Background
This invention relates to a socket to couple an integrated circut
having pins to a printed circuit board, and generally to electrical couplings that
mechanically couple one electrical component to another in a fashion that
heat expansion of one component affects the other component.
Many electrical connectors physically and electrically connect one electronic dev ce
to another. For example, a variety of sockets may be used to connect one packaged
integrated circuit electronic device to a printed circuit board. Thus, the connector or socket
physically connects the two elements together and provides for electrical communication
between the two devices.
In some cases, when the devices are exposed to high temperatures, failure may occur
due to the differential thermal expansion of the physically connected devices. If one device
expands more than the other, and the devices have a physical connection between them, one
of the devices may fail mechanically either at the physical connection or in portions
mechanically coupled to the physical connection.
One example of a situation where such failures may occur is in connection with
surface mount packages. Surface mount packages connect to printed circuit boards by heat
bonding or soldering the package to the board. Instead of using electrical pins and plugs (like
conventional electrical outlets utilize), heat bonded or soldered electrical connections cai be
done quickly and in an automated fashion.
However, when a connector is exposed to heat, it normally expands. When it is n
physical contact with one or more other devices, and those devices have different coefficients
of thermal expansion, failure of the connection between the components may result. In nan^
cases, the properties of a material that make it a good connector material may make the
material a poor material for other applications. Therefore, when materials with differen:
coefficients of thermal expansion are physically connected together, and exposed to heat, the
possibility of mechanical failure exists.
Thus, there is a continuing need for a way to reduce differential heat expansion
between electrical components.
Summary
In accordance with one embodiment, an electrical coupling includes
a body and a structure coupled to the body. The structure limits the thermal
expansion of the body.
Accordingly, the present invention provides a socket to couple an
integrated circuit having pins to a printed circuit board comprising : a body
having an upper side with openings to receive the pins of said integrated
circuit and a lower side having surface mount connections to surface mount
said body to said printed circuit board, said body being formed of an electrical
insulator; an array of conductive wires extending through said body includin g
a first set of wires extending in a first direction and a second set of wires
extending substantially transversely thereto, each of said wires in each seit
being spaced sufficiently to allow said openings to extend between adjacent
wires in each set, such that the pins of the integrated circuit may be plugged
int said openings in said socket ; and the coefficient of thermal expansion of
said wires matching the coefficient of thermal expansion of said printed circuit
board.
Brief Description of the Drawings
Figure 1 is an enlarged cross-sectional view of a socket accordance
with one embodiment of the invention ;
Figure 2 is a side elevational view of the socket shown in Figure 1 i i
position between an integrated circuit package and a printed circuit board ;
Figure 3 is a top plan view of the embodiment shown in Figure 2 ; and
Figure 4 is a cross-sectional taken generally along the line 4-4 h
Figure 2.
Detailed Description
Referring to Figure 1, an electrical connector 10 may be utilized to couple one or
more electrical components or devices together. The connector 10 provides both an electrical
and a mechanical coupling between the components. In one embodiment, the connector 10
may be a surface mount socket which allows one electrical component to be coupled by
surface mounting techniques to another electrical component. The connector 10 may ir elude
a body 14 which, in one embodiment, may be formed of molded plastic. A plurality of
surface mount contacts 12 which, in one embodiment of the invention, may be solder balls
for implementing a ball grid array socket are secured to the connector 10. While the
connector 10 may use a variety of other electrical connection techniques, surface mount
connections are desirable in one embodiment.
Extending through the body 14 is a thermal expansion controlling structure 16. The
structure 16 limits the thermal expansion of the body 14. Thus, in general, the structure 16
has a lower coefficient of thermal expansion than the body 14 and thereby limits its thermal
expansion if it is bonded to the structure 16 and if the structure 16 has a stiffness greater than
or equal to that of the body 14. In one embodiment of the invention, the structure 16 may be
formed of a plurality of discrete elements 16 which may be connected to the body 14 by a
variety of conventional techniques, including overmolding the structure 16 into the bod> 14.
The components forming the structure 16 maybe filamentary. Corresponding
elements of the structure 16 may extend in other directions to provide thermal stability in
those directions as well. For example, a criss-cross pattern of filamentary elemenis may form
the structure 16, limiting thermal expansion in at least two directions.
In one embodiment of the invention, the structure 16 may be formed of metallic ! |
filaments. For example, one advantageous filament material is copper. In some crises, -Ji
copper dominates the thermal characteristics of electronic devices to which the connector 10
may be coupled. For example, printed circuit boards (PCBs) have mechanical chaiacteristics,
which in some cases, may be strongly influenced by their copper conductors which traverse
the PCB. Thus, the thermal characteristics (and particularly the thermal expansion
characteristics) of the connector 10 may be matched to those of devices to which the
connector 10 may be mechanically secured. Where those devices are characterized by the
thermal characteristics of copper, making the structure 16 of copper wire may be
advantageous.
While the structure 16 is illustrated as being a plurality of copper wires, other metals
may be used as well. In addition, fibers may be used which have desirable thermal ;xpansion
characteristics. In general, any structure 16 which matches or causes the aggregate
characteristics to match the thermal expansion characteristics of a device to which the
connector 10 is coupled may provide enhanced thermal characteristics.
Turning now to Figure 2, the connector 10 may couple a pair of electronic devices 18
and 20. In the embodiment illustrated in Figure 2, the electronic device 18 may be a
packaged integrated circuit device. The electronic device 20 may be a printed circuit board.
Thus, if the connector 10 is a surface mount socket, the contacts 12 may form a surface
mount connection to the electronic device 20 (for example, a PCB). However, the connection!
between the devices 10 and 18 may take a variety of other forms as well.
In one illustrative embodiment, a pin and hole connection or pin grid array (I GA)
technique may be used to connect the devices 10 and 18 while a surface mount technique
may be used to connect the devices 10 and 20. However, the scope of the present invention is
in no way limited to the particular connection technique utilized.
Referring now to Figure 3, a surface mount connection may be achieved between the
connector 10 and the electronic device 20 which may be a PCB. With the electronic device
18 removed and in an embodiment in which a pin and hole connection technique is utilized,
as shown in Figure 4, the connector 10 may include a plurality of holes 22 which receive pins
on the electronic device 18 and provide both an electrical and a mechanical connection. The
structure 16 in the embodiment illustrated in Figure 4 is formed of a transverse network of
filaments 16a and 16b. The filaments may be formed in the connector 10, extending through
the region between adjacent rows and columns of holes 22. Thus, the structure 16 may
achieve desirable thermal characteristics without adversely affecting the electrical
characteristics of the connector 10. In some embodiments, by making the structure 16 oui of
an insulator, the possibility of inadvertent shorts may be decreased.
Referring again to Figure 2, if the thermal characteristics of the electronic device 20
are such that the device experiences less thermal expansion than the connector 10, men
mechanical failure could occur in the connection between the two devices. This is because
the connector 10 may expand more or less than the device 20. For example, in some cases, it
may be desirable to form the connector 10 out of a liquid crystal polymer (LCP).
For example, a liquid crystal polymer may have desirable molding characteristics
which make it a desirable candidate for forming a connector 10 which acts as a socket for
another integrated circuit device. However, LCPs have coefficients of thermal expansion
which may be significantly greater than those of conventional PCBs formed of common PCB
materials such as FR4. Thus, when the devices are exposed to heat, differential th