Patent Application
20090120916
A recent trend in reducing size and cost of electronic systems is the increased use of surface mount components, which mount to one side of a printed circuit board (“PCB”). Such components may require less space on a PCB, and alleviate PCB routing constraints, as compared to components having pins that mount through holes of the PCB. However, reliability of an electronic system is often determined, at least in part, by the reliability of soldered connections among devices and PCBs of the system, and it can be problematic to ensure reliable connections of surface mounted components to a PCB.
One example of a surface mount component is a Ball Grid Array (“BGA”) package that includes solder balls laid out in a grid. BGA packages may be installed by using hot, forced air or infrared heat applied to a substantial area of a PCB, or the entire PCB, to melt (or “reflow”) the solder balls. The amount of heat required to insure that all of the solder balls of a BGA are properly reflowed can create collateral damage to other adjacent components on the PCB, or damage connections between the components and the PCB.
Some embodiments disclosed include systems and methods for melting one or more solder masses. The mass, in some embodiments, is used to form an electrical connection between an electrical component and a PCB where the PCB includes an aperture (e.g., a via). The system, in one embodiment, includes a laser which is able to be directed at the solder mass through the aperture. In one embodiment the laser is attached to a translatable positioning device for the purpose of translating said laser to a location from which a beam emitted from said laser is aimed through the aperture at the solder mass.
In other embodiments a detector is used for calibration. The detector can be used to receive the beam and determine its intensity after passing through the aperture. (This is done before the component has been positioned for installation).
In other embodiments a camera is associated with said laser. The camera makes reference to a fiducial mark such that laser position is determinable when a control system receives information from said camera regarding said fiducial mark.
Embodiments of the system also include the use of an optical device. The optical device receives the laser beam and changes a characteristic of the beam. In one embodiment, the characteristic is focus.
In other embodiments, the laser is located remotely from a translatable laser positioning device. In these embodiments one or more fiber optic cables are used to deliver the laser beam emitted into one or more optical devices on the positioning device. The optical devices aim and focus the laser light for transmission at the solder. In other embodiments, a fiber optic splitter arrangement might be used to divide a single beam into many.
A laser 120(1) of through-via laser reflow system 100(1) emits a beam 110(1) of electromagnetic energy that reflows one of solder balls 30(1)-30(4) of component 20(1) to PCB 10(1). For example,
Through-via laser reflow system 100(1) includes an optional mechanical positioning subsystem 140(1) that moves at least beam 110(1) in one or both of the directions of arrows 145, 145′ so that beam 110(1) aims accurately into a specific via 15 (e.g., any of vias 15(1)-15(4), or other vias 15 not shown in
Through-via laser reflow system 100(1) may include an optical alignment subsystem (not shown) having an illumination source, a processor, and a camera for capturing an image of a PCB 10 (e.g., PCB 10(1)) and/or alignment marks thereon. The processor may perform pattern recognition on the image to determine a position of PCB 10 relative to system 100(1), in order to position subsystem 140(1) so that beam 110(1) aims at a specific via 15.
System 100(1) may include apparatus that adjusts parameters of beam 100(1) for optimum performance in various ways. For example, optics 130(1) may include a focusing subsystem that adjusts a spot size and shape of beam 110(1) and thereby compensates for (a) variations in distance between system 100(1) and PCB 10(1) and/or component 20(1), (b) variations in size and shape among vias 15, and/or (c) other manufacturing variables (e.g., composition of solder balls 30). Beam 110(1) may be a form of electromagnetic energy that performs its intended purpose, such as ultraviolet light, visible light, infrared light or microwaves. System 100(1) may include circuitry (not shown) for turning laser 120(1) on or off. Laser 120(1) may be a continuous wave laser, or may be a pulse laser. Laser 120(1) may be operable to adjust wavelength and/or power of beam 110(1). System 100(1) may include mechanical and/or optical apparatus (not shown) for diverting or absorbing beam 110(1) when beam 110(1) is not in use.
It is understood that additional mechanical positioning subsystems (not shown) may also be utilized to position beam 110(2) in directions besides those depicted by arrows 145, 145′. For example, such positioning subsystems may move beam 110(2) in and out of the cross-sectional plane illustrated in
Use of fiber splitter 150, fiber optic lines 132(3)-132(6) and optional optics 160(1)-160(4) to facilitate reflow of solder balls 30(5)-30(8) improves manufacturing throughput of system 100(3) relative to system 100(1). Again, the depiction of four beams 110 reflowing four solder balls 30 is illustrative only, it should be apparent that modifications may be made to generate any number of beams 110 to melt a corresponding number of solder balls 30. Characteristics of fiber splitter 150, of fiber optic lines 132(3)-132(6) and of optional optics 160(1)-160(4) may be individually configured to optimize reflow for solder balls and/or vias that are not identical in shape, size or solder ball composition.
Optics 160(1)-160(4), fiber optic lines 132(3)-132(6) and/or fiber splitter 150 may couple with a mechanical support element 165(2) so that they maintain alignment relative to each other while positioning subsystem 140(2) moves. Collectively, optics 160(1)-160(4), fiber optic lines 132(3)-132(6), fiber splitter 150 and support element 165(2) may form an optical subsystem (“OSS”) 167(1) that is tailored to the arrangement of vias on board 10(2). OSS 167(1) may be removable as a unit from system 100(2) by removing support element 165(2) from positioning subsystem 140(2) and disconnecting fiber splitter 150 from fiber optic line 132(2) (or by disconnecting line 132(2) from optics 130(3). OSS 167(1) and other OSSs (not shown) may install interchangeably on system 100(3) as manufacturing demands may require, for reflowing solder balls of components having different via arrangements.
Beam splitters 170(1)-170(4) and optics 175(1)-175(4) may couple with a mechanical support element 165(3) so that the beam splitters and optics maintain alignment relative to each other while positioning subsystem 140(4) moves. Collectively, beam splitters 170(1)-170(4), optics 175(1)-175(4) and support element 165(3) may form an OSS 167(2) that is tailored to the arrangement of vias on board 10(2). OSS 167(2) and other OSSs (not shown) may install interchangeably on system 100(4) as manufacturing demands may require, for reflowing solder balls of components having different via arrangements.
It should be apparent that system 100(4) uses free space optics (e.g., beam splitters 170(1)-170(4) and optional optics 175(1)-175(4)) analogously to system 100(3)'s use of corresponding fiber coupled optics. Use of beam splitters 170(1)-170(4) to generate beams 110(8)-110(11) to reflow solder balls 30(5)-30(8) improves manufacturing throughput of system 100(4) relative to system 100(1). Characteristics of beam splitters 170(1)-170(4) and of optional optics 175(1)-175(4) may be individually configured to optimize reflow for solder balls and/or vias that are not identical in shape, size or solder ball composition. It is appreciated that other combinations of free space optics and fiber optics may be utilized in various embodiments, and that all such combinations are contemplated by the present disclosure.
A camera 180 mounts with positioning subsystem 140(5); camera 180 forms images of a field of view 185. Light emanates from one or more illuminators 190; camera 180 captures light that reflects from features of PCB 10(2), including fiducial mark 17. Camera 180 transmits image data of PCB 10(2) to a processor (not shown) that utilizes pattern recognition processing to determine a location of camera 180, and thus a location of positioning subsystem 140(5), with respect to fiducial mark 17. System 100(5) may utilize location information of vias 15(5)-15(8) and other vias 15 (not shown) with respect to fiducial mark 17 (e.g., information from a design database utilized to generate PCB 10(2)), along with the location of positioning subsystem 140(5) with respect to fiducial mark 17 to determine positioning information for aiming laser beams through any of vias 15.
Extensions of the technique described above will be apparent to those skilled in the art of registering positioning systems to workpieces; for example, a PCB 10 may include multiple registration marks 17 so that whose location of a positioning subsystem 140 may be determined relative to each of marks 17 in order to calculate scaling factors and correct for rotational misalignment.
For example, in a first example, system 100(5) may align to a fiducial mark 17 of PCB 10(2), then aim a laser beam through a via of PCB 10(2) (e.g., may aim laser beam 110(11) through via 15(8), as shown). Intensity and/or image data formed by detector 210 may indicate that the via is blocked (e.g., optically opaque) or not blocked. If a via is blocked, the processor may abort assembly of PCB 10(2) since the via may be entirely missing, or blocked by foreign matter; aborting assembly in such a case may preclude costly rework or scrap.
In a second example, system 100(5) may align to a fiducial mark 17 of PCB 10(2), then may move a laser beam in increments, thus “stepping” it across one or more selected vias. Intensity and/or image data formed by detector 210 at each of the “steps” may be utilized to calculate fine alignment corrections to improve a coarse alignment provided by aligning to fiducial mark 17. This procedure may be repeated, for example, at multiple vias across a PCB so that scaling, translational and rotational factors of the PCB may be determined.
In a third example, system 100(5) may align one or more laser beams at a time with detector 210 without PCB 10(2) loaded in place. Intensity and/or image data formed by detector 210 may be utilized to determine a power output of laser 120(4), and/or information of beam splitters 170(1)-170(4) or optics 175(1)-175(4) (e.g., data that may help to determine whether any of the beamsplitters or optics are degraded or misaligned, or whether any optical path thereamong is blocked).
It is also contemplated that rather than mounting on a mechanical positioning subsystem, a detector 200 may be fixedly mounted on a through-via laser reflow system, and may be mounted in a location such that lasers, optics or OSSs may be positioned so as to receive laser beams from various sources (e.g., different instances of a laser 120, optics 160 or optics 175).
In a step 402, the process accepts user input. User input may, for example, specify a type of PCB and/or component to be mounted thereon, start or stop single steps or automated sequences of calibration and/or processing, manually control positioning subsystems, lasers, illumination and/or cameras, or request output of information. It is appreciated that step 402 may occur many times in the execution of process 400 (as often as a user of a through-via laser reflow system feels it necessary to assert control, or request information, from such a system). An example of step 402 is processor 300 accepting user input through external I/O 350,
Steps 410 through 435 perform calibration of system 100. Step 410 positions a laser, optics, or an OSS such that a laser beam is in a predetermined position for calibration, and a detector will be in a predetermined position so as to receive the laser beam. An example of step 410 is one of mechanical positioning subsystems 140(1)-140(4) moving so that a laser beam 110 is in a predetermined position, and a mechanical positioning subsystem 210 moving so that detector 200 receives laser beam 110. Step 415 emits a laser beam, and receives the laser beam in a detector, so that attributes of a laser and/or optics can be measured. An example of step 415 is one of lasers 120(1)-120(4) emitting electromagnetic energy that is transmitted and/or directed by one or more of optics 130(1)-130(4), fiber optic line 132(1)-132(6), fiber splitter 150, beam splitters 170(1)-170(4) and optics 160(1)-160(5) or 175(1)-175(4) as one or more of laser beams 110(1)-110(15), and then detector 200 receiving the laser beam.
Step 420 processes detector data generated in step 415 for calibration purposes. An example of step 420 is processor 300 comparing actual laser power against a desired laser power and calculating a power correction that is subsequently used to adjust laser power so that a correct amount of power is received at a solder ball to be reflowed. Another example of step 420 is processor 300 processing image data to determine whether a laser beam is forming a desired spot size, and calculating position information for focusing subsystems to adjust focus. Step 425 determines whether data (e.g., raw detector data from step 415, or such data after processing in step 420) is within defined tolerances. If the data is not within tolerances, process 400 may terminate at step 430, with an indication that the system requires adjustment or repair before processing can continue. An example of step 425 is processor 300 comparing laser intensity data with defined tolerances. If the data is within tolerances, step 435 decides whether more calibration steps need to be performed. An example of step 435 is processor 300 determining whether all calibration steps of a predetermined set of calibration steps have been performed. If so, process 400 returns to step 410; if not, process 400 continues with step 440.
Steps 440 through 480 perform setup and PCB validation utilizing system 100. Step 440 moves subsystems of a through-via laser reflow system 100 to PCB load positions, and loading a PCB 10. An example of step 440 is positioning subsystems 140 moving to a predetermined load position, and a user of system 100 (or a loading machine) loading one of PCBs 10(1)-10(2) into system 100. Step 445 performs an alignment. An example of step 445 is processor 300 (a) controlling positioning subsystems 140 so that camera 180 images fiducial mark 17 on one of PCBs 10(1)-10(2); (b) controlling illuminators 190 to generate suitable lighting of fiducial mark 17; (c) controlling camera 180 to generate image information of fiducial mark 17; (d) processing image information of fiducial mark 17 to determine location and/or rotational corrections; and, optionally, (e) controlling positioning subsystems 140 to implement the location and/or rotational corrections.
In step 450, processor 300 controls a positioning subsystem to position one or more of a laser 120, optics 130(1)-130(4), beam splitters 170(1)-170(4) and optics 160(1)-160(5) or 175(1)-175(4) (or collectively, an OSS 167 incorporating such elements) to align a laser beam 110 to a via of PCB 10, and positions detector 200 to receive the laser beam. An example of step 450 is processor 300 (not shown in
Step 460 processes detector data generated in step 455 for PCB validation purposes. An example of step 460 is processor 300 comparing actual laser power received in step 455 against a desired laser power (which may depend, for example, on a via size determined from a PCB design database, and may depend on a type and/or quantity of solder to be reflowed). Another example of step 460 is processor 300 processing image data to determine intensity at each of a sequence of positions, to complete a fine alignment of the laser beam to via locations, as discussed above. Step 465 determines whether data (e.g., raw detector data from step 455, or such data after processing in step 460) is within defined tolerances. If the data is not within tolerances, process 400 may terminate at step 470, with an indication that one or more vias of PCB are blocked or missing, so that continued processing may result in scrap product. An example of step 425 is processor 300 determining that laser intensity data obtained in step 455 is below a defined tolerance. If the data is within tolerances, step 475 decides whether more vias need to be checked. An example of step 475 is processor 300 determining whether any vias to be checked on a PCB 10 remain to be checked. If so, process 400 returns to step 450; if not, process 400 ends with step 480, with an aligned PCB 10 having been checked and found ready to have a component installed thereto.
Process 500 can begin in one of two ways. One way is for a system 100 to first execute process 400 described above, ending at step 480; thus step 480 is shown in dashed outline in process 500. Another way of beginning process 500 is to load and optionally align a PCB utilizing steps 505 and 510; these steps are the same as steps 440 and 445, respectively, of process 400. Process 500 may also include a step 502 of accepting user input that may, for example, specify a type of PCB and/or component to be mounted thereon, start or stop single steps or automated sequences of calibration and/or processing, manually control positioning subsystems, lasers, illumination and/or cameras, or request output of information. It is appreciated that step 502 may occur many times in the execution of process 500 (as often as a user of a through-via laser reflow system feels it necessary to assert control, or request information, from such a system). An example of step 502 is processor 300 accepting user input through external I/O 350,
Once a PCB is loaded, process 500 continues with step 515, which loads a component 20 to be reflowed onto a PCB 10 (e.g., loads component 20(1) onto PCB 10(1) or component 20(2) onto PCB 10(2)). An example of step 515 a user of system 100 (or a loading machine) loading a component 20 onto PCB 10. In step 520, processor 300 controls a positioning subsystem to position one or more of a laser 120, optics 130(1)-130(4), beam splitters 170(1)-170(4) and optics 160(1)-160(5) or 175(1)-175(4) (or collectively, an OSS 167 incorporating such elements) to align one or more laser beams 110 to one or more vias of PCB 10. An example of step 520 is processor 300 controlling positioning subsystem 140(3) to position OSS 167(1) to align laser beams 110(3)-110(6) to vias 15(5)-15(8), as shown in
The execution of the above processes using the disclosed systems is significantly superior to the conventional methods of installing BGA packages which use hot, forced air or infrared heat. These conventional techniques involve exposing a substantial area of the PCB, or sometimes the entire PCB, to melt (or “reflow”) the solder balls. The processes disclosed here, however, do not expose the PCB to heat in remelting the BGA solder balls. Thus, there is no collateral damage done to the PCB, collateral components, or connections between the components on the PCB.
This also eliminates verification processes necessary with the prior art methods. Because the prior art processes involve heat exposure to the PCB, post-processing inspections are normally required for BGA installations. These inspections are necessary to insure that the board and related components have not been not damaged by the heat administered. The inspection process typically requires testing, X-ray observations, and other time consuming procedures necessary to ensure that the board is still fully operational. With the processes and systems here, however, only the mounted components need to be tested, since the integrity of the PC board and its already existing components are not compromised during the reflow process.
The changes described above, and others, may be made in the through-via laser reflow system described herein without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between.
