Heat sink mounting and method of making

A heat sink mounting for a semi-conductor device includes a base member having a base body defining a generally cylindrical recess and a downwardly extending stem portion. The base body further defines an annular groove extending around the side surface of the cylindrical recess. A cap member detachably engages the base member and encloses the cylindrical recess. The cap member includes a tab arrangement which extends radially outward from the bottom of the cylindrical side wall of the cap member to engage the annular groove.

BACKGROUND OF THE INVENTION 
The present invention relates to a heat sink mounting for a semi-conductor 
device and to a method of making the mounting. More particularly, the 
invention contemplates a mounting which can be disassembled for 
replacement of the semi-conductor device if the device does not meet 
quality control testing. 
Heat sink mountings are commonly provided for semi-conductor devices which 
carry substantial current loads. High current levels can produce harmful 
heating of a semi-conductor device unless the heat is properly dissipated. 
Heat sink mountings of the type to which the present invention is 
directed, as shown for example in U.S. Pat. No. 4,049,185, issued Sept. 
20, 1977, to Nippert, commonly include a base member having a base body 
for supporting the semi-conductor device on an upper surface and a 
downwardly extending threaded stem. The mounting is typically attached to 
a heat sink panel by screwing the stem into a threaded hole in the panel. 
The surface upon which the semi-conductor is supported is usually defined 
within a recess in the top of the base body. Quite often a steel tube 
surrounds the recess and extends a substantial distance above the top of 
the base body. This steel tube may be brazed in position, as shown in U.S. 
Pat. No. 4,049,185, or permanently mechanically joined to the base member, 
as disclosed in U.S. Pat. Nos. 4,198,874 issued Aug. 3, 1965 to Doll, 
3,374,014, issued Mar. 19, 1968 to Kull, and 3,918,625, issued Nov. 11, 
1975 to Nippert. 
The components of the semi-conductor device, assembled within the steel 
tube, include a semi-conductor disc, on top of which is positioned a 
silver disc. A contact disc attached to an upwardly extending contact 
shaft is positioned on the silver disc. The shaft is surrounded by an 
electrically non-conductive bushing which, in turn, is pushed downward by 
means of one or more spring washers. The spring washers are held in place 
by a spacer washer which is secured to the steel tube in any of several 
fashions. In one approach, the steel tube is crimped slightly above the 
washer to prevent upward movement in the tube. In another approach, tabs 
are punched from the side wall of the steel tube and bent inward to 
contact the top of the spring washer, thereby holding all of the component 
parts together. 
After the various parts are assembled, the device is tested. If a device 
does not pass the inspection test, it is necessary to throw away the 
mounting elements along with the defective semi-conductor disc with most 
prior art heat sink mountings. This results in unacceptably high scrap 
costs, however, since the high conductivity copper from which a typical 
base member is formed is relatively expensive. 
U.S. Pat. No. 3,025,435, issued Mar. 13, 1962, to Green discloses a heat 
sink mounting which includes a base member and a cylindrical tube portion. 
The exterior of the lower end of the tube portion and the interior of the 
base member recess are threaded such that the heat sink mounting may be 
taken apart for repair if the semi-conductor element does not operate 
properly. While offering the advantage that it can be disassembled, the 
heat sink mounting structure of the Green U.S. Pat. No. 3,025,435 
requires the somewhat difficult and time consuming operation of machining 
threads on the elements to be joined. 
Accordingly, it is seen that there is a need for a simple heat sink 
mounting structure for a semi-conductor device, which structure may be 
disassembled to permit replacement of a defective semi-conductor element. 
SUMMARY OF THE INVENTION 
The heat sink mounting according to the present invention for a 
semi-conductor device comprises a base member and a cap member. The base 
member includes a base body, defining a generally cylindrical recess in 
its upper surface, and a downwardly extending stem portion. The base body 
further includes a plurality of inwardly extending flanges which are 
spaced around the opening of the cylindrical recess and which define open 
areas therebetween. The cap member has a substantially cylindrical side 
wall and a plurality of tabs extending radially outward from the bottom of 
the cylindrical side wall. The tabs are sized and spaced around the side 
wall in corrspondence to the size and spacing of the open areas between 
the flanges. The heat sink mounting may be assembled by first inserting 
the bottom of the cap member into the cylindrical recess with the tabs 
aligned with the open areas so as to pass therethrough. Then, the cap 
member is rotated such that the tabs are positioned beneath the flanges. 
The bottom of the cylindrical recess may define a raised pedestal surface 
in the center of the recess. The base body may include an annular ridge 
surrounding the opening of the cylindrical recess. 
The base body may define an annular groove in the side surface of the 
cylindrical recess beneath the inwardly extending flanges. The tabs are 
held in the annular groove beneath the flanges. The cap member may define 
an upper portion extending radially inward from the top of the cylindrical 
side wall. Alternatively the cap member may be substantially open at its 
upper end. 
The heat sink mounting may comprise a base member including a base body, 
defining a generally cylindrical recess in its upper surface, and a 
downwardly extending stem portion. The base body further defines an 
annular groove extending around the side surface of the cylindrical 
recess, and tube means for detachably engaging the base member and 
enclosing the cylindrical recess. The tube means has a substantially 
cylindrical side wall. Further, the tube means includes tab means 
extending radially outward from the bottom of the cylindrical side wall 
for engaging the annular groove and holding the tube means in the recess. 
The tube means may include an upper portion which extends radially inward, 
defining a central hole for receiving a contact of the semi-conductor 
device. Alternatively, the tube means may be substantially open at its 
upper end. 
The tube means may define a slot extending axially along the side wall 
completely therethrough. The outer diameter of the tube means may be 
reduced by forcing the sides of the slot toward each other, thereby 
permitting the tube means to be inserted into the recess and the annular 
groove to be engaged by the tab means. 
The tab means may comprise a plurality of spring arms extending generally 
downward along the side wall and a plurality of tabs. Each such tab 
extends radially outward from an assorted one of the spring arms, whereby 
the spring arms may be flexed radially inward to permit the tube means to 
be inserted into the recess such that the annular groove is engaged by the 
plurality of tabs. 
The base member may define a plurality of notches spaced around the opening 
to the recess. Each notch descends downward along the side surface of the 
recess to the annular groove. The tab means comprises a plurality of tabs 
extending radially outward from the bottom of the cylindrical side wall of 
the tube means. The tabs are sized and spaced in correspondence to the 
notches. The heat sink mounting may be assembled by first inserting the 
bottom of the tube means into the cylindrical recess, with the tabs 
aligned with the notches so as to pass downward therealong to the annular 
groove. The tube means is then axially rotated such that the tabs are 
positioned in the groove, but out of alignment with the notches. 
A method of making a heat sink mounting for a semi-conductor device, 
including a high conductivity copper base member and a cap member 
detachably mounted thereon, in which the cap member has a cylindrical side 
wall and tab means extending radially outward from the bottom of the 
cylindrical side wall, comprises the steps of: 
(a) forming a copper billet having an upper locating recess of reduced 
diameter; 
(b) brazing a steel ring on the copper billet in the upper locating recess; 
(c) extruding the copper billet and the steel ring to form a base member 
having a base body defining a generally cylindrical recess and a 
downwardly extending stem portion; 
(d) machining the interior of the cylindrical recess to provide an annular 
groove extending around the side surface of the cylindrical recess; and 
(e) securing the cap member to the base member by inserting the cap member 
in the cylindrical recess with the tab means positioned in the annular 
groove. 
The cap member may define a slot extending axially along the side wall 
completely therethrough and the step of securing the cap member to the 
base member may include the steps of: 
(a) reducing the outer diameter of the cap member by forcing the sides of 
the slot toward each other; 
(b) inserting the cap member into the cylindrical recess; and 
(c) releasing the cap member to permit the cap member to increase in 
diameter such that the tab means engages the annular groove. 
The tab means may comprise a plurality of spring arms extending generally 
downward along the side wall and a plurality of tabs, each such tab 
extending radially outward from an associated one of the spring arms. The 
step of securing the cap member to the base member includes the steps of 
flexing the spring arms radially inward, inserting the cap member into the 
cylindrical recess, and releasing the spring arms to permit the tabs to 
move radially outward and engage the annular groove. 
The steel ring may define a plurality of notches spaced around its inner 
diameter, and the step of extruding the copper billet and the steel ring 
may include the step of extruding the billet to define a plurality of 
notches spaced around the cylindrical opening and descending downward 
along the side surface of the recess. The step of machining the interior 
of the cylindrical recess may include the step of machining the annular 
groove around the surface such that the annular groove communicates with 
the notches. 
The tab means may comprise a plurality of tabs extending radially outward 
from the bottom of the cylindrical side wall and the step of securing the 
cap member to the base member may include the steps of inserting the 
bottom of the cap member into the cylindrical recess with each of the tabs 
passing downward along a respective one of the notches to the annular 
groove, and rotating the cap member such that the tabs are then positioned 
in the groove, but out of alignment with the notches. The step of 
machining the interior of the cylindrical recess may include the step of 
machining the bottom of the recess to provide a raised pedestal surface in 
the center of the cylindrical recess. 
Accordingly, is is an object of the present invention to provide a heat 
sink mounting and a method of making the mounting in which the cap member 
of the mounting may be detached from the base member after assembly 
thereto in the event that the semi-conductor element is defective; to 
provide such a mounting and method of making the mounting in which the 
base member includes a base body defining a generally cylindrical recess 
and an annular groove extending around the side surface of the recess, and 
in which the tube means includes tab means extending radially outward from 
the bottom of the cylindrical side wall of the tube means for engaging the 
annular groove; to provide such a mounting and method of making the 
mounting in which the tube means defines a slot extending axially along 
the side wall and completely therethrough, to permit the diameter of the 
tube means to be reduce by forcing the sides of the slot toward each other 
during insertion of the tube means into the recess; to provide such a 
mounting and method of making the mounting in which the tab means includes 
a plurality of spring arms having tabs extending radially outward, such 
that the spring arms may be flexed radially inward during insertion of the 
tube means into the recess; and to provide such a heat sink mounting and 
method of making the mounting in which the base member defines a plurality 
of notches spaced around the opening, descending downward along a side 
surface of the recess and the tab means comprises a plurality of tabs 
extending radially outward from the bottom of the cylindrical side wall of 
the tube means, which tabs are sized and space in correspondence to the 
notches to permit them to move downward along the notches to the annular 
groove prior to rotation of the tube means. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference is made to FIGS. 1-3 which illustrate a first embodiment of a 
heat sink mounting for a semi-conductor device, constructed according to 
the present invention. The mounting includes a base member 10, having a 
base body 12 defining a generally cylindrical recess 14 in the upper 
surface of the base body. The base member also has a downwardly extending 
stem portion 16 which typically is threaded. The stem portion 16 of the 
heat sink mounting can be screwed into a thermally conductive heat sink 
support and the body 12 is hexagonal in shape to facilitate this 
operation. The heat sink mounting further includes a tube means comprising 
a cap member 18 for detachably engaging the base member 10 and enclosing 
the cylindrical recess 14. Preferably, the base member 10 is formed of a 
high conductivity copper material and the cap member 18 made of steel. 
Other materials may, however, also be used. 
The heat sink mounting contains a plurality of elements 20 which are 
stacked within the recess 14, as shown in FIG. 2, and which collectively 
make up the semi-conductor device. A disc of semi-conductor material 22 is 
positioned on a raised pedestal surface 24, generally located in the 
center of the bottom of recess 14. The surface 24 makes electrical contact 
with one side of the disc 22. The base body 12 therefore is included in 
the electrical circuit utilizing the semi-conductor device. The opposite 
side of the semi-conductor disc 22 is contacted by a silver disc 24 which, 
in turn, is contacted by a contact member 26. Contact member 26 includes a 
lower disc portion 28 and a contact shaft 30 extending upward through a 
central hole 32 in the cap member 18. 
Positioned on the shaft 30 is a bushing 34, made of a ceramic or similar 
electrically nonconductive material. Bushing 34 keeps the contact member 
26 out of electrical contact with a flat washer 36. As best seen in FIG. 
2, washer 36 contacts the outer surface of insulating bushing 34 and the 
inner surface of the cap member 18, holding the elements 20 centrally 
within the heat sink mounting. Pressing downward on the washer 36 are a 
pair of spring washers 38 and 40 which are also in contact with an upper 
portion 42 of the cap member 18. Washers 38 and 40 press the stacked 
elements 20 of the semi-conductor device together, maintaining all of the 
elements in good electrical contact with each other, while at the same 
time allowing for dimensional variations which may occur as the 
semi-conductor device is operated and the elements 20 are heated above 
ambient temperature. 
The base body in the embodiment of FIGS. 1-3 has a plurality of inwardly 
extending flanges 44 which define therebetween a plurality of notches or 
open areas 46. Each of the notches 46 descends downward along the side 
surface of the recess 14 to an annular groove 48 which is defined beneath 
the flanges 44. The cap member 18 includes a plurality of tabs 50 
extending radially outward from the bottom of the cylindrical side wall 52 
of the cap member. These tabs are sized and spaced in correspondence to 
the sizing and spacing of the notches 46. The device is assembled by 
stacking the elements 20 in the recess 14, and then inserting the bottom 
of cap 18 into the cylindrical recess 14 with the tabs aligned with the 
notches. The tabs pass downward through the notches to the annular groove 
48. Next, the cap member 18 is axially rotated, as indicated by arrow 54 
in FIG. 3, such that the tabs 50 are positioned in groove 48 out of 
alignment with notches 46. The spring washers 38 and 40 maintain a spring 
force on the cap member 18, holding the upper surfaces of the tabs 40 in 
contact with bottom surfaces of the flanges 44. 
The heat sink mounting of the present invention is advantageous in that it 
permits the elements 20 of the semi-conductor device to be assembled in 
the mounting and subjected to quality control testing, while also 
permitting the replacement of the disc 22 should it prove to be defective. 
It will be appreciated that the high conductivity copper of the base 
member is relatively expensive. The heat sink mounting of the present 
invention therefore provides substantial savings by reducing the number of 
such mountings which are scrapped. 
FIGS. 4A-4E illustrate the method by which the heat sink mounting of the 
present invention is made. A cylindrical copper billet 56, shown in FIG. 
4B, is formed having an upper locating recess 58 of reduced diameter and 
approximately 0.02 inches in depth. A steel ring 60, shown in FIG. 4A, is 
provided having a central opening pattern which corresponds generally to 
the pattern defined by the flanges 44 and the spaces 46 of the base body. 
The steel ring 60 is substantially thicker than the depth of recess 58, on 
the order of 0.040 to 0.050 inch. Steel ring 60 is brazed onto the copper 
billet 56 in the upper locating recess 58, as shown in FIG. 4C. 
Next, the copper billet 56 and the steel ring 60 are extruded, as shown in 
FIG. 4D, to form a base member having a base body 12 defining a generally 
cylindrical recess 14 and a downwardly extending stem portion 16. The 
extrusion process forms the hexagonal outer shape of the body 12 from the 
substantially cylindrical billet 56. The lower part 62 of the upper die 
element 64 is configured in a shape corresponding to that of the opening 
in the steel ring 60 shown in FIG. 4A. As a consequence, as it presses 
downward forming part of the recess 14, it also forms the notches 46 in 
the recess 14. During the extrusion process, the annular ridge 65 is also 
formed in the upper surface of the base body 12, surrounding the recess 
14. This annular ridge is formed from the steel material of ring 60 and, 
as is known, is used to weld an outer cover element onto the base member. 
Next, the upper die portion 64 is raised and the base member 10 is ejected 
from the lower die elements 66 and 68 by ejection pin 70. As seen in FIG. 
4E, the bottom of the recess 14 is then machined to produce the groove 48 
in the side surface of the recess 14 and the pedestal surface 24. 
Additionally, threads 72 are roll formed and/or machined onto the stem 
portion 16 of the base body 10. 
FIG. 5 illustrates an alternative construction for the tube means. It 
should be noted that the cap member 74 is completely open at its upper end 
and does not define an inwardly extending upper portion, such as portion 
42 shown in FIG. 1. When using the cap member 74 of FIG. 5, the side walls 
of the cap member 74 are punched or crimped after the elements 20 are 
stacked in the recess 14 so as to engage the top of the spring washers 38 
and 40 and hold the elements together in compression. 
Although requiring this additional assembly operation, the cap member 74 of 
FIG. 5 detachably engages the base member of the heat sink mounting. The 
base member used with the cap member 74 of FIG. 5 need not have the 
notches 46 shown in FIG. 1. Rather, in order to permit the cap member 74 
to be inserted into the recess 14 of the base body, the cap member 74 is 
reduced in diameter by forcing the sides of slot 76 toward each other. The 
diameter of flange 78 is therefore reduced such that it is less than the 
inner diameter of the recess 14. The cap member 74 is inserted into the 
recess 14 and released. The cap member 74 then expands outward toward its 
noncompressed shape, with the flange 78 seating itself in the annular 
groove 48 of the base body. 
FIG. 6 illustrates yet another version of the tube means for the heat sink 
mounting. The tab means comprises a plurality of spring arms 80 which 
extend generally downward along the side wall 82, and a plurality of tabs 
84 which extend radially outward from associated ones of the spring arms. 
The spring arm 80 may be flexed radially inward to permit the tube means 
to be inserted in the recess 14 of a base member. The arms 80 then move 
outward as the tabs 84 snap into the annular groove 48 in the base body. 
As with the tube means of FIG. 5, the side wall 82 is punched or crimped 
after the elements 20 are stacked in the recess 14 so as to engage the top 
of the spring washers 38 and 40 and hold the elements together in 
compression. 
It will be apparent that the construction of the cap members shown in FIGS. 
5 and 6 provides for ready disassembly of the heat sink mounting by 
removal of the cap member from the base member, should the semi-conductor 
device fail the requisite quality control testing. To perform this 
operation, the punched or crimped portions of the tube member are bent 
back and the elements 20 are removed. The tube member is then removed from 
the base member. It will be appreciated that the tube member is destroyed 
by this demounting operation, but the base member and most of the elements 
20 may be reused. 
It will be appreciated that while the cap members of FIGS. 5 and 6 are 
shown with open upper ends, such members could be constructed with an 
inwardly extending portion, similar to portion 42 in FIG. 1. Further, 
while the configuration of the cap members of FIGS. 5 and 6 is such that 
notches 46 are not required for their insertion into a base member body, 
nevertheless, these cap members could be used in conjunction with base 
members having such notches. 
It will be appreciated that various modifications may be in the shape of 
the base member and the position of annular groove in the side surface. 
The base body 12 of FIG. 7 includes an annular groove which is positioned 
at the bottom of the recess 14. The base body is relatively thin and has a 
relatively long tube means 18 mounted thereon. In contrast, base body 12 
of FIG. 8 is substantially thicker and, due to the positioning of annular 
groove 48 near the top of the recess 14, requires a much shorter tube 
means 18. The base member 12 and the tube means 18 of the heat sink 
mounting of FIG. 8 provide the same amount of interior space for the 
elements of the semi-conductor device as is provided by the mounting of 
FIG. 7. The base body 12 of FIG. 9, on the other hand, has its annular 
groove 48 positioned intermediate the bottom of the recess 14 and the top 
of the recess 14. Due to the fact that the semi-conductor components 20 
are held within the heat sink mounting by the inwardly extending portion 
42, the tube means 18 need not extend upward as far as would be required 
if the tube means were completely open at its upper end. 
Having described the invention in detail and by reference to preferred 
embodiments thereof, it will be apparent that modifications and variations 
are possible without departing from the scope of the invention defined in 
the appended claims.