Method and apparatus for detecting through-hole voids in multi-layer printed wiring board

Claim 1

A method of detecting a through-hole void existing on a surface of a through-hole which is formed with an electrical conductor for interconnecting wiring patterns of upper layers and wiring patterns of lower layers in a multi-layer printed circuit board comprising the steps of: emitting an exciting beam having a wavelength limited to a value within an optimum wavelength band which is capable of exciting a fluorescent light through said through-hole void from a layer material which is exposed at the through-hole void; focusing said exciting beam over said through-hole and illuminating said through-hole with said exciting beam by a focusing/illuminating optical system in which said exciting beam has an incident angle which is not less than 10° in order to let said exciting beam reflect many times between said surface of said through-hole such that said exciting beam impinges upon said layer material in an almost horizontal direction through said through-hole void; converging said fluorescent light emitted into said through-hole from said through-hole void, by means of said focusing optical means at an illuminating side; filtering said fluorescent light; and, detecting said through-hole void for its presence on the basis of an electrical signal converted by a photoelectric conversion means which detects said converged fluorescent light after filtering.

Claim 2

A method of detecting a through-hole void existing on a surface of a through-hole which is formed with an electrical conductor for interconnecting wiring patterns of upper layers and wiring patterns of lower layers in a multi-layer printed circuit board comprising the steps of: emitting an exciting beam having a wavelength limited to a value within an optimum wavelength band which is capable of exciting a fluorescent light through said through-hole void from a layer material which is exposed at the through-hole void; focusing said exciting beam over said through-hole and illuminating said through-hole with said exciting beam by a focusing/illuminating optical system in which said exciting beam has an incident angle which is not less than 10° in order to let said exciting beam reflect many times between said surface of said through-hole such that said exciting beam impinges upon said layer material in an almost horizontal direction through said through-hole void; converging said fluorescent light emitted into said through-hole from said through-hole void, by means of said focusing optical means at an illuminating side; filtering said fluorescent light; and, detecting said through-hole void for its presence on the basis of an electrical signal converted by a photoelectric conversion means which detects said converged fluorescent light after filtering.

Claim 7

An apparatus for detecting a through-hole void existing on a surface of a through-hole which is formed with an electrical conductor for interconnecting wiring patterns of upper layers and wiring patterns of lower layers in a multi-layer printed wiring board comprising: a light source means for emitting an exciting beam having a wavelength limited to a value within an optimum wavelength band which is capable of exciting a fluorescent light through said through-hole void from a layer material which is exposed at said through-hole void; an illuminating/focusing optical system having a numerical aperture which is not less than sin 10° for focusing said exciting beam over said through-hole obliquely in order to let said exciting beam reflect many times between said surface of said though hole such that said exciting beam impinges upon said layer material in an almost horizontal direction through said through-hole void; a fluorescent light detecting optical system for converging said fluorescent light at the illuminating side; an absorption filter for passing only said fluorescent light emitted into said through-hole through said through-hole void from said layer material; and, a photoelectric conversion means for converting said focused fluorescent light detected through said absorption filter into an electrical signal which is used to detect said through-hole void for its presence automatically.

Claim 8

An apparatus for detecting a through-hole void existing on a surface of a through-hole which is formed with an electrical conductor for interconnecting wiring patterns of upper layers and wiring patterns of lower layers in a multi-layer printed wiring board comprising: a light source means for emitting an exciting beam having a wavelength limited to a value within an optimum wavelength band which is capable of exciting a fluorescent light through said through-hole void from a layer material which is exposed at said through-hole void; an illuminating/focusing optical system having a numerical aperture which is not less than sin 10° for focusing said exciting beam over said through-hole obliquely in order to let said exciting beam reflect many times between said surface of said though hole such that said exciting beam impinges upon said layer material in an almost horizontal direction through said through-hole void; a fluorescent light detecting optical system for converging said fluorescent light at the illuminating side; an absorption filter for passing only said fluorescent light emitted into said through-hole through said through-hole void from said layer material; and, a photoelectric conversion means for converting said focused fluorescent light detected through said absorption filter into an electrical signal which is used to detect said through-hole void for its presence automatically.

Claim 22

An apparatus particularly useful for detecting through-hole voids in through-holes of multi-layer printed wiring boards having small aspect ratios of through-hole diameter relative to circuit board thickness, wherein a through-hole void is detected at a side from which a detection process originates, comprising: an exciting beam generating means for generating an exciting beam possessing a wavelength that will change when impinged upon wiring board material; a first optical means for focussing and directing the exciting beam to enter the through-hole in a near horizontal direction whereby the exciting beam can reflect off the walls of the through-hole many times and allow the exciting beam to impinge the through-hole void in a near horizontal manner; a second optical means for converging luminescent beams generated by the impingement of the exciting beam upon the wiring board material, said luminescent beams having a different wavelength than the exciting beam whereby the luminescent beam can be detected on the side of the multi-layer wiring board from which the exciting beam is generated; a detecting means for detecting the luminescent beams, said luminescent beams indicating that a through-hole void is present in the through-hole.

Claim 23

An apparatus particularly useful for detecting through-hole voids in through-holes of multi-layer printed wiring boards having small aspect ratios of through-hole diameter relative to circuit board thickness, wherein a through-hole void is detected at a side from which a detection process originates, comprising: an exciting beam generating means for generating an exciting beam possessing a wavelength that will change when impinged upon wiring board material; a first optical means for focussing and directing the exciting beam to enter the through-hole in a near horizontal direction whereby the exciting beam can reflect off the walls of the through-hole many times and allow the exciting beam to impinge the through-hole void in a near horizontal manner; a second optical means for converging luminescent beams generated by the impingement of the exciting beam upon the wiring board material, said luminescent beams having a different wavelength than the exciting beam whereby the luminescent beam can be detected on the side of the multi-layer wiring board from which the exciting beam is generated; a detecting means for detecting the luminescent beams, said luminescent beams indicating that a through-hole void is present in the through-hole.