Browse Prior Art Database

Reworkable Engineering Change Pad Metallurgy

IP.com Disclosure Number: IPCOM000047195D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Kumar, AH: AUTHOR [+3]

Abstract

This process uses a relatively thin Au layer on the engineering change pad, which reduces the cost of the pad and the cost of fabrication. High density modern semiconductor packaging technology utilizes engineering change pads on the surface of multi-device substrates, as disclosed in U.S. Patent 3,968,193. These pads are conventionally formed by screening a refractory base pad, sintering, and subsequently depositing a Ni layer, followed by electroplating a heavy Au layer with a thickness in the range of 9-12 mm. These pads are costly because of the Au content and the complex steps necessary to selectively electroplate the Au. In this process a Ni layer is deposited on the screened refractory pad, as described previously, but only a thin Au layer, of a thickness on the order of 3 mm, is deposited on the Ni layer.

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Reworkable Engineering Change Pad Metallurgy

This process uses a relatively thin Au layer on the engineering change pad, which reduces the cost of the pad and the cost of fabrication. High density modern semiconductor packaging technology utilizes engineering change pads on the surface of multi-device substrates, as disclosed in U.S. Patent 3,968,193. These pads are conventionally formed by screening a refractory base pad, sintering, and subsequently depositing a Ni layer, followed by electroplating a heavy Au layer with a thickness in the range of 9-12 mm. These pads are costly because of the Au content and the complex steps necessary to selectively electroplate the Au. In this process a Ni layer is deposited on the screened refractory pad, as described previously, but only a thin Au layer, of a thickness on the order of 3 mm, is deposited on the Ni layer. Before the Au is deposited, the areas on the substrate that do not receive the Au layer, i.e., the solder pads for joining the device to the substrate, are covered with a photoresist layer. The Au is then deposited over the entire substrate surface by sputter deposition techniques to the desired thickness. Subsequently, the photoresist and overlying Au over the covered areas are removed and the substrate heated to 350OE- 400OEC for 15-20 minutes to cause limited interdiffusion between the Ni and the remaining Au. The Au is removed from the substrate by ultrasonic cleaning.

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