Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-04-08
2001-10-30
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S262000
Reexamination Certificate
active
06310301
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to electronic devices and, more specifically, to a surface mountable circuit board and a method of manufacturing therefor.
BACKGROUND OF THE INVENTION
Electronic devices for power supplies and other electronic assemblies are conventionally provided in a protective package. The packaged electronic devices are conventionally mounted directly to a circuit board, the devices cooperating to form a circuit functioning, perhaps, as a power supply.
As with other types of electronic components, the trend in the design of power supplies has been towards achieving an increased power and device density and a lower device profile. Since many surface-mount devices are typically smaller than traditional through-hole devices, one way to achieve higher device density is to employ surface-mount electronic devices, to the exclusion of the larger through-hole mounted devices.
Some complex circuits may require more board real estate than is available with a single circuit board. Many designs, therefore, employ an auxiliary circuit board mounted to a primary circuit board. Electronic devices may then be surface mounted to both the primary and auxiliary circuit boards, significantly increasing device density. In designs requiring multiple circuit boards, the circuit boards are typically assembled separately using conventional automated pick-and-place equipment. The circuit boards are then mounted together in a separate manufacturing step. The auxiliary circuit board is typically mountable to the primary circuit board via through-hole pins. The leads of the auxiliary circuit board are typically soldered to the primary circuit card manually.
Since the primary circuit board typically contains a large number of surface mount components, the auxiliary circuit board may be the only through-hole mounted component on the primary circuit board. A separate or additional manufacturing step is thus required to mount the auxiliary circuit board to the primary circuit board, thereby increasing the complexity and overall cost of the electronic assembly incorporating the circuit boards.
Accordingly, what is needed in the art is a circuit board capable of being surface mounted to another circuit board using the same reflow soldering process used to mount the other surface mount electronic devices.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides an inter-substrate conductive mount for a surface mountable circuit board, a method of manufacturing the circuit board and a surface mountable power magnetic device. In one embodiment, the circuit board includes: (1) a substrate, (2) an inter-substrate conductive mount composed of a material having a melting point above a solder reflow temperature and including a compliant solder joint at an interface of the substrate and (3) a solder located proximate the conductive mount, the conductive mount of a sufficiently low weight such that a surface tension of a liquid state of the solder is sufficient to maintain the conductive mount in contact with the substrate as the solder is brought to the reflow temperature, the conductive mount being capable of mounting the substrate to an adjacent substrate and providing a conductive path therebetween.
The present invention, in one aspect, introduces the broad concept of an inter-substrate conductive mount for a surface mountable circuit board. The conductive mount has a compliant solder joint that improves the co-planarity of the circuit board during the reflow soldering process.
In one embodiment of the present invention, the substrate includes a conductive layer and a via coupled in electrical communication therewith. The conductive mount may, therefore, be located proximate the via. Those skilled in the art are familiar with through-hole vias in circuit boards. In a related embodiment, the conductive mount has a compound curved surface thereon. The conductive mount may, therefore, be partially recessed in the via to cause the compound curved surface to contact a proximal perimeter of the via. Of course, the broad scope of the present invention is not limited to a conductive mount of a specific geometry.
In one embodiment of the present invention, the substrate is selected from the group consisting of an epoxy-glass substrate, a paper phenolic substrate, and an insulated metal substrate. In a preferred embodiment, the substrate is an FR
4
substrate. Those skilled in the pertinent art are familiar with a variety of substrate materials.
In one embodiment of the present invention, the conductive mount is selected from the group consisting of a hollow tin/lead plated copper ball, a solid ball composed of high temperature solder and a solid metal ball. Of course, the conductive mount may be of any geometry, including any substantially spherical, cylindrical or toroidal shape. Alternatively, the conductive mount may have a substantially cubical or rectangular shape. In either case, the conductive mount is of a sufficiently low weight such that a surface tension of the liquid state of the solder is sufficient to maintain the conductive mount in contact with the lower conductive layer as the circuit board passes through the reflow soldering process.
In one embodiment of the present invention, the solder is a tin/lead solder composition. The solder, therefore, will transition to a liquid state as the circuit board passes through the reflow soldering process. In a related embodiment, the tin/lead solder composition is selected from the group consisting of a 60/40 Sn/Pb composition and a 63/37 Sn/Pb composition. The present invention may advantageously avoid the use of high temperature, lead-free solder, although such materials may be readily employed as required by an application.
In one embodiment of the present invention, the circuit board further includes an electrical component having a lead mounted on a pad on the conductive layer. The electrical component may be a power device, a magnetic device or other devices as required by a particular application.
In one embodiment of the present invention, the conductive mount is compatible with a through-hole mounting hole on the adjacent substrate. The conductive mount may thus enable the circuit board to be mounted to the adjacent substrate via the through-hole mounting hole,
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 5541828 (1996-07-01), Rozman
patent: 5588848 (1996-12-01), Law et al.
patent: 5724016 (1998-03-01), Roessler et al.
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patent: 6002172 (1999-12-01), Desai et al.
patent: 6137164 (2000-10-01), Yew et al.
U.S. Patent Application entitled “Methods of Manufacturing a Power Magnetic Device and Tool for Manfacturing the Same” by Roessler. et al.; Ser. No. 08/777,342; Filed Dec. 27, 1996.
U.S. Patent Application entitled “Board-Mountable Power Supply Module” by Rozman, et al.; Ser. No. 08/879,478; Filed Jun. 20, 1997.
U.S. Patent Application entitled “Methods of Manfacturing a Magnetic Device and Tool for Manufacturing the Same” by Roessler, et al.; Ser. No. 08/908,887; Filed Aug. 8, 1997.
U.S. Patent Application en
Heinrich Randy T.
Roessler Robert J.
Truong Thang D.
Wilkowski Matthew A.
Woods, Jr. William L.
Gaffin Jeffrey
Norris Jeremy
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