Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
1999-12-13
2004-12-14
Nguyen, Truc T. T. (Department: 2833)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
C439S083000, C439S330000, C439S457000, C439S525000, C439S476100
Reexamination Certificate
active
06830462
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to an electrical connector and, more particularly, to a ball grid array (BGA) connector having a housing that can accommodate thermal cycling and circuit substrate or circuit board deformation or warpage characteristics.
BACKGROUND OF THE INVENTION
The drive to reduce the size of electronic equipment, particularly personal portable devices, and to add additional functions to such equipment, has resulted in an ongoing drive for miniaturization of all components, especially electrical connectors. Efforts to miniaturize connectors have included reducing the pitch between terminals in single or double row linear connectors, so that a relatively high number of I/O or other lines can be interconnected by connectors that fit within tightly circumscribed areas on the circuit substrates allotted for receiving connectors.
The drive for miniaturization has also been accompanied by a shift in preference to surface mount techniques (SMT) for mounting components on circuit boards. The confluence of the increasing use of SMT and the required fine pitch of linear connectors has resulted in approaching the limits of SMT for high volume, low cost operations. Reducing the pitch of the terminals increases the risk of bridging adjacent solder pads or terminals during reflow of solder paste. To satisfy the need for increased I/O density, array connectors have been proposed. Such connectors have a two dimensional array of terminals mounted on an insulative substrate and can provide increased density. However, these connectors present certain difficulties with respect to attachment to the circuit substrate by SMT techniques because the surface mount tails of most, if not all, of the terminals must be beneath the connector body. As a result, the mounting techniques used must be highly reliable because it is difficult to visually inspect the solder connections to repair them if faulty.
In the mounting of an integrated circuit (IC) on a plastic or ceramic substrate, the use of a ball grid array (BGA) and other similar packages has become common. In a BGA package, spherical solder balls attached to the IC package are positioned on electrical contact pads of a circuit substrate to which a layer of solder paste has been applied, typically by use of a screen or mask. The unit is then heated to a temperature at which the solder paste and at least a portion or all of the solder ball melt and fuse to an underlying conductive pad formed on the circuit substrate. The IC is thereby connected to the substrate without need of external leads on the IC.
While the use of BGA and similar systems in connecting an IC to a substrate has many advantages, a corresponding means for mounting an electrical connector or similar component on a printed wiring board (PWB) or other substrate has yet to be developed. It is important for most situations that the substrate-engaging surfaces of the solder balls are coplanar to form a substantially flat mounting interface, so that in the final application the balls will reflow and solder evenly to a planar printed circuit board substrate. Any significant differences in solder coplanarity on a given substrate can cause poor soldering performance when the connector is reflowed onto a printed circuit board.
Another problem presented in soldering connectors to a substrate is that connectors often have insulative housings that have relatively complex shapes, for example, ones having numerous cavities. Residual stresses in such housings can result from the molding process, from the buildup of stress as a result of contact insertion, or a combination of both. These housings may become warped or twisted either initially or upon heating to temperatures necessary in SMT processes, such as temperatures necessary to reflow the solder balls. Such warping or twisting of the housing can cause a mismatch between the connector assembly and the PWB, resulting in unreliable soldering because the surface mounting elements, such as solder balls, are not sufficiently in contact with the solder paste or close to the PWB prior to soldering.
One drawback of BGA packages is that the coefficient of thermal expansion (CTE) of the material used in the connector housing is very different from the CTE of the PWB. The different CTEs affects the performance and reliability of the electrical connections by causing stress on solder joints and wire bonds, thereby leading to deformation and warpage of the PWBs or IC chips and chip carriers that are to be connected to the package. The greater the differential displacements created by CTE mismatch during thermal changes, the greater concern for the electrical integrity of the system.
BGA packages are subjected to high temperatures during processing, testing and soldering. Accordingly, it is important that the package be able to withstand high temperature variations without inhibiting or degrading a reliable electrical connection. A need, therefore, exists for reliably and efficiently mounting high density electrical connectors on substrates by surface mounting techniques.
SUMMARY OF THE INVENTION
The present invention is directed to a connector for reducing the effects of the differential in the coefficient of thermal expansion of the connectors and the underlying circuit board. The connector in accordance with the present invention can be mounted on a known circuit board or the like and could receive an electrical component or a mating connector. The present invention preferably uses ball grid array (BGA) surface mount technology.
Electrical connectors according to the present invention provide high I/O density and reliable attachment to circuit substrates by SMT techniques. These connectors exhibit high coplanarity along the mounting interface. Coplanarity of the surface mounting interface of the connector is maintained by providing an insulative connector housing in which stress buildup is avoided. The present invention accommodates the deformation or warpage caused by thermal cycling that would otherwise cause the stress buildup. The connector avoids stress buildup by providing a connector housing that incorporates compliant sections corresponding to the areas where the greatest deformation in the connector is expected. According to this aspect of the invention, the housing has notches or slots at locations furthest from the neutral point (NP) of the connector (i.e., around the corners). By means of this arrangement, stress buildup is avoided, so as to minimize warping and twisting of the housing.
Electrical connectors of the present invention are ones in which one or more terminals are connectable by a fusible electrically conductive material to a substrate. This fusible electrically conductive material is a solder mass, preferably comprising a solder ball that can be reflowed to provide the primary electrical current path between the terminal and a circuit substrate.
The foregoing and other aspects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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FCI Americas Technology Inc.
Nguyen Truc T. T.
Woodcock & Washburn LLP
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