1. Field of the Invention
This invention pertains to electrical contacts. In particular, this invention pertains to electrical contacts between and for interconnecting spaced printed circuit boards (PCBs) and/or off-board components. The electrical contact includes a deformable segment adapted to alleviate stress on the connections with slight changes in the spacing between the PCBs.
2. Description of the Related Art
Numerous electrical contact designs have been developed for connecting a printed circuit board (hereinafter “PCB”) with off-board component and/or other PCBs. Representative contact designs include pins, posts, lugs, and tabs.
Surface mounting technology (“SMT”) is a widely used method of securing electrical contacts to PCBs. This method includes providing an electrical contact to a “pick-and-place” machine, which picks up the electrical contact and places it at a predetermined position on a conductive pad or land on the surface of a PCB. The contact is then usually soldered to the PCB.
Once the base of the contact is secured to a PCB, the tip of the contact may be secured to a second PCB or an off-board component using a variety of techniques, including soldering, friction fitting, and clamping. For example, the tip of the contact can be fitted through an aperture or hole within a second PCB, using a through-the-hole (TTH) approach, and held within the aperture by friction and/or subsequent soldering.
In general, a contact is attached to a PCB using a rigid or inflexible bond, such as soldering. Unfortunately, these rigid, relatively small bonds are not able to resist much mechanical stress. Thus, relative movement of connected PCBs, for example, due to thermal expansion, often results in broken bonds and/or contacts.
To alleviate mechanical stress created by relative movement of the interconnected parts, electrical contacts that are deformable, compliant, and/or flexible are used as connections between PCBs and/or off-board components. For example, compliant electrical contacts are described in U.S. Pat. Nos. 4,642,889, 4,751,119, 5,317,479, 5,446,161, and 6,184,587. However, these previously described compliant electrical contacts do not have at least one deformable section that is symmetrical or otherwise balanced about the centerline thereof and, thus, are prone to uneven deformation and excessive lateral flexibility. In the case of pin-shaped contacts, the applicants are unaware of any prior example having at least one symmetrical or otherwise balanced compliant section.
Electrical contacts that are internally re-enforced by solder have also been developed, as described in U.S. Pat. No. 5,816,868 (assigned to Zierick Manufacturing Corp.). The solder wicks or flows from the conductive land on the PCB into a channel within the electrical contact. However, if too much solder is wicked away from the conductive land, the bond between the conductive land and the electrical contact is weakened. Excessive capillary flow of solder is especially troublesome for pin contacts, which often have small bases and long pin sections that wick a relatively large amount of solder from the conductive land.
It is an object of the present invention to provide an electrical contact that is deformable, compliant, and/or flexible to alleviate mechanical stress created by relative movement of printed circuit boards and/or off-board components interconnected by the electrical contact.
It is also an object of the present invention to provide a pin-type electrical contact having at least one deformable segment along the length thereof that may alleviate stress created by relative movement of printed circuit boards and/or off-board components interconnected by the electrical contact.
It is another object of the present invention to provide such a pin-type electrical contact that has a symmetrical or otherwise balanced configuration to provide even expansion and avoid excessive lateral expansion.
It is a further object of the present invention to provide an electrical contact that stops or breaks the capillary flow of solder therein, so as to control the amount of solder that is wicked up from the conductive land into the electrical contact.
These and other objects of the present invention are accomplished by an electrical contact having a base section and a pin section, which extends from the base section at an angle substantially perpendicular to the base section. The pin section comprises two overlapping legs that are joined at a tip. Each leg has a deformable segment or segments that can expand or contract along the direction of the leg to alleviate stress created by relative movement of printed circuit boards and/or off-board components interconnected by the electrical contact. The deformable segments have members that project or extend in opposing directions relative to an axis of the pin section, so that the segments are symmetrical or otherwise balanced, which prevents the segments from twisting and/or expanding unevenly. In one embodiment of the present invention, each leg has a deformable segment having a outwardly curved or “C” shape. In another embodiment of the present invention, each leg has a deformable segment in the shape of a rectangular frame. The rectangular frames allow the electrical contact to withstand mechanical stresses normally experienced between interconnected printed circuit boards due to the possibility of deflection or deformation of the transverse portions of the rectangular frames. Moreover, due to their configurations, the deformable segments define at least one opening where the two legs of the pin section are not overlapping, which stops or breaks the capillary flow of solder between the legs when the electrical contact is soldered to a conductive land on a PCB. The amount of solder that flows into the electrical contact is selectively controlled or limited by the selected placement of the deformable segments.
Other objects and features of the present invention may become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to accompanying drawings, in which:
Referring to the figures and, in particular,
Base 110 has a generally flat surface suitable for attachment to a flat conductive surface of a PCB, which is frequently referred to as a “land” or “pad” (not shown). Base 110 is generally U-shaped with a transverse segment 112 perpendicularly connected to a pair of parallel segments 114 and 116. Preferably, parallel segments 114 and 116 each have at least one inward protrusion designated, respectively, as 115 and 117 (see FIG. 2). Base 110 is preferably square in configuration, to conform to the typical shape of the lands on printed circuit boards. However, base 110 may be any desired or selected shape with any desired dimensions-and area. Transverse segment 112 may be, for example, about 0.10 inch along its longest (i.e., outer) edge, while parallel segments 114 and 116 may each be, for example, about 0.070 when measured along their respective longest (i.e., outer) sides.
Electrical contact 100 has two pin legs 120 and 130 extending substantially perpendicularly from base 110 in its operative shape of FIG. 1. First pin leg 120 has a first deformable section 125, while second pin leg 130 has a second deformable section 135. Sections or segments 125, 135 are deformable so that they can expand and contract along the central axis C of electrical contact 100, which extends in the direction of legs 120, 130. First deformable section 125 defines a first opening 170 (see FIGS. 2 and 5), while second deformable section 135 defines a second opening 175. First pin leg 120 and second pin leg 130 are connected at an intermediate portion 140, which defines the tip of electrical contact 100. Preferably, intermediate portion 140 is narrowed or necked down compared to pin legs 120 and 130.
First pin leg 120 may, for example, have a length of about 0.2 inch to about 0.245 inch. The width of first pin leg 120 is about 0.036 inch. Intermediate portion 140 is from about 0.25 inch to about 0.35 inch long and about 0.25 inch wide. Second pin leg 130, like first pin leg 120, may be about 0.2 inch to about 0.245 inch in length and about 0.036 inch in width.
Referring again to
Once the blank for electrical contact 100 has been made (i.e., stamped), it is folded or bent into an operative shape, as shown in FIG. 1. Transition segment 118 is bent to place base 110 in a plane substantially perpendicular to first and second pin legs 120 and 130. Intermediate portion 140 is bent to bring first and second leg portions 120 and 130 into a juxtaposed orientation. End 150 is moved into the plane of base 110 by bending a second intermediate connecting portion 252, and positioning end 150 between parallel segments 114 and 116.
Protuberances 115 and 117 hold end 150 between parallel segments 114 and 116. It will be appreciated that a combination of protuberances and indentations will provide an effective locking mechanism that prevents electrical contact 100 from deforming prior to being mounted on a PCB. Thus, electrical contact 100 maintains the integrity during picking and placement, which preferably includes the steps of severing electrical contact 100 from a strip of electrical contacts, gripping electrical contact 100 at the pick-up point, and placing the electrical contact 100 on a land on a printed circuit board.
Electrical contact 100 is made from a conductive material. Preferably, the conductive material used to make electrical contact 100 is a metal. More preferably, the conductive material used to make electrical contact 100 is a malleable metal that is shaped into a flat sheet from which electrical contact 100 may be stamped. Preferred metals for use in electrical contact 100 include brass, aluminum, tin, copper, silver, and combinations and alloys thereof. For the embodiments described in detail hereby, electrical contact 100 is stamped from a sheet of brass about 0.013 inch thick.
Referring to
The shape of deformable segment or section 125 has the overall appearance of a rectangular frame defining opening 170. Moreover, the shape of deformable section 125 is symmetrical about centerline c. The overall rectangular structure of deformable section 125 resists uneven expansion and/or twisting. In other words, deformable section 125 responds to mechanical stresses along directions parallel to the centerline c without moving substantially out of its original plane. Expansion of deformable section 125 primarily results from the deflection or deformation of the transverse or horizontal members 515, 516, 518, 519.
Vertical members 512 and 513 may both be, for example, about 0.050 inch in length and about 0.013 inch in width. Horizontal members 515, 516, 518, and 519 may all be, for example, about 0.027 inch wide and 0.013 inch long. The orientation of vertical members 512, 513 with horizontal members 515, 516, 518, and 519 defines a space 170 that may be about 0.024 long and about 0.064 wide.
As shown in
Referring to
Referring to
First and second pin legs 820 and 830 extend vertically from base 810 at an angle substantially perpendicular to base 810. First pin leg 820 has a first deformable section 825, while second pin leg 830 has a second deformable section 835. First pin leg 820 and second pin leg 830 are connected at an intermediate portion 840, which defines the tip of electrical contact 800. Preferably, intermediate portion 840 is narrowed or necked down compared to pin legs 820 and 830.
The shape of both deformable sections 825 and 835 is exemplified by reference specifically to first deformable section 825. First deformable section 825 is curved out of alignment with first pin leg 820. Deformable section 825 will normally have a smoothly curved shape, such as a “C.” When compressed or stretched along centerline c, deformable section 825 will have a modified “C” shape or other shape depending on the degree of compression or stretching.
As illustrated in
Referring to
The dimensions of channel 180, 880 will depend on numerous factors, including the nature of the solder paste, the cleanliness and size of the land or pad, and the orientation of the board during installation. Channel 180, 880 may be about 0.0015 inch wide. Further details of capillary flow in channel 180, 880 is provided in U.S. Pat. No. 5,816,868, which is incorporated into the description of the present invention in its entirety.
Referring again to
By controlling the amount of solder that flows into channel 180, the advantages of the capillary flow can be achieved without risking the penalties of excessive wicking of the solder away from the conductive land, such as a weakened bond between the electrical contact and the PCB. Moreover, stopping the flow of solder before the solder reaches the tip of electrical contact 100 avoids the risk that the solder will undesirably or prematurely bond to the through-hole of a second or upper PCB.
The second embodiment of the present invention, as described in reference to
As stated above, an additional benefit of controlling the capillary action is increased solder joint integrity between base 110 and the conductive land oh the PCB. Since part of the melted solder is pulled into channel 180, the remaining solder between the terminal and the PCB solder pad is relatively thinner than the solder thickness of a conventional solder joint. A thin layer of solder is desirable, since the solder alloy has a low yield strength and, thus, a larger amount of solder withstands less mechanical stress. The integrity of the solder joint is very important because there is no other mechanical means to fasten the terminal to the PCB board.
The preferred method of installing electrical contact 100 on a PCB employs a pick-and-place machine, several types of which are well known in the art. Commonly, pick-and-place machines use vacuum suction to pick up the selected electrical contact and place it on the PCB. Referring to
Referring to
The present invention having been described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made herein without departing from the spirit and scope of the invention as defined in the appended claims.
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