Browse Prior Art Database

Gas Discharge Device to Test for Signal Plane to Signal Plane Incipient Shorts in Drilled but Unplated Circuit Cards and Boards

IP.com Disclosure Number: IPCOM000061041D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Guarnieri, CR: AUTHOR [+3]

Abstract

A method and apparatus is provided for testing fiber glass circuit boards and cards for incipient short defects at the stage of manufacture where they have been laminated and drilled but the holes have not yet been plated. It tests for incipient shorts from one of several signal planes to another signal plane when neither is connected to the edge or surface of the board and when a continuous sheet of Cu covers both surfaces of the board. It handles the case where there are many distinct signal plane nets (several hundred) each connecting to a few holes and at risk (if defective) of connecting to several times as many holes. The test requires no mechanical contact to the holes under test and is non-destructive.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 49% of the total text.

Page 1 of 3

Gas Discharge Device to Test for Signal Plane to Signal Plane Incipient Shorts in Drilled but Unplated Circuit Cards and Boards

A method and apparatus is provided for testing fiber glass circuit boards and cards for incipient short defects at the stage of manufacture where they have been laminated and drilled but the holes have not yet been plated. It tests for incipient shorts from one of several signal planes to another signal plane when neither is connected to the edge or surface of the board and when a continuous sheet of Cu covers both surfaces of the board. It handles the case where there are many distinct signal plane nets (several hundred) each connecting to a few holes and at risk (if defective) of connecting to several times as many holes. The test requires no mechanical contact to the holes under test and is non- destructive. Once the unwet fiber, hollow fiber or cracked fiber glass defects which constitute the incipient shorts have been located by this test, they can be corrected by injection of new epoxy and redrilling; alternatively, the board or card may be scrapped before any further investment is made in it. Conduction of a gaseous plasma through the defective material is employed to detect a defect which would be difficult to find by the variation of dielectric or conductive properties between holes even if some means were provided to contact them and avoid the surface conductors. Thus, the gaseous plasma is used to greatly increase the electrical conductivity along the defect. The defect is detected as a current flow rather than as gas luminescence. Moreover, it is the discharging of the previously charged signal plane by plasma conduction through the defect to the second set of signal holes which allows this tell-tale current to flow. Fig. 1 schematically illustrates the method. All voltages are kept so low that there is no appreciable sputtering of material, let alone any chance of more severe damage. The test fixture requires a plated version of the desired product to be used as a template for the testing of the sample board or card. This template 10 is wired to appropriate switching apparatus (30, 32) to apply the voltages specified below in the proper sequences to test the various signal plane nets and to detect the tell- tale current if there is any. Also required is a single planar anode 12 as large as the sample, or larger, provided with a switch 14 to connect it sequentially to ground, to positive voltage Va1, which +100 V, and finally to positive voltage Va2, which may be about +30 V. Also provided is a filament 16 which ignites and maintains a plasma containing both electrons and positive ions, which are chosen to be He ions but can also be Ne, Ar, Penning mixture or other gasses known in the art to supply a convenient discharge plasma. In particular, this gas may be chosen to etch the smeared epoxy. The sample board or card 18 under test is held in a fixture 22 between the template 10 and the anode 1...