Browse Prior Art Database

High-Density Electrical Substrate Manufacturing Process

IP.com Disclosure Number: IPCOM000122181D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 4 page(s) / 119K

Publishing Venue

IBM

Related People

Frankeny, RF: AUTHOR [+3]

Abstract

A process is described for producing a thin 2S/1P circuit card (2 signal layers/1 ground plane) with isolated via holes and groundplane contacts. The process disclosed particularly relates to the technique for producing isolated vias.

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

High-Density Electrical Substrate Manufacturing Process

      A process is described for producing a thin 2S/1P circuit
card (2 signal layers/1 ground plane) with isolated via holes and
groundplane contacts.  The process disclosed particularly relates to
the technique for producing isolated vias.

      The starting point for such a construction is a
dielectric/metal/ dielectric laminate.  For the purpose of this
process description, the metal core is represented as copper-clad
Invar or CIC.  Alternatively, other metal core materials may be used.

      The dielectric used in this process description is epoxy-coated
polyimide film (represented as DIE).  However, the process described
is not wholly dependent on the dielectric used in such laminates
structures.  Such a starting material is shown in Figure 1.  Holes
are then punched, mechanically drilled, or laser drilled in this
laminate which will serve as vias for electronic interconnects
between sides of the card as shown in Figure 2.

      In order to create a reservoir for subsequent filling with an
electrodeposited dielectric, the laminate shown in Figure 2 is etched
with a chemical solution to remove a small amount of the metal core
material in each via as shown in Figure 3.

      Any of a number of chemical etchants may be used depending on
the core metal to be removed.  For CIC laminates, solutions of
hydrochloric acid and cupric chloride or ferric chloride are
effective, as well as certain persulfate or peroxide/sulfuric acid
solutions. Etching rate can be regulated through adjustment of
solution concentrations, temperature, and agitation.

      At this point, the exposed metal in the laminate core may be
electroplated if desired to provide a metal diffusion barrier between
the core metal and the dielectric which will be used to fill the
reservoir.

      Via isolation is accomplished through use of an electrodeposit
(ED) or electrophoretic dielectric coating. The characteristics of
such a coating are that it deposits only where there is an electrical
potential and that it is self-limiting in thickness.  For via
isolation, such characteristics are ideal in that it is desirable to
deposit dielectric only on the metal core surfaces exposed by the
hole- producing operation and to deposit such dielectric at a
controlled thickness.

      To produce the isolated vias, electrical contact is established
with the core metal and the part is immersed in a bath of the ED
coating.  A voltage is applied between the part and elec...