Browse Prior Art Database

Packaging of Integrated Circuits

IP.com Disclosure Number: IPCOM000078181D
Original Publication Date: 1972-Nov-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 4 page(s) / 59K

Publishing Venue

IBM

Related People

McIntosh, CM: AUTHOR [+2]

Abstract

A package for integrated circuit chips is assembled by joining flat layers in their final shape (after firing, sintering, etc.) to each other in a special technique. The layers may carry conductor lines, may have through ("via") holes, and they may consist of a wide variety of materials. The top layer of the package has on its top surface, sites for connecting integrated circuit chips by solder reflow joining and other methods. The bottom layer may carry pads for input/output pins, edge connectors or other input/output connections.

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Packaging of Integrated Circuits

A package for integrated circuit chips is assembled by joining flat layers in their final shape (after firing, sintering, etc.) to each other in a special technique. The layers may carry conductor lines, may have through ("via") holes, and they may consist of a wide variety of materials. The top layer of the package has on its top surface, sites for connecting integrated circuit chips by solder reflow joining and other methods. The bottom layer may carry pads for input/output pins, edge connectors or other input/output connections.

A large number (up to several thousand) of reliable interconnections between two not perfectly flat layers can be made, only if the connecting material forms elevations or lumps and is initially soft or ductile to provide contact at all connection sites, when the two sheets are stacked one on top of the other. The surface of the connected sites must be wettable by the connecting material as is, or in its molten state. The connecting material must not dissolve or otherwise attack the surface material of the connection site. If a gas is released during the joining of the interconnections, or if a corrosive residue is left, the sealing of the package must be done in a separate step, after the joining and any required cleaning step.

A wide variety of materials and processes can be adapted to the above requirements. The following is an example:

Flat sheets of fired alumina of 0.006" thickness and 0.625" x 0.625" size have holes of 0.008" diameter punched into them by a laser beam, wherever via connections are required. Conductor line patterns are screen printed onto the sheets, using a paste consisting of a viscous volatile vehicle and particles of molybdenum (97% by weight) and manganese (7% by weight). A frame of
0.020" width is also screen printed on both sides at the edges of each layer (unless the package is to be sealed by glass; see below). Through holes are also filled with the paste by screen printing. The layers are then heated in forming gas at 1200 degrees C to burn off the paste vehicle, and to sinter the molybdenum and manganese particles to each other and to the surface of the ceramic layer.

The molybdenum manganese conductor lines then are plated with a thin (1,000-25,00A degrees) layer of electroless nickel by the usual techniques (activation of the molybdenum surfaces by dipping a palladium chloride solution, rinsing and dipping in the electroless plating bath.) The nickel layer makes the molybdenum wettable by most solders and brazes and acts as a diffusion barrier. Small amounts of a paste, containing a volatile viscous vehicle and particles of a solder or braze, are applied to the sites where interconnections between layers are to be made. The layers are stacked and heated to above the melting point of the solder or braze, joining the layers to each other and the wettable connection sites only.

After cooling, the spaces between the layers are cleaned from...