DE102005022354A1 - Method of treating objects using laser radiation esp. for boring or shaping electronic circuit substrates - Google Patents

Abstract

The method involves generating a laser beam. The beam is directed to a given target point on the object via a deflector and lens. The treatment is interrupted for a given period of time if the deflector is controlled such that the beam makes a jump from a first to a second target point. The time period is made up of a control time for controlling the deflector and a waiting time after the control time. The waiting time is dependent on the distance between the first and second target points. Independent claims also cover a method in which the deflector is controlled so the speed of the jump depends on the distance between the target points.

Description

method for processing objects by means of laser radiation The invention relates to a method for processing objects by means of laser radiation, in particular for drilling and / or structuring electronic Circuit substrates in which a laser beam from a laser light source is generated, the laser beam over a deflection unit and an optical system along a beam path predetermined target points of an object is directed.

The Material processing by means of laser beams has by the rapid Development of laser technology in recent years increasingly Gained importance. In the field of electronics manufacturing is through the increasing miniaturization of the components a laser processing of printed circuit boards or substrates as well as of electronic components an indispensable tool to electronic assemblies preferably compact build. In this case, holes are made in by means of laser radiation drilled multilayer substrates, the holes having a diameter, compared to the hole diameters of conventional mechanical Drilling methods drilled holes significantly is smaller. Assuming that the laser power of the exactly known to the substrate laser beam can not only through holes, but also blind holes be bored.

Be blind holes drilled in particular in multilayer printed circuit boards in which several metallic layers through dielectric intermediate layers are electrically non-conductive separated from each other. By a subsequent Metallization of a blind hole can be certain metallic layers be contacted with each other. In this way, electronic can Circuits not only two-dimensional, but also in the third Dimension be formed and thus the integration density of electronic assemblies compared to substrates with only a metal layer or with two metal layers can be significantly increased.

• A) Zum einen soll die Präzision des Bohrvorgangs möglichst genau sein. Dies bedeutet, dass der Laserstrahl mit einer möglichst genau definierten Leistungsdichte mit hoher räumlicher Genauigkeit auf einen vorgegebenen Zielpunkt gelenkt werden soll. Dazu sind hochwertige Ablenkeinheiten erforderlich, welche üblicherweise zwei um zueinander senkrechte Achsen drehbar gelagerte Spiegel aufweisen, über die der zu bearbeitende Laserstrahl gelenkt wird. Die reale Spiegelbewegung soll einem entsprechenden Ansteuersignal für den jeweiligen Spiegel mit möglichst geringen Abweichungen erfolgen.
• B) Zum anderen sollen moderne Laserbearbeitungsmaschinen einen immer hohen Durchsatz ermöglichen. Beim Bohren von Löchern versteht man darunter die maximale Anzahl an Löchern, die innerhalb einer vorgegebenen Zeit in ein elektronisches Schaltungssubstrat gebohrt werden können. Auch dafür ist maßgeblich die Ablenkeinheit einer Laserbearbeitungsmaschine verantwortlich, welche den Laserstrahl möglichst schnell zwischen zwei voneinander beabstandeten Zielpunkten bewegen sollte, so dass die Zeitspanne zwischen zwei Laserbearbeitungen an voneinander beabstandeten Zielpunkten möglichst gering ist. Um eine schnelle Sprungbewegung zwischen zwei voneinander beabstandeten Zielpunkten zu erreichen, werden die Motoren von Ablenkeinheiten derart angesteuert, dass eine möglichst schnelle Spiegelbewegung erzeugt wird. Dies führt zu großen Beschleunigungen, hohen Geschwindigkeiten und großen Abbremsbeschleunigungen und hat zur Folge, dass die Sollposition eines Spiegels am Ende der Sprungbewegung häufig nicht unmittelbar erreicht wird. So kommt es vor, dass die Ablenkspiegel über ihre Endposition hinaus schwingen, wobei sie ihre gewünschte Endposition durchfahren und erst nach einer bestimmten Zeit an diese Endposition zurückkehren.

In particular, two interrelated demands are placed on modern and competitive machines for laser processing in the electronics sector.

• A) Firstly, the precision of the drilling process should be as accurate as possible. This means that the laser beam with a power density defined as precisely as possible with high spatial accuracy is to be directed to a predetermined target point. These high-quality deflection units are required, which usually have two mutually perpendicular axes rotatably mounted mirror over which the laser beam to be processed is directed. The real mirror movement should be a corresponding drive signal for the respective mirror with the smallest possible deviations.
• B) On the other hand, modern laser processing machines should enable a high throughput. Hole drilling is the maximum number of holes that can be drilled into an electronic circuit substrate within a given time. This is also largely responsible for the deflection of a laser processing machine, which should move the laser beam as quickly as possible between two spaced apart target points, so that the time between two laser processing at spaced target points is minimized. In order to achieve a rapid jump movement between two spaced-apart target points, the motors are controlled by deflection units in such a way that the fastest possible mirror movement is generated. This leads to large accelerations, high speeds and large Abbremsbeschleunigungen and has the consequence that the desired position of a mirror at the end of the jump movement is often not directly achieved. Thus, it happens that the deflecting mirrors oscillate beyond their final position, passing through their desired end position and only returning to this end position after a certain time.

Around while such a transient around the end position around a to prevent fuzzy material processing, the to be processed Laser beam during switched off or blocked for a certain waiting time. Within this waiting time can the one or more corresponding deflection mirrors also actually in come to rest in their final position. However, this has the disadvantage that the laser processing not only during the jump of the Deflection unit, but also during the subsequent waiting period is interrupted and thus the throughput is reduced.

Of the Invention is based on the object, a method for processing specify of objects by means of laser radiation, which is a rapid material processing and thus enables a high throughput of processed objects.

The object underlying the invention is achieved by a method for processing objects by means of laser radiation, in particular for drilling and / or structuring of electronic circuit carriers. According to the invention, a laser beam is generated by a laser source and the laser beam via a deflection unit and an optical system along a beam path to predetermined target point of an object. The laser processing is interrupted for at least a certain period of time at the latest when the deflection unit is controlled in such a way that the beam path performs a jump movement from a first target point to a second target point, which is spaced from the first target point. The determined time period consists of a drive time for the corresponding control of the deflection unit and a waiting time beginning with the end of the drive time, which depends on the distance of the first target point from the second target point.

Of the Invention is based on the finding that the duration and the Type of transient response of deflecting mirrors, inter alia, of the maximum speed reached depend on the mirror movement. Because this top speed to a great extent also on the distance of the jump between two spaced target points depends on the object to be processed, It follows that the duration and type of settling of deflecting mirrors from the jump length depends. On In this way, the waiting time is determined by the respective Jump distance determined. Such a dynamically adjusted waiting time Having the jump distance has the advantage that always the shortest possible waiting time chosen can be within the transient of a deflection mirror indeed finished. this leads to in comparison to the state of the art on average to significantly shorter waiting times. According to the state The technology is independent of the jump distance always uses a comparatively long wait, in the for all potential The deflection mirrors also actually keep their end position stable to reach.

There at a big one Jump distance in general, the deflection mirror a longer settling time in order to achieve stable reaching their final position, is at far jumps in Usually a long wait is kept until the laser processing continues becomes. For a short jump, usually only one relatively short transient response is expected to become common only a shorter one Waiting time respected.

The Method according to claim 2 has the advantage that for interruption the laser processing no additional optical switching elements or shading elements required are. Thus, the interruption of the laser processing almost arbitrary fine, i. within the time interval of two consecutive Laser pulses are set.

According to claim 3, the deflection unit is controlled by a control unit, in a function is stored, which has a fixed correlation between the distance of the first target point from the second target point and the waiting time describes. This correlation can be seen in advance of the actual material processing, for example, by a spatially resolving detector be determined, which is the real mirror movement through the position one above the Mirror on the spatially resolved Detected deflected laser beam detector. Unless this correlation applies to all Jump movements is determined for a specific material processing are required for each jump movement uses the optimal waiting time. By the avoidance of unnecessary long waiting times will thus increase the process speed accordingly elevated.

According to claim 4, the deflection unit is controlled by a control unit, in of which a table is deposited, each of which has a specific bandwidth of distances assigns a waiting time from the second destination to the first destination. This has the advantage that not for all jumps the correlation between jump length and optimal waiting time must be determined, but that the potential Jumps are divided into different discrete classes, each of which has a certain waiting time. Thus, can at a reasonable cost to determine compared to State of the art on average significantly reduced waiting times the effective Process speed can be increased easily.

According to claim 5, the deflection unit is controlled such that an effective Speed of the jump movement also from the distance of the first target point depends on the second target point. This has the advantage that shorter jump distances with a faster compared to the prior art mirror movement accomplished become. Long jumps can with a lower speed of the correspond to the deflection mirror accomplished so that as a result of a shortened transient response altogether a shorter one Interruption of laser processing is required. It takes place So a holistic optimization of jumping speed and a subsequent waiting time to the shortest possible time span, in which the laser processing must be interrupted. To this In this way, the process speed can be further increased.

The each optimal speed of the jump movement can be as well in the form of a function to be experimentally determined in advance or in the form of a table in a memory of a control unit be filed.

The object underlying the invention is further achieved by a method for processing objects by means of laser radiation having the features of independent claim 6. According to the invention, a laser light source is a La serstrahl generated and directed the laser beam via a deflection unit in an optical system along a beam path to predetermined target points of an object. The laser processing is interrupted at the latest for a certain period of time, when the deflection unit is controlled such that the beam path performs a jump movement from a first target point to a second target point, which is spaced from the first target point. According to the invention, the deflection unit is controlled such that an effective speed of the jump movement depends on the distance of the first target point from the second target point.

Of the The invention is based on the finding that the period of time in the laser processing interrupted in a jump of the deflection unit must be, that can reduce the speed the jump movement to the respective jump distance dynamically adjusted becomes. Thus, the deflection unit at short jump distances, which usually to a lower mirror speed and thus to a low or lead to no transient to a mirror end position, im Compared to the prior art can be increased slightly without the transient phase a deflection mirror is considerably extended. Likewise has become that proved at large Jump distances by a correspondingly gentler control of Deflection mirror though the jump time until the first reaching the desired Extended slightly, the time until the mirror has settled in its stable end position is, but can be significantly reduced. In comparison to the stand the technique is a shorter overall Interruption of the laser processing sufficient, so that also the Process speed increased can be.

According to claim 7, the effective speed during the jump movement is varied. So For example, the deflection unit may include a first portion of the Jump movement with a higher Speed and a second section of the jump movement with to be moved at a low speed. The speed variation can However, also be done continuously, so that the deflection initially very is moved quickly and slowly towards the end of the jump movement approaching the destination point. It is also conceivable that the stable target position is the fastest is reached when the deflection unit during the Jump movement first moved quickly and then slowly.

It it is noted that a variation of the speed while of course, the leap also combined with a dynamic adjustment of the waiting time described above can be.

Further Advantages and features of the present invention will become apparent the following exemplary description of presently preferred embodiments.

In the drawing show in schematic representations

1 a laser processing machine for drilling holes,

2 a dynamic adaptation of waiting times to the jump distance,

3 a dynamic adaptation of waiting times to the jump distance by means of a defined segmentation of possible jump distances, and

4 a dynamic adaptation of the control of deflection units to the respective jump distances to be achieved.

At It should be noted that in the drawing the Reference numerals of like or corresponding elements only in its first digit and / or by letters attached to the reference number differ.

In the 1 illustrated laser processing machine 100 includes a laser light source 110 , which is a laser beam 111 emitted. The laser light source 110 According to the embodiment shown here, a diode-pumped solid-state laser, in particular a Nd: YLF laser, is optically pumped through semiconductor diodes arranged around the active laser medium. The W laser radiation is generated in a known manner by frequency multiplication by means of an optical nonlinear crystal.

It should be understood that the invention can be practiced with laser light sources that emit laser light in other spectral optical ranges. In the field of electronics production, CO ₂ laser light sources emitting in particular in the near infrared spectral range are used in addition to W laser light sources.

The laser beam 110 meets a distraction unit 130 which has two, not shown about mutually perpendicular axes rotatably mounted Galvo mirror over which the laser beam 110 can be selectively positioned on a two-dimensional edit field. The one by the deflection unit 130 deflected laser beam is via an imaging optics 140 For example, an F-theta optic as a processing laser beam 141 on the substrate to be processed 150 directed.

The substrate comprises a dielectric layer 151 , the top and bottom of each of a metallic layer 152 is covered. The metallic layers are structured in a manner not shown to form interconnects. For generating electrical connections between the two metal layers 152 become microholes 153 drilled whose walls can be metallized in a known manner. To create the microholes 153 becomes the processing laser beam 141 each by means of a jump movement 155 to a drilling position 154 centered and then with a via the imaging optics 140 set spot size F in the region of the drilling position in a circular motion around the center of the hole to be drilled, so that in each case a micro hole is generated.

During the jump movement 155 The laser processing is interrupted to avoid unwanted damage to the top metal layer between different micro holes 152 to effect. Since the galvo mirrors have a low, but nevertheless a not insignificant mechanical inertia, the mirror end position, in which a subsequent micro hole 153 to be drilled at the end of the jump movement is not achieved instantaneously. Rather, the mechanical inertia generally leads to a transient response, in which the respective deflection mirror settles on the new end position. Consequently, to prevent inaccurate material processing at the new target position, the laser processing is not only during the jump movement 155 but also interrupted for a certain waiting time within which the respective deflection mirror actually reaches its end position stable.

2 shows a dynamic adaptation of the waiting time to different jump distances. The control and the real oscillation behavior of a deflection mirror is shown in a coordinate system in which the time t is plotted on the abscissa and the deflection s of the beam path of a laser beam s deflected via the galvo mirror is plotted on the ordinate. This deflection s is connected via a simple geometric relationship with the respective angular position of the galvo mirror. How out 2 can be seen, a short jump takes place by a drive signal 260s which leads to a real mirror movement 265S leads. With such a short jump only a relatively low speed of the deflection mirror is achieved. Therefore, at the end of the rising edge of the ramp-type drive signal 260s only to comply with a relatively short waiting time T _WS , within which the deflecting mirror reaches its target position stable and within which to avoid blurred processing of the laser beam must not hit the object to be processed.

A jump with a larger jump distance is triggered by a drive signal 260l reached, which leads to a mirror movement 265l leads, the Spiegelendposition not by a gentle settling, but by a damped transient response with two in 2 clearly recognizable overshooters 266l reached. The settling time is significantly longer in the long jump compared to the short jump, so that a longer waiting time T _WL must be met in the after the end of the rising edge of the drive signal 260l The laser processing to avoid a fuzzy material processing also still needs to be interrupted.

By each optimally adapted to the jump distance, i. for one Transient of the respective deflection mirror sufficient, total however possible short wait can be the time span in which the material processing is interrupted, and thus reduces the process speed improved become. By such a dynamic adaptation of the waiting time to the respective jump length Can when drilling holes the throughput without an apparatus or constructive change a known laser processing machine can be significantly increased.

It should be noted that the real drive signal for a deflection unit is of a step shape as are the drive signals 260s and 260l may differ. The drive signals 260s and 260l For the sake of clarity, they are shown to correspond to perfect mirror motion of a massless mirror. Such perfect mirror motion would have no delay at the beginning of the rising edge and no overshoot at the end of the rising edge.

3 illustrates a particularly advantageous embodiment of the invention. The waiting time does not have to be determined for every theoretically conceivable jump length in advance of the actual laser processing. The possible jump distances are divided into different jump ranges s0, s1, s2, s3, s4 and s5, wherein each jump range is assigned a fixed waiting time. So are the jumps caused by a first drive signal 360a and by a second drive signal 360b are generated, within the first jump range s ₀ , so that at the end of the rising edge of the respective drive signal, a waiting time T _{W0 is} maintained. A third drive signal 360c leads to a jump distance that is within the jump range s ₁ , so that a slightly longer waiting time T _{W1 is} provided. A fourth drive signal 360d leads to a mirror movement, which leads to a jump in the beam path of the laser beam to be processed in Sprungweitenbe rich s ₃ leads. This jump is assigned a waiting time T _W3 . Correspondingly, a fifth drive signal leads 360e to a jump in a jump range s ₅ , which has a waiting time T _W5 result.

In the 3 shown division of the jump distances in different jump areas has compared to the prior art, even if not for each jump the optimal waiting time is determined, a significant increase in the overall process speed result.

4 shows a dynamic adaptation of the jump speed to the jump distance and the associated reduction of the time span in which no precise laser processing is possible. According to the state of the art (see the left-hand curve in each case), the jump speed with which the laser beam to be processed is moved between two spaced-apart target positions is selected independently of the jump distance. This results in a short jump, which by a drive signal 460sa is generated, a mirror movement 465sa which has no overshoot. Material processing is not possible during a jump time T _JSa . However, because the mirror movement 465sa has no overshoots, the jump speed may be increased without overshoots being generated. Thus, according to the embodiment described here, a drive signal 460sb applied to the corresponding deflection, which drive signal 460sb a steeper rising edge compared to the rising edge of the drive signal 460sa having. The rising edge of the drive signal 460sb is just so steeply chosen that in a generated mirror movement 465sb also no overshoots occur. This ensures that the laser processing only has to be interrupted within a significantly reduced compared to the time period T _JSa time T _JSb . Thus, the mirror is moved as fast as possible for short jumps on the one hand, and on the other hand, so slowly that the corresponding deflecting mirror comes to rest as quickly as possible in its end position. The laser processing then only has to be interrupted for as short a time as possible.

According to the prior art, a further jump is made by a drive signal 460la generated, with a real mirror movement 465la is generated after reaching the end position for the first time still some overshoots 466la having. The laser processing must therefore be interrupted within a period of time T _JLa until the corresponding deflection mirror completely comes to rest in its end position. According to the embodiment of the invention described here, a drive signal is obtained to achieve a large jump distance 460lb applied to the respective deflection mirror, which in comparison to the drive signal 460la has flatter rising edge. As a result, this leads to a lower jump speed of the respective deflection mirror, so that after reaching the end position of the mirror no or only very weak overshoots are generated. Overall, however, the mirror _comes to rest in a significantly shorter time T _JLb compared to the time T _JLa , so that also the laser processing only for one compared to the mirror movement 465la shorter period must be interrupted.

Overall, therefore, shorter interruption times can be realized by optimizing the jump speed to the respective desired jump distance. For the overall performance of a laser processing machine in particular the time gain is decisive, which in short jumps by a significantly steeper in comparison to the prior art drive signal 460sa is produced. Drilling or structuring processes are usually optimized for the shortest possible jump distances, so that a reduction in the interruption time in short jumps has a particularly high impact on the overall performance of a laser processing machine.

100

Laser processing machine

110

Laser light source (UV)

111

W laser beam

130

Ablenkseinheit (Galvo)

140

imaging optics

141

processing laser beam

150

substratum

151

dielectric layer

152

metallic layer

153

micro hole

154

drilling position

155

jumping motion

F

spot size

260s

control signal short jump

260l

control signal long jump

265S

mirror movement short jump

265l

mirror movement long jump

266l

overshoots

T _WS

waiting period short jump

T _WL

waiting period long jump

360a

first control signal

360b

second control signal

360c

third control signal

360d

fourth control signal

360e

fifth drive signal

T _W0

waiting period 0

T _W1

waiting period 1

T _W3

waiting period 3

T _W5

waiting period 5

S ₀

Jump Long range 0

S ₁

Jump Long range 1

S ₂

Jump Long range 2

S ₃

Jump Long range 3

S ₄

Jump Long range 4

S ₅

Jump Long range 5

460sa

control signal short jump (prior art)

460sb

control signal short jump (dynamic adjustment)

460la

control signal long jump (prior art)

460lb

control signal long jump (dynamic adjustment)

465sa

mirror movement short jump (prior art)

465sb

mirror movement short jump (dynamic adjustment)

465la

mirror movement long jump (prior art)

465lb

mirror movement long jump (dynamic adjustment)

466l

overshoots

T _JSa

jump time short jump (prior art)

T _JSb

jump time short jump (dynamic adjustment)

T _JLa

jump time long jump (prior art)

T _JLb

jump time long jump (dynamic adjustment)

Claims (7)

Method for processing objects by means of laser radiation, in particular for drilling and / or structuring electronic circuit substrates, in which a laser light source ( 110 ) a laser beam ( 111 ), • the laser beam ( 111 ) via a deflection unit ( 130 ) and an optic ( 140 ) along an optical path ( 141 ) to predetermined target points of an object ( 150 ), and • the laser processing is interrupted for at least a certain period of time at the latest when the deflection unit ( 130 ) is controlled such that the beam path ( 141 ) a jump movement ( 155 ) from a first target point to a second target point spaced from the first target point, wherein the determined time period is composed of - a drive time ( 260s . 260l ) for the corresponding control of the deflection unit ( 130 ) and - one with the end of the activation time ( 260s . 260l ) Waiting time (T _WS , T _WL ), which depends on the distance of the first target point from the second target point. Method according to Claim 1, in which a pulsed laser beam ( 111 ) and the laser processing by a missing triggering of the laser light source ( 110 ) is interrupted. Method according to one of Claims 1 to 2, in which the deflection unit ( 130 ) is driven by a control unit in which a function is stored, which describes a fixed correlation between the distance of the first target point from the second target point and the waiting time (T _WS , T _WL ). Method according to one of Claims 1 to 2, in which the deflection unit ( 130 ) is controlled by a control unit in which a table is stored, which in each case a certain bandwidth of distances (S ₀ , S ₁ , S ₂ , S ₃ , S ₄ , S ₅ ) of the first target point from the second target point a waiting time ( T _W0 , T _W1 , T _W2 , T _W3 , T _W4 , T _W5 ). Method according to one of claims 1 to 4, wherein the deflection unit ( 130 ) is controlled such that an effective speed of the jump movement ( 155 ) depends on the distance of the first target point from the second target point. Method for processing objects by means of laser radiation, in particular for drilling and / or structuring electronic circuit substrates, in which a laser light source ( 110 ) a laser beam ( 111 ), • the laser beam ( 111 ) via a deflection unit ( 130 ) and an optic ( 140 ) along an optical path ( 141 ) to predetermined target points of an object ( 150 ), and • the laser processing is interrupted for at least a certain period of time at the latest when the deflection unit ( 130 ) is controlled such that the beam path ( 141 ) a jump movement ( 155 ) from a first aiming point to a second aiming point which is spaced from the first aiming point, the deflecting unit (16) 130 ) is controlled such that - an effective speed of the jump movement ( 155 ) depends on the distance of the first target point from the second target point. Method according to Claim 6, in which the effective speed during the jump movement ( 155 ) is varied.