FIELD OF THE INVENTION

The present invention relates generally to production of electronic products, and particularly to methods and systems for controlling a laser repair process of electronic circuits.

BACKGROUND OF THE INVENTION

Various techniques have been developed for controlling processes, such as laser-based repair of electronic circuits.

For example, U.S. Patent Application Publication 2005/0226287 describes a laser processing system having a femtosecond laser, frequency conversion optics, beam manipulation optics, target motion control, processing chamber, diagnostic systems and system control modules. The laser processing system allows for the utilization of the unique heat control in micromachining, and the system has greater output beam stability, continuously variable repetition rate and unique temporal beam shaping capabilities.

U.S. Patent Application Publication 2007/0092128 described an apparatus and method for automatically inspecting and repairing printed circuit boards includes an inspection functionality automatically inspecting printed circuit boards and providing a machine readable indication of regions thereon requiring repair. An automatic repair functionality employs the machine readable indication to repair the printed circuit boards at some of the regions thereon requiring repair. An automatic repair reformulation functionality automatically re-inspects printed circuit boards following an initial automatic repair operation, and provides to the automatic repair functionality a reformulated machine readable indication of regions thereon requiring repair.

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein provides a method including directing a laser beam to impinge on a section of a substrate for removing a layer formed on the section. At least a spectral component indicative of layer material removed from the layer, is detected from light emitted from the section in response to the impinged laser beam. Based on the detected spectral component, the laser beam in controlled or stopped from impinging on the section.

In some embodiments, directing the laser beam includes directing a pulsed laser beam. In other embodiments, the substrate includes a printed circuit board (PCB) having a laminate and the layer includes a copper defect. In yet other embodiments, the method includes detecting, from the light emitted from the section, an additional spectral component, which is indicative of substrate material removed from the substrate.

In an embodiment, controlling or stopping the laser beam includes setting a stopping time based on both the spectral component and the additional spectral component. In another embodiment, in response to detecting that both the spectral component and the additional spectral component are above a predefined threshold, redirecting the laser beam to impinge on the layer within the section.

In some embodiments, controlling or stopping the laser beam includes performing at least one operation selected from a list of operations consisting of: (i) blocking the laser beam, (ii) switching-off the laser beam, and (iii) directing the laser beam to a subsequent section of the substrate. In other embodiments, detecting at least the spectral component includes detecting one or more spectral emissions selected from a list of spectral emissions consisting of: (a) fluorescence, (b) plasma, (c) Raman, (d) infrared heat radiation, and (E) Laser Induced Breakdown Spectroscopy (LIBS).

There is additionally provided, in accordance with an embodiment of the present invention, a system, including an optical assembly, a detection assembly and a processor. The optical assembly is configured to direct a laser beam to impinge on a section of a substrate, and the laser beam is configured to remove a layer formed on the section. The detection assembly is configured to detect, from a light emitted from the section in response to the impinged laser beam, a spectral component indicative of layer material removed from the layer. The processor is configured to control or stop the laser beam from impinging on the section, based on the detected spectral component.

In some embodiments, the optical assembly includes at least one of an acousto-optic modulator (AOM), a scanning mirror, and focusing optics.

The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram of a system for repairing electronic circuits utilizing laser, in accordance with an embodiment of the present invention;

Figs. 2A, 2B and 2C are graphs showing spectral component of emitted light, which is indicative of copper removed from a substrate, in accordance with an embodiment of the present invention; and Fig. 3 is a flow chart that schematically illustrates a method for controlling a process of removing a defect from electronic circuit using spectral components of light emitted from the defect during the process, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

OVERVIEW

Sometimes, various types of defects may occur during a fabrication process of an electronic component or module, such as in a printed circuit board (PCB). For example, when forming a pattern of copper traces on a laminate of the PCB, a defect comprising undesired layer of copper, may occur between the copper traces. It is important to remove the defect without damaging the laminate, which is typically under the copper, so as to maintain the functionality of the PCB .

Embodiments of the present invention that are described hereinbelow provide improved techniques for repairing an electronic module, such as a PCB, by removing defects occurred during the fabrication of the PCB . For example, removing a defect comprising undesired layer of copper formed between traces of a designed copper pattern formed on a laminate of the PCB.

In principle, it is possible to remove the defect from a section of the PCB, using an iterative process of ablating a portion of the defect, followed by inspecting the section, and repeating the process until the entire defect is removed. Such iterative process reduces the risk of damaging the PCB laminate, however, each inspection step, consumes time and reduces the throughput of the defect removal process.

In some embodiments, a system for repairing PCBs by removing defects using laser ablation, comprises an optical assembly, one or more detection assemblies, and a processor. The optical assembly is configured to direct a laser beam to impinge on a section of the PCB substrate. The laser beam is configured to remove the defect formed on the section, using the impinged laser beam for ablating the undesired or excess layer of copper. In the context of the present disclosure and in the claims, the term “copper layer” refers to any sort of undesired copper defect, such as but not limited to excess copper section, or copper remaining, or copper splash, or an excess pattern of copper, or a segregation copper defect, or a combination of copper with a foreign material, or any other sort of defect comprising copper.

In some embodiments, the one or more detection assemblies are configured to detect, from a light induced and emitted from the section in response to the impinged laser beam, a spectral component indicative of copper removed from the defect.

Note that the interaction between the laser beam and the excess copper of the defect, induces the light emitted from the defect at the section. Therefore, in the context of the present disclosure and in the claims, the term “emitted light” refers to the light which is induced in response to the laser beam impinging on the copper, so that the induced light is emitted from the ablated copper.

Moreover, in the context of the present disclosure and in the claims, the term “spectral component” refers to one or more spectral lines of copper and/or other elements that are of interest to be detected. For example, the spectral component of copper may comprise one or more of the following spectral lines having wavelengths of about 5700 Angstroms (A), about 5782 A, about 6000 A, and about 6150 A, or any other suitable wavelength.

The term spectral component may also refer to the spectral component emitted by the laminate or any other material of interest.

Note that the spectral component constitutes a fingerprint for the presence of the copper defect on the substrate of the PCB, and for the ablation process for removing the undesired copper defect.

In some embodiments, using the disclosed techniques for removing the defect has several advantages, such as but not limited to: (a) defect identification - detecting the one or more spectral components emitted during the ablation is indicative of the defect presence, and is independent of the intensity of the detected signal that may vary, e.g., due to geometrical factors, such as surface roughness or shape of the defect, (b) accurate spatial monitoring - the same laser beam is used both for the ablation and for inducing the emitted and detected spectral component of light, therefore, no optical boresight error can occur and the detected spectral components is emitted from the actual location being ablated, and (c) real-time indication and control - the detection assemblies receive in real-time the one or more spectral components emitted in response to each pulse of the laser beam that impinges on the section having the defect, therefore, enabling real-time control and adjustment of the ablation process, which is described in detail herein.

In some embodiments, the processor is configured to control the laser beam, for example, to reduce the laser power, and/or to change the scan rate, and/or to adjust the beam profile, and/or the beam spot size and/or to control any other suitable parameter of the laser beam.

In other embodiments, the processor is configured to: (i) set a stopping time for the laser beam based on the detected spectral component, and subsequently or at the same time, (ii) stop the laser beam from impinging on the section at the set stopping time. In the context of the present disclosure and in the claims, the term stopping time is also referred to herein as “end-point” of ablating the copper defect.

In some embodiments, the optical assembly may comprise an acousto-optic modulator (AOM), which is configured to: (a) block or pass (on/off) the laser beam from reaching the PCB, (b) control the intensity of the laser beam, and (c) control the number of pulses of the laser beam that pass the AOM and impinge of the surface of the PCB. In some embodiments, the processor is configured to stop the laser beam from impinging on the surface of the PCB section, by controlling the AOM or other components of the optical assembly.

In some embodiments, (i) the detection assemblies may comprise fast spectrometers configured for detecting from the emitted light, at least one additional spectral component, and/or (ii) the system may comprise one or more additional detection assemblies. The detection assemblies (e.g., fast spectrometers) and/or the one or more additional detection assemblies, are configured to detect from the light induced and emitted during the ablation process, an additional spectral component, which is indicative of the substrate material, e.g., the laminate, removed from the PCB section during the ablation.

In some embodiments, in response to receiving from the additional detection assembly a signal indicative of the laminate spectral component, the processor is configured to set the stopping point based on the laminate spectral component.

In some embodiments, the system may comprise a camera assembly, which is configured to acquire images of the PCB section before the ablation, e.g., for accurately directing the laser beam to the defect, and/or after the ablation, e.g., for verifying that the entire defect has been removed and no damage has occurred to the laminate.

In some embodiments, after concluding the defect removal from the section, the processor is configured to move the PCB relative to the optical assembly, so as to position the optical assembly for removing a subsequent defect located at a subsequent section of the PCB.

The disclosed techniques are applicable, mutatis mutandis, for repairing other types of electronic components and modules, such as but not limited to Flat Panel Displays (FPD).

Moreover, the disclosed techniques reduce the cycle time and increases accuracy of repairing processes of PCB and other electronic components and modules, and therefore, reduce the production costs and improves quality of PCBs and electronic products.

SYSTEM DESCRIPTION

Fig. 1 is a block diagram of a system 11 for repairing electronic circuits of a sample 21, in accordance with an embodiment of the present invention. In the present example, sample 21 comprises a printed circuit board (PCB), but in other embodiments, sample 21 may comprise any other suitable type of component or module on an electronic product, as described below.

In some embodiments, system 11 comprises an optical assembly 13 having a laser source, referred to herein as a laser 12, which is configured to emit a laser beam 25. In the present example, laser 12 is configured to emit pulses of green laser having a 532 nm wavelength, but in other embodiments, laser 12 maybe configured to emit any other suitable type and wavelength of laser beam, such as but not limited to 1064 nm or 266 nm.

In the context of the present disclosure and in the claims, the terms “laser beam 25,” “beam 25” and “laser beam” are used interchangeably and refer to the beam emitted from laser 12 toward sample 21 and manipulated by components of optical assembly 13 of system 11, which is described in detail herein.

In some embodiments, optical assembly 13 comprises an acousto-optic modulator (AOM) 16, a scanner 18 and focusing optics 24, which are described in detail below. In some embodiments, beam 25 is configured to pass through optical assembly 13, and be directed to sample 21 for repairing electronic circuits produced on the surface of sample 21.

In some embodiments, optics 14 is configured to shape and focus beam 25 before entering AOM 16, which is configured to (a) block or pass (on/off) laser beam 25 toward sample 21, (b) control the intensity of beam 25, and (c) control the number of pulses of beam 25 that pass toward sample 21.

In some embodiments, scanner 18 may comprise a scanning mirror or any other suitable type of scanner, which is configured to direct beam 25 to impinge on a section of sample 21 for removing a layer, such as copper, formed on the respective section of sample 21. Scanner 18 is further configured to scan beam 25 at any suitable scan rate (e.g., typical scan rates are between, but not limited to, about 10 mm/sec to about 1000 mm/sec), using any scanning scheme (interleaved, or spiral, or any other sort of scanning scheme) across the intended locations on the surface of sample 21.

In the context of the present disclosure, the terms "about" or "approximately" for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein.

In some embodiments, focusing optics 24 is configured to focus beam 25, which is directed to the intended locations on the surface of sample 21. As shown in Fig. 1, optical assembly 13 is configured to scan laser beam 25 to impinge on the desired section of sample 21.

Note that during the beam scanning, a first beam 25 may impinge on a first section of sample 21 at about a right angle, and a second beam 25 may impinge on the surface of a second, different section, at any suitable angle other than a right angle.

Reference is now made to an inset 19 showing the surface of a section of sample 21. In the present example, the section of sample 21 comprises a layer 22 comprising copper or copper alloy, which is patterned on a substrate 23, such as a laminate of the aforementioned PCB. Sometimes, a defect 17, in the present example, undesired excess pattern of copper, may occur during the production of the PCB. The excess pattern of copper may cause, for example, electrical shorts between traces of layer 22, which may impair the functionality of the PCB .

Reference is now made back to the general view of Fig. 1. In some embodiments, system 11 is configured to repair such defects 17 occurred on a section of sample 21, by directing beam 25 to impinge on the surface of the respective section, so as to remove defects 17 using a laser ablation process. In response to the impinged laser beam 25, light is emitted from the surface of sample 21. In the present example, some of the light is at about a right angle from sample 21, referred to herein as a beam 30, which is an on-axis beam, and other beams of light, referred to herein as beams 32, which are off-axis beams, are from sample 21 at other angles as shown in Fig. 1.

DETECTING SPECTRAL COMPONENT INDICATIVE OF COPPER REMOVED FROM THE SUBSTRATE

In some embodiments, system 11 comprises detection assemblies (DAs) 34 and 44, which are configured to detect beams 30 and 32, respectively. Note that, compared to beam 32, beam 30 is detected when passing through focusing optics 24, and therefore, typically (but not necessarily) contains more, as well as different, information as compared to the information received from beam 32. Note that beams 32 are not passing through focusing optics 24, and therefore, have less interference compared to beam 30. Thus, a combination of beams 30 and 32 provides a complementary light induced and emitted from sample 21.

In some embodiments, system 11 comprises a beam splitter (BS) 29, which is configured to direct beam 30 to DA 34. In some embodiments, DA 34 is configured to detect from beam 30, spectral component indicative of the copper of defect 17, which is removed during the ablation process, from substrate 23 of sample 21.

In some embodiments, DA 34 comprises one or more filters 37, which are configured to pass the one or more respective spectral components indicative of the copper, also referred to herein as the copper spectral component, and to block other spectral components of beam 30. DA 34 further comprises (i) optics 36, which is configured to focus the emitted light comprising the one or more copper spectral components (SCs) that passes through one or more filter 37, and (ii) one or more detectors 35, which are configured to detect the copper SC.

In some cases, at least part of laser beam 25 may be reflected and/or scattered from the surface of sample 21, and may cause saturation of one or more detectors 35, thus blindness to the spectral component of interest. In some embodiments, at least one of filters 37 and 47 may also comprise a rejection filter, which is configured to attenuate or block the laser light, which is reflected and/or scattered from sample 21.

In the context of the present disclosure, the detected spectral component constitutes a fingerprint indicative of the presence and ablation of the undesired copper of defect 17 undesirably formed on the surface of substrate 23.

In some embodiments, DA 44, which is configured to detect the off-axis beams, e.g., beams 32, comprises a filter 47, which is configured to pass the copper SC, and to block other spectral components of beam 30. DA 44 further comprises (i) optics 46, configured to focus and shape the copper SC that pass through one or more filters 47, and (ii) one or more detectors 45, which are configured to detect one or more copper SCs.

In some embodiments, DAs 34 and 44 are configured to detect any suitable type of spectral emission, such as one or more spectral emissions selected from a list of spectral emissions consisting of: (a) fluorescence, (b) plasma, (c) Raman, (d) infrared heat radiation, and (E) Laser Induced Breakdown Spectroscopy (LIBS)

In some embodiments, system 11 comprises a processor 33, which is configured to receive from DAs 34 and 44 signals indicative of the detected copper SC. Based on the received signals, processor 33 is configured to set a stopping time for directing laser beam 25 to defect 17 on a section of sample 21, and to stop beam 25 from impinging on the section at the set stopping time, also referred to herein as an end-point, of the laser ablation process.

In some embodiments, processor 33 is configured to control active components of optical assembly 13, such as but not limited to laser 12, AOM 16 and scanner 18, so as to stop beam 25 from impinging on the aforementioned section of sample 21. In the example of Fig. 1, system 11 comprises a controller 46, which is configured to control AOM 16, and a controller 48, which is configured to control scanner 18. In other embodiments, processor 33 is configured to directly control at least one of AOM 16 and scanner 18. Similarly, system 11 may comprise a controller (not shown), which is configured to control laser 12. All the controllers described above are configured to exchange control signals and other types of data with processor 33.

In some embodiments, processor 33 is configured to synchronize the operation of DAs 34 and 44 with laser beam 25 impinging on the section of sample 21. For example, processor 33 is configured to “open” at least one of DAs 34 and 44 for detecting the emitted light only at a predefined time delay (e.g., a few micro seconds) after one or more pulses of laser beam 25 impinges on defect 17. Note that the emission of the spectrum component may be time dependent, thus, controlling the detection timing may improve the signal-to-noise ratio (SNR) of the detected spectral component. In some embodiments, laser 12 comprises any suitable laser, such as but not limited to a passive Q-Switch micro laser, supplied by Teem Photonics of Grenoble, France, which is configured to emit pulses of laser beam 25. In such embodiments, processor 33 is configured to control AOM 16 for stopping or passing beam 25, and for setting the intensity and number of pulses of beam 25, applied to sample 21 by laser 12.

In yet other embodiments, system 11 may comprise, in addition to laser 12, an ultraviolet (UV) laser, which is aligned with the optical path of laser 12 and is configured to direct an UV beam to the same position on sample 21 that laser 12 directs laser beam 25.

In some embodiments, DAs 34 and 44 or additional DAs, are configured to detect the spectral response emitted from sample 21. Note that the detected spectral response is enhanced by the UV beam, and the DAs are configured to produce a signal having improved SNR (due to the present of the UV beam), which is indicative of the detected one or more spectral component of copper emitted from defect 17.

In some embodiments, processor 33 holds one or more sections of sample 21 having defects 17 to be removed by laser ablation. Processor 33 is configured to control the repairing process of defects 17 at the respective sections, by controlling scanner 18 for scanning laser beam 25 over the one or more respective sections of sample 21.

In some embodiments, system 11 comprises an additional beam splitter, referred to herein as BS 15, and a camera assembly (CA) 20, which is configured to acquire images of sample 21. The images acquired by camera module 20 may be used, for example, for reviewing the target section before and/or after removing defects 17 by laser beam 25, or for other purpose, such as for navigating system 11 to the sections of sample 21 having defects 17.

In some embodiments, CA 20 comprises a camera optical assembly (COA) (not shown), which is configured to direct a light beam to illuminate sample 21 , and a camera (not shown) which is configured to receive, via BS 15, a light beam 28 reflected from sample 21. CA 20 is configured to transmit the acquired images to processor 33.

In some embodiments, processor 33 is configured to prevent optical boresight error that may occur between CA 20 and laser Beam 25, for a desired position on the surface of sample 21.

In other embodiments, because processor 33 is configured to set the stopping time for directing laser beam 25 to sample 21, a visual verification that defect 17 has been removed from sample 21, may not be required, and therefore CA 20 may be omitted from the configuration of system 11.

In some embodiments, system 11 comprises electrical cables 40, which are configured to conduct the signals received from DAs 34 and 44, and the control signals exchanged between processor 33, the active components of system 11, (e.g., laser 12, AOM 16 and scanner 18), and camera assembly 20.

Typically, processor 33 comprises a general-purpose processor, which is programmed in software to carry out the functions described herein. The software may be downloaded to the processor in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. Similarly, the controllers described above, comprise general-purpose controllers, programmed in software to carry out the functions described herein.

DETECTING SPECTRAL COMPONENT INDICATIVE OF SUBSTRATE MATERIAL REMOVED FROM THE SUBSTRATE

In some cases, laser beam 25 may impinge, at the same time, on a defect 17 comprising the excess pattern of copper, and on substrate 23, for example, when laser beam 25 is directed (intentionally or unintentionally) to a side-wall of defect 17 located at the aforementioned section of sample 21.

In some embodiments, system 11 comprises one or more additional detection assemblies (not shown), which are configured to detect from beams 30 and 32, an additional spectral component, which is indicative of the substrate material, e.g., laminate, removed from substrate 23 during the ablation.

In some embodiments, DAs 34 and 44 may comprise additional filters (not shown), configured to pass the spectral component of the laminate, which is unintentionally removed from substrate 23 during the ablation. These additional filters are configured to block other spectral components (not of the laminate) of beams 30 and 32.

In some embodiments, the additional filters may be fitted on DAs 34 and 44, e.g., in addition to filters 37 and 47. In alternative embodiments, at least one of filters 37 and 47 is configured to pass both spectral components of the copper and the laminate.

In some embodiments, when beam 25 impinges on both defect 17 and substrate 23 at the same time, copper and laminate may be ablated from sample 21. In response to the ablation, processor 33 may receive, from DAs 34 and 44 or from the aforementioned one or more additional DAs, signals indicative of both copper spectral components and laminate spectral components. In such embodiments, processor 33 may (i) stop laser beam 25 from impinging on the aforementioned side-wall of the respective section of sample 21, and (ii) redirect laser beam 25 to impinge solely on defect 17 so as to ablate copper from defect 17 without ablating laminate or any other material from substrate 23. In other embodiments, at least one of DAs 34 and 44 may comprise a spectrometer, which is configured to detect from at least one of beams 30 and 32, the spectral component of copper, and to produce a signal indicative of the detected spectral component of copper. In an embodiment, the spectrometer may comprise a multi element line sensor/detector based spectrometer, from Ocean Insight of Rochester, NY, USA.

In some embodiments, the spectrometer may also be configured to detect and produce signals indicative of the spectral component of both the copper and the laminate at the same time, so that in response to receiving such signals, processor 33 may stop laser beam 25 from impinging on substrate 23.

In some embodiments, at least one of detectors 35 and 45 and/or at least one of the aforementioned spectrometers may comprise fast detection capabilities, so as to shorten the detection time, and to tighten the real-time monitoring and control of the ablation process. In such embodiments, at least one of detectors 35 and 45 may comprise fast photodiodes provided, for example, by Thorlabs Inc. Newton, New Jersey, United States, and/or fast spectrometers produced, for example, by Ocean Insight of Rochester, NY, USA.

In alternative embodiments, system 11 may comprise and suitable combination of DAs and/or spectrometers and/or any other suitable subsystems configured to detect spectral components of the copper and/or other foreign materials constituting defects 17 on substrate 23.

In some embodiments, processor 33 may receive from a defect inspection system (not shown), a defect file comprising coordinates of first and second defects 17 located at first and second respective sections of sample 21. In some embodiments, processor 33 may control a motion control subsystem (not shown) to position the first section in close proximity to optical assembly 13, so as to remove the first defect using the laser beam 25, as described above. In some embodiments, after concluding the ablation of the first defect, e.g., by setting the stopping time and stopping laser beam 25 from impinging on the first section at the set stopping time, processor 33 is configured to control optical assembly 13 to direct laser beam 25 to the second section, so as to remove the second defect. For example, processor 33 may control AOM 16 to block laser beam 25 from impinging on the first section, and further control, e.g., the aforementioned motion control subsystem, to move sample 21 and laser 12 relative to one another, so as to perform the ablation of the second defect at the second section. Additionally or alternatively, in case the first and second defects are in close proximity to one another, after concluding the removal of the first defect, processor 33 may control scanner 18 to redirect laser beam 25 to the second defect, without using the motion control system.

As described above, after concluding the removal of one or more defects 17 from the first and second sections of sample 21, processor 33 is configured to control the motion control subsystem to move sample 21 relative to system 11, so as to perform verification of the defects removal from the first and second sections.

In some embodiments, system 11 is configured to ablate other sort of defects occurring on other sort of surfaces, such that the defect comprises material other than copper, and/or the surface comprising material other than laminate.

For example, a polymer defect may occur, e.g., during a solder mask process, in a section having a designed pattern of copper. In such embodiments, optical assembly 13 is configured to direct laser beam 25 to the polymer defect, and at least one of DAs 34 and 44 is configured to detect one or more spectral components, which are induced by laser beam 25 impinging on the defect. The one or more spectral components are emitted, as components of light beams 30 and 32, from the polymer defect and are detected by at least one of DAs 34 and 44.

In such embodiments, processor 33 is configured to control the ablation process based on detected spectral components of at least the polymer defect and the copper pattern. Therefore, when the detected signals are indicative of one or more spectral components of copper, and/or in the absence of spectral components of the polymer defect in the detected signals, processor 33 is configured to control optical assembly 13 to stop laser beam from impinging on the section comprising the polymer defect, or to control optical assembly to control parameters of laser beam 25, for example, for attenuation of laser beam 25.

This particular configuration of system 11 is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such a system. Embodiments of the present invention, however, are by no means limited to this specific sort of example system, and the principles described herein may similarly be applied to other sorts of defect repair systems.

Fig. 2A is a graph 70 showing detection of one or more copper spectral components 72 of light, emitted over time from sample 21, during ablation of defect 17, in accordance with an embodiment of the present invention. The vertical axis denotes the intensity of the one or more copper spectral components and the horizontal axis denotes a time axis.

In the example of Fig. 2A, defect 17 comprises copper having a thickness of 18 pm. A dual-headed axis 76 shows the ablation time of defect 17, whereas markers 78 and 79 show, respectively, the starting time of the laser and stopping time of the spectral component emitted from the copper layer. In the example of Fig. 2A, the ablation time is about 85 milliseconds. Graph 70 also shows noise 74 of the detection. Note that after marker 79, copper spectral component 72 does not appear in graph 70, because defect 17 has been removed. Note that once the copper spectral component disappears, the laser is set to off, so as to avoid or minimize undesired damage to the underlying laminates layer.

In some embodiments, processor 33 is configured to set the ablation stopping time using any suitable technique. For example, processor 33 may set a threshold for the signal intensity of copper spectral component 72. In this example, when the signal intensity is lower than the threshold over a predefined time interval, processor 33 controls, e.g., AOM 16 and scanner 18 for stopping laser beam 25 to impinge on the section having defect 17, at the set stopping time shown by marker 79. In other embodiments, processor 33 may use any other suitable technique for setting the ablation stopping time.

Fig. 2B is a graph 80 showing copper spectral component 82 of light, emitted over time from sample 21, during ablation of defect 17, in accordance with an embodiment of the present invention. The vertical axis denotes the intensity of the copper spectral component and the horizontal axis denotes a time axis.

In the example of Fig. 2B, defect 17 comprises copper having a thickness of 12 pm. A dual-headed axis 86 shows the ablation time of defect 17, whereas markers 88 and 89 show, respectively, the starting time and stopping time of the ablation. In the example of Fig. 2B, the ablation time is about 45 milliseconds, substantially lower the ablation time of Fig. 2A above. Graph 80 also shows noise 84 of the copper spectral component. Note that after marker 89, copper spectral component 82 does not appear in graph 80, because defect 17 has been removed.

In some embodiments, processor 33 is configured to set the ablation stopping time shown by marker 89 using any suitable technique, as described in Fig. 2A above.

Fig. 2C is a graph 90 showing copper spectral component 92 of light, emitted over time from sample 21, during ablation of defect 17, in accordance with an embodiment of the present invention. The vertical axis denotes the intensity of the copper spectral component and the horizontal axis denotes a time axis.

In the example of Fig. 2C, defect 17 comprises copper having a thickness of 7 pm. A dualheaded axis 96 shows the ablation time of defect 17, whereas markers 98 and 99 show, respectively, the starting time and stopping time of the ablation. In the example of Fig. 2C, the ablation time is about 20 milliseconds, substantially lower the ablation times of Figs. 2A and 2B above. Graph 90 also shows noise 94 of the copper spectral component. Note that after marker 99, copper spectral component 92 does not appear in graph 90, because defect 17 has been removed.

In some embodiments, processor 33 is configured to set the ablation stopping time shown by marker 99 using any suitable technique.

Reference is now made to a general view of graphs 2A, 2B and 2C, which are based on experiments carried out by the inventors of the present invention, e.g., for demonstrating the disclosed concept. In some embodiments, processor 33 is configured to set the stopping time based on the detected spectral component of the copper of defect 17. Graphs 2A, 2B and 2C show similar starting times, by respective markers 78, 88 and 98, and different stopping times, by respective markers 79, 89 and 99. As described above, the stopping times are set by processor 33 due to the respective thicknesses, 18 pm, 12 pm, and 7 pm, of the copper of defect 17.

In other embodiments, system 11 may comprise one or more additional DAs, configured to detect the spectral component of the laminate or any other material of substrate 23 being ablated by laser beam 25. In such embodiments, the laminate spectral component is not detected by DAs 34 and 44, and therefore is not used by processor 33 for setting the stopping time of the ablation process for removing defect 17.

In the present example, in the example of graphs 2A, 2B and 2C, the copper spectral component may be detected solely by DAs 34.

In other embodiments, processor 33 is configured to hold a threshold for detection of the laminate spectral component. In such embodiments, when receiving from the aforementioned one or more additional DAs, a signal comprising the laminate spectral component at a level higher than the threshold, processor 33 is configured to set the stopping time, and to control, e.g., AOM 16 and/or scanner 18 stop impinging laser beam 25 on the section having defect 17.

As described in Fig. 1 above, processor 33 may control AOM 16 to block laser beam 25 from impinging on the respective section. Alternatively, processor 33 may control scanner 18 and/or the aforementioned motion control subsystem, to move sample 21 relative to laser 12, so as to direct laser beam 25 to impinge on another section of sample 21, for removing another defect 17 occurred on substrate 23.

Fig. 3 is a flow chart that schematically illustrates a method for controlling a process of removing defect 17 from sample 21, using spectral components of light emitted from defect 17 during the process, in accordance with an embodiment of the present invention.

The method begins at a laser directing step 100, with directing laser beam 25 to impinge on a section of substrate 23 of sample 21, so as to remove the copper layer of defect 17 occurred on the section. In the present example, sample 21 comprises PCB having substrate 23 comprising laminate.

At a detecting step 102, in response to the impinged laser beam 25, at least one of DAs 34 and 44, detects from light emitted from the section of sample 21, a spectral component indicative of copper removed from sample 21.

Note that the detected spectral component constitutes a fingerprint for the presence of the undesired copper layer on the surface of substrate 23, and for the ablation process thereof. At a decision step 104, processor 33, which holds a predefined threshold for the emitted level of one or more spectral components (SCs), checks whether the detected SC exceeds the threshold. For example, one the one hand, when the detected SC of copper exceed a copper SC threshold, the ablation has not been completed. On the other hand in absence of copper SC in the detected signals, or when the level of detected copper SC is below the copper SC threshold, the ablation has to be stopped or at least adjusted so as to prevent damage to the laminate layer of the section. Therefore, in case the detected SC of copper exceeds the threshold, the method loops back to step 100 so as to continue the ablation of the copper layer in defect 17.

In case the detected SC of copper is below the copper SC threshold, the method proceeds to an ablation controlling step 104, which terminates the method. At ablation controlling step 104, processor 33 controls or stops laser beam 25 based on the detected one or more SCs. For example, in absence of copper SC the processor may set the stopping time (shown as markers 79, 89 and 99, of respective graphs 70, 80 and 90) for laser beam 25. As described in Figs. 1 and 2 above, the stopping time is based on the detected copper spectral component of the light (e.g., beams 30 and 32) emitted from ablated defect 17. Process 33 is further configured to stop laser beam 25 from impinging on the section of sample 21, at the set stopping time.

In other embodiments, e.g., when the copper SC is still detected but at a level lower than the copper SC threshold, processor 33 is configured to control optical assembly for adjusting laser beam 25, so as to prevent or minimize damage to the laminate material of sample 21 (e.g., the aforementioned PCB).

As described in Fig. 1 above, in other embodiments, at least one of DAs 34 and 44 are configured for detecting spectral component of the laminate or another material of the PCB. In such embodiments, at detecting step 102, in addition to the coper spectral component, DAs 34 and 44 may detect spectral component indicative of laminate removed from sample 21.

Moreover, in such embodiments, in decision step 104, processor is configured to check whether or not one or more SCs other than copper SC, e.g., laminate SC, has been detected by one or more of DAs 34 and 44. If not, the method loops back to step 100 so as to proceed with the ablation as described above.

In case one or more laminate SCs have been detected, the method proceeds to step 104, for controlling or stopping laser beam 25. For example, controlling the impinging position of laser beam 25 so as to ablate defect 17 without damaging the laminate, or stopping laser beam 25 from impinging on the respective section, and therefore, prevent damaging the laminate.

Although the embodiments described herein mainly address removal of copper defects occurred on a PCB, the methods and systems described herein can also be used in other applications, such as removing any type of defect from any type of substrate using laser ablation, and in other laser-based processes for producing electronic circuits, such as but not limited to controlling drilling holes and/or vias through copper layer where stopping the laser drilling is important in order to prevent damaging layers and/or laminate located in close proximity to the designed hole/via. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.