JP2010212353A - Bump forming method, substrate where bump is formed by the method, and bump forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for forming a bump, which manufactures a tall bump at a low cost. <P>SOLUTION: A bump forming device BS which forms a bump for circuit connection on a substrate W where an electric circuit is formed, is equipped with: a substrate holding device 1 for holding the substrate W; and a jetting device 3 which causes fine copper particles G supplied to a nozzle 30 to disperse in the gas stream inside the nozzle for flowing down, so that they are jetted along with gas from a jetting opening 35 at a lower end. The fine copper particles G are jetted along with the gas from the jetting opening 35 against the substrate W held by the substrate holding device 1, to collide with to be bonded, such that a copper bump is formed on the surface of the substrate W under a normal temperature and normal pressure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bump forming method for forming bumps for circuit connection on a substrate on which an electric circuit is formed, a substrate on which bumps are formed by this method, and a bump forming apparatus.

  A typical example of a substrate on which an electric circuit is formed is a printed wiring board on which components such as an IC and a transistor are mounted. In the printed wiring board, in order to electrically connect an electric circuit formed on the board and a component mounted on the board and a lead wire for external drawing, a bump for circuit connection (Bump: (Protrusions) are formed. In a multilayer wiring board, bumps, also referred to as vias, are formed inside the substrate for interlayer connection of a plurality of wiring layers.

  Conventionally, as a method for forming such a bump, for example, a plating method in which solder is plated on a copper foil pattern formed on a substrate, or a solder paste is imprinted into an opening portion of a screen printed resist pattern, and a reflow process A solder paste imprinting method that heats and melts at a temperature is used. (See, for example, Patent Documents 1 and 2).

JP 2001-284786 A JP 2004-14565 A

  However, the height of the bump formed by plating is about several tens of μm at most, and it is difficult to form a bump higher than this. For this reason, for example, a pad for mounting a component having a large current capacity such as a power transistor or a transformer, a pad for connecting a circuit having such a large current capacity and a lead wire for external lead, or a circuit having a large current capacity. A substrate including a bump having a low conductor resistance and a height of about 100 μm, such as vias connected between layers, has a problem that it is difficult to form by a one-step plating method.

  On the other hand, in the solder paste imprinting method, the solder paste is embedded in the openings of the screen-printed resist pattern and melted and fixed by reflow, so that a bump having a relatively high height can be formed. However, this method has a problem in that the process is complicated and it takes time and cost to manufacture the substrate, and a resist pattern or the like has to be manufactured again each time the circuit pattern of the substrate is changed.

  The present invention has been made in view of the above problems, and an object thereof is to provide a bump forming method, a bump forming apparatus, and the like that can manufacture a bump having a low conductor resistance and a high height at a low production cost. To do.

  To achieve the above object, the first aspect of the present invention is a bump forming method for forming bumps for circuit connection on a substrate on which an electric circuit is formed. This bump forming method is configured to form metal bumps on a substrate at normal temperature and normal pressure by placing metal fine particles on a gas jet and spraying them from a nozzle to collide with the substrate.

  2nd this invention is a board | substrate with which the bump was formed, and is comprised by forming a bump with the bump formation method in any one of Claims 1-3.

  The third aspect of the present invention is a bump forming apparatus for forming bumps for circuit connection on a substrate on which an electric circuit is formed. The bump forming apparatus includes a substrate holding device that holds a substrate on which an electric circuit is formed, and metal fine particles supplied to the nozzle are dispersed in a gas flowing in a flow path provided in the nozzle to flow down. An injection device that injects the gas together with the gas from the injection port provided at the downstream end of the substrate, the metal fine particles are injected from the injection port on the gas jet to the substrate held by the substrate holding device, and fixed by collision. Bumps are formed on the substrate at normal temperature and normal pressure.

  In the present invention, metal fine particles are placed on a gas jet and jetted onto a substrate to be fixed by collision, and bumps are formed at normal temperature and normal pressure. For this reason, bumps with low conductor resistance and high height can be manufactured at low production costs.

It is a schematic block diagram of a bump formation apparatus. It is a top view of the II-II arrow in FIG. It is a schematic diagram for demonstrating the flow of the metal microparticles | fine-particles in the injection nozzle vicinity, and formation of a bump. It is an enlarged photograph of the copper bump formed in the board | substrate W by bump formation conditions-1. It is a graph which shows the relationship between the injection time of copper fine particles, and the bump height of the copper bump formed in the board | substrate. It is an enlarged photograph of the connection part which connected the copper lead wire to the copper bump formed by bump formation condition-2 by laser welding.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. First, a bump forming apparatus BS for carrying out a bump forming method according to the present invention will be described with reference to FIG.

  Broadly speaking, the bump forming apparatus is roughly divided into a substrate holding device 1 that holds a substrate W on which an electric circuit is formed, a moving mechanism 2 that relatively moves the substrate W held on the substrate holding device 1 and the nozzle 30, and a nozzle. 30 has a flow path for allowing metal fine particles to flow down together with the gas, and controls the injection of the metal fine particles by the injection device 3 that injects the gas jet from the injection port 35 that opens at the downstream end of the flow channel. And a control device 8 including a movement control unit 82 for controlling the relative movement between the substrate W and the nozzle 30 by the moving mechanism 2.

  The substrate holding device 1 is configured to be able to be fixedly held in a state where the substrate W is positioned with respect to the ejection device 3. Examples of the configuration of the substrate holding device 1 include a configuration in which a porous member such as a ceramic porous or a metal porous is used and the substrate W is attracted and fixed to the upper surface of the table 10. The table 10 is configured to have sufficient rigidity with respect to the injection force of a solid-gas mixed phase flow composed of metal fine particles and gas injected from the injection device 3.

  As shown in a plan view taken along the line II-II in FIG. 1, in this configuration, a plurality of positioning pins 12 are provided on the table 10 so as to be movable in and out, and the side edges of the substrate W placed on the table are arranged. A configuration is shown in which the substrate W is positioned at a reference position on the table by applying to the positioning pins 12. The support surface (table upper surface) 11 that supports the substrate W is formed flat with a relatively high flatness with respect to the substrate W, and when the exhaust path inside the table is exhausted by a vacuum generator or the like, The air in the vicinity of the support surface is sucked through the fine holes of the porous member, and the substrate W is sucked into the support surface 11 and firmly fixed and held. Instead of the vacuum suction method using such a porous member, the periphery of the substrate W may be mechanically fixed to the table 10 by a plurality of clamps.

  The moving mechanism 2 relatively moves the substrate W held by the substrate holding device 1 and the nozzle 30. Here, the substrate W and the nozzle 30 may be configured to move either. However, in the illustrated configuration, two directions in a horizontal plane perpendicular to the injection axis CL of the injection device 3 extending vertically are provided. 1 shows a configuration example using an XY stage 20 that moves the table 10. The XY stage 20 includes an X-axis moving mechanism 21 that moves the table 10 in the X-axis direction, and a Y-axis moving mechanism 22 that moves the table 10 in the Y-axis direction. An XY stage type moving mechanism is shown. The relative movement in the vertical direction between the substrate W and the nozzle 30 is configured such that the nozzle 30 is moved up and down with respect to the table 10 by a Z-axis driving mechanism that is not shown in detail.

  The injection device 3 disperses the metal fine particles supplied to the nozzle 30 in a gas flowing through a flow path provided in the nozzle 30 and causes the metal fine particle to flow down from the injection port 35 provided at the downstream end. . As such an injection device, for example, an injection device (referred to as a single tube type injection device) disclosed in Japanese Patent Application Laid-Open No. 2000-94332 related to the present applicant, or Japanese Patent Application Laid-Open No. 2006-224205 related to the present applicant. There is an injection device (referred to as a composite tube type injection device) as disclosed in the publication. The present invention can be applied to any of the above-described injection devices, but FIG. 1 shows a configuration example in which a composite tube type injection device is applied as the injection device 3. The injection direction may be horizontal.

  The injection device 3 includes a nozzle 30 for injecting metal fine particles together with a gas, a fine particle supply unit 40 for supplying metal fine particles G to the nozzle 30, a gas supply unit 45 for supplying injection gas to the nozzle 30, and an injection port 35, a fine particle collecting device 55 for sucking metal fine particles ejected from 35 but not fixed to the substrate W is provided.

  The nozzle 30 is provided with a pipe-like supply nozzle 32 that extends vertically inside the body 31 serving as a base, and is connected to the gas supply unit 45 via a gas supply pipe 46 connected to the upper end of the supply nozzle 32. Gas (referred to as supply gas) is supplied. A hole 33 through which the metal fine particles can pass is formed through the wall surface at the upper and lower intermediate portions of the supply nozzle 32, and the fine particle supply groove 43 formed around the hole 33 passes through the fine particle introduction path 42. The metal fine particles G stored in the fine particle tank 41 are supplied. The metal fine particles G can be used in an appropriate composition depending on the characteristics of the bumps to be formed. For example, copper (Cu) fine particles having a mean particle size of 10 [μm] or less, leaded / lead-free (lead-free) Examples include solder fine particles, silver (Ag), and gold (Au) fine particles.

On the distal end side of the supply nozzle 32, an acceleration nozzle 34 having a diameter larger than that of the supply nozzle 32 extends downward (in the ejection direction) and is provided coaxially. An ejection port 35 is formed at the distal end of the acceleration nozzle 34. The distal end portion of the supply nozzle 32 and the proximal end portion of the acceleration nozzle 34 are disposed so as to overlap each other, and an annular acceleration gas jet passage 36 having a narrow width is formed in this overlapping portion. An acceleration gas introduction path 37 connected to the acceleration gas injection flow path 36 is formed at the base end portion of the acceleration nozzle 34, and the gas supply unit 45 is connected to the acceleration nozzle 34 via the acceleration gas supply pipe 47 connected to the acceleration gas introduction path 37. Gas (referred to as acceleration gas) is supplied. The supply gas and the acceleration gas may be nitrogen (N ₂ ) gas, helium (He) gas, dry air (Air), or a combination thereof, which is generally used as a carrier gas. Each supply pressure is controlled by the injection control unit 81 of the control device 8.

  On the tip side of the acceleration nozzle 34, an outer cylinder member 50 having a diameter larger than that of the acceleration nozzle extends vertically and is provided coaxially. The outer peripheral side of the injection port 35 is disposed so as to surround the injection region JA of the metal fine particles. Is done. The outer cylinder member 50 is supported on the outer peripheral side of the acceleration nozzle 34 so as to be slidable up and down via a seal member (not shown), and the acceleration nozzle 34 is moved by the outer cylinder moving mechanism 25 that moves the outer cylinder member 50 up and down. It is comprised so that relative movement up and down is possible. The vertical movement of the outer cylinder member 50 by the outer cylinder moving mechanism 25 is controlled by the injection control unit 81. The outer cylinder moving mechanism 25 can be configured using, for example, a spring and an electromagnet or a direct acting solenoid, a rack and pinion, a lead screw, and the like provided between the nozzle body 31 and the outer cylinder member 50. The inner diameter of the outer cylinder member 50 is set to be somewhat larger than the outer diameter (injection diameter) on the substrate surface of the injection region JA of the metal fine particles injected onto the substrate W.

  A seal portion 51 made of an elastic material is provided at the distal end portion of the outer cylinder member 50. The seal portion 51 is formed of an elastic material made of a polymer material whose hardness is lower than that of the substrate W. When the outer cylinder member 50 is pressed against the substrate W, the seal portion 51 is elastically deformed flexibly so that there is no gap between the inner and outer circumferences. The partition is blocked so that the metal fine particles G ejected from the ejection port 35 do not diffuse in the radial direction. For example, the seal portion 51 is bonded to the tip of the outer cylinder member 50 by adhering a rubber sponge punched in an annular shape to the tip of the outer cylinder member 50 or by fixing a rubber boot molded in a bellows shape to the tip of the outer cylinder member 50. Provided.

  For this reason, when the outer cylinder member 50 is moved downward relative to the acceleration nozzle 34 by the outer cylinder moving mechanism and the seal portion 51 of the outer cylinder member is pressed against the substrate W, the outer cylinder member 50 is surrounded by the inner peripheral side of the outer cylinder member 50. An injection chamber 52 that is blocked from the space is formed. An exhaust port 53 that penetrates the wall surface is formed in the outer cylinder member 50, and a particulate collection device 55 is connected through an exhaust tube 54. The fine particle collecting device 55 includes a vacuum blower for sucking a solid-gas mixed phase fluid (gas and metal fine particles) on the inner peripheral side of the outer cylinder member, a fine particle collecting device for separating and collecting metal fine particles from the solid-gas mixed phase particles, and the like. The fine metal particles injected from the injection port 35 into the injection chamber 52 but not fixed to the substrate W are sucked and collected. The operation of the particulate collection device 55 is controlled by the control device 8.

  In the bump forming apparatus having such a configuration, the table 10 on which the substrate W is sucked and held is moved by the X-axis moving mechanism 21 and the Y-axis moving mechanism 22, for example, a copper foil pattern pad (electrode) formed on the substrate W. Positioning is performed so that P is positioned on the injection axis CL of the injection device 3. Next, the nozzle 30 is moved downward by the Z-axis moving mechanism, and the distance h between the lower end of the acceleration nozzle 34 and the surface of the substrate W, that is, the nozzle gap is set to a predetermined height. Further, the outer cylinder is moved downward by the outer cylinder moving mechanism 25, and the seal portion 51 is pressed against the substrate surface. Thereby, the circumference | surroundings of injection area | region JA are enclosed by the street, and the injection chamber 52 is formed. Then, the particulate collection device 55 is activated to exhaust the injection chamber 52, and the injection processing by the injection device 3 is performed.

  The injection processing is performed by supplying gas from the gas supply unit 45 to the nozzle. Here, the injection form of the metal fine particles G includes injection by only supply of the supply gas, injection by only supply of the acceleration gas, injection combining the both, and the like, which are controlled by the control device 8. The operation in the case of jetting in combination will be described. The control device 8 supplies the supply gas from the gas supply unit 45 to the proximal end side of the supply nozzle 32 through the gas supply pipe 46, and from the gas supply unit 45 through the acceleration gas supply pipe 47 and the acceleration gas introduction path 37. The acceleration gas is supplied to the base end side of the acceleration nozzle 34.

  When the supply gas is supplied to the base end side of the supply nozzle 32, fine particles are generated by the ejector effect of the gas flow flowing in the supply nozzle 32 and the turbulent flow effect generated in the step portion between the gas supply pipe 46 and the supply nozzle 32. The metal fine particles G located in the supply groove 43 are sucked into the supply nozzle 32 through the hole portion 33 and flow downward in the supply nozzle while being dispersed by the gas flow.

  At this time, the accelerating gas supplied to the accelerating gas introduction passage 37 is jetted into the accelerating nozzle through the annular accelerating gas jet channel 36 at a high speed. A large negative pressure is generated by the high-speed gas flow ejected from the pipe, and a large turbulent flow is generated because the channel cross-sectional area of both channels rapidly expands. Therefore, the metal fine particles flowing down the supply nozzle 32 are sucked into the accelerating nozzle, and are entrained in the turbulent flow, dispersed in the accelerating gas, accelerated by the jet of the accelerating gas, and injected from the injection port 35 at the downstream end. Is done.

  As schematically shown in FIG. 3, the ejected metal fine particles collide with the substrate W and adhere to the pad P of the copper foil pattern, and are sequentially deposited to form the ejected metal composition bump B. . The metal fine particles not fixed to the substrate W are prevented from diffusing in the radial direction by the outer cylindrical member 50 covering the injection area JA, and are collected by the fine particle collecting device 55 via the exhaust tube 54 connected to the exhaust port 53. The Here, the outer cylinder member 50 is set to an extent that the inner diameter is somewhat larger than the outer diameter of the injection region JA. For this reason, the metal fine particles ejected from the ejection port 35 do not diffuse from the pad forming region and adhere to the surrounding circuit pattern and remain.

  Note that the distance (nozzle gap) h between the surface of the substrate W and the ejection port 35 is set by controlling the height position of the lower end of the acceleration nozzle by moving the nozzle 30 up and down by a Z-axis moving mechanism, and is normally 0. It is set at a height of about 5 to 2 [mm]. Further, the injection speed of the metal fine particles G is set by controlling the type and pressure of the supply gas and acceleration gas supplied to the nozzle 30, and is less than the speed of sound of the gas used (for example, the supply gas and the acceleration gas are air In this case, the fuel is injected at a speed of 300 [m / sec] or less.

  The bump forming apparatus as described above was manufactured, and as a result of intensive research on the formation of bumps on the substrate W, the inventor achieved an average particle size with the nozzle 30 having an inner diameter of the acceleration nozzle 34 of 0.5 [mm] or more. Bump formation with a height of 100 [μm] or more was realized using metal fine particles having a diameter of 10 [μm] or less. Hereinafter, specific examples of bump formation will be described with reference to experimental data in which copper bumps (referred to as copper bumps) are formed on a substrate.

  In the present embodiment, the injection nozzle 3 having an inner diameter of the acceleration nozzle 34 of 1 [mm] is used, the nozzle gap h is set to 1 [mm], and copper fine particles are injected under the following bump formation condition-1 to obtain a substrate. Copper bumps were formed by collision and fixing to W. In addition, the copper bump is formed in a state where the substrate W and the nozzle 30 are fixed without being relatively moved, including the bump formation condition-2 described below.

(Bump formation condition-1)
Substrate W: Alumina ceramic (Al ₂ O ₃ ) substrate on which a copper thin film having a thickness of about 1 to 2 [μm] is formed. Metal fine particles G: Copper fine particles having an average particle diameter of 1 [μm] Used gas : Helium (He)
・ Supply gas pressure: 0 [MPa]
・ Acceleration gas pressure: 0.2 [MPa]
・ Injection time: 1, 5, 10 [sec]

Figure 4 an enlarged photograph of the bump formation conditions copper bumps B ₁ formed on the substrate W by -1, B _2, B _3, copper bumps B ₁ .about.B ₃ bump height is formed with the injection time of the fine copper particles FIG. 5 shows the relationship. The bump height (expressed as the maximum film thickness in FIG. 5) was measured from the surface of the substrate W to the top of the copper bump, excluding whisker-like protrusions formed at the upper end.

As understood from FIG. 4, copper bumps are directly formed on the substrate so that the copper fine particles sprayed onto the substrate W sequentially collide and adhere and accumulate, and rise upward. The bump height exceeds 300 [μm] for the copper bump B ₁ with a spray time of only 1 second, and the conical bump close to 800 [μm] for the copper bump B ₂ with a spray time of 5 seconds. Is formed.

  Next, using the injection device 3 having a nozzle inner diameter of 1 [mm] as in the above example, the nozzle gap was set to 1 [mm], and copper bumps were formed according to the following bump formation condition-2.

(Bump formation condition-2)
Substrate W: Pad portion having a diameter φ1 [mm] in an alumina ceramic circuit board on which a circuit pattern is formed by a copper thin film having a thickness of about 1 to 2 [μm] on the surface. [μm] Copper fine particles and gas used: Helium (He)
・ Supply gas pressure: 0 [MPa]
・ Acceleration gas pressure: 0.5 [MPa]
・ Injection time: 3 [sec]

At this time, like the copper bump B ₁ in FIG. 4, a dish-shaped or bowl-shaped copper bump rising upward is formed on the pad portion having a diameter of φ1 [mm], and the measured bump height is 160 μm. ]Met.

  In this way, by the bump forming method in which the copper fine particles are jetted onto the substrate W by the jetting device 3 and fixed by collision, the bump height is 100 [ It has been demonstrated that solid copper bumps exceeding [μm] can be formed with high efficiency.

  In the above, the embodiment in which the inner diameter of the accelerating nozzle 34 is φ1 [mm] at the injection port 35 has been described. However, the inner diameter of the accelerating nozzle 34 is suitably in the range of about 0.5 to 2 [mm]. Can be used. For example, the nozzle inner diameter is 0.8 [mm] or 1.5 [mm] according to the diameter of the pad formed on the substrate W, or an acceleration nozzle having an appropriate inner diameter is used. The moving mechanism 2 can move the substrate W in a circular manner in a horizontal plane relative to the nozzle to form a copper bump having a desired diameter.

  In addition, copper fine particles are illustrated as an example of metal fine particles. However, depending on the specifications of the bumps to be formed, metal fine particles of other composition such as fine particles of gold, silver, lead-free solder fine particles not containing zinc are used. Bumps can also be formed. According to the technique of forming solder bumps on copper foil pads by spraying fine particles of lead-free solder, a reflow solder that has been used in the past after producing a substrate with a bump height of 100 [μm] or more in a simple process The parts can be mounted using the production equipment.

Next, FIG. 6 shows that a copper lead L having a width × thickness of 0.6 × 0.2 [mm] is placed on the copper bump B ₅ formed on the copper foil pad according to the bump formation condition-2. FIG. 5 is an enlarged photograph of a connection portion connected by laser welding after condensing and irradiating laser light having an infrared wavelength from above.

  From this enlarged photograph, it is confirmed that the lead wire L and the copper bump are melted together and are firmly connected electrically and mechanically. For this reason, according to the board manufacturing method in which components such as lead wires and power transistors are laser welded to the copper bumps formed by this method, a complicated and multi-step process is required as in the board manufacturing method using reflow soldering. It is possible to produce a circuit board on which electrical components are mounted with a very simple manufacturing process. In addition, since the circuit board can be manufactured without using solder, there is no problem of lead and halogen caused by solder, which can contribute to environmental protection.

BS bump forming device 1 substrate holding device 2 moving mechanism 3 spraying device 8 control device 30 nozzle (32 supply nozzle, 34 acceleration nozzle)
35 Injection port 40 Fine particle supply unit (suction device)
45 Gas supply unit 50 Outer cylinder member 51 Sealing part 55 Particulate collection device G Metal particulate P Pad B, B ₁ , B ₂ , B ₃ , B ₅ Bump L Lead wire (component)

Claims (6)

A bump forming method for forming a bump for circuit connection on a substrate on which an electric circuit is formed,
A bump forming method characterized in that metal fine particles are placed on a gas jet, ejected from a nozzle, collided with the substrate and fixed, and bumps are formed on the substrate at room temperature and normal pressure.   The bump forming method according to claim 1, wherein the bump is a pad for electrically connecting a component to the electric circuit.   The bump forming method according to claim 1, wherein the metal fine particles are copper fine particles having an average particle diameter of 10 μm or less.   The board | substrate with which the bump was formed by the bump formation method in any one of Claims 1-3. A bump forming apparatus for forming bumps for circuit connection on a substrate on which an electric circuit is formed,
A substrate holding device for holding a substrate on which an electric circuit is formed;
An injection device that disperses the metal fine particles supplied to the nozzle in a gas flowing through a flow path provided in the nozzle and injects the gas together with gas from an injection port provided at a downstream end of the flow path; Prepared,
The metal fine particles are jetted onto the gas jet from the jet port and fixed by collision on the substrate held by the substrate holding device, and bumps are formed on the substrate at room temperature and normal pressure. A bump forming apparatus. An outer cylinder member disposed around the injection region of the metal fine particles on the outer peripheral side of the injection port;
A suction device that evacuates a gap formed between the outer periphery of the injection port and the inner periphery of the outer cylinder member, and sucks the metal fine particles injected from the injection port but not fixed to the substrate; Prepared,
The outer cylinder member has a seal portion formed of an elastic material at a tip portion surrounding the injection port, and is arranged to be movable in the injection axis direction of the metal fine particles with respect to the injection port.
The metal fine particles are ejected from the ejection port in a state where the seal portion is in contact with the surface of the substrate and the ejection port is covered by the outer cylinder member and the inner peripheral side of the outer cylinder member is exhausted by the suction device. The bump forming apparatus according to claim 5, wherein the bump forming apparatus is configured as described above.