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Process for Providing Fine Line Structures on Printed Circuit Boards

IP.com Disclosure Number: IPCOM000110399D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Johann, K: AUTHOR [+3]

Abstract

Fine-line copper structures on printed circuit boards are provided either by electroless plating, using a pattern plating process, or by electroplating, followed by subtractive etching.

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This is the abbreviated version, containing approximately 83% of the total text.

Process for Providing Fine Line Structures on Printed Circuit Boards

       Fine-line copper structures on printed circuit boards are
provided either by electroless plating, using a pattern plating
process, or by electroplating, followed by subtractive etching.

      In the latter process, through-holes have often been protected
by resist tenting during etching.  As the increase in the integration
density of semiconductor components leads to higher input/output
densities as well as to a reduced thickness and spacing of the
fine-line structures, the copper lands around the through-holes
become too small to allow photofoil protection.

      A new process is described below which overcomes these
shortcomings by combining direct copper plating with a positive
photoresist.

      Proposed process:
      1.  Conventional process with conventional substrate materials
1 (e.g., FR4/glass without a sacrificial foil) until the
through-holes have been drilled (Fig. 1).
      2.  Activation of surface and through-holes (e.g., by a gas,
such as SO3, and chemical nickel deposition) (Fig. 1).
      3.  Deposition of a substantially homogeneous copper layer 2
(10 - 20 mm) on the surface and in the through-holes (Fig. 2).
      4.  Deposition of positive resist 3 (e.g., in an
electrophoretic bath) (about 10 mm), followed by a smoothing step
(Fig. 3).
      5.  Definition of the circuit lines in resist 3 by conventional
photolithographic steps...