Browse Prior Art Database

Separator Sheets Used to Prevent Interdiffusion of Copper

IP.com Disclosure Number: IPCOM000109022D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 98K

Publishing Venue

IBM

Related People

Harvey, RD: AUTHOR [+3]

Abstract

Disclosed is a method for preventing stacked thin metal foils from adhering together during stress relieving involving high temperature cycles. Metals interdiffuse at elevated temperatures, causing the thin metal foils or sheets to bond together. When the foul does not readily separate in the stack, damage from handling leads to excessive scrap.

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Separator Sheets Used to Prevent Interdiffusion of Copper

       Disclosed is a method for preventing stacked thin metal
foils from adhering together during stress relieving involving high
temperature cycles.  Metals interdiffuse at elevated temperatures,
causing the thin metal foils or sheets to bond together.  When the
foul does not readily separate in the stack, damage from handling
leads to excessive scrap.

      Under low temperature and atmospheric conditions, most metals
will not interdiffuse.  However, the stress relieving operation
requires processing at elevated temperatures in excess of 500 degrees
centigrade.  At these temperatures, sufficient energy is available to
promote substitutional diffusion.  Under normal conditions,
interdiffusion will still not occur due to the formation of oxides on
the metal surface.  Oxidation will adversely affect electrical
conductivity; therefore, stress relieving must be performed under a
hydrogen-reducing atmosphere or in a vacuum.  Both of these
atmospheres will remove any existing oxides and prevent further
oxidation but will also permit metal-to-metal contact and
interdiffusion.

      To eliminate interdiffusion between sheets, the product foils
are separated by a metal that is not soluble in the product metal
(see the figure).  The metal for the separator sheets is selected by
reviewing the phase diagrams for the metals in contact between the
product and separator sheets.  The temperature range and the
solubility limits must both be considered on the phase diagrams.  For
example, molybdenum, chromium, and titanium will not interdiffuse
with copper at the stress-relieving temperatures for the copper Invar
copper (CIC) sheets.

      Trials using molybdenum separator sheets were found to prevent
adhesion due to interdiffusion.  However, the thermal expansion
coefficient of the molybdenum was sufficiently different from the CIC
sheets that the CIC sheets wrinkled upon cooling from the stress
relieving temperature.  Other trials using CIC sheets with chemically
treated surfaces as separator sheets prevented interdiffusion and
wrinkling.  Wrinkling was avoided since the product sh...