Metal fusion bonding – Process – Plural joints
Reexamination Certificate
2001-01-03
2001-10-02
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S056300, C156S048000, C156S060000
Reexamination Certificate
active
06296173
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a technique for attaching grid array modules to a substrate utilizing independent solder material.
BACKGROUND OF THE INVENTION
One common technique in the manufacturing of populated circuit cards or circuit boards is to mechanically and electrically connect various components such as I/C chip modules to attachment pads on a substrate, such as epoxy-impregnated fiberglass or polyimide, or other rigid material by flip chip bonding. In connecting the modules, a very common way is to provide a module with what is known as a ball grid array (BGA) of solder balls or column grid array, (CGA) of solder material. The balls or columns are arranged in a pre-determined pattern corresponding to the pattern of attachment pads on the substrate known as a footprint. The module is placed on the substrate with the solder balls or columns contacting the attachment pads. Typically solder paste or the like is applied to the attachment pads on the substrate. This will provide the flux required and also cause the solder balls or columns to adhesively adhere to the attachment pads thus maintaining alignment with the solder balls or columns during heating and reflow of the solder. Heat is then applied to reflow the solder to form a mechanical and electrical connection. In production, this technique works quite well in most instances.
However, sometimes reworking of the populated substrate is required in which a module which has been attached needs to be removed and replaced with another module. This entails melting the solder, removing the module, and cleaning the pads and the substrate. Solder paste then is applied to the pads, and another module is attached by contacting the solder balls or columns thereon with the solder paste and reflowing the solder. In such case of reworking, it is difficult to provide the proper amount of solder paste on each of the pads on the substrate to form the proper bond. It is also necessary to align the solder balls or columns on the module. This is a time-consuming operation and frequently needs several iterations.
Therefore, it is a principal object of the present invention to provide an improved technique for applying the proper amount of solder paste between the attachment pads on a substrate and the solder balls or columns on a grid array contact of module for joining the module to the substrate.
SUMMARY OF THE INVENTION
A method and device for attaching a module having a ball grid array or column grid array of solder material thereon arranged in a given pattern or footprint to a substrate having an array of connector pads arranged in the same pattern is provided. A preformed alignment device is provided having an array of through holes therein aligned in the same pattern or footprint as the ball grid array or column pattern on the module and the pattern of contact pads on the substrate. The through holes in the preform are filled with a solder material which can be either a solder paste or a solid solder. The solder preferably is a lead-tin eutectic, but in any event has a melting point of less than about 240° C. The preform with the solder-filled through holes is interposed between the module and the substrate with the solder in the holes in contact with the solder balls or columns and the contact pads. Heat is applied to reflow the solder in the holes to join the module to the substrate. Depending upon the composition of the solder of the balls or columns, they might or might not melt. In the case of solid solder, thin films of flux material can be applied to opposite faces of the preform to prevent the solder from dislodging therefrom and to act as a flux when the solder is reflowed.
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Davis John Gillette
Kielbasa Joseph Michael
Dunn Tom
Hogg William N.
International Business Machines - Corporation
Stoner Kiley
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