Method and apparatus for providing novel hybrid circuit assembly carrier bracket

An apparatus and method (200) for providing a hybrid circuit assembly carrier bracket are included wherein the bracket is constructed and arranged to provide controlled placement of at least a first power transistor (124, 126) and to provide a highly efficient thermal transfer and dissipating arrangement. The bracket is constructed and arranged to provide for placement of at least a first substrate for a hybrid circuit assembly thereon, and includes at least a first power transistor aperture (120, 122) with at least two bracket projections (146, 148) for permitting placement of said transistor on plural electrical contacts (104, 106). The heat generated by components on the circuit board(s) is transferred and dissipated substantially by biasing at least one bracket projection member resiliently against a heat sink (108, 110, 112, 114, 116, 118).

FIELD OF THE INVENTION 
The present invention relates generally to hybrid circuit assembly brackets 
and more particularly, to thermally dissipative hybrid circuit assembly 
brackets. 
BACKGROUND 
Certain problems are typically associated with design and assembly of 
brackets for hybrid circuits that use power transistors which are solder 
reflowed to common substrates. Many of these assemblies generate a 
considerable amount of power, and thus require brackets that have good 
heat sinking characteristics. Power transistors are typically placed in a 
depression on a bracket such that side transistor leads are located at a 
desired height for allowing solder reflow of said leads to selected hybrid 
circuits. Thus, correct placement of the power transistors generally 
requires that a height from a bottom of a transistor lead to a bottom of a 
transistor flange be within a very close degree of precision of a selected 
measurement in order to assure satisfactory electrical connection of the 
power transistor upon solder reflow to a substrate. Milling of a bottom of 
the transistor flange is costly and somewhat unreliable. 
It is also desirable to reduce assembly fixtures required for electrical 
attachment of the power transistors, thus providing a more easily 
assembled and more maintenance free assembly. 
There is a need for an efficient thermally dissipative carrier bracket for 
a hybrid circuit assembly that also minimizes power transistor assembly 
fixtures. 
SUMMARY OF THE INVENTION 
A carrier bracket for at least a first substrate for a first hybrid circuit 
assembly having transistor contact areas and at least a first power 
transistor that has at least a bottom flange and a plurality of leads and 
a method for providing the bracket are set forth. The bracket comprises a 
support unit for supporting and positioning at least a first substrate for 
a hybrid circuit assembly, and at least a first heat sink derived from the 
support unit. The support unit includes at least a first aperture for 
guiding placement of the bottom flange of the transistor such that the 
transistor occupies the aperture, thus providing heat sinking capability 
and permitting suspension of the transistor from, and solderable 
connection to, transistor contact areas of the assembly utilizing the 
transistor leads.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1, numeral 100, is a front, top, and right perspective view of an 
exemplary embodiment of a carrier bracket for at least a first substrate 
for a first hybrid circuit assembly in accordance with the present 
invention, constructed and arranged to provide efficient thermal 
dissipation and to minimize power transistor assembly fixtures. The 
carrier bracket is utilized to support at least a first substrate (103, 
105) for a first hybrid circuit assembly having transistor contact areas 
(104, 106) and at least a first power transistor (124, 126) that has at 
least a bottom flange (128, 130) and a plurality of leads (132, 134, 136, 
138). The bracket comprises a support unit (102) for supporting and 
positioning at least a first hybrid circuit assembly and has at least a 
first heat sink (108, 110, 112, 114, 116, 118), described in more detail 
below, derived from the support unit. 
The support unit (102) includes at least a first aperture (120, 122) for 
guiding placement of the bottom flange (128, 130) of the transistor such 
that the transistor (124, 126) occupies the aperture (120, 122). Heat 
sinking capability is provided in that the bottom flange (128, 130) of the 
transistor is permitted to extend below the support unit (102), permitting 
contact with a selected heat sink. That is, where selected, the transistor 
(124, 126) is allowed to directly rest on a heat sink below the support 
unit. Use of the aperture (120, 122) to position the transistor permits 
suspension of the transistor (124, 126) from, and solderable connection 
to, transistor contact areas (104, 106) of the assembly utilizing the 
transistor leads (132, 134, 136, 138). 
The support unit (102) comprises a substantially planar conductive sheet 
having further apertures in an open configuration. The open configuration 
permits formation of a plurality of heat sinks (108, 110, 112, 114, 116, 
118) from the support unit (102), each heat sink being formed by placing 
sets of at least two apertures, typically narrow linear apertures in 
proximity such that said apertures enclose all but a minimal portion of a 
selected area of the supporting unit (102), leaving narrow portions of the 
supporting unit (102) connecting the enclosed area, the heat sink (108, 
110, 112, 114, 116, 118). Thus, the heat sinks are similar to islands 
derived from the substrate unit (102) that are connected to the substrate 
unit by at least a first peninsula (narrow portion of the substrate). 
Further, each heat sink (108, 110, 112, 114, 116, 118) may be adapted, 
typically by bending to form heat transfer tabs that extend into a plane 
below that of the planar conductive sheet for facilitating thermal 
dissipation. Thus, heat from the substrate is transferred to the bracket 
heat sinks (at location Xs), and then to the heat transfer tabs of the 
heat sinks (at location Ys), providing stress relief to selected areas (at 
location Xs) of the heat sinks. Soldering the substrate to the stress 
relieved areas (at location Xs) allows for thermal expansion and 
contraction, minimizing stress on those solder joints. Thus, adaption of 
the heat sinks comprises substantially utilizing a first portion (at 
location Xs) of each heat sink in the plane of the conductive sheet to 
provide thermal contact with the substrate and, where selected, to provide 
a stress-relieved position for establishing a substrate-heat sink solder 
joint. Further, a second portion (at location Ys) of each heat sink, 
wherein each second portion extends into a plane below that of the planar 
conductive sheet, for at least facilitating heat transfer away from the 
first portion (at location Xs). 
The planar conductive sheet is selected from a material selected from the 
group consisting of metals, and is typically copper. 
The planar conductive sheet further includes at least a first substrate 
stop (140) for securing placement of at least the first hybrid circuit 
assembly. A substrate stop is a projection that allows placement of a 
hybrid circuit assembly on the planar conductive sheet such that said 
assembly tends to remain in a particular location. The at least first 
substrate stop is typically one of: press-formed from the planar 
conductive sheet, formed by bending the planar conductive sheet, and 
shaped by an aperture in the planar conductive sheet and is positioned by 
providing a bend at the base of the substrate stop such that the stop 
projects above the plane of the planar conductive sheet. 
The bracket may be selected to provide for positioning of further devices. 
Thus, typically, where at least two substrate stops are formed 
substantially on opposing sides of the planar conductive sheet by bending 
the planar conductive sheet, the bent portions of the planar conductive 
sheet are further shaped to form snap-in clamps (142, 144). Such snap-in 
clamps typically are formed by three bends, giving a v shaped notch 
appearance. 
Guidance is provided for placement of the transistor (124, 126) where the 
at least first aperture (120, 122) for guiding placement of the bottom 
flange (128, 130) of the transistor is shaped to provide at least two 
projections (146, 148) from the bracket. Where selected, to provide 
further control of placement of the transistor, at least two projections 
are bent into a plane different from that of the planar conductive sheet 
as transistor guides. 
FIG. 2, numeral 200, illustrates steps for a method for forming a carrier 
bracket for at least a first substrate for a first hybrid circuit assembly 
having transistor contact areas and at least a first power transistor that 
has at least a bottom flange and a plurality of leads in accordance with 
the present invention. The method comprises the steps of: providing a 
substantially planar conductive support sheet (typically a copper 
sheet)(202), providing at least a first heat sink derived from the support 
sheet (204), positioning at least a first hybrid circuit assembly thereon 
(206), and providing at least a first transistor positioning aperture 
(208) for guiding placement of the bottom flange of the transistor such 
that the transistor occupies the aperture, provides heat sinking 
capability and permits suspension of the transistor from, and solderable 
connection to, transistor contact areas of the assembly utilizing the 
transistor leads. 
The method may be further selected to including the step of providing 
apertures in the substantially planar conductive in an open configuration 
that permit formation of a plurality of heat sinks from the metal sheet 
such that: 
each heat sink is attached to the sheet by at least a first portion of the 
sheet, and 
each heat sink may be adapted to extend into a plane below that of the 
sheet for facilitating thermal dissipation. 
The method may be further selected to include the step of providing at 
least a first substrate stop for securing placement of at least the first 
hybrid circuit assembly, described more fully above. 
Also, the method may be further selected to include the step of shaping the 
at least first aperture for guiding placement of the bottom flange of the 
transistor to provide at least two projections from the bracket, described 
more fully above. 
Although a description of an embodiment of the present invention has been 
described and shown in the drawings, the scope of the invention is defined 
by the claims which follow.