Patent Publication Number: US-2015064876-A1

Title: Separating device and separating method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-180230, filed Aug. 30, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a separating device and a separating method. 
     BACKGROUND 
     In general, electronic circuits mounted on a substrate are joined to the substrate using, for example, one or more solder balls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view illustrating an apparatus for separating an electronic device from a mounting substrate, according to a first embodiment. 
         FIGS. 2A and 2B  are cross sectional views illustrating ways a chip may be separated from a mounting substrate according to the first embodiment. 
         FIG. 3  is a flow chart illustrating a method of separating a chip from a mounting substrate according to the first embodiment. 
         FIG. 4  is a cross sectional view illustrating a separating device according to a first variation of the first embodiment. 
         FIG. 5  is a cross sectional view illustrating a separating device according to a second variation of the first embodiment. 
         FIG. 6  is a cross sectional view illustrating a separating device according to a third variation of the first embodiment. 
         FIG. 7  is a cross sectional view illustrating a separating device according to a second embodiment. 
         FIGS. 8A and 8B  are cross sectional views illustrating ways of separating a chip from a mounting substrate according to the second embodiment. 
         FIG. 9  is a flow chart illustrating a method of separating a chip from a mounting substrate according to the second embodiment. 
         FIG. 10  is a cross sectional view illustrating a device for separating a chip from a mounting substrate according to a variation of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a device for separating a chip from a mounting substrate and a separating method for a chip that prevents excessive damage to the chip is provided. 
     According to one embodiment, a separating device that removes a chip connected to a mounting substrate through a connecting material from the mounting substrate is provided. The separating device includes a heating unit that heats the mounting substrate to a temperature less than a melting point of the connecting material. 
     According to one embodiment, a separating method for removing a chip connected to a mounting substrate through a connecting material from the mounting substrate is provided. The separating method includes heating the mounting substrate to a temperature less than a melting point of the connecting material. 
     Hereinafter, embodiments are described with reference to the drawings. 
     A first embodiment is described herein. 
     As illustrated in  FIG. 1 , a separating device  1  according to the embodiment is a device for removing a chip  102  connected to a mounting substrate  100  through a connecting material such as solder balls  101  from the mounting substrate  100 . In the mounting substrate  100 , there is wiring (not illustrated) made of metal such as copper and an electrode pad  104  within a base material  103  made of resin material. The electrode pad  104  is exposed to the mounting surface  100   a  of the mounting substrate  100 . 
     The separating device  1  includes a heating unit  11  for holding and heating the mounting substrate  100 . The heating unit  11  is a heater of, for example, resistant heating type, which heats the mounting substrate  100  to a temperature less than the melting point of the solder ball  101  and preferably, to a temperature less than the glass transition point of the resin material forming the base material  103  of the mounting substrate  100 . The melting point of the solder ball  101  is, for example, 220 to 240° C., although this depends on the composition thereof. The glass transition point of the resin material is, for example, about 180° C. although this depends on the type of resin material. 
     Further, the separating device  1  includes a holding unit  12  for holding the chip  102 . Within the holding unit  12 , there is an absorption tool  13  for holding the chip  102 . Further, within the holding unit  12 , there is a cooling unit  14  for cooling the chip  102 . The cooling unit  14  is, for example, a tank that contains liquid nitrogen. Further, within the holding unit  12 , there is h an ultrasonic wave applying unit  15  for applying an ultrasonic wave to the solder balls  101 . Further, the separating device  1  is provided with a shearing tool  16  which presses the chip  102  in a direction parallel to the mounting surface  100   a  of the mounting substrate  100 . 
     Next, the operation of the separating device, and a method of separating a chip from a mounting substrate according to the first embodiment, is described. 
     As illustrated in  FIG. 2A  and in Step S 11  of  FIG. 3 , the mounting substrate  100  is mounted on the heating unit  11 . In  FIG. 3 , the shearing tool  16  (referring to  FIG. 1 ) is not depicted with the mounting substrate  100 . The solder ball  101  is joined to the electrode pad  104  of the mounting substrate  100 . Electrode pads (not illustrated in  FIG. 3 ) of the chip  102  are joined to the solder ball  101 . According to this embodiment, the chip  102  is mounted on the mounting substrate  100  through the solder balls  101 . 
     The chip  102  may be, for example, a chip of a Ball Grid Array (BGA) type and, for example, a NAND flash memory or a large scale integrated circuit (LSI) built on the silicon substrate. The solder balls  101  are joined to the lower surface of the chip  102  in a matrix configuration and are, respectively, joined to the electrode pads  104  of the mounting substrate  100 . 
     Next, as illustrated in Step S 12  of  FIG. 3 , by applying vacuum through the absorption tool  13  of the holding unit  12 , the holding unit  12  holds the chip  102 . Further, by supplying liquid nitrogen  51  into the cooling unit  14 , the holding unit  12  cools the chip  102 . In this state, as illustrated in Step S 13  of  FIG. 3 , the heating unit  11  heats the mounting substrate  100 . The temperature of the mounting substrate that results from the heating is a temperature that is less than that of the melting point of the solder ball  101 ; preferably, the temperature is less than the glass transition point of the resin material forming the base material  103  of the mounting substrate  100  (e.g., a temperature of, less than 180° C.). In this embodiment, the ultrasonic wave applying unit  15  of the holding unit  12  supplies an ultrasonic wave. This ultrasonic wave is applied to the solder balls  101  through the chip  102 . 
     According to this embodiment, the mounting substrate  100  is heated by the heating unit  11  and is thermally expanded. Therefore, a force going from the central portion to the peripheral portion of the chip  102  is applied to each solder ball  101  from the mounting substrate  100 . On the other hand, as it is cooled by the cooling unit  14 , the chip  102  is thermally contracted, or it is at least restrained from thermally expanding. Therefore, the respective solder balls  101  are restrained from moving by the chip  102  and a force going from the peripheral portion to the central portion of the chip  102  is applied to the solder balls  101 . 
     According to this embodiment, mutually adverse forces from the mounting substrate  100  and the chip  102  are applied to the solder balls  101 , thereby generating a shearing force. This shearing force is larger for solder balls  101  joined in the more peripheral portion of the chip  102 . Further, due to the ultrasonic wave applied by the ultrasonic wave applying unit  15 , the solder balls  101  fatigue and are easily fractured. As the result, at least the solder balls  101  joined in the peripheral portion of the chip  102  fracture. On the other hand, in some cases, the solder balls  101  joined in the central portion of the chip  102  do not fracture. 
     Next, as illustrated in  FIG. 2B , where the holding unit  12  is not depicted, the shearing tool  16  is arranged on the lateral side of the chip  102 . As illustrated in Step S 14  of  FIG. 3 , the shearing tool  16  pushes against the chip  102  in a horizontal direction, that is, in a direction parallel to the mounting surface  100   a  of the mounting substrate  100 . According to this embodiment, an equal shearing force is applied to all the solder balls  101  that do not fracture. As a result, in the process shown in  FIG. 2A , even when the solder balls  101  joined in the central portion of the chip  102  do not fracture, all the solder balls  101  fracture in the process shown in  FIG. 2B . According to this embodiment, the chip  102  can be removed from the mounting substrate  100 . 
     Hereafter, potential effects of the embodiment are described. 
     After the chip  102  is mounted on the mounting substrate  100 , when some defect happens in the chip  102 , the chip  102  is removed from the mounting substrate  100  by heating the solder balls  101  and is examined. However, if the solder balls  101  are heated to a temperature greater than or equal to their melting point, the chip  102 , which is also heated with the solder balls  101 , is damaged by heating. If the chip  102  is damaged by heating, a defect that results from the heat damage may not be targeted for examination. Further, the heat damage may cause another defect that originally would not have occurred in the chip  102 . 
     Therefore, in the embodiment, the heating unit  11  heats and thermally expands the mounting substrate  100 , and the cooling unit  14  cools and contracts the chip  102 , or at least does not thermally expand the chip to a large extent. According to this embodiment, a shearing force is applied to the solder balls  101 , which can fracture the solder balls  101 . Thus, in the embodiment, the chip  102  is not heated to the melting point of the solder ball  101 , but instead to a lower temperature than the melting point of the solder balls. Thus, the solder balls  101  are fractured by the application of a mechanical force. Therefore, the chip  102  is rarely damaged by heating. Further, the chip  102  is cooled by the cooling unit  14  and can be prevented from being damaged by heat. As a result, the chip  102  having a defect generated can be removed from the mounting substrate  100  for examination of the defect, thereby enabling accurate examination. 
     Further, in the embodiment, since the heating temperature by the heating unit  11  is set at a temperature less than the glass transition point of the resin material forming the base material  103 , the mounting substrate  100  can be restrained from being thermally damaged. However, when the mounting substrate  100  is not reused after removing the chip  102 , the heating temperature by the heating unit  11  is not restricted to a temperature less than the glass transition point of the resin material, but may be raised to an upper limit in the range where the chip  102  is free from heat damage. 
     Further, in the embodiment, after heat stress is applied to the solder balls  101  in the process shown in  FIG. 2A , a shearing force is applied to the solder balls  101  by the shearing tool  16  in the process shown in  FIG. 2B . According to this embodiment, even when the solder balls  101  joined to the central portion of the chip  102  are not fractured by the heat stress, these solder balls  101  may be fractured. 
     Further, when the solder balls  101  are sheared by the shearing tool  16 , at least the solder balls  101  joined in the peripheral portion of the chip  102  have already been fractured and, therefore, a shearing force can be concentrated on the remaining solder balls  101 . Further, since a solder ball  101  which is not fractured is nonetheless damaged by heat stress, this damage serves as a starting point of fracture. According to this embodiment, the remaining solder balls  101  can be reliably fractured, hence enabling removal of the chip  102  from the mounting substrate  100 . 
     Further, in the embodiment, the ultrasonic wave applying unit  15  applies an ultrasonic wave to the solder balls  101 . This also accelerates the fracture of the solder balls  101 . 
     In the embodiment, although the example depicted provides a cooling unit  14  within the holding unit  12 , the cooling unit  14  does not need to be provided. When the chip  102  is positively heated, a heat stress can be generated in the solder balls  101 . Further, if the holding unit  12  is formed of a material of high heat conductivity (for example, copper), the chip  102  can be cooled through discharging heat through the holding unit  12 . 
     Further, when the heat stress can fracture most of the solder balls  101 , the shearing tool  16  does not necessarily need to be provided. In this case, by pulling the chip  102  using the holding unit  12 , the chip  102  can be removed from the mounting substrate  100 . 
     Next, a first variation of the first embodiment is described. 
     As illustrated in  FIG. 4 , in a separating device  1   a  according to the first variation, the lower portion  12   a  of the holding unit  12  is exchangeable. A plurality of lower portions  12   a  of various sizes are prepared and exchanged according to the size of the chip  102 . According to this first variation, optimal holding units  12  that are suitable for chips  102  of varying sizes can be realized. The structure, operation, and effects, other than those disclosed above, are the same as those in the first embodiment. 
     Next, a second variation of the first embodiment is described. 
     As illustrated in  FIG. 5 , in a separating device  1   b  according to the second variation, the cooling unit  14  is positioned lower than the ultrasonic wave applying unit  15 , which is shown as positioned on the side of the holding unit  12 . According to this variation, the chip  102  can be more efficiently cooled. The structure, operation, and potential effects, other than those disclosed above, are the same as those in the first embodiment. 
     Next, a third variation of the first embodiment is described. 
     As illustrated in  FIG. 6 , the separating device  1   c  according to the first embodiment is provided with a cylindrical tube  18  covering the solder balls  101 , the chip  102 , and the holding unit  12 . Further, the separating device  1   c  is not provided with a cooling unit within the holding unit  12 . 
     In this example, by blowing a cool air downward from the top of the device, the chip  102  is cooled by the tube  18 . According to this, the same effect as that of the first embodiment can be obtained. The structure, operation, and effect, other than those disclosed above, are the same as those of the first embodiment. 
     Next, a second embodiment is described. 
     As illustrated in  FIG. 7 , a separating device  2  according to the second embodiment is different from the above-mentioned separating device  1  (referring to  FIG. 1 ) of the first embodiment in that the shearing tool  16  is not provided and that a dispenser  17  is provided. The dispenser  17  is an injecting means that holds a thermosetting material  52  that is in a liquid or semi-cured state, and which discharges the thermosetting material  52  from a nozzle  17   a  at the lower end. The thermosetting material  52  is a thermally expandable material capable of expanding by the application of heat, light, such as ultraviolet light or infrared light, or vibration from an electromagnetic wave or ultrasonic wave. In the second embodiment, for example, a material that expands upon heating is used. The structure, other than the above-mentioned components of the separating device  2 , is the same as that in the above-mentioned separating device  1 . 
     Next, the operation of the separating device thus constituted, namely, a method of separating a chip from a mounting substrate according to the second embodiment, is described. 
     As illustrated in  FIG. 8A  and in Step S 21  of  FIG. 9 , the mounting substrate  100  is mounted on the heating unit  11 . The chip  102  is mounted on the mounting substrate  100  through the solder balls  101 . As illustrated in Step S 22  of  FIG. 9 , while inclining the dispenser  17  and discharging the thermosetting material  52  from the nozzle  17   a  of the dispenser  17 , the thermosetting material  52  is injected between the mounting substrate  100  and the chip  102 . The thermosetting material  52  may be a resin material which is cured and expanded by heating. For example, polyimide resist can be used. 
     Next, as illustrated in  FIG. 8B  and in Step S 23  of  FIG. 9 , while the absorption tool  13  of the holding unit  12  is holding the chip  102 , the heating unit  11  heats the mounting substrate  100 . According to this, the thermosetting material  52  is heated through the mounting substrate  100 . As a result, the thermosetting material  52  is cured and thermally expanded. According to this embodiment, the chip  102  is raised upward to separate from the mounting substrate  100 . In this embodiment, the location of a fracture depends on the portion of the chip  102  that is joined to the mounting substrate. For example, the electrode pad  104  of the mounting substrate  100  may be separated from the base material  103 . The heating temperature at this point has to be a temperature at which the thermosetting material  52  may be cured and thermally expanded, while being less than the melting point of the solder ball  101 . In addition, the heating temperature is less than the glass transition point of the resin material forming the base material  103 . 
     In this embodiment, the chip  102  may be cooled by the cooling unit  14 . This can protect the chip  102  from heat damage and a fracture can be accelerated by the generation of a shearing force due to heat stress. Alternatively, an ultrasonic wave may be generated by the ultrasonic wave applying unit  15 . This can also accelerate a fracture. 
     Thereafter, as illustrated in Step S 24  of  FIG. 9 , the thermosetting material  52  is removed. For example, by irradiating a laser light to the thermosetting material  52 , the thermosetting material  52  is decomposed. Alternatively, using chemicals, the thermosetting material  52  is dissolved. According to this embodiment, the chip  102  can be removed from the mounting substrate  100 . 
     Next, potential effects of the embodiment are described. 
     According to the second embodiment, after the dispenser  17  injects the thermosetting material  52  between the chip  102  and the mounting substrate  100 , the thermosetting material  52  is heated so as to be cured and expanded, and hence to apply a separating force to the chip  102  and the mounting substrate  100 . According to this embodiment, the chip  102  is not heated to such a temperature as to melt the solder balls  101 , but a mechanical force is generated between the chip  102  and the mounting substrate  100  to remove the chip  102  from the mounting substrate  100 . According to this embodiment, the chip  102  can be removed from the mounting substrate  100  while being restrained from heat damage. 
     The structure, operation, and effects, other than those mentioned above with respect to the second embodiment, are the same as those in the above mentioned first embodiment. 
     Next, a variation of the second embodiment is described. 
     As illustrated in  FIG. 10 , in the variation, a bead  53  is used as a thermal expanding material. The bead  53  is a sphere, for example, made of a hard resin material. 
     At first, the beads  53  are interposed between the mounting substrate  100  and the chip  102 . Next, by heating the beads  53 , the beads  53  are thermally expanded, to apply a separating force to the chip  102  and the mounting substrate  100 . According to this, the chip  102  can be removed from the mounting substrate  100 . 
     Also in this variation, by generating a mechanical force through a thermal expansion, the chip  102  can be removed from the mounting substrate  10 , while being restrained from heat damage. Further, according to the variation, after the chip  102  is removed from the mounting substrate  100 , the beads  53  that are the expanding material are easily removed. 
     The structure, operation, and effects, other than those mentioned with respect to the above-mentioned variation, are the same as those in the above-mentioned second embodiment. 
     In addition, the type of the bead  53  is not restricted to any one particular type. However, the size of the bead  53  before expansion should be small enough to allow the bead to be interposed between the mounting substrate  100  and the chip  102 , the size of the bead  53  after expansion should be large enough to allow the bead to make contact with both the mounting substrate  100  and the chip  102 , and the hardness of the bead after the expansion should be high enough to fracture a part of the joining structure, including the solder balls  101  the electrode pad  104 , and the base material  103  of the mounting substrate  100 . 
     Although the second embodiment and the variation thereof show the use of an expanding material that is thermally expansible by heating, the disclosed embodiments are not restricted to such materials. For example, a material that expands through irradiation or application of a magnetic field may be used. Alternatively, a material that expands by using a chemical method may be used. According to these variations, heat damage to the chip  102  is more likely to be avoided. 
     According to the embodiments as mentioned above, a separating device and a separating method of a chip capable of restraining a damage of the chip is provided. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.