Inductor devices – Core forms casing
Reexamination Certificate
2002-04-24
2004-04-06
Mai, Anh (Department: 2832)
Inductor devices
Core forms casing
C336S212000, C336S208000, C336S198000
Reexamination Certificate
active
06717500
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electronic components and more particularly concerns low profile surface mountable electronic components having an improved structure for increasing the performance of the component.
Over the last decade the electronics industry has made many advances with respect to electronic components. One of the more significant advances was the introduction of the Surface-Mount Device (SMD) or surface mount technology. SMDs allow electrical components to be mounted on one side of a PCB, without requiring the leads of the components to be inserted through the printed circuit board (PCB) and soldered to the reverse side of the PCB, (i.e., an older method of mounting components to PCBs referred to as through-hole technology). An SMD component has small metalized pads (terminals or leads) connected to its body, which correspond to solder pads (or lands) located 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 of the PCB. Then, the component is placed on the PCB, 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 size of electronic circuits has decreased, thereby enabling smaller electronic devices to be manufactured. Current electronic circuits are mainly limited by the size of components used on the PCB. Meaning, if the electronic components can be made smaller, the circuits themselves can be made smaller as well. Unfortunately, there are some electronic components that have been more difficult to configure for SMD technology. For example, over the years many advances have been made in creating surface mount single winding components such as inductors. To date, however, there have only been minimal advances with respect to multi-winding components such as transformers. This is, at least in part, due to the difficulty in obtaining high quality multi-winding components that are robust enough to handle the conditions SMD components are exposed to during their production and use.
For example, in the conventional SMD transformer shown in
FIG. 9
, the component is constructed using a plastic bobbin (or coilform) upon which the windings of the component are wound. A problem with this configuration is that the plastic bobbins or coilforms are often times incapable of handling the extreme heat or high temperatures the component is exposed to during its manufacturing. A particular drawback to this type of component is the amount of warping or deformation the bobbin experiences when the component covered PCB (or populated PCB) passes through the re-flow oven in order to create the electrical connection between the component and the PCB. During this solder reflow stage, the populated PCB is heated to a high enough temperature (e.g., 200° C.-260° C.) to heat the metalized pads of the component and the corresponding lands on the PCB and to liquify the solder paste therebetween so that an electrical connection (or solder joint) can be established between the metalized pads and lands once the solder lowers in temperature. Often times, this temperature increase is enough to deform or warp the plastic bobbin causing the component and its solder joint to incur unwanted stress due to the deformation. Such deformations or warping may prevent the component from retaining its low profile shape or desired height from the surface of the PCB, and may cause the component or circuit to experience failures over their lifetime. For example, warping may induce enough strain on the solder joint to actually lift the land or solder pad and trace up from the PCB. Such an act can cause the trace or solder joint to break away formt he PCB creating an open circuit condition or a condition in which the circuit may only work intermittently.
In order to reduce the risk of such warping or deformation, the solder reflow stage could be conducted at a lower temperature; however, such an adjustment may result in the metalized pads, lands, and/or solder paste failing to reach a sufficient temperature to make a solid electrical and mechanical connection to the PCB. For example, if the metalized pad of the component does not heat to a sufficient temperature it may not bond with the melted solder paste causing a cold solder joint to be formed and resulting in either a poor/intermittent electrical connection between that pad of the component and its corresponding land on the PCB, or an open circuit condition in the circuit of the PCB.
Another drawback to using plastic bobbins for multi-winding components is that the component typically is required to use terminal pins extending out from the body of the component, thereby increasing the overall amount of space needed for the component. Given that the current desire in the industry is to make smaller components and smaller circuits, this increase in the space requirement for the component may make the component impractical for certain applications. Moreover, by having terminal pins extending from its side, the component leaves exposed current carrying coils and pins which can be shorted together by loose fragments within the circuit housing and/or inadvertently touched by individuals servicing or testing the electronic circuit. Thus, such a configuration allows for the component and circuit to be damaged, and increases the risk of electrical shock.
Although the terminal pins of the component of
FIG. 9
are shielded by its core halves when assembled, other components using terminal pin configurations do not shield the exposed coil windings of the terminal pins which can increase the amount of noise, such as electromagnetic interference (EMI) and/or radio frequency interference (RFI), caused by the component. For example, with current running through the exposed coil windings, the electric or magnetic lines of flux of the component will be widely disbursed about the component. This increases the likelihood of the component causing interference with other components in the circuit and prevents the component from operating as optimally as it can due to disbursed flux lines.
The use of terminal pins also increases the cost for manufacturing the component because it requires the wire from the windings to be wound about the terminal pins and then dipped into a solder pool or bath, (i.e., dip soldering), in order to remove the wire insulation and create an electrical connection or solder joint between the wire winding and the terminal pin of the component. The need for additional equipment and/or manual labor to hand wind the component increases the cost of the component and makes it less likely to be used in a number of applications. Furthermore, when the component is dip soldered, the plastic bobbin is again exposed to high temperatures which may result in further warping or deformations.
Another problem associated with the shaped core and bobbin configuration of
FIG. 9
, is that it does not have a seamless flat top portion for allowing industry standard pick-and-place equipment to position the component on the PCB, and thus does not have a configuration that is easy to implement into the traditional tape and reel carrier format used by a majority of the electronics industry. Such a configuration also increases the cost of manufacturing the overall circuit by requiring specialized equipment for placement of the component, or by requiring manual placement of the component, which increases the amount of time and cost needed to fully assembly the circuit, making the component less likely to be used in a majority of applications.
A solution to several of the problems associated with plastic bobbins was created by Coilcraft, Incorporated of Cary, Ill., which involved replacing the plastic bobbin/te
Caramela Chris
Garcia Nelson
Girbachi Catalin Constantin
Hess Scott
Rehak Richard D.
Coilcraft, Incorporated
Fitch Even Tabin & Flannery
Mai Anh
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