Abstract:
A carrier of circuit boards includes a base frame having a plurality of first card guides disposed on its upper surface, the first card guides for securing respective first side edges of a corresponding plurality of circuit boards, a plurality of second card guides for securing respective second side edges of the plurality of circuit boards, and a plurality of adjustment members, each being for individually adjusting a distance between a respective pair of one first card guide and one second card guide. A method of preparing a carrying arrangement for a plurality of circuit boards includes providing a carrier for the plurality of circuit boards. Groups of circuit boards having different vertical on-edge dimensions may be interconnected and/or tested by being placed together and individually snugly held on a single carrier shelf.

Description:
BACKGROUND 
   1. Field of the Invention 
   The invention relates to manufacturing and testing processes and, more particularly, to improved apparatus for carrying of circuit boards. 
   2. Background of the Invention 
   Printed circuit boards carrying electronic and related components are typically produced in a fashion where per-unit cost is a factor to be minimized. Circuit boards may be produced in a high volume manufacturing where any incremental advantage in processing of the circuit boards can effect substantial benefits for the manufacturer. In a typical processing, a bare circuit board may be pretested for continuity, stuffed with components and soldered, cleaned, functionally tested and visually inspected, burned-in according to various criteria, tested, assembled into an assembly, retested, etc. By improving any of the individual processes, a large benefit may result, such as higher yields, lower rework, etc. One such manufacturing advantage may be realized by considering simple quality control logistics and the effects of implementing known testing techniques. Such manufacturing and testing may include handling circuit boards by use of a circuit board carrier. 
   Many quality control and like methods used in manufacturing are adapted for processing and testing of assembled circuit boards. For example, a failure occurring when a component is first operated may be referred-to as an “infant mortality” that happens during a “burn-in” period. By way of over-simplified example, say a component of a circuit board has a 80% chance of meeting required specifications after an initial operation period. And, in this example, if there are three ‘80% good’ components installed in a circuit board, the likelihood of obtaining a working circuit board becomes (0.80×0.80×0.80)51.2%. If the same three components are each ‘99% good,’ the likelihood of obtaining a working circuit board having the three components becomes (0.99×0.99×0.99)97%. A general rule of thumb is that a cost of culling out failed components increases ten-fold for each successive manufacturing process step. Therefore, it makes sense to efficiently test each component to assure the component is near 100% good, before installing the component in the circuit board. The same principle applies to assembled circuit boards as components of a larger system. Performing testing and various cycling on individual circuit boards is necessary to identify rejects. Such processing should be efficient for reducing manufacturing costs while still optimizing quality. For example, by utilizing a circuit board carrier, various fixturing and handling problems may be simplified. Providing thorough testing of individual circuit boards, before they are installed in a larger piece of equipment, assures higher yield for a final assembly line. 
   When a circuit board has been stuffed, assembled, soldered, cleaned, tested, visually inspected, etc., the assembled circuit board may be calibrated and functionally tested, for example, by placing the unit under test into a simulation or functional test apparatus. At a convenient point in the manufacturing/testing process, the circuit boards may be loaded into a circuit board carrier. The circuit boards that pass inspection may be loaded via the carrier into an environmental chamber where they are each connected to a load, powered-up, and subjected to increased and/or reduced temperature, humidity, vibration, and other stimuli in a ‘shock cycling’ that accelerates the process of infant mortality. Such cycling may include monitoring certain electrical operating characteristics while the circuit board is undergoing extreme changes in temperature or other environmental parameter. A range for temperature or other cycling parameters typically depends on an intended use for an end product, e.g., consumer goods, military products, etc. For example, consumer type electrical products may have environmental or reliability requirements determined by a regulating agency such as UL, CSA, NEMA, etc. By comparison, a military product having a circuit board may be required to withstand a more intensive burn-in and testing phase, for example by subjecting the circuit board to more extreme temperature shock cycles, vibration, etc. Many potential defects are heat related or a result of a mechanical defect such as a loose wire, and such failures are more likely to occur or manifest themselves by use of such burn-in test cycling, whereupon the defective circuit boards are culled out and reworked or scrapped. In addition, since circuit components are required to interact within a circuit board, the combined functionality of the circuit as a whole is also stressed by the environmental cycling. Circuit boards that survive the environmental testing are more likely to perform successfully in the end product for years to come. 
   Due to the complexity and number of components in most circuit boards, it is usually required to perform thorough testing, wherein carriers are used for handling and electrical hookups. It is typically highly advantageous to increase the circuit board yield percentage even slightly. 
   Various kinds of testing may be performed on circuit boards by attaching loads and by doing ‘live’ functional testing either separately or in combination with the environmental cycling. Carriers typically support the circuit boards on edge in a parallel spaced-apart relation and may include electrical connectors for engaging the circuit boards. A carrier may have electrical connectors for electrically connecting the carrier, and its individual circuit boards, to an external device including, for example, a power source, current meter, fuse, signal generator, logic circuit, data collection device, etc. While such carriers generally facilitate efficient manufacturing, they are not adaptable for being easily customized. 
   OBJECTS OF THE INVENTION 
   It is an object of the invention to provide an improved circuit board carrier overcoming some of the problems and shortcomings of the prior art, including those referred to above. 
   Another object of the invention is to provide a test system adaptable to being customized for testing of circuit boards having different geometries and dimensions. 
   Another object of the invention is to provide a circuit board test/burn-in system readily adaptable for testing of groups of circuit boards, including groups of circuit boards interacting with one another, for example, by operating in a master-slave relation. 
   Still another object of the invention is to provide a system for securing multiple size circuit boards per carrier level. 
   Yet another object of the invention is to provide a carrier having independent card guide adjustment at each position. 
   Another object of the invention is to provide a general carrier design that is adaptable for use of different mechanisms and for use of structure for customizing individual shelf locations. 
   How these and other objects are accomplished will become apparent from the following descriptions and the drawings. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, a carrier of circuit boards includes a base frame having a plurality of first card guides disposed on its upper surface, the first card guides for securing respective first side edges of a corresponding plurality of circuit boards, a plurality of second card guides for securing respective second side edges of the plurality of circuit boards, and a plurality of adjustment members, each being for individually adjusting a distance between a respective pair of one first card guide and one second card guide. 
   In another aspect of the invention, a method of preparing an arrangement for testing of a plurality of circuit boards includes providing a carrier for the plurality of circuit boards, the carrier including a base frame having a plurality of first card guides disposed on its upper surface, the first card guides for securing respective first side edges of a corresponding plurality of circuit boards, a plurality of second card guides for securing respective second side edges of the plurality of circuit boards, and a plurality of adjustment members, each being for individually adjusting a distance between a respective pair of one first card guide and one second card guide. 
   In another aspect of the invention, a method includes securing a first circuit board having a first width in a first slot disposed on a surface of a carrier, and securing a second circuit board having a second width in a second slot disposed on the surface of the carrier and adjacent the first slot, the second width being different from the first width, where the securing provides card guides for abutting opposite edges of the first and second circuit boards. 
   In another aspect of the invention, a method includes providing a carrier having a single shelf for snugly carrying, on-edge, a plurality of circuit boards having respectively different on-edge vertical dimensions. 
   In another aspect of the invention, a carrier of circuit boards includes means for securing respective first side edges of a corresponding plurality of circuit boards, means for securing respective second side edges of the plurality of circuit boards, and adjustment means for individually adjusting a distance between a respective pair of one first card guide and one second card guide. 
   As a result of implementing the present invention, each individual circuit board being carried may be accommodated even though dimensions of circuit boards may vary. Individual circuit boards having different dimensions may be snugly secured in a carrier. Such allows for carrying any mixture of circuit boards, including circuit boards that are grouped for a particular reason. Accordingly, different circuit boards may be interconnected while being loaded onto a carrier, so that cooperation among a group of boards may be tested and/or used for self-adjustment, calibration, and other operations. The independently-adjustable circuit board carrier may be configured and adapted for virtually any circuit board processing environment and requirements. For example, the carrier may be easily customized for testing of different circuit boards having corresponding different geometries and dimensions. 
   Additional advantages and a more complete understanding of the present invention may be derived by referring to the detailed description of preferred embodiments and claims when considered in connection with the figures, wherein like reference numbers refer to similar items throughout the figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a circuit board carrier having independently adjustable cells according to an exemplary embodiment of the invention. 
       FIG. 2  is a detailed view of an adjustment structure for one of the cells of the circuit board carrier of  FIG. 1 . 
       FIG. 3  is an end view of the adjustment structure of  FIG. 2 . 
       FIG. 4  is a side view of the circuit board carrier of  FIG. 1 . 
       FIG. 5  is a schematic side view of an alignment mechanism utilized in an alternative structure for individually adjusting a height of a card guide for one of the cells of a circuit board carrier according to an exemplary embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1–4  show a circuit board carrier  10  according to an exemplary embodiment of the invention. A shelf  11  is formed of a lightweight yet strong material such as aluminum and has a rectangular peripheral shape. Side brackets  12  are positioned in a row along opposite lengthwise top edges of the shelf  11 . The side brackets  12  are formed in an “L” shape. The bottom portion  13  of the end-most side bracket  15  facing inwards so that the outer-face  18  of an outer bracket  15  may be made approximately flush with an end face  16  of the shelf  11 . The side brackets  12 ,  14 ,  15  are attached at their respective bottoms  17 ,  13  to the shelf  11  with suitable fasteners such as rivets, welds, bolts, washers, and nuts, or other suitable fastening system such as spring metal inserts, twist fasteners, etc. Although sections of the carrier  10  may be described only with reference to one side of the carrier  10 , it is understood that a preferable application has a symmetrical structure when practicable. 
   Top brackets  21 ,  22  are each formed with a length approximately the same as the length dimension of the shelf  11 . One or both of the end-most side brackets  14 ,  15  along each of the carrier sides may be formed as an integral part of the respective top bracket  21  by simply bending the top bracket  21  at ninety degrees at the length-end portions. Any of the top brackets  21 ,  22  or end-most side brackets  14 ,  15  may optionally have attached a handle or other device for carrying the carrier  10 , and/or may have slots or other suitable structure for simplifying a manufacturing or testing process, for example, by providing a location for gripping or securing the carrier  10  to a rack, etc. 
   The side brackets  12 ,  14 ,  15  may be positioned along the length of the shelf  11  at regular intervals so that the side brackets  12 ,  14 ,  15  are parallel and provide regularly dimensioned cells  30  adjacent one another. The carrier  10  may have the side brackets  12 ,  14 ,  15  permanently fixed at lateral locations by welding, rivets, or similar method for securing the respective bottom portion  17 ,  13  to the shelf  11 . Similarly, side brackets  12 ,  14 ,  15  each have an upper lateral portion  24  for securing the side bracket  12 ,  14 ,  15  to the corresponding top bracket  21  or  22  by use of a same welding, riveting, or similar method. Optionally, the shelf  11  may be provided with multiple mounting holes at each potential side bracket location, so that the user may create cells  30  having different lateral dimensions by securing respective ones of the side brackets  12 ,  14 ,  15  in chosen ones of the multiple holes. Alternatively, mounting hole(s)  28 ,  29  of a bottom portion  17 ,  13  may be elongated so the user is able to slide the side brackets  12 ,  14 ,  15  laterally and tighten the side brackets  12 ,  14 ,  15  at a desired lateral location. 
   The side brackets  12 ,  14 ,  15  each have a lengthwise vertical slot  41  located in the middle portion of long bracket face  42 . As shown, card guide bracket  50  includes horizontal portion  54  and vertical portion  56 . Card guide bracket  50  may be secured at its lengthwise ends to opposing side brackets  12 ,  112 . For example, at each end of card guide bracket  50  a thumbscrew  43  has a threaded member that passes through round washer  44  and square washer  45  via square washer slot  48 . The thumbscrew  43  threaded member then passes through vertical portion  52  of card guide bracket  50  and is threaded into a t-slot nut  49  inserted into a rectangular hole in vertical portion  52  of card guide bracket  50 . T-slot nut  49  may also extend laterally into square washer  48 . When thumbscrews  43  at each end of card guide bracket  50  are loose, the user may move card guide bracket  50  to a desired vertical position and then tighten thumbscrews  43  to fix the card guide bracket  50  at such location. Various structures may be used for securing a card guide bracket  50  at an upper position including a wedge nut, a releasing clip, and others. 
   One alternate structure may employ known T-slotted rails as side brackets, thereby providing a system that may secure a nut or other fastener to avoid a possibility of the nut working loose and detaching from a carrier  10 . The side brackets  12 ,  14 ,  15  may have incremental markings that provide a structure for determining a vertical height of card guide bracket  50 . For example, a ruler type straight edge on long bracket face  42  may be used for assuring that card guide bracket  50  is at a same vertical height at each of its ends, and a height of a card guide bracket  50  may be recorded by the user for documenting the test setup. 
   Lower card guides  61  are located on top surface  19  of shelf  11  and are positioned to be perpendicular to the lengthwise axis of shelf  11 . In this exemplary embodiment, two lower card guides  61  are located at a linear position within a given cell  30  so that a circuit board may be inserted into cell  30  with its circuit board edge engaged with lower card guides  30 . Upper card guides  71  are located at an underside of each of card guide brackets  50  and are positioned to be directly above the corresponding lower card guides  61 . As such, card guides  61 ,  71  have a structure where the circuit board under test (“UUT”) is oriented perpendicularly with respect to upper surface  19  of shelf  11 . When installing such UUT, it may be advantageous to slightly loosen card guide bracket  50  by loosening the corresponding pair of thumb screws  43  and then by subsequently tightening thumb screws  43  while pressing down slightly on card guide bracket  50 , the UUT may be snugly secured between the card guides  61 ,  71 . In such a case, manufacturing deviations in a width of the UUT are obviated by a structure that assures a snug fit. This is especially important for accurately controlling the test environment. For example, when the carrier is placed on a vibration table or similar apparatus, the snug fit of the UUTs in carrier  10  provides for accurate vibration of the UUT. Similarly, by snugly fitting the UUTs in the carrier  10 , the UUTs are protected from shifting damage caused by movement of the carrier within the manufacturing area such as, for example, by being loaded onto carts. For example, by snugly fitting the UUTs within carrier  10 , a chance of individual UUTs falling out of the carrier and being damaged is greatly reduced. 
   Electrical or optical connectors may be provided in a carrier  10  for interfacing electrical power, loads, and/or test connections to individual circuit boards such as, for example, by using known edge card connectors (not shown) that are wired to a female multi-prong electrical connector located on an exterior face of the carrier  10 . Various configurations for providing electrical or optical connection to individual circuit boards in a carrier are known. For example, U.S. Pat. No. 5,528,161 granted to Liken et al., herein incorporated by reference, discloses a carrier adapted for electrical connections. In another example, cables and circuit board connector systems such as those disclosed for use in automated test equipment (ATE) in U.S. Pat. No. 6,462,532 granted to Smith, incorporated by reference, may be adapted for providing interconnection between circuit boards loaded into a carrier  10 . The invention is intended to be adaptable to any given electrical and/or optical connections requirements of a particular circuit board application. 
   In addition, the ability to individually adjust dimensions of a test cell  30  allows for testing and functional operation cycling of groups of circuit boards. Such a group may utilize electrical or optical interconnection between individual circuit boards along shelf  11 . For example, circuit boards of different types and sizes may be installed in adjacent cells  30  and may have cables or optical paths interconnecting the circuit boards. In such manner, the circuit boards may be functionally adjusted with respect to one another and may be tested and cycled as a group. Such a group, for example, may be in a master-slave configuration, may be tuned for a particular performance criteria (e.g., frequency related, resonance, mutual reactance properties, matched pair, mutual timing requirements, etc.), may depend on data transfer or other communication from one circuit board to another, may be logically interconnected, may require simultaneous parametric testing, etc. Another example of cooperation between separate circuit boards loaded into carrier  10  includes communicating of electrical information for calibrating a performance of at least one of the circuit boards of a group. Many other applications exist for treating circuit boards as a group in a performance testing, operation, and/or adjustment or calibration process. By providing for individually adjusting a card guide bracket  50  to snugly fit a circuit board of various width, carrier  10  uniquely provides for burn-in and testing of cooperating circuit boards having different physical dimensions and thereby provides a higher quality for a final assembly that includes the circuit boards of a group. 
   It may be advantageous to provide maximum air flow through carrier  10  so that a uniform heat and humidity condition exists for individual UUTs. Various factors include heating and air circulation properties of a chamber, room, test rack, or other, self-heating of the UUT, radiation properties and surface areas of materials and structures, electrical power dissipation, size of a volume occupied by a UUT, etc. By reducing the area of surfaces of carrier  10  near the UUTs, the air circulation is improved. Shelf  11  is formed with cutouts  67  in a central portion of the main shelf surface  19 . The cutout areas  68  are separated by strips  62  on which the lower card guides  61  are located. Similarly, the card guide brackets  50  have cutout areas  58  that provide for air circulation while maintaining structural strength of the carrier assembly  10 . It will be understood that control of various aspects of a carrier such as, for example, air flow is important for control of heating, cooling, humidity, altitude/pressure conditions, etc., in a stress chamber or other manufacturing type process. Greater accuracy of testing and burn-in is achieved, obtaining tighter uniformity throughout the chamber for consistent stress on products being tested. 
   As a result of providing independently adjustable cells  30  of a circuit board carrier  10 , deviations in width of a circuit board being carried by carrier  10  may be accounted-for by loosening and re-tightening card guide brackets  50  to snug the card guides  61 ,  71  against the circuit board, thereby preventing movement of the circuit board within carrier  10 . Although bare printed circuit boards may be supplied with a very small tolerance for size variation, various effects of assembling the circuit board may slightly change its dimensions such as, for example, solder adhering to a location near a circuit board edge being engaged by a card guide  61 ,  71 , slight warping of the circuit board due to wave soldering, cleaning, or other manufacturing process, etc. 
   Another example for assuring that a card guide bracket is at a same vertical height at each of its ends is a structure that includes an alignment mechanism  80  such as a gear and track. As shown in  FIG. 5 , each side bracket  82  of a cell  30  has a pair of opposing track-like surfaces  81  that engage a gear wheel  85  located in an adjusting block  90 . The track-like surface  81  is formed of a series of alternating projections  83  and grooves  84 . A thumb wheel (not shown) is attached to a shaft  86  and is adapted to be easily turned by a user, so that gear wheel  85  moves up or down side bracket  82  along tracks  81 . Such vertical movement of gear wheel  85  carries associated adjusting block  90  and card guide bracket  50  up or down with respect to side bracket  82 . Side bracket  82  on each end of a cell  30  has the gear and track structure, assuring the corresponding card guide bracket  50 , connected at an end portion  59  thereof to the respective adjusting block  90 , is kept parallel to bottom card guides  61  and top surface  19  of shelf  11 . In such manner, upper card guide  71  may be maintained parallel to top surface  19  of shelf  11 . 
   A locking member  87  prevents rotation of gear wheel  85  when locking member  87  is engaged. Different types of mechanisms may be employed as a locking member  87  including, for example, a spring-loaded pin device, a set screw, a latch, a lever arm, etc.  FIG. 5  shows gear wheel  85  at an uppermost position with respect to side bracket  82 , the alignment mechanism  80  being structured to prevent gear wheel  85  from disengaging from tread  81  if a user attempts to raise the card guide bracket  50  too high. Optionally, side bracket  82  may include a single track surface  81  rather than a pair of track surfaces  81 . Various other apparatus may be used for aligning or measuring a height of the upper card guide  71 , such as by utilizing shafts and releasable slider devices (not shown) in place of the side brackets  82  and alignment mechanisms  80 . Such releasable sliders may be structured for allowing a simple squeezing or twisting action to release a slider for sliding movement along the respective shaft. By engraving ruler type markings along the shaft, accurate documentation of the card guide setup may be effected. 
   The aligning type structure of  FIG. 5  differs from a non-aligning structure since a non-aligning structure allows one end of card guide bracket  50  to be at a different vertical height compared to the other end of the card guide bracket  50 , whereas the aligning structure maintains a same vertical height for the respective two opposite ends. As a result, a structure such as a  FIG. 1  type apparatus adapted to be a non-aligning structure provides a user with the capability to snugly fit the card guides  61 ,  71  to a circuit board having an irregular width, whereas the aligning structure of  FIG. 5  allows a user to assure parallel orientation of card guides  61 ,  71 . Particular advantages exist for both an aligning structure and a non-aligning structure, for example setting an aligned vertical height to a predetermined setting may assure a controlled test setup without a need to further tighten or loosen a locking device  87  or as shown in the  FIG. 2  embodiment. The aligning structure may be easier to configure for a user desiring to quickly modify a carrier  10  for different groups of circuit boards having different dimensions. 
   A preferred burn-in/test system combines an environmental chamber for temperature and other conditioning and a functional test system to weed out bad products. Products that are loaded into such a chamber may be subjected to elevated/reduced temperatures and other environmental conditions, stressed by varying a load power and/or input voltage to a UUT, and subjected to various stimuli. State-of-the-art environmental and testing systems are available from Thermotron Industries of Holland, Mich. A chamber may itself have shelves adapted for installing ones of carrier  10  loaded with UUTs, or may be structured for receiving carts or other transporting apparatus (not shown) adapted for holding a number of individual carriers  10 . Electrical connections to individual carriers  10  may be made via one or more levels of connectors, for example, high-temperature rated military style connectors connecting to wiring harnesses and/or various modules including wiring modules, load modules, etc. 
   Depending on a particular application, the shelf  11 , side brackets  12 ,  14 ,  15 ,  82  and/or top brackets  21 ,  22  may be adapted for being transported by a conveyor belt, cart, trolley, hook, etc. For example, when a cart used in a particular environmental chamber has a structure of an “angle-iron” type frame (see, e.g., U.S. Pat. No. 4,683,424, at  FIG. 5 ) with fixed dimensions between adjacent frame members, a carrier  10  may be adapted to fit between opposing angled frame members so that carrier  10  is adapted to the angled frame members as spaced-apart guide tracks for being installed or removed from the cart. In such a case, extension members (not shown) may be bolted on or otherwise attached to an appropriate part of the carrier  10  structure for providing the carrier  10  with a correct lengthwise, widthwise, or height dimension. Such a structure is thereby adapted for being customized for a particular transport and/or manufacturing type apparatus. Since the carrier  10  is able to snugly hold circuit boards, a manufacturing process may transport carrier  10  without causing transport damage to or dropping of the individual circuit boards. 
   The present inventor has determined that it is beneficial to snugly fit circuit boards of various dimensions on a single carrier shelf, to reduce potential handling damage, provide tighter control over circuit board manufacturing, better facilitate controlled vibration testing without allowing a flopping around of a circuit board under test, allow for interconnection of different circuit boards on a carrier shelf for performing live testing and calibration of circuit boards used as a group, for providing easily adaptable circuit board fixturing, etc. 
   While the principles of the invention have been shown and described in connection with specific embodiments, it is to be understood that such embodiments are by way of example and are not limiting.