# US 6,576,869 B1 · Method and apparatus for drilling microvia holes in electrical circuit interconnection packages > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,576,869 B1 - Document ID: US6576869B1 - Status: Granted - Kind: B1 - Application number: 09/724,046 - Filed: 2000-11-27 - Granted: 2003-06-10 - Earliest claimed: 1998-05-27 - Assignees: Excellon Automation; Exitech Limited - Inventors: Malcolm Charles Gower; Philip Thomas Rumsby; Dafydd Wyn Thomas - Web page: https://patentgrep.com/patent/US6576869B1 ## CPC - H05K 3/0032: {of organic insulating material} - B23K 26/0624: {using ultrashort pulses, i.e. pulses of 1 ns or less} - B23K 26/389: {of fluid openings, e.g. nozzles, jets} - H05K 3/0035: {of blind holes, i.e. having a metal layer at the bottom} - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM ## Abstract This invention relates to using mid-infrared high-power pulsed laser radiation sources for drilling high-quality microvia interconnection holes in printed circuit (wiring) boards and other electrical circuit packages. ## Claims ### Claim 1 A method of drilling a microvia hole in an electrical circuit interconnection package which is a laminate of at least one metal layer and at least one dielectric layer, said method comprising the steps of: providing a pulsed laser radiation source emitting radiation having a wavelength in the mid-infrared range, wherein said wavelength is longer than 3 μm and shorter than 8 μm; and focusing said radiation on the electrical circuit interconnection package at a location where the microvia hole is to be formed. ### Claim 2 (depends on 1) A method according to claim 1, wherein said pulsed laser radiation source comprises a Holmium laser, producing radiation at 2.1 μm wavelength. ### Claim 3 (depends on 1) A method according to claim 1, wherein said pulsed laser radiation source comprises an Erbium laser, producing radiation at 2.9 μm wavelength. ### Claim 4 (depends on 1) A method according to claim 1, wherein said pulsed laser radiation source comprises a gas carbon monoxide laser, producing said radiation having said wavelength in a range from about 5 to about 6 μm. ### Claim 5 (depends on 1) A method according to claim 1, wherein said pulsed laser radiation source comprises a laser and an optical parametric oscillator, tunable between about 3 and about 4.8 μm, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric oscillator, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 6 (depends on 1) A method according to claim 1, wherein said pulsed laser radiation source comprises a laser and an optical parametric amplifier, tunable between about 3 and about 4.8 μm, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric amplifier, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 7 (depends on 1) A method according to claim 1, wherein the pulsed laser radiation source produces an average laser radiation power of greater than 2 watts. ### Claim 8 (depends on 1) A method according to claim 1, wherein said at least one metal layer comprises a copper layer being drilled by said radiation having said wavelength which is in a range of from above 3 μm to about 5 μm. ### Claim 9 (depends on 8) A method according to claim 8, wherein the pulsed laser radiation source comprises a Holmium laser. ### Claim 10 (depends on 8) A method according to claim 8, wherein the pulsed laser radiation source comprises an Erbium laser. ### Claim 11 (depends on 8) A method according to claim 8, wherein the pulsed laser radiation source comprises a laser and an optical parametric oscillator, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric oscillator, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 12 (depends on 8) A method according to claim 8, wherein the pulsed laser radiation source comprises a laser and an optical parametric amplifier, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric amplifier, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 13 (depends on 8) A method according to claim 8, wherein the pulsed laser radiation source has an irradiation fluence of greater than 10 J/cm2. ### Claim 14 (depends on 1) A method according to claim 1, wherein said at least one dielectric layer is drilled by said radiation having said wavelength which is in a range of from above 3 μm to below 8 μm. ### Claim 15 (depends on 14) A method according to claim 14, wherein the pulsed laser radiation source comprises a Holmium laser. ### Claim 16 (depends on 14) A method according to claim 14, wherein the pulsed laser radiation source comprises an Erbium laser. ### Claim 17 (depends on 14) A method according to claim 14, wherein the pulsed laser radiation source comprises a carbon monoxide laser. ### Claim 18 (depends on 14) A method according to claim 14, wherein the pulsed laser radiation source comprises a laser and an optical parametric oscillator, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric oscillator, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 19 (depends on 14) A method according to claim 14, wherein the pulsed laser radiation source comprises a laser and an optical parametric amplifier, and the providing step comprises: emitting, by said laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by said optical parametric amplifier, the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 20 (depends on 14) A method according to claim 14, wherein the dielectric layer comprises a polymer based material, and the wavelength of the radiation is chosen to match a strong absorption or absorptions in the material. ### Claim 21 (depends on 20) A method according to claim 20, wherein the pulsed laser radiation source comprises a carbon monoxide laser which emits said radiation having said wavelength which matches strong absorptions in said polymer based material corresponding to carbon-oxygen, carbon-hydrogen and carbon-nitrogen bond excitations. ### Claim 22 (depends on 20) A method according to claim 20, wherein the pulsed laser radiation source comprises an Erbium laser which emits laser radiation having a laser wavelength which matches a strong absorption in a resin material used as the dielectric layer. ### Claim 23 (depends on 20) A method according to claim 20, wherein the dielectric layer comprises fibres or dispersed particles of reinforcing materials, and the wavelength of the pulsed laser radiation from the source is chosen to match a strong absorption or absorptions in the reinforcing material. ### Claim 24 (depends on 20) A method according to claim 20, wherein the dielectric layer comprises a dielectric material having a water content, and the pulsed laser radiation source comprises an Erbium laser emitting laser radiation having a laser wavelength of about 2.9 μm which overlaps the strong excitation of hydroxyl bonds in the water. ### Claim 25 (depends on 14) A method according to claim 14, wherein the wavelength of the radiation is chosen such that the radiation drills the microvia hole in the metal layer, which is a copper layer, without inducing collateral damage to the dielectric layer made of insulating material and underlying the copper layer. ### Claim 26 (depends on 25) A method according to claim 25, wherein the pulsed laser radiation source comprises an Erbium laser emitting laser radiation having a laser wavelength of 2.94 μm. ### Claim 27 (depends on 1) A method according to claim 1, wherein the microvia hole is a blind microvia hole drilled in the dielectric layer and having a bottom defined by the metal layer which is a copper layer, the pulsed laser radiation source emitting said radiation having said wavelength in the mid-infrared spectral region, wherein said radiation is sufficiently strong to remove said dielectric layer but incapable of removing the copper layer thereby the drilling of said blind microvia hole self-limiting at the copper layer beneath the dielectric layer. ### Claim 28 (depends on 27) A method according to claim 27, wherein the wavelength matches an absorptive feature of the material of the dielectric layer. ### Claim 29 A laser drilling tool for drilling a microvia hole in a printed circuit board which is a laminate of at least one conductive layer and at least one dielectric layer, said tool comprises a pulsed laser radiation source emitting radiation in the infrared wavelength range, wherein said wavelength is longer than 3 μm and shorter than 8 μm. ### Claim 30 (depends on 29) A laser drilling tool according to claim 29, wherein the pulsed laser radiation source comprises a Holmium laser. ### Claim 31 (depends on 29) A laser drilling tool according to claim 29, wherein the pulsed laser radiation source comprises an Erbium laser. ### Claim 32 (depends on 29) A laser drilling tool according to claim 29, wherein the pulsed laser radiation source comprises a laser for emitting an initial radiation having an initial wavelength shorter than said wavelength; and an optical parametric oscillator coupled for receiving said initial radiation and for converting the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 33 (depends on 29) A laser drilling tool according to claim 29, wherein the pulsed laser radiation source comprises a laser for emitting an initial radiation having an initial wavelength shorter than said wavelength; and an optical parametric amplifier coupled for receiving said initial radiation and for converting the initial radiation having said initial wavelength into said radiation having said wavelength. ### Claim 34 (depends on 29) A laser drilling tool according to claim 29, wherein the pulsed laser radiation source comprises a carbon monoxide laser. ### Claim 35 (depends on 29) A laser drilling tool according to claim 29, further comprising a system architecture which focuses the radiation on the printed circuit board at a location where the microvia hole is to be drilled. ### Claim 36 (depends on 35) A laser drilling tool according to claim 35, further comprising a motorized table for supporting the printed circuit board and moving the printed circuit board relative to and underneath the focused radiation. ### Claim 37 (depends on 29) A laser drilling tool according to claim 29, wherein the microvia hole comprises blind and through microvia holes drilled in the dielectric layer of the printed circuit board. ### Claim 38 (depends on 29) A laser drilling tool according to claim 29, wherein the microvia hole comprises blind and through microvia holes drilled in the conductive layer which is laminated on top the dielectric layer. ### Claim 39 (depends on 29) A laser drilling tool according to claim 29, wherein the tool drills holes in a percussion mode. ### Claim 40 (depends on 29) A laser drilling tool according to claim 29, wherein the tool drills holes in a trepanning mode. ### Claim 41 (depends on 29) A laser drilling tool according to claim 29, wherein the microvia hole is less than 100 μm in diameter. ### Claim 42 A method of drilling a microvia hole in a printed circuit board having a copper layer laminated on top a dielectric layer, said method comprising the steps of: emitting laser radiation from a pulsed laser radiation source, said laser radiation having a wavelength of from about 1.5 μm to about 5 μm; and focusing said radiation on the copper layer of the printed circuit board at a location where the microvia hole is to be drilled; wherein the pulsed laser radiation source has an irradiation fluence of greater than 10 J/cm2. ### Claim 43 (depends on 42) The method of claim 42, wherein said laser radiation is emitted from a Holmium laser and said wavelength is about 2.1 μm. ### Claim 44 (depends on 42) The method of claim 42, wherein said laser radiation is emitted from a Erbium laser and said wavelength is about 2.9 μm. ### Claim 45 (depends on 42) The method of claim 42, wherein said wavelength is chosen to match a strong absorption in a material of the dielectric layer so that the radiation is absorbed strongly by the underlying dielectric layer. ### Claim 46 (depends on 45) The method of claim 45, wherein the dielectric layer is made of a resin, and said wavelength is about 2.9 μm which matches a strong absorption in the resin. ### Claim 47 (depends on 46) The method of claim 46, wherein said laser radiation is emitted from a Erbium laser which has said wavelength of about 2.9 μm. ### Claim 48 (depends on 46) The method of claim 46, wherein said emitting step comprises emitting, by a laser, initial radiation having an initial wavelength shorter than said wavelength; and converting, by at least one of an optical parametric oscillator and an optical parametric amplifier, the initial radiation having said initial wavelength into said radiation having said wavelength, said at least one of an optical parametric oscillator and an optical parametric amplifier is tuned at about 2.9 μm. ### Claim 49 (depends on 45) The method of claim 45, wherein the dielectric layer is made of an insulating material having a water content, and said wavelength is about 2.9 μm which overlaps the strong excitation of hydroxyl bonds in the water. ### Claim 50 (depends on 42) The method of claim 42, wherein the printed circuit board further has another copper layer laminated to and underlying the dielectric layer, said method further comprising the steps of: adjusting the fluence of the radiation after the copper layer has been drilled through, said adjusted fluence being sufficient to remove a material of the dielectric layer but insufficient to remove copper; and drilling the dielectric layer underlying the copper layer with the adjusted radiation, said drilling self-limiting at said another copper layer beneath the dielectric layer. ### Claim 51 (depends on 50) The method of claim 50, wherein said adjusting is conducted without changing the wavelength of said radiation. ### Claim 52 (depends on 51) The method of claim 51, wherein said laser radiation is emitted from a Erbium laser and said wavelength is about 2.9 μm.