Browse Prior Art Database

Structure and Method for Pin Braze Pads

IP.com Disclosure Number: IPCOM000107732D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 92K

Publishing Venue

IBM

Related People

Ahmed, S: AUTHOR [+4]

Abstract

Disclosed is a structure for I/O pads on ceramic or polyimide surfaces of substrates to which I/O pins can be joined with suitable brazing alloys such as gold-tin, lead-tin, tin-antimony or copper-silver. The intent of the proposed structure is the prevention of galvanic corrosion of the pin pads in the presence of condensed moisture during service.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Structure and Method for Pin Braze Pads

       Disclosed is a structure for I/O pads on ceramic or
polyimide surfaces of substrates to which I/O pins can be joined with
suitable brazing alloys such as gold-tin, lead-tin, tin-antimony or
copper-silver.  The intent of the proposed structure is the
prevention of galvanic corrosion of the pin pads in the presence of
condensed moisture during service.

      I/O pad structures are traditionally fabricated by either thick
film or thin film methods and comprise a sandwich structure of
dissimilar metals with a noble metal (e.g., gold) top layer and base
metal(s) such as Ni-Mo, Ti-Cu-Cr, etc., comprising the bottom layers.
The gold surface of the pads facilitates good wetting of the brazing
alloy to the pad while the base metal layers serve as diffusion
barriers or as adhesion layers to the substrate surface.  In such
struc tures, the base metals are exposed at the edges of the pads as
well as at other defect locations.  In the presence of condensed
moisture, the gold surface forms corrosion causing galvanic cells
with the base metals which could lead to rapid, catastrophic failure
of the pin pads.

      In the proposed structure, the pin pads are overlaid with a
protective polymeric coating with circular openings in the coating
provided over the middle portions of the pin pad to accommodate the
pin head and the braze material.  The polymeric material should have
low permeability to moisture, good thermal stability and
compatibility with other substrate processing and use conditions.
Polyimides, and in particular, BPDA-PDA type such as PI-5878*, are
well suited for this application.  After the pins are properly brazed
to the pads, the braze material and the pin head completely fill the
opening, butting against the sidewall of the opening.  Also...