Abstract:
A reflow module of a reflow oven including a reflow fixture housed within a compartment of the reflow oven, removable side ports attached to the reflow fixture for controlling air flow through the reflow module and a chamber housing encasing the reflow fixture within the compartment of the reflow oven. A reflow oven incorporating the reflow module may include a reflow fixture having a plurality of air tubes and at least one orifice fixture plate removably attached to the reflow fixture, wherein the at least one orifice fixture plate includes a plurality of orifices for directing airflow into the plurality of air tubes.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a reflow air management system and related method, and more particularly, to a reflow oven having “quick change” side ports to toggle airflow paths to provide uniform temperature distribution to a semiconductor chip during reflow soldering. 
       BACKGROUND OF THE INVENTION 
       [0002]    Reflow soldering is a process in which a solder paste, made of powdered solder and flux, is used to temporarily hold components to attachment pads, after which the assembly is carefully heated in order to solder the joint. The assembly may be heated using an infrared lamp, or more commonly, by passing it through a carefully-controlled oven, or soldering with a hot air pencil. Reflow soldering is the most common method of attaching surface mount components, such as semiconductor chips, to a circuit board. Soldering forms a strong, long-lasting metallurgical bond between the surfaces being joined, both for structural integrity of the assembly and electrical conductivity of the electronic circuits. 
         [0003]    The goal of the reflow process is to melt the solder alloy particles within the solder paste without overheating and damaging the electrical components. There are usually four stages of the reflow process, each having a distinct thermal profile, including: preheat, thermal soak, reflow and cooling. A conventional reflow oven may be used for reflow soldering of surface mount electronic components to printed circuit boards (PCBs). These ovens must maintain a particular reflow profile which fits within the specification or tolerance limit set by the user to ensure that the reflow soldering work does not overheat or cool too quickly. As semiconductors continue to decrease in product size, the real estate between each semiconductor is also decreasing to increase throughput. 
         [0004]    Reflow is one of the hardest thermal processes to control with a high ramp up rate and a short pull down rate while maintaining uniformity of the specification for the end product. This problem of temperature profile uniformity has led many to develop several different reflow oven configurations. Most commonly, reflow ovens are large conveyor-type ovens that carry several moving parts. Conventional reflow ovens often include infrared/convection ovens. 
         [0005]    Infrared ovens typically contain multiple heating zones, which can be individually controlled to maintain a desired temperature. These heating zones may be followed by one or more cooling zones. The printed circuit board moves through the oven on a conveyor belt, and is therefore subjected to a controlled time-temperature profile. In these ovens, the heat source is normally from ceramic infrared heaters, which transfer the heat to the assemblies by means of radiation. Infrared ovens which also use fans to force heated air towards the assemblies in combination with ceramic infra-red heaters are called infrared convection ovens. 
         [0006]    Because these ovens have conveyors and other moving parts, these moving parts experience friction, which eventually injects metallic debris particles into the reflow path. During the thermal process, if the debris particles happens to land between these chips, there is a great potential to cause arcing or a short circuit. Currently, if one part breaks during the reflow cycle not only is the entire line shut down but the entire product in the oven at the time of shut down is suspect and usually rejected. Furthermore, these conventional ovens often include large housings which require a large amount of floor space to accommodate the conveyor belt configuration. 
         [0007]    Accordingly, it is desirable to develop a reflow oven having minimal or no moving parts exposed in the batch configuration. It is also desired to provide a smaller oven housing, which will not require such a large space in a user facility. 
       SUMMARY OF THE INVENTION 
       [0008]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0009]    The reflow air management system in accordance with the present invention overcomes many of the problems encountered in the conventional reflow ovens discussed above. Example embodiments of the invention include a reflow module of a reflow oven including a reflow fixture housed within a compartment of the reflow oven, removable side ports attached to the reflow fixture for controlling air flow through the reflow module and a chamber housing encasing the reflow fixture within the compartment of the reflow oven. In example embodiments, the removable side ports may include at least one slide plate slidably attached at an end of the reflow fixture. The reflow module may also include a performance pack providing the energy components to power the reflow oven, wherein the performance pack includes a cooling coil, a heater, a blower wheel and a motor. In other embodiments, the reflow module includes a boat carrier having a plurality of shelves attached to a generally L-shaped base. 
         [0010]    Example embodiments of the present invention also include a reflow oven incorporating the reflow module. The reflow oven may include a reflow fixture having a plurality of air tubes and at least one slide plate slidably attached to the reflow fixture, wherein the at least one slide plate includes a plurality of orifices for directing airflow into the plurality of air tubes. In other embodiments the reflow oven may include: means for blowing an airstream along outside surfaces of a reflow fixture; means for directing the airstream through at least one outer plate and through a plurality of orifices within at least one slide plate; and means for further directing the airstream into a plurality of air tubes, wherein air flow through each of the plurality of air tubes may be separately controlled. 
         [0011]    Alternate embodiments of the invention include a method of controlling airflow during a reflow stage, including: blowing an airstream along outside surfaces of a reflow fixture using a blower wheel; directing the airstream through at least one outer plate and through a plurality of orifices within at least one slide plate; and further directing the airstream into a plurality of air tubes, wherein air flow through each of the plurality of air tubes may be separately controlled. The method may also include directing the airstream through a plurality of tube openings along each of the plurality of air tubes and further directing the airstream through a plurality of bracket orifices and onto at least one semiconductor chip. 
         [0012]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a plan view illustrating a reflow oven incorporating a reflow air management system (RAMS) according to an embodiment of the invention. 
           [0014]      FIG. 2  is an exploded view of a reflow module of the reflow oven shown in  FIG. 1 . 
           [0015]      FIG. 3  is an exploded view of the RAMS of the reflow oven shown in  FIG. 1 . 
           [0016]      FIG. 4A  is an exploded view of a side of an air tube of the RAMS shown in  FIG. 3 . 
           [0017]      FIG. 4B  is a plan view of an underside of the air tube of  FIG. 4A , without of its brackets. 
           [0018]      FIG. 5  is a top view of the reflow oven shown in  FIG. 1 , showing the air flow path through the oven. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Example embodiments of the present invention provide a reflow air management system (RAMS) which utilizes a direct airflow manifold to manage and control airflow during the reflow of semiconductor chips. Airflow can be changed using “quick-change” side ports to toggle airflow paths that provide uniform temperature distribution to the chip in a batch format. Because the RAMS is static and contains no moving parts, arcing or short circuits are less likely to occur. Some embodiments will now be described with reference to the drawing figures, in which like reference numbers refer to like parts throughout. 
         [0020]      FIG. 1  is a plan view illustrating a reflow oven  100  incorporating a RAMS  105  according to an embodiment of the invention. In this embodiment, the RAMS  105  includes a reflow fixture  107 , which is housed within a compartment or drawer  110  of the reflow oven  100 . In example embodiments, the drawer  110  may be approximately 1-3 feet deep to accommodate the RAMS  105 . In example embodiments of the invention, the RAMS  105  also includes a boat carrier  115 , which may include shelves  115   a  attached to a generally L-shaped carrier base  115   b  including a backplate  115   b ′ (as best shown in  FIG. 2 ) to accommodate rows of semiconductor boats  120 , is fixed to a door  125  of the drawer  110 . In example embodiments the boats  120  may hold central processing unit chips, personal computer boards or any other electronics. 
         [0021]      FIG. 2  is an exploded view of a reflow module  230  of the reflow oven  100  shown in  FIG. 1 . In example embodiments of the invention, the reflow module  230  includes: the drawer door  125 , the boat carrier  115 , the reflow fixture  107 , a chamber housing  240  and a performance pack  245 . In example embodiments of the invention, the performance pack  245  includes the energy components needed to drive the reflow oven  100  specifically including: a cooling coil  245   a  to provide cool air during the controlled cooling stage of reflow, a heater  245   b  to provide hot air during the rapid heating stage of reflow, a blower wheel  245   c  to drive air flow, a motor  245   d  to provide power to the performance pack  245  and air deflectors  245   e  (shown in  FIG. 5 ) to direct air flow towards the RAMS  105 . In example embodiments, the cooling coil  245   a  may be stainless steel and the heater  245   b  may be a resistive heater. The reflow fixture  107  may be specially designed for a particular reflow stage or alternatively, may be removed for non-reflow stages. 
         [0022]      FIG. 3  is an exploded view of the RAMS  105  of the reflow oven  100  shown in  FIG. 1  (without the carrier backplate  115   b ′). In example embodiments of the invention, the reflow fixture  107  is bookended by a pair of slide plates  350   a ,  350   b  and outer plates  355   a ,  355   b . The slide plates  350   a ,  350   b  provides variously sized orifices  360  to control airflow and thereby, provide the appropriate reflow profile for a particular system. The slide plates  350   a ,  350   b  may be slidably removable plates which can be changed for each user system. In example embodiments, the outer plates  355   a ,  355   b  are also slidably attached. The RAMS  105  may also include air deflectors  363   a ,  363   b  to prevent air from flowing around the sides of the RAMS  105 . In example embodiments of the invention, air is directed through each air tube  365  of the RAMS  105 . 
         [0023]      FIGS. 4A and 4B  provide alternate views of an air tube of the RAMS shown in  FIG. 3 . In example embodiments, the air tube may be shaped like a cylinder, prism or any other tube shape. The RAMS  105  may include a plurality of air tubes  365 , each having a plurality of openings  467  along the underside of each tube  365  to direct airflow to each individual semiconductor chip on the semiconductor boats  120 . In these embodiments, a u-shaped bracket  470  is attached to each opening of each of the tubes  365  using screws  475 . In some embodiments of the invention, there are 4 brackets  470  per tube  365 . The brackets  470  may additionally include variously sized bracket orifices  473  to further control air flow. In some embodiments of the invention, air flow shields  480  may be used to prevent each chip from receiving airflow from a neighboring chip. 
         [0024]      FIG. 5  is a top view of the reflow oven shown in  FIG. 1 , showing the air flow path A through the oven  100 . In a method of controlling airflow during a reflow stage, the blower wheel  245   c  sends cool or hot air, depending on which phase of reflow is occurring, along the outsides of the RAMS  105 . In example embodiments of the invention, the air can be an inert gas such, as argon, nitrogen, or other inert gases. In example embodiments of the invention, the air flow A is directed through the pair of outer plates  355   a ,  355   b  and through the orifices  360  of the slide plates  350   a ,  350   b  and into each air tube  365  of the RAMS  105 . Air flow through each air tube  365  may be separately controlled. The air path continues through air tubes  365  and into each of the plurality of tube openings  467  and through each bracket orifice  473  and onto each semiconductor chip on the boats  120 . 
         [0025]    Several features of the invention help to direct the airflow path A, thereby ensuring uniformity of the reflow profile. Air deflectors  363   a ,  363   b  prevent air flow from flowing around the RAMS  105 . Another set of air deflectors  245   e  help direct air flow towards and into the RAMS  105 . In some embodiments of the invention, the performance pack  245  may also include a Venturi cone  585  to improve the venturi effect of the airflow into the blower wheel  245   c . As mentioned above, the air flow shields  480  (shown in  FIG. 4 ) may be used to prevent each chip from receiving airflow from a neighboring chip. 
         [0026]    The many advantages of the reflow oven  100  of the present invention would be readily understood by one of ordinary skill in the art. The unique change plates  350   a ,  350   b  controlling air flow into the RAMS  105  provide versatility of the system such that the system may be tuned without changing the air tubes. Furthermore, the orifices  360 , which may have build-up that potentially alters the desired air profile, may be cleared off when the plates  350   a ,  350   b  are removed. Example embodiments of the reflow oven  100  of this invention also substantially reduce the problems with existing reflow conveyor ovens that substantially decrease available floor space. In addition, the modular and unique jet flow design, offers the end user the flexibility to alter product lines without significant interruption. Because of the sealed environment and static processing, there are no moving parts or particulate contamination issues incurred within the reflow oven  100 . Many different recipes and product configurations can be tested simultaneously because airflow can be controlled for each individual air tube  365 . 
         [0027]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.