Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
• • 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
• • 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

Definitions

• the invention relates to a method for operating a laser system for processing substrates with a gas laser, in particular a CO 2 laser, in which in a gas-filled laser resonator, to which a high-frequency voltage for generating a predetermined pump power is applied during a respective working phase and in which a pulsed laser beam with a predetermined repetition frequency is generated by means of a good switch, which is directed to a processing position by a deflection unit, generates a predetermined number of pulses there during a working phase and is then directed to a next processing position by the deflection unit in a jump phase, whereby during the jump phase from one processing position to the next, the laser beam is switched off and does not emit any pulses to the outside.
• a gas laser in particular a CO 2 laser
• a gas-filled laser resonator to which a high-frequency voltage for generating a predetermined pump power is applied during a respective working phase and in which a pulsed laser beam with a predetermined repetition frequency is generated by means of
• DE 10145184 AI describes a method for laser drilling holes in a circuit substrate, in which a CO ? -Laser is used.
• a CO ? -Laser When drilling circuit boards with CO 2 lasers, a certain application-dependent number of laser pulses is required per hole.
• Such a pulse sequence is also called a burst.
• the duty cycle from the time in which pulses with a defined pulse frequency are emitted to the time in which no pulses are emitted is also called the duty cycle. This duty cycle must not exceed a characteristic value, because otherwise the available lasers are given the high pulse power the cooling of the gas can no longer take place and thus the efficiency drops.
• WO 02/082596 A2 describes a CO ? -Laser source described for such applications in which the resonator with a
• Cow device For the energy conditions in the resonator during a respective pulse sequence, the cooling can be set so that the temperature or energy conditions in the resonator are kept at the same level and the pulses within this pulse sequence are also of the same size. However, it should be noted that if the number of pulses in a pulse sequence is too high, the pulse height drops.
• the aim of the invention is therefore to modify a method of the type mentioned in the introduction in such a way that even with different distances between the processing positions and correspondingly different switch-off times of the laser beam loss of time allows a constant processing quality at all processing positions.
• this aim is achieved in that the high-frequency pump voltage is applied intermittently to the laser resonator during the jump phases in such a way that the energy level in the resonator is kept at approximately the same level as during the working phases.
• the duty cycle or the duty cycle between pulse sequences and pulse pauses is kept approximately the same even in the times of laser shutdown, so that the cooling of the gas is also controlled in a defined manner and thus the energy level in the resonator even during the breaks. This means that when the laser is switched on again, pulses of the same level as in the previous pulse sequence can be emitted immediately.
• the resonator can be controlled with the high-frequency pump voltage during the jump phases in different variants. It is thus possible to continuously modulate the high-frequency voltage during these jump phases. But it is also possible for a defined switch-off time at the beginning and / or at the end of the
• the method according to the invention can be expanded in such a way that the modulation of the high-frequency voltage not only during the jump phases when processing a specific processing field, but also during longer breaks, for example when changing from one processing field to a next or when the system is in a standby operating state is continued at the resonator.
• Various criteria, in particular the properties of the special laser resonator, must be taken into account in order to determine the necessary duty cycle in the modulation according to the invention.
• This duty cycle is therefore preferably determined experimentally by, for example, drilling at different pulse-pause ratios of the high-frequency voltage with the laser switched off, and examining the quality of the holes.
• it is also possible to determine the energy level prevailing in the resonator by emitting test pulses from the laser and measuring the pulse heights. The pulse heights can be measured by means of a photodiode or the like.
• FIG. 1 shows a schematic representation of a gas laser system for the application of the method according to the invention
• FIG. 2 shows the various signals effective for generating laser pulses in the laser resonator
• FIGS. 4, 5 and 6 corresponding time diagrams with the control pulses for the laser resonator in the method according to the invention in three different variants.
• FIG. 1 shows a laser system for a method according to the invention.
• a resonator 1 with a gas mixture, preferably with CO ? , filled chamber is provided, to which a high-frequency voltage RF is applied via an electrode system 2.
• the resonator 1 is also cooled via a cooling system 3 with corresponding coolant connections.
• a good switch 4 in the form of an electro-optical modulator arrangement, which is supplied with high-frequency voltage via a corresponding pulse control 5, a mirror arrangement, likewise only shown schematically, is used 6 pulses sent through a window 7 into the resonator 1 and passed there via further mirror arrangements 8.
• a clever arrangement of the mirrors in a small space increases the effective length of the active resonator.
• laser pulses LP are generated, which are directed via an output window 9 out of the resonator and via a deflection unit 10 with movable mirror arrangements onto a workpiece 11 in order to machine this workpiece there, for example to drill holes, at the respective working positions.
• the workpiece 11 is arranged on an adjustable table 12, whereby certain machining fields of the workpiece can be brought into the area of the laser beam.
• Both the table 12 and the deflection unit 10 are controlled by a positioning system 13, which in turn is controlled by a central control unit 14.
• This central control unit 14 also coordinates the high-frequency voltage RF at the resonator and the generation of the pulses via the good switch 4 or its control 5.
• This system according to FIG. 1 is known and is described with its essential elements in WO 02/082596 A2.
• FIG. 2 shows the pulse diagram of a system according to FIG. 1 in a conventional operating mode.
• the control device 14 applies the high-frequency voltage RF to the resonator at time tbl, which is in the excitation state for the duration of this applied voltage. If the control device 5 then applies trigger pulses TP to the good switch 4, the resonator emits a corresponding pulse sequence of laser pulses LP.
• Figure 3 shows a corresponding pulse sequence when drilling holes at different distances on a circuit board (in Figures 3 to 6, all signals are shown, for example, low active; of course, a representation with high active would also be possible).
• An example is shown in which individual work phases APH1, APH2 and APH3 each serve to drill a hole, while between the work phases each because jump phases SPH1 and SPH2 enable the beam deflection to jump from the first hole to the second, etc.
• the jump phases are of different lengths since the distances between the holes to be drilled are different. In practice, this involves, for example, distances of the order of 200 ⁇ m to 50 mm, with a jump taking about 200 ⁇ s to 300 ms.
• FIG. 3 shows a corresponding pulse sequence when drilling holes at different distances on a circuit board (in Figures 3 to 6, all signals are shown, for example, low active; of course, a representation with high active would also be possible).
• An example is shown in which individual work phases APH1, APH2 and
• FIG. 4 shows a first example of an operating mode according to the invention.
• the triggering of the laser is deactivated via the good switch in the jump phases as before in the conventional method.
• the RF (radio frequency) power is applied intermittently over the entire jump phase with a predetermined duty cycle from tl to t2, so that the overall ratio of the jump phases SPH to the working phases APH ("RF power OFF" to "RF power ON ”) is balanced. This compensates for the voltage phase SPH, which is larger in comparison to the working phase APH, and a balanced energy level is achieved.
• FIG. 5 shows a somewhat modified embodiment with the same lengths of the working phases APH1 to APH3 and the intermediate jumping phases SPH1 and SPH2 as in the previous example.
• the intermittent modulation of the RF power is designed right at the beginning of the jump phase.
• the excitation of the resonator is permanently switched off or on for a predetermined pause time PZ with the length t3 until the start of the next working phase.
• FIG. 6 in another variant it is possible to start the jump phase SPH1 or SPH2 with a defined pause time PZ of length t3 or different lengths and then to start the intermittent RF power until the start of the next work phase put on the resonator. It is also possible to combine the variants of FIGS.
• the laser pulse sequences LPF1, LPF2 and LPF3 and the resulting work phases APH1, APH2 and APH3 can also be of different lengths.

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Citations (2)

• 2004
  • 2004-04-16 CN CNA2004800246788A patent/CN1845811A/zh active Pending
  • 2004-04-16 JP JP2006530165A patent/JP2007507870A/ja active Pending
  • 2004-04-16 KR KR1020067002455A patent/KR20060060672A/ko not_active Application Discontinuation
  • 2004-04-16 WO PCT/EP2004/050555 patent/WO2005032758A1/de active Application Filing

Patent Citations (2)

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