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COPPER LAMINATE EDGE ISOLATION METHOD

IP.com Disclosure Number: IPCOM000030315D
Publication Date: 2004-Aug-05
Document File: 4 page(s) / 215K

Publishing Venue

The IP.com Prior Art Database

Abstract

This invention relates to the electrical isolation of the edges of a panel of laminate material. Exemplary panels are capacitive materials that are typically 2" X 2" square, and consist of three (3) layers as follows: Two copper foils, such as 36 micron thick rolled annealed (RA) copper foils, are on the outsides, and one dielectric, e.g., at a thickness of about 16 micron, is in the middle. In the process of shearing the material, the copper foil tends to smear along the cut edges of the panel, thus electrically joining the outer two layers of copper foil. In order to electrically test the panel (as may be dictated by customer requirements), it is necessary to electrically isolate the two copper surfaces from each other. Thus far, no practical way has been discovered to electrically isolate the Cu surfaces at the edges of the laminate material. Described herein is a method to perform the isolation, along with some hypotheses on how to optimally perform the method in a production environment. The basic method that has proven to work experimentally is chemical etching.

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This invention relates to the electrical isolation of the edges of a panel of laminate material. Exemplary panels are capacitive materials that are typically 2” X 2“ square, and consist of three (3) layers as follows: Two copper foils, such as 36 micron thick rolled annealed (RA) copper foils, are on the outsides, and one dielectric, e.g., at a thickness of about 16 micron, is in the middle. 

 

In the process of shearing the material, the copper foil tends to smear along the cut edges of the panel, thus electrically joining the outer two layers of copper foil. In order to electrically test the panel (as may be dictated by customer requirements), it is necessary to electrically isolate the two copper surfaces from each other.

 

Thus far, no practical way has been discovered to electrically isolate the Cu surfaces at the edges of the laminate material. Described herein is a method to perform the isolation, along with some hypotheses on how to optimally perform the method in a production environment.

 

The basic method that has proven to work experimentally is chemical etching. The experiments performed to date have been with Perma-Etch®, which is a solution composed of DI water, 180 grams/liter of Sulfuric Acid, and 20 grams/liter of Peroxide. In all cases, the Perma-Etch® was heated to approximately 105 degrees Fahrenheit.

 

Photo 1 is a picture of the edge of a sample of laminate material, before the edges have been isolated:

 

 

 

Photo 1: Edge of Single Sheet of laminate as sheared.

In the first experiment, a single sheet of laminate measuring approximately 1” square was lowered into a beaker of etchant, such that 1/8” of the edge was fully immersed. This experiment was repeated for etching times of 1, 2, 3 & 4 minutes. The results were that 1 minute was insufficient for the edge isolation to occur, and all other times were sufficient. Photo 2 is a picture of the edge of a sample of laminate material, after the edges have been isolated by 2 minutes of etching: 

 

 

 

 

Photo 2: Edge of Single Sheet of Laminate, 2 minutes of etching

 

 

The experiments were repeated for a stack of thirty-six (36) single sheets of laminatematerial, each measuring approximately 1” square. This stack was sheared together such that the single sheared edge was highly coplanar. Photo 3 shows the condition of the stack of sheets prior to etching:

 

 

 

  Photo 3: Stack of Laminate Sheets prior to Etching

 

As before, this stack of sheets was lowered into a beaker of etchant, such that 1/8” of the edge of the stack was fully immersed. Photo 4 shows the results of this experiment:

 

 

 

Photo 4: Stack of Laminate Sheets After Etching

 

 Although it is difficult to see from Photo 4, some of the edges were not fully isolated, due to very small particles of copper debris clinging to the side walls of the dielectric. For this reason, the experiment was repeated using an ultrasonic bath of the same Perma-Etch etchant, but ultrasonica...