Abstract:
A system and method of repairing electrical circuits including employing a laser and at least one laser beam delivery pathway for laser pre-treatment of at least one conductor repair area of a conductor formed on a circuit substrate and employing the laser and at least part of the at least one laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined conductor location.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to electrical circuit repair generally. 
       CROSS-REFERENCE TO RELATED APPLICATION 
       [0002]    This application claims benefit of Israeli Patent Application No. 197349 entitled “A Method and System for Electrical Circuit Repair”, filed 2 Mar. 2009; the above noted prior application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0003]    The following publications are believed to represent the current state of the art: 
         [0004]    U.S. Pat. Nos. 4,752,455; 4,970,196; 4,987,006; 5,173,441 and 5,292,559; 
         [0005]    “Metal deposition from a supported metal film”, Bohandy, B. F. Kim and F. J. Adrian, J. Appl. Phys. 60 (1986) 1538; and 
         [0006]    “A study of the mechanism of metal deposition by the laser-induced forward transfer process”, F. J. Adrian, J. Bohandy, B. F. Kim, and A. N. Jette, Journal of Vacuum Science and Technology B 5, 1490 (1989), pp. 1490-1494. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention seeks to provide an improved system and method for electrical circuit repair. 
         [0008]    There is thus provided in accordance with a preferred embodiment of the present invention a method of repairing electrical circuits including employing a laser and at least one laser beam delivery pathway for laser pre-treatment of at least one conductor repair area of a conductor formed on a circuit substrate and employing the laser and at least part of the at least one laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined conductor location. 
         [0009]    In accordance with a preferred embodiment of the present invention the pre-treatment includes laser ablation. Preferably, the laser is operated at different power levels during the laser pre-treatment and the application to the donor substrate. 
         [0010]    In accordance with a preferred embodiment of the present invention the pre-treatment includes pre-treatment of a substrate repair area and pre-treatment of a conductor repair area. Additionally, the laser ablation produces surface roughening of the substrate repair area and the conductor repair area. Additionally, the pre-treatment of the substrate repair area and the pre-treatment of the conductor repair area include different extents of surface roughening. 
         [0011]    Preferably, the at least one conductor repair area is selected by automated optical inspection. 
         [0012]    In accordance with a preferred embodiment of the present invention the method of repairing electrical circuits also includes employing the laser and the at least one laser beam delivery pathway for laser ablation of excess conductor material. Additionally, the excess conductor material is formed by material detached from the donor substrate. Additionally or alternatively, the laser ablation of excess conductor material is performed subsequent to the application of at least one laser beam to a donor substrate, which is in turn performed subsequent to the laser pre-treatment. 
         [0013]    There is also provided in accordance with another preferred embodiment of the present invention a method of repairing electrical circuits including employing a laser and at least one laser beam delivery pathway for laser ablation of excess conductor material in at least one conductor repair area of a conductor formed on a circuit substrate and employing the laser and at least part of the at least one laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined conductor location. 
         [0014]    In accordance with a preferred embodiment of the present invention the laser ablation of excess conductor material effects repair of short circuits. Preferably, the laser is operated at different power levels during the laser ablation and the application to the donor substrate. 
         [0015]    In accordance with a preferred embodiment of the present invention the method of repairing electrical circuits also includes surface roughening of the at least one conductor repair area. Preferably, the at least one conductor repair area is selected by automated optical inspection. 
         [0016]    There is further provided in accordance with yet another preferred embodiment of the present invention a method of repairing electrical circuits including pre-treatment of at least one circuit substrate repair area of a circuit substrate and of at least one conductor repair area of a conductor formed on the circuit substrate and lying adjacent the at least one circuit substrate repair area and applying at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined circuit substrate location in the at least one circuit substrate repair area and to at least one predetermined conductor location in the at least one conductor repair area, thereby to at least partially overlap a portion of the conductor at the at least one conductor repair area and to form at least an extension of the conductor in the at least one circuit substrate repair area. 
         [0017]    In accordance with a preferred embodiment of the present invention the pre-treatment includes laser ablation. Additionally, the laser ablation produces surface roughening. 
         [0018]    Preferably, the pre-treatment and the applying are carried out by the same laser. Additionally, the pre-treatment and the applying are carried out by the same laser at different power levels. 
         [0019]    In accordance with a preferred embodiment of the present invention the pre-treatment of the substrate repair area and of the conductor repair area are carried out by the same laser at different power levels. Additionally, the pre-treatment of the substrate repair area and of the conductor repair area include different extents of surface roughening. 
         [0020]    Preferably, the at least one predetermined substrate location in the at least one substrate repair area and the at least one predetermined conductor location in the at least one conductor repair area are selected by automated optical inspection. 
         [0021]    There is even further provided in accordance with still another preferred embodiment of the present invention a system for repairing electrical circuits including a laser and a laser beam delivery pathway, laser pre-treatment functionality utilizing the laser and at least part of the laser beam delivery pathway for laser pre-treatment of at least one conductor repair area of a conductor formed on a circuit substrate and conductor deposition functionality utilizing the laser and at least part of the laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined conductor location. 
         [0022]    There is yet further provided in accordance with another preferred embodiment of the present invention a system for repairing electrical circuits including a laser and a laser beam delivery pathway, excess conductor ablation functionality employing the laser and at least part of the laser beam delivery pathway for laser ablation of excess conductor material in at least one conductor repair area of a conductor formed on a circuit substrate and conductor deposition functionality employing the laser and at least part of the laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined conductor location. 
         [0023]    Preferably, the laser ablation of excess conductor material effects repair of short circuits. 
         [0024]    There is still further provided in accordance with yet another preferred embodiment of the present invention a system for repairing electrical circuits including a laser and a laser beam delivery pathway, pre-treatment functionality employing the laser and at least part of the laser beam delivery pathway for treatment of at least one circuit substrate repair area of a circuit substrate and of at least one conductor repair area of a conductor formed on the circuit substrate and lying adjacent the at least one circuit substrate repair area and conductor deposition functionality employing the laser and at least part of the laser beam delivery pathway for application of at least one laser beam to a donor substrate in a manner which causes at least one portion of the donor substrate to be detached therefrom and to be transferred to at least one predetermined circuit substrate location in the at least one circuit substrate repair area and to at least one predetermined conductor location in the at least one conductor repair area, thereby to at least partially overlap a portion of the conductor at the at least one conductor repair area and to form at least an extension of the conductor in the at least one circuit substrate repair area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0026]      FIG. 1  is a simplified illustration of a system for repairing electrical circuits, constructed and operative in accordance with a preferred embodiment of the present invention; 
           [0027]      FIG. 2  is a simplified illustration of an embodiment of the optical subsystem of the system of  FIG. 1 ; 
           [0028]      FIGS. 3A-3H  are simplified sectional illustrations showing the operation of the system of  FIG. 1 . 
           [0029]      FIG. 4  is a simplified illustration of additional functionality of the system of  FIG. 1 ; 
           [0030]      FIGS. 5A-5C  are simplified sectional illustrations showing the operation of the functionality of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0031]    Reference is now made to  FIG. 1 , which is a simplified illustration of a system for repairing electrical circuits, constructed and operative in accordance with a preferred embodiment of the present invention, and to  FIG. 2 , which is a simplified illustration of an embodiment of the optical subsystem of the system of  FIG. 1 . 
         [0032]    As seen in  FIG. 1 , the system preferably comprises a chassis  100  which is preferably mounted on a conventional optical table  102 . The chassis  100  defines an electrical circuit inspection location  104  onto which an electrical circuit, such as a printed circuit board (PCB)  106 , to be inspected may be placed. The PCB  106  typically has one or more of various types of defects, such as excess conductor defects and missing conductor defects, for example cut  110 . 
         [0033]    A bridge  112  is arranged for linear motion relative to inspection location  104  along a first inspection axis  114  defined with respect to chassis  100 . An optical head assembly  116  is arranged for linear motion relative to bridge  112  along a second inspection axis  118 , perpendicular to first inspection axis  114 . 
         [0034]    In accordance with a preferred embodiment of the present invention, as seen in detail in  FIG. 2 , the optical head assembly  116  preferably includes an inspection subassembly  120  and a repair subassembly  122 . It is a particular feature of the present invention that the inspection subassembly  120  and the repair subassembly  122  share at least some optical components. 
         [0035]    The system preferably also includes a control assembly  124 , preferably including a computer  126  having a user interface  128  and including software modules operative to operate the inspection subassembly  120  and repair subassembly  122 . Control assembly  124  preferably receives a defect location input from an automatic optical inspection system, not shown, such as a Discovery 8000 system, commercially available from Orbotech Ltd. of Yavne, Israel. 
         [0036]    As seen in  FIG. 2 , optical head assembly  116  includes inspection subassembly  120  and repair subassembly  122 . Inspection subassembly  120  is a parafocal imaging system, which includes a camera  150 , such as a Basler CMOS camera available from Basler, Inc. of Exton Pa. imaging location  152  on PCB  106  along an optical axis  154 . Camera  150  views location  152  through a focusing object lens  160 , having a typical focal length of 100-150 mm, a partial reflective mirror  162  and an objective lens module  164 , such as a 5×/0.14 objective lens module, commercially available from Mitutoyo Ltd. of Japan. 
         [0037]    In accordance with an embodiment of the invention, inspection subassembly  120  and repair subassembly  122  are arranged to at least partly share the same optical path along optical axis  154 . The repair subassembly  122  includes a pulsed laser source  170 , such as a passive Q-switch micro laser available from Teem Photonoics of Grenoble, France, operative to generate a pulsed laser beam  174 . A suitable micro laser may be selected, for example, from laser heads operative to output beams at a wavelength of 532 nm or at 1064 nm, depending on the application. Pulsed beam  174  is passed through collimating optics  178 , which may include two lenses  180  and  182 , having focal lengths of 80 mm and −150 mm respectively, operative to collimate the laser beam  174  to a preferred spot size of 0.5-3.0 mm. Laser beam  174  is then reflected by mirror  184  and is then adjusted to a specific diameter by a beam expender  185 , including multiple lenses  186  placed and adjusted for the required size of collimated output beam. Lenses  186  may include lenses such as a 28 mm plano-convex lens, a −10 mm biconcave lens and a 129 mm plano-convex lens, respectively. Laser beam  174  is then directed by a lens  188  to impinge on a two-axis fast steering mirror (FSM)  190 , commercially available from Newport Corporation, and then passes through a lens  192 , such as a 108 mm meniscus lens, a mirror  194  and a lens  196 , such as plano convex 338 mm lens. Lenses  188 ,  192  and  196  maintain the position of the beam on the FSM  190 , which is located after lens  188 , and the input aperture of objective lens module  164 . Beam  174  then impinges on beam splitter  198 , which directs beam  174  through objective lens module  164  along axis  154 . In accordance with a preferred embodiment of the invention, the lenses and optical components are arranged as shown and are suitably coated for operation in conjunction with the selected wavelength of laser beam  174 . 
         [0038]    Reference is now made to  FIGS. 3A-3H , which are simplified sectional illustrations showing the operation of the system of  FIG. 1 .  FIG. 3A  shows a typical missing conductor defect, such as cut  110  ( FIG. 1 ). Initially, as noted above, the control assembly  124  receives an input identifying the type and location of the defect, typically from an automatic optical inspection system. 
         [0039]    In the stage shown in  FIG. 3A , the control assembly  124  causes the optical head assembly  116  to be displaced so that objective lens module  164  overlies the defect and is focused on the defect. An image of the defect is acquired, preferably at two wavelength bands, preferably centered at approximately 600 nm and 500 nm, and a fluorescence image, centered at approximately 400 nm, is also preferably acquired. 
         [0040]    The image is analyzed by control assembly  124  and is preferably compared to a reference, such as CAM data, thereby to confirm the existence and type of defect and to provide a detailed contour of the defect, preferably including definition of at least one conductor repair area  250  and at least one substrate repair area  252 . 
         [0041]    Turning now to  FIGS. 3B ,  3 C and  3 D, it is seen that laser pretreatment of conductor repair area  250  and substrate repair area  252  is carried out. It is a particular feature of the present invention that the objective lens module  164  need not be displaced from its orientation relative to the defect at this stage since the laser and the inspection subassembly share the same focus. 
         [0042]    It is appreciated that the pre-treatment of conductor repair area  250  and of substrate repair area  252  are typically different. The general purpose of the pretreatment of conductor repair area  250  and substrate repair area  252  is to provide enhanced adhesion between a conductor material to be deposited and the existing conductor and substrate by surface roughening thereof, through laser ablation. For example, if a Q-switched microchip 30 milliwatt 532 nm laser producing sub-nanosecond pulses is employed, roughening of the substrate and conductor surfaces is achieved by using a spot size, typically, of 10 micron diameter, to produce an X-Y grid of trenches, typically having a depth of 4-6 microns. It is appreciated that depending on the composition of the substrate and of the conductor, the laser energy impinging on a unit area of the surface is varied, for example, by varying the scan speed of the laser beam on the surface or by adjusting the power of the impinging laser beam. 
         [0043]    Reference is now made to  FIG. 3E , which illustrates initial laser beam impingement on a donor substrate  270  and resulting deposition of a conductor material  272 , forming part of donor substrate  270 , onto substrate repair area  252 , and to  FIGS. 3F and 3G , which illustrate further laser beam impingement on donor substrate  270  and resulting deposition of conductor material  272  onto substrate repair area  252 . As seen in  FIGS. 3E ,  3 F and  3 G, the donor substrate  270  is preferably located at a distance, designated by reference H 1 , typically about 50-300 microns, above the surface of the conductor repair area  250  and the laser beam is focused on the donor substrate  270  by suitable displacement of the objective lens module  164 . 
         [0044]    Donor substrate  270  is typically made of a material transparent to the laser&#39;s wavelength, which may be rigid, such as glass, or flexible, such as plastic, which is coated on one side with a thin layer of conductor material  272 . 
         [0045]    As seen in  FIGS. 3E ,  3 F and  3 G, the height of the conductor, designated H 2 , is typically about 5-50 microns, the thickness of the donor substrate  270 , designated by  113 , is typically in the range of 500-3000 microns, and the thickness of conductor material  272 , designated by  114 , is typically in the range of 0.5-3 microns. 
         [0046]    Preferably the inspection subassembly is employed before and during deposition to monitor the X-Y position of the donor substrate  270  in order to ensure that conductor material  272  is present at all relevant times in a region covering all expected laser beam impingement locations thereon. This functionality is enabled by the fact that the laser and the inspection subassembly share the same focus. 
         [0047]    It is a particular feature of the invention that the same laser which is used for surface roughening is also used for deposition. Here, deposition is achieved, for example, if a Q-switched microchip 30 milliwatt 532 nm laser producing sub-nanosecond pulses is employed, by using a spot of size typically of 10 micron diameter, to fill in conductor repair area  250  and substrate repair area  252 . 
         [0048]      FIG. 3H  illustrates the conductor repair area  250  and substrate repair area  252  following the completion of deposition over the conductor repair area  250  and substrate repair area  252 . It is appreciated that, while in the illustrated embodiment shown in  FIGS. 3E ,  3 F,  3 G and  3 H the deposited material appears as individual deposits, the resulting conductor formed thereby takes on a generally uniform appearance. 
         [0049]    Typically, following the completion of the deposition, a subsequent inspection of conductor repair area  250  and substrate repair area  252 , similar to inspection described in reference to  FIG. 3A , is performed. 
         [0050]    Reference is now made to  FIG. 4 , which is a simplified illustration of additional functionality of the system for repairing electrical circuits of  FIG. 1 , and to  FIGS. 5A-5C , which are simplified sectional illustrations showing the operation of the functionality of  FIG. 4 . 
         [0051]    As seen in  FIG. 4 , the system for repairing electrical circuits of  FIG. 1 , which includes control assembly  124 , computer  126  and user interface  128 , has identified an excess conductor defect  300  in PCB  106 . 
         [0052]    In the illustrated example shown in  FIG. 4 , and as seen particularly in  FIG. 5A , the excess conductor defect  300  includes first and second excess conductor material regions  302  and  304 . First excess conductor material region  302  lies between conductors  310  and  312  and second excess conductor material region  304  lies between conductors  312  and  314 . It is appreciated that excess conductor defect  300  may be formed during the manufacturing of PCB  106  ( FIG. 1 ) or may result from residual conductor material deposited during the process of  FIGS. 3E-3H  due to sputtering. 
         [0053]    In the stage shown in  FIG. 5A , the control assembly  124  causes the optical head assembly  116  ( FIGS. 1 and 2 ) to be displaced so that objective lens module  164  ( FIG. 2 ) overlies the defect and is focused on the defect. An image of the defect is acquired, preferably at two wavelength bands, preferably centered at approximately 600 nm and 500 nm, and a fluorescence image, centered at approximately 400 nm, is also preferably acquired. 
         [0054]    The image is analyzed by control assembly  124  and is preferably compared to a reference, such as CAM data, thereby to confirm the existence and type of defect and to provide a detailed contour of the defect, preferably including definition of at least one conductor removal area, in the illustrated example, first and second excess conductor material regions  302  and  304 . 
         [0055]    Turning now to  FIGS. 5B and 5C , it is seen that laser ablation of the excess conductor material in first and second excess conductor material regions  302  and  304  is carried out. It is a particular feature of the present invention that the objective lens module  164  need not be displaced from its orientation relative to the defect at this stage since the laser and the inspection subassembly share the same focus. 
         [0056]    It is appreciated that the laser ablation of first and second excess conductor material regions  302  and  304  is achieved, typically, if a Q-switched microchip 30 milliwatt 532 nm laser producing sub-nanosecond pulses is employed, by using a spot size, typically, of 5-20 microns diameter. It is appreciated that depending on the composition of the excess conductor material, the laser energy impinging on a unit area of the surface is varied, for example, by varying the scan speed of the laser beam on the surface or by adjusting the power of the impinging laser beam. 
         [0057]    Preferably the inspection subassembly is employed before and during laser ablation to monitor the X-Y position of PCB  106  in order to ensure that the laser beam impinges on first and second excess conductor material regions  302  and  304  while not impinging on conductors  310 ,  312  and  314 . This functionality is enabled by the fact that the laser and the inspection subassembly share the same focus. 
         [0058]    It is a particular feature of the invention that the same laser which is used for surface roughening and deposition, as described with reference to  FIGS. 1-3H , is also used for laser ablation. 
         [0059]    Typically, following the completion of the laser ablation, a subsequent inspection of PCB  106 , similar to inspection described in reference to  FIG. 5A , is performed. 
         [0060]    It is appreciated that the laser ablation functionality described hereinabove with reference to FIGS.  4  and  5 A- 5 C for performing laser ablation of excess conductor material regions  302  and  304  may also be used on the same PCB  106  together with the surface roughening and deposition functionalities described hereinabove with reference to  FIGS. 3A-3H , if multiple defects are found on PCB  106  or to remove excess conductor material deposited during the deposition process. 
         [0061]    It is also appreciated that both the surface roughening and deposition functionalities, described hereinabove with reference to  FIGS. 3A-3H , and the laser ablation functionality, described hereinabove with reference to FIGS.  4  and  5 A- 5 C, may be each be employed, as needed, one or more times, in any suitable order, in either multiple locations or the same location on PCB  106 . 
         [0062]    It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the present invention includes both combinations and subcombinations of various features described herein and improvements and variations which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.