WO2007078148A2 - Flip chip mount type of bump, manufacturing method thereof, and bonding method for flip chip using non conductive adhesive - Google Patents

Flip chip mount type of bump, manufacturing method thereof, and bonding method for flip chip using non conductive adhesive Download PDF

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Publication number
WO2007078148A2
WO2007078148A2 PCT/KR2007/000032 KR2007000032W WO2007078148A2 WO 2007078148 A2 WO2007078148 A2 WO 2007078148A2 KR 2007000032 W KR2007000032 W KR 2007000032W WO 2007078148 A2 WO2007078148 A2 WO 2007078148A2
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WO
WIPO (PCT)
Prior art keywords
bump
metal
mushroom
flip chip
bumps
Prior art date
Application number
PCT/KR2007/000032
Other languages
French (fr)
Other versions
WO2007078148A3 (en
Inventor
Young Ho Kim
Tae Sung Oh
Sang Mok Lee
Original Assignee
Industry-University Cooperation Foundation, Hanyang University
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Filing date
Publication date
Application filed by Industry-University Cooperation Foundation, Hanyang University filed Critical Industry-University Cooperation Foundation, Hanyang University
Priority claimed from KR1020070000555A external-priority patent/KR100843632B1/en
Publication of WO2007078148A2 publication Critical patent/WO2007078148A2/en
Publication of WO2007078148A3 publication Critical patent/WO2007078148A3/en

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Definitions

  • the present invention relates to a flip chip bump, a manufacturing method thereof, and a flip chip bonding method using a non-conductive adhesive, and more particularly, to a flip chip bump which can increase the effect of plastic deformation by virtue of a low pressure applied during flip chip bonding and achieve improved durability by reducing the trapping of a non-conductive adhesive therein, a method for manufacturing the flip chip bump, and a flip chip bonding method.
  • a Controlled-Collapse Chip Connection (C4) technique of IBM Corp. is a technique in which a chip and a substrate are bonded to each other by melting a 95Pb-5Sn or 97Pb-3Sn solder having a high melting point at a high temperature of 300 0 C or more.
  • C4 technique has the drawback of damage to the substrate, etc. because of excessive thermal energy caused by the high-temperature bonding process of 300 ° C or more.
  • the C4 technique also has the drawback of degradation in the reliability of the resulting flip chip structure due to thermal expansion caused by a great temperature difference.
  • a method using a low melting-point solder such as a Sn-Bi solder has proposed.
  • this has a drawback of degradation in the reliability of a bonded joint due to an intermetallic compound that is produced by a reaction between a liquid-phase solder and an under bump metal in the course of mounting or bonding the solder.
  • Most conventional methods using the reflow of a solder should include a solder flux coating process, a residual flux removal process, an under-fill process, etc., and therefore, suffer from drawbacks of complicated processes and expensive manufacturing costs.
  • ACA anisotropic conductive adhesive
  • ACF anisotropic conductive film
  • isotropic conductive adhesive conductive particles are physically captured and bonded between bumps and electrodes upon receiving a predetermined pressure and heat applied thereto.
  • a bonding method using ACF is widely used in techniques for mounting drive devices to information displays including a thin film transistor-liquid crystal display (TFT-LCD).
  • TFT-LCD thin film transistor-liquid crystal display
  • examples of a metal bump for use in an ACF process include an Au bump formed by electroplating, and an Au/Ni bump formed by electroless- plating.
  • the Au bump is the most widely used bump by virtue of superior heat conductivity and electric conductivity as well as a high physical or chemical stability thereof.
  • the Au/Ni bump prepared by electroless-plating is also widely used because it ensures selective bump formation without a photolithography process and omits a vacuum deposition process and thus, can reduce manufacturing costs of the bump.
  • the method using an ACF has been preferred because it is more eco- friendly than the methods using a solder bump and has advantages of a low- temperature process, simplified overall process and high reliability.
  • the method using an ACF has the problem that the bonding area obtained by the conductive particles included in the ACF is much smaller than the area of the bump, thus causing an increased contact resistance.
  • the pitch of bumps the risk of a short circuit between the bumps increases, and excessive contact resistance or poor bonding may be caused by a reduced size of the bumps.
  • a bonding method using a non-conductive adhesive uses a mechanical contact between the metal bump and a metal pad.
  • the non-conductive adhesive is usable in the form of a paste or film, and a bonding process can be performed at a curing temperature of the adhesive, the overall process can be performed at a relatively low temperature in a simplified manner.
  • the adhesive can be cured by ultraviolet light rather than heat, and this makes a heating process unnecessary.
  • the bonding method using the non-conductive adhesive has various advantages of facilitating the formation of a fine pitch, reducing manufacturing costs, and achieving superior electric properties via a reduced contact resistance between the metal bump and the metal pad.
  • FIGS. Ia and Ib are diagrams illustrating the trapping phenomenon caused when using the non-conductive adhesive.
  • bumps 101 are formed on the IC chip 110 and a non-conductive adhesive is coated therebetween.
  • a part of the non-conductive adhesive 103 may trap into a region A between each bump 101 and the corresponding metal electrode 102.
  • the trapped non-conductive adhesive 103 acts to increase a contact resistance between the bump 101 and the metal electrode 102 and in the worst case, causes a short circuit.
  • metal bumps for use on chips have been manufactured by an electroplating method, an electro-less plating method, or a method using a stud bump, and Au is the most widely used material for the manufacture of the metal bumps.
  • Au has a high yield strength of 30MPa and a high hardness H B of approximately 20, Au needs a relatively high pressure, for bonding thereof.
  • U.S. Patent No. 5,928,458 discloses a method in which an Au stud bump is prepared and is plastically deformed by use of a high pressure of 80-100 g/bump (784- 980 mN/burap) .
  • Korean Patent Laid-open Publication No. 2001-0104626 discloses a bonding method using an Au ball bump under pressure of 980 mN/bump (100 g/bump).
  • a paper published in Thin Solid Films discloses a technique in which an Au stud bump is prepared and is plastically deformed by use of a high pressure of 80-100 g/bump (784- 980 mN/burap) .
  • Korean Patent Laid-open Publication No. 2001-0104626 discloses a bonding method using an Au ball bump under pressure of 980 mN/bump (100 g/bump).
  • a paper published in Thin Solid Films discloses a technique in which an Au ball bump under pressure of 980 mN/bump
  • Au/Ni bump is prepared by an electro-less plating method and compressed by
  • WO No. 2001-052317 discloses a bonding method using a bump made of an easily plastic-deformable Sn-Pb alloy.
  • the recent trend is to use a Pb-free solder in accordance with various environmental regulations restricting the use of Pb.
  • Korean Patent Laid-open Publication No. 1998-0085069 discloses a bonding method using a Sn-Ag alloy bump.
  • Japanese Patent Laid-open Publication No. Hll-0010385 discloses a method for manufacturing a bump using Sn-Ag and Sn-Cu alloys.
  • Japanese Patent Laid-open Publication No. 2000-0077448 discloses a bump using a Sn-Ag-In alloy and a bonding method using the same. In this method, a chip is bonded to a substrate via a reflow process performed at a temperature more than a melting point of the Sn-based alloy.
  • the Sn-based alloy is advantageous for easy plastic deformation, but has a limit in the formation of the bump. It is well known that the above described limit can be efficiently conquered by preparing a bump by use of an easily plastically deformable material to have a geometrical shape suitable for easy plastic deformation.
  • FIGS. 2a and 2b are diagrams illustrating a flip chip bonding using bumps having different heights from each other.
  • bumps 201 are formed on the chip 210.
  • bonding using the bumps 201 causes the bumps 201 to fail to come into contact with the metal electrodes 202 as illustrated in the region B of FIG. 2b, thereby resulting in poor bonding between the substrate 200 and the chip 210.
  • U.S. Patent No. 6,791,195 discloses Au ball bumps formed by a stud bumping method.
  • preparation of the ball bumps is difficult.
  • the ball bumps are formed one by one by use of a wire bonder, the greater the number of bumps, the process time may increase excessively.
  • the present invention has been made in view of the above problems, and it is an object of the present invention to provide a flip chip bump which can allow a geometrical plastic deformation at a low pressure by a simplified process and improve the reliability of a bonded joint, a method for manufacturing the flip chip bump, and a flip chip bonding method using a non-conductive adhesive.
  • a flip chip bump comprising'- a chip", a plurality of patterned under bump metal formed on the
  • the spherical reflowed bump and the mushroom bump may comprise any one material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn and alloys thereof.
  • the bump comprises a single metal bump, or a Pb-free solder bump comprising pure Sn, or a Sn-metal alloy containing any one selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof .
  • the mushroom bump has a column and a head, and the column and the head are made of the same material as each other or different materials from each other. More preferably, the column and the head of the mushroom bump comprises pure Sn, or a Sn-metal alloy containing Sn and any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag and Zn and alloys thereof, or any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof.
  • the column is made of pure Sn, or the Sn-metal alloy containing Sn
  • the head is made of the Sn-metal alloy, or a metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof.
  • the mushroom bump has pores formed therein.
  • the pores may be formed in the column or head of the mushroom bump, or in both the column and head.
  • the spherical reflowed bump and mushroom bump further comprises an oxidation-resistant film, and the oxidation-resistant film comprises a material selected from the group consisting of Ag, Au and Pt.
  • a method for manufacturing a spherical reflowed bump comprising:
  • ⁇ 34> a) forming a plurality of patterned under bump metal on the chip;
  • ⁇ 36> c) depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, and then, performing a reflow process, so as to manufacture the spherical reflowed bump.
  • the method further comprises removing the photoresist layer.
  • a method for manufacturing a mushroom bump comprising:
  • ⁇ 4i> c' depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, so as to manufacture the mushroom bump;
  • the mushroom bump is formed by depositing the material selected from the group consisting of a metal, Pb-free metal, and a combination thereof, to have a height higher than the photoresist layer.
  • the mushroom bump has a column and a head.
  • the column and the head may be formed by depositing the same material, or may be formed by depositing two or more different materials from each other.
  • a flip chip bonding method using a flip chip bump comprising:
  • the thermal compression is performed at a temperature of
  • pressure applied upon the thermal compression is within a range of 20-100MPa.
  • a spherical or mushroom shaped bump can be prepared with a simplified process, to enable the manufacture of a so-called “spherical reflowed bump” or “mushroom bump”.
  • the bump can allow geometrical plastic deformation thereof under a low pressure and this results in an improved reliability in the bonded joint of the resulting flip chip bump.
  • FIGS. Ia and Ib are diagrams illustrating a trapping phenomenon caused when using a non-conductive adhesive
  • FIGS. 2a and 2b are diagrams illustrating a flip chip bonding using bumps having a height difference
  • FIGS. 3a and 3b are sectional views illustrating a chip formed with spherical reflowed bumps and a chip formed with mushroom bumps, respectively;
  • FIGS. 4a and 4b are sectional views of different examples of composite mushroom bumps according to the present invention.
  • FIGS. 5a to 5c are sectional views of different examples of mushroom bumps having pores according to the present invention.
  • FIG. 6 is a schematic view illustrating sequential steps of a method for manufacturing spherical reflowed bumps according to a first embodiment of the present invention
  • FIG. 7 is a schematic view illustrating sequential steps of a method for manufacturing spherical reflowed bumps according to a second embodiment of the present invention.
  • FIG. 8 is a schematic view illustrating sequential steps of a method for manufacturing mushroom bumps according to a third embodiment of the present invention.
  • FIG. 9 is a schematic view illustrating sequential steps of a method 32
  • FIG. 10 is a diagram illustrating a flip chip bonding method according to an embodiment of the present invention.
  • FIG. 11 is a diagram illustrating a flip chip bonding method using mushroom bumps each having a column and a head made of the same material as each other;
  • FIG. 12 is a diagram illustrating a flip chip bonding method using composite mushroom bumps each having a column and a head made of heterogeneous materials!
  • FIG. 13 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in a head thereof according to another embodiment of the present invention; ⁇ 67> FIG.
  • FIG. 14 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in a column thereof according to a further embodiment of the present invention
  • FIG. 15 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in both a column and a head thereof according to a still further embodiment of the present invention
  • FIG. 16a is a scanning electron micrograph illustrating spherical Sn reflowed bumps prepared by Example 1
  • FIG. 16b is an enlarged micrograph of FIG. 16a
  • FIG. 17a is a scanning electron micrograph illustrating Sn bumps prepared by Comparative Example 1
  • FIG. 17b is an enlarged micrograph of
  • FIG. 21 is a scanning electron micrograph illustrating a sample that is bonded by use of Sn bumps of Comparative Example 1, in which a non-conductive adhesive is trapped in the interface of the bumps;
  • FIGS. 22a and 22b are scanning electron micrographs illustrating a bump bonding under pressure of 40 MPa and a bump bonding under pressure of 80 MPa, respectively;
  • FIG. 23 is a scanning electron micrograph illustrating Sn mushroom bumps prepared by Example 2;
  • FIG. 24 is a scanning electron micrograph illustrating Cu mushroom bumps prepared by Example 3;
  • FIG. 25a is a scanning electron micrograph illustrating Sn/Cu composite mushroom bumps prepared by Example 4, and
  • FIG. 25b is an enlarged optical micrograph illustrating the cross section of the Sn/Cu composite mushroom bump; and
  • FIG. 26 is a scanning electron micrograph illustrating column-shaped Cu bumps prepared by Comparative Example 2.
  • a flip chip bump according to the present invention has a spherical or mushroom shape.
  • spherical reflowed bump means a spherical bump processed by a reflow process.
  • muscle bump represents a mushroom-shaped bump prepared by a plating process without a reflow process.
  • the flip chip bump according to the present invention comprises: ⁇ 83> a chip
  • ⁇ 84> a plurality of patterned under bump metal formed on the chip; and ⁇ 85> spherical reflowed bumps or mushroom bumps formed on the under bump metal.
  • FIG. 3a is a sectional view illustrating a chip formed with spherical reflowed bumps
  • FIG. 3b is a sectional view illustrating a chip formed with mushroom bumps.
  • the flip chip bump according to an exemplary embodiment of the present invention includes a chip 10, a plurality of patterned under bump metal 11 formed on the chip 10, and spherical reflowed bumps 30 formed on the under bump metal 11.
  • the flip chip bump according to another exemplary embodiment of the present invention includes a chip 10, a plurality of patterned under bump metal 11 formed on the chip 10, and mushroom bumps 50 formed on the under bump metal 11.
  • the spherical reflowed bumps 30 or mushroom bumps 50 may be any ones selected from metal bumps and Pb-free solder bumps.
  • the present invention has no special limit in the constituent material of the under bump metal, and any materials used in the field of semiconductors are available.
  • the bumps according to the present invention comprise any one material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn and alloys thereof.
  • the bumps include single metal bumps, or Pb-free solder bumps comprising pure Sn, or a Sn-metal alloy containing any one alloy selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof .
  • the content of the metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof is less than 5 wt% on the basis of the overall Sn- metal alloy.
  • the Sn-metal alloy may be a Sn-Ni or Sn-Cu alloy.
  • the alloying component has the function of lowering the surface tension and melting point of Sn, thereby achieved improved ductility and superior bonding properties via plastic deformation.
  • the mushroom bump 50 is divided into a column and a head.
  • the column and the head may be made of the same material as each other.
  • the mushroom bump 50 may be a composite mushroom bump in which the column and the head are made of heterogeneous materials.
  • the column and the head of the composite mushroom bump comprises pure Sn, or a Sn-metal alloy containing Sn and any one metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof, or a single metal selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof.
  • the head and the column of the composite mushroom bump are made of different materials from each other.
  • the column is made of Sn and the head is made of Cu or Ni, to prepare a Sn/Cu or Sn/Ni (column/head) bump.
  • the column is made of Cu or Ni and the head is made of Sn, to prepare a Cu/Sn, Ni/Sn (column/head) bump.
  • FIGS. 4a and 4b are cross-sectional views of different examples of the composite mushroom bump according to the present invention.
  • the composite mushroom bump formed on the chip 10 includes a column 7a made of Cu or Ni and a head 8a made of Sn.
  • the composite mushroom bump formed on the chip 10 includes a column 7a made of Sn and a head 8b made of Cu or Ni .
  • the spherical reflowed bump or mushroom bump according to the present invention is configured to have pores therein if necessary.
  • the pores have the function of allowing stress, caused by pressure applied during bonding of the chip and the substrate, to be concentrated therein, thereby increasing the effect of plastic deformation even when a low pressure is applied.
  • the bump having the pores may a variety of shapes as shown in FIGS. 5a to 5c, by changing various conditions of, for example, an electroplating, such as the density of current, pH of a plating solution, and other pretreatment conditions, etc.
  • FIGS. 5a to 5c are cross-sectional views illustrating different examples of the mushroom bump having pores according to the present invention.
  • the mushroom bump shown in FIG. 5a includes a column 7 formed with pores 21 and a head 8.
  • the mushroom bump shown in FIG. 5b includes a column 7 and a head 8 formed with pores 21.
  • the mushroom bump shown in FIG. 5c includes a column 7 and a head 8, which are formed with pores 21.
  • the spherical reflowed bump or mushroom bump may further include an oxidation-resistant film, and the oxidation-resistant film includes a material selected from the group consisting of Ag, Au, and Pt.
  • a method for manufacturing a flip chip bump including the above described spherical reflowed bump comprising the steps of: ⁇ iO3> a) forming a plurality of patterned under bump metal formed on the chip; ⁇ iO4> b) coating a photoresist on the patterned under bump metal and developing the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside; and ⁇ iO5> c) depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, and then, performing a reflow process, to prepare the spherical reflowed bump.
  • the method further comprises: before or after the reflow process of the step c), the step of removing the photoresist layer.
  • ⁇ iO7> Specifically, in the first step a), the under bump metal is formed on the chip, and then, under bump metal patterns is formed via conventional etching processes.
  • ⁇ iO8> The present invention has no limit in a deposition process for forming the under bump metal.
  • the deposition process may be any one selected from the group consisting of a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an electro-less plating process, and an electroplating process.
  • the coated photoresist is developed such that the resulting photoresist layer has an opening, through which a part of the under bump metal is exposed to the outside.
  • the photoresist may be a positive photoresist or negative photoresist.
  • the photoresist is subjected to baking and patterning processes, so as to form the photoresist layer having the opening.
  • the thickness of the photoresist layer and the size of the opening are factors of determining the shape of a finally prepared bump.
  • a spherical bump is prepared.
  • a mushroom bump is prepared.
  • the shape of the mushroom bump can be changed by using two or more photoresist layers as occasion demands.
  • the material selected from the group consisting of a metal, Pb-free metal, and a combination thereof is deposited on the under bump metal inside the opening, and the deposited material is subjected to a reflow process, so as to prepare the spherical reflowed bump.
  • the shape of the bump can be changed by removing the photoresist layer before or after performing the reflow process.
  • the material deposited inside the opening may be a material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn, and alloys thereof, so as to prepare a single metal bump, or may be pure Sn or a Sn- metal alloy containing Sn and any one metal selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof, so as to prepare a Pb-free solder bump.
  • the Pb-free solder bump takes the form of an alloy using Sn and any one selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof.
  • a Sn-Ni or Sn-Cu bump is possible.
  • the deposition of the bump forming material is performed 17 WJI SM I J ⁇ VS, ⁇ Wt»
  • the reflow process is performed in a conventional manner.
  • the deposited layer can vary under the influence of a surface tension thereof and the photoresist layer can serve as a dam, to enable the preparation of an arched spherical bump.
  • the reflow process serves to achieve a uniform bump composition, a uniform bump height, and an increased bonding strength between the under bump metal and the bump.
  • the reflow process is performed within a predetermined reflow time range of 0.1-120 seconds under a vacuum condition of 150-300 mtorr by flow of a mixture gas comprising 85-95 wt% of Ar and 5-15 wt% of H 2 .
  • the reflow process is performed at a temperature more than 232 0 C that is a melting point of Sn, preferably, at a temperature higher than the melting point of Sn by 20-30°C, and more preferably, at a temperature range of 232-280°C, so as to prepare a spherical reflowed bump having a ball shape.
  • the present invention also has no limit in the removal of the photoresist layer, and the photoresist layer is removed by a conventional method that is well known in the art by those skilled in the art.
  • the spherical reflowed bump is subjected to an oxidation- resistant film forming process.
  • the oxidation-resistant film includes one material selected from the group consisting of Ag, Au, and Pt, and is prepared by a conventional deposition method.
  • FIG. 6 is a schematic view illustrating sequential steps of the method for manufacturing the spherical reflowed bump according to a first embodiment of the present invention.
  • a photoresist layer 4 having an opening is formed on the chip 10 on which the under bump metal 11 was previously formed via a plurality of patterning processes.
  • the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 30a.
  • the photoresist layer 4 is removed such that only the under bump metal 11 and the bump forming layer 30a are remained on the chip 10.
  • FIG. 7 is a schematic view illustrating sequential steps of a method for manufacturing the spherical reflowed bump according to a second embodiment of the present invention.
  • the photoresist layer 4 having an opening is formed on the chip 10 on which the under bump metal formed previously 11.
  • the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 40a.
  • the shape of the bump forming layer 40a varies to form an arched spherical bump
  • the photoresist layer 4 is removed such that only the under bump metal 11 and the spherical bump 40 are remained on the chip
  • a method for manufacturing the flip chip bump including the mushroom bump according to the present invention comprises the steps of:
  • ⁇ 131> a 1 forming a plurality of patterned under bump metal on the chip; ⁇ 132> b 1 ) coating a photoresist on the patterned under bump metal and etching the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside," ⁇ 133> c') depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, so as to prepare a mushroom bump; and ⁇ 134> d') removing the photoresist layer.
  • the steps a') to c 1 ) follow the above description related to the corresponding steps of the method for manufacturing the spherical reflowed bump.
  • the deposition process performed in the step c') for preparing the mushroom bump is performed by depositing one material selected from the group consisting of a metal, a Pb- free metal, and a combination thereof by an electroplating or electro-less plating method, to have a height beyond the height of the photoresist layer.
  • FIG. 8 is a schematic view illustrating sequential steps of a method for manufacturing the mushroom bump according to a third embodiment of the present invention.
  • the photoresist layer 4 having an opening is formed on the chip 10 on which the patterned under bump metal 11 formed previously.
  • the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 50a.
  • FIG. 9 is a schematic view illustrating sequential steps of a method for manufacturing the mushroom bump according to a fourth embodiment of the present invention.
  • photoresist layers 4a and 4b each having an opening are formed on the chip 10 on which the patterned under bump metal 11 formed previously.
  • the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 60a.
  • a flip chip bonding method using the resulting flip chip bump comprises the steps of'-
  • the patterned under bump metal is formed on the chip, and then, the reflow spherical bumps or mushroom bumps are formed on the under bump metal.
  • the formation of the under bump metal and the bumps follows the above description.
  • the metal electrodes are formed on the substrate.
  • the substrate may be selected from the group consisting of a ceramic substrate, a glass substrate, a plastic substrate, a printed circuit substrate, and a flexible substrate, but is not limited thereto. That is, all kinds of substrates applicable to flip chip bonding are possible. Also, the metal electrodes are selectable from all kinds of metal materials used in the field of semiconductors.
  • the bumps are formed on the under bump metal of the chip.
  • the bumps may be metal bumps or Pb-free solder bumps.
  • the non-conductive adhesive is coated on the substrate to cover the metal electrodes.
  • the non-conductive adhesive may be a non- conductive adhesive conventionally used in this art, and a representative example thereof is epoxy based resin.
  • the chip and the substrate are aligned to face each other such that the bumps and the metal electrodes are electrically connected to each other, and then, are thermally compressed.
  • the thermal compression condition is adjustable depending on the kind of metals constituting the bumps
  • the thermal compression is preferably performed at a temperature of 200 "C or less, and more preferably, at a temperature range of 80-200 0 C, and most preferably, at a temperature range of 150-200 "C. If the thermal compression temperature is below the above range, it may cause incomplete curing of the adhesive and consequently, poor bonding. Conversely, if the thermal compression temperature exceeds the above range, it may cause degradation of the chip or substrate and thus, is uneconomical due to an increase of manufacturing costs.
  • pressure to be applied during the thermal compression is adjusted to a bonding pressure range of 20-100 MPa, and preferably, a range of 30-50 MPa. If the applied pressure is below the above range, the bumps may fail to come into contact of the metal electrodes. Conversely, if the applied pressure exceeds the above range, there is a risk of damage to the chip or substrate, or an uneconomical increase of manufacturing costs.
  • the thermal compression is performed within the above temperature and pressure ranges, thereby achieving an improved reliability of the flip chip joint.
  • FIG. 10 is a diagram illustrating a flip chip bonding method according to an embodiment of the present invention.
  • the bumps are spherical bumps.
  • metal electrodes 22 are formed on a substrate 20, and a non-conductive adhesive 70 is coated over the substrate 20 to cover the metal electrodes 22.
  • FIGS. 11 and 12 area diagrams illustrating a flip chip bonding method using mushroom bumps according to another embodiment of the present invention.
  • no reference numerals are designated to the corresponding elements for convenient illustration, and no under bump metal and non-conductive layer are illustrated.
  • FIG. 11 is a diagram illustrating a flip chip bonding method using mushroom bumps in which a column and a head thereof are made of the same material as each other.
  • the mushroom bumps are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes.
  • the chip and the substrate are bonded to each other via thermal compression.
  • the mushroom bumps can be plastically deformed upon receiving pressure even if the mushroom bumps have a difference in height. In this way, the bonding of the chip and the substrate can be accomplished.
  • FIG. 12 is a diagram illustrating a flip chip bonding method using composite mushroom bumps in which a column and a head thereof are made of heterogeneous materials.
  • the composite mushroom bumps are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes.
  • the column and the head of each composite mushroom bump are made of different materials from each other, and any one of the column and the head includes Sn.
  • the chip and the substrate are bonded to each other via thermal compression.
  • the mushroom bumps can be plastically deformed upon receiving pressure even if the mushroom bumps have a difference in height. In this way, the bonding of the chip and the substrate can be accomplished.
  • FIGS. 13 to 15 are diagrams illustrating a flip chip bonding method using mushroom bumps having pores according to different embodiments of the present invention.
  • FIG. 13 is a diagram illustrating a flip chip bonding method using mushroom bumps having pores formed in a head thereof according to another embodiment of the present invention.
  • the mushroom bumps each having pores formed in the head thereof are formed on the chip, and the chip is arranged to face the substrate formed with the metal electrodes.
  • the head of each mushroom bump is made of easily plastically deformable Sn or a Sn-based alloy.
  • the chip and the substrate are bonded to each other via thermal compression.
  • the bonding of the chip and the substrate can be accomplished even if the mushroom bumps have a difference in height.
  • the pores formed in the head of each bump can be reduced in size upon receiving pressure, thereby acting to compensate for the height difference between the mushroom bumps.
  • FIG. 14 is a diagram illustrating a flip chip bonding method using mushroom bumps having pores formed in a column thereof according to a further embodiment of the present invention.
  • the mushroom bumps each having pores formed in the column thereof are formed on the chip, and the chip is arranged to face the substrate formed with the metal electrodes.
  • the column of each mushroom bump is made of easily plastically deformable Sn or a Sn based alloy.
  • the chip and the substrate are bonded to each other via thermal compression.
  • the bonding of the chip and the substrate can be accomplished even if the mushroom bumps have a difference in height.
  • the pores formed in the column of the bump can be reduced in size upon receiving pressure, thereby acting to compensate for the height difference between the mushroom bumps.
  • FIG. 15 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in both the column and the head thereof according to a still further embodiment of the present invention.
  • the mushroom bumps each having pores formed in both the column and the head thereof are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes.
  • the column and the head of each mushroom bump are made of easily plastically deformable Sn or a Sn based alloy.
  • the chip and the substrate are bonded to each other via thermal compression.
  • the pores formed in the column and the head of the bump can be reduced in size, thereby acting to compensate for the height difference between the mushroom bumps. In this way, the bonding of the chip and the substrate can be accomplished.
  • the spherical reflowed bumps or mushroom bumps are formed for bonding of the chip and the substrate, and the bumps are made of a plastically deformable material, so as to achieve an improved reliability of the flip chip joint.
  • an average bonding pressure applied to each bump during the flip chip bonding is within a range of 15-100 mN/bump, and preferably, is approximately 20 mN/bump (2 g/bump, the size of the bump : 25//m x 25 ⁇ m).
  • a electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 ⁇ m. After coating a polyacrylic photoresist on the under bump metal on chip, ultraviolet light was exposed to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the bump metal on chip is exposed to the outside. Sn was deposited on the under bump metal inside the opening to have a thickness of 30 ⁇ m.
  • a reflow process was performed for 50 seconds while injecting a mixture gas of Ar and H2 (partial gas pressure ratio of 9:1) at a vacuum pressure of 270 mtorr and a temperature of 250 °C . Then, the photoresist layer was removed such that the Au on the ITO substrate and the spherical Sn refloweded bumps were formed on the ITO substrate. In this case, a bump pitch was 30 ⁇ m.
  • Example 1 Manufacture of column-shaped Sn bump ⁇ 187> This was performed in the same manner as Example 1 except for that the bump was formed by electroplating Sn without the reflow process.
  • Experimental Example 1 Analysis of bump shape ⁇ 189> A scanning electron microscope was used to inspect the shapes of the bumps obtained by Example 1 and Comparative Example 1, and the results were shown in FIGS. 16 and 17. :19O>
  • FIG. 16a is a scanning electron micrograph illustrating spherical Sn reflowed bumps prepared by Example 1
  • FIG. 16b is an enlarged micrograph of FIG. 16a.
  • FIG. 17a is a scanning electron micrograph illustrating Sn bumps prepared by Comparative Example 1
  • FIG. 17b is an enlarged micrograph of FIG. 17a.
  • ⁇ i9i> Referring to FIGS. 16 and 17, it can be understood that spherical Sn bumps were uniformly formed by Example 1 of the present invention, and that the column-shaped bumps were formed when not performing the reflow process.
  • FIG. 18 is an optical micrograph illustrating a sample that is bonded by use of spherical Sn reflowed bumps of Example 1, in which no non- conductive adhesive is trapped in the interface of the bumps
  • FIG. 19 is an optical micrograph illustrating a sample that is bonded by use of Sn bumps prepared by Comparative Example 1, in which a non-conductive adhesive is trapped in the interface of the bumps.
  • FIG. 20 is a scanning electron micrograph illustrating a sample that is bonded by use of the spherical Sn reflowed bums prepared by Example 1
  • FIG. 21 is a scanning electron micrograph illustrating the cross section of a sample that is bonded by use of the Sn bumps prepared by Comparative Example 1.
  • FIGS. 22a and 22b are scanning micrograph illustrating the cross sections of bumps that are bonded by pressure of 40 MPa and by pressure of 80 MPa, respectively.
  • a electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 ⁇ m. After coating a polyacrylic photoresist on the under bump metal, ultraviolet light was irradiated to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the electrode pad layer is exposed to the outside. Sn was deposited on the under bump metal within the opening to have a thickness of 35 ⁇ m, so as to cover a part of the upper surface of the photoresist layer.
  • a electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 ⁇ m. After coating a polyacrylic photoresist on the under bump metal, ultraviolet light was irradiated to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the under bump metal is exposed to the outside. Then, Sn was deposited on the under bump metal by a thickness of 20 ⁇ m, to have the same height as the photoresist layer, and Cu was deposited by a thickness of 15 ⁇ m to cover Sn and a part of the photoresist layer.
  • FIG. 23 is a scanning electron micrograph illustrating Sn mushroom bumps prepared by Example 2
  • FIG. 24 is a scanning electron micrograph illustrating Cu mushroom bumps prepared by Example 3.
  • FIG. 25a is a scanning electron micrograph illustrating Sn/Cu composite mushroom bumps prepared by Example 4, and
  • FIG. 25b is an enlarged micrograph of FIG. 25a.
  • FIG. 26 is a scanning electron micrograph illustrating column-shaped Cu bumps prepared by Comparative Example 2.
  • the mushroom bumps of Example 3 and Comparative Example 2 can achieve reduced contact resistance when the same pressure is applied thereto. Also, it can be understood that the mushroom bumps can be bonded at a lower pressure than that of the column- shaped bumps. Furthermore, it can be understood that the Sn bumps have a lower contact resistance value than that of the Cu bumps.
  • the bumps of Examples 2 to 4 according to the present invention have no trapping of the non-conductive adhesive.
  • the column-shaped bumps of Comparative Example 2 exhibit a serious bonding failure rate of 30%.
  • Example 5 ⁇ 228> This was performed in the same manner as Example 4 except for that an Ag oxidation-resistant film was formed on a surface of the Sn/Cu (column/head) composite mushroom bump.
  • Example 6 ⁇ 230> This was performed in the same manner as Example 5 except for depositing Ni instead of Cu, to prepare a Sn/Ni (column/head) composite mushroom bump. [Industrial Applicability]
  • the flip chip bonding method of the present invention can be efficiently used in displays using a chip-on glass (COG) and chip-on plastic (COP), image sensor packages, low-temperature flip chip bonding packages, etc.
  • COG chip-on glass
  • COP chip-on plastic

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Abstract

Disclosed are a flip chip bump (30), a manufacturing method thereof, and a flip chip bonding method using a non-conductive adhesive (70). More particularly, disclosed are a flip chip bump (30) having a spherical or mushroom shape, which can increase the effect of plastic deformation by virtue of a low pressure applied during flip chip bonding and achieve improved durability by reducing the trapping of a non-conductive adhesive (70) therein and consequently, improved reliability of the bonding joint, a method for manufacturing the flip chip bump (30), and a flip chip bonding method.

Description

[DESCRIPTION]
[Invention Title]
FLIP CHIP MOUNT TYPE OF BUMP, MANUFACTURING METHOD THEREOF, AND BONDING METHOD FOR FLIP CHIP USING NON CONDUCTIVE ADHESIVE
[Technical Field]
<i> The present invention relates to a flip chip bump, a manufacturing method thereof, and a flip chip bonding method using a non-conductive adhesive, and more particularly, to a flip chip bump which can increase the effect of plastic deformation by virtue of a low pressure applied during flip chip bonding and achieve improved durability by reducing the trapping of a non-conductive adhesive therein, a method for manufacturing the flip chip bump, and a flip chip bonding method.
[Background Art]
<2> In accordance with the tendency of modern digitalization and informationization, demand for a variety of electronic products is rapidly increasing and the electronic products are much smaller, lighter and faster, and have better performance. Thereby, there is an urgent requirement of a technical development for manufacturing highly reliable electronic devices with low costs. One of important techniques for realizing the technical development is an electronic packaging technique.
<3> Current semiconductor techniques pursue a line width of a micron or less, cells of a million or more, faster performance, better heat emission, etc. However, semiconductor packaging techniques are backward relative to other semiconductor techniques, and thus, in most cases, the performance of semiconductors is determined by packaging and incidental electric interconnection methods.Actual Iy, the delay of overall electric signals caused in high-speed electronic products mostly occurs by the package delay between chips. To solve this problem, a variety of semiconductor packaging techniques have been developed in the order of a thin small outline package (TSOP), a ball grid array (BGA), a chip size package (CSP), and a flip chip technique. <4> A flip chip technique using solder bumps has been developed in various manners since it has proposed by IBM Corp. in the 1960s. Of a variety of flip chip techniques, a Controlled-Collapse Chip Connection (C4) technique of IBM Corp. is a technique in which a chip and a substrate are bonded to each other by melting a 95Pb-5Sn or 97Pb-3Sn solder having a high melting point at a high temperature of 3000C or more. However, such the C4 technique has the drawback of damage to the substrate, etc. because of excessive thermal energy caused by the high-temperature bonding process of 300°C or more. The C4 technique also has the drawback of degradation in the reliability of the resulting flip chip structure due to thermal expansion caused by a great temperature difference. To solve the problem of the high temperature bonding process, a flip chip technique for bonding a chip to a substrate via a reflow process of a Pb-Sn solder having a low melting point of 182°C has been developed and used, but this technique causes environmental pollution via Pb.
<5> Accordingly, a method using a low melting-point solder such as a Sn-Bi solder has proposed. However, this has a drawback of degradation in the reliability of a bonded joint due to an intermetallic compound that is produced by a reaction between a liquid-phase solder and an under bump metal in the course of mounting or bonding the solder. Most conventional methods using the reflow of a solder should include a solder flux coating process, a residual flux removal process, an under-fill process, etc., and therefore, suffer from drawbacks of complicated processes and expensive manufacturing costs.
<6> In addition, there have proposed bonding methods using a conductive adhesive or conductive film, for example, an anisotropic conductive adhesive (ACA), anisotropic conductive film (ACF), or isotropic conductive adhesive. In these bonding methods, conductive particles are physically captured and bonded between bumps and electrodes upon receiving a predetermined pressure and heat applied thereto.
<7> Of the above methods, a bonding method using ACF is widely used in techniques for mounting drive devices to information displays including a thin film transistor-liquid crystal display (TFT-LCD). In this bonding method, after ACF having conductive particles uniformly distributed in an adhesive is located between Au bumps of a drive device and electrodes of an LCD panel, pressure and heat are applied to the ACF such that the conductive particles are captured and bonded between the bumps and the electrodes.
<8> Generally, examples of a metal bump for use in an ACF process include an Au bump formed by electroplating, and an Au/Ni bump formed by electroless- plating. The Au bump is the most widely used bump by virtue of superior heat conductivity and electric conductivity as well as a high physical or chemical stability thereof. The Au/Ni bump prepared by electroless-plating is also widely used because it ensures selective bump formation without a photolithography process and omits a vacuum deposition process and thus, can reduce manufacturing costs of the bump.
<9> The method using an ACF has been preferred because it is more eco- friendly than the methods using a solder bump and has advantages of a low- temperature process, simplified overall process and high reliability. However, the method using an ACF has the problem that the bonding area obtained by the conductive particles included in the ACF is much smaller than the area of the bump, thus causing an increased contact resistance. In addition, the smaller the pitch of bumps, the risk of a short circuit between the bumps increases, and excessive contact resistance or poor bonding may be caused by a reduced size of the bumps.
<io> To compensate for the above described problems, methods using a double layer ACF (Hitachi), an area array ACF (Sumitomo), a dielectric dam (Samsung), a micro-connector (Casio), etc. have been developed, but these methods are rarely used currently because of their complicated process and high manufacturing costs.
<ii> Recently, the study about a flip chip bonding technique using a metal bump and a non-conductive adhesive (NCA) has been active. d2> A bonding method using a non-conductive adhesive uses a mechanical contact between the metal bump and a metal pad. In this bonding method, since the non-conductive adhesive is usable in the form of a paste or film, and a bonding process can be performed at a curing temperature of the adhesive, the overall process can be performed at a relatively low temperature in a simplified manner. Also, if necessary, the adhesive can be cured by ultraviolet light rather than heat, and this makes a heating process unnecessary. The bonding method using the non-conductive adhesive has various advantages of facilitating the formation of a fine pitch, reducing manufacturing costs, and achieving superior electric properties via a reduced contact resistance between the metal bump and the metal pad.
<13> However, when using the non-conductive adhesive, there may occur a trapping phenomenon in which a part of the non-conductive adhesive remained between the bump and the pad during bonding.
<14> FIGS. Ia and Ib are diagrams illustrating the trapping phenomenon caused when using the non-conductive adhesive. Referring to FIG. Ia, to bond a substrate 120 having metal electrodes 102 and an IC chip 110 to each other, bumps 101 are formed on the IC chip 110 and a non-conductive adhesive is coated therebetween. Then, if pressure and heat are applied to bond the chip 110 to the substrate 120, as shown in FIG. Ib, a part of the non-conductive adhesive 103 may trap into a region A between each bump 101 and the corresponding metal electrode 102. The trapped non-conductive adhesive 103 acts to increase a contact resistance between the bump 101 and the metal electrode 102 and in the worst case, causes a short circuit.
<15> Meanwhile, metal bumps for use on chips have been manufactured by an electroplating method, an electro-less plating method, or a method using a stud bump, and Au is the most widely used material for the manufacture of the metal bumps. However, since Au has a high yield strength of 30MPa and a high hardness HB of approximately 20, Au needs a relatively high pressure, for bonding thereof.
<16> As a representative example of the method using a stud bump, U.S. Patent No. 5,928,458 discloses a method in which an Au stud bump is prepared and is plastically deformed by use of a high pressure of 80-100 g/bump (784- 980 mN/burap) . <17> Korean Patent Laid-open Publication No. 2001-0104626 discloses a bonding method using an Au ball bump under pressure of 980 mN/bump (100 g/bump). <18> A paper published in Thin Solid Films discloses a technique in which an
Au/Ni bump is prepared by an electro-less plating method and compressed by
2 pressure of 1000 kgf/cm , for bonding thereof (cf. Development and reliability of non-conductive adhesive flip chip packages).
<i9> WO No. 2001-052317 discloses a bonding method using a bump made of an easily plastic-deformable Sn-Pb alloy. However, the recent trend is to use a Pb-free solder in accordance with various environmental regulations restricting the use of Pb.
<20> As a representative example, Korean Patent Laid-open Publication No. 1998-0085069 discloses a bonding method using a Sn-Ag alloy bump. Also, Japanese Patent Laid-open Publication No. Hll-0010385 discloses a method for manufacturing a bump using Sn-Ag and Sn-Cu alloys. Japanese Patent Laid-open Publication No. 2000-0077448 discloses a bump using a Sn-Ag-In alloy and a bonding method using the same. In this method, a chip is bonded to a substrate via a reflow process performed at a temperature more than a melting point of the Sn-based alloy.
<2i> The Sn-based alloy is advantageous for easy plastic deformation, but has a limit in the formation of the bump. It is well known that the above described limit can be efficiently conquered by preparing a bump by use of an easily plastically deformable material to have a geometrical shape suitable for easy plastic deformation.
<22> A paper published in IEEE Trans on Electronic Packaging Manufacturing (cf. The flip chip bump interconnection for millimeter-wave GaAs MMIC) proposes to maximize the effect of plastic deformation by use of an acute tail bump having not passed through a coining process. However, when a large number of bumps have to be formed, the method has a limit in its use because of a slow bump forming speed thereof. <23> In the case of conventionally used Au bumps, they have been manufactured by an electroplating or electro-less plating method and thus, are difficult to achieve a uniform bump height on the nature of the plating method.
<24> FIGS. 2a and 2b are diagrams illustrating a flip chip bonding using bumps having different heights from each other. Referring to FIGS. 2a and 2b, to bond a substrate 220 having metal electrodes 202 and an IC chip 210 to each other, bumps 201 are formed on the chip 210. In this case, if the bumps 201 have a height deviation, bonding using the bumps 201 causes the bumps 201 to fail to come into contact with the metal electrodes 202 as illustrated in the region B of FIG. 2b, thereby resulting in poor bonding between the substrate 200 and the chip 210.
<25> To solve the above problem, although U.S. Patent No. 6,930,399 discloses a technique in which Au stud bumps are subjected to a coining process to achieve a uniform height, the disclosed technique has the drawback that the coining process needs a high pressure and is complicated.
<26> To solve the problem of the conventional process, U.S. Patent No. 6,791,195 discloses Au ball bumps formed by a stud bumping method. However, when using only the stud bumping method without a reflow process, preparation of the ball bumps is difficult. Moreover, since the ball bumps are formed one by one by use of a wire bonder, the greater the number of bumps, the process time may increase excessively. [Disclosure] [Technical Problem]
<27> Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a flip chip bump which can allow a geometrical plastic deformation at a low pressure by a simplified process and improve the reliability of a bonded joint, a method for manufacturing the flip chip bump, and a flip chip bonding method using a non-conductive adhesive. [Technical Solution] <28> In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a flip chip bump comprising'- a chip", a plurality of patterned under bump metal formed on the
' chip! and a spherical reflowed bump or mushroom bump formed on the under bump metal .
<29> In this case, the spherical reflowed bump and the mushroom bump may comprise any one material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn and alloys thereof. Preferably, the bump comprises a single metal bump, or a Pb-free solder bump comprising pure Sn, or a Sn-metal alloy containing any one selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof .
<30> Preferably, the mushroom bump has a column and a head, and the column and the head are made of the same material as each other or different materials from each other. More preferably, the column and the head of the mushroom bump comprises pure Sn, or a Sn-metal alloy containing Sn and any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag and Zn and alloys thereof, or any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof. Most preferably, the column is made of pure Sn, or the Sn-metal alloy containing Sn, and the head is made of the Sn-metal alloy, or a metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof.
<3i> If necessary, the mushroom bump has pores formed therein. The pores may be formed in the column or head of the mushroom bump, or in both the column and head.
<32> The spherical reflowed bump and mushroom bump further comprises an oxidation-resistant film, and the oxidation-resistant film comprises a material selected from the group consisting of Ag, Au and Pt.
<33> In accordance with another aspect of the present invention, there is provided a method for manufacturing a spherical reflowed bump comprising:
<34> a) forming a plurality of patterned under bump metal on the chip;
<35> b) coating a photoresist on the patterned under bump metal and etching 2007/000032
the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside; and
<36> c) depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, and then, performing a reflow process, so as to manufacture the spherical reflowed bump.
<37> Before or after the reflow process of the step c), the method further comprises removing the photoresist layer.
<38> In accordance with a further aspect of the present invention, there is provided a method for manufacturing a mushroom bump comprising:
<39> a1) forming the plurality of patterned under bump metal on the chip;
<4o> b') coating a photoresist on the patterned under bump metal and developing the photoresist, to form a photoresist layer having an opening, through which a part of under bump metal is exposed to the outside;
<4i> c') depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, so as to manufacture the mushroom bump; and
<42> d') removing the photoresist layer.
<43> In this case, the mushroom bump is formed by depositing the material selected from the group consisting of a metal, Pb-free metal, and a combination thereof, to have a height higher than the photoresist layer. Preferably, the mushroom bump has a column and a head. The column and the head may be formed by depositing the same material, or may be formed by depositing two or more different materials from each other.
<44> In accordance with yet another aspect of the present invention, there is provided a flip chip bonding method using a flip chip bump comprising:
<45> forming the plurality of patterned under bump metal on the chip;
<46> forming a spherical reflowed bump or mushroom bump on the patterned under bump metal;
<47> forming a metal electrode on a substrate;
<48> coating a non-conductive adhesive to cover the metal electrode; and <49> aligning the chip and the substrate to face each other and thermally compressing the chip and the substrate. <50> Preferably, the thermal compression is performed at a temperature of
200°C or less, and preferably, at a temperature range of 80-200°C .
Preferably, pressure applied upon the thermal compression is within a range of 20-100MPa.
[Advantageous Effects]
<52> According to the present invention, a spherical or mushroom shaped bump can be prepared with a simplified process, to enable the manufacture of a so- called "spherical reflowed bump" or "mushroom bump". The bump can allow geometrical plastic deformation thereof under a low pressure and this results in an improved reliability in the bonded joint of the resulting flip chip bump. [Description of Drawings]
<53> The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which".
<54> FIGS. Ia and Ib are diagrams illustrating a trapping phenomenon caused when using a non-conductive adhesive;
<55> FIGS. 2a and 2b are diagrams illustrating a flip chip bonding using bumps having a height difference;
<56> FIGS. 3a and 3b are sectional views illustrating a chip formed with spherical reflowed bumps and a chip formed with mushroom bumps, respectively;
<57> FIGS. 4a and 4b are sectional views of different examples of composite mushroom bumps according to the present invention;
<58> FIGS. 5a to 5c are sectional views of different examples of mushroom bumps having pores according to the present invention;
<59> FIG. 6 is a schematic view illustrating sequential steps of a method for manufacturing spherical reflowed bumps according to a first embodiment of the present invention;
<60> FIG. 7 is a schematic view illustrating sequential steps of a method for manufacturing spherical reflowed bumps according to a second embodiment of the present invention;
<6i> FIG. 8 is a schematic view illustrating sequential steps of a method for manufacturing mushroom bumps according to a third embodiment of the present invention;
<62> FIG. 9 is a schematic view illustrating sequential steps of a method 32
11
for manufacturing mushroom bumps according to a fourth embodiment of the present invention; <63> FIG. 10 is a diagram illustrating a flip chip bonding method according to an embodiment of the present invention; <64> FIG. 11 is a diagram illustrating a flip chip bonding method using mushroom bumps each having a column and a head made of the same material as each other; <65> FIG. 12 is a diagram illustrating a flip chip bonding method using composite mushroom bumps each having a column and a head made of heterogeneous materials! <66> FIG. 13 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in a head thereof according to another embodiment of the present invention; <67> FIG. 14 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in a column thereof according to a further embodiment of the present invention; <68> FIG. 15 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in both a column and a head thereof according to a still further embodiment of the present invention; <69> FIG. 16a is a scanning electron micrograph illustrating spherical Sn reflowed bumps prepared by Example 1, and FIG. 16b is an enlarged micrograph of FIG. 16a; <70> FIG. 17a is a scanning electron micrograph illustrating Sn bumps prepared by Comparative Example 1, and FIG. 17b is an enlarged micrograph of
FIG. 17a; <7i> FIG. 18 is an optical micrograph illustrating a sample that is bonded by use of spherical Sn reflowed bumps of Example 1, in which no non- conductive adhesive is trapped in the interface of the bumps; <72> FIG. 19 is an optical micrograph illustrating a sample that is bonded by use of Sn bumps of Comparative Example 1, in which a non-conductive adhesive is trapped in the interface of the bumps; <73> FIG. 20 is a scanning electron micrograph illustrating a sample that is bonded by use of spherical Sn reflowed bumps of Example 1, in which substantially no non-conductive adhesive is trapped in the interface of the bumps! <74> FIG. 21 is a scanning electron micrograph illustrating a sample that is bonded by use of Sn bumps of Comparative Example 1, in which a non-conductive adhesive is trapped in the interface of the bumps; <75> FIGS. 22a and 22b are scanning electron micrographs illustrating a bump bonding under pressure of 40 MPa and a bump bonding under pressure of 80 MPa, respectively; <76> FIG. 23 is a scanning electron micrograph illustrating Sn mushroom bumps prepared by Example 2; <77> FIG. 24 is a scanning electron micrograph illustrating Cu mushroom bumps prepared by Example 3; <78> FIG.25a is a scanning electron micrograph illustrating Sn/Cu composite mushroom bumps prepared by Example 4, and FIG. 25b is an enlarged optical micrograph illustrating the cross section of the Sn/Cu composite mushroom bump; and <79> FIG. 26 is a scanning electron micrograph illustrating column-shaped Cu bumps prepared by Comparative Example 2.
[Best Mode]
<80> Flip chip bump <8i> A flip chip bump according to the present invention has a spherical or mushroom shape. Herein, the term "spherical reflowed bump" means a spherical bump processed by a reflow process. Also, the term "mushroom bump" represents a mushroom-shaped bump prepared by a plating process without a reflow process.
<82> The flip chip bump according to the present invention comprises: <83> a chip;
<84> a plurality of patterned under bump metal formed on the chip; and <85> spherical reflowed bumps or mushroom bumps formed on the under bump metal.
<86> FIG. 3a is a sectional view illustrating a chip formed with spherical reflowed bumps, and FIG. 3b is a sectional view illustrating a chip formed with mushroom bumps.
<87> Referring to FIG. 3a, the flip chip bump according to an exemplary embodiment of the present invention includes a chip 10, a plurality of patterned under bump metal 11 formed on the chip 10, and spherical reflowed bumps 30 formed on the under bump metal 11.
<88> Referring to FIG. 3b, the flip chip bump according to another exemplary embodiment of the present invention includes a chip 10, a plurality of patterned under bump metal 11 formed on the chip 10, and mushroom bumps 50 formed on the under bump metal 11.
<89> The spherical reflowed bumps 30 or mushroom bumps 50 may be any ones selected from metal bumps and Pb-free solder bumps.
<9o> The present invention has no special limit in the constituent material of the under bump metal, and any materials used in the field of semiconductors are available.
<9i> In particular, the bumps according to the present invention comprise any one material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn and alloys thereof. Preferably, the bumps include single metal bumps, or Pb-free solder bumps comprising pure Sn, or a Sn-metal alloy containing any one alloy selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof .
<92> Preferably, the content of the metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof is less than 5 wt% on the basis of the overall Sn- metal alloy. More preferably, the Sn-metal alloy may be a Sn-Ni or Sn-Cu alloy. The alloying component has the function of lowering the surface tension and melting point of Sn, thereby achieved improved ductility and superior bonding properties via plastic deformation.
<93> The mushroom bump 50 is divided into a column and a head. In this case, the column and the head may be made of the same material as each other. Alternatively, the mushroom bump 50 may be a composite mushroom bump in which the column and the head are made of heterogeneous materials. Preferably, the column and the head of the composite mushroom bump comprises pure Sn, or a Sn-metal alloy containing Sn and any one metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof, or a single metal selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof. Here, it is noted that the head and the column of the composite mushroom bump are made of different materials from each other. For example, the column is made of Sn and the head is made of Cu or Ni, to prepare a Sn/Cu or Sn/Ni (column/head) bump. Conversely, the column is made of Cu or Ni and the head is made of Sn, to prepare a Cu/Sn, Ni/Sn (column/head) bump.
<94> FIGS. 4a and 4b are cross-sectional views of different examples of the composite mushroom bump according to the present invention.
<95> Referring to FIG.4a, the composite mushroom bump formed on the chip 10 includes a column 7a made of Cu or Ni and a head 8a made of Sn. Referring to FIG. 4b, the composite mushroom bump formed on the chip 10 includes a column 7a made of Sn and a head 8b made of Cu or Ni .
<96> The spherical reflowed bump or mushroom bump according to the present invention is configured to have pores therein if necessary. The pores have the function of allowing stress, caused by pressure applied during bonding of the chip and the substrate, to be concentrated therein, thereby increasing the effect of plastic deformation even when a low pressure is applied. The bump having the pores may a variety of shapes as shown in FIGS. 5a to 5c, by changing various conditions of, for example, an electroplating, such as the density of current, pH of a plating solution, and other pretreatment conditions, etc.
<97> FIGS. 5a to 5c are cross-sectional views illustrating different examples of the mushroom bump having pores according to the present invention.
<98> The mushroom bump shown in FIG. 5a includes a column 7 formed with pores 21 and a head 8. The mushroom bump shown in FIG. 5b includes a column 7 and a head 8 formed with pores 21. Also, the mushroom bump shown in FIG. 5c includes a column 7 and a head 8, which are formed with pores 21. <99> By preparing the spherical or mushroom-shaped bumps using a plastically deformable metal material, it is possible to prevent the problem of poor bonding caused by a height difference of the bumps. <ioo> The spherical reflowed bump or mushroom bump may further include an oxidation-resistant film, and the oxidation-resistant film includes a material selected from the group consisting of Ag, Au, and Pt. <ioi> Method for manufacturing a flip chip bump <iO2> In one embodiment of the present invention, a method for manufacturing a flip chip bump including the above described spherical reflowed bump comprising the steps of: <iO3> a) forming a plurality of patterned under bump metal formed on the chip; <iO4> b) coating a photoresist on the patterned under bump metal and developing the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside; and <iO5> c) depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, and then, performing a reflow process, to prepare the spherical reflowed bump. <iO6> The method further comprises: before or after the reflow process of the step c), the step of removing the photoresist layer. <iO7> Specifically, in the first step a), the under bump metal is formed on the chip, and then, under bump metal patterns is formed via conventional etching processes. <iO8> The present invention has no limit in a deposition process for forming the under bump metal. The deposition process may be any one selected from the group consisting of a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an electro-less plating process, and an electroplating process. <iO9> In the step b), after the photoresist is coated on the patterned under bump metal, the coated photoresist is developed such that the resulting photoresist layer has an opening, through which a part of the under bump metal is exposed to the outside. Here, the photoresist may be a positive photoresist or negative photoresist.
<iio> Specifically, after coating the photoresist on the under bump metal, the photoresist is subjected to baking and patterning processes, so as to form the photoresist layer having the opening. In this case, the thickness of the photoresist layer and the size of the opening are factors of determining the shape of a finally prepared bump.
<πi> For example, when a bump forming material is deposited by a height lower than the height of the photoresist layer, a spherical bump is prepared. On the other hand, when the bump forming material is deposited by a height higher than the height of the photoresist layer, a mushroom bump is prepared. In this case, the shape of the mushroom bump can be changed by using two or more photoresist layers as occasion demands.
<ii2> In the step c), the material selected from the group consisting of a metal, Pb-free metal, and a combination thereof is deposited on the under bump metal inside the opening, and the deposited material is subjected to a reflow process, so as to prepare the spherical reflowed bump. In this case, the shape of the bump can be changed by removing the photoresist layer before or after performing the reflow process.
<ii3> The material deposited inside the opening may be a material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn, and alloys thereof, so as to prepare a single metal bump, or may be pure Sn or a Sn- metal alloy containing Sn and any one metal selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof, so as to prepare a Pb-free solder bump. Also, as occasion demands, the Pb-free solder bump takes the form of an alloy using Sn and any one selected from Au, Cu, Ni, Bi, In, Ag, Zn, and alloys thereof. Preferably, a Sn-Ni or Sn-Cu bump is possible.
<ii4> In this case, the deposition of the bump forming material is performed 17 WJI SM I J< VS, ύWt»
by aligning a metal mask with the under bump metal and then, performing a vacuum deposition process, an electroplating or electro-less plating, a stud bumping process using a wire bonder, or a screen or stencil printing process.
<ii5> The reflow process is performed in a conventional manner. With the implementation of the reflow process, the deposited layer can vary under the influence of a surface tension thereof and the photoresist layer can serve as a dam, to enable the preparation of an arched spherical bump. In addition to providing the spherical bump, the reflow process serves to achieve a uniform bump composition, a uniform bump height, and an increased bonding strength between the under bump metal and the bump.
<ii6> Preferably, the reflow process is performed within a predetermined reflow time range of 0.1-120 seconds under a vacuum condition of 150-300 mtorr by flow of a mixture gas comprising 85-95 wt% of Ar and 5-15 wt% of H2.
In one example for preparing a Sn bump, the reflow process is performed at a temperature more than 2320C that is a melting point of Sn, preferably, at a temperature higher than the melting point of Sn by 20-30°C, and more preferably, at a temperature range of 232-280°C, so as to prepare a spherical reflowed bump having a ball shape.
<ii7> The present invention also has no limit in the removal of the photoresist layer, and the photoresist layer is removed by a conventional method that is well known in the art by those skilled in the art.
<ii8> Additionally, the spherical reflowed bump is subjected to an oxidation- resistant film forming process.
<ii9> The oxidation-resistant film includes one material selected from the group consisting of Ag, Au, and Pt, and is prepared by a conventional deposition method.
<12O> FIG. 6 is a schematic view illustrating sequential steps of the method for manufacturing the spherical reflowed bump according to a first embodiment of the present invention.
<i2i> Referring to FIG. 6a, a photoresist layer 4 having an opening is formed on the chip 10 on which the under bump metal 11 was previously formed via a plurality of patterning processes. <i22> Referring to FIG. 6b, the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 30a. <i23> Referring to FIG. 6c, the photoresist layer 4 is removed such that only the under bump metal 11 and the bump forming layer 30a are remained on the chip 10. <i24> Referring to FIG. 6d, as a result of performing the reflow process, the shape of the bump forming layer 30a varies into a spherical shape under the influence of a surface tension thereof, thereby preparing a flip chip bump formed with the reflow bump 30. <i25> FIG. 7 is a schematic view illustrating sequential steps of a method for manufacturing the spherical reflowed bump according to a second embodiment of the present invention. <126> Referring to FIG. 7a, the photoresist layer 4 having an opening is formed on the chip 10 on which the under bump metal formed previously 11. <i27> Referring to FIG. 7b, the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 40a. <128> Referring to FIG.7c, as a result of performing the reflow process, the shape of the bump forming layer 40a varies to form an arched spherical bump
40. <129> Referring to FIG. 7d, the photoresist layer 4 is removed such that only the under bump metal 11 and the spherical bump 40 are remained on the chip
10, to complete a flip chip bump. <13O> In another embodiment of the present invention, a method for manufacturing the flip chip bump including the mushroom bump according to the present invention comprises the steps of:
<131> a1) forming a plurality of patterned under bump metal on the chip; <132> b1) coating a photoresist on the patterned under bump metal and etching the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside," <133> c') depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, so as to prepare a mushroom bump; and <134> d') removing the photoresist layer. <135> The steps a') to c1) follow the above description related to the corresponding steps of the method for manufacturing the spherical reflowed bump. <136> In the method of the present embodiment, the deposition process performed in the step c') for preparing the mushroom bump is performed by depositing one material selected from the group consisting of a metal, a Pb- free metal, and a combination thereof by an electroplating or electro-less plating method, to have a height beyond the height of the photoresist layer.
In this case, the column and the head of the mushroom bump may be formed via deposition of a single material, or may be formed of different materials from each other. <137> FIG. 8 is a schematic view illustrating sequential steps of a method for manufacturing the mushroom bump according to a third embodiment of the present invention. <138> Referring to FIG. 8a, the photoresist layer 4 having an opening is formed on the chip 10 on which the patterned under bump metal 11 formed previously. <139> Referring to FIG. 8b, the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 50a. <i40> Referring to FIG. 8c, the photoresist layer 4 is removed, to prepare a flip chip bump in which the under bump metal 11 and the mushroom bump 50 are formed on the chip 10. <i4i> FIG. 9 is a schematic view illustrating sequential steps of a method for manufacturing the mushroom bump according to a fourth embodiment of the present invention. <142> Referring to FIG. 9a, photoresist layers 4a and 4b each having an opening are formed on the chip 10 on which the patterned under bump metal 11 formed previously. <143> Referring to FIG. 9b, the bump forming material is deposited on the exposed under bump metal 11 inside the opening, to form a layer 60a.
<144> Referring to FIG. 9c, the photoresist layers 4a and 4b are removed, to prepare a flip chip bump in which the under bump metal 11 and a mushroom bump 60 are formed on the chip 10.
<i45> Flip chip bonding method using the flip chip bump
<146> A flip chip bonding method using the resulting flip chip bump comprises the steps of'-
<147> forming a plurality patterned under bump metal on a chip;
<148> forming spherical reflowed bumps or mushroom bumps on the patterned under bump metal;
<149> forming metal electrodes on a substrate;
<15O> coating a non-conductive adhesive to cover the metal electrodes; and
<i5i> aligning the chip and the substrate to face each other and thermally compressing the chip and the substrate.
<152> Specifically, the patterned under bump metal is formed on the chip, and then, the reflow spherical bumps or mushroom bumps are formed on the under bump metal. The formation of the under bump metal and the bumps follows the above description.
<i53> Next, the metal electrodes are formed on the substrate. The substrate may be selected from the group consisting of a ceramic substrate, a glass substrate, a plastic substrate, a printed circuit substrate, and a flexible substrate, but is not limited thereto. That is, all kinds of substrates applicable to flip chip bonding are possible. Also, the metal electrodes are selectable from all kinds of metal materials used in the field of semiconductors.
<i54> Subsequently, the bumps are formed on the under bump metal of the chip. As described above, the bumps may be metal bumps or Pb-free solder bumps.
<155> Thereafter, the non-conductive adhesive is coated on the substrate to cover the metal electrodes. The non-conductive adhesive may be a non- conductive adhesive conventionally used in this art, and a representative example thereof is epoxy based resin.
<156> Next, the chip and the substrate are aligned to face each other such that the bumps and the metal electrodes are electrically connected to each other, and then, are thermally compressed.
<157> Although the thermal compression condition is adjustable depending on the kind of metals constituting the bumps, the thermal compression is preferably performed at a temperature of 200 "C or less, and more preferably, at a temperature range of 80-200 0C, and most preferably, at a temperature range of 150-200 "C. If the thermal compression temperature is below the above range, it may cause incomplete curing of the adhesive and consequently, poor bonding. Conversely, if the thermal compression temperature exceeds the above range, it may cause degradation of the chip or substrate and thus, is uneconomical due to an increase of manufacturing costs.
<158> Also, pressure to be applied during the thermal compression is adjusted to a bonding pressure range of 20-100 MPa, and preferably, a range of 30-50 MPa. If the applied pressure is below the above range, the bumps may fail to come into contact of the metal electrodes. Conversely, if the applied pressure exceeds the above range, there is a risk of damage to the chip or substrate, or an uneconomical increase of manufacturing costs. In the present invention, the thermal compression is performed within the above temperature and pressure ranges, thereby achieving an improved reliability of the flip chip joint.
<159> FIG. 10 is a diagram illustrating a flip chip bonding method according to an embodiment of the present invention. In this case, the bumps are spherical bumps.
<i60> Referring to FIGS. 10a and 10b, the under bump metal 11 and the spherical reflowed bumps 30 are formed on the chip 10.
<i6i> Referring to FIGS. 10c and 1Od, metal electrodes 22 are formed on a substrate 20, and a non-conductive adhesive 70 is coated over the substrate 20 to cover the metal electrodes 22.
<i62> Referring to FIGS. 1Oe and 1Of, after aligning the chip 10 and the substrate 20 to face each other, the chip 10 and the substrate 20 are thermally compressed, to achieve a flip chip bonding using the spherical reflowed bumps 30.
<163> FIGS. 11 and 12 area diagrams illustrating a flip chip bonding method using mushroom bumps according to another embodiment of the present invention. In these drawings, no reference numerals are designated to the corresponding elements for convenient illustration, and no under bump metal and non-conductive layer are illustrated.
<164> First, FIG. 11 is a diagram illustrating a flip chip bonding method using mushroom bumps in which a column and a head thereof are made of the same material as each other.
<165> Referring to FIG. 11a, the mushroom bumps are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes. Referring to FIG. lib, the chip and the substrate are bonded to each other via thermal compression. In this case, as a result of forming the mushroom bumps with a plastically deformable material, the mushroom bumps can be plastically deformed upon receiving pressure even if the mushroom bumps have a difference in height. In this way, the bonding of the chip and the substrate can be accomplished.
<166> FIG. 12 is a diagram illustrating a flip chip bonding method using composite mushroom bumps in which a column and a head thereof are made of heterogeneous materials.
<167> Referring to FIG. 12a, the composite mushroom bumps are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes. In this case, the column and the head of each composite mushroom bump are made of different materials from each other, and any one of the column and the head includes Sn.
<168> Referring to FIG. 12b, the chip and the substrate are bonded to each other via thermal compression. In this case, as a result of forming any one of the column and the head of the composite mushroom bump with a plastically deformable material, the mushroom bumps can be plastically deformed upon receiving pressure even if the mushroom bumps have a difference in height. In this way, the bonding of the chip and the substrate can be accomplished.
<i69> FIGS. 13 to 15 are diagrams illustrating a flip chip bonding method using mushroom bumps having pores according to different embodiments of the present invention.
<17O> FIG. 13 is a diagram illustrating a flip chip bonding method using mushroom bumps having pores formed in a head thereof according to another embodiment of the present invention.
<i7i> Referring to FIG. 13a, the mushroom bumps each having pores formed in the head thereof are formed on the chip, and the chip is arranged to face the substrate formed with the metal electrodes. In this case, the head of each mushroom bump is made of easily plastically deformable Sn or a Sn-based alloy.
<i72> Referring to FIG. 13b, the chip and the substrate are bonded to each other via thermal compression. In this case, as a result of forming the head of the mushroom bump with the plastically deformable material, the bonding of the chip and the substrate can be accomplished even if the mushroom bumps have a difference in height. Also, the pores formed in the head of each bump can be reduced in size upon receiving pressure, thereby acting to compensate for the height difference between the mushroom bumps.
<173> FIG. 14 is a diagram illustrating a flip chip bonding method using mushroom bumps having pores formed in a column thereof according to a further embodiment of the present invention.
<174> Referring to FIG. 14a, the mushroom bumps each having pores formed in the column thereof are formed on the chip, and the chip is arranged to face the substrate formed with the metal electrodes. In this case, the column of each mushroom bump is made of easily plastically deformable Sn or a Sn based alloy.
<i75> Referring to FIG. 14b, the chip and the substrate are bonded to each other via thermal compression. In this case, as a result of forming the column of the mushroom bump with the plastically deformable material, the bonding of the chip and the substrate can be accomplished even if the mushroom bumps have a difference in height. Also, the pores formed in the column of the bump can be reduced in size upon receiving pressure, thereby acting to compensate for the height difference between the mushroom bumps.
<i76> FIG. 15 is a diagram illustrating a flip chip bonding method using mushroom bumps each having pores formed in both the column and the head thereof according to a still further embodiment of the present invention.
<177> Referring to FIG. 15a, the mushroom bumps each having pores formed in both the column and the head thereof are formed on the chip, and the chip is aligned to face the substrate formed with the metal electrodes. In this case, the column and the head of each mushroom bump are made of easily plastically deformable Sn or a Sn based alloy.
<178> Referring to FIG. 15b, the chip and the substrate are bonded to each other via thermal compression. In this case, as the column and the head of the mushroom bump are plastically deformed upon receiving pressure applied upon the thermal compression, the pores formed in the column and the head of the bump can be reduced in size, thereby acting to compensate for the height difference between the mushroom bumps. In this way, the bonding of the chip and the substrate can be accomplished.
<179> As stated above, in the present invention, the spherical reflowed bumps or mushroom bumps are formed for bonding of the chip and the substrate, and the bumps are made of a plastically deformable material, so as to achieve an improved reliability of the flip chip joint. Moreover, an average bonding pressure applied to each bump during the flip chip bonding is within a range of 15-100 mN/bump, and preferably, is approximately 20 mN/bump (2 g/bump, the size of the bump : 25//m x 25μm). It can be understood that the above pressure value is very lowered as compared to the conventional pressure of 980 mN/bump (100 g/bump, the size (diameter) of the bump : 85 μm) as disclosed in U.S. Patent No. 5,298,458 and Korean Patent Laid-open Publication No. 2001-0104626. i80> The above described flip chip bonding is available in a variety of fields including displays using a chip-on glass (COG) and chip-on plastic (COP), image sensor packages, low-temperature flip chip bonding packages, etc. [Mode for Invention]
<i8i> Hereinafter, the present invention will be described in more detail on the basis of the following Examples, but the present invention is not limited thereto.
<182> [Example]
<183> Example 1 : Manufacture of spherical Sn reflowed bump
<184> A electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 μm. After coating a polyacrylic photoresist on the under bump metal on chip, ultraviolet light was exposed to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the bump metal on chip is exposed to the outside. Sn was deposited on the under bump metal inside the opening to have a thickness of 30 μm.
<185> Subsequently, a reflow process was performed for 50 seconds while injecting a mixture gas of Ar and H2 (partial gas pressure ratio of 9:1) at a vacuum pressure of 270 mtorr and a temperature of 250 °C . Then, the photoresist layer was removed such that the Au on the ITO substrate and the spherical Sn refloweded bumps were formed on the ITO substrate. In this case, a bump pitch was 30 μm.
<186> Comparative Example 1 : Manufacture of column-shaped Sn bump <187> This was performed in the same manner as Example 1 except for that the bump was formed by electroplating Sn without the reflow process. <i88> Experimental Example 1 : Analysis of bump shape <189> A scanning electron microscope was used to inspect the shapes of the bumps obtained by Example 1 and Comparative Example 1, and the results were shown in FIGS. 16 and 17. :19O> FIG. 16a is a scanning electron micrograph illustrating spherical Sn reflowed bumps prepared by Example 1, and FIG. 16b is an enlarged micrograph of FIG. 16a. Also, FIG. 17a is a scanning electron micrograph illustrating Sn bumps prepared by Comparative Example 1, and FIG. 17b is an enlarged micrograph of FIG. 17a.
<i9i> Referring to FIGS. 16 and 17, it can be understood that spherical Sn bumps were uniformly formed by Example 1 of the present invention, and that the column-shaped bumps were formed when not performing the reflow process.
<192> Experimental Example 2 : Analysis of bonding properties
<193> An optical microscope was used to inspect the bonded shapes of the bumps prepared by Example 1 and Comparative Example 1, and the results were shown in FIGS. 18 and 19. In this case, after epoxy resin as a non- conductive adhesive was coated on a glass substrate, pressure of 80 MPa is applied to the bums at a temperature of 100 °C for 270 seconds, for bonding of the bumps.
<194> FIG. 18 is an optical micrograph illustrating a sample that is bonded by use of spherical Sn reflowed bumps of Example 1, in which no non- conductive adhesive is trapped in the interface of the bumps, and FIG. 19 is an optical micrograph illustrating a sample that is bonded by use of Sn bumps prepared by Comparative Example 1, in which a non-conductive adhesive is trapped in the interface of the bumps.
<195> Referring to FIG. 18, it can be understood that clear bonding without trapping of the nonconductive adhesive can be accomplished when using the spherical Sn reflowed bumps of Example 1. As compared to FIG. 18, it can be understood from FIG. 19 illustrating Comparative Example 1 that the Sn bumps have highly irregular bonding properties. These results show that it is possible to increase adhesion performance between the chip and the substrate when using the spherical Sn bumps via the reflow process.
<196> Experimental Example 3 : Analysis of trapping phenomenon of non- conductive adhesive ϊi97> A scanning electron microscope was used to inspect the trapping degree of the non-conductive adhesive after bonding of the bumps prepared by Example 1 and Comparative Example 1, and the results were shown in FIGS. 20 and 21. 2
27
In this case, the bonding was performed in the same manner as Experimental Example 2.
<198> FIG. 20 is a scanning electron micrograph illustrating a sample that is bonded by use of the spherical Sn reflowed bums prepared by Example 1, and FIG. 21 is a scanning electron micrograph illustrating the cross section of a sample that is bonded by use of the Sn bumps prepared by Comparative Example 1.
<199> Referring to FIG. 20, it can be understood that, when using the spherical Sn reflowed bumps of Example 1, no non-conductive adhesive is trapped in the bumps. As compared to FIG. 20, it can be understood from FIG. 21 illustrating the bumps of Comparative Example 1 that the non-conductive adhesive was excessively trapped in the bumps (as shown by the black region).
<200> Experimental Example 4 '• Analysis of contact resistance and penetration rate
<201> The contact resistance, standard deviation, and failure rate caused by trapping of the non-conductive adhesive were measured while changing pressure applied upon bonding of the substrate and the spherical Sn reflowed bumps of Example 1, and the results were shown in the following Table 1 and FIG.22.
<202> [Table 1] <203>
Figure imgf000028_0001
FIGS. 22a and 22b are scanning micrograph illustrating the cross sections of bumps that are bonded by pressure of 40 MPa and by pressure of 80 MPa, respectively.
<204> Referring to Table 1 and FIG. 22, when applying pressure of 40 MPa and pressure of 80 MPa, the bumps have relatively low contact resistances, and no non-conductive adhesive was trapped in the bumps at both the pressures. In particular, it can be understood that, when the bumps are bonded by pressure higher than 80 MPa, the contact surface area of the substrate and the chip increases, resulting in a reduced contact resistance. <205> Example 2 : Manufacture of Sn mushroom bump
<206> A electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 μm. After coating a polyacrylic photoresist on the under bump metal, ultraviolet light was irradiated to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the electrode pad layer is exposed to the outside. Sn was deposited on the under bump metal within the opening to have a thickness of 35 μm, so as to cover a part of the upper surface of the photoresist layer.
<207> Subsequently, the photoresist layer was removed such that the Au electrode pad layer on the ITO substrate and the Sn mushroom bumps were formed.
<208> Example 3 : Manufacture of Cu mushroom bump
<209> The Au electrode pad layer and the Cu mushroom bumps were formed on the ITO substrate in the same manner as Example 2 except for using Cu instead of Sn.
<2io> Example 4 : Manufacture of Sn/Cu composite mushroom bump
<2ii> A electrode pad layer was formed on an ITO substrate by depositing Au by a thickness of 10 μm. After coating a polyacrylic photoresist on the under bump metal, ultraviolet light was irradiated to the coated photoresist, so as to form a photoresist layer. The photoresist layer was developed to form an opening through which the under bump metal is exposed to the outside. Then, Sn was deposited on the under bump metal by a thickness of 20 μm, to have the same height as the photoresist layer, and Cu was deposited by a thickness of 15 μm to cover Sn and a part of the photoresist layer.
<2i2> Subsequently, the photoresist layer was removed such that the Au electrode pad layer on the ITO substrate and the Sn/Cu (column/head) composite mushroom bumps were formed.
<2i3> Comparative Example 2 : Manufacture of column-shaped Cu bump
<2i4> Column-shaped Cu bumps were formed by depositing Cu up to the height of the photoresist layer and removing the photoresist layer, in the same manner as Example 2.
<2i5> Experimental Example 5 : Analysis of bump shape
<2i6> A scanning electron microscope was used to compare the shapes of the bumps prepared by Examples 2 to 4 and Comparative Example 2, and the results were shown in FIGS. 23 to 26.
<2i7> FIG. 23 is a scanning electron micrograph illustrating Sn mushroom bumps prepared by Example 2, FIG. 24 is a scanning electron micrograph illustrating Cu mushroom bumps prepared by Example 3. Also, FIG. 25a is a scanning electron micrograph illustrating Sn/Cu composite mushroom bumps prepared by Example 4, and FIG. 25b is an enlarged micrograph of FIG. 25a. FIG. 26 is a scanning electron micrograph illustrating column-shaped Cu bumps prepared by Comparative Example 2.
<2i8> Referring to FIGS. 23 to 26, it can be understood that all the bumps of Examples 2 to 4 and Comparative Example 2 have a uniform shape.
<2i9> Experimental Example 6 : Analysis of contact resistance and trapping phenomenon
<220> After bonding the bumps prepared by Examples 2 to 4 and Comparative Example 2, the contact resistance and failure rate of the bumps were measured on the basis of pressure, and the results were shown in Table 2. In this case, after epoxy resin as a non-conductive adhesive was coated over Ti deposited throughout a glass substrate, pressure is applied to the bumps at a temperature of 150 °C for 90 seconds, for bonding of the bumps. The failure rate means a percentage with respect to the number of failed bumps caused as the non-conductive adhesive is remains under the bumps.
<22i> [Table 2] <222>
<223>
<224>
Figure imgf000031_0001
Referring to Table 2, it can be understood that the mushroom bumps of Example 3 and Comparative Example 2 can achieve reduced contact resistance when the same pressure is applied thereto. Also, it can be understood that the mushroom bumps can be bonded at a lower pressure than that of the column- shaped bumps. Furthermore, it can be understood that the Sn bumps have a lower contact resistance value than that of the Cu bumps.
<225> It can be understood that the Sn/Cu composite mushroom bumps of Example 4 can achieve a sufficient bonding effect even if low pressure is applied thereto.
<226> Moreover, the bumps of Examples 2 to 4 according to the present invention have no trapping of the non-conductive adhesive. On the other hand, the column-shaped bumps of Comparative Example 2 exhibit a serious bonding failure rate of 30%.
<227> Example 5 <228> This was performed in the same manner as Example 4 except for that an Ag oxidation-resistant film was formed on a surface of the Sn/Cu (column/head) composite mushroom bump.
<229> Example 6 <230> This was performed in the same manner as Example 5 except for depositing Ni instead of Cu, to prepare a Sn/Ni (column/head) composite mushroom bump. [Industrial Applicability]
<23i> As apparent from the above description, the flip chip bonding method of the present invention can be efficiently used in displays using a chip-on glass (COG) and chip-on plastic (COP), image sensor packages, low-temperature flip chip bonding packages, etc.
<232> Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS] [Claim 1]
<234> A flip chip bump comprising: <235> a chip;
<236> a plurality of patterned under bump metal formed on the chip; and <237> a spherical reflowed bump or mushroom bump formed on the under bump metal .
[Claim 2]
<238> The flip chip bump according to claim 1, wherein the spherical reflowed bump and the mushroom bump comprise any one material selected from the group consisting of Au, Cu, Sn, Ni, Bi, In, Ag, Zn and alloys thereof.
[Claim 3]
<239> The flip chip bump according to claim 1, wherein the spherical reflowed bump and the mushroom bump comprise a single metal bump, or a Pb-free solder bump comprising pure Sn or a Sn-metal alloy containing any one metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof.
[Claim 4]
<240> The flip chip bump according to claim 3, wherein the content of the metal selected from Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof is less than 5 wt% on the basis of the overall content of the Sn-metal alloy.
[Claim 5]
<24i> The flip chip bump according to claim 1, wherein the mushroom bump has a column and a head, and the column and the head are made of the same material as each other or different materials from each other.
[Claim 6]
<242> The flip chip bump according to claim 1, wherein the column of the mushroom bump comprises pure Sn, or a Sn-metal alloy containing Sn and any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag and Zn and alloys thereof, and
<243> the head of the mushroom bump comprises the Sn-metal alloy, or any one metal selected from the group consisting of Au, Cu, Ni, Bi, In, Ag, Zn and alloys thereof.
[Claim 7] <244> The flip chip bump according to claim 1, wherein the mushroom bump has pores formed in the column or the head, and formed in both the column and the head.
[Claim 8]
<245> The flip chip bump according to claim 1, further comprising: <246> an oxidation-resistant film formed at a surface of the spherical reflowed bump or mushroom bump.
[Claim 9]
<247> A method for manufacturing a spherical reflowed bump comprising: <248> forming a plurality of patterned under bump metal on the chip; <249> coating a photoresist on the patterned under bump metal and etching the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside; and <250> depositing a material, selected from the group consisting of a metal,
Pb-free metal, and a combination thereof, on the under bump metal inside the opening, and then, performing a reflow process, so as to manufacture the spherical reflowed bump, and <25i> wherein, before or after the reflow process of the step c), the method further comprises removing the photoresist layer.
[Claim 10] c252> The method for manufacturing the spherical reflowed bump according to claim 9, wherein the under bump metal is formed by performing any one process selected from the group consisting of a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an electro-less plating process, and an electroplating process.
[Claim 11] 253> The method for manufacturing the spherical reflowed bump according to claim 9, wherein the material, selected from the group consisting of a metal,
Pb-free metal, and a combination thereof, is formed by performing any one selected from the group consisting of a vacuum deposition process, an electroplating or electro-less plating process, a stud bumping process using a wire bonder and a screen or stencil printing process.
[Claim 12]
<254> The method for manufacturing the spherical reflowed bump according to claim 9, wherein the reflow process is performed within a reflow time range of 0.1-120 seconds under a vacuum condition of 150-300 mtorr by use of a mixture gas comprising 85-95 wt% of Ar and 5-15 wt% of H2.
[Claim 13]
<255> The method for manufacturing the spherical reflowed bump according to claim 9, wherein the reflow process is performed at a temperature range of 232-280°C.
[Claim 14]
<256> The method for manufacturing the spherical reflowed bump according to claim 9, further comprising:, after manufacturing the spherical reflowed bump, forming an oxidation-resistant film at a surface of the bump.
[Claim 15]
<257> A method for manufacturing a mushroom bump comprising: <258> forming a plurality of patterned under bump metal on the chip; <259> coating a photoresist on the patterned under bump metal and developing the photoresist, to form a photoresist layer having an opening, through which a part of the under bump metal is exposed to the outside;
<260> depositing a material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, on the under bump metal inside the opening, so as to manufacture the mushroom bump! and 26i> removing the photoresist layer.
[Claim 16]
262> The method for manufacturing the mushroom bump according to claim 15, wherein the under bump metal is formed by performing any one process selected from the group consisting of a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an electro-less plating process, and an electroplating process.
[Claim 17]
<263> The method for manufacturing the mushroom bump according to claim 15, wherein the material, selected from the group consisting of a metal, Pb-free metal, and a combination thereof, is formed by performing any one process selected from an electroplating process and an electro-less plating process.
[Claim 18]
<264> The method for manufacturing the mushroom bump according to claim 15, wherein the mushroom bump has a column and a head, and the column and the head are made of the same material as each other or different materials from each other.
[Claim 19]
<265> The method for manufacturing the mushroom bump according to claim 15, further comprising:, after manufacturing the mushroom bump, forming an oxidation-resistant film at a surface of the bump.
[Claim 20]
<266> A flip chip bonding method using a flip chip bump comprising: <267> forming a plurality of patterned under bump metal on the chip; <268> forming a spherical reflowed bump or mushroom bump, according to any one of claims 1 to 8, on the patterned under bump metal; <269> forming a metal electrode on a substrate;
<270> coating a non-conductive adhesive to cover the metal electrode; and <27i> aligning the chip and the substrate to face each other and thermally compressing the chip and the substrate.
[Claim 21] c272> The flip chip bonding method according to claim 20, wherein the substrate is selected from the group consisting of a ceramic substrate, a glass substrate, a plastic substrate, a printed circuit board, and a flexible substrate.
[Claim 22] 273> The flip chip bonding method according to claim 20, wherein the thermal compression is performed at a temperature of 200°C or less.
[Claim 23]
<274> The flip chip bonding method according to claim 20, wherein the thermal compression is performed at a temperature range of 80-200°C.
[Claim 24]
<275> The flip chip bonding method according to claim 20, wherein pressure applied upon the thermal compression is within a range of 20-100MPa.
[Claim 25]
<276> The flip chip bonding method according to claim 20, wherein pressure applied upon the thermal compression is within a range of 30-50MPa.
[Claim 26]
<277> The flip chip bonding method according to claim 20, wherein an average bonding pressure applied per the bump during the flip chip bonding is within a range of 15-100 mN/bump.
PCT/KR2007/000032 2006-01-04 2007-01-03 Flip chip mount type of bump, manufacturing method thereof, and bonding method for flip chip using non conductive adhesive WO2007078148A2 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR10-2006-0000989 2006-01-04
KR20060000989 2006-01-04
KR10-2007-0000555 2007-01-03
KR1020070000555A KR100843632B1 (en) 2006-01-04 2007-01-03 Flip chip mount type of bump, manufacturing method thereof, and bonding method for flip chip using non conductive adhesive

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI550825B (en) * 2014-12-05 2016-09-21 財團法人工業技術研究院 Package structure for light emitting devices

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Publication number Priority date Publication date Assignee Title
KR100521081B1 (en) * 2002-10-12 2005-10-14 삼성전자주식회사 Fabrication and installation method of flip chip
KR100568006B1 (en) * 2003-12-12 2006-04-07 삼성전자주식회사 Forming Method for Concave Solder Bump Structure of Flip Chip Package

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI550825B (en) * 2014-12-05 2016-09-21 財團法人工業技術研究院 Package structure for light emitting devices

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