Patent Publication Number: US-2012031953-A1

Title: Apparatus for bump reflow and methods of forming bumps using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2010-0075912, filed on Aug. 6, 2010, the entire contents of which are hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure herein relates to an apparatus for bump reflow and methods for forming bumps using the same, and more particularly, to an apparatus for wafer level bump reflow and methods for forming wafer level bumps using the same. 
     2. Description of the Related Art 
     Recently, a demand for flip chip packages is increasing and technology of the flip chip packages is being further developed as performance of semiconductor devices and systems relevant to the semiconductor devices becomes highly advanced. In particular, as the design rule is shrunken, intervals of pads are being reduced and the wire bonding process has reached as it can go. To overcome these limitations, the demand for flip chip technology is being on the rise. 
     In the flip chip technology, a sufficient distance between a printed circuit board (PCB) and a die (semiconductor chip) is required to secure an underfill, and a solder of great volume is required to achieve sufficient physical and electrical contact. Therefore, an effective approach to secure the underfill and to achieve a sufficient physical and electrical contact is desired. 
     SUMMARY OF THE INVENTION 
     Accordingly, embodiments of the present general inventive concept provide apparatus for wafer level bump reflow capable of forming a solder bump of which volume is great enough to provide a sufficient underfill gap during a packaging process. 
     Embodiments of the inventive concept also provide methods for forming bumps using apparatus for wafer level bump reflow capable of forming a solder bump of which volume is great enough to provide a sufficient underfill gap during a packaging process. 
     Additional features, utilities, and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     Embodiments of the present general inventive concept provide methods of forming a wafer level bump. The methods include forming at least one pre-bump on a first surface of a wafer, and performing a bump reflow process with respect to the wafer to form a bump while the first surface of the wafer faces downward. 
     In some embodiments, the bump may be formed in elliptical shape having a major axis perpendicular to the first surface of the wafer. 
     In other embodiments, the bump reflow process may be a process in which heat is applied to a second surface of the wafer opposite to the first surface. 
     In still other embodiment, the pre-bump may be solder material containing copper. 
     Other embodiments of the present general inventive concept provide an apparatus for wafer level bump reflow. The apparatus include a reflow region where a wafer having at least one pre-bump on a first surface is disposed with the first surface facing downward and bump reflow process is performed with respect to the wafer to form at least one bump. 
     In some embodiments, the reflow region may include a turret type reflow part having at least one wafer stage on which the wafer is disposed with the first surface facing downward, and a heating part applying heat to a second surface of the wafer opposite to the first surface. The turret reflow part may be rotated in certain direction. The apparatus may further include a wafer guide provided in the wafer stage to restrain movement of the wafer on the wafer stage. The wafer guide may be in contact with at least three point of the wafer to restrain the movement of the wafer. The wafer stage may have a concave shape with a depth larger than a height of the pre-bump. The wafer stage may have a hole shape bored through the turret type reflow part. The heating part may be configured to be moved up and down. 
     In other embodiments, the reflow region may include a conveyer type reflow part to move the wafer, and the heating part to apply heat to the second surface of the wafer. The wafer may be received at a jig with the first surface facing downward while being spaced apart from the conveyer type reflow, and the jig is mounted on the conveyer type reflow part. The jig may include a receiving part to contain the wafer, a support plate to mount the jig on the conveyer type reflow part, and a support part connecting the support plate and the receiving part to support the receiving part. The receiving part may have a partially opened annular shape with a C-shaped cross section such that the wafer is contained in the receiving part. The receiving part may include a plurality of segments which are spaced apart from each other. The support part may include support columns, a number of the support columns corresponding to a number of the segments of the receiving part. The support part may include at least three support columns. 
     In still other embodiments, the apparatus may further include a loading part to receive a plurality of wafers with facing the first surfaces upward and delivering the wafer to the reflow region, and an unloading part to unload the wafer on which the bump was formed in the bump reflow process from the reflow region and to receive the wafer with the first surface facing upward. The apparatus may further include a first transfer delivering the wafer from the loading part to the reflow region with the first surface facing downward, and a second transfer delivering the wafer from the reflow region to the unloading part with the first surface facing upward. 
     Other embodiments of the present general inventive concept provide a method of forming a wafer level bump, including forming at least one pre-bump on a first surface of a wafer, positioning the wafer to have the at least one pre-bump facing downward, and performing a bump reflow process to form at least one bump on the first surface of the wafer from the at least one pre-bump. 
     In some embodiments, the performing of the bump reflow process may include heating the at least one pre-bump to form the at least one bump on the first surface of the wafer. The heating may include applying heat to a second surface of a wafer located on an opposite side from the first surface of the wafer. 
     In some embodiments, the positioning of the wafer may include positioning the wafer to align the major axis of the at least one bump to the first surface of the wafer. 
     In some embodiments, the forming the at least one pre-bump may include forming the at least one pre-bump to face upward on the first surface of the wafer. 
     In some embodiments, a shape of the at least one pre-bump may be a t-shape. 
     In some embodiments, a shape of the at least one bump may be a round shape. 
     In some embodiments, gravity may shape the pre-bump to flow away from the wafer to form the at least one bump during the bump reflow process. 
     In some embodiments, the method may further include performing a deflux process with respect to the at least one bump of the wafer. 
     Other embodiments of the present general inventive concept provide an apparatus for wafer level bump reflow, including a reflow part to receive a wafer having at least one pre-bump on a first surface of the wafer and to hold the wafer to have the first surface downward, and a heating part to heat the at least one pre-bump to form at least one bump on the first surface. 
     In some embodiments, the heating part may heat the at least one pre-bump by applying heat to a second surface of a wafer located on an opposite side from the first surface of the wafer. 
     In some embodiments, the apparatus may further include a first transfer unit to deliver the wafer from a loading part containing wafers having pre-bumps to the reflow part. The first transfer unit may be a first robot arm having a first blade shaped end to carry the wafer and configured to be rotated by the first robot arm to flip the wafer. 
     In some embodiments, the apparatus may further include a second transfer unit to deliver the wafer from the reflow part to an unloading part to unload the wafer after the at least one bump is formed. The second transfer unit may be a second robot arm having a second blade shaped end to carry the wafer and configured to be rotated by the second robot arm to flip the wafer. 
     In some embodiments, the reflow part may be a turret type including at least one wafer stage to receive the wafer with the first surface facing downward toward the gravity. The turret type may be configured to rotate in one direction to move the wafer in a circular motion. The at least one wafer stage may have a concave shape with a depth deeper than a height of the wafer such that the pre-bump does not contact a bottom of the concave shape when the wafer is received at the at least one wafer stage. The at least one wafer stage may have a hole shape bored through the turret type. 
     In some embodiments, the reflow part may be a conveyer type having at least one jig mounted thereto and configured to move the at least one jig, the at least one jig being configured to receive the wafer with the first surface facing downward toward the gravity. The at least one jig may include a receiving part configured to receive the wafer with the first surface facing downward toward the gravity, a support plate to mount the receiving part on the conveyer type, a support part to connect the support plate and the receiving part to support the receiving part. The receiving part may have a partially opened annular shape with a C-shaped cross section to receive the wafer through the partially opened area. The receiving part may include a plurality of segments which are spaced apart from each other and a partially opened area to receive the wafer. The support part may include a plurality of support columns corresponding to the segments of the receiving part. 
     Other embodiments of the present general inventive concept provide system for wafer level bump reflow, the system including a wafer including a first surface having at least one pre-bump, and a second surface on an opposite side from the first surface, and a reflow part to hold the wafer to have the first surface downward during a bump reflow process to form at least one bump on the first surface from the at least one pre-bump. 
     In some embodiment, the system may further include a heating part to heat the at least one pre-bump to form the at least one bump on the first surface during the bump reflow process. The heating part may heat the at least one pre-bump by applying heat to the second surface of a wafer located on an opposite side from the first surface of the wafer. 
     In some embodiment, the system may further include a first transfer unit to deliver the wafer from a loading part containing wafers having pre-bumps to the reflow part. The first transfer unit may be a first robot arm having a first blade shaped end to carry the wafer and configured to be rotated by the first robot arm to flip the wafer. 
     In some embodiment, the system may further include a second transfer unit to deliver the wafer from the reflow part to an unloading part to unload the wafer after the at least one bump is formed. The second transfer unit may be a second robot arm having a second blade shaped end to carry the wafer and configured to be rotated by the second robot arm to flip the wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. These and/or other features, utilities, and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view illustrating an apparatus for wafer level bump reflow according to an embodiment of the inventive concept; 
         FIG. 2  is a plan view illustrating a reflow part of an apparatus for wafer level bump reflow according to an embodiment of the inventive concept; 
         FIGS. 3A and 33  are cross-sectional views taken along line I-I′ of  FIG. 1 , illustrating reflow parts of the apparatus for wafer level bump reflow according to embodiments of the inventive concept; 
         FIG. 4  is a perspective view illustrating an apparatus for wafer level bump reflow according to another embodiment of the inventive concept; 
         FIG. 5  is a cross-sectional view taken along line II-II′ of  FIG. 4 ; 
         FIGS. 6A and 7A  are plan views illustrating jigs of an apparatus for wafer level bump reflow according to other embodiments of the inventive concept, and  FIGS. 6B and 7B  are front views illustrating the jigs, respectively; and 
         FIGS. 8 through 11  are cross-sectional views illustrating a method for forming a wafer level bump according to an embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The embodiments of the present general inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present general inventive concept to those skilled in the art. 
     Hereinafter, exemplary embodiments of the present general inventive concept will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a perspective view illustrating an apparatus for wafer level bump reflow according to an embodiment of the present general inventive concept.  FIG. 2  is a plan view illustrating a reflow part of an apparatus for wafer level bump reflow according to an embodiment of the present general inventive concept.  FIGS. 3A and 3B  are cross-sectional views taken along line ‘I-I’ of  FIG. 1 , illustrating reflow parts of the apparatus for wafer level bump reflow according to embodiments of the present general inventive concept. 
     Referring to  FIG. 1  through  FIG. 3B , an apparatus for wafer level bump reflow  100  includes a loading part  110 , a first transfer  115 , a reflow region  120 , a second transfer  150 , and an unloading part  160 . 
     A wafer W has an active surface on one side and a rear surface opposite to the active surface on the other side. A plurality of pads  172  may be disposed on the active surface of the wafer W. A plurality of pre-bumps  174  may be disposed on the pads  172 , respectively. 
     The loading part  110  may provide a space to receive a plurality of wafers W in order to deliver the wafer W to the reflow region  120 . A plurality of wafers W may be received in the loading part  110  with the active surface facing upward. At the loading part  110 , a flux coating process may be performed with respect to the pre-bumps  174  of the wafer W. According to one embodiment, several loading parts  110  may be provided. 
     The first transfer  115  may deliver the wafer W from the loading part  110  to the reflow region  120  with the active surface facing downward. The first transfer  115  may be a robot arm having a blade shaped end  117 . The first transfer  115  can rotate the blade shaped end  117  in order to turn the wafer W to have the active surface facing downward. The blade shaped end  117  of the first transfer  115  may include two layered blades or an absorber on a surface of the blade in order to deliver and to turn the wafer W. 
     The reflow region  120  may include a turret type reflow part  130  and a heating part  140 . The turret type reflow part  130  may have at least one wafer stage  135  where the wafer W is mounted with the active surface facing downward. The heating part  140  may be disposed to apply heat to the wafer W on the wafer stage  135 . In this case, with the wafer W facing downward, the heating part  140  is disposed to apply heat to the rear surface of the wafer W. The heating part  140  may include a plurality of sectors such that each of the sectors separately applies heat to the wafer W. The turret type reflow part  130  may be rotated in a certain direction. As the turret type reflow part  130  is rotating, the wafer W may be applied with heat at several temperatures by the heating part  140 . By the bump reflow process applying heat to the wafer W at the reflow region  120 , the pre-bumps  174  disposed on the active surface of the wafer W can be transform into bumps  174   a  of  FIG. 10  or  11 . 
     In one embodiment, several wafer stages  135  may be provided. The wafer stage  135  may have either a concave shape  135   a  having a depth larger than the height of the pre-bump  174  or a hole shape  135   b  bored through the turret type reflow part  130 . A wafer guide  137  may be provided in the wafer stage  135 . The wafer guide  137  may restrain movement of the wafer W disposed on the wafer stage  135 . Further, the wafer guide  137  may provide a support for the wafer W such that the pre-bump  174  does not contact the bottom of the wafer stage  135  of the concave shape  135   a . Also, the wafer guide  137  may be in contact with the entire edge of the wafer W or at least three points of the edge of the wafer W, as illustrated in  FIG. 2 . 
     The heating part  140  can be moved up and down. The first transfer  115  can put the wafer W on the wafer stage  130  of the turret type reflow part  130  while the heating part  140  is moved up, and heat can be applied to the wafer W to perform the bump reflow process while the heating part  140  is moved down. 
     The second transfer  150  may deliver the wafer W from the reflow region  120  to the unloading part  160  with the active surface facing downward. The second transfer  150  may be a robot arm having a blade shaped end  157  similar to the components of the first transfer  115 . The second transfer  150  can rotate the blade shaped end  157  in order to turn the wafer W to have the active surface facing upward. The blade shaped end  157  may include two layered blades or an absorber on a surface of the blade to deliver and to turn the wafer W. 
     The unloading part  160  may provide a space to receive a plurality of wafers W which have bumps formed in the bump reflow process at the reflow region  120  and are unloaded from the reflow region  120 . The wafer W may be received at the unloading part  160  with the active region facing upward. A deflux process may be performed with respect to the bumps of the wafer W at the unloading part  160 . In one embodiment, several unloading parts  160  may be provided. 
       FIG. 4  is a perspective view illustrating an apparatus for wafer level bump reflow according to another embodiment of the present general inventive concept.  FIG. 5  is a cross-sectional view taken along line ‘II-II’ of  FIG. 4 .  FIGS. 6A and 7A  are plan views illustrating jigs of an apparatus for wafer level bump reflow according to other embodiments of the present general inventive concept, and  FIGS. 6B and 7B  are front views illustrating the jigs, respectively. 
     Referring to  FIG. 4  through  FIG. 7B , an apparatus for wafer level bump reflow  200  may include a loading part  210 , a first transfer  215 , a reflow region  220 , a second transfer  250  and an unloading part  260 . 
     A wafer W has an active surface on one side and a rear surface opposite to the active surface on the other side. A plurality of pads  172  may be disposed on the active surface of the wafer W. A plurality of pre-bumps  174  may be disposed on the pads  172 , respectively. 
     The loading part  210  may provide a space to receive a plurality of wafers W in order to load the wafers W to the reflow region  220 . The wafer W may be received at the loading part  210  with the active surface facing upward. A flux coating process with respect to the pre-bumps  174  may be performed at the loading part  210 . According to one embodiment, several loading parts  210  may be provided. 
     The first transfer  215  may deliver the wafer W from the loading part  210  to the reflow region  220  with the active surface facing downward. The first transfer  215  may be a robot arm having a blade shaped end  217 . The first transfer  215  can rotate the blade shaped end  217  to turn the wafer W to have the active surface of the wafer facing downward. The blade shaped end  217  may include two layered blades or an absorber on a surface of the blade to deliver and turn the wafer W. 
     The reflow region  220  may include a conveyer type reflow part  230  and a heating part  240 . A jig  235  may be mounted on the conveyer type reflow part  230 . The jig  235  may support the wafer W such that the wafer W is received at the jig  235  away from the conveyer type reflow part  230  with the active surface facing downward. The heating part  240  may be disposed to apply heat to the wafer W at the jig  235 . In this case, with the wafer W facing downward, the heating part  240  is disposed to apply heat to the rear surface of the wafer W. The heating part  240  may have a plurality of sectors divided in one direction in which wafer W is moved, such that each of the sectors separately applies heat to the wafer W at the reflow region  220 . The pre-bumps  174  disposed on the active surface of the wafer W may be transformed to bumps  174   a  of  FIG. 10  or  11  in the reflow process at the reflow region  220 . 
     The jig  235  may include a receiving part  235   t , a support plate  235   b  and support part  235   s . The receiving part  235   t  may receive the wafer W with the active surface facing downward. The support plate  235   b  may support the jig  235  such that the jig  235  can be mounted on the conveyer type reflow part  230  stably. The support part  235   s  may connect the support plate  235   b  to the receiving part  235   t  and may support the receiving part  235   t . The support part  235   s  may be at least three support columns which are higher than the pre-bump  174  in height. 
     The jig  235  may be a removable jig  235 A or a mount jig  2356 . The removable jig  235 A may include the receiving part  235   t  which is partially opened annular type with C-shaped cross section such that the wafer can be received via the partially opened area. The receiving part  235   t  of the removable jig  235 A may be used without being attached on the conveyer type reflow part  230  because the receiving part  235   t  is formed into one body. Thus the apparatus for wafer level bump reflow  200  may include a jig loading part (not shown) and a jig unloading part (not shown) such that the removable jig  235 A can be loaded on or unloaded (removed) from the conveyer type reflow part  230 . 
     The mount jig  235 B may include a receiving part  235   ta  which is a partially opened annular type such that the wafer can be received via the partially opened area. The receiving part  235   ta  may be formed of a plurality of segments which have C-shaped cross section and are separated from each other to form an annular shape. For example, the receiving part  235   ta  in the example shown in  FIG. 7A  has three segments having C-shaped cross section. The support part  235   sa  of the mount jig  235 B may include a plurality of support columns  235   sa . The number of the support columns  235   sa  may correspond to the number of the segments of the receiving part  235   ta . Since the receiving part  235   ta  of the mount jig  235 B is formed of the plurality of segments, the mount jig  235 B may be used as being mounted or attached on the conveyer type reflow part  230 . If the support plate  235   ba  of the mount jig  235 B includes a flexible material, the receiving part  235   ta  may be continuously used while being mounted or attached on the conveyer type reflow part  230  via the support columns  235   sa  and the support plate  235   ba  because the segments of the receiving part  235   ta  are connected to the support plate  235   ba  through the support columns  235   sa.    
     The second transfer  250  may unload the wafer W which is disposed with the active surface facing downward at the reflow region  220 . The second transfer  250  may unload the wafer W with the active surface facing upward. The second transfer  250  may be a robot arm with a blade shaped end  257 . The second transfer  250  may rotate the blade shaped end  257  to turn the wafer W to have the active surface facing upward. The blade shaped end  257  may include two layered blades or an absorber on a surface of the blade to deliver and to turn the wafer W. 
     The unloading part  260  may provide a space to receive a plurality of wafers W which are unloaded from the reflow region  220  and have the bumps formed in the bump reflow process at the reflow region  220 . The wafer W may be received to the unloading part  260  with the active surface facing upward. A deflux process may be performed with respect to the bumps of the wafer W at the unloading part  260 . In one embodiment, several unloading parts  260  may be provided. 
     Using the apparatus according to embodiments of the present general inventive concept, the pre-bump disposed on the active surface of the wafer faces downward while the bump reflow process is performed with respect to the wafer. Therefore, the bump on the active surface is prevented from collapsing due to the gravity during the bump reflow process while preventing solder material from falling down on the active surface of the wafer. The embodiment of the present general inventive concept can provide a semiconductor device having a solder bumper which is large enough to provide a sufficient underfill gap and has high reliability. In addition, the solder bump may be tall enough to provide a sufficient underfill gap in the packaging process. Further, fine pitch between the solder bumps may be achieved to provide a semiconductor device which has improved integrity while having a solder bump with a great volume enough to provide sufficient underfill gap and improved integrity. 
       FIGS. 8 through 11  are cross-sectional views illustrating a method for forming a wafer level bump according to an embodiment of the present general inventive concept. 
     Referring to  FIG. 8 , a pre-bump  174  is formed on each pad  172  of a wafer W which has a plurality of the pads  172  on an active surface  176 . The pre-bump  174  may include a solder material containing copper. 
     Referring to  FIGS. 9 and 10 , the wafer W is flipped such that the active surface  176  is facing downward, as illustrated in  FIG. 9 . For example, the active surface  176  may face toward a direction of the gravitational force. Then, a bump  174   a  is formed in a bump reflow process in which heat is applied to a rear surface  178  being opposite to the active surface  176  of the wafer W, as illustrated in  FIG. 10 . The bump  174   a  may be formed into elliptical shape which has its major axis X perpendicular to the active surface  176  of the wafer W. For example, the wafer W may be disposed with respect to gravity such that the bump  174   a  may be formed to have its major axis X perpendicular to the active surface  176  of the wafer W. 
     Referring to  FIG. 11 , the wafer W with the bump  174   a  is flipped such that the active surface  176  faces upward. The wafer W may be divided into a plurality of chips using a cutting process such as a sawing thereby forming discrete semiconductor devices or semiconductor packages. 
     Since the bump reflow process is performed while the pre-bump on the active surface  176  of the wafer is facing downward, the solder bump formed in the method according to the embodiment of the present general inventive concept is tall, and fine pitch between the solder bumps is achieved, such that a semiconductor device can be provide with improved integrity while having the solder bump tall enough to provide a sufficient underfill gap. 
     The memory device or memory system according to embodiments of the present general inventive concept may be formed into a variety of packages. For example, the nonvolatile memory system can be mounted as a PoP (Package on Package), a BGAs (Ball grid arrays), a CSPs (Chip Scale Packages), a PDIP (Plastic Dual In-line Package), a Die in Waffle Pack, a Die in Wafer Form, a COB (Chip On Board), a CERDIP (Ceramic Dual In-line Package), a MQFP (Plastic Metric Quad Flat Pack), a TQFP (Thin Quad Flat Pack), a SOIC (Small Outline), a SSOP (Shrink Small Outline Package), a TSOP (Thin Small Outline), a TQFP (Thin Quad Flat Pack), a SIP (System In Package), a MCP (Multi Chip Package), a WFP (Wafer-level Fabricated Package), a WSP (Wafer-level Processed Stack Package and etc. 
     According to embodiments of the present general inventive concept, the pre-bump disposed on the active surface of the wafer is facing downward while the bump reflow process is performed with respect to the wafer. Therefore, the bump is prevented from collapsing in the bump reflow process. The embodiment of the present general inventive concept can provide a semiconductor device having a solder bump which is large enough to provide a sufficient underfill gap. In addition, the solder material does not fall down on the active surface of the wafer during the bump reflow process, such that the semiconductor device can be improved in reliability with the sufficient underfill gap in a packaging process. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents. Thus, to the maximum extent allowed by law, the scope of the present general inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.