TWI899357B - Method and system for controlling a laser repair process of electronic circuits - Google Patents

Abstract

A method includes, 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.

Description

Method and system for controlling laser repair processing of electronic circuits

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

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

For example, U.S. Patent Publication No. 2005/0226287 describes a laser processing system comprising a femtosecond laser, frequency conversion optics, beam steering optics, target motion control, a processing chamber, a diagnostic system, and a system control module. The laser processing system allows for unique thermal control in micromachining and features greater output beam stability, continuously variable repetition rates, and unique temporal beam shaping capabilities.

U.S. Patent Application Publication No. 2007/0092128 describes an apparatus and method for automatically inspecting and repairing printed circuit boards, including an inspection functionality for automatically inspecting the printed circuit board and providing a machine-readable indication of areas requiring repair. An automatic repair functionality uses the machine-readable indication to repair the printed circuit board at areas requiring repair. An automatic repair and reconfiguration functionality automatically re-inspects the printed circuit board after an initial automatic repair operation and provides the automatic repair functionality with a reconfiguration machine-readable indication of areas requiring repair.

One embodiment of the invention described herein provides a method comprising directing a laser beam to impinge on a section of a substrate to remove a layer formed on the section. Light emitted from the section in response to the impinging laser beam is detected by at least one optical component indicating the layer material removed from the layer. Based on the detected optical component, the laser beam is 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 layer, and the laminate layer includes a copper defect. In still other embodiments, the method includes detecting an additional spectral component of the light emitted from the segment that indicates substrate material removed from the substrate.

In one embodiment, controlling or stopping the laser beam includes setting a dwell time based on both the optical component and the additional optical component. In another embodiment, the laser beam is redirected to impinge on the layer within the segment in response to detecting that both the optical component and the additional optical component are above a predetermined threshold.

In some embodiments, controlling or stopping the laser beam includes performing at least one operation selected from a list consisting of: (i) blocking the laser beam, (ii) shutting off the laser beam, and (iii) directing the laser beam to a subsequent section of the substrate. In other embodiments, detecting at least the optical component includes detecting one or more optical emissions selected from a list consisting of: (a) fluorescence, (b) plasma, (c) Raman, (d) infrared thermal radiation, and (e) laser-induced avalanche spectroscopy (LIBS).

According to one embodiment of the present invention, a system is further provided that includes 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 a spectral component indicating layer material removed from the section through light emitted from the section in response to the impinging laser beam. 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 lens, and focusing optics.

The present invention will be more fully understood from the following detailed description of the embodiments of the present invention in conjunction with the drawings, wherein:

11: System

12: Laser

13: Optical assembly

14: Optical devices

15: Beam Splitter (BS)

16: Acousto-Optical Modulator (AOM)

17: Defects

18: Scanner

19: Illustration

20: Camera Assembly (CA)

21: Sample

22: Layer

23:Substrate

24: Focusing Optics

25: Beam

28: Beam

29: Beam Splitter (BS)

30: Beam

32: Beam

33: Processor

34: Detection Assembly (DA)

35: Detector

36: Optical devices

37: Filter

40: Cable

44: Detection Assembly (DA)

45: Detector

46: Optical Devices/Controllers

47: Filter

48: Controller

70: Charts

72: Copper Spectrum Components

74: Noise

76: Double-ended shaft

78:Mark

79: Marker

80: Charts

82: Copper Spectrum Components

84: Noise

86: Double-ended shaft

88:Mark

89: Marker

90: Charts

92: Copper Spectrum Components

94: Noise

96: Double-ended shaft

98:Mark

99:Mark

100: Steps

102: Step

104: Step

106: Step

FIG1 is a block diagram of a system for repairing electronic circuits using lasers according to an embodiment of the present invention; FIG2A, FIG2B, and FIG2C are diagrams showing a spectroscopic component for emitting light to indicate copper removal from a substrate according to an embodiment of the present invention; and FIG3 is a flow chart schematically illustrating a method for controlling a process for removing defects from electronic circuits using a spectroscopic component for emitting light from a defect during a process according to an embodiment of the present invention.

Overview

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

The embodiments of the present invention described below provide improved techniques for repairing an electronic module, such as a PCB, by removing defects that occur during the PCB's manufacturing process. For example, the removal of a defect includes an undesirable copper layer formed between traces of a designed copper pattern formed on a laminate of the PCB.

In principle, defects can be removed from a section of the PCB using an iterative process of etching out a portion of the defect, then inspecting the section and repeating the process until the entire defect is removed. This iterative process reduces the risk of damaging the PCB laminate; however, each inspection step is time-consuming and reduces the throughput of the defect removal process.

In some embodiments, a system for repairing a PCB by removing defects using laser ablation includes 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 a PCB substrate. The laser beam is configured to remove defects formed on the section by ablating unwanted or excess copper using the impact laser beam. In the context of the present invention and the scope of the patent application, the term "copper layer" refers to any type of undesirable copper defect, such as (but not limited to) an excess copper region, or a copper residue, or a copper splash, or an excess copper pattern, or a separate copper defect, or a combination of copper and a foreign substance, or any other type of defect including copper.

In some embodiments, one or more detection assemblies are configured to sense and emit light from the segment in response to an impinging laser beam to detect a spectroscopic component indicative of copper removed from the defect.

It should be noted that the interaction between the laser beam and the excess copper in the defect induces light emission from the defect at that section. Therefore, in the context of the present invention and the scope of the patent application, the term "emitted light" refers to light induced in response to the laser beam impinging on the copper, such that the induced light is emitted from the ablated copper.

Furthermore, in the context of the present invention and the scope of the patent application, the term "spectral component" refers to one or more spectral lines of the copper and/or other components of interest to be detected. For example, the spectral component of copper may include one or more of the following spectral lines having wavelengths of approximately 5700 angstroms (Å), approximately 5782 Å, approximately 6000 Å, and approximately 6150 Å, or any other suitable wavelength.

The term optical component may also refer to optical components emitted by a laminate or any other material of interest.

Attention should be paid to the presence of copper defects on the substrate of the PCB that forms the optical component and to the fingerprint of the etching process used to remove the undesirable copper defects.

In some embodiments, using the disclosed techniques to remove defects has several advantages, such as, but not limited to: (a) defect identification - detecting one or more spectral components emitted during ablation indicates the presence of a defect, independent of the intensity of the detected signal which may vary, for example, due to geometric factors such as surface roughness or the shape of the defect, (b) accurate spatial monitoring - the same laser beam is used for ablation and (c) Real-time indication and control - the detection assembly receives one or more optical spectroscopic components in response to each pulse of the laser beam that strikes the defective section, thereby achieving 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 laser power and/or change the scan rate, and/or adjust the beam profile and/or spot size and/or any other suitable parameter of the laser beam.

In other embodiments, the processor is configured to: (i) set a dwell time for the laser beam based on the detected spectral component and, subsequently or simultaneously, (ii) stop the laser beam from impinging on the segment at the set dwell time. In the context of the present invention and the scope of the claims, the term dwell time also refers to the "end point" of the etched copper defect.

In some embodiments, the optical assembly may include an acousto-optic modulator (AOM) configured to: (a) block or pass (turn 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 through the AOM and strike 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 assembly may include a fast spectrometer configured for self-emitted light detection, at least one additional spectroscopic component, and/or (ii) the system may include one or more additional detection assemblies. The detection assembly (e.g., a fast spectrometer) and/or the one or more additional detection assemblies are configured to sense and emit light during the ablation process to detect substrate material (e.g., a laminate) removed from the PCB section during the ablation process.

In some embodiments, in response to receiving a signal from the additional detection assembly indicating a laminar pressure spectroscopy component, the processor is configured to set a stopping point based on the laminar pressure spectroscopy component.

In some embodiments, the system may include a camera assembly configured to acquire images of the PCB section before ablation, for example, to accurately direct the laser beam to the defect, and/or after ablation, for example, to verify that the entire defect has been removed and that no damage has occurred to the laminate.

In some embodiments, after completing defect removal from a section, the processor is configured to move the PCB relative to the optical assembly to position the optical assembly to remove a subsequent defect located in a subsequent section of the PCB.

The disclosed techniques can be applied, mutatis mutandis, to repair other types of electronic components and modules, such as (but not limited to) flat panel displays (FPDs).

Furthermore, the disclosed technology reduces the cycle time of PCBs and other electronic components and modules and improves the accuracy of the repair process, thereby reducing production costs and improving the quality of PCBs and electronic products.

System Description

FIG1 is a block diagram of a system 11 for repairing an electronic circuit of a sample 21 according to an embodiment of the present invention. In this example, the sample 21 comprises a printed circuit board (PCB), but in other embodiments, the sample 21 may comprise any other suitable type of component or module on an electronic product, as described below.

In some embodiments, system 11 includes an optical assembly 13 having a laser source (referred to herein as a laser 12) configured to emit a laser beam 25. In this example, laser 12 is configured to emit pulses of green laser light having a wavelength of 532 nm, but in other embodiments, laser 12 can be configured to emit any other suitable type and wavelength of laser light, such as, but not limited to, 1064 nm or 266 nm.

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

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

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

In some embodiments, the scanner 18 may include a scanning mirror or any other suitable type of scanner configured to direct the light beam 25 to impinge on a section of the sample 21 to remove a layer (e.g., copper) formed on the respective section of the sample 21. The scanner 18 is further configured to scan the light beam 25 across the desired location on the surface of the sample 21 using any scanning scheme (interlaced scanning, spiral scanning, or any other type of scanning scheme) at any suitable scanning rate (e.g., typical scanning rates ranging from, but not limited to, about 10 mm/second to about 1000 mm/second).

In the context of this invention, the term "about" or "approximately" used for any numerical value or range indicates a suitable dimensional tolerance that allows the part or assembly of components to function for its intended purpose.

In some embodiments, focusing optics 24 are configured to focus beam 25 directed to a desired location on the surface of sample 21. As shown in FIG1 , optical assembly 13 is configured to scan laser beam 25 to impinge on a desired section of sample 21.

It should be noted that during beam scanning, a first beam 25 may impinge on a first section of the sample 21 at approximately 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 inset 19 showing the surface of a section of sample 21. In this embodiment, the section of sample 21 includes a layer 22 patterned on a substrate 23 (such as a laminate of the aforementioned PCB) comprising copper or a copper alloy. Occasionally, during PCB production, a defect 17 (in this example, an undesirable excess pattern of copper) may occur. This excess pattern of copper can cause, for example, electrical shorts between traces of layer 22, which can impair the functionality of the PCB.

Referring back to the general view of FIG. 1 , in some embodiments, system 11 is configured to repair defects 17 present on a section of sample 21 using a laser ablation process by directing a light beam 25 to impinge on the surface of the respective section. In response to the impinging laser beam 25 , light is emitted from the surface of sample 21 . In this example, some of the light (herein referred to as light beam 30 , which is an on-axis beam) is at approximately a right angle to sample 21 , while other light beams (herein referred to as light beam 32 , which are off-axis beams) are at other angles to sample 21 , as shown in FIG. 1 .

Detection of Spectroscopic Assembly Indicating Copper Removal from Substrate In some embodiments, system 11 includes detection assemblies (DAs) 34 and 44 configured to detect beams 30 and 32, respectively. Note that beam 30 is detected while passing through focusing optics 24 compared to beam 32 and, therefore, typically (but not necessarily) contains more and different information than the information received from beam 32. Note that beam 32 does not pass through focusing optics 24 and, therefore, has less interference than beam 30. Thus, a combination of beams 30 and 32 provides a complementary beam sensed and emitted from sample 21.

In some embodiments, system 11 includes a beam splitter (BS) 29 configured to direct light beam 30 to DA 34. In some embodiments, DA 34 is configured to detect spectroscopic components of copper from light beam 30 that indicate defects 17 removed from substrate 23 of sample 21 during an ablation process.

In some embodiments, the DA 34 includes one or more filters 37 configured to pass one or more respective optical components (also referred to herein as copper spectral components) indicating copper and block other optical components of the light beam 30. The DA 34 further includes (i) optics 36 configured to focus emitted light, including one or more copper spectral components (SCs) passing through the one or more filters 37, and (ii) one or more detectors 35 configured to detect copper SCs.

In some cases, at least a portion of the laser beam 25 may be reflected and/or scattered from the surface of the sample 21 and may cause saturation of one or more detectors 35, thereby blinding the spectral component of interest.

In some embodiments, at least one of filters 37 and 47 may also include a rejection filter configured to attenuate or block laser light reflected and/or scattered from sample 21.

In the context of the present invention, the detected optical spectrum component constitutes a fingerprint indicating the presence of unwanted copper and corrosion of defects 17 that are undesirably formed on the surface of the substrate 23.

In some embodiments, a DA 44 configured to detect off-axis beams (e.g., beam 32) includes a filter 47 configured to pass copper SCs and block other optical components of beam 30. DA 44 further includes (i) optics 46 configured to focus and shape the copper SCs passing through one or more filters 47, and (ii) one or more detectors 45 configured to detect the 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) plasmon, (c) Raman, (d) infrared thermal radiation, and (e) laser-induced avalanche spectroscopy (LIBS).

In some embodiments, system 11 includes a processor 33 configured to receive signals from Da 34 and 44 indicating detected copper SC. Based on the received signals, processor 33 is configured to set a stop 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 stop 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) to prevent beam 25 from impinging on the aforementioned section of sample 21. In the example of FIG. 1 , system 11 includes a controller 46 configured to control AOM 16 and a controller 48 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 include a controller (not shown) configured to control laser 12. All of these controllers 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 the laser beam 25 impinging on a section of sample 21. For example, processor 33 is configured to "turn on" at least one of DAs 34 and 44 to detect emitted light only a predetermined time delay (e.g., a few microseconds) after one or more pulses of laser beam 25 impinge on defect 17. It should be noted that the emission of optical components can be time-dependent, and therefore, controlling the detection timing can improve the signal-to-noise ratio (SNR) of the detected optical components.

In some embodiments, laser 12 comprises any suitable laser, such as, but not limited to, a passive Q-switched microlaser supplied by Teem Photonics of Grenoble, France, configured to emit pulses of laser beam 25. In these embodiments, processor 33 is configured to control AOM 16 to stop or pass beam 25, and to set the intensity and number of pulses of beam 25 applied by laser 12 to sample 21.

In other embodiments, in addition to laser 12, system 11 may include an ultraviolet (UV) laser aligned with the optical path of laser 12 and configured to direct a UV beam onto sample 21 at the same location where laser 12 directs laser beam 25.

In some embodiments, DAs 34 and 44 or additional DAs are configured to detect spectral responses emitted from sample 21. Note that the detected spectral responses are enhanced by the UV beam, and the DAs are configured to generate a signal with an improved SNR (attributed to the presence of the UV beam), indicating the detection of one or more spectral components of copper emitted from defect 17.

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

In some embodiments, the system 11 includes an additional beam splitter (referred to herein as BS 15) and a camera assembly (CA) 20 configured to acquire images of the sample 21. The images acquired by the camera assembly 20 can be used, for example, to review the target section before and/or after the defect 17 is removed by the laser beam 25, or for other purposes, such as for navigating the system 11 to the section of the sample 21 having the defect 17.

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

In some embodiments, processor 33 is configured to prevent optical line-of-sight errors that may occur between CA 20 and laser beam 25 for a desired location on the surface of sample 21.

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

In some embodiments, system 11 includes cables 40 configured to carry signals received from DAs 34 and 44 and control signals exchanged between processor 33, 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 programmed in software to implement the functionality described herein. The software may be downloaded to the processor electronically, for example, over a network, or alternatively or additionally, it may be provided and/or stored on non-transitory tangible media (such as magnetic, optical, or electronic memory). Similarly, the controller described above comprises a general-purpose controller programmed in software to implement the functionality described herein.

Spectroscopic component for detecting and indicating removal of substrate material from a substrate

In some cases, for example, when laser beam 25 is directed (intentionally or unintentionally) back toward a sidewall of defect 17 located at the aforementioned section of sample 21, laser beam 25 may simultaneously impinge on a defect 17 comprising an excess pattern of copper and substrate 23.

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

In some embodiments, DAs 34 and 44 may include additional filters (not shown) configured to pass optical components of the laminate that are inadvertently removed from substrate 23 during ablation. These additional filters are configured to block other optical components of beams 30 and 32 (not of the laminate).

In some embodiments, additional filters may be mounted on DAs 34 and 44, for example, in addition to filters 37 and 47. In an alternative embodiment, at least one of filters 37 and 47 is configured to pass both the copper and laminate optical components.

In some embodiments, when beam 25 simultaneously impinges on defect 17 and substrate 23, copper and the laminate may be etched from sample 21. In response to the etch, processor 33 may receive signals indicative of both the copper optical component and the laminate optical component from DAs 34 and 44, or from one or more additional DAs. In these embodiments, processor 33 may (i) stop laser beam 25 from impinging on the aforementioned sidewalls of the respective sections of sample 21, and (ii) redirect laser beam 25 to impinge only on defect 17, thereby etching copper from defect 17 without etching the laminate or any other material from substrate 23.

In other embodiments, at least one of DAs 34 and 44 may include a spectrometer configured to detect copper spectral components from at least one of light beams 30 and 32 and generate a signal indicative of the detected copper spectral components. In one embodiment, the spectrometer may include a multi-element line sensor/detector-based spectrometer from Ocean Insight of Rochester, New York, USA.

In some embodiments, the spectrometer can also be configured to simultaneously detect and generate signals indicative of optical components of both the copper and laminate so that in response to receiving these signals, the processor 33 can stop the laser beam 25 from impinging on the substrate 23.

In some embodiments, at least one of detectors 35 and 45 and/or at least one of the aforementioned spectrometers may include fast detection capabilities to shorten detection time and enhance real-time monitoring and control of the ablation process. In such embodiments, at least one of detectors 35 and 45 may include fast photodiodes provided by, for example, Thorlabs Inc. of Newton, New Jersey, USA, and/or fast spectrometers manufactured by, for example, Ocean Insight of Rochester, New York, USA.

In alternative embodiments, the system 11 may include a suitable combination of a DA and/or a spectrometer and/or any other suitable subsystems of optical components configured to detect copper and/or other foreign matter constituting the defect 17 on the substrate 23.

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

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

In some embodiments, system 11 is configured to etch other types of defects occurring on other types of surfaces, such that the defects comprise materials other than copper and/or include surfaces of materials other than laminates.

For example, a polymer defect may occur in a region of a copper design, such as during a solder mask process. In these embodiments, optical assembly 13 is configured to direct laser beam 25 toward the polymer defect, and at least one of DAs 34 and 44 is configured to detect one or more optical components responsive to the laser beam 25 impinging on the defect. The one or more optical components are emitted from the polymer defect as components of beams 30 and 32 and detected by at least one of DAs 34 and 44.

In these embodiments, processor 33 is configured to control the ablation process based on at least the detected spectral components of the polymer defect and the copper pattern. Thus, when the detected signal indicates one or more spectral components of copper and/or when the spectral components of the polymer defect are absent in the detected signal, processor 33 is configured to control optical assembly 13 to stop the laser beam from impinging on the segment including the polymer defect, or to control the optical assembly to control parameters of laser beam 25 to, for example, attenuate laser beam 25.

This particular configuration of system 11 is presented as an example to illustrate some of the problems solved by embodiments of the present invention and to demonstrate the application of these embodiments to enhance the performance of such a system. However, embodiments of the present invention are in no way limited to this particular type of exemplary system, and the principles described herein can be similarly applied to other types of defect repair systems.

FIG2A is a graph 70 showing detection of one or more copper spectral components 72 of light emitted from sample 21 over time during ablation of defect 17 according to an embodiment of the present invention. The vertical axis specifies the intensity of the one or more copper spectral components and the horizontal axis specifies a time axis.

In the example of Figure 2A , defect 17 comprises copper having a thickness of 18 μm. A double-ended axis 76 shows the erosion time of defect 17, while marks 78 and 79 respectively show the start time of the laser and the stop time of the optical component emitted from the copper layer. In the example of Figure 2A , the erosion time is approximately 85 milliseconds. Graph 70 also shows the detected noise 74. Note that after mark 79, the copper optical component 72 does not appear in graph 70 because defect 17 has been removed. Note that once the copper optical component disappears, the laser is turned off to avoid or minimize undesirable damage to the underlying laminate.

In some embodiments, processor 33 is configured to use any suitable technique to set the ablation stop time. For example, processor 33 may set a threshold value for the signal strength of copper optical component 72. In this example, when the signal strength falls below the threshold value for a predefined time interval, processor 33 controls, for example, AOM 16 and scanner 18 to stop laser beam 25 from impinging on the section having defect 17 at the set stop time indicated by marker 79. In other embodiments, processor 33 may use any other suitable technique to set the ablation stop time.

FIG2B is a graph 80 showing a copper spectral component 82 of light emitted from sample 21 over time during ablation of defect 17 according to an embodiment of the present invention. The vertical axis specifies the intensity of the copper spectral component and the horizontal axis specifies a time axis.

In the example of Figure 2B , defect 17 comprises copper having a thickness of 12 μm. A double-ended spindle 86 shows the etch time for defect 17, while markers 88 and 89 show the start and stop times of the etch, respectively. In the example of Figure 2B , the etch time is approximately 45 milliseconds, substantially lower than the etch time in Figure 2A . Graph 80 also shows the noise 84 of the copper spectral component. Note that after marker 89, the copper spectral component 82 does not appear in graph 80 because defect 17 has been removed.

In some embodiments, processor 33 is configured to use any suitable technique to set the etch stop time indicated by marker 89, as described above in FIG. 2A.

FIG2C is a graph 90 showing a copper spectral component 92 of light emitted from sample 21 over time during ablation of defect 17 according to an embodiment of the present invention. The vertical axis specifies the intensity of the copper spectral component and the horizontal axis specifies a time axis.

In the example of FIG2C , defect 17 comprises copper having a thickness of 7 μm. Double-ended spindle 96 shows the etch time for defect 17, while markers 98 and 99 show the start and stop times of the etch, respectively. In the example of FIG2C , the etch time is approximately 20 milliseconds, substantially lower than the etch times shown in FIG2A and FIG2B . Graph 90 also shows noise 94 for 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 use any suitable technique to set the etch stop time indicated by marker 99.

Reference is now made to a general view of Figures 2A, 2B, and 2C, which are based on experiments performed by the inventors of the present invention, for example, to demonstrate the disclosed concepts. In some embodiments, processor 33 is configured to set a stop time based on the detected optical spectrum of copper defect 17. Figures 2A, 2B, and 2C show similar start times, as indicated by respective labels 78, 88, and 98, and different stop times, as indicated by respective labels 79, 89, and 99. As described above, the stop times were set by processor 33 due to the respective thicknesses of copper defect 17 being 18 μm, 12 μm, and 7 μm.

In other embodiments, system 11 may include one or more additional DAs configured to detect spectral components of the laminate or any other material of substrate 23 that is ablated by laser beam 25. In these embodiments, the spectral components of the laminate are not detected by DAs 34 and 44 and, therefore, are not used by processor 33 to set a stop time for the ablation process used to remove defect 17.

In this example, in the examples of Figures 2A, 2B, and 2C, the copper optical component can be detected only by DA 34.

In other embodiments, the processor 33 is configured to maintain a threshold value for detecting the laminate optical spectrum component. In these embodiments, when a signal including the laminate optical spectrum component is received from the one or more additional DAs at a level above the threshold value, the processor 33 is configured to set a stop time and control, for example, the AOM 16 and/or the scanner 18 to stop the laser beam 25 from impinging on the section having the defect 17.

As described above in FIG. 1 , processor 33 can control AOM 16 to block laser beam 25 from impinging on the respective sections. Alternatively, processor 33 can control scanner 18 and/or the aforementioned motion control subsystem to move sample 21 relative to laser 12 to direct laser beam 25 to impinge on another section of sample 21 to remove another defect 17 present on substrate 23.

FIG3 is a flow chart schematically illustrating a method for controlling a process of removing a defect 17 from a sample 21 using a spectroscopic component of light emitted from the defect 17 during the process, according to an embodiment of the present invention.

The method begins with a laser guidance step 100, in which a laser beam 25 is directed to impinge on a section of a substrate 23 of a sample 21 to remove a copper layer having a defect 17 present in the section. In this embodiment, the sample 21 comprises a PCB having a substrate 23 including a laminate.

At a detection step 102, light emitted from the section of sample 21 in response to the impinging laser beam 25, at least one of DAs 34 and 44, detects a spectral component indicating removal of copper from sample 21.

It should be noted that the presence of an undesirable copper layer and a fingerprint of its etching process on the surface of the substrate 23 constituting the optical component was detected.

At a decision step 104, processor 33, which maintains a predefined threshold for the emission level of one or more spectral components (SCs), checks whether the detected SC exceeds the threshold. For example, if the detected Cu SC exceeds a Cu SC threshold, etching is not yet complete. If no Cu SC is present in the detected signal, or if the detected Cu SC is less than the Cu SC threshold, etching must be stopped or at least adjusted to prevent damage to the laminate in that section. Therefore, in the event that the detected SC of copper exceeds the critical value, the method loops back to step 100 to continue etching the copper layer in the defect 17.

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

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

As described above in FIG. 1 , in other embodiments, at least one of DAs 34 and 44 is configured to detect optical components of another material of the laminate or PCB. In these embodiments, in addition to the copper optical components, DAs 34 and 44 can detect optical components of the laminate that have been removed from sample 21 during detection step 102 .

Furthermore, in these embodiments, in decision step 104, the processor is configured to check whether one or more SCs other than copper SCs (e.g., laminated SCs) have been detected by one or more of DAs 34 and 44. If not, the method loops back to step 100 to continue etching as described above.

If one or more laminate SCs have been detected, the method proceeds to step 104 to control or stop the laser beam 25. For example, the impact position of the laser beam 25 is controlled to etch the defects 17 without damaging the laminate, or the laser beam 25 is stopped from impacting the respective sections and, thus, preventing damage to the laminate.

While the embodiments described herein primarily address the removal of copper defects occurring on PCBs, the methods and systems described herein may 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) controlled drilling of holes and/or vias through copper layers, where stopping the laser drill is important to prevent damage to layers and/or laminates near the designed holes/vias.

Therefore, it will be understood that the above embodiments are cited by way of example only, and the present invention is not limited to what has been particularly shown and described herein. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications thereof not disclosed in the prior art that would occur to a person skilled in the art upon reading the foregoing description.

Documents incorporated by reference into this patent application shall be considered an integral part of this application, except that to the extent such incorporated documents define any term in a manner that conflicts with an express or implied definition in this specification, only the definition in this specification shall control.

100: Step 102: Step 104: Step 106: Step

Claims (15)

A method for controlling a laser repair process of an electronic circuit comprises: directing a laser beam to impinge on a region of a substrate to remove a layer formed on the region; detecting at least one optical component indicative of layer material removed from the region from light emitted from the region in response to the impinging laser beam; detecting an additional optical component indicative of substrate material removed from the substrate in response to the light emitted from the region; and controlling or stopping the laser beam from impinging on the region based on the detected optical component and the detected additional optical component. The method of claim 1, wherein directing the laser beam comprises directing a pulsed laser beam. The method of claim 1, wherein the substrate comprises a printed circuit board (PCB) having a laminate layer and the layer comprises a copper defect. The method of claim 1, wherein controlling or stopping the laser beam comprises setting a stop time based on both the optical component and the additional optical component. The method of claim 1, wherein in response to detecting that both the spectral component and the additional spectral component are above a predetermined threshold, the laser beam is redirected to impinge on the layer within the segment. The method of claim 1, wherein controlling or stopping the laser beam comprises performing at least one operation selected from a list of operations consisting of: (i) blocking the laser beam, (ii) turning off the laser beam, (iii) adjusting power, and (iv) directing the laser beam to a subsequent section of the substrate. The method of claim 1, wherein detecting at least the spectroscopic component comprises detecting one or more spectral emissions selected from a list of spectral emissions consisting of: (a) fluorescence, (b) plasmon, (c) Raman, (d) infrared thermal radiation, and (e) laser induced avalanche spectroscopy (LIBS). A system for controlling a laser repair process of an electronic circuit includes: an optical assembly configured to direct a laser beam to impinge on a section of a substrate, wherein the laser beam is configured to remove a layer formed on the section; a detection assembly configured to detect, from light emitted from the section in response to the impinging laser beam, a spectral component indicating layer material removed from the layer and an additional spectral component indicating substrate material removed from the substrate; and a processor configured to control or stop the laser beam from impinging on the section based on the detected spectral component and the detected additional spectral component. The system of claim 8, wherein the optical assembly is configured to direct a pulsed laser beam. The system of claim 8, wherein the optical assembly comprises at least one of an acousto-optic modulator (AOM), a scanning mirror, and focusing optics. The system of claim 8, wherein the substrate comprises a printed circuit board (PCB) having a laminate layer and the layer comprises a copper defect. The system of claim 8, wherein the processor is configured to set a stop time based on both the optical spectral component and the additional optical spectral component. The system of claim 8, wherein in response to detecting that both the optical component and the additional optical component are above a predetermined threshold, the processor is configured to redirect the laser beam to impinge on the layer within the segment. The system of claim 8, wherein the processor is configured to control or stop the laser beam by performing at least one operation selected from a list of operations consisting of: (i) blocking the laser beam, (ii) turning off the laser beam, (iii) adjusting power, and (iv) directing the laser beam to a subsequent section of the substrate. The system of claim 8, wherein the detection assembly is configured to detect one or more spectral emissions selected from a list of spectral emissions consisting of: (a) fluorescence, (b) plasmon, (c) Raman, (d) infrared thermal radiation, and (e) laser induced avalanche spectroscopy (LIBS).