Browse Prior Art Database

Etching Process for Elimination of Chrome Barrier Layer

IP.com Disclosure Number: IPCOM000112409D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Imken, RL: AUTHOR

Abstract

Disclosed is an enhancement to processing of reference plane foil used in the fabrication of a high density electronic carrier [1,2] As disclosed in [2], the creation of blind holes in the reference plane foil permits the construction of very small vias which can be differentiated in processing to produce groundplane and isolated connections. To achieve this structure, the reference plane foil construction requires an etch barrier layer to prevent etching of through holes. Typically, Copper/Invar/Copper foil is sputtered with chrome and copper, and then copper electroplated on the sputtered copper surface to create the foil structure shown in Fig. 1. After etching from the CIC side through an etch mask, blind holes such as those shown in Fig. 2 are formed.

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Etching Process for Elimination of Chrome Barrier Layer

      Disclosed is an enhancement to processing of reference plane
foil used in the fabrication of a high density electronic carrier
[1,2]  As disclosed in [2], the creation of blind holes in the
reference plane foil permits the construction of very small vias
which can be differentiated in processing to produce groundplane and
isolated connections.  To achieve this structure, the reference plane
foil construction requires an etch barrier layer to prevent etching
of through holes.  Typically, Copper/Invar/Copper foil is sputtered
with chrome and copper, and then copper electroplated on the
sputtered copper surface to create the foil structure shown in Fig.
1.  After etching from the CIC side through an etch mask, blind holes
such as those shown in Fig. 2 are formed.

      The disclosed process change utilizes a two step etching
process which eliminates the need for an additional etch barrier
layer by preferentially etching the copper and invar layers of the
CIC foil in sequential fashion.  This allows one of the copper layers
of the CIC to serve as an etch barrier.  Fig. 3 shows the result of
preferentially etching the top copper layer in the CIC structure with
an etchant which is passive toward the invar layer.  Fig. 4 shows the
result of then etching the invar layer with an etchant which is
passive toward the copper.  The resultant blind hole provides the
needed structure for further processing.

      Examples of chemical solutions which have prove...