Patent Application
20060057897
Generally, the invention relates to electrical connectors. More particularly, the invention relates to ball grid array (“BGA”) connectors that allow for relative movement between the connector housing and lead frame assemblies contained within the housing, even after the connector is connected to a substrate such as a printed circuit board.
Printed circuit boards (“PCBs”) are commonly used to mount electronic components and to provide electrical interconnections between those components and components external to the PCB. One problem with conventional PCBs is flexing. PCBs flex under the weight of attached electrical components when subject to vibrations, assembly, and handling loads. Ultimately, the PCB with attached electrical components are assembled in a chassis, such as in a computer system. Handling and transit of the chassis assembly can cause PCB flexing under the weight of the components.
Additionally, electrical components are becoming increasingly heavy. Electrical components that are attached to the PCB include, among others, the heat sink and fan assembly which is attached to the central processing unit (CPU). These assemblies often are upwards of a pound or more in weight, putting an increased burden on the PCB.
In an effort to increase electrical component density on the PCB, electrical components may be attached to the PCB using BGA technology. A BGA microprocessor, for example, makes its electrical connection via a solder ball on each connector of the BGA of the electrical microprocessor and the electrical contacts on the surface of the PCB. BGA components require a rigid substrate to which they are attached. In effect, these BGA components are soldered directly to the circuit board without intervening contacts or wires. BGA components commonly incorporate tens or hundreds of solder connections between the ball-grid package and the circuit board. Any appreciable circuit board flexing may cause the solder connections to shear, compress, fatigue, and subsequently break.
There is a significant need in the art to provide a BGA connector that has the ability to flex under various loads to minimize stresses imposed on the solder ball connections.
An electrical connector according to the invention may include a leadframe assembly and a connector housing. The leadframe assembly may include a lead frame and an electrical contact extending at least partially through the lead frame. The housing contains the leadframe assembly in one or more directions and also allows the leadframe assembly to move relative to the housing in one or more directions. The housing and leadframe assemblies may move relative to one another even after the connector is mounted to a printed circuit board. An electrical connector according to the invention may be used in back panel applications, for example.
The leadframe assembly may include a tab extending therefrom via which the leadframe is contained by the housing. The tab may extend from the lead frame, or from the electrical contact. The connector housing may include a tab receptacle that defines an opening into which the tab extends. To allow for movement of the tab within the opening, the opening may be larger than the cross-sectional area of the tab. The tab receptacle may be resilient to facilitate insertion of the leadframe assembly into the housing.
The connector may also include a contact receiving wafer having an aperture that extends therethrough. A terminal portion of the contact extends at least partially into the aperture. The aperture allows the terminal portion of the contact to move in one or more directions, and also contains the terminal portion in each direction.
A solder ball may be connected to the terminal portion of the contact. The solder ball may have a diameter that is larger than the width of the aperture. Thus, the wafer may be contained between the solder ball and the lead frame, and movement of the contact into the aperture may be restricted.
The contacts 211 may be dual beam receptacle contacts, for example. Such a dual beam receptacle contact may be adapted to receive a complementary beam contact during mating with an electrical device. As shown in
An IMLA 115 may also include one or more containment tabs 204. In an example embodiment, a respective tab 204 may be disposed on each end of the IMLA 115. For example, the contact 211 at the end of the IMLA 115 may have a tab 204 that extends beyond a face of the overmolded housing 215. In such an embodiment, the tab 204 may be made of the same material as the contact 211 (e.g., electrically conductive material). Alternatively, the tabs 204 may extend from the overmolded housing 215, and may be attached to the overmolded housing 215 or integrally formed with the overmolded housing 215. In such an embodiment, the tab 204 may be made of the same material as the overmolded housing 215 (e.g., electrically insulating material).
As best seen in
To allow movement of the IMLAs 115 in the Y-direction, the lead frames 215 need not extend all the way to the inner surface 305 of the tab receptacle 302. When an end of the overmolded housing 215 meets the inner surface 305 of the associated tab receptacle 302, the tab receptacle 302 prevents the overmolded housing 215 from moving any further in the Y-direction. The distance the IMLA 115 may move relative to the housing 101 in the Y-direction may be controlled by regulating the distance between the end of the overmolded housing 215 and the inner surface 305 of the housing 101. Thus, the tab receptacles 302 may contain the IMLAs 115 in the Y-direction within the housing 101, while allowing movement of the IMLAs in the Y-direction.
To allow movement of the IMLA 115 relative to the housing 101 in the X- and Z-directions, the receptacle openings 322 may be made slightly larger than the cross-section (in the X-Z plane) of the tabs 204 that the openings 322 are adapted to receive. When the tab 204 meets one of the faces 332, the face 332 prevents the tab 204 (and, therefore, the overmolded housing 215) from moving any farther in whichever direction the IMLA 115 is moving (e.g., the X- or Z-direction). The relative difference in size between the receptacle opening 322 and the cross-section of the tab 204 determines the amount the IMLA 115 may move relative to the housing 101 in the X- and Z-directions. Thus, the tab receptacles 302 may contain the IMLAs 115 in the X- and Z-directions, while allowing movement of the IMLAs in the X-Z plane.
In an example embodiment of the invention, the tabs 204 may have dimensions of about 0.20 mm in the X-direction and about 1.30 mm in the Z-direction. The receptacle openings 322 may have dimensions of about 0.23 mm in the X-direction and about 1.45 mm in the Z-direction. The distance between each end of the overmolded housing 215 and the respective inner surface 305 of the housing 101 may be about 0.3 mm.
As shown in
According to an aspect of the invention, the connector 100 may include a contact receiving substrate or wafer 107 that contains the terminal ends of the contacts, while allowing for movement of the terminal ends. The wafer 107 may be made of an electrically insulating material, such as a plastic, for example.
As best seen in
As shown, the apertures 456 may be generally square, though it should be understood that the apertures 456 may be defined to have any desired shape. In an example embodiment of the invention, the terminal portions 216 of the contacts 211 may have dimensions of about 0.2 mm by about 0.3 mm. The apertures 456 may have dimensions of about 0.6 mm by about 0.6 mm.
To manufacture the connector 100, the IMLAs 115 may be inserted and latched into the housing 101 as described above. The wafer 107 may then be set on the ball-side faces 229 of the overmolded housing 215, with the terminal portions 216 of the contacts 211 extending into the apertures 456. Respective solder balls 120 may then be formed on the terminal portions 216 of the contacts 211 using known techniques.
To form a solder ball on a terminal end of the contact, solder paste may be deposited into the aperture 456 into which the terminal end of the contact extends. A solder ball may be pressed into the solder paste against the surface of the wafer 107. To prevent the contact from being pulled into the housing through the aperture, the diameter of the solder ball may be greater than the width of the aperture. The connector assembly (which includes at least the contact in combination with the housing and the wafer) may be heated to a temperature that is greater than the liquidous temperature of the solder. This causes the solder to reflow, form a generally spherically shaped solder mass on the contact tail, and metallurgically bond the solder ball to the contact.
Preferably, the aperture 456 has a width that is less than the diameter of the solder ball so that the solder ball prevents the contact from being able to be pulled into the housing. Similarly, the diameter of the solder ball being greater than the width of the aperture enables the wafer 107 to be contained between the solder balls 120 and the overmolded housings of the lead frame assemblies.
As shown in
The IMLAs may be free to move with respect to the housing 115, as described above, prior to reflow of the solder balls. This movement, or float, allows the IMLAs to self-align during reflow of the solder balls. For example, when the solder balls liquefy during reflow, surface tension in the liquid solder produces a self-aligning effect. The present invention allows the IMLAs to benefit from the self-aligning properties of the liquid solder balls. Once reflow is complete, the contacts, housing, and solder posts are fixed with respect to the PCB. The affixed solder posts help prevent forces acting on the housing, in a direction parallel to the PCB, to transmit to the solder balls.
It is to be understood that the foregoing illustrative embodiments have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the invention. Words which have been used herein are words of description and illustration, rather than words of limitation. Further, although the invention has been described herein with reference to particular structure, materials and/or embodiments, the invention is not intended to be limited to the particulars disclosed herein. Rather, the invention extends to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.
The subject matter disclosed and claimed herein is related to the subject matter disclosed and claimed in co-pending U.S. patent application Ser. No. 10/294,966, filed Nov. 14, 2002, which is a continuation-in-part of U.S. patent applications Ser. Nos. 09/990,794, filed Nov. 14, 2001, now U.S. Pat. No. 6,692,272, and Ser. No. 10/155,786, filed May 24, 2002, now U.S. Pat. No. 6,652,318. The subject matter disclosed and claimed herein is related to the subject matter disclosed and claimed in U.S. patent applications Nos. [TBSL: attorney docket FCI-2835/2757B], filed on even date herewith, and Ser. No. 10/634,547, filed Aug. 5, 2003. The contents of each of the above-referenced U.S. patents and patent applications is herein incorporated by reference in its entirety.
