Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-08-21
2003-04-15
Chervinsky, Boris (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S707000, C361S713000, C361S719000, C174S050510, C165S080300, C165S185000
Reexamination Certificate
active
06549409
ABSTRACT:
BACKGROUND
This invention relates to a power converter assembly.
A typical DC-to-DC power converter assembly, for example, includes power-dissipating semiconductor components, such as transistors, SCRs, and rectifiers, magnetic energy storage elements, such as transformers and output filter inductors that have magnetic cores surrounded by one or more windings and electric energy storage elements, such as input and output filter capacitors.
A DC-DC power converter is often packaged in a rectangular “brick” format, as shown in FIG.
1
. Heat dissipated by components within the converter
100
is withdrawn through a metal surface
102
, referred to as a baseplate. Electrical connections to the converter are made through pins
104
.
In one known kind of power converter assembly, as shown in
FIG. 2
, the baseplate
103
includes a metal plate
102
bonded to an insulating layer
106
. Components on the top surface
108
of the insulating layer
106
, such as transformer
110
and resistor
112
, are interconnected by conductive traces
113
on surface
108
. Power dissipating components (e.g., a power semiconductor
114
) are mounted directly on the top surface of the insulating medium so that dissipated heat is removed through the baseplate. A printed circuit board assembly
116
, which also has conductive traces
117
that interconnect control electronics and other components (e.g., an integrated circuit
118
), is mounted above the baseplate
103
on standoffs
119
. Electrical connections between the printed circuit board assembly
116
and components and traces on the top surface of the baseplate
103
are made through pins
120
and component leads (e.g., a lead
122
of power semiconductor
114
). (As used herein the terms “component” and “circuit element” refer to electronic or energy storage components (e.g., semiconductors, resistors, capacitors and magnetic devices) and excludes interconnection devices (e.g, termination pins, connectors) and packaging and assembly elements (e.g., standoffs, cases).)
Another known kind of power converter assembly, shown in
FIG. 3A
, also has a baseplate assembly
124
and a printed circuit board assembly
126
. Power dissipating devices
128
are mounted on the baseplate assembly. The printed circuit board assembly includes components, such as a transformer
130
and an output inductor
132
, mounted on a printed circuit board
127
. A non-conductive case
129
attaches to the baseplate
124
, enclosing the printed circuit board assembly
126
. The power converter assembly
100
is filled with an encapsulating material (not shown).
As shown in
FIG. 3B
, and described in U.S. Pat. No. 5,722,508, “Packaging Electrical Circuits” (assigned to the same assignee as this application and incorporated by reference), the baseplate assembly
124
may include a metal heat-spreading plate
142
separated from the metal plate
102
by an insulating sheet
144
. Power dissipating components
128
include a semiconductor die
134
mounted on and connected to conductive pads
136
on the surface of an insulating substrate
138
. The substrate
138
is connected to the heat spreading plate
142
by solder
140
. Conductive traces
146
on the printed circuit board
127
connect to conductive pads
136
on the power-dissipating device
128
through solder
148
.
In a third known kind of power converter assembly, shown in
FIGS. 4A and 4B
, a printed circuit board assembly
150
includes components
160
a
,
160
b
mounted on both sides of a printed circuit board
152
. A “printed circuit transformer” on the circuit board assembly includes a magnetic core
154
, which passes through holes
156
a
,
156
b
in the printed circuit board. Windings (not shown), formed by conductive etches on the surfaces of one or more layers of the printed circuit board, surround the holes
156
a
,
156
b
and the core. The distances by which the core
154
extends above and below the printed circuit board
152
are approximately equal. Power dissipating semiconductors
158
, and other components of various heights
160
b
, are mounted on the side of the printed circuit board which faces an inside surface
162
of a metal case
164
. An encapsulant
166
fills the space between the printed circuit board assembly
150
and the metal case. Heat from the power dissipating components
158
passes through the encapsulant
166
and into the metal case
164
.
SUMMARY
In general, in one aspect the invention features a power converter assembly comprising a heat sinking plate, a circuit board structure having a side that faces and is spaced by a gap from a surface of the heat sinking plate that is nearer to said side, a dissipative semiconductor component mounted on said side, and an encapsulating material filling the gap, the gap being characterized by an average thermal-resistance of less than 3° C.−in
2
/Watt.
Implementations of the invention may include one or more of the following features. The heat sinking plate may be planar. The circuit board structure may include a planar circuit board that holds power conversion elements of a power converter circuit. The power conversion elements may include a transformer having cores and in which no portion of any of the cores lies in the gap. The power conversion elements include the semiconductor component. The semiconductor component may include a MOSFET or a diode. The average thermal resistance may be less than 2° C.−in
2
/Watt. The average thermal resistance may be less than 1° C.−in
2
/Watt.
In general, in another aspect of the invention, components on the circuit board structure together comprise a power conversion circuit that is capable of accepting power from a source and delivering power to a load, the components including a semiconductor component mounted on the side of the circuit board that faces the surface of the heat sinking plate. The circuit board divides the total volume occupied by the assembly into a gap volume between the circuit board and the plate, and a remaining volume, the gap volume being no more than 25% of the total volume.
Implementations of the invention may include one or more of the following features. The power conversion elements may include a transformer having cores and in which no portion of any of the cores lies in the gap. The gap volume may be no more than 15% of the total volume, preferably no more than 10% of the total volume.
In general, in another aspect of the invention, the gap has a gap volume that is enclosed by (a) the surface of the heat sinking plate, (b) the side of the circuit board that faces the surface of the heat sinking plate, and (c) a perimeter surface that connects the perimeters of (a) and (b) and which extends perpendicular to, and upward from, the surface of said heat sinking plate. The upper volume is enclosed by (a) the surface of the heat sinking plate, (b) an imaginary plane that is parallel to and spaced above the side of the circuit board which does not face the surface of the heat sinking plate, the plane being tangent to the top of a component without intersecting any other component, and (c) the perimeter surface. The gap volume is no more than 25% of the upper volume.
In general, in another aspect of the invention, no part of the permeable core of a magnetic power conversion component faces the side of the circuit board that faces the surface of the heat sinking plate.
Among the advantages of the invention are that internal temperature rises of components within a power converter may be kept small while the circuit board and baseplate of a power converter can be fabricated less expensively, more easily, and with higher yield than when heat-dissipating devices are mounted directly on the baseplate before the baseplate is attached to the circuit board assembly. A larger number of small power dissipating semiconductor devices can be used because the assembly technique is relatively forgiving and yield losses are still within acceptable levels. This permits placing the switching devices in locations on the board that are closer to the portions of the
Evans Michael D.
Saxelby, Jr. John R.
Vinciarelli Patrizio
Chervinsky Boris
Fish & Richardson P.C.
VLT Corporation
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