Inductor devices – Core forms casing
Reexamination Certificate
1999-10-28
2001-09-04
Mai, Anh (Department: 2832)
Inductor devices
Core forms casing
C336S090000
Reexamination Certificate
active
06285272
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electronic components, and more particularly concerns low profile surface mountable inductive components.
BACKGROUND
The electronics industry is continually called upon to make products smaller and more powerful. Applications such as mobile phones, portable computers, computer accessories, hand-held electronics, etc., create a large demand for smaller electrical components. These applications further drive technology to research new areas and ideas with respect to miniaturizing electronics. Often times, applications specifically require “low profile” components due to constraints in height and width. Unfortunately, the technology is often limited due to the inability to make certain components smaller, faster, or more powerful. Nowhere can this be seen more than in the struggle to manufacture smaller electrical circuits.
Originally, components were mounted on a printed circuit board (PCB) by inserting the leads of the component through the PCB and soldering them to solder pads on the opposite side of the PCB, (called through-hole technology). This technique left half of the PCB unpopulated because one side had to be reserved for solder pads and solder. Therefore, in order to fit more components in a particular circuit, the PCBs were made larger, or additional PCBs were required.
The solution to this problem came in the form of Surface-Mount Devices (SMD), or Surface-Mount Technology. SMDs allow electrical components to be mounted on one side of a PCB, (i.e., without having the leads inserted through-holes). An SMD device has small solder pads (or leads) connected to its body, which correspond to solder pads or lands placed on the surface of the PCB. Typically the PCB is run through a solder-paste machine (or screen printer), which puts a small amount of solder on the solder pads on the PCB. Next, a glue dot is inserted on the PCB where the component is to rest. Then, the component is placed on the PCB (held by the glue dot), and the PCB is sent through a re-flow oven to heat the solder paste and solder the component leads to the PCB solder pads. The primary advantage to this technique is that both sides of the PCB can now be populated by electronic components. Meaning one PCB today can hold an amount of electrical components equal to two PCBs in the past.
As a result of this advancement in technology, the current electronic circuits are mainly limited by the size of components used on the PCB. Meaning, if the electronic components are made smaller, the circuits are smaller as well. Unfortunately, there are some electronic components that can simply not be produced any smaller than they currently are. Usually this is because the desired parameters for the component cannot be achieved when using smaller parts. A good example of this is inductive components. Inductive components are often used in stepper motors, transformers, servos, relays, inductors, antennas, etc. Typical applications requiring such components include radio frequency (RF), switching power supplies, converters, data communications, processor/controller circuits, signal conditioning circuits, biasing oscillators, DC-DC converters, DC-AC converters, chokes, IC inverters, filters, etc. Certain parameters of these components are affected by the size of parts used. For instance, in inductors, wire gauge determines both the DC resistance and the current carrying ability of the component.
Several attempts have been made to compensate for components requiring a minimum amount of size in order to use them in smaller circuit applications. For example, U.S. Pat. No. 5,760,669, issued Jun. 2, 1998, to Dangler et al., discloses a low profile inductor/transformer component having a wire coil within a core set which is disposed at least partially within a recess in a header. To achieve its low profile status, Dangler uses a header with a plurality of projections extending from the header's side. A core set is disposed within the header and a pre-wound coil is inserted around the core set. At least one end of the pre-wound coil is wrapped around at least one of the header projections, thereby increasing the size of the coil without raising the height of the component. Unfortunately, this structure creates an awkward sized component with exposed conductive wires capable of being damaged. In addition, the need for pre-wound coils, upper and lower core attachments (the core set), and a header having projections is costly and takes up valuable space on the PCB. Such a device does not answer the growing need for smaller components.
Another attempt to produce low profile surface mount coil assemblies is disclosed in U.S. Pat. No. 5,796,324, issued Aug. 18, 1998, to Ross et al. Ross discloses a coil wound bobbin having posts that are capable of suspending the coil either above or alongside a PCB. The ends of the coil wire are wrapped on the posts to form wire terminations. These posts are the only part of the component that need to be soldered to the PCB. Unfortunately, suspending the coil above or alongside the PCB does not reduce the amount of space required for the circuit as a whole. Suspending the wire above the board simply raises the height of the circuit. Suspending the coil alongside the PCB raises the width requirement for the circuit.
Accordingly, it has been determined that the need exists for an improved low profile inductive component which overcomes the aforementioned limitations and which further provides capabilities, features and functions, not available in current devices.
SUMMARY OF THE INVENTION
A low profile inductive component in accordance with the invention comprises a low profile body having spread apart soldering pads for electrically and mechanically attaching the body to a printed circuit board. The body defines an aperture between the pads. A core is disposed in the aperture. A wire is wound around the core and has first and second ends connected to the soldering pads. The core has integral flange ends, with the upper flange being smaller than a lower flange. The body has spacers on its lower surface which bear against the lower flange to retain the core such that it does not fully pass through the aperture of the body. This structure allows for the upper flange to be disposed in the aperture of the body with the lower flange abutting the spacer so as to position the flange above the plane of the solder pads.
In another embodiment, the body is constructed such that the lower flange of the core extends beyond the solder pads so that when mounted on a printed circuit board the lower flange extends into an aperture in the PCB. With such a construction, the height of the inductive component above the board will be lower than the height of the prior described embodiment.
An advantage to using this component is that the wire wound around the core is not exposed and the inductive component takes on a slim wafer shape, making it ideal for low profile applications. A further advantage is that the component retains a traditional shape and has no awkward protruding members, thereby making it suitable for vacuum placement surface mount applications, for densely populated PCBs, and/or applications requiring components that use a minimal amount of space.
REFERENCES:
patent: 4926151 (1990-05-01), Morinaga
patent: 5541567 (1996-07-01), Fogel et al.
patent: 5760669 (1998-06-01), Dangler et al.
patent: 5796324 (1998-08-01), Ross et al.
Boytor James G.
Girbaci Catalin C.
Gogny Helen O.
Coilcraft, Incorporated
Fitch Even Tabin & Flannery
Mai Anh
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