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Modified Single Seed Process for Copper Clad Printed Circuit Boards

IP.com Disclosure Number: IPCOM000120687D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Markovich, VR: AUTHOR [+2]

Abstract

Disclosed is a modified seeding process for electroless copper deposition which prevents blistering of electroless copper deposits by selectively seeding only non-conducting, dielectric areas of the printed circuit board (PCB) preferentially to exposed copper areas. A further benefit to the disclosed process is an increase in the lifetime of the seed bath (which is very costly) due to decreased rates of seed "dragout" or depletion.

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Modified Single Seed Process for Copper Clad Printed Circuit Boards

      Disclosed is a modified seeding process for electroless copper
deposition which prevents blistering of electroless copper deposits
by selectively seeding only non-conducting, dielectric areas of the
printed circuit board (PCB) preferentially to exposed copper areas.
A further benefit to the disclosed process is an increase in the
lifetime of the seed bath (which is very costly) due to decreased
rates of seed "dragout" or depletion.

      The primary problem with electroless copper plating on copper
foil surfaces is the tendency of the surface to blister.  This is
attributable to hydrogen evolution from the precious metal (Pd/Sn)
seed during electroless copper deposition.  The following equilibria
show that while hydrogen evolution occurs on Pd surfaces (equation
1), it does not occur on Cu surfaces (equation 2) during the
oxidation of formaldehyde (methylene glycolate) in the electroless
copper bath.
      2H2C(OH)O- + 2OH- ---   2HCO2- + 2H2 + 2e-      (1)
      H2C(OH)O-  + 2OH- ---   2HCO2- + 2H2O + 2e-     (2)

      The standard seed process consists of a preclean, conditioner
and colloidal seed.  The conditioner is a high molecular weight
cationic polyelectrolyte Reten (Reten is a registered trademark of
Hercules, Inc.) or equivalent and functions by adsorbing on a wide
variety of surfaces (e.g., epoxy, glass and copper), resulting in
uniform seed adsorpti...