Molded Housing With Integral Heatsink

The present invention relates generally to the field of housings for electronic control modules, and in particular to heat-sinking structures of those housings.

Modern electronic control modules products are typically constructed using circuit components mounted to a substrate, often a printed circuit board. Some of these control modules are constructed using molded printed circuit boards. Molded printed circuit boards can be fabricated using what is commonly referred to as two-color plastic. In this type of structure the two plastics are sequentially molded into an appropriate shape to hold the circuit components. One of the two plastic materials can be plated with metal that, once soldered, acts to physically captivate and electrically connect the circuit components.

An attribute of the two-color plastic process is that it can be used to construct housings for enclosing the substrate described above. In fact, the substrate and the housing can be fabricated as one physical part, rather than two separate components. This type of structure is often referred to as a Molded Interconnect Device (MID).

An important performance requirement of control modules is to deliver significant amounts of energy. While delivering this energy heat is generated by certain of those circuit components, typically power transistors, as a byproduct of the inefficiency of those circuit components. Heat can significantly shorten the life of all of the circuit components of the control module and so a mechanism for conducting the heat away from those circuit components is required. Plastic is not an efficient conductor of heat.

Conventional approaches for conducting heat include heat-sink structures that are tightly thermally-coupled to the power transistors (and other heat generating components). These heat-sinks are positioned physically to isolate the generated heat from the non-heat-generating circuit components, and also to efficiently remove heat from the heat-generating components. Typically, heat-sinks are constructed of a metal material.

Manufacturing electronic control modules with metal heat-sinks is bothersome. For one, a separate component needs to be assembled to the control module. Managing the manufacture of the metal heat-sink, and guarantying an efficient thermal coupling during the life of the control module between the heat-generating circuit components and the metal heat-sink, is difficult at best.

Moreover, metal heat-sinks add undesirable mass to the control module, which in adverse vibration and shock environments such as in an automotive application, can significantly shorten the useful life of the control module because of physical failure of the coupling between the heat-generating circuit components and the metal heat-sink.

Additionally, for metal heat-sinks to be thermally efficient they are typically mounted between the heat-generating circuit components and an outside surface of the control module. This arrangement is difficult to seal against external contaminants--such as those found in an automotive environment.

Electrical isolation between various heat-generating circuit components is also important in many applications. Conventionally, either separate heat-sinks, or electrical isolation devices are use to effect this electrical isolation. Electrical isolation devices add to the thermal inefficiency of the structure.

What is needed is a simple, minimum component, with thermally efficient electrical isolation, and which offers an environmentally robust and reliable heat-sinking solution for control module packaging.

FIG. 1 is a cross-sectional view of a molded housing with an integral heat-sink, in accordance with a first embodiment of the invention; and

FIG. 2 is a cross-sectional view of a molded housing with an integral heat-sink, in accordance with a second embodiment of the invention.

A plastic housing assembly is constructed with a non-plateable plastic wall portion, and a plateable plastic wall portion positioned abutting the non-plateable plastic wall portion. The plateable plastic wall portion has a via disposed therethrough commencing at an outer surface and extending to an inner surface. A heat-generating component is coupled to the inner surface. The via, the inner surface of the plateable plastic wall portion, and the outer surface of the plateable plastic wall portion, are preferably plated with metal so that heat produced by the heat-generating component is conducted away from the inner surface plateable plastic wall portion to the outer surface of the plateable plastic wall portion. The invention can be better understood with reference to the drawings.

FIG. 1 is a cross-sectional view of a molded housing with an integral heat-sink, in accordance with a first embodiment of the invention. Essentially, this embodiment offers a thermally efficient and reliable heat-sinking solution for control module packaging by intermixing a plateable and non-plateable plastic in a housing configuration.

In FIG. 1, a first plastic wall portion 101 commences at a first outer surface 103, and extends to a first inner surface 105 oriented opposing the first outer surface 103. Both the first outer surface 103, and the first inner surface 105 are non-plateable. This non-plateable material can be made from many different plastics. Typically a thermoset material is used but other materials such as thermoplastic-type materials may also be used.

A second plastic wall portion 107 is positioned abutting 109 the first plastic wall portion 101. In practice, the first plastic wall portion 101 is injected into a mold first and soon thereafter the second plastic wall portion 107 is progressively injected or vice-versa. The second plastic wall portion 107 commences at a second outer surface 111 positioned proximal the first outer surface 103 of the first plastic wall portion 101, and extends to a second inner surface 113 positioned proximal the first inner surface 105 of the first plastic wall portion 101. Both the second outer surface 111 and the second inner surface 113 of the second plastic wall portion 107 are plateable. The second plastic wall portion 107 is typically made using a thermoset material, although a thermoplastic material may be used.

The mold used to hold the injected plastics includes a feature that creates a via 115 through the second plastic wall portion 107. This via 115 extends between the second outer surface 111 and the second inner surface 113. In a post injection process the via 115, second outer surface 111, and the second inner surface 113 are plated. Typically, this thermally-conductive material 117 is copper, but may be any other thermally conductive, and/or electrically conductive material.

A heat-generating component 119 is disposed coupled to the second inner surface 113. As shown in FIG. 1, the via 115 can be arranged in an array which more effectively conducts heat away from the heat-generating component 119. In a typical application the heat-generating component 119 is a power transistor, and the power transistor is coupled to the thermally-conductive material 117 of the second inner surface 113, with a solder connection 121.

Next, a second embodiment will be described including multiple heat-generating components that require electrical isolation.

FIG. 2 is a cross-sectional view of a molded housing with an integral heat-sink, in accordance with a second embodiment of the invention.

In this embodiment a plastic housing assembly is constructed using the first plastic wall portion 101 with a first section 101" commencing at the first outer surface 103, and extending to the first inner surface 105 oriented opposing the first outer surface 103 as in the first embodiment. The first plastic wall portion 101 also has a second section 101' commencing at the first outer surface 103, and extending to a third inner surface 105' oriented opposing the first outer surface 103 and apart from the first inner surface 105. Here the first outer surface 103, the first inner surface 105, and the third inner surface 105' are all non-plateable.

The second plastic wall portion 107 has a first section 107' positioned abutting 109 the first section 101" of the first plastic wall portion 101. The first section 107' of the second plastic wall portion 107 commences at a second outer surface 111, positioned proximal the first outer surface 103 of the first section 101" of the first plastic wall portion 101, and extends to a second inner surface 113' positioned proximal the first inner surface 105 of the first section 101' of the first plastic wall portion 101. The second plastic wall portion 107 has a pedestal section 107" which extends above the first section 107' of the second plastic wall portion 107. The pedestal section 107" commences at the second outer surface 111 and extends to a pedestal surface 113" opposing the second outer surface 111 and positioned apart from or above the second inner surface 113'. The pedestal surface 113" is plateable.

In FIG. 2, the via 115 is disposed through the pedestal section 107" of the second plastic wall portion 107, extends between the second outer surface 111 and the pedestal surface 113", the via 115 includes a thermally-conductive material 117 disposed thereon. Both second outer surface 111 and the pedestal surface 113" also have the thermally-conductive material 117 disposed thereon so that there is a continuous low resistance thermal path between the second outer surface 111 and the pedestal surface 113".

Next, as in the first embodiment, a heat-generating component 119 is disposed coupled to the pedestal surface 113" using solder or other suitable material.

Another portion of the structure consists of a third plastic wall portion 213 having a first section 215 positioned abutting 217 the first section 101" of the first plastic wall portion 101. The first section 215 of the third plastic wall portion 213 commences at the second outer surface 111 positioned proximal the first outer surface 103 of the first section 101" of the first plastic wall portion 101, and extends to a third inner surface 219 positioned proximal the first inner surface 105 of the first section 101" of the first plastic wall portion 101. The third plastic wall portion 213 has a pedestal section 221 extending above the first section 215 of the third plastic wall portion 213. The pedestal section 221 commences at the second outer surface 111 and extends to a pedestal surface 223 opposing the second outer surface 111 and positioned apart from the third inner surface 219. The pedestal surface 223 is also plateable. Another via, or array of vias 224, is disposed through the pedestal section 221 of the third plastic wall portion 213 and extends between the second outer surface 111 and the pedestal surface 223. The another via 224 has thermally-conductive material 222 disposed thereon extending coupling the second outer surface 111 and the another pedestal surface 223 .

Next, another heat-generating component 225 is disposed coupled to the pedestal surface 223. Here, the heat-generating component 225 is power transistor and is coupled to the another thermally-conductive material 222 of the pedestal surface 223, with another solder connection 121'.

The first section 101" of the first plastic wall portion 101 acts to electrically isolate the heat-generating components 119 and 225.

Alternatively, in this second embodiment, the heat-generating components 119 and 225 are coupled to their respective pedestal surfaces 113" and 223 via a substrate 201. The substrate 201 is coupled to the thermally-conductive material 117 of the pedestal surface 113" with a first solder connection 121 and the heat-generating component 119 is coupled to the substrate 201 with a second solder connection 203. A metalized via 205 thermally connects the first solder connection 121 and the second solder connection 203. In this configuration the substrate 201 is coupled to the thermally-conductive material 222 of the pedestal surface 223 with a third solder connection 121' and the power transistor 225 is coupled to the substrate 201 with a fourth solder connection 227. The substrate 201 has another metalized via 229 disposed therethrough thermally connecting the third solder connection 121' and the fourth solder connection 227.

The plastic housing assembly can also include an electrical connector portion 207 positioned extending through the first plastic wall portion 101 for electrically connecting 209 the heat-generating component 119 to the electrical connector portion 207, and the another heat-generating component 225 is electrically connected 231 to the electrical connector portion 207.

Furthermore, an electrically insulating material 276 can be disposed in contact with the first outer surface 103, and the second outer surface 111 to form an electrical isolation barrier. Preferably, the electrically insulating material 276 is an adhesive material. Additionally, a metal plate 278 can be disposed in contact with the electrically insulating material 276. This is done to effect more rapid heat spreading and adding thermal mass to absorb thermal transients thus minimizing temperature rise of the heat generating component 119. The electrically insulating material 276 is used to isolate different electrical potentials of the circuits associated with the components 119 and 225.

Alternatively, if electrical isolation is not required, the metal plate 278 can be placed in contact with the second outer surface 111, if all of the outer surfaces 111 are at the same electrical potential. The metal plate 278 provides more rapid heat spreading and adds thermal mass to absorb thermal transients thus minimizing temperature rise of the heat generating component 119.

Note also that the vias 115 and 224 may comprise an array of individual vias for better thermal conductivity performance.

The described structure offers a simple, minimum component, with thermally efficient electrical isolation, and which offers an environmentally robust and reliable heat-sinking solution for control module packaging.