The present invention is generally directed to an electronic assembly and, more specifically, to an electronic assembly with a backplate having at least one thermal insert.
Traditionally, electronic assemblies utilized in an automotive environment have utilized a number of different techniques to remove excessive heat from high-power integrated circuit (IC) dies. Traditionally, the ICs, which have been electrically connected to a substrate, have been heatsinked to a metal backplate. The thermal performance of the heatsink-IC die interface has been improved through a number of techniques, e.g., by using a thermal grease, a thermal film or soldering a non-active side of the die to the heatsink.
An advantage of thermally connecting the IC die to the heatsink with a solder is that solder generally has a very high bulk conductivity and practically no interfacial resistance, as it creates a bond with the backside of the flip-chip and the heatsink. However, one problem with using a solder as a thermal interface material is that solder requires a solderable interface for bonding. Today, the majority of heatsink backplates implemented in electronic assemblies in the automotive environment are aluminum, which is used primarily due to the fact that it is relatively inexpensive, can be cast-molded and is relatively light-weight. Unfortunately, aluminum does not offer a solderable surface.
As an alternative to aluminum, some manufacturers have proposed implementing a copper or plated copper backplate. Unfortunately, a plated copper backplate may be approximately five times as costly as that of an aluminum backplate and, in general, weighs at least twice as much as a same-sized aluminum backplate. Although copper stamping could be utilized to create the backplate, such a backplate would still be at least two times the cost of an aluminum backplate. Furthermore, copper is difficult to machine and cannot be formed from a casting. Thus, the cost and weight disadvantages of a copper backplate make the utilization of solder as a thermal interface material substantially less attractive.
What is needed is an economical electronic assembly that provides for improved thermal performance of high-power integrated circuits (ICs) of the assembly.
A technique for manufacturing an electronic assembly, according to one aspect of the present invention, includes a number of steps. Initially, a backplate that includes a cavity is provided. Next, an insert, which functions as a heatsink and includes at least an outer surface that is made of copper, is inserted within the cavity. Then, a substrate, with a first side of an integrated circuit (IC) die mounted to a first side of the substrate, is provided. The IC die is electrically connected to one or more of a plurality of electrically conductive traces formed on the first side of the substrate. The first side of the substrate is then positioned in contact with at least a portion of the first side of the backplate. A second side of the IC die is positioned in thermal contact with the heatsink and a solder is utilized to provide a thermally conductive interface, between at least a portion of the second side of the IC die and the heatsink.
According to another aspect of the present invention, the substrate and at least a portion of the backplate are overmolded with an overmold material. In this embodiment, the overmold material substantially underfills the IC die and bonds the insert to the backplate. According to a different aspect of the present invention, the substrate is a printed circuit board (PCB). According to another embodiment of the present invention, the solder is an Indium-based solder. According to another aspect of the present invention, the IC die may be a flip-chip. According to a different aspect of the present invention, the backplate is made of aluminum. According to another embodiment, an adhesive is positioned between at least a portion of the first side of the substrate and the first side of the backplate. The insert may be electrically isolated from the backplate. In one or more embodiments, the cavity is formed as a through-hole and the insert may have a cylindrical shape.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
An electronic assembly constructed according to various embodiments of the present invention provides a relatively low-cost assembly with a solderable heatsink that provides a relatively efficient thermal heat dissipation structure for high-power integrated circuit (IC) dies, such as flip-chips. In a majority of electronic products, a small number of IC dies typically consume the majority of the power required for the products. As noted above, one technique to increase the dissipation of waste energy in IC dies is to solder a non-active backside of the die to a metal heatsinking backplate. According to one embodiment of the present invention, as a solderable area is only required in flip-chip areas, plated metal heatsinks or inserts, e.g., metal cylinders, are inserted into a relatively low-cost backplate, e.g., an aluminum backplate. Alternatively, a low-cost plastic backplate may also be used, assuming that the metal pedestals are in contact with a cold plate. The solderable surfaces of the insert facilitate the use of very high-thermal conductive solders, such as Indium, which has an 86 W/mK conductivity, as a thermal interface material between a flip-chip and its associated heatsink. Due to the fact that an intermetallic joint is formed between the flip-chip and the heatsink, thermal resistance, at the joint interface, is substantially zero.
According to one embodiment of the present invention, metal inserts are manufactured from a round metal stock that has been cut to a desired length. The end surfaces of the cut round metal stock are then machined to a specified surface finish. A solderable coating is then applied to at least the end surfaces of the cut round metal stock. The coating may be, for example, an electroless nickel/gold plating, a tin/copper/zinc plating or other suitable plating material. The plated inserts are then pressed into cavities, e.g., through-holes or pockets, in a backplate, which may be made from aluminum. The holes may be formed during the casting process or may be formed by machining. It should be appreciated that, when implemented within an overmolded product, the overmold compound can form a seal and help bond the insert to the backplate.
In applications in which a backside of an IC die is required to be electrically insulated from a metal backplate, an electrically insulating thermally conductive jacket may be attached to or formed on an external surface of the insert, prior to installation in the backplate. When the insert is a copper cylinder, or a plated copper cylinder, the insert provides good thermal conductivity, as the thermal contact surface area of the copper cylinder to the backplate is relatively large, i.e., the cylinder circumference times the height of the cylinder in contact with the backplate. It should also be appreciated that waste energy may also be conducted through the ends (Z-axis) of the insert. The jacket may be, for example, a ceramic-filled plastic or other thermally conductive electrically insulating material.
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Accordingly, an electronic assembly has been described herein that exhibits improved thermal performance, which is facilitated by soldering an end of an insert, which is installed in a backplate, to a non-active side of an integrated circuit (IC) die.
The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.