Electrical circuit board and method for making the same

A multi-layer circuit board with heat pipes and a method for forming a multi-layer circuit board with heat pipes. The method includes forming channels in a first and second pre-circuit assembly and attaching the first pre-circuit assembly to the second pre-circuit assembly such that the channels cooperatively form a heat pipe.

(1) FIELD OF INVENTION

The present invention relates to a method for making an electrical circuit board and more particularly, to a method for making a multi-layer electrical circuit board having pipes, tunnels and/or caverns which are formed within the circuit board and/or through various portions of the circuit board, and which allow heat emanating from components which are contained within the circuit board to be efficiently dissipated.

(2) BACKGROUND OF THE INVENTION

Multi-layer circuit boards contain and/or include electrical components which selectively and operatively populate opposed first and second surfaces (i.e., top and bottom surfaces) of each board (or other respective interior portions of each board), thereby desirably allowing each of the electrical circuit boards to contain and/or include a relatively large amount of electrical components which efficiently and densely populate the respective boards.

Due to the relatively dense component population, substantial amounts of heat are produced and/or generated within relatively small areas of the circuit boards. This generated heat undesirably prevents the components from properly functioning and may even irrevocably damage or destroy these components. Therefore it is desirable to form, create and/or manufacture circuit boards that are adapted to disperse and/or dissipate heat away from such heat producing components.

Pipes, tunnels and/or caverns, commonly referred to as “heat pipes”, may be used to disperse, dissipate and/or translate heat within these multi-layer circuit boards. Conventional heat pipes typically comprise an elongated material which forms a pair of open ends and which further forms a tunnel extending down the length of the elongated material and communicating with each of the open ends. By way of example and without limitation, a conventional heat pipe is typically operatively placed within an electronic assembly such that a first portion of the pipe is disposed near a warm or heat emitting component of the equipment and a second portion of the pipe is disposed near a cooler or heat absorbing area of the assembly, thereby allowing the pipe to transfer heat away from the heat emitting component toward the cooler or heat absorbing area.

One drawback associated with these conventional heat pipes is that they are typically made and/or manufactured from “additional” materials that are not needed for the functioning of the electronics equipment within which the heat pipes reside. Employing heat pipes which use additional materials is especially undesirable in a multi-layer circuit board which is designed to support and/or contain several electrical components in a relatively small amount of space. Particularly, such additional materials add both unwanted size and weight to multi-layer circuit boards.

Consequently, there is a need for circuit boards created by a method which allows many small electrical components to densely populate respective layers within the circuit boards, while still allowing heat to be dissipated and/or dispersed away from heat-emitting components. Specifically, there is a need for a method of creating heat pipes within multi-layer circuit boards which are integrally formed within the circuit boards such that very little “excess” or additional material is needed to create the heat pipes.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a method for forming heat pipes within multi-layer circuit boards which overcomes the various previously delineated drawbacks of conventional heat pipes.

It is a second object of the present invention to provide heat pipes that are integrally manufactured from the original materials that are used when making a multi-layer circuit board.

According to a first aspect of the present invention a circuit board is disclosed. The circuit board includes a first and second pre-circuit assembly each including a first and second core metal portion, the first and second core metal portions respectively including a first and second channel; wherein the first pre-circuit assembly is attached to the second pre-circuit assembly such that the first and second channels cooperatively form a heat pipe.

According to a second aspect of the present invention, a method for producing a multi-layer circuit board having a heat pipe is disclosed. The method includes the steps of: providing a first and second pre-circuit assembly respectively having a first and second core metal portion; applying protective layers to the pre-circuit assemblies, effective to leave a first exposed portion on the first core metal portion and a second exposed portion on the second core metal portion; removing the first and second exposed portions to respectively form a first and second channel within the first and second core metal portions; and attaching the first pre-circuit assembly to the second pre-circuit assembly effective to cause the first and second channel to cooperatively form a pipe within the circuit board.

These and other objects, aspects, and advantages of the present invention will become apparent upon reading the following detailed description in combination with the accompanying drawings.

Referring now toFIGS. 1(a)–(g), there is shown a method and/or process for selectively forming a multi-layer electrical circuit board10in accordance with a preferred embodiment of the present invention. It shall be understood that whileFIGS. 1(a)–(g) illustrate sectional side views of only portions of pre-circuit assemblies12,14and/or of circuit board10, the concept and/or steps of the method or process of the present invention may be used on an entire circuit board. For a fuller view of a circuit board100having a heat pipe formed according to the present invention, reference will be made toFIGS. 2(a) and2(b).

Referring now toFIG. 1(a), there is shown and/or provided a pair of pre-circuit assemblies12,14which are formed in accordance with the teachings of the present invention. Each pre-circuit assembly12,14includes a core metal portion16which is preferably manufactured and/or formed from a conventional aluminum material. Each pre-circuit assembly12,14also includes an outer pipe member18and two inner pipe members20which are preferably formed from a conventional copper material. Furthermore, each pre-circuit assembly12,14includes an outer support member22, an inner support member24, and “flip chip” pads26,28which are also preferably formed from a conventional copper material. As illustrated inFIG. 1(a), members18,20,22,24and pads26,28are all attached, coupled and/or connected in a conventional manner (e.g., adhesively secured) to core metal portions16.

Pre-circuit assemblies12,14may be formed, provided and/or manufactured in a variety of known and conventional manners. In one preferred embodiment, pre-circuit assemblies12,14are formed and/or manufactured by conventionally attaching, bonding and/or adhering copper plates (not shown) to inner and outer surfaces32,34of core metal portions16followed by selective removal of portions of the copper plates in a conventional manner (e.g., by etching) to form members18,20,22,24and pads26,28as shown inFIG. 1(a).

Referring now toFIG. 1(b), there is shown pre-circuit assemblies12,14which have protective layers36selectively applied in a conventional manner to cover portions of assemblies12,14. In one non-limiting embodiment, protective layers36are comprised of a commercially available dielectric “etch-resistant” material which is applied to pre-circuit assemblies12,14in a conventional manner using a conventional press. Preferably, protective layers36are applied to cover significantly all of the surface area of pre-circuit assemblies12,14with the exception of uncovered and/or exposed portions38,40.

Referring now toFIG. 1(c), there is shown pre-circuit assemblies12,14which include apertures and/or channels46,48. Apertures and/or channels46,48are formed within member16in a conventional manner (e.g., by etching). In one non-limiting embodiment, channels46,48are etched by immersing pre-circuit assemblies12,14in a conventional and commercially available etchant material, effective to remove and/or “etch away” a portion of each core metal portion16such that the inner pipe members20“border” or partially form channels46,48. In the non-limiting embodiment of the invention shown inFIG. 1(c), exposed portions38,40are selectively etched to form channels46,48which extend to and/or abut outer pipe members18. However, it will be appreciated that exposed portions38,40may be removed to form channels46,48in a variety of other sizes and geometric configurations. Further, exposed portions38,40need not be removed such that they extend to and/or abut outer pipe members18, rather, exposed portions38,40may be formed or created by removing only a portion of the thickness50of core metal portions16. In this situation, core metal portions16will entirely define channels46,48and, therefore, render outer pipe members18unneeded and/or extraneous. Once channels46,48have been formed, protective layers36may be removed in a known and conventional manner to yield the assemblies12,14as shown inFIG. 1(d).

Referring now toFIG. 1(e), there is shown circuit board10made in accordance with the teachings of the present invention. Circuit board10is made, formed and/or manufactured by attaching and/or coupling pre-circuit assemblies12,14to a core member62. Core member62is preferably manufactured from an aluminum, copper or other conductive material. In the non-limiting embodiment shown inFIG. 1(e), pre-circuit assemblies12,14are attached to core member62through the use of conventional adhesive layers64,66. In one particular non-limiting embodiment pre-circuit assemblies12,14are adhesively secured to core member62by conventional and commercially available adhesive layers64,66through the use of a one-step laminating process.

In the non-limiting embodiment shown inFIG. 1(e), core member62includes an opening and/or aperture74which substantially corresponds to and communicates with channels46,48. That is, aperture74of core member62substantially aligns with channels46,48when pre-circuit assemblies12,14are attached, coupled and/or connected to core member62, and cooperates with channels46,48to create and/or form a pipe, cavern and/or tunnel78which extends within circuit board10. Opening and/or aperture74is formed and/or created within core member62in a conventional manner (e.g., by routing, stamping, drilling, punching and/or etching). In the preferred embodiment of the present invention, channels46,48are substantially identical in shape and size as they extend within, into and/or through portions of circuit board10, and aperture74substantially and continuously interconnects channel46to channel48such that pipe78is a continuous opening that extends within, into and/or through portions of circuit board10.

In one non-limiting embodiment of the present invention, a wicking material (not shown) is selectively applied to the surfaces which cooperatively form and/or define pipe78. That is, a wicking material is applied to those portions or surfaces of pre-circuit assemblies12,14, adhesive materials64,66, and core member62which cooperatively form and/or define pipe78. Preferably, the wicking material is applied to the aforementioned surfaces prior to the step of connecting and/or laminating pre-circuit assemblies12,14to core member62.

Referring now toFIG. 1(f), circuit board10is shown after it has been further formed and/or processed according to the teachings of the preferred embodiment of the present invention. In this non-limiting embodiment, portions of core metal portions16have been removed in a conventional manner (e.g., by etching, drilling, routing or stamping), thereby forming connection portions80. Connection portions80connect and/or attach outer pipe members18to inner pipe members20and outer support members22to inner support members24.FIG. 1(g) illustrates a top view of the portion of circuit board10inFIG. 1(f). As can be seen in the non-limiting embodiment ofFIG. 1(g), outer pipe member18and pipe78extend across the portion of circuit board10shown inFIG. 1(g) and outer support member22is substantially square shaped and resides near member18.

Referring now toFIG. 2(a) there is shown a top view of a circuit board100or a portion of a circuit board100which includes an entire pipe78according to the teachings of the preferred embodiment of the invention. It should be appreciated that circuit board10may comprise a portion of circuit board100. Further, referring toFIG. 2(b), there is shown a sectional side view of circuit board100taken along line2b—2bofFIG. 2(a). In this non-limiting embodiment, pipe or tunnel78extends through circuit board100and forms a generally rectangular shape.

Also illustrated inFIGS. 2(a) and2(b) are through-holes, apertures and/or vias84which have been formed within circuit board100and which are disposed adjacent to or in relative close proximity to heat pipe78. In the non-limiting embodiment shown inFIGS. 2(a) and2(b), vias84have been formed by selectively removing portions of core layer62and adhesive layers64,66from areas87such that vias84extend through circuit board100and between inner pipe members20and inner support members24and between outer pipe members18and outer support members22. In this non-limiting embodiment of the present invention, vias84have been formed in a conventional manner (e.g., by punching, etching and/or drilling) and selectively receive a material86(e.g., solder) with high thermal conductivity. When vias84receive and retain such a material86, the material86tends to attract, absorb and/or dissipate heat from pipe78very quickly and efficiently, thereby allowing heat pipe78to remove greater amounts of heat from other portions of circuit board100. For even greater and faster heat dissipation, a conventional heat sink79may be attached and/or coupled to material86in a known and conventional manner. In the embodiment shown inFIGS. 2(a) and2(b), heat is emitted by a hot power device88into heat pipe78. From there, the heat is removed or “drawn” from heat pipe78by material86and is thereby “vented” out of circuit board100to heat sink79.

In a further embodiment of the circuit board, a conventional cooling material or fluid (i.e., a fluid with high thermal conductivity) may be placed in the pipe78such that the fluid is free to flow and or move through the pipe78as indicated by arrows81. Such fluids may be liquid, gas and/or vapor as long as they can quickly absorb heat from warm areas (e.g., areas near hot power device88) and quickly purge heat to cooler areas (e.g., areas containing material86). In one embodiment of the invention, a sealing member90is removed from member18to form an aperture or hole92, which communicates with pipe78, and the cooling fluid is selectively inserted or placed into pipe78. Member90is then replaced and/or reattached (i.e., welded) in its original position, thereby sealing the cooling fluid within pipe78.

It should be understood that this invention is not to be limited to the exact construction or embodiment described above but that various changes may be made without departing from the spirit or scope of the invention.