Board-mounted thermal path connector and cold plate

The present invention discloses an improved method and apparatus for dissipating heat from printed circuit boards and electronic devices mounted thereon. Printed circuit boards are provided with apertures therethrough for receiving thermal conductor pads. The thermal conductor pads may be secured in the apertures through the use of glue or by means of an interference fit. Glue may also be deposited on top of the thermal conductor pad to secure an electronic device thereto. The glue is cured in a manner that limits its thickness to a minimum value. The electronic device may be further secured to the printed circuit board by wave soldering. The opposite end of the thermal conductor pad contacts the cold plate.

FIELD OF THE INVENTION 
The present invention relates generally to a cold plate adapted for use 
with printed circuit board assemblies to provide enhanced heat 
dissipation, and more particularly, to a thermal conductor pad mounted in 
a printed circuit board, thereby providing a thermally conductive path 
between electronic devices mounted on the printed circuit board and the 
cold plate on which the printed circuit board itself is mounted. 
BACKGROUND OF THE PRIOR ART 
In the field of high-speed computers, high-density, high-speed electronic 
devices exhibit above-average power consumption characteristics. Such 
power consumption leads to extreme heat generation. A cooling apparatus 
must be able to efficiently dissipate heat from the electronic devices. 
The co-pending and commonly assigned U.S. patent application Ser. No. 
07/284,992, filed Dec. 14, 1988, by August et al., entitled "COOLING PLATE 
WITH INTERBOARD CONNECTOR APERTURES FOR CIRCUIT BOARD ASSEMBLIES", 
describes a cooling plate for heat dissipation that is particularly 
adapted for use with stacks of printed circuit boards. The cooling plate 
includes apertures and mounting means for Z-axis connector assemblies so 
that printed circuit boards attached to either side of the cooling plate 
may be electrically interconnected. Externally, the cooling plate has a 
fixed pattern of the heat conductive pads that are substantially identical 
to the pattern of devices on a printed circuit board attached to the 
cooling plate. The use of such fixed patterns prevent specific cooling 
plates from being used with more than one configuration of printed circuit 
board. Each printed circuit board has a different pattern of devices 
thereon, and thus requires a different cooling plate. In addition, careful 
manufacturing of the cooling plate and equally careful mounting of devices 
on the printed circuit board is required to ensure optimal heat 
dissipation. 
The commonly assigned U.S. Pat. No. 4,628,407, issued Dec. 9, 1986, to 
August et al., entitled "CIRCUIT MODULE WITH ENHANCED HEAT TRANSFER AND 
DISTRIBUTION", describes a printed circuit board used in a high 
performance computer. A printed circuit board stack is disclosed which 
includes a heat-conducting plate situated therein. The printed circuit 
boards contain thermally conductive paths from each circuit device mounted 
thereon through the printed circuit board to locations in contact with the 
cooling plate. This system provides good heat dissipation properties, but 
tolerance variations in the thickness of the printed circuit board can 
affect the thickness of the thermal compound between the thermal connector 
and the circuit device. 
SUMMARY OF THE INVENTION 
To overcome the limitations in the prior art described above, and to 
overcome other limitations that will become apparent upon reading and 
understanding the present specification, the present invention discloses 
an improved method and apparatus for dissipating heat from printed circuit 
boards and electronic devices mounted thereon. The printed circuit board 
has an aperture therethrough for receiving a thermal conductor pad. The 
pad may be secured in the printed circuit board by means of glue or a 
press fit. Glue may be deposited on top of the pad to secure and provide a 
thermal path from an electronic device to the pad. The glue is cured in a 
manner that limits its thickness to a minimum value. A wave soldering 
process, or other method of attachment, is used to further secure the 
electronic device to the printed circuit board. The end of the thermal 
conductor pad adjacent the cold plate provides a large nickel-plated 
surface area for contacting the cold plate. The interface between the pad 
and the cold plate may be metal-to-metal or it may be filled with a 
thermal grease or other thermally conductive material. 
The present invention provides improved thermal characteristics over prior 
art cold plates. Variations in the thickness of printed circuit boards no 
longer affect heat dissipation. The installation process ensures that the 
thermal interface between the thermal conductor pad and the electronic 
device is minimized. 
Manufacturing and assembly advantages are simplified using the present 
invention. The cost of creating custom bump patterns is eliminated by 
manufacturing the cold plates with smooth generic surfaces. Thus, generic 
cold plates can be fitted to any number of differently configured printed 
circuit boards. In addition, careful alignment of the printed circuit 
boards on the cold plate is no longer necessary. 
Because the thermal conductor pad is removable from the cold plate, the 
present invention also provides for simpler inspection and repair. Printed 
circuit boards can be easily removed from the cold plate, in contrast to 
prior art cold plates with bump patterns thereon where the printed circuit 
boards are often glued to the cold plate to ensure proper heat transfer. 
The present invention also provides a significantly improved method for 
attaching power and ground connections to the printed circuit boards via 
the cold plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the following detailed description of the preferred embodiment, 
reference is made to the accompanying drawings which form a part hereof 
and in which is shown by way of illustration a preferred embodiment in 
which the invention may be practiced. It is to be understood that other 
embodiments may be utilized and that structural changes may be made 
without departing from the scope of the present invention. 
The present invention discloses an improved method and apparatus for 
dissipating heat from printed circuit boards and electronic devices 
mounted thereon. In the present invention, printed circuit boards are 
provided with apertures therethrough for receiving thermal conductor pads. 
The thermal conductor pads are engaged in the aperture of the printed 
circuit board by means of a press fit or glue. Glue is deposited on the 
top surface of the thermal conductor pad to secure the electronic device 
thereon and to provide a better thermal path. The electronic device is 
first aligned and then pressed onto the top surface of the thermal 
conductor pad, thereby securing the electronic device to the thermal 
conductor pad. The glue is cured in a manner (e.g., with force applied to 
the electronic device) that limits its thickness to a minimum value. Wave 
soldering, or other means of attachment, further secures the electronic 
device to the printed circuit board. 
The opposite end of the thermal conductor pad contacts the cold plate. This 
interface between the thermal conductor pad and the cold plate may be an 
interference fit or a thermal grease interface. 
In FIG. 1, a cold plate 10 is described, wherein elements with solid 
outlines are external features of the cold plate 10 and elements with 
dotted outlines are internal features of the cold plate 10. The cold plate 
10 is similar in construction to that described in the copending and 
commonly assigned application Ser. No. 07/284,992, filed Dec. 14, 1988, by 
August et al., entitled "COOLING PLATE WITH INTERBOARD CONNECTOR APERTURES 
FOR CIRCUIT BOARD ASSEMBLIES", which application is hereby incorporated by 
reference. The cold plate 10 contains a fluid inlet manifold 12, fluid 
passages 22, and a fluid outlet manifold 14. Interspersed throughout all 
the fluid passages 22 are a plurality of heat-dissipating fins 24. Mounted 
along the edges 16 and 18 of the cold plate 10 are zero-insertion-force 
(ZIF) edge connectors (not shown) of the type described in the co-pending 
and commonly assigned application Ser. No. 07/351,871, filed May 12, 1989, 
by August et al., entitled "TWO PIECE ZIF CONTROL WITH SLIDING BLOCK", 
which application is hereby incorporated by reference. Flange 20 on the 
end of the cold plate 10 contains threaded bolt holes (not shown) for 
mounting the cold plate 10 and attached printed circuit boards to the 
ground contact shown in FIG. 3. The cold plate 10 is also comprised of a 
plurality of power busses 26 and ground conductor strips 28. The ground 
conductor strips 28 are an integral part of surface of the cold plate 10. 
The power busses 26 reside in apertures 30 of the cold plate 10 and are 
sandwiched within the cold plate 10 by the printed circuit boards on 
either side. The power busses 26 and ground conductor strips 28 make 
contact with corresponding electrical strips on the printed circuit 
boards. These strips on the printed circuit boards, which complete the 
electrical circuits when in contact with the power busses 26 and ground 
conductor strips 28, are shown in more detail in FIG. 5. The cold plate 
10, power busses 26, ground conductor strips 28, and apertures 30 are all 
coated with an insulating finish in the area where electrical contact is 
not desired. 
FIG. 2 is a cross-sectional side view of the power bus 26. Portions 38 of 
the power bus 26 are used to contact the corresponding strips on the 
printed circuit boards. Printed circuit boards are attached to the cold 
plate 10 by means of spacers/connectors 36 mounted through apertures 34. 
Printed circuit boards may be attached on both sides of the cold plate 10. 
FIG. 3 is a cross-sectional side view of a dovetail socket connector 40 
mounted on an edge of the cold plate 10. FIG. 4 is a front view of the 
dovetail socket connector 40 of FIG. 3. In the preferred embodiment, 
electrically discontinuous areas 52, 54, 56, and 58 along the length of 
the dovetail socket 40 make electrical contact with the respective power 
and ground contacts 26 and 28. The dovetail socket 40 then makes contact 
with connector 42, which also has electrical discontinuities along its 
length. Grooves 44 and 46 are cut in opposing faces of the dovetail socket 
connector 40. The grooves 44 and 46 are transverse to the direction of 
insertion of a connector 42. Conductor strips 48 and 50 are mounted in 
these grooves 44 and 46, respectively, and contact power busses (not 
shown) or ground conductors (not shown) on either side of the connector 
42. Thus, the arrangement results in a low-insertion-force power and 
ground plug system. 
Those skilled in the art will recognize that an alternative embodiment 
could use the cold plate 10 as the connector 42 with the dovetail socket 
connector 40 mounted on another element. In such an alternative 
embodiment, the power busses 26 and ground conductor strips 28 in the cold 
plate 10 would make electrical contact with the conductor strips 48 and 50 
when the cold plate 10 was inserted into the dovetail socket connector 40. 
FIG. 5 is a top view of a printed circuit board 60 used in the preferred 
embodiment, also referred to as a quarter-board because it covers 
one-quarter of the surface area of the cold plate 10. Printed circuit 
boards 60 are symmetrical with regard to the cold plate 10, and the power 
busses 26 and ground conductor strips 28 thereof, and may be rotated 180 
degrees on the cold plate 10 and still make the correct electrical contact 
with the power busses 26 and ground conductor strips 28. The printed 
circuit board 60 has strips 68, 70, and 72 that contact the power busses 
26 and ground conductor strips 28 on the cold plate 10 to complete the 
electrical circuits supplying power to the electrical devices mounted on 
the printed circuit board 60. FIG. 5 also shows the apertures 62 in the 
printed circuit board 60 where the thermal conductors are mounted. The 
apertures 62, and the surrounding area 64, may be plated-through for 
improved thermal conductivity. Surrounding the apertures 62 are electrical 
vias 66 for signal, power, and ground signals for the electronic device 
mounted over the aperture 62. 
FIG. 6 is cross-sectional side view of a thermal conductor pad 76 mounted 
in an aperture 62 of the printed circuit board 60. The thermal conductor 
pad 76 is pushed up through the aperture 62 until flush with the surface 
of the printed circuit board 60 or extending slightly therefrom. The 
thermal conductor pad 76 may be secured in the aperture 62 by means of the 
press fit or glue. Glue is deposited on the top surface 80 of the thermal 
conductor pad 76 to secure the electronic device 74 thereon and to provide 
a better thermal path. The electronic device 74 is first aligned and then 
pressed onto the top surface 80 of the thermal conductor pad 76, thereby 
securing the electronic device 74 to the thermal conductor pad 76. The 
glue is cured in a manner (e.g., with force applied to the electronic 
device 74) that limits its thickness to a minimum value. Wave soldering, 
or other means of attachment, further secures the electronic device 74 to 
the printed circuit board 60. A large nickel-plated surface area 78 of the 
thermal conductor pad 76 provides for enhanced contact with the cold plate 
10. A thermal grease or other thermally conductive material may be applied 
to the interface 82 to enhance the heat sink properties of the apparatus. 
Alternatively, the thermal conductor pad 76 may directly abut the cold 
plate 10. 
FIG. 7 is a top view of the thermal conductor pad 76. The thermal conductor 
pad 76 is generally rectangular in shape and comprised of a suitable 
thermally conductive material. The large nickel-plated surface area 78 
provides for enhanced thermal contact with the cold plate 10. Thus, the 
thermal conductor pad 76 provides an improved heat sink flow path from the 
electronic device 74 to the cold plate 10. 
As illustrated herein, the present invention provides improved thermal 
characteristics over prior art cold plates. Variations in the thickness of 
printed circuit boards do not affect heat dissipation performance. In 
addition, the thermal conductor pad provides a large nickel-plated surface 
area for contacting the cold plate. An interference fit ensures that the 
thermal interface between the thermal conductor pad and the cold plate is 
minimized. Alternatively, a thermal grease may fill the interface between 
the thermal conductor pad and the cold plate so that the thermal 
resistance is minimized. 
Manufacturing and assembly advantages are simplified using the present 
invention. The cost of creating custom bump patterns is eliminated by 
manufacturing the cold plates with smooth generic surfaces. Thus, generic 
cold plates can be fitted to any number of differently configured printed 
circuit boards. In addition, careful alignment of the printed circuit 
boards on the cold plate is no longer necessary. 
Because the thermal conductor pad is removable from the cold plate, the 
present invention also provides for simpler inspection and repair. Printed 
circuit boards can be easily removed from the cold plate assembly, in 
contrast to prior art cold plates with bump patterns thereon where the 
devices mounted onto the printed circuit boards are often glued to the 
thermal bumps which are an integral part of the cold plate to ensure 
proper thermal characteristics. 
The present invention also provides a significantly improved method for 
attaching power and ground connections to the printed circuit boards via 
the cold plate. 
Although a preferred embodiment has been illustrated and described for the 
present invention, it will be appreciated by those of ordinary skill in 
the art that any apparatus which is calculated to achieve the same purpose 
may be substituted for the specific configuration shown. This application 
is intended to cover any adaptations or variations of the present 
invention. Therefore, it is manifestly intended that this invention be 
limited only by the claims and the equivalents thereof.