Abstract:
Pin supported printed circuit boards are provided with torsion spring locking assemblies in which torsion springs surround the pins and are captured at one end and have free ends that are deflected, causing a tight grip onto the pins. The result is a pin locking mechanism that is inexpensive and robust due to the elongated contact of the spring with the pin that firmly locks the pin in place, with the extended spring contact protecting the pins against abrading and scoring while providing exceptional locking force.

Description:
RELATED APPLICATIONS  
       [0001]     This Application claims benefit of U.S. Provisional Patent Application No. 60/675,999 filed Apr. 29, 2005, entitled Apparatus to Support a Circuit Board, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to the support of work pieces and more particularly to a locking mechanism for locking pins used to support a work piece having an irregular contour.  
       BACKGROUND OF THE INVENTION  
       [0003]     As described in U.S. Pat. No. 5,984,293, there is a requirement for a universal fixture for supporting printed circuit board assemblies during stencil printing, pick-and-place processing and other printed circuit board assembly processes including the dispensing of conductive adhesives on the top surfaces of printed circuit boards. These particular operations suffer from printed circuit board flexure during manufacture. For instance, with current technologies, printed circuit boards must be maintained flat to within one one-thousandth of an inch to establish a datum plane for printed circuit boards. Not only must the lateral position of the circuit board be maintained to exacting tolerances, due to the flexure or warping of the board during processing, the boards must be robustly supported, especially for dispensing, printing and pick-and-place operations in which the components placed in these operations can on occasion press on the printed circuit board and deflect it.  
         [0004]     This type of tolerance control during printed circuit board assembly is also critical when, for instance, one seeks to deposit an exact amount of solder paste through a stencil at precise positions over a circuit board. For single-sided boards flatness is not a problem. However, supporting a double-sided board that has been partially populated on its underside presents especially severe challenges.  
         [0005]     Note that, in order for components to be mounted by pick-and-place machines or the like, conductive adhesive or solder paste must be positioned on a flat flip surface of the circuit board that already carries components on its underneath side. If the circuit board flexes during stenciling, the spacing between the apertures of the stencil and board will vary. This can cause the squeegeed solder paste to spread out on the board more than intended, which can cause shorts.  
         [0006]     Moreover, instead of using a stencil, oftentimes a syringe-type adhesive injector is required. Not only must the lateral position of the syringe injector tip be controlled, but also the position of the tip of the injection needle must be precisely spaced from the top of the circuit board to provide a highly defined conductive adhesive spot. If the distance varies between the tip and the top surface of the circuit board, either an over-amount of the conductive adhesive will be deposited or the syringe-type needle will punch into the circuit board, at which point its exit orifice is occluded, blocking the release of conductive adhesive.  
         [0007]     In the past, the support of contoured or irregular bottom sides of double-sided printed circuit boards has been accomplished through the use of an array of pins, sometimes called pogo pins, which are upwardly biased against the irregular surfaces of the circuit board caused by the underside components. Such a process is described in the aforementioned U.S. Pat. No. 5,984,293, in which once the pins are positioned by pressing the circuit board with the underside components against the pins, a translating apertured plate grabs the pins and locks the pins in place so that multiple circuit boards can be subsequently positioned on this pin array structure.  
         [0008]     Self-conforming support systems involving an array of pins or a bed of nails are described in U.S. Pat. Nos. 6,264,187; 6,029,966; and 6,726,195. In each of these patents the locking mechanism is a translating apertured plate that grabs one side of the pins after they have been positioned by the pressing down of the circuit board on the pin array.  
         [0009]     The problem with translating-plate locking mechanisms is that the apertures in the translating plate dig into the sides of the plastic pins, scoring them and generally rendering them unusable after a number of such operations.  
         [0010]     One such pogo pin structure is manufactured by Production Solutions, Inc. of Poway, Calif., called the Red-E-Set board support system that involves arrays of pins carried by pin-locating bars. These pins are pneumatically actuated to contact the underside of the populated printed circuit board. Since these pins are plastic, the sliding plate locking structure digs into the pins after a number of actuations and causes failures.  
         [0011]     Another type of irregular or conformal support system is manufactured by Airline Hydraulics Corporation of Bensalem, Pa. in the form of their Gridlock SMT support system. This system is described in U.S. Pat. No. 6,702,272, which shows a locking system involving a ball/channel arrangement, with the ball contacting the pin as it slides down the channel by gravity after the pin has reached its desired extension. To unlock the pins, a vacuum initially lifts the balls away from the pins to release them. To lock the pins, the vacuum is released and the balls fall by gravity into the hardened steel pins. To unlock the pins, the vacuum is re-established. As will be appreciated, sealing of this ball/channel structure is complicated and internal air leaks can occur if proper sealing is not maintained.  
         [0012]     Thus such a locking system is expensive and complicated due to the number of parts and air seals necessary. Moreover, since the pins are cylindrical and the balls are round, the contact between the two is only at a point. It will be appreciated that single point locking is somewhat less robust than all-around contact would be. While the Gridlock system is said to be usable for printers, chip shooters, pick-and-place machines and dispensers used in surface mount technology (SMT) assembly, the complicated locking system with its multiple balls, channels and seals makes such printed circuit board support prohibitively expensive.  
         [0013]     It will be appreciated that double-sided circuit boards can also be supported by magnetically actuated pins. However, magnetic locking of the pins is not easily achieved because of the relatively high magnetic fields that must be created, and some components are sensitive to magnetic fields.  
         [0014]     Another type of supporting system for irregularly shaped articles is discussed in U.S. Pat. No. 4,200,272, which utilizes pneumatically operated clamping bladders to lock the pins, whereas U.S. Pat. Nos. 5,722,646; 4,684,113; 5,157,438; 5,820,983; and 5,819,394 describe other methods for supporting irregularly shaped articles in the manufacturing process.  
         [0015]     Moreover, U.S. Pat. Nos. 6,252,415; 6,834,243; 5,656,943; 6,641,430; and 6,676,438 describe pin block structures for supporting work pieces for manufacture and testing.  
         [0016]     As mentioned above, such positioning tools or supports have found usage in surface mount technology in which components are mounted on two sides of a printed circuit board. Because of the increased demands on the flatness of the printed circuit board during fabrication and population, one requires a support structure that is easily pre-configured for the underside of populated boards to be able to assure a flat topside for further printed circuit board assembly and processing.  
         [0017]     It is noted that in order to properly maintain the planar structure of the printed circuit board, the pins need to be spaced no more than 0.75 inches apart so as to eliminate any flexure of the printed circuit board therebetween. Note also that the thickness of typical double-sided circuit boards is on the order of 0.031 to 0.62 inches.  
         [0018]     In summary, it is known that printed circuit boards routinely flex during printed circuit board assembly, and that this flexing must be eliminated.  
       SUMMARY OF INVENTION  
       [0019]     Rather than utilizing the locking mechanisms described above in which pins are physically clamped in place utilizing either a translating apertured plate or a ball/channel assembly, and rather than utilizing magnetic actuation and locking mechanisms, in the subject invention a pin bar is provided with an upwardly projecting array of pins, each surrounded by a locking torsion spring. One leg of each spring is anchored or secured to the bar and the free leg is deflected to decrease the inside diameter of the spring creating a solid lock around the pin to lock it in place. In one embodiment a number of pin-carrying bars are mounted to a frame, with the number of bars secured to the frame creating support for printed circuit boards as large as 24″×24″.  
         [0020]     In a setup procedure, the circuit board is placed on four equally high support pins on each corner. The circuit board may have many components of various heights, shapes and forms on the bottom side, presenting an irregular surface.  
         [0021]     A flat plate larger than the circuit board is placed on top of the circuit board and secured in that position. The pins are now activated traveling upwards and will come in contact with the circuit board or a component of that circuit board, pushing the board with components up against the flat support plate. The force of the pins is regulated pneumatically to avoid excessive force. The pin support pins have now conformed to the bottom side of the circuit board. The pins are then locked into place by the strangling effect of the torsion springs around the pins. This is done by deflecting the free ends of the torsion springs by, for instance, 15°, with the movement of the free ends tightening the springs around respective pins. In one embodiment, the free end deflection is accomplished by a translating notched bar designed to capture the free ends of the springs in the notches and to deflect them to tighten the springs around associated pins. In one embodiment, the springs are made of steel music wire, with the torsion spring having a 0.0158 inside diameter when relaxed for pins having a 0.0157 outside diameter. Note that the relaxed inside diameter provides a sliding fit for the pins.  
         [0022]     It will be appreciated that when the torsion spring is deflected on itself around a pin, it provides uniform pressure about the pin from all directions due to the strangling of the pin by the associated spring. As a result of the elongated and uniform contact, the locking action does not gouge or otherwise damage the pins. Moreover, the holding power of such a torsion spring is exceptional, since the frictional contact is along the entire outer surface of the pin and along the entire length of the spring. As a result, the torsion spring is captivated.  
         [0023]     In operation, when the populated training circuit board underside contacts the pins and the pins are moved upwardly with a pressure of, for instance, 30 psi, the pins are locked into place by the strangulation provided by the deflection of the free spring end. Thus, once having provided a sample printed circuit board called a training board and having positioned it above the pin structure, having the pins moved upwardly to contact the underside of the board and its components where the pins stop, and having locked the stopped pins, the same pin array support may be used for many hundreds of operations without recalibration.  
         [0024]     Note, the pins exert upward pressure on the board and its components. Moreover, the upward pressure of the pins, which may be regulated, cannot lift the board because during the training run it is maintained in place or captured by a heavy plate; or the plate is clamped in place to the base of the support system. Thus with the flat plate in place and clamped, when the pins are locked, the top surface of the training board will be flat.  
         [0025]     The anaconda effect of the springs strangling the pins in place is extremely effective as can be seen by the fact that the pins in one embodiment cannot be moved by a force of 10 pounds or more per pin.  
         [0026]     As will be appreciated, there are few moving parts to this locking mechanism, the only movement being the movement of the free ends of the springs, with the other ends of the springs being fixed or anchored to the assembly or bar carrying the pins.  
         [0027]     Thus, rather than having translating apertured plates, magnetically actuated pin locks and ball detent apparatus for locking the pins, in the subject invention a simple, inexpensive torsion spring is used to surround and lock each pin.  
         [0028]     The subject multi-pin structure may be used in a wide variety of printed circuit board assembly operations. Importantly, it may be used to support double-sided circuit boards to provide a flat top surface. This flatness is essential in stenciling, pick-and-place and dispensing operations.  
         [0029]     It is noted that while boards to be stenciled or screen-printed may be warped, if properly supported by the subject locked-pin system, the weight and pressuring of the stenciling squeegee flattens the warped boards against the locked support pins during these operations.  
         [0030]     For other board assembly operations warped boards can be straightened by a vacuum system that forces the board onto the locked pins.  
         [0031]     Moreover, with the subject support system, one can readily control the spacing of dispensing tips from a flat double-sided board for those operations requiring the dispensing of conductive epoxies or other adhesives at precise points with controlled lateral spreads. Since the subject locked pin array system maintains with vacuum warp correction the flatness of all portions of the top surface of a circuit board to a thousandth of an inch, this permits the syringe-type injectors to be brought down to a pre-calculated spacing between the injection nozzle tip and the surface of the board without the use of complicated and expensive laser board position sensing systems.  
         [0032]     In terms of pick-and-place machines, the flatness of the printed circuit board assisted by vacuum warp correction permits the use of a high-speed machine without regard to circuit board flex problems. Because of the flatness maintained by the subject system, the stroke needed in placing components can be accurately pre-calculated, again without laser assist.  
         [0033]     In summary, pin supported printed circuit boards are provided with torsion spring locking assemblies in which torsion springs surround the pins and are anchored at one end and have free ends that are deflected, causing a tight grip onto the pins. The result is a pin locking mechanism that is inexpensive and robust due to the elongated contact of the spring with the pin that firmly locks the pin in place, with the extended spring contact protecting the pins against abrading and scoring while providing exceptional locking force.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]     These and other features of the subject invention will be better understood in connection with a Detailed Description, in conjunction with the Drawings, of which:  
         [0035]      FIG. 1  is a diagrammatic illustration of the inverting of a circuit board, populated on one side such that the populated elements point downwardly;  
         [0036]      FIG. 2  is a diagrammatic illustration of the circuit board of  FIG. 1  inverted with components on the underneath side;  
         [0037]      FIG. 3  is a diagrammatic illustration of the underside-populated printed circuit board of  FIG. 2  positioned over the subject support system, in which the printed circuit board is to be positioned underneath and aligned with a stencil;  
         [0038]      FIG. 4A  is a diagrammatic illustration of the stencil of  FIG. 3  aligned over the printed circuit board supported by the subject pin array;  
         [0039]      FIG. 4B  is a diagrammatic illustration of solder paste spreading under a stencil due to board flexure.  
         [0040]      FIG. 5  is a diagrammatic illustration of patterned solder on top of the printed circuit board of  FIG. 1  after having been stenciled over the board, showing the effect of overlapping areas of deposits of solder on the circuit board of  FIG. 1 ;  
         [0041]      FIG. 6A  is a diagrammatic illustration of the use of a pick-and-place machine to place components on the top surface of the board of  FIG. 5 ;  
         [0042]      FIG. 6B  is a diagrammatic illustration of the effect of board flexure on stroke calculation and component placement for the pick-and-place operation of  FIG. 6A ;  
         [0043]      FIG. 6C  is a diagrammatic illustration of the effect of the bowing of the circuit board on the leads from a component that is to be placed on the board by a pick-and-place machine, illustrating bending of the leads due to the bowing;  
         [0044]      FIG. 7  is a diagrammatic illustration of the soldering of the picked-and-placed components to the topside of the board of  FIG. 6A  in a reflow solder operation;  
         [0045]      FIG. 8  is a diagrammatic illustration of the use of an array of pins on adjacent pin bars indicating initial retracted or down pin position, also showing four fixed plate support posts;  
         [0046]      FIG. 9  is a schematic diagram of the limiting of the pin extensions by components on the underneath side of the board as well as the board, also showing a fixed flat plate on top of the circuit board for limiting the upward motion of the circuit board caused by the upward extension of the pins in the pin array;  
         [0047]      FIG. 10  is a diagrammatic illustration of the subject locking mechanism for the pins of  FIG. 9 , illustrating each of the pins being surrounded by a helical torsion spring having one end secured to the pin bar and having the opposite end free for movement, illustrating the loose fit of the spring around the pin;  
         [0048]      FIG. 11  is a diagrammatic illustration of the translation of a notched bar to move the free ends of the springs of  FIG. 10  in the direction illustrated so as to lock the pins in position by strangulation due to collapse the spring around the associated pin;  
         [0049]      FIG. 12  is a diagrammatic illustration of the position of the pins whose extension is dictated by the underside of the board and the components thereon, with the heights locked into place by the deflection of the free ends of the torsion springs;  
         [0050]      FIG. 13  is a sectional view of an array of pins within a pin-bar assembly, illustrating relaxed springs around associated pins, with the movement of the free ends of the pins to the right for locking;  
         [0051]      FIG. 14  is a top view of the sliding fit of a relaxed torsion spring about an associated pin, with the direction of contraction of the torsion spring about the associated pin indicated by the arrows;  
         [0052]      FIG. 15  is a top view of the spring and pin assembly of  FIG. 14 , illustrating the tightening of a spring securely about an associated pin with the movement of the free end by approximately 15° to strangle the pin preventing movement;  
         [0053]      FIG. 16  is a cross-sectional view of the array of  FIG. 13  in which the springs strangle about the associated pins; and,  
         [0054]      FIG. 17  is a cross-sectional view of the pin bar of  FIG. 16 , showing the extension of the various pins as they contact the underside of the board and the associated components when the circuit board in position and clamped to the support posts at the four corners thereof, showing the position of the pins that are to be locked. 
     
    
     DETAILED DESCRIPTION  
       [0055]     What is now presented is a method for using a pin array support that is trained on a bottom side populated circuit board in which the pins extend to touch the bottom side of the board where they are then locked in place.  
         [0056]     Referring now to  FIG. 1 , what is illustrated is a training board  10  having a number of components  14  populated on the topside  16  of the printed circuit board. Upon population of the components on top of the to-be double-sided printed circuit training board, it is inverted or flipped over as illustrated by arrow  18  so as to achieve the orientation illustrated in  FIG. 2  with components  14  pointed in a downward direction. The result is an irregular or contoured underside. It will be appreciated that being able to support such circuit board that is bottom side populated to provide a flat top surface requires a support structure that can be configured to accommodate and support the various components on the underneath side of the circuit board as well as the board itself.  
         [0057]     Referring to  FIG. 3 , training board  10  is supported at its corners by four equal height corner supports or posts  20  affixed to a base or support  22  having pins  24  extending from longitudinally running pin bars  25  to support the array of pins, with the circuit board positioned above the pin bars at its four corners. A flat plate is placed on top of the circuit board and fastened so the circuit board cannot move upwardly. This is done in one embodiment by a weighted plate and in another embodiment by clamping the plate to the support carrying the pin bars.  
         [0058]     In an operation to be described, the pins that are initially retracted so as to present a flat surface when mounting the training board are extended to touch the underside of the training board, with the board being restrained from upward movement caused by the extending pins due to the plate on top. Once the pins touch the underside of the board and its components, they force the board up against the plate. Thereafter the pins are locked in place by the subject torsion spring locking system. Once locked, the flat plate is removed and the boards to be processed are supported on the locked pins, with the support guaranteeing a flat top surface for the rest of the boards in the run.  
         [0059]     Once having the pin array trained to a particular board, there are a number of board processing operations that benefit from the maintenance of a flat top surface.  
         [0060]     In one board-processing operation involving stenciling, one deposits solder paste through a fine-pitch stencil in which inter-aperture spacings are often no more than 0.006 inches. A stencil  26  is, as usual, supported in tension in a rigid frame and has apertures  28  therethrough. The flat stencil is then placed on top of surface  29  of printed circuit board  10 . Note that it is the function of the subject support system that the top surface is maintained flat for this and all other operations.  
         [0061]     In a follow-on procedure, solder is squeegeed over stencil  26  and through its apertures, with the squeegee exerting downward pressure. This downward pressure flattens any upwardly bowed boards onto the locked pins. This establishes a flat top board surface onto which the flat stencil is in contact across the entire top surface. The result is that solder paste is printed onto the circuit board through a stencil that is in intimate contact with the board top surface. Note that if the board were warped downwardly, this would cause a gap between the bottom of the stencil and the top of the board such that an aperture  28  is spaced from top surface  29  of circuit board  10 . This can cause a solder spread that can result in shorting, especially for fine pitch patterns.  
         [0062]     As will be appreciated, with modem circuit boards, the pitch for the patterned solder for some of the components is so fine that any error in the formation of a fine-pitch solder pattern can cause shorting and board failure.  
         [0063]     As illustrated in  FIG. 4A , with stencil  26  pre-stretched, in place and aligned, and with the circuit board appropriately supported, apertures  28  in stencil  26  are in intimate contact with the top surface of the circuit board so as to assure proper solder deposition. However, as shown in  FIG. 4B , if the board is not properly supported such that its top surface is not flat, then a downwardly warped board portion  29  is spaced from apertures  28  in stencil  26 . As a result, it can be seen that printed solder paste  30  extends laterally over board  10  as illustrated at  31 . One problem with the solder paste spread is shorting. Another problem is the mess caused by the excess solder paste on the underneath side of the stencil that can get over subsequent circuit boards.  
         [0064]     As illustrated in  FIG. 5 , for a warped board not supported by the subject system, solder has been squeegeed over the stencil and the stencil has been removed, leaving printed solder paste  30  on the top surface  29  of board  10 . However, at regions  31 , shorted solder regions can exist if the board was not supported properly to provide a planar top surface underneath the flat stencil.  
         [0065]     As illustrated in  FIG. 6A , in another board fabrication operation a pick-and-place machine  32  is used to populate top surface  29  of board  10  with components  34  that are placed on patterned solder or other conductive adhesive points such that when, in  FIG. 7 , board  10  is removed and subjected to solder-melting temperatures in a reflow solder process as indicated by arrows  33 , the components on the top surface  29  of board  10  are bonded to the conductive patterns on the top surface of the board.  
         [0066]     Referring to  FIG. 6B , board  10  is shown warped or flexed at  35  such that component  34  is spaced from the top surface of board  10  as illustrated at  36 . This is caused by the component having been positioned from the originally calculated stroke  37 . The stroke describes the downward movement of the pick-and-place head, taking into account the thickness of the particular component. Thus as shown at  38 , the head of the pick-and-place tool is stopped at a position calculated assuming the top surface of the circuit board is flat. Note that legs  39  do not make contact with the top surface  29  of board  10 .  
         [0067]     As shown in  FIG. 6C , if board  10  is bowed or warped upwardly, a lead  39 ′ from component  34  may be bent, displaced or at least mispositioned when head  32  is brought down. If lead  39 ′ exerts undue lateral pressure on solder paste  41 , since it is soft, the paste may smudge or spread out to adjacent solder pads where shorting occurs. This can be a severe problem when spacing between solder pads is on the order of 6 mils.  
         [0068]     Referring back to  FIG. 6A , in an optional embodiment, to take care of the warped board problem, a vacuum is provided to suck the board down on the locked pins to provide a flat pick-and-place surface. This eliminates the problem of having to provide laser stroke feedback to adjust the stroke for non-flat boards.  
         [0069]     Thus it is extremely important that the double-sided board be appropriately supported by easily locked pins to maintain an ascertainable flat top surface to assure a proper pick-and-place operation.  
         [0070]     How the top portion of the boards of  FIGS. 1 through 6  is maintained flat is shown in  FIG. 8  to be accomplished by the subject pogo pin or bed-of-nails pin array  40  that includes a number of side-by-side pin bars  25  in one embodiment. The bars carry a number of pins  24 , shown in their fully retracted positions to permit positioning of an underside populated training board on top, where the training board is supported by the equal height fixed corner posts  20 .  
         [0071]     As illustrated in  FIG. 9 , training board  10  is placed over the pin array and is supported over the array by posts  20 . Note, initially the pins retracted or down. A flat plate  45  is then placed on top of the circuit board and is clamped in place to prevent upward movement of board  10  when the pins are extended. As an alternative to clamping, plate  45  can be made of heavy material or a weight can be placed on top of the plate. However, clamping is preferred due to the combined upward pressure provided by the pneumatic extension of the pins which would require the use of excessive and unwieldy weights. In any event the plate and board are clamped down onto corner posts  20  above on pin array  40  so that the height of the board above the pin array is fixed.  
         [0072]     After the board is clamped into position, the pins are extended in one embodiment by the application of air pressure. As a result, various of the pins, here illustrated at  46  and  48 , are limited in their upward extension by the clamped underside of the board and its components  14 .  
         [0073]     Thus, the pins come to rest on the undersides of all of the components or on bare board, with the entire training board  10  being supported on the corner posts and the pins with its topside completely flat. This is because in the training phase the board was in contact with the flat underside of plate  45 .  
         [0074]     The pins in one embodiment are spaced no more than 0.625 inches apart to meet the planar requirement for the top surface of the circuit board.  
         [0075]     Once the pins are extended up to conform to the irregular contour of the underside of the circuit board, the pins are to be locked in place so that the pin array support can be used again and again for like-configured double-sided circuit boards.  
       Pin Locking  
       [0076]     The locking problem that is not well enough addressed in the past is how to lock the pins in position after they have been extended.  
         [0077]     Referring to  FIGS. 10 and 11 , it can be seen that each of the pins  50  is surrounded with a torsion spring  52  that has one anchored end  54  secured to the bar from which the pin extends. A free end  58  protrudes from the bottom of the spring. This end can be deflected clockwise so that as illustrated in  FIG. 11  the spring contracts as illustrated at  76  about its associated pin to strangle it and hold it in place. The flexing of end  58  by approximately 15° causes the spring to contract around the pin along the extended length of the spring. It is the elongated contact of the spring around the pin at all points about the periphery of the pin that causes extremely secure locking of the pin in place when the free ends are deflected as illustrated. Not only is there continuous and contiguous contact by the spring with the pin, as opposed to point contact or aperture edge contact as in the past, the length of frictional contact with the pin by the contracted spring provides an extended contact with the spring to securely lock the pin in position.  
         [0078]     This is quite different from previous locking mechanisms in which a ball contacts the pin at one point or in which the side of an aperture of a translating plate presses against the side of a pin. The subject system is also much more robust than magnetic locking systems. It is noted that magnetic locking mechanisms are prone to failure due to the inability to maintain the high level of magnetism necessary to provide a secure lock. Moreover, high magnetic fields can damage some components.  
         [0079]     As a result, the locking of the pins by torsion springs forms an economical, extremely robust locking system.  
         [0080]     In order to deflect the spring ends, a translatable member  70  is provided that in one embodiment has notches  72  that cooperate with free ends  58  of springs  52  to move the free ends upon translation of the notched member in the direction of arrow  60 .  
         [0081]     This simple mechanism for tightening the springs around associated pins is illustrated by the tightened springs  75  along an extended frictional contact zone  76 . The tightening or pin strangulation requires only the translation of a member with appropriately configured notches or apertures to catch and hold the free ends of the springs. Thus the pins are easily and securely locked into place as illustrated at  50 ′ at the appropriate extensions.  
         [0082]     As illustrated in  FIG. 12 , an exemplary pin extension pattern  80  is illustrated in which pins  24  from pin bars  25  are locked to appropriate heights or extensions by operation of the subject locking mechanism. Here the member  70  may be translated by air pressure or the translatable member may be mechanically manipulated.  
         [0083]     More particularly and referring now to  FIG. 13 , in one embodiment each of pins  24  is located in a barlike subassembly or pin bar  25  that includes a longitudinally running wall  82 , with ends  54  of pins  24  secured against movement by the wall.  
         [0084]     Referring to  FIG. 14 , spring  52  is shown in its open or relaxed condition prior to deflection of end  58  counterclockwise to the right. Here it can be seen that end  54  is secured against movement by wall  82 .  
         [0085]     As illustrated by arrows  94 , with deflection of end  58  to the right as illustrated at  FIG. 15 , the spring compresses around, contracts around or strangles pin  24  to prevent pin movement.  
         [0086]     Referring to  FIGS. 16 and 17 , each of the pins extends through a top plate  84  of the pin bar through associated apertures  86 , with a translatable member  88  having notches  90  to provide walls  92  that co-act with the free ends  58  of springs  52 .  
         [0087]     The result, as illustrated in  FIG. 16 , is that springs  52  tightly engage associated pins  24 , with ends  58  having been moved as illustrated by notch wall  92  of translatable member  88 . Here in one embodiment air pressure introduced at fitting  95  acts on piston  96  to translate member  88  to the right a predetermined distance. This distance is that which provides the optimal deflection of the free ends of the springs.  
         [0088]     The net result as illustrated in  FIG. 17  is that pins  24  are locked to the positions shown against circuit board  10  and components here illustrated at  96  that depend down from the underneath side of circuit board  10 .  
         [0089]     When the extended pins  24  are locked in place by springs  52 , their positions are maintained from board to board. In one embodiment, air pressure  102  is introduced into pipe  104  to bias pins  24  when not locked up through apertures  86  in plate  84 , with seals  106  used about the base of pins  24  to seal the pins into associated channels  108  in a subassembly block  110 .  
         [0090]     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.