Abstract:
A printed circuit board (PCB) drilling apparatus that greatly increases the speed, accuracy and depth of the drilling process as well as increasing the life of the drill bits by decoupling the reactionary forces encountered in the positioning and drilling functions of the apparatus in the x,y and z axes from the components that accomplish the positioning, measuring and drilling of the stacked printed circuit boards. The part of the apparatus that moves and drills as well as the feedback position sensors are mounted to a set of vibration isolation pads that absorb the vibrations that would disturb the feedback sensors. Additionally, the force frame of the apparatus that experiences the reactionary force movements are decoupled from the metrology frame of the apparatus that house the feedback sensors, also increasing the throughput and accuracy.

Description:
[0001]    The present invention involves a novel design for a printed circuit board (PCB) substrate drilling machine that greatly increases the speed, accuracy and depth of the drilling process as well as increasing the life of the drill bits. 
       BACKGROUND OF THE INVENTION 
       [0002]    There is a huge industry developed around the demand to drill multiple, spaced holes (through or non-through) in substrates such as electronic wafers, thin film electronics, organic packaging substrates, gtlass, silicon wafers, sapphires or the like. These holes or patterned drillings may be used for electrical connections, filtration, cytology, bioassays, chemotaxis, or particle monitoring and have diameters that commonly lie in the micron range. Not only must the holes be identical to each other in diameter but also must be placed at precise locations and with the right geometry with respect to the substrate or adjacent holes. 
         [0003]    Generally, such drilling machines see movement in all three axes simultaneously. The substrate is positionally moved in the horizontal x axis beneath a drill that plunges in the z vertical axis after the drill has been positionally moved in the Y horizontal axis atop the substrate by a gantry unit. Drilling is initiated once the substrate is in the proper position as indicated by a set of metrology positioning sensors on the machine and at least one pressure foot has secured the PCB substrate on the x axis table to the z axis drill unit. This positioning prior to drilling occurs extremely rapidly by computer control, cycling up to thousands of times per minute. Pursuant to Newton&#39;s third law of motion, each of these three positioning or drilling movements creates a reactionary force in the structure of the PCB substrate drilling machine. Since it is this machine that metrology positioning sensors are coupled to, the settling time or lag for the PCB substrate to be positioned within the acceptable ranges of the feedback sensors is slowed by the effects of the reactionary forces, thus slowing the positioning process and adding slight inaccuracies in the positioning and eventual placement of the holes in the PCB. 
         [0004]    Prior art PCB substrate drilling systems rely on the use of a massive, heavy machine base to minimize these reactionary forces coupled with light moving masses, however, these reactionary forces still inherently reside in the machine and serve to limit the speed and accuracy at which the machine can function. When drilling micro holes or vias of 100 microns or less in diameter at a rates higher than 15 cycles per second, the positioning accelerations increase to meet the point to point positioning commands and the disturbances that are injected into the heavy machine base cause the settling time at the end of each positioning to become longer thus cancelling out any move time reduction gained by the improved acceleration of the lighter moving masses. Additionally, the sensors operate with moderately large settling windows (in the 0.1 micron range) in the x and y axes. These prior art solutions that increase the mass of the machine base (reaction mass) and make the moving masses lighter do not completely address the root cause of the problem—that the unitary base design supports both the the metrology system and the drilling system. 
         [0005]    Henceforth, a PCB substrate drilling machine with improved accuracy and speed, faster and deeper drilling depth (increased PCB substrate stack heights), longer drill bit life, less drill bit breakage and a higher machine throughput would fulfill a long felt need in the substrate drilling and surface patterning industry. This new invention utilizes and combines known and new technologies in a unique and novel configuration to overcome the aforementioned problems and accomplish this. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention, which will be described subsequently in greater detail, relates to a PCB substrate drilling apparatus adapted to provide both speed and accuracy for the user resulting in a higher throughput. More particularly, to a PCB substrate drilling apparatus that decouples any reactionary forces from the x axis and y axis positioning away from the measurement and positioning components, and balances the z axis drilling forces of the apparatus so as to enable a much more efficient operation capable of drilling a larger stack of PCB substrates. It has many of the advantages mentioned heretofore and many novel features which are not anticipated, rendered obvious, suggested, or even implied by any of the prior art, either alone or in any combination thereof. 
         [0007]    In accordance with the invention, an object of the present invention is to provide an improved PCB substrate drilling apparatus having a decoupled force frame and metrology frame to enable enhanced positioning and drilling. 
         [0008]    It is another object of this invention to provide an improved PCB substrate drilling apparatus capable of surpassing the current number of stacked PCB substrates that can be drilled at the same time and remain within operational tolerances. 
         [0009]    It is a further object of this invention to provide a PCB substrate drilling apparatus that maximizes the life of the drill bits and increases the precision of the location of the drilled holes. 
         [0010]    It is still a further object of this invention to provide for a PCB substrate drilling apparatus that minimizes or eliminates all reactionary force effects from the positioning and drilling functions that are created by the apparatuses&#39; moving components. 
         [0011]    The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements. Other objects, features and aspects of the present invention are discussed in greater detail below. 
         [0012]    There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a front view of a prior art PCB substrate drilling apparatus illustrating the operational and reactionary forces; 
           [0014]      FIG. 2  is a front view of the PCB substrate drilling apparatus of the present invention illustrating the separation of the operational and reactionary forces; 
           [0015]      FIG. 3  is a perspective view of the PCB substrate drilling apparatus; 
           [0016]      FIG. 4  is a front view of the PCB substrate drilling apparatus; 
           [0017]      FIG. 5  is a side view of the PCB substrate drilling apparatus; 
           [0018]      FIG. 6  is a back view of the PCB substrate drilling apparatus; 
           [0019]      FIG. 7  is a top view of the PCB substrate drilling apparatus; 
           [0020]      FIG. 8  is a perspective view of the z axis drill unit; 
           [0021]      FIG. 9  is a front view of the z axis drill unit; and 
           [0022]      FIG. 10  is a side view of the z axis drill unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    All discussion of the geometry involved in describing the present invention is made with reference to a three dimensional Cartesian Coordinate System where the z axis is vertical and pointing up (positive up), so that the x and y axes lie on a horizontal plane where the x axis is shown as positive pointing “out of the page” towards the viewer, and they axis is shown as positive on the right side of the z axis. 
         [0024]    Generally, PCB substrate drilling machines perform four functions: staging (positioning) of the PCB substrates to be drilled in the correct x axis location on their moveable table, locating the drilling unit in the correct y axis location above the PCB substrate stacks on the moveable table; feedback sensor measurement and verification of the location of the moveable table in relation to the drilling unit; and plunging the drill bit in the z axis into the stacked PCB substrates. In the prior art devices, the measurement function (metrology) is accomplished by position feedback sensors located on the same frame of the device that accomplishes the positioning and drilling. This frame has a huge mass base, generally a planar granite or cement slab, into which the reactionary forces of the positioning and drilling functions is passed. Its large mass minimizes any reactionary force movement that is experienced by this slab, thereby passing very little of these reactionary forces onto the actual positioning, measuring and drilling components. This has several benefits. First, it minimizes the settling time of the positioning feedback sensors (the time after the positioning of the moveable table is completed until the sensor sees no further movement or backlash and can initiate the signal to begin the drilling.) Second, it prevents any additional, unwanted movement of the x axis movable table, the y axis moveable trolly and the z axis drilling unit which will reduce the accuracy of the PCB stack location. Third, and lastly, it helps ensure that the drill bits enter the PCB board stacks at precisely 90 degrees and thus do not drift too far off of their desired mark on the bottom PCB substrate. 
         [0025]    Albeit, these reactionary force movements are minimized with this fix—but not neglible. While these unwanted movements may have been acceptably minimized with large scale drilling, this is not the case with PCB substrate holes which are in the 10-100 micron range. In this huge mass base or frame, the reaction forces when absorbed, turn into low accelerations and one must hope the position feedback sensors are not disturbed at a frequency that will cause a loss in system accuracy. The primary reason why this heavy base design is so prominent is because of the prominent the use of ball screw drives. However, with the advent of cost competitive linear motors it is now possible to make a machine tool architecture that utilizes the decoupled force frame/metrology frame architecture. 
         [0026]    Total elimination of these reactionary force movements would drastically improve the operation of such devices. The present apparatus deals with the removal of these reactionary force movements in all axes in two ways that result in a new apparatus architecture. First, the present apparatus separates or decouples the apparatus into two frames—a force frame to accept the x axis and y axis reactionary forces, and a metrology frame that houses the feedback sensors used to position the PCB substrate stacks for drilling. The importance of keeping the reactionary force movements from disturbing position feedback is critical, for the feedback sensor unit is only as good as the environment it is in. If the frame that the feedback sensor encoders are positioned on has extensive vibrations, it will lose its ability to properly measure the x, y and z axis positions of the apparatus&#39; components as indicated by the encoding strips. (Although, generally position feedback is done by a feedback sensor unit that has an encoding strip and an optical encoder that senses the encoing stip, it is know that other position feedback sensor units may be utilized with this present invention.) Second, it utilizes a balanced reactionary force drill unit that passes no reactionary forces from the downward and upward stroke of the drill spindle onto the metrology frame. The combination of these fixes eliminates all of the movement from reactionary forces in all three axes resulting in shorter cycle times (due to quicker positioning sensor settling times), less drill bit wear and breakage (due to precise 90 degree drilling geometry), higher multiple PCB substrate stacks (due to less drill bit wander.) 
         [0027]    Simply stated, the output of the present invention far exceeds that of the prior art and provides a much more accurately positioned hole on the PCB substrates.  FIG. 1  illustrates the operational concept of the prior art and  FIG. 2  illustrates the operational concept of the present invention&#39;s decoupled force frame/metrology frame design that results in the enhanced machine stability. 
         [0028]    It is to be noted that for the purposes of clarity the position feedback sensors, the drilling and drive computer, the pressure feet and the drill drive equipment are not illustrated as they are well known in the industry and their inclusion in the figures would just serve to hamper the clarity for the overall representation and understanding of the present invention. In the preferred embodiments, a zero impact pressure foot would be utilized as disclosed in EP 0266397 A4, EP 0461733 B1 and EP 0461733 A2. 
         [0029]    Looking at  FIGS. 3-7  the general arrangement of all components of the PCB substrate drilling apparatus (the apparatus)  2  can best be seen. A reactionary force frame base mass  4  made of a dense material such as granite, steel or concrete rests directly on the ground and serves to support the remainder of the apparatus&#39;s components. It generally weighs in the several ton range at a minimum. Actual weight varies with the size of the apparatus it is coupled to. It is separated from the metrology frame support base  20  by a set of vibration isolation dampeners  8 . These dampeners serve two functions. They prevent any reactionary force motion or other vibrations from the base mass force frame  4  from being transmitted to the metrology frame support base  20  and table assembly  6 , and they absorb any vibrations in the metrology frame support base  20  that would disturb the feedback sensors. These vibration isolation dampeners  8  are of an elastomeric polymer, although a metal spring or other compressible isolator that is well known in the industry could be substituted. The vibration isolation dampeners  8  may be mounted top and bottom on a set of plates  10  that are in turn affixed to the base mass force frame  4  and the metrology frame support base  20 . Although depicted in sets of two and being located at the four corners of the assembly  2 , the actual placement and number of isolation dampeners may vary depending upon the size and configuration of the assembly. Although not shown in the figures, in an alternate embodiment the isolation dampers are placed at the horizontal center of gravity plane of the metrology frame support base. The design illustrated in  FIG. 3  would be modified such that the uppermost (top) plate of the pair of metal plates  10  would fit up into a stopped orifice in the metrology frame support base such that its vertical position was vertically aligned with the horizontal center of gravity plane for the metrology frame support base. The top of this stopped orifice would serve as the upper contact point between the metrology frame support base  20  and the isolation damper  8 . This type of modification would be well known it the field of art. This aids to further eliminate any parasitic reactionary force disturbances. 
         [0030]    The x axis moving table assembly  6  has an x axis moving table  12  coupled to the traveling arm  14  of the x axis linear drive unit. The x axis linear drive unit drives the traveling arm  14  along a stationary track  16  based on a signal generated by the master control computer. On this moving table  12  are located the encoding strips that enable the optical encoders mounted on the metrology frame support base  20  to determine the table&#39;s position and relay it to the computing means for generation of x axis drive signals to the x axis linear drive unit to move the traveling arm  14 , as well as the stacks of PCB substrate for drilling, which are mounted on the traveling table  12 . The x axis traveling arm  14  is coupled to the stationary drive track  16  of the x axis linear drive unit for linear motion in the x axis by a low friction bearing means. Additional low friction bearings  18  act as a support between the bottom face of the x axis moving table  12  and the top face of the metrology frame support base  20 . The stationary drive track  16  is not coupled or connected to the metrology frame support base  20 , rather the stationary drive track  16  of the x axis linear drive unit is directly coupled to the base mass force frame  4  by the x axis reactionary force movement transfer means  22 . This is a stanchion made of a pair of rigid arms connected by a beam  23  made of a steel, a metal, a polymer or composite construction thereof, that the x axis stationary drive track  16  is affixed to. It is an extension of the base mass force frame  4 . (Although it is known that the x axis reactionary force movement transfer means  22  may have a different physical configuration, it will remain a connection between the x axis stationary drive track  16  and the base mass force frame  4  and must isolate the x axis traveling arm  14  from the metrology frame support base  20 . Since the base mass force frame  4  is directly coupled to the ground, connecting the x axis reactionary force movement transfer means  22  directly to the ground rather than to the base mass force frame is deemed the equivalent to connecting the x axis reactionary force movement transfer means  22  to the base mass force frame  4 . This alternate method of design would be an alternate embodiment of the present invention.) 
         [0031]    As the x axis moving table  12  and traveling support arm  14  of the linear drive unit move in the x axis, the reactionary force experienced in the x axis stationary drive track  16  of the linear drive unit is transmitted through the x axis reactionary force movement transfer means  22  to the base mass force frame  4  which is in turn transferred to the ground. It is known that in other embodiments the x axis reactionary force movement transfer means  22  may be of a single rigid arm and may be affixed differently to the stationary drive. 
         [0032]    The y axis moving trolley assembly has a y axis moving carriage  24  coupled to the y axis travelling arm  26  of the y axis linear drive unit. The y axis linear drive unit drives the y axis moving carriage  24  along a y axis stationary (generally magnetic) drive track  28  based on a signal generated by the master control computer. This y axis traveling arm  26  is coupled to the y axis stationary drive track  28  for the y axis linear drive unit and is adapted for linear motion in the y axis by a low friction bearing means  30 . Additional low friction y axis bearings  30  act as a support between the back face of the y axis moving trolley  24  and the front face of the metrology frame support base&#39;s y axis support block  32 . The y axis support block is an extension of the metrology frame support base  20 . (Although shown as a U shaped block projecting normally from the section of the metrology frame support base  20  that the traveling table  12  is supported on, it is known that any configuration that is capable of supporting the y axis moving trolley  24  could be substituted provided that it was isolated from the base mass force frame  4 .) 
         [0033]    The y axis stationary drive track  28  is decoupled from the metrology frame support base&#39;s y axis support block  32  (and the rest of the metrology frame support base  20 ) by virtue of its direct coupling to the base mass force frame  4  by the y axis reactionary force movement transfer means  34 . This is a rigid stanchion made of pair of rigid arms with a planar member extending between them. It can be made of a steel, a metal, a polymer or composite construction thereof and it is connected to and supports the y axis stationary drive track  36 . As the y axis moving carriage  24  and traveling arm  26  of the y axis linear drive unit move in the y axis, the reactionary force experienced in the y axis stationary drive track  28  of the y axis linear drive unit is transmitted through the y axis reactionary force movement transfer means  34  to the base mass force frame  4  which is in turn transferred to the ground. It is known that in other embodiments the y axis reactionary force movement transfer means  34  may employed. (Although it is known that the y axis reactionary force movement transfer means  34  may have a different physical configuration, it will remain a connection between the y axis stationary drive track  28  and the base mass force frame  4  and must isolate the y axis stationary drive  36  from the metrology frame force base  20 . Since the base mass force frame  4  is directly coupled to the ground, connecting the y axis reactionary force movement transfer means  22  directly to the ground rather than to the base mass force frame  4  is deemed the equivalent to connecting the y axis reactionary force movement transfer means  32  to the base mass force frame  4 . This alternate method of design would be an alternate embodiment of the present invention.) 
         [0034]    Looking at  FIGS. 8-10  the general arrangement of the z axis balanced reactionary force drill unit  36  can best be seen. As stated earlier, for purposes of clarity the spindle rotating drive components (the drill drive equipment) and the zero impact pressure foot components that secure the PCB substrates prior to the drilling are not illustrated. Each of these are subjects of earlier patents, and are well known in this field of art and do not impose vibrational movements that are meaningful to the accuracy of the PCB substrate positioning. 
         [0035]    The drill unit  36  is mounted and oriented on the y axis moving carriage  24  such that its linear axis and z axis drill stroke reside at 90 degrees to the horizontal plane of the x axis moving table  12  and the horizontal plane in which the y axis moving carriage travels. The drill unit  36  has a base plate  38  to which is affixed an upper guide sleeve  40  and a lower guide sleeve  42  each of which house low friction guide bushing assemblies such as 5-25 micron orificed or porous carbon air sleeves. The drill unit  36  has a spindle  44  that resides inside the low friction guide bushing assembly housed in the lower guide sleeve  42 . The lower guide sleeve also houses the spindle motor. The spindle  44  holds a drill bit and is rotated at a high speed. The spindle  44  is driven or plunged downward in the z axis by a z axis spindle drive unit that applies an electric pulse that is provided to the voice coil  46  which is of a cup shaped design that fits up into a mating recess in the bottom of the voice coil magnet assembly  48 . The voice coil magnet assembly  48  is made of a voice coil magnet that is coupled to a reaction mass and is partially housed within a low friction guide bushing assembly housed within the upper guide sleeve  40 . There is a slender linear member flexure  50  connecting the spindle  44  to the voice coil  46 . This flexure  50  deflects slightly to keep any angular distortion or deviance from the z axis travel of the spindle  44  minimized. 
         [0036]    This conjoined voice coil magnet and reaction mass (voice coil magnet assembly)  48  has a mass several times greater than that of the voice coil  46 , flexure  50  and spindle  44  combined. In this manner, when the electric pulse is sent to the voice coil  46  which resides partially within the recess in the bottom of the voice coil magnet, the magnetic field generated in the voice coil  46  pushes against the magnetic field of the voice coil magnet and reaction mass  48 , and because the mass of the voice coil  46 , flexure  50  and spindle  44  combination is much lesser than the mass of the voice coil magnet and reaction mass  48 , the combination of the voice coil  46 , flexure  50  and spindle  44  are driven downwards in the z axis. Simultaneously, the magnet and reaction mass  48  are driven upwards in the z axis. The ratio of the length of the upwards stroke of the voice coil magnet and reaction mass  48  to the length of the downwards stroke of the voice coil  46 , flexure  50  and spindle  44  is proportional to their masses. If the mass of the voice coil magnet and reaction mass  48  is 10 times that of the voice coil  46 , flexure  50  and spindle  44  combined, then for every one inch of spindle motion in the negative z axis there will be a reactionary 0.1 inch movement of the magnet and reaction mass  48  in the positive z axis and vice versa. Since the reactionary force movement created when the spindle  44  plunges its bit downward into the PCB substrate is dealt with by the opposing (balancing) movement of the magnet and reaction mass  48  upwards, there is no unresolved forces or movement passed onto the drill unit  36  and the metrology frame base  20 . Thus, there are no unresolved reactionary forces to disturb either the position feed back sensors or the drilling geometry of the spindle  44 . 
         [0037]    Additionally, to aid in the minimizing of the reactionary forces, and to ensure that the spindle and magnet always return or “settle” to the same position, a multi axis pivotable phase linkage  52  is connected between the voice coil  46  and the voice coil magnet assembly  48 . This phase linkage is made of a series of sequentially connected linear members. In  FIG. 9  the first member  56  (which is a linear arm) has a distal pivotal connection  53  to the voice coil  46  and a proximate pivotal connection to a first end of an intermediate connection member  55 . A stationary pivot  54  is affixed to the bottom of the upper guide sleeve  40  and is aligned on the linear axis of the spindle  44 . The first member  56  passes horizontally through the pivot  54  such that the ratio of the distance from the pivot  54  to the distal pivotal connection  53  compared to the distance from the pivot  54  to the proximate pivotal connection  56 , is the same ratio as that of the mass of the voice coil magnet and reaction mass  48  to that of the mass of the voice coil  46 , flexure  50  and spindle  44  combined. The second end of the intermediate connection member  55  is connected to the last connection member  57  which is affixed to the voice coil  46 . 
         [0038]    It is to be noted that the voice coil  46  and said voice coil magnet coupled to said reaction mass  48  each simultaneously move in opposite directions along the z axis. Since the mass of said voice coil  46 , spindle  44  and said flexure  50  is less than a mass of said voice coil magnet coupled to said reaction mass  48 , the amount of their linear movements are in proportion to their masses. For example, if the combined mass of the voice coil  46 , spindle  44  and said flexure  50  is 100 grams and the combined mass of said voice coil magnet coupled to said reaction mass  48  is 1000 grams, then the voice coil  46 , spindle  44  and said flexure  50  will move 10 times further and in the opposite z axis direction than the voice coil magnet coupled to said reaction mass  48  will move. 
         [0039]    The decoupled force frame/metrology frame design in conjunction with the balanced reactionary force drill unit attempt to bring all of the net reactionary forces derived form the positioning and drilling functions of the apparatus to zero within the metrology frame so as to allow much more efficient operation of the feedback sensors. This in turn increases the throughput of the device by allowing shorter sensor settle times, higher drill cycle times, more accurate drilling geometry, less broken bits and a longer bit life. 
         [0040]    The above description will enable any person skilled in the art to make and use this invention. It also sets forth the best modes for carrying out this invention. There are numerous variations and modifications thereof that will also remain readily apparent to others skilled in the art, now that the general principles of the present invention have been disclosed. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.