Electronic module housing and assembly with integral heatsink

An electronic module housing (30) with an integral heatsink (32) is provided as part of an electronic module assembly (31). The heatsink (32) has a general U-shape formed by a pair of opposing sidewalls (33, 34) rising upward from a central intermediate portion (37) having a planar surface (38) for mounting a module substrate thereon. Plastic housing material is molded about the heatsink so as to form an interior module receiving cavity (50). The cavity is generally defined by the heatsink sidewalls (33, 34) and a pair of molded plastic opposing sidewalls (55, 56) provided between the heatsink sidewalls. Preferably heat conductive mounting ear portions (40, 41) extend from ends (43, 44) of the heatsink sidewalls and permit thermally mounting the housing to another heatsinking structure. Preferably molded interior plastic sidewalls (57, 58) separate the heatsink sidewalls (33, 34) from the cavity (50). The preferred housing and assembly configuration has reduced size and weight and provides sufficient mechanical protection and increased thermal power dissipation for a module (39 ) in the cavity.

FIELD OF THE INVENTION 
The present invention relates to the field of electronic module housings 
and assemblies which include such housings. More specifically, the present 
invention relates the field of such housings and assemblies which include 
heatsinks. 
BACKGROUND OF THE INVENTION 
Housings have been provided with an interior cavity for receiving an 
electronic module wherein the housing provides mechanical protection for 
the module. Such housings may also protect the module from environmental 
contaminants by partially or substantially totally sealing the module 
within an interior housing cavity. If the module must dissipate a 
substantial amount of power, the housing may also have to provide a 
heatsink function or at least permit the module in the housing to be 
connected to a heatsink. Some prior housings have combined the protection 
and heatsink requirements by essentially constructing the housing in the 
form of a metal box configuration having one open side to permit mounting 
the module within the formed metal box. 
A combined metal box housing and heatsink configuration, such as noted 
above, generally results in the housing have a substantial weight which 
may be undesirable in many applications. In addition, such a configuration 
also presents potential problems in providing external electrical access 
to the module contained within the housing while also sealing the module 
against external environmental containments. Also, when providing an all 
metal box type housing structure, care must be taken to avoid undesired 
electrical shorting of the module within the housing to the metal box 
sidewalls of the housing unless the metal box is made substantially larger 
than the electronic module. Increasing housing size to avoid this 
potential problem is undesirable since this will increase both the size 
and weight of the housing. 
A prior art combined housing and heatsink configuration has been suggested 
which involves providing a heatsink block having convective cooling fins 
and then molding around a portion of this heatsink block four plastic 
sidewalls to define an interior module receiving cavity. This suggested 
structure is shown in FIGS. 1 and 2 of the present application. This prior 
structure provides a pair of plastic molded mounting ears having holes 
therethrough to provide for mounting the combined housing and heatsink 
structure. With regard to the combined housing and heatsink shown in FIGS. 
1 and 2, while this structure substantially reduces the total weight of 
the housing which would be required for an all metal box type structure, 
the amount of heatsink capacity provided by this structure has been found 
to be somewhat limited since convective cooling fins provided as part of 
the heatsink block can provide only a limited amount of cooling for a 
module mounted within the housing. Also, it is necessary to accurately 
control the mounting torque when installing this type of housing to 
prevent cracking the plastic mounting ears of such a housing. 
What is needed is an improved housing having heatsink capability which 
overcomes the above mentioned disadvantages of the prior housings. 
SUMMARY OF THE INVENTION 
An electronic module housing having an integral heatsink is provided. The 
housing includes: a heatsink having a general U-shape configuration formed 
by a pair of upstanding opposing sidewalls rising upward from opposite 
ends of a central intermediate portion, the central intermediate portion 
having a planar surface suitable for mounting a substantially planar 
module substrate thereon; and plastic housing material molded about and 
contacting the heatsink and forming an interior module receiving cavity, 
the interior cavity having an open side and generally defined by the pair 
of upstanding opposing heatsink sidewalls, the central intermediate 
portion of the heatsink and a pair of molded plastic opposing sidewalls 
provided between and extending between the pair of heatsink sidewalls. By 
providing the electronic module housing as described above, the heatsink 
provides a planar surface for mounting a module substrate thereto while 
the heatsink sidewalls can conduct heat away from the substrate and the 
heatsink and plastic sidewalls provide protection for components in the 
interior cavity. 
The preferred embodiment of the present invention contemplates the heatsink 
sidewalls each having a heat conductive ear portion with a hole 
therethrough to allow mounting the housing to an additional heat 
conductive component and thereby conducting heat away from the central 
intermediate portion to which a module substrate may be mounted. Since 
these mounting ears are part of the heatsink and are therefore preferably 
formed of heat conducting metal, this avoids cracking the mounting ears 
when mounting the housing to another structure. Preferably heatsink 
convective cooling fins are also provided to enable the heatsink to 
dissipate heat by both convection and conduction. In addition, interior 
molded plastic sidewalls are provided on the heatsink sidewalls and 
separate them from the interior cavity thus avoiding potential electrical 
shorts from the module to the heatsink sidewalls. 
The above noted features result in providing a compact and inexpensive 
single component electronic module housing having an integral heatsink. 
The configuration of the present preferred embodiment minimizes the size 
of the housing while providing extensive heatsink capacity and avoiding 
the above discussed disadvantages of prior housings having an integral 
heatsink. Preferably, an assembly using such a housing is provided wherein 
an electronic circuit module is provided within the heatsink interior 
cavity. A substrate of the circuit module is planarly and thermally 
conductively mounted to the planar surface provided on the heatsink 
central intermediate portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, the configuration of a prior electronic module 
housing and assembly is illustrated wherein the present invention 
represents an improvement over this configuration. FIG. 1 illustrates an 
aluminum heatsink block 10 having a plurality of convective cooling fins 
11 provided on a bottom surface of the block 10. A planar surface 12 is 
provided on which a substrate of an electronic circuit module 13 (shown in 
FIG. 2) will be thermally conductively mounted. A peripheral recess groove 
14 is provided as part of the heatsink block 10 and an additional planar 
surface 15 is provided which is parallel to and somewhat lower than the 
planar surface 12. FIG. 1 also illustrates a plastic molded connector pin 
subassembly 16 having a main plastic body 17 and a plurality of connector 
pins 18 projecting through the plastic body 17. The plastic body 17 is 
intended for mounting on the planar surface 15 such that portions of the 
connector pins 18 will be positioned above or in contact with conductor 
pads provided on a ceramic substrate 19 that forms the base substrate for 
the electronic circuit module 13. 
The heatsink block 10 and subassembly 16 shown in FIG. 1 are mated to each 
other and then a plastic over molding process is performed so as to form 
an electronic module housing 20 shown in FIG. 2. The housing 20 forms part 
of an electronic module assembly 21 shown in FIG. 2. The housing 20 
comprises four molded plastic sidewalls 22 which are formed about the 
heatsink block 10. The peripheral groove 14 provides a recess to ensure 
attachment of the sidewalls 22 to the heatsink block 10. The four plastic 
sidewalls 22, together with the surfaces 12 and 15 of the heatsink block, 
form five sides of an interior cavity 23 in which the circuit module 13 is 
provided and into which portions of the pins 18 extend. A pair of plastic 
mounting ears 24 extend from an opposing pair of the sidewalls 22 to 
permit mounting the assembly 21 to another structure. A plastic connector 
pin shroud 25 is also formed during the molding process to protect ends of 
the pins 18 that are external to the cavity 23. Electrical bonding wires 
are provided between portions of the pins 18 within the cavity and 
conductor pads on the substrate 19. While no cover is shown in FIG. 2, 
preferably the assembly 21 will have a cover to close the interior cavity 
23. 
The prior art assembly and housing shown in FIGS. 1 and 2 has the advantage 
of minimizing the weight of the protective housing for the circuit module 
13 while providing some heatsink capability for the module. However, when 
such a configuration is utilized for a high power circuit module, such as 
a solid state relay, due to the limited amount of heatsinking capability 
provided by the heatsink 10, only a limited maximum current capability is 
provided for the module. Many times a larger maximum current capability is 
required, but substantially increasing the size of housing is not 
desirable. Also, providing plastic mounting ears for the assembly and 
housing of FIG. 2 requires careful process control to avoid cracking the 
plastic mounting ears during mounting the assembly to another structure 
due to the use of excessive torque in screwing the mounting ears to 
another structure. 
FIGS. 3 and 4 illustrate the configuration of an improved electronic module 
housing 30 and an improved electronic module assembly 31 which uses the 
housing 30. Referring to FIG. 3, a heatsink 32 is illustrated as having a 
general U-shape configuration formed by a pair of upstanding opposing 
sidewalls 33 and 34 which rise upward from opposite ends 35 and 36, 
respectively, of a central intermediate portion 37 of the heatsink. The 
central intermediate portion 37 has a planar surface 38 suitable for 
mounting a substantially planar ceramic module substrate 39 (shown in FIG. 
4) thereon. Each of the sidewalls 33 and 34 have an associated heat 
conductive ear portion 40 and 41, respectively, extending from the 
sidewall parallel to the central portion planar surface 38. Each of the 
ear portions 40 and 41 have at least one through hole 42 therein to permit 
thermal conductive mounting of the heatsink 32 to another heat conductive 
structure. Each of the ear portions 40 and 41 extend in opposite 
directions with respect to one another from ends 43 and 44 of the heatsink 
sidewalls 33 and 34, respectively. The ends 43 and 44 are opposite ends 45 
and 46, respectively, of the sidewalls 33 and 34, and ends 45 and 46 are 
positioned adjacent the central intermediate portion 37 of the heatsink 
32. 
Preferably, the entire heatsink 32 shown in FIG. 3 comprises a single 
unitary metal structure at least substantially formed from aluminum. 
Preferably, the central intermediate portion 37 of the heatsink 32 
includes external heatsink convective cooling fins 47 that are positioned 
between the upstanding heatsink sidewalls 33 and 34 and extend from a 
surface of the heatsink central intermediate portion 37 located below the 
heatsink planar surface 38. 
The heatsink 32 shown in FIG. 3 is preferably utilized as a component in 
the electronic module housing 30 shown in FIG. 4 wherein plastic housing 
material is overmolded about portions of the heatsink 32 to form the 
housing 30. During this molding process connector pins 48 are also 
overmolded such that they have end portions 49 which extend into an 
interior module receiving cavity 50 in which the planar module substrate 
39, and other components, of an electronic module 51 will be positioned. 
End portions 52 of the pins 48 are also provided within a plastic molded 
connector shroud 53 formed during the overmolding process wherein the end 
portions 52 are external to the interior cavity 50. This is accomplished 
in the following manner. 
Plastic housing material is molded about and contacts the heatsink 32 so as 
to form the interior module receiving cavity 50. This cavity has an open 
side 54 and is generally defined by the pair of upstanding opposing 
heatsink sidewalls 33 and 34 and a pair of molded plastic opposing 
sidewalls 55 and 56 provided between and extending between the pair of 
heatsink sidewalls 33 and 34. The heat conductive ear portions 40 and 41 
of the heatsink 32 extend away from the interior cavity 50 and the 
heatsink convective cooling fins 47 also extend from the central 
intermediate portion 37 away from the interior cavity 50. 
It is contemplated that the plastic sidewalls 55 and 56 and the plastic 
connector shroud 53 are all formed as part of the same plastic overmolding 
process. This process also includes forming interior plastic sidewalls 57 
and 58 which are provided on said heatsink sidewalls 33 and 34, 
respectively, and separate these heatsink sidewalls from the interior 
cavity 50. The resultant structure comprises a continuous sidewall plastic 
shell peripheral structure formed by the interior plastic sidewalls 57 and 
58 and the pair of opposing plastic sidewalls 55 and 56. These plastic 
sidewalls form the interior boundaries of the interior cavity 50 with the 
heatsink central intermediate portion 37 closing one open end of this 
sidewall plastic shell peripheral structure leaving the open side 54 
forming the other end of the peripheral structure. The use of the interior 
plastic sidewalls 57 and 58 aids in electrically insulating the circuit 
module 51 and connector pins 48 from the heatsink sidewalls 33 and 34 
while thermal conductivity to the sidewalls 33 and 34 is provided via the 
central intermediate portion 37 of the heatsink. This configuration also 
assists in minimizing thermal expansion mismatch stresses that may be set 
up between the plastic molding material and the heatsink. 
As shown in FIG. 4, the module substrate 39 of the module 51 is thermally 
conductively planarly mounted on the planar surface 38 of the heatsink. 
This occurs after the plastic overmolding process used to form the housing 
30. Bonding wires 59 connect conductor pads on the substrate 39 to the end 
portions 49 of the connector pins 48 that are provided within the cavity 
50. A removable cover 60 is illustrated in FIG. 4 above the cavity 50 
wherein this separate cover will contact at least the plastic molded 
sidewalls 55 and 56 and close the open side 54 of the cavity 50 thereby 
sealing the cavity against environmental contaminants. 
The above noted structure allows substantially greater heatsink capacity 
for the electronic module housing 30 and its resultant assembly 31. This 
is because heatsinking is now not only provided by the convective cooling 
fins 47, but also by the upstanding heatsink walls 33 and 34 and their 
potential heatsinking connection via the heatsink ears 40 and 41 to other 
heatsinking structure. Thus a combined convection cooling and thermal 
conduction effect has been provided which draws heat away from the ceramic 
substrate 39 of the electronic module 51 and provides substantial 
heatsinking capacity. This has been found to provide a substantial 
increase in the maximum current capability for a solid state relay used in 
the electronic module assembly 31 as contrasted with the assembly 21 shown 
in FIGS. 1 and 2. In addition, the providing of the interior plastic 
sidewalls 57 and 58 electrically insulates the heatsink sidewalls from 
components within the interior cavity 50 and thereby prevents accidental 
shorting of these components, and the pins 48, to the heatsink sidewalls. 
The providing of the heatsink as a U-shape configuration minimizes the 
total weight of the assembly since it has been found unnecessary to 
surround the internal cavity by four heat conducting heatsink sidewalls. 
Protection for the cavity 50 is accomplished by the pair of plastic 
sidewalls 55 and 56 in combination with the plastic sidewalls 57 and 58 
and the pair of heatsink sidewalls 33 and 34 together with the central 
intermediate portion 37 of the heatsink and the cover 60. 
It should be noted that overhanging lips or ridges 61 and 62 of the 
heatsink 32 are provided so as to ensure the gripping of the molded 
plastic to the heatsink 32. In addition, preferably molded plastic 
projections 63 are provided on the top side of the connector pins 48 with 
regard to some of the portions 49 of these pins that extend into the 
cavity 50. The bottom sides of these pins are already supported by molded 
plastic. This configuration helps rigidize the pins and prevents their 
movement during the making of electrical connections to the circuit module 
51 via the bonding wires 59. 
Also, because the mounting holes 42 are provided in heat conductive ear 
portions 40 and 41 of the heatsink 32, wherein the heatsink is preferably 
a metal structure, it is no longer necessary to be concerned about 
cracking the mounting ear portions due to excessive use of torque during 
the mounting process. The metal ear portions 40 and 41 can easily 
withstand substantial amounts of mounting torque unlike the plastic ear 
portions 24 shown in FIG. 2. In addition, preferably the housing 30 will 
not require the use of a molded pin subassembly such as subassembly 16 
since the plastic forming the housing 30 can be directly molded around the 
pins 48. 
While I have shown and described specific embodiments of this invention, 
further modifications and improvements will occur to those skilled in the 
art. All such modifications and improvements which retain the basic 
underlying principles disclosed and claimed herein are within the scope of 
this invention.