Multi-deck power converter module

A multi-deck power converter module assembly for connection with a substrate (e.g., a host board) having connection regions disposed on its surface includes a second circuit board positioned over a first circuit board, the second circuit board having apertures extending from an upper surface to a lower surface of the second circuit board. At least two rail members are positioned over the second circuit board, each rail member having a first and a second plurality of holes. A pair of spacers are disposed between the first and second circuit boards, each spacer extending through one of the apertures of the second circuit board and received within one of the first plurality of holes of one of the rail members. Terminal pins are attached to the first circuit board, at least one terminal pin extending through the second circuit board and a corresponding one of the second plurality of holes for connection to one of the connection regions on the substrate. Each of the second plurality of holes is sized to allow the rail members to be slidably positioned over the terminal pins during assembly of the power converter module.

BACKGROUND OF THE INVENTION 
This invention relates to power converter modules, particularly multi-deck 
power converter modules. 
In computer, data communication and telecommunication applications, power 
converters (e.g., DC-DC converters) are provided in modular form and 
designed to be mounted on a host board (e.g., motherboard) to provide 
power for other circuits on the host board. Recently, greater attention 
has been directed toward reducing the size while maintaining energy 
efficiency and performance of the power converter so that the overall size 
of the host board can be reduced or the complexity of the host board can 
be increased. 
One approach for decreasing the size of modular power converters is to use 
a multi-deck approach in which two or more circuit boards are physically 
stacked one above the other and electrically interconnected to each other. 
In a multi-deck arrangement, one board is positioned above another board 
with the upper board having terminal pins which mount to the lower board. 
The multi-deck arrangement is particularly advantageous in applications in 
which the height of the power module can be sacrificed for layout area on 
the host board. In addition, multi-decked arrangements offer the advantage 
of allowing electronic components to be mounted to both sides of the upper 
board of the modular power converter. 
SUMMARY OF THE INVENTION 
This invention provides a multi-deck power converter module including rail 
members which mechanically support the terminal pins used to electrically 
interconnect the individual boards of the module to each other, as well as 
to the circuit board to which the module is mounted. The rail members are 
part of an open-frame arrangement which provides the electronic components 
of the power converter improved access to cooling air (e.g., provided by a 
circulating fan), thereby providing a cooler running module. 
In general, the invention features, a multi-deck power converter module 
assembly for connection with a substrate (e.g., a host board) having 
connection regions disposed on its surface. The power converter includes a 
first circuit board and a second circuit board positioned over the first 
circuit board. The second circuit board has apertures extending from an 
upper surface to a lower surface. At least two rail members are positioned 
over the second circuit board, each rail member having a first and a 
second plurality of holes. A pair of spacers are disposed between the 
first and second circuit boards, each spacer extending through one of the 
apertures of the second circuit board and received within one of the first 
plurality of holes of one of the rail members. Terminal pins are attached 
to the first circuit board, at least one terminal pin extending through 
the second circuit board and a corresponding one of the second plurality 
of holes of the rail members for connection to one of the connection 
regions on the substrate. Each of the second plurality of holes is sized 
to allow the rail members to be slidably positioned over the terminal pins 
during assembly of the power converter module. 
The invention utilizes rail members to mechanically support the terminal 
pins before, during and after mounting to a host board. Thus, solder 
joints at the electrical interconnections between the boards of the power 
converter are not necessary for mechanical support. Mechanical support for 
the terminal pins is particularly important when the module is being 
soldered to a host board or other wiring substrate. Without support for 
the terminal pins during this soldering operation, the terminal pins can 
come loose and separate from the individual boards (particularly, the 
board furthest from the heat sink) of the module. 
The ability to attach and remove the rail members from the spacers of the 
power converter module provides another important advantage. The 
manufacturer is able to keep an available inventory of assembled 
multi-deck power converter modules without rail members. The inventory can 
be used to supply open-frame power converter modules by sliding the rail 
members over the terminal pins. Alternatively, the inventory can be used 
as well to supply power converter modules potted and encased within a 
housing or cover member. 
Embodiments of the invention may include one or more of the following 
features. 
Each of the rail members includes standoffs which, contact and space the 
module from the substrate when the module assembly is mounted to the 
substrate. The standoffs ensure adequate spacing for the components 
mounted on opposing surfaces of the boards of the power converter and 
establish the length of the terminal pins extending from the converter. 
The standoffs also precisely control the height of the module with respect 
to the substrate. Precise height control is particularly important, for 
example, in applications in which a single large heat sink (i.e., "cold 
plates") is positioned over a number of electronic parts mounted on the 
substrate. In such applications, the top surfaces of each of the 
electronic parts must be substantially the same height to ensure proper 
contact with the heat sink. 
Each of the rail members includes an opening to allow increased air flow to 
circuit boards, thereby reducing the operating temperature of the power 
converter module. Each of the spacers have shoulders for accurate 
positioning of the circuit boards with respect to each other. The upper 
end of each spacer is knurled to capture the rail member. The first 
circuit board includes a heat sink attached thereto. The first and second 
circuit boards are electrically interconnected. The multi-deck power 
converter module assembly is a DC-DC converter. 
Other features and advantages of the invention will become apparent from 
the following description of the preferred embodiments and from the claims 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, a power converter module 10 includes a pair of 
printed circuit boards (PCBs), the first being a power board 12, the other 
being a control board 14, each having a number of electronic components 
16, 17 soldered thereto. During assembly, control board 14 is positioned 
over power board 12 to provide a multi-deck arrangement. In operation, 
power converter module 10 is mounted to a host board 5 (FIG. 4) which 
receives the module so that control board 14 is adjacent host board 5. As 
shown in FIG. 4, with power converter module 10 in its mounted position, 
surface 13 of power board 12 is exposed to receive, for example, a finned 
heat sink. 
Power board 12 is formed of an aluminum substrate 18 having a thickness of 
about 0.062 inches over which a thin insulative layer (not shown) is 
deposited. A conductive metal pattern (not shown) is laid out over the 
insulative layer to interconnect components 16 (e.g., resistors, 
capacitors, etc.). Components 16 may also include a planar transformer 17, 
such as those described in co-pending application, Ser. No. 08/693,878, 
assigned to the assignee of this application, and incorporated herein by 
reference. Components 16 which are mounted to power board 12 are 
associated with the power handling and generating circuitry for power 
converter module assembly 10 and, therefore, generate a relatively large 
amount of heat. Aluminum substrate 18 serves as a heat sink for 
dissipating heat generated by the circuitry mounted on power board 12. 
Input/output (I/O) terminals 32 are soldered to power board 12 and extend 
through plated-thru holes 34 in control board 14. 
Control board 14 is formed of an insulating substrate 22 (e.g., glass epoxy 
laminate) having a thickness of about 0.032 inches. Control board 14 
includes a conductive metal pattern (not shown) for interconnecting 
components 16 mounted to the control board and associated with the control 
circuitry and, therefore, generate much lower level signals as compared to 
power board 12. Pin terminals 24, soldered to control board 14, 
interconnect power converter module 10 to host board 5. For reasons which 
are discussed below, control board 14 is slightly smaller than power board 
12. 
Power converter module assembly 10 also includes spacers 26 which are 
secured within holes 28 at the four corners of power board 12 and extend 
through holes 30 of control circuit 14. Spacers 26, formed here of 
stainless steel, are used to maintain a preselected spacing between power 
board 12 and control board 14 and the length of terminal pins 24, 32 
extending from module assembly 10. Spacers 26 have a body 27 and ends 29a, 
29b which have a diameter less than that of body 27, thereby providing 
shoulders 31 at each end of body 27. End 29a is knurled to facilitate a 
tight fit within a corresponding hole 28 of power board 12. End 29b is 
also knurled for reasons discussed below. In the illustrated embodiment, 
spacers 26, when mounted within holes 28, extend upwardly about 400 mils 
from the surface of power board 12. Spacers 26 also include a threaded 
thru-hole 33 which can be used to secure a heat sink to surface 13 of 
power board 12 (FIG. 4). Alternatively, threaded thru-holes 33 can be used 
to secure module assembly 10 to host board 5. 
Referring to FIG. 2, power converter module 10 is shown with control board 
14 spaced from power board 12 using spacers 26 and with I/O terminals 32 
and terminals pins 24 extending through holes 30 of the control board. In 
this state of assembly, power converter module 10 is ready for operation. 
Referring to FIGS. 1 and 3, power converter module 10 further includes a 
pair of rail members 36 formed of molded thermoplastic. Each rail member 
36 has a pair of end walls 38 bridged by a sidewall 40 and a top wall 42. 
Top wall 42 includes a first set of holes 44 which are slidingly 
positioned over I/O terminals 32 and pin terminals 24. Each rail member 36 
also includes, at each end, a second set of holes 46, larger than holes 
44, each of which receives a knurled end 29b of spacer 26. Holes 46 are 
sized to provide a relatively tight fit between knurled ends 29b, thereby 
capturing and securing rail members 36 to module assembly 10. 
The first set of holes are sized to closely fit around and mechanically 
support I/O terminals 32 and terminal pins 24, while still allowing rail 
members 36 to be slidingly removed from the I/O terminals and pin 
terminals, respectively. 
As discussed above, control board 14 is sized to be slightly smaller than 
power board 12 so that when rail members are positioned over I/O terminals 
32 and pin terminals 24 rail members 36 rest on the upper surface of power 
board 12. 
As is shown in FIG. 3, sidewalls 40 include an opening 48 which extends a 
major portion of the length of the sidewall to allow air provided from, 
for example, a cooling fan to flow between power board 12 and control 
board 14. Molded around the periphery of each hole 46 are standoffs 50 
which extend above the surface of top wall 42 and precisely control the 
height of power converter module when it is mounted to the host board. 
Other embodiments are within the claims. For example, the embodiment 
discussed above included a power circuit board 12 and a control circuit 
board 14; however, the invention is applicable to power converter module 
assemblies having multi-deck arrangements with more than two circuit 
boards. 
It should also be appreciated that a relatively thin sheet, formed of an 
insulative material, could be positioned to lie over components of control 
board 14 prior to mounting rail members 36 to provide a surface upon which 
labelling information (e.g., pin identification and their voltages,, 
manufacturer, etc.). The thin sheet would include holes sized to fit over 
spacers 26 as well cutouts through which the terminal pins extend. Spacers 
26 may be lengthened slightly to account for the thickness of the 
insulative sheet.