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Browse Prior Art Database

Circuit Board Manufacture

IP.com Disclosure Number: IPCOM000048130D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Canestaro, MJ: AUTHOR [+4]

Abstract

Defects in circuit boards sometimes occur because very small bubbles of air are entrapped between the laminate and the layer of photoresist used to manufacture the circuit board. The air is entrapped in the form of bubbles with a diameter of less than a mil and ranging in length in excess of 5 mils. These bubbles are invisible to the naked eye.

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Circuit Board Manufacture

Defects in circuit boards sometimes occur because very small bubbles of air are entrapped between the laminate and the layer of photoresist used to manufacture the circuit board. The air is entrapped in the form of bubbles with a diameter of less than a mil and ranging in length in excess of 5 mils. These bubbles are invisible to the naked eye.

Photoresist includes a free radical which initiates the polymerization, an organic monomer to produce the required crosslinking in the film and an oxygen inhibitor. The oxygen inhibitor is added to the photoresist to prevent the polymeric reaction from occurring in the photoresist in the presence of air. Without this oxygen inhibitor the photoresist would be virtually impossible to manufacture or store prior to photoprocessing because oxygen would initiate chemical reactions prior to photoprocessing. These self initiating chemical reactions would interfere with the desired photoprocessing reaction.

The air entrapped in the microscopic bubbles between the photoresist and the circuitry provides a source of oxygen which reacts with the oxygen inhibitor in the photoresist and prevents complete polymerization of the photoresist at the interface. Hence, after the photoresist has been exposed In the normal manner, there are small microscopic bubbles and cylinders composed of incompletely polymerized photoresist. During subsequent processing this incompletely polymerized photoresist leaches from the walls...