EP1480780A1 - Laser machining method - Google Patents

Laser machining method

Info

Publication number
EP1480780A1
EP1480780A1 EP03709643A EP03709643A EP1480780A1 EP 1480780 A1 EP1480780 A1 EP 1480780A1 EP 03709643 A EP03709643 A EP 03709643A EP 03709643 A EP03709643 A EP 03709643A EP 1480780 A1 EP1480780 A1 EP 1480780A1
Authority
EP
European Patent Office
Prior art keywords
laser
pulse
substrate
holes
drilled
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03709643A
Other languages
German (de)
French (fr)
Inventor
Hubert De Steur
Eddy Roelants
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Via Mechanics Ltd
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1480780A1 publication Critical patent/EP1480780A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • 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
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
    • B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1ns or less
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • 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
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • 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
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • B23K26/382—Removing material by boring or cutting by boring
    • B23K26/389—Removing material by boring or cutting by boring of fluid openings, e.g. nozzles, jets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • 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
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/36—Electric or electronic devices
    • B23K2101/42—Printed circuits
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/0011—Working of insulating substrates or insulating layers
    • H05K3/0017—Etching of the substrate by chemical or physical means
    • H05K3/0026—Etching of the substrate by chemical or physical means by laser ablation
    • H05K3/0032—Etching of the substrate by chemical or physical means by laser ablation of organic insulating material

Definitions

  • the invention relates to a laser processing method for the rapid drilling of holes in dielectric substrates.
  • blind holes can also be drilled in addition to through holes, which are particularly important for multilayer printed circuit boards, since a subsequent metallization of a blind hole makes different metallic layers of the multilayer printed circuit board electrically conductive with one another can be connected and thus the integration density on a substrate can be increased significantly.
  • a laser processing device is known, by means of which holes with a diameter between 50 and 200 ⁇ can be drilled in multi-layer substrates.
  • a continuously pumped, Q-switched Nd: YAG laser is used as the laser light source, which generates light pulses in the ultraviolet spectral range after frequency conversion.
  • the individual light pulses have one average pulse power of approximately 250 mW and a pulse length of the order of 100 ns. This results in a relatively low energy of the individual light pulses of approximately 25 nJ, so that a large number of laser pulses must be used to drill a single hole.
  • the pulse repetition frequency is limited to a few kHz
  • the throughput ie the number of holes that can be drilled per unit of time
  • the throughput is correspondingly low, so that with this laser processing device it depends on the material and the thickness of the layers to be drilled per unit of time only a relatively small number of holes can be drilled.
  • pulsed CO 2 lasers with a wavelength of 9.2-10.6 ⁇ m or pulsed solid-state lasers, such as, for example, Nd: YAG lasers or Nd: YV0 4 -Lasers with a fundamental wavelength of 1064 n can be used.
  • Nd: YAG lasers or Nd: YV0 4 -Lasers with a fundamental wavelength of 1064 n can be used.
  • the use of such conventional CO 2 laser light sources emitting in the infrared spectral range has the disadvantage that the laser pulses generated are relatively long with a pulse length of the order of ⁇ s.
  • the substrate to be processed is exposed to a high thermal load, so that the geometry of the drilled holes deviates significantly from the optimal (cylindrical or conical) shape due to a burr or precipitation at the edge of the hole, thus reducing the quality of the drilled holes .
  • the precipitates arise, for example, from solidified steam, which was previously generated by sublimation from the substrate material as a result of heating by the laser beam.
  • the precipitate can also consist of small grains of solid substrate material which are thrown onto the edge of the hole due to a strong inhomogeneous heating of the substrate.
  • DE 100 20 559 discloses a method for processing a material with ultrashort laser pulses in the visible or in the near-infrared spectral range.
  • Laser pulses with a pulse duration of less than 300 ps and a repetition rate between 100 kHz and 1 GHz are generated by means of a laser light source.
  • the intensity of individual laser pulses is amplified in an optical amplifier from the total laser pulses generated.
  • the amplified laser pulses, which have a pulse duration of less than 300 ps and a repetition rate between 1 Hz and 1 MHz, are used for material processing.
  • the non-amplified pulses, which are also directed onto the material to be processed, are used for an examination of the material to be processed.
  • the so-called optical coherence tomography for example, is suitable as an examination method.
  • the invention has for its object to provide a method for drilling holes in dielectric substrates, wherein a large number of high quality holes can be drilled within a short period of time.
  • the invention is based on the knowledge that with suitable parameters, ie the wavelength, the pulse lengths, the repetition rate and the pulse energy of the processed laser beam, both the throughput, ie the number of holes drilled per unit of time, and the resulting hole quality can be improved.
  • a Q-switched C0 2 laser is used to generate the pulsed laser beam.
  • the Q0 2 laser can be Q-switched using a so-called acousto-optical switch.
  • a CdTe crystal, for example, which is excited to mechanical vibrations with a frequency in the MHz range, is suitable for this.
  • the focusing of the processing laser beam according to claim 4 to a diameter of 50 to 200 microns can be realized in particular if the laser beam emitted by the laser light source is broadened by means of a beam expansion in front of the actual focusing optics. It is pointed out that the use of a beam expansion results in a smaller depth of focus of the laser beam to be processed, so that the distance between the focusing optics and the object surface to be processed must be maintained with the highest possible accuracy. In this way, undesired widening or conical geometries of the drilled holes can be avoided.
  • the drilling of so-called blind holes according to claim 5 is used in particular in the processing of multilayer substrates.
  • the hole is drilled either by means of a single laser pulse or by means of a sequence of laser pulses directed one after the other at the object to be processed.
  • a sequence of several laser pulses it must be ensured that the individual laser pulses hit the same place on the object as possible to avoid poor hole quality.
  • pulses with a maximum length of 150 ns are preferably used.
  • a pulse repetition frequency of at least 50 kHz and preferably a pulse repetition frequency between 60 kHz is suitable and 100 kHz.
  • the processing of an epoxy material such as the material RCC (resin coated copper) frequently used as a standard substrate in electronics production, requires a pulse repetition frequency of at least 80 kHz and preferably a pulse repetition frequency of approximately 100 kHz.
  • FIG. 1 shows the drilling of holes through a substrate in a schematic representation
  • FIG. 2 shows a graphical representation of the maximum achievable throughput of drilled holes as a function of the thickness of the LCP substrate used.
  • the drilling is carried out by means of a laser processing device in that a laser beam emitted by a C0 2 laser, not shown, with a wavelength of 9.2 ⁇ 0.2 ⁇ m is expanded by means of a beam expander 1 such that the diameter of the laser beam is increased by a factor of 1.5 to 2 compared to the diameter of the laser beam at the coupling-out mirror of the laser.
  • the flared one The laser beam is deflected by 90 ° by means of a deflection unit 2, which contains at least two movable mirrors (not shown).
  • the deflected laser beam is then focused by means of telecentric focusing optics 3 such that a laser beam 4 with an effective focus diameter of 100 ⁇ m to 200 ⁇ m is directed onto the object to be processed, which is a single-layer substrate 6 according to the exemplary embodiment shown here.
  • the two mirrors of the deflection unit 2 are mounted in such a way that the laser beam 4 can be directed to any desired location within a predetermined range on the surface of the substrate 6 within a short time.
  • the substrate 6 is made of the material LCP.
  • This material is offered, for example, under the name Vectra H840 by the company Ticona or under the name Zenite 7738 by the company Dupont de Nemours.
  • other dielectric materials such as FR4 or the epoxy material RCC, can also be used for the substrate.
  • the laser beam 4 generated by the Q-switched C0 2 laser light source emits laser light pulses with a repetition frequency of at least 50 kHz with a pulse duration of less than 150 ns and with a pulse energy of at least 0.7 mJ.
  • the diameter of the laser beam 4 striking the substrate 6 to be processed is 100 ⁇ m to 200 ⁇ m. In this way, holes 5 with a diameter of 120 ⁇ m to 250 ⁇ m are drilled, the resulting hole quality being considerably improved compared to holes drilled with conventional laser processing devices.
  • the imaging unit 2 in order to achieve a high throughput of drilled holes, the imaging unit 2 must be designed in such a way that the laser beam 4 directed onto the substrate 6 to be processed moves quickly from a position on the substrate surface that is as precisely defined as possible can be directed to another position of the substrate surface that is also as precisely defined as possible.
  • a fast deflection unit 2 because of the relatively large pulse energies, the short pulse lengths and the wavelength of the laser beam 4 used, both a high throughput of drilled holes can be achieved and the thermal load on the substrate material can be minimized and thus a burr or deposits all around the drilled hole can be avoided.
  • FIG. 2 shows the result of an experimental investigation in which the maximum number of holes that can be drilled with a high hole quality is shown graphically as a function of the thickness of the substrate.
  • the thickness d in mm is plotted on the abscissa.
  • the ordinate indicates the throughput N / t of holes drilled per second.
  • the substrate used is in turn made of the material LCP. The thinner the LCP substrate to be drilled, the higher the throughput of drilled holes. With a thickness of 0.5 mm, 300 holes can be drilled per second. With a thickness of 0.4 mm, the number of holes that can be drilled with a constant quality increases to 500 per second. With a thickness of 0.15 mm, the throughput of drilled holes increases further to 1250 holes per second.
  • LCP substrates with a thickness of 0.4 mm are often used as so-called injection molding substrates in electronics production, so that the throughput of drilled holes of 500 per second compared to the throughput that can be achieved with conventional laser processing machines, is significantly increased.
  • the invention provides a laser processing method for quickly drilling holes in dielectric substrates (6).
  • a Q-switched C0 2 laser is used as the laser light source, which generates a pulsed laser beam (4) with a pulse repetition frequency greater than 50 kHz, with pulse lengths shorter than 200 ns and with an energy per laser pulse of at least 10 "4 joules
  • the laser beam (4) is deflected onto the substrate (6) to be processed by means of the parameters which characterize the laser beam (4), both a high throughput of drilled holes (5) and a high hole quality can be ensured a 0.4 mm thick LCP substrate is drilled 500 holes per second, the geometry of the drilled holes is approximately cylindrical or approximately conical, the high throughput and the simultaneously high hole quality are a consequence of the selected wavelength, the short pulse length, the high repetition rate and also in comparison to conventional laser processing devices in the field of Electronics manufacturing high pulse energy.

Abstract

The invention relates to a laser machining method for rapidly drilling holes in dielectric substrates (6). A Q-switched CO2 laser is used as a laser light source whereby generating a pulsed laser beam (4) with a pulse repetition frequency greater 50 kHz, with pulse durations shorter than 200 ns and with an energy per laser pulse of at least 10-4 joules. The laser beam (4) is directed onto substrate (6) to be machined by means of a diverting unit. The cited parameters that characterize the laser beam (4) ensure both a high production rate of drilled holes (5) as well as a high hole quality. For example, 500 holes per second can be drilled in a 0.4 mm-thick LCP substrate, whereby the shape of the drilled holes is approximately cylindrical or conical. The high production rate and the simultaneously high hole quality are a consequence of the selected wavelength, the short pulse duration, the high repetition rate, and of the pulse energy which is high compared to that of conventional laser machining devices used for manufacturing electronics.

Description

Beschreibungdescription
LaserbearbeitungsverfahrenLaser processing method
Die Erfindung betrifft ein Laserbearbeitungsverfahren zum schnellen Bohren von Löchern in dielektrische Substrate.The invention relates to a laser processing method for the rapid drilling of holes in dielectric substrates.
Die Materialbearbeitung mittels Laserstrahlen hat durch die rasante Entwicklung der Lasertechnologie in den letzten Jahren zunehmend an Bedeutung gewonnen. Insbesondere auf dem Gebiet der Elektronikfertigung ist durch die zunehmende Miniaturisierung der Bauelemente eine Laserbearbeitung von Leiterplatten bzw. Substraten zu einem unverzichtbaren Werkzeug geworden, um die aufgrund der Miniaturisierung der Bauelemente erforderliche Mikrostrukturierung von Bauelementen und/oder Substraten zu ermöglichen. So können beispielsweise Löcher in Substrate gebohrt werden, welche einen Durchmesser aufweisen, der im Vergleich zu den Lochdurchmessern von mit herkömmlichen Bohrern gebohrten Löchern wesentlich kleiner ist. Unter der Voraussetzung, dass die Laserleistung des auf das Substrat treffenden Laserstrahls genau bekannt ist, können außer Durchgangslöchern auch sogenannte Sacklöcher gebohrt werden, die insbesondere für mehrschichtige Leiterplatten wichtig sind, da durch eine nachfolgende Metallisierung eines Sackloches verschiedene metallische Schichten der mehrschichtigen Leiterplatte elektrisch leitend miteinander verbunden werden können und somit die Integrationsdichte auf einem Substrat deutlich erhöht werden kann.Material processing using laser beams has become increasingly important in recent years due to the rapid development of laser technology. In the field of electronics production in particular, the increasing miniaturization of the components has made laser processing of printed circuit boards or substrates an indispensable tool in order to enable the microstructuring of components and / or substrates required due to the miniaturization of the components. For example, holes can be drilled in substrates that have a diameter that is significantly smaller compared to the hole diameters of holes drilled with conventional drills. Provided that the laser power of the laser beam striking the substrate is precisely known, so-called blind holes can also be drilled in addition to through holes, which are particularly important for multilayer printed circuit boards, since a subsequent metallization of a blind hole makes different metallic layers of the multilayer printed circuit board electrically conductive with one another can be connected and thus the integration density on a substrate can be increased significantly.
Aus der US 5,593,606 ist eine Laserbearbeitungsvorrichtung bekannt, mittels der Löcher mit einem Durchmesser zwischen 50 und 200 μ in mehrschichtige Substrate gebohrt werden können. Als Laserlichtquelle wird ein kontinuierlich gepumpter, gütegeschalteter Nd:YAG-Laser verwendet, welcher nach einer Frequenzkonvertierung Lichtpulse im ultravioletten Spektralbereich erzeugt. Die einzelnen Lichtpulse haben eine mittlere Pulsleistung von ungefähr 250 mW und eine Pulslänge in der Größenordnung von 100 ns . Damit ergibt sich eine verhältnismäßig geringe Energie der einzelnen Lichtpulse von ungefähr 25 nJ, so dass zum Bohren eines einzigen Lochs eine Vielzahl von Laserpulsen verwendet werden muss. Da ferner die Puls-Repetitionsfrequenz auf wenige kHz begrenzt ist, ist der Durchsatz, d.h. die Anzahl an Löchern, die pro Zeiteinheit gebohrt werden können, entsprechend gering, so dass mit dieser Laserbearbeitungsvorrichtung abhängig von dem Material und der Dicke der zu durchbohrenden Schichten pro Zeiteinheit nur eine relativ geringe Anzahl von Löchern gebohrt werden kann.From US 5,593,606 a laser processing device is known, by means of which holes with a diameter between 50 and 200 μ can be drilled in multi-layer substrates. A continuously pumped, Q-switched Nd: YAG laser is used as the laser light source, which generates light pulses in the ultraviolet spectral range after frequency conversion. The individual light pulses have one average pulse power of approximately 250 mW and a pulse length of the order of 100 ns. This results in a relatively low energy of the individual light pulses of approximately 25 nJ, so that a large number of laser pulses must be used to drill a single hole. Furthermore, since the pulse repetition frequency is limited to a few kHz, the throughput, ie the number of holes that can be drilled per unit of time, is correspondingly low, so that with this laser processing device it depends on the material and the thickness of the layers to be drilled per unit of time only a relatively small number of holes can be drilled.
Ferner ist bekannt, dass zur Materialbearbeitung und insbesondere auch zum Bohren von Löchern in Substrate gepulste C02-Laser mit einer Wellenlänge von 9,2-10,6 μm oder gepulste Festkörperlaser, wie zum Beispiel Nd:YAG-Laser oder Nd: YV04-Laser mit einer Grundwellenlänge von 1064 n verwendet werden können. Die Verwendung derartiger im infraroten Spektralbereich emittierenden herkömmlichen C02- Laserlichtquellen hat den Nachteil, dass die erzeugten Laserpulse mit einer Pulslänge in der Größenordnung von μs relativ lang sind. Damit ist das zu bearbeitende Substrat einer hoher thermischen Belastung ausgesetzt, so dass die Geometrie der gebohrten Löcher durch einen Bohrgrat oder durch Niederschläge am Rand des Loches erheblich von der optimalen (zylindrischen bzw. kegelförmigen) Form abweicht und somit die Qualität der gebohrten Löcher reduziert ist. Die Niederschläge entstehen beispielsweise durch verfestigten Dampf, welcher zuvor durch Sublimation aus dem Substratmaterial infolge der Erhitzung durch den Laserstrahl erzeugt wurde. Der Niederschlag kann aber auch aus kleinen Körnern des festen Substratmaterials bestehen, welche aufgrund einer starken inhomogenen Erhitzung der Substrates an den Rand des Loches geschleudert werden. Aus der DE 100 20 559 ist ein Verfahren zur Bearbeitung eines Materials mit ultrakurzen Laserpulsen im sichtbaren oder im nah-infraroten Spektralbereich bekannt. Dabei werden mittels einer Laserlichtquelle Laserpulse mit einer Pulsdauer von weniger als 300 ps und mit einer Repetitionsrate zwischen 100 kHz und 1 GHz erzeugt. Von den insgesamt erzeugten Laserpulsen wird die Intensität einzelner Laserpulse in einem optischen Verstärker verstärkt. Die verstärkten Laserpulse, welche eine Pulsdauer von weniger als 300 ps und eine Repetitionsrate zwischen 1 Hz und 1 MHz aufweisen, werden für eine Materialbearbeitung verwendet. Die nicht verstärkten Pulse, welche ebenfalls auf das zu bearbeitende Material gerichtet werden, werden für eine Untersuchung des zu bearbeitenden Materials verwendet. Als Untersuchungsmethode eignet sich beispielweise die sog. optische Kohärenztomographie .It is also known that for material processing and in particular also for drilling holes in substrates, pulsed CO 2 lasers with a wavelength of 9.2-10.6 μm or pulsed solid-state lasers, such as, for example, Nd: YAG lasers or Nd: YV0 4 -Lasers with a fundamental wavelength of 1064 n can be used. The use of such conventional CO 2 laser light sources emitting in the infrared spectral range has the disadvantage that the laser pulses generated are relatively long with a pulse length of the order of μs. This means that the substrate to be processed is exposed to a high thermal load, so that the geometry of the drilled holes deviates significantly from the optimal (cylindrical or conical) shape due to a burr or precipitation at the edge of the hole, thus reducing the quality of the drilled holes , The precipitates arise, for example, from solidified steam, which was previously generated by sublimation from the substrate material as a result of heating by the laser beam. However, the precipitate can also consist of small grains of solid substrate material which are thrown onto the edge of the hole due to a strong inhomogeneous heating of the substrate. DE 100 20 559 discloses a method for processing a material with ultrashort laser pulses in the visible or in the near-infrared spectral range. Laser pulses with a pulse duration of less than 300 ps and a repetition rate between 100 kHz and 1 GHz are generated by means of a laser light source. The intensity of individual laser pulses is amplified in an optical amplifier from the total laser pulses generated. The amplified laser pulses, which have a pulse duration of less than 300 ps and a repetition rate between 1 Hz and 1 MHz, are used for material processing. The non-amplified pulses, which are also directed onto the material to be processed, are used for an examination of the material to be processed. The so-called optical coherence tomography, for example, is suitable as an examination method.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Bohren von Löchern in dielektrische Substrate zu schaffen, wobei innerhalb einer kurzen Zeitdauer eine Vielzahl von qualitativ hochwertigen Löchern gebohrt werden kann.The invention has for its object to provide a method for drilling holes in dielectric substrates, wherein a large number of high quality holes can be drilled within a short period of time.
Diese Aufgabe wird gelöst durch ein Verfahren mit den Merkmalen des unabhängigen Anspruchs 1.This object is achieved by a method with the features of independent claim 1.
Der Erfindung liegt die Erkenntnis zugrunde, dass bei geeigneten Parametern, d.h. die Wellenlänge, die Pulslängen, die Repetitionsrate und die Pulsenergie des bearbeiteten Laserstrahls sowohl der Durchsatz, d.h. die Anzahl der gebohrten Löcher pro Zeiteinheit erhöht als auch die resultierende Lochqualität verbessert werden kann. Erfindungsgemäß wird zur Erzeugung des gepulsten Laserstrahls ein gütegeschalteter C02-Laser verwendet. Die Güteschaltung des C02-Lasers kann mittels eines sogenannten akustooptischen Schalters realisiert werden. Dafür eignet sich beispielsweise ein CdTe-Kristall, welcher mit einer Frequenz im MHz Bereich zu mechanischen Schwingungen angeregt wird. Die Fokussierung des bearbeitenden Laserstrahls gemäß Anspruch 4 auf einen Durchmesser von 50 bis 200 μm kann insbesondere dann realisiert werden, wenn der von der Laserlichtquelle emittierte Laserstrahl vor der eigentlichen Fokussieroptik mittels einer Strahlaufweitung verbreitert wird. Es wird darauf hingewiesen, dass die Verwendung einer Strahlaufweitung eine geringere Tiefenschärfe des zu bearbeitenden Laserstrahls zur Folge hat, so dass der Abstand zwischen der Fokussieroptik und der zu bearbeitenden Objektoberfläche mit einer möglichst hohen Genauigkeit eingehalten werden muss. Auf diese Weise können unerwünschte Verbreiterungen oder konischen Geometrien der gebohrten Löcher vermieden werden.The invention is based on the knowledge that with suitable parameters, ie the wavelength, the pulse lengths, the repetition rate and the pulse energy of the processed laser beam, both the throughput, ie the number of holes drilled per unit of time, and the resulting hole quality can be improved. According to the invention, a Q-switched C0 2 laser is used to generate the pulsed laser beam. The Q0 2 laser can be Q-switched using a so-called acousto-optical switch. A CdTe crystal, for example, which is excited to mechanical vibrations with a frequency in the MHz range, is suitable for this. The focusing of the processing laser beam according to claim 4 to a diameter of 50 to 200 microns can be realized in particular if the laser beam emitted by the laser light source is broadened by means of a beam expansion in front of the actual focusing optics. It is pointed out that the use of a beam expansion results in a smaller depth of focus of the laser beam to be processed, so that the distance between the focusing optics and the object surface to be processed must be maintained with the highest possible accuracy. In this way, undesired widening or conical geometries of the drilled holes can be avoided.
Das Bohren von sogenannten Sacklöchern gemäß Anspruch 5 wird insbesondere bei der Bearbeitung von Mehrschichtsubstraten verwendet .The drilling of so-called blind holes according to claim 5 is used in particular in the processing of multilayer substrates.
Gemäß Anspruch 6 wird abhängig von dem Substratmaterial und der Dicke bzw. der Tiefe des zu bohrenden Loches das Loch entweder mittels eines einzigen Laserpulses oder mittels einer Abfolge von nacheinander auf das zu bearbeitende Objekt gerichteten Laserpulse gebohrt. Bei der Verwendung einer Abfolge von mehreren Laserpulsen ist darauf zu achten, dass zur Vermeidung einer schlechten Lochqualität die einzelnen Laserpulse möglichst an der gleichen Stelle des Objekts auftreffen. Bei durchgeführten Experimenten hat sich herausgestellt, dass dafür eine räumliche Überlappung der resultierenden Fokusflächen von mindestens 66% eingehalten werden sollte.According to claim 6, depending on the substrate material and the thickness or the depth of the hole to be drilled, the hole is drilled either by means of a single laser pulse or by means of a sequence of laser pulses directed one after the other at the object to be processed. When using a sequence of several laser pulses, it must be ensured that the individual laser pulses hit the same place on the object as possible to avoid poor hole quality. Experiments carried out have shown that a spatial overlap of the resulting focus areas of at least 66% should be maintained.
Gemäß Anspruch 7 werden für die Bearbeitung von Substraten aus dem Substratmaterial LCP (Liquid Cristalline Polymer) , welches hervorragende elektrische Eigenschaften bis hin zu Frequenzen von 40 GHz aufweist und welches nahezu undurchdringbar sowohl für Feuchtigkeit, Sauerstoff als auch für andere Gase und Flüssigkeiten ist, bevorzugt Pulse mit einer Länge von maximal 150 ns verwendet.According to claim 7 for processing substrates from the substrate material LCP (Liquid Crystalline Polymer), which has excellent electrical properties up to frequencies of 40 GHz and which is almost impenetrable for both moisture, oxygen and for other gases and liquids, pulses with a maximum length of 150 ns are preferably used.
Zur Bearbeitung des mit einem Glasfasermaterial mechanisch verstärkten dielektrischen Substrats FR4 (Flame Retard 4), wie beispielsweise das Material C-1080 der Firma ISOLA, eignet sich gemäß Anspruch 8 eine Puls-Wiederholfrequenz von mindestens 50 kHz und bevorzugt eine Puls-Wiederholfrequenz zwischen 60 kHz und 100 kHz.For processing the dielectric substrate mechanically reinforced with a glass fiber material FR4 (flame retard 4), such as the material C-1080 from ISOLA, a pulse repetition frequency of at least 50 kHz and preferably a pulse repetition frequency between 60 kHz is suitable and 100 kHz.
Gemäß Anspruch 9 erfordert die Bearbeitung eines Epoxy Materials, wie beispielsweise das als Standardsubstrat in der Elektronikfertigung häufig verwendete Material RCC (Resin Coated Copper) , eine Puls-Wiederholfrequenz von mindestens 80 kHz und bevorzugt eine Puls-Wiederholfrequenz von annähernd 100 kHz.According to claim 9, the processing of an epoxy material, such as the material RCC (resin coated copper) frequently used as a standard substrate in electronics production, requires a pulse repetition frequency of at least 80 kHz and preferably a pulse repetition frequency of approximately 100 kHz.
Weitere Vorteile und Merkmale der vorliegenden Erfindung ergeben sich aus der folgenden beispielhaften Beschreibung einer derzeit bevorzugten Ausführungsform.Further advantages and features of the present invention result from the following exemplary description of a currently preferred embodiment.
In der Zeichnung zeigenShow in the drawing
Figur 1 das Bohren von Löchern durch ein Substrat in einer schematischen Darstellung und Figur 2 eine graphische Darstellung des maximal erreichbaren Durchsatzes von gebohrten Löchern in Abhängigkeit der Dicke des verwendeten LCP-Substrates .1 shows the drilling of holes through a substrate in a schematic representation and FIG. 2 shows a graphical representation of the maximum achievable throughput of drilled holes as a function of the thickness of the LCP substrate used.
Gemäß dem in Figur 1 dargestellten Ausführungsbeispiel der Erfindung erfolgt das Bohren mittels einer Laserbearbeitungsvorrichtung dadurch, dass ein von einem nicht dargestellten C02-Laser emittierter Laserstrahl mit einer Wellenlänge von 9,2 ± 0,2 μm mittels eines Strahlaufweiters 1 derart aufgeweitet wird, dass der Durchmesser des Laserstrahls im Vergleich zu dem Durchmesser des Laserstrahls am Auskoppelspiegel des Lasers um einen Faktor 1,5 bis 2 vergrößert wird. Der aufgeweitete Laserstrahl wird mittels einer Ablenkeinheit 2, welche zumindest zwei nicht dargestellte bewegliche Spiegel enthält, um 90° abgelenkt. Der abgelenkte Laserstrahl wird dann mittels einer telezentrischen Fokussieroptik 3 derart fokussiert, dass ein Laserstrahl 4 mit einem wirksamen Fokusdurchmesser von 100 μm bis 200 μm auf das zu bearbeitende Objekt gerichtet wird, welches gemäß dem hier dargestellten Ausführungsbeispiel ein einschichtiges Substrat 6 ist. Die beiden Spiegel der Ablenkeinheit 2 sind derart gelagert, dass der Laserstrahl 4 innerhalb einer kurzen Zeit auf beliebige Stellen innerhalb eines vorgegebenen Bereiches auf der Oberfläche des Substrates 6 gerichtet werden kann.According to the exemplary embodiment of the invention shown in FIG. 1, the drilling is carried out by means of a laser processing device in that a laser beam emitted by a C0 2 laser, not shown, with a wavelength of 9.2 ± 0.2 μm is expanded by means of a beam expander 1 such that the diameter of the laser beam is increased by a factor of 1.5 to 2 compared to the diameter of the laser beam at the coupling-out mirror of the laser. The flared one The laser beam is deflected by 90 ° by means of a deflection unit 2, which contains at least two movable mirrors (not shown). The deflected laser beam is then focused by means of telecentric focusing optics 3 such that a laser beam 4 with an effective focus diameter of 100 μm to 200 μm is directed onto the object to be processed, which is a single-layer substrate 6 according to the exemplary embodiment shown here. The two mirrors of the deflection unit 2 are mounted in such a way that the laser beam 4 can be directed to any desired location within a predetermined range on the surface of the substrate 6 within a short time.
Das Substrat 6 ist aus dem Material LCP hergestellt. Dieses Material wird beispielsweise unter der Bezeichnung Vectra H840 von der Firma Ticona oder unter der Bezeichnung Zenite 7738 von der Firma Dupont de Nemours angeboten. Es wird allerdings darauf hingewiesen, dass für das Substrat auch andere dielektrische Materialien, wie beispielsweise FR4 oder das Epoxy Material RCC, verwendet werden können.The substrate 6 is made of the material LCP. This material is offered, for example, under the name Vectra H840 by the company Ticona or under the name Zenite 7738 by the company Dupont de Nemours. However, it is pointed out that other dielectric materials, such as FR4 or the epoxy material RCC, can also be used for the substrate.
Der von der nicht dargestellten gütegeschalteten C02- Laserlichtquelle erzeugte Laserstrahl 4 emittiert mit einer Repititionsfrequenz von mindestens 50 kHz Laserlichtpulse mit einer Pulsdauer von weniger als 150 ns und mit einer Pulsenergie von mindestens 0,7 mJ. Der Durchmesser des auf das zu bearbeitende Substrat 6 auftreffenden Laserstrahls 4 beträgt 100 μm bis 200 μm. Auf diese Weise werden Löcher 5 mit einem Durchmesser von 120 μm bis 250 μm gebohrt, wobei die resultierende Lochqualität im Vergleich zu Löchern, die mit herkömmlichen Laserbearbeitungsvorrichtungen gebohrt wurden, erheblich verbessert ist.The laser beam 4 generated by the Q-switched C0 2 laser light source, not shown, emits laser light pulses with a repetition frequency of at least 50 kHz with a pulse duration of less than 150 ns and with a pulse energy of at least 0.7 mJ. The diameter of the laser beam 4 striking the substrate 6 to be processed is 100 μm to 200 μm. In this way, holes 5 with a diameter of 120 μm to 250 μm are drilled, the resulting hole quality being considerably improved compared to holes drilled with conventional laser processing devices.
Es wird darauf hingewiesen, dass zur Erreichung eines hohen Durchsatzes an gebohrten Löchern die Abbildungseinheit 2 derart ausgebildet sein muss, dass der auf das zu bearbeitende Substrat 6 gelenkte Laserstrahl 4 zügig von einer möglichst genau definierten Position auf der Substratoberfläche zu einer anderen, ebenfalls möglichst genau definierten Position der Substratoberfläche gelenkt werden kann. Bei Verwendung einer derart schnellen Ablenkeinheit 2 kann somit aufgrund der relativ großen Pulsenergien, aufgrund der kurzen Pulslängen und der verwendeten Wellenlänge des Laserstrahls 4 sowohl ein hoher Durchsatz an gebohrten Löchern erreicht als auch die thermische Belastung des Substratmaterials minimiert und somit ein Bohrgrat oder Ablagerungen rund um das gebohrte Loch vermieden werden.It is pointed out that, in order to achieve a high throughput of drilled holes, the imaging unit 2 must be designed in such a way that the laser beam 4 directed onto the substrate 6 to be processed moves quickly from a position on the substrate surface that is as precisely defined as possible can be directed to another position of the substrate surface that is also as precisely defined as possible. When using such a fast deflection unit 2, because of the relatively large pulse energies, the short pulse lengths and the wavelength of the laser beam 4 used, both a high throughput of drilled holes can be achieved and the thermal load on the substrate material can be minimized and thus a burr or deposits all around the drilled hole can be avoided.
Figur 2 zeigt das Ergebnis einer experimentellen Untersuchung, bei der die maximale Anzahl an Löchern, welche mit einer hohen Lochqualität gebohrt werden können, in Abhängigkeit von der Dicke des Substrates grafisch dargestellt wird. Dabei ist auf der Abszisse die Dicke d in der Einheit mm aufgetragen. Die Ordinate gibt den Durchsatz N/t der gebohrten Löcher pro Sekunde an. Das verwendete Substrat ist wiederum aus dem Material LCP hergestellt. Je dünner das zu durchbohrende LCP-Substrat ist, desto höher ist der Durchsatz an gebohrten Löchern. Bei einer Dicke von 0,5 mm können 300 Löcher pro Sekunde gebohrt werden. Bei einer Dicke von 0,4 mm erhöht sich die Anzahl der Löcher, die mit einer gleichbleibenden Qualität gebohrt werden können, auf 500 pro Sekunde. Bei einer Dicke von 0,15 mm erhöht sich der Durchsatz an gebohrten Löchern weiter bis auf 1250 Löcher pro Sekunde.FIG. 2 shows the result of an experimental investigation in which the maximum number of holes that can be drilled with a high hole quality is shown graphically as a function of the thickness of the substrate. The thickness d in mm is plotted on the abscissa. The ordinate indicates the throughput N / t of holes drilled per second. The substrate used is in turn made of the material LCP. The thinner the LCP substrate to be drilled, the higher the throughput of drilled holes. With a thickness of 0.5 mm, 300 holes can be drilled per second. With a thickness of 0.4 mm, the number of holes that can be drilled with a constant quality increases to 500 per second. With a thickness of 0.15 mm, the throughput of drilled holes increases further to 1250 holes per second.
Es wird darauf hingewiesen, dass LCP-Substrate mit einer Dicke von 0,4 mm häufig als sogenannte Spritzgusssubstrate in der Elektronikfertigung eingesetzt werden, so dass der Durchsatz an gebohrten Löchern von 500 pro Sekunde gegenüber dem Durchsatz, welcher mit herkömmlichen Laserbearbeitungsmaschinen erreicht werden kann, erheblich erhöht ist. Zusammenfassend schafft die Erfindung ein Laserbearbeitungsverfahren zum schnellen Bohren von Löchern in dielektrische Substrate (6) . Als Laserlichtquelle wird ein gütegeschalteter C02-Laser verwendet, welcher einen gepulsten Laserstrahl (4) mit einer Puls-Wiederholfrequenz größer als 50 kHz, mit Pulslängen kürzer als 200 ns und mit einer Energie pro Laserpuls von mindestens 10"4 Joule erzeugt. Mittels einer Ablenkeinheit wird der Laserstrahl (4) auf das zu bearbeitende Substrat (6) gelenkt. Mit den genannten den Laserstrahl (4) charakterisierenden Parametern kann sowohl ein hoher Durchsatz an gebohrten Löchern (5) als auch eine hohe Lochqualität gewährleistet werden. So können beispielweise in ein 0,4 mm dickes LCP-Substrat 500 Löcher pro Sekunde gebohrt werden, wobei die Geometrie der gebohrten Löcher annähernd zylindrisch bzw. annähernd kegelförmig ist. Der hohe Durchsatz und die gleichzeitig hohe Lochqualität sind eine Folge der gewählten Wellenlänge, der kurzen Pulslänge, der hohen Repetitionsrate und der ebenfalls im Vergleich zu herkömmlichen Laserbearbeitungsvorrichtungen im Bereich der Elektronikfertigung hohen Pulsenergie. It is pointed out that LCP substrates with a thickness of 0.4 mm are often used as so-called injection molding substrates in electronics production, so that the throughput of drilled holes of 500 per second compared to the throughput that can be achieved with conventional laser processing machines, is significantly increased. In summary, the invention provides a laser processing method for quickly drilling holes in dielectric substrates (6). A Q-switched C0 2 laser is used as the laser light source, which generates a pulsed laser beam (4) with a pulse repetition frequency greater than 50 kHz, with pulse lengths shorter than 200 ns and with an energy per laser pulse of at least 10 "4 joules The laser beam (4) is deflected onto the substrate (6) to be processed by means of the parameters which characterize the laser beam (4), both a high throughput of drilled holes (5) and a high hole quality can be ensured a 0.4 mm thick LCP substrate is drilled 500 holes per second, the geometry of the drilled holes is approximately cylindrical or approximately conical, the high throughput and the simultaneously high hole quality are a consequence of the selected wavelength, the short pulse length, the high repetition rate and also in comparison to conventional laser processing devices in the field of Electronics manufacturing high pulse energy.

Claims

Patentansprüche claims
1. Laserbearbeitungsverfahren zum schnellen Bohren von Löchern in dielektrische Substrate , bei dem • als Laserlichtquelle ein gütegeschalteter C02-Laser verwendet wird, welcher einen gepulsten Laserstrahl (4)1. Laser processing method for the rapid drilling of holes in dielectric substrates, in which • a Q-switched C0 2 laser is used as the laser light source, which emits a pulsed laser beam (4)
- mit einer Puls-Wiederholfrequenz größer als 50 kHz,- with a pulse repetition frequency greater than 50 kHz,
- mit Pulslängen kürzer als 200 ns und- with pulse lengths shorter than 200 ns and
- mit einer Energie pro Laserpuls von mindestens 10-4 Joule erzeugt, und- generated with an energy per laser pulse of at least 10 -4 joules, and
• der Laserstrahl (4) mittels einer Ablenkeinheit (2) auf das zu bearbeitende Substrat (6) gelenkt wird.• The laser beam (4) is directed onto the substrate (6) to be processed by means of a deflection unit (2).
2. Laserbearbeitungsverfahren gemäß Anspruch 1, bei dem ein Laserstrahl (4) mit einer Wellenlänge im Bereich von 9,2 ±2. Laser processing method according to claim 1, wherein a laser beam (4) with a wavelength in the range of 9.2 ±
0,2 μm verwendet wird.0.2 μm is used.
3. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis3. Laser processing method according to one of claims 1 to
2, bei dem Laserpulse mit einer Energie von 0,7 mJoule verwendet werden.2, using laser pulses with an energy of 0.7 mJoules.
4. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis4. Laser processing method according to one of claims 1 to
3, bei dem der Laserstrahl (4) auf das zu bearbeitende Substrat (6) mit einem Durchmesser von 50 μm - 200 μm fokussiert wird.3, in which the laser beam (4) is focused on the substrate (6) to be processed with a diameter of 50 μm - 200 μm.
5. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis5. Laser processing method according to one of claims 1 to
4, bei dem Sacklöcher in das zu bearbeitende Substrat (6) gebohrt werden.4, in which blind holes are drilled in the substrate (6) to be processed.
6. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis6. Laser processing method according to one of claims 1 to
5, bei dem ein Loch (5) mittels eines einzigen Laserpulses oder mittels mehrerer Laserpulse gebohrt wird, welche nacheinander auf das zu bearbeitende Substrat (6) gerichtet werden. 5, in which a hole (5) is drilled by means of a single laser pulse or by means of a plurality of laser pulses, which are successively directed onto the substrate (6) to be processed.
7. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis 6, bei dem ein LCP-Substrat bearbeitet wird, wobei Pulslängen kürzer als 150 ns verwendet werden.7. Laser processing method according to one of claims 1 to 6, in which an LCP substrate is processed, wherein pulse lengths shorter than 150 ns are used.
8. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis 6, bei dem ein mit einem Glasfasermaterial mechanisch verstärktes dielektrisches Substrat bearbeitet wird, wobei eine Puls-Wiederholfrequenz von mindestens 50 kHz und insbesondere von 60 kHz bis 100 kHz verwendet wird.8. Laser processing method according to one of claims 1 to 6, in which a mechanically reinforced with a glass fiber dielectric substrate is processed, wherein a pulse repetition frequency of at least 50 kHz and in particular from 60 kHz to 100 kHz is used.
9. Laserbearbeitungsverfahren gemäß einem der Ansprüche 1 bis 6, bei dem ein Epoxy Material bearbeitet wird, wobei eine Puls-Wiederholfrequenz von mindestens 80 kHz und insbesondere von annähernd 100 kHz verwendet wird. 9. Laser processing method according to one of claims 1 to 6, in which an epoxy material is processed, wherein a pulse repetition frequency of at least 80 kHz and in particular of approximately 100 kHz is used.
EP03709643A 2002-03-05 2003-02-24 Laser machining method Withdrawn EP1480780A1 (en)

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DE10209617A DE10209617C1 (en) 2002-03-05 2002-03-05 Laser processing method, for rapidly boring holes in dielectric substrates, comprises deviating a laser beam produced by a carbon dioxide laser onto the substrate to be processed using a deviating unit
DE10209617 2002-03-05
PCT/DE2003/000579 WO2003074224A1 (en) 2002-03-05 2003-02-24 Laser machining method

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