Browse Prior Art Database

MC Substrate Chrome Artwork Mask

IP.com Disclosure Number: IPCOM000053075D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Athawes, WH: AUTHOR [+2]

Abstract

Metallized ceramic (MC) substrate surface metallurgy is made up of three layers of metal Cr, Cu and Cr. Circuitry is formed by a triple etch process. A photoresist mask is used to form the circuit lines and, after developing the resist, the balance of the unprotected metallurgy is removed by the triple etch process. In the chip attach area (solder pads), which require a solder connection, a chrome mask is used for the next photoetch process. This process removes the Cr and exposes the Cu in the shape of the pad or finger for subsequent tinning.

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MC Substrate Chrome Artwork Mask

Metallized ceramic (MC) substrate surface metallurgy is made up of three layers of metal Cr, Cu and Cr. Circuitry is formed by a triple etch process. A photoresist mask is used to form the circuit lines and, after developing the resist, the balance of the unprotected metallurgy is removed by the triple etch process. In the chip attach area (solder pads), which require a solder connection, a chrome mask is used for the next photoetch process. This process removes the Cr and exposes the Cu in the shape of the pad or finger for subsequent tinning.

Normal pads by design are circular in shape. However, pads contained in a voltage bus are determined by the shape and size of the select land. This select size, or chrome mask, for the voltage bus is .0024 inch larger than the normal pad. A larger diameter pad is required to allow for artwork registration for a second pass chrome etch.

The previous design practice was to use a .0024-inch oversize select land on circuit lines which require for electrical reasons a line size at least the equivalent of a pad diameter. Since this pad is contained in the electrode passing through a pad location, the select size determines the size of the finger pad. For example, a chip requires a .005-inch diameter pad on the substrate. The select size required is a diameter of .0074 inch, but the tolerance on the pad size is + .001 inch. Therefore, of necessity, a pad was designed which is .0014 inch oversize a...