Abstract:
A conveyor system ( 30 ) comprises: a boat ( 20 ), a feed belt ( 36 ), a feed pulley ( 38 ), and improved railings ( 34 ). The boat ( 20 ) is adapted to carry a component or components, such as semiconductor chips ( 32 ), therein. The feed belt ( 36 ) is driven by the feed pulley ( 38 ). The feed belt ( 36 ) is adapted to move the boat ( 20 ) along the conveyor system ( 30 ). The improved railings ( 34 ) are adapted to retain the boat ( 20 ) and to define a path for the boat ( 20 ). A set of bearings ( 44 ) are coupled to each of the improved railings ( 34 ) in locations such that the boat ( 20 ) will contact the bearings ( 44 ) rather than the railings ( 34 ) for at least part of the path as the boat ( 20 ) moves along the conveyor system ( 30 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to an improvement in a railing for a boat conveyor system in a production line. 
     BACKGROUND 
     In a mass production fabrication line where parts are transported and indexed for a series of fabrication steps, it is typically highly desirable to reduce or eliminate downtime in the production line. Because many production lines run all the time (i.e., 24 hours per day and 7 days per week) to keep up with production demands and to maximize the use of each machine, even small amounts of repeated downtime can add up to large expenses due to less efficiency. There can be many different causes of downtime, and thus there is often a continual search for anything that may cause down time so that a solution may be found to reduce or eliminate such downtime. Hence, ways to reduce downtime in a production line are highly desirable. 
     Another economic consideration for production lines is the life of a part or machine. In general, the more life that can be obtained from a given machine can translate into lower capital expenses, leaving room for higher profit margins. Thus, there is often a continual need or search for ways to make parts and equipment last longer, especially in a mass production line. 
     In the production of semiconductor devices or electronic devices for example, a part or system being fabricated is often transported from one station to another on a “boat.” A “boat” in this context is a carriage tray designed to hold a wafer, part, component, or system being produced, and designed to fit within and to be moved by an indexing conveyor system. Sometimes a boat is designed to hold a component firmly and/or in a precise position, whereas some boats merely provide one or more slots or indentations for loosely carrying a component to a subsequent station. FIG. 1 shows an example of a boat  20  used in packaging processes during the production of semiconductor devices. The boat  20  shown in FIG. 1 has an array of cavities  22  formed therein adapted to hold semiconductor chips during packaging processes. During production, indexing the boat  20  with a conveyor system is often used to align the component or system for the next step of fabrication. Hence, if or when the indexing for a station or stations gets out of alignment or gets shifted, it can cause indexing downtime for corrections. Thus, there is a need for a way to decrease indexing downtime in a production line. 
     One problem that may be a cause of premature part wear and/or indexing errors is friction in the boat conveyer system. Therefore, there is often a need to identify or locate such friction areas and to eliminate or reduce such friction problems. 
     BRIEF SUMMARY OF THE INVENTION 
     The problems and needs outlined above are addressed by the present invention. In accordance with one aspect of the present invention, a conveyor system is provided, which comprises: a boat, a railing, and a bearing. The railing is adapted to retain the boat and to define at least part of a path for the boat as it moves along the conveyor system. The bearing is coupled to the railing at a location so that the boat will contact the bearing rather than the railing for at least part of the path as the boat moves along the conveyor system. 
     In accordance with another aspect of the present invention, a conveyor system is provided, which comprises: a boat, a feed belt, a feed pulley, and railings. The boat is adapted to carry a component therein. The feed belt is driven by the feed pulley. The feed belt is adapted to move the boat along the conveyor system. The railings are adapted to retain the boat and to define a path for the boat. A set of bearings are coupled to each of the railings in locations such that the boat will contact the bearings rather than the railings for at least part of the path as the boat moves along the conveyor system. 
     In accordance with yet another aspect of the present invention, an improved railing for a conveyor system is provided. The improved railing comprises a set of bearings coupled to the railing and extending from the railing. The bearings are adapted to provide rolling surfaces for a boat that is restrained by the railing as the boat moves along the conveyor system. 
     In accordance with still another aspect of the present invention, a method of producing an electronic component is provided. The method comprises the steps of: (i) providing a conveyor system comprising: (a) a boat adapted to carry the electronic component therein, (b) a feed belt driven by a feed pulley, the feed belt being adapted to move the boat along the conveyor system, (c) a railing to retain the boat and to define a path for the boat, and (d) a set of bearings coupled to the railing in locations such that the boat will contact the bearings rather than railing for at least part of the path as the boat moves along the conveyor system; (ii) moving the boat from one location to another location with the feed belt; and (iii) directing the path of the boat with the bearings. 
     In accordance with another aspect of the present invention, a method of improving a conveyor system that is adapted to move a boat along a path defined by one or more railings using a feed belt is provided. The method comprises the step of replacing at least some of the one or more railings with one or more improved railings, wherein the one or more improved railings each comprises a set of bearings coupled to and extending from the improved railing in locations such that the boat will contact the bearings rather than the railing along at least part of the path defined by the one or more railings as the boat moves along the conveyor system. The method may further comprise the steps of: reducing friction between the boat and the one or more railings as the boat moves along the conveyor system as a result of the replacing at least some of the one or more railings step; and reducing wear between the boat and the one or more railings due to the reducing friction step. The method may further comprise the steps of: reducing indexing errors during the step of moving the boat from one location to another location, as a result of the replacing at least some of the one or more railings step; and reducing indexing downtime during production as a result of the reducing indexing error step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon referencing the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a boat from the prior art that is adapted to carry semiconductor chips therein; 
     FIG. 2 is a top view of a conveyor system of a preferred embodiment of the present invention; and 
     FIG. 3 is a perspective view of the conveyor system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout the various views, a preferred embodiment of the present invention is illustrated and described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations of the present invention based on the following description of the preferred embodiment. 
     Often production line equipment can be further improved and made more reliable to, among other things, reduce production downtime for repairs and/or adjustments in the equipment. An embodiment of the present invention provides such an improvement and has proven to reduce downtime, as well as reducing indexing errors. 
     The following description and FIGS. 2 and 3 pertain to a preferred embodiment of the present invention. The preferred embodiment is an improved indexing conveyor system  30  used in packaging processes for the production of semiconductor chips  32 . FIG. 2 is a top view of the conveyor system  30  of the preferred embodiment. FIG. 3 is a perspective view of the improved front railing  34  of the preferred embodiment. 
     The conveyor system  30  of the preferred embodiment is part of an Alphasem SL9002 machine used in ball grid array packaging and die attach operations for semiconductor chips  32 . Other machines in which the preferred embodiment may be employed will be apparent to one of ordinary skill in the art with the benefit of this disclosure. The conveyor system  30  shown in FIGS. 2 and 3 is adapted to move and transport the boat  20  of FIG. 1 from one process station to the next in an automated production line. For example, at one station the boat  20  may be indexed to positions for dispensing material onto each chip  32  loaded on the boat  20 . And at the next station the boat  20  may be indexed to positions for bonding a package onto each chip  32 , for example. 
     As best shown in FIG. 3, a feed belt  36  driven by a feed pulley  38  propels the boat  20  as the feed belt  36  moves about the feed pulleys  38  (only one feed pulley  38  shown in FIG.  3 ). An o-ring  37  is located on the feed pulley  38  adjacent to the feed belt  36 . The boat  20  contacts the o-ring  37  at the feed pulley  38  instead of the feed belt  36 . The use of the o-ring  37  here on the feed pulley  38  provides better grip on the boat  20  than the feed belt  36  during index movements, and thus reduces indexing problems and improves indexing accuracy. Also, the use of the o-ring  37  prolongs the life of the feed belt  36 , and the o-ring  37  is typically less expensive to replace than the feed belt  36 . 
     A set of lead frame clamp rollers  40  press downward against the boat so that the boat is pressed against the feed belt  36  and/or the o-ring  37  for better traction. Each lead frame clamp roller  40  has an o-ring  41  on its roller to provide a rubber on metal contact instead of a metal on metal contact, which greatly reduces or eliminates wear between the roller  40  and the boat  20 . Also, the o-rings  41  are easily and inexpensively replaceable when they wear out. Railings  34 ,  42  extend along the conveyor system on each side of the boat  20  to direct the path of the boat  20  as it moves along the conveyer system  30 . 
     One of the top machine downtime contributors of the indexing conveyor machines for ball grid array die attach operations is indexing errors or feed system errors. According to test studies, almost 95% of non-productive time for ball grid array die attach operations on an indexing conveyor machine is due to indexing errors or feed system errors. Thus, any improvements that will reduce such indexing errors and feed system errors will likely result in much less non-productive time, which may translate into higher efficiencies and greater profits. 
     Current indexing conveyor systems used in packaging processes for the production of semiconductor chips are often configured in a way that the boat  20  rubs against the front railing (prior front railing not shown) of the conveyor system  30  as the boat  20  moves from one station to another. Such rubbing may cause additional friction in the system  30 , which may result in greater energy requirements to move the boat  20 . Also, such rubbing may cause more wear to the boat  20  and/or the front railing. Often such rubbing can cause metal filings to accumulate where the rubbing occurs, which may introduce unwanted contaminates into the production area. Furthermore, such rubbing may prevent the boat  20  from moving smoothly in a continuous manner and with precision of movement, which may lead to indexing errors. When indexing errors exceed an allowable threshold, the production line may need to be shut down to correct the indexing errors. 
     The inventors of the present invention recognized these rubbing problems contributing to the indexing and feeding errors, and conceived the present invention to address these rubbing problems stated above. As shown in FIGS. 2 and 3, the preferred embodiment of the present invention incorporates a set of bearings  44  coupled to the front railings  34  of the conveyor system  30 . Thus as the boat  20  moves along the conveyor system  30 , instead of the boat  20  rubbing against the front railing  34 , the boat  20  contacts and rolls along the outer surfaces of the bearings  44 . Because the boat  20  rolls across the bearings  44  rather than rubbing against the front railing  34 , much of the friction between the boat  20  and the front railing  34  is eliminated, the production of metal filings due to friction is reduced or eliminated, the wear on the boat  20  and/or front railing  34  is significantly reduced or eliminated, and the indexing and feeding errors are reduced. As a result, indexing error downtime may be reduced and non-value-added activities may be reduced by use of the preferred embodiment of the present invention. 
     In another embodiment (not shown), the rear railing  42  may also incorporate a set of bearings to further improve the system  30 . However, the addition of bearings on the rear railing  42  becomes an economic issue of comparing the results of the improvements with the cost of the improvements. Thus, in some cases where there are sufficient performance and efficiency gains from merely incorporating a front railing  34  with bearings  44  (as in the preferred embodiment), the preferred embodiment may be the best mode. In other machines or systems (not shown), it may be the best mode to have bearings incorporated in the front and rear railings  34 ,  42  in accordance with another embodiment of the present invention. 
     An embodiment of the present invention may be incorporated into an existing system, as in the preferred embodiment described above. In alternative, the present invention may be incorporated into the design of a new machine and provided by a manufacturer of the conveyor system. Hence, there can be many applications of an embodiment of the present invention. 
     Although only the preferred embodiment is shown herein, one of ordinary skill in the art having the benefit of this disclosure will realize that there may be many other embodiments of the present invention that vary from the preferred embodiment but are still defined by the claims. Thus, it will be appreciated by those skilled in the art having the benefit of this disclosure that an embodiment of the present invention provides an innovative improvement in a railing for a boat conveyor system in a production line. It should be understood that the drawings and detailed description herein are to be regarded in an illustrative rather than a restrictive manner, and are not intended to limit the invention to the particular forms and examples disclosed. On the contrary, the invention includes any further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments apparent to those of ordinary skill in the art, without departing from the spirit and scope of this invention, as defined by the following claims. Therefore, it is intended that the following claims be interpreted to embrace all such further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments.