit board surface. In
some situations it is preferrable to mount the heat sink 27
parallel to but spaced from the surface of the circuit board 10.
In such cases, the stud 20 may be manufactured with an axially
thickened flange 21. Alternatively, where relatively large
spacing between the base 26 of the heat sink and the surface of the
circuit board 10 is requ;red, such as for better circulation of
cooling air around the heat sink or to permit cleaning under the
heat sink or the like, the stud 20 may include a stand-off shank
as illustrated in Figure 3.
In the alternative embodiment illustrated in Figure 3,
the stud 20 comprises an elongated cylindrical shaft having a
relatively thin flange 21 radially extending therefrom. In this
embodiment, however, the flange 21 may be near the central portion
of the shaft. A slightly enlarged knurled or serrated base 22 is
provided on the shaft adjacent one side of the flange 21 and the
remainder of the shaft on the same end as the knurled base 22 is
provided with standard threads or the like to accept standard
nuts. Obviously, other means for securing the semiconductor case
to the shaft 20 such as swage clasps or the like may be employed
instead of the threaded connections shown. A stand-off shank 40
which is radially enlarged with respect to the head end 42 is
interposèd between the flange 21 and the head 42. Since the stand-
o~f shank 40 is radially enlarged with respect to the head 42,
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46~33
a shoulder 41 is provided which rests on the top surface of the
circuit board 10 when the head 42 is inserted in the mounting
holes 35 in the circuit board. Accordingly, the base 26 of the
heat sink 27 is spaced from the circuit board 10 by the axial
length of stand-off shank 40. Therefore the stud 20 of Figure 3
may be manufactured with the axial length of stand-off shank 40 of
any lenyth des;red to provide the required spacing between the
circuit board and the heat sink.
It will be readily appreciated that the funct;ons of
flange 21 and stand-off shank 40 can be accomplished by a single
radially enlarged shaft or axially thickened flange. It will be
further appreciated that the radial dimensions of the stand-off
shank are determined by the diameter of the mounting holes 35 in
the circuit board. Accordingly, the diameter of the shank 40 need
not necessarily be the same as th~t of the remainder of the shaft 20
as shown, but may be larger than that of the remainder of the
shaft, depending upon the diameter of the mounting holes 35
in which the stud is to be mounted, so that a shoulder 41 is
provided between the head 42 and the stand-off shank 40. Further-
more, since only the head 42 will be soldered to the circuit board,
only the head 42 need be coated or pre-tinned with a solder-
promoting material. If desired, however, the entire stud 20 may be
pre-tinned.
While the invention has been described with particular
reference to specific embodiments thereof, it is to be understood
that the forms of the invention described in detail are to be
taken as preferred embodiments thereof, and that various changes
and modificat;ons may be resorted to without departing from the
spirit and scope of the invention as defined by the appended
claims.
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