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Seal Band Pretinning and Cap Sealing Without Chemical Flux

IP.com Disclosure Number: IPCOM000042184D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Ahmad, N: AUTHOR [+5]

Abstract

Fluxless pretinning and sealing of hermetic caps to substrate-carrying chips are performed in a clean hydrogen gas atmosphere at low temperatures of 220-250ŒC using lead preforms encapsulated with Sn, instead of eutectic solder. Referring to the drawing which is an exploded sectional view, a solder preform 12 is joined to a seal band pad 11 on the periphery of a substrate 10 carrying chips 15 to be enclosed hermetically by cap 13. The preform 12 is joined to the pad either during the pin-brazing operation, or thereafter, in an atmosphere of clean hydrogen gas 20. Gas 20 is supplied to the confined space 21 within a belt furnace or a chamber 19 housing the substrate 10 during the joining operation.

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Seal Band Pretinning and Cap Sealing Without Chemical Flux

Fluxless pretinning and sealing of hermetic caps to substrate-carrying chips are performed in a clean hydrogen gas atmosphere at low temperatures of 220- 250OEC using lead preforms encapsulated with Sn, instead of eutectic solder. Referring to the drawing which is an exploded sectional view, a solder preform 12 is joined to a seal band pad 11 on the periphery of a substrate 10 carrying chips 15 to be enclosed hermetically by cap 13. The preform 12 is joined to the pad either during the pin-brazing operation, or thereafter, in an atmosphere of clean hydrogen gas 20. Gas 20 is supplied to the confined space 21 within a belt furnace or a chamber 19 housing the substrate 10 during the joining operation. Prior to the joining of the preform 12 to the pad 11, the substrate 10 has been cleaned, preferably by mechanical scrubbing, to remove boron and nitrogen compunds. After chips 15 have been joined to the substrate 10 by the C-4 solder ball bonding process, the KOVAR* cap 13 is bonded to the pretinned seal band 11 at 220OEC in the clean hydrogen gas-containing atmosphere. The preforms 12 employed are clad with a surface of Sn to reduce the Pb at the surface to improve subsequent capping. The preforms are made of a core 17 of PbSn alloy clad with a thin film 18 (about 50 micrometers thick) of Sn top and bottom. Using the clean hydrogen gas, which has excellent capacity as a reducing agent, permits pretinning at 2...