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Metallurgy System for Pin Attachment to MLC

IP.com Disclosure Number: IPCOM000041281D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Ainslie, NG: AUTHOR [+3]

Abstract

A given number of semiconductor chip packaging approaches have utilized MLC (multilayer ceramic) technology. Conventionally, input/output (I/O) pins are brazed on the bottom surface for I/O's to a printed circuit (PC) board. The pins can be brazed with 80% Au/20% Sn alloy which is very expensive or with Cu/Ag eutectic alloy which must be brazed at temperatures of 900ŒC or higher. This alloy (Cu/Ag eutectic) is also known to be susceptible to Ag migration. A new cost-effective metallurgy system for pin attachment for low cost MLC is described here. Fig. 1 shows a Cu solder pin system for MLC. The Cu (copper) is screened or plated over a Mo (molybdenum) pad. A Au (gold) flash of approximately 10-15 u" is plated over the copper for corrosion protection.

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Metallurgy System for Pin Attachment to MLC

A given number of semiconductor chip packaging approaches have utilized MLC (multilayer ceramic) technology. Conventionally, input/output (I/O) pins are brazed on the bottom surface for I/O's to a printed circuit (PC) board. The pins can be brazed with 80% Au/20% Sn alloy which is very expensive or with Cu/Ag eutectic alloy which must be brazed at temperatures of 900OEC or higher. This alloy (Cu/Ag eutectic) is also known to be susceptible to Ag migration. A new cost-effective metallurgy system for pin attachment for low cost MLC is described here. Fig. 1 shows a Cu solder pin system for MLC. The Cu (copper) is screened or plated over a Mo (molybdenum) pad. A Au (gold) flash of approximately 10-15 u" is plated over the copper for corrosion protection. The solder, Pb/Sn (40% Pb/60% Sn), is screened similar to the way 80% Au/20% Sn is normally screened on MLC modules. Preforms of solder may also be utilized. In the Au/Cu/Mo system the Cu will react with the solder to form a higher (than solder) melting alloy. Avoidance of Ni is necessary due to the formation of very brittle Niz Snw intermetallic. This alloy system will be capable of handling solder reflow and wave soldering to printed circuit cards. A protective coating for corrosion, migration and also strength enhancement is possible. This coating may consist of a plastic or low melting glass. The Cu reacts with the Pb/Sn solder as follows: Cu + Sn T Cux Sny (high melti...