METHOD OF DETECTING FLAWS IN PLATED-THROUGH-HOLES OF CIRCUIT MODULES USING ULTRAVIOLET LIGHT

• US 3,808,434 A
• Filed: 12/16/1971
• Issued: 04/30/1974
• Est. Priority Date: 12/16/1971
• Status: Expired due to Term

• Current Assignee: AT&T, Inc.
• Original Assignee: Ernst A. Gutbier
• Inventors: Gutbier, Ernst A.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Willis, Davis L.
• Application Number:
  US05/208,814
• Time in Patent Office: 866 Days
• Field of Search: 250/71R,71T,302
• US Class Current: 250/302
• CPC Class Codes: G01N 21/6447 by visual observation
• CPC Class Codes: G01N 21/95692 Patterns showing hole parts, e.g. honeycomb filtering structures
• CPC Class Codes: G02B 21/0016 Technical microscopes, e.g. for inspection or measuring in industrial production processes

Abstract

A circuit module has copper sheets or conductors bonded to opposite sides of a fluorescent insulating sheet with metal plated-through-holes connecting conductors on opposite sides of the insulating sheet. Ultraviolet radiation is impinged on a first side of the module while it is observed by an operator from an angle of 5* to 90* on the other side of the module. Any flaw in plating of the plated-through-holes exposes the insulating material in the holes resulting in the emission of visible light which can be readily observed. A mask may be placed over etched areas of the circuit module to prevent light being emitted by the etched areas. Also, ultraviolet radiation may be impinged upon circuit patterns which are masked to sense any irregularity or flaw in those circuit patterns.

Claims

1. A process of inspecting plated-through-holes in a circuit module wherein the insulating layer in the circuit module has impregnated therein a fluorescent material which produces visible light when irradiated with ultraviolet radiation, comprising:

irradiating the circuit module on a first side with ultraviolet radiation; and

sensing visible light emanating from the second side of the circuit module at an angle between 5* and 90* to the circuit module to determine if any plated-through-holes in the circuit module have flaws therein.

2. A process as defined in claim 1 wherein the first side has conductors formed thereon and the exposed surfaces of the insulating layer on the first side are masked to prevent visible light from being produced by the exposed insulating layer.

3. A process as defined in claim 1 wherein the visible light emanating from the second side of the circuit module is sensed at an angle between 20* and 40* to the circuit module to determine if any plated-through-holes in the circuit module have flaws therein.

4. A process as defined in claim 2 wherein the second side has conductors formed thereon and which includes:

masking the exposed surfaces of the insulating layer on the second side to expose only the conductors;

irradiating the second side with ultraviolet radiation; and

sensing visible light emanating from the second side of the circuit module at an angle between 5* and 90* to the circuit module to determine if any conductors on the second side or any plated-through-holes in the circuit module have flaws therein.