# US 5,350,487 A · Method of etching polyimide

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- Number: US 5,350,487 A
- Document ID: US5350487A
- Status: Granted
- Kind: A
- Application number: 08/057,005
- Filed: 1993-05-03
- Granted: 1994-09-27
- Earliest claimed: 1993-05-03
- Inventors: Thomas J. Ameen; John A. Payak; Jerome M. Cangelosi
- Web page: https://patentgrep.com/patent/US5350487A

## CPC

- H05K 3/002: {by liquid chemical etching}
- H10W 70/095: {of vias therein}
- H10W 70/688: {Flexible insulating substrates}
- H10W 99/00: Subject matter not provided for in other groups of this subclass
- H05K 1/0346: {containing N}
- H05K 2201/0154: Polyimide
- H05K 2203/0285: Using ultrasound, e.g. for cleaning, soldering or wet treatment
- H05K 2203/0793: Aqueous alkaline solution, e.g. for cleaning or etching
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

The present invention relates to methods of etching polyimide from a substrate and to the etched substrates prepared according to such methods. In one embodiment, the present invention provides a method of etching polyimide from a substrate, comprising the steps of: providing a basic bath; ultrasonically agitating said basic bath; exposing said substrate containing polyimide to said basic bath; rinsing said substrate with hot water; optionally repeating the aforementioned steps at least once; and recovering an etched substrate. In another embodiment, the present invention provides a method of etching polyimide from a substrate, comprising the steps of: providing a basic bath; exposing said substrate containing polyimide to said basic bath; rinsing said substrate with hot water; maintaining the high loading capacity of said basic bath after exposure of polyimide to said basic bath, comprising cooling at least a portion of said basic bath thereby precipitating particles and separating the particles from said basic bath prior to reuse of said basic bath; and recovering an etched substrate.

## Claims

### Claim 1

A method of etching polyimide from a substrate, comprising the steps of:
(a) providing a basic bath;
(b) exposing said substrate containing polyimide to said basic bath;
(c) rinsing said substrate with hot water;
(d) maintaining a high loading capacity for said basic bath after exposure of polyimide to said basic bath, comprising cooling at least a portion of said basic bath thereby forming a precipitate and separating said precipitate from said basic bath prior to reuse of said portion of said basic bath returning said portion of said basic bath to said basic bath to maintain the high loading capacity of said basic bath; and
(e) recovering an etched substrate.

### Claim 2 (depends on 1)

The method of claim 1 wherein steps (b) and (c) are repeated at least once.

### Claim 3 (depends on 1)

The method of claim 1 wherein step (d) is continuous.

### Claim 4 (depends on 1)

The method of claim 1 wherein said basic bath is at a temperature from about 200.degree. F. to about 230.degree. F.

### Claim 5 (depends on 1)

The method of claim 1 wherein said basic bath comprises an alkali metal hydroxide.

### Claim 6 (depends on 5)

The method of claim 5 wherein the alkali metal hydroxide in said basic bath is at a concentration from about 10 to about 12 normal.

### Claim 7 (depends on 5)

The method of claim 5 wherein the alkali metal is potassium.

### Claim 8 (depends on 1)

The method of claim 1 wherein the portion of said basic bath in step (e) is cooled to a temperature below about 140.degree. F.

### Claim 9 (depends on 1)

The method of claim 1 wherein the portion of said basic bath in step (e) is cooled to a temperature below about 120.degree. F.

### Claim 10 (depends on 1)

The method of claim 1 wherein the particles are separated from said basic bath with a filter.

### Claim 11 (depends on 1)

The method of claim 1 wherein said hot water in step (c) is at a temperature above about 165.degree. F.

### Claim 12 (depends on 1)

The method of claim 1 wherein the etched substrate of step (e) is a hybrid circuit.

### Claim 13 (depends on 1)

The method of claim 1 wherein the etched substrate of step (e) is a printed circuit board.

### Claim 14 (depends on 1)

The method of claim 1 wherein the etched substrate of step (e) is a tape automated bonding structure.

### Claim 15 (depends on 1)

The method of claim 1 wherein said basic bath is ultrasonically agitated.