JP2001127421A - Ball mounter and mounting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for mounting solder balls on a board while correcting warpage. SOLUTION: Warpage of a board is corrected by pressing a head having a lower surface, provided with a plurality of protrusions and suction holes, against a board. After the board is held flatly by means of a vacuum chuck pad provided on a board mounting base, solder balls are separated from the suction holes and mounted on the board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball mounting apparatus and a ball mounting method for mounting a ball on a substrate.
More specifically, the present invention relates to a ball mounting apparatus and a ball mounting method for mounting a ball by flattening the warpage of a substrate.

[0002]

2. Description of the Related Art On a substrate on which a plurality of semiconductor elements are mounted,
A technique for mounting thousands of solder balls at a time has been put to practical use. Commonly used substrates include a tape substrate, a printed circuit board, and a semiconductor wafer. FIG. 5 shows an example of a large-sized tape substrate on which 4480 solder balls are mounted at one time. The tape substrate 22 has 56 ICs 23 mounted thereon, and 28 ICs among them are molded together with a sealing resin 24. (a) is a plan view of the tape substrate,
(B) is a front view of the tape substrate, (c) is a bottom view of the tape substrate, and small white circles described in the bottom view (c) are solder balls mounted on electrodes of a multilayer tape substrate having via holes. is there.

FIG. 6 shows a deviation amount (m) from a predetermined reference point.
m) represents the warpage of the tape substrate. There is a difference of 0.66 mm between the position where the deflection (warpage) is maximum and the position where the deflection is minimum. Even if the tape substrate having such a large amount of warpage is simply placed on the mounting table and sucked by the vacuum suction pad, the substrate does not adhere to the mounting table and becomes flat. Therefore, the substrate is pressed until the substrate is sucked by the vacuum suction pad, thereby flattening the substrate. In practice, the substrate is pressed against the mounting table until the substrate becomes flat. The pressing force at this time is 1.3 to 1.5 kg. When the mounting of the solder ball is performed in a state where the substrate is warped, the solder ball adsorbed by the suction hole corresponding to the position where the substrate is warped and raised is pushed into the suction hole and bites.
As a result, even when the vacuum is applied to the pickup head to break the vacuum of the pickup head in the process of mounting the solder ball on the substrate and further raise the pickup head to accelerate the detachment of the solder ball, the solder ball is still removed from the pickup head. There is a disadvantage that the probability of not separating from the substrate is significantly increased. Further, if the ball is dropped from the sky in consideration of the warpage, the ball mounting position is displaced, which is impossible. Also, if the solder balls are mounted on the board without fixing the board to the mounting table, the warpage of the board will return to the original when the pickup head is raised. In contrast, there is a disadvantage that the solder balls cannot be mounted on the substrate under uniform conditions.

Recently, attempts have been made to form bumps on an 8 to 12 inch wafer by a ball mounting method. Since a protective film for protecting the semiconductor circuit portion is applied to the semiconductor wafer side of the semiconductor wafer, the wafer is warped due to polymerization shrinkage of the protective film and the like. The amount of warpage does not matter when the substrate has a small diameter such as a 3-inch wafer. However, as the diameter of the wafer increases, the amount of warpage increases and a defect occurs in the ball mounting process. Further, the tape substrate has an essential disadvantage that the warpage is increased due to the low rigidity of the tape.

As a known technique related to the present invention, a method of mounting solder balls on a warped substrate (Japanese Patent Laid-Open No. 09-2)
No. 98356). FIG. 8 discloses this, in which a solder ball is pressed by a pin pin (ejector pin) 26 via a pressing rubber 25 so that the solder ball can be pressed against the substrate following the warpage of the substrate. An elastic force of the pressurized rubber and a viscoelastic force of the flux act on the pressed solder ball. Since the elastic force of the pressurized rubber is much larger than the viscoelastic force of the flux and the solder balls are soft and easily deformed with a low load, it is not possible to eliminate all the solder balls that bite into the tip of the ejector pin or the suction hole. The method of correcting the warpage of the substrate is not a solder ball mounting substrate but an example of a printed circuit board to be soldered, which is disclosed in Japanese Patent Application Laid-Open No. Hei.

[0006]

As described above, the prior art does not disclose or suggest any method and means for mounting a solder ball after correcting a warped substrate to be flat and fixing it to a mounting table. . The ball mounting apparatus and the mounting method according to the present invention are such that, by flattening the warped substrate and mounting the ball on the substrate, the solder ball is pressed and bites into the suction port and the ejector pin to cause a defective ball mounting. The first object is to prevent the following. Another object is to reduce the difference in mounting conditions due to warpage of the substrate when mounting the ball.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a ball mounting apparatus according to the present invention has a ball supply section, a table for mounting and positioning a substrate, and a pickup having a plurality of suction holes on its lower surface. A ball mounting device comprising a moving mechanism for moving a head and a pickup head, wherein a protrusion having a height higher than the height of a ball sucked in a suction hole is provided on a lower surface of the pickup head.

The present invention also relates to a ball mounting method for mounting balls adsorbed on a plurality of suction holes provided on a lower surface of a pickup head on a substrate, wherein a step of printing a flux on the substrate, A step of adsorbing a ball, a step of moving a pickup head over a substrate, a step of pressing a projection provided on a lower surface of the pickup head against the substrate to substantially flatten the substrate, and mounting the ball on the substrate from a suction hole. This is a ball mounting method including a step and a step of separating the pickup head from the substrate.

Next, the present invention relates to a ball mounting method for mounting a ball sucked in a plurality of suction holes provided on a lower surface of a pickup head on a substrate, the method comprising: Holding the substrate that has been flattened flat on a mounting table, adsorbing a ball to the lower surface of the pickup head, applying flux to the lower part of the solder ball, moving the pickup head onto the substrate, This is a ball mounting method including a step of mounting a ball on a substrate from a suction hole and a step of separating a pickup head from the substrate.

Further, the present invention provides a ball mounting method for mounting a ball sucked in a plurality of suction holes provided on a lower surface of a pickup head on a substrate, the method comprising: correcting the substrate to be substantially flat; The method includes a step of adsorbing the solder ball on the lower surface of the pickup head, a step of mounting the ball on the substrate from the suction hole, and a step of separating the pickup head from the substrate.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a front view of the ball mounting device used in the embodiment. 1 is a solder ball supply unit, 2 is a solder ball, 3 is a vibrator for giving a vibration to the solder ball, 4 is a pickup head of the solder ball, 5 is a lower surface of a pickup head having a plurality of suction holes, and 6 is a pickup head. 4 is a cavity portion, 7 is an XYZθ table for positioning the pickup head 4 in the XYZθ direction and pressurizing in the Z direction, 8
Is a base on which the XYZθ table 7 moves, 9 is a base 8
A Z-direction drive device for largely moving the head in the Z-direction, 10 a vacuum pump for reducing the pressure in the cavity 6 of the pickup head 4, 11 a linear light source, 12 a substrate on which solder balls are mounted, and 13 a substrate mounted on top. X with table 18
Table 14 is a YZθ table, 14 is a pipe connected to the vacuum pump 10 to depressurize the cavity 6, 27 is a pressurizing device composed of an air cylinder, 28 is a spring having a counterbalance function for finely adjusting the pressing force. . Although the XYZ θ tables are used for positioning the substrate and the pickup head, if there is only one θ table, there is no practical problem. The pickup head moving mechanism includes an XYZθ table 7, a base 8, and a Z-direction driving device 9. After the pickup head is positioned by the XYZθ table 7 and lowered to a predetermined position by the Z-direction driving device 9, the projection 17 is pressed against the substrate 12 by the pressing device 27, and the substrate 12 is pressed against the mounting table 18 to be flat.

FIG. 2 shows an example of a pickup head according to the present invention. Reference numeral 2 denotes a solder ball, 15 suction holes for sucking solder balls, 16 an optical sensor for detecting light from the light source 11, and 17 a projection for flattening the substrate 12. The protrusions 17 are provided on the lower surface 5 of the pickup head, and FIG. 2 illustrates five protrusions. The required number of projections is determined according to the warpage of the substrate, the rigidity of the substrate, and the size of the substrate. The number of protrusions is the minimum number when one is provided near the center of the substrate, and 3 to 9 are provided near the center and the periphery. When the area is small, the number is further increased. When correcting the warpage of the semiconductor wafer, the semiconductor wafer has a scribe line width of about 50 μm, and the diameter of the projection 17 is about 30 μm to press the scribe line. Alternatively, a semiconductor circuit portion on which no bump is formed is pressed. When the semiconductor circuit portion is pressed, the material of the protrusion 17 is made of an elastic material or an elastic material such as rubber is provided at the tip of the protrusion so as not to break the protective film or the circuit. The height of the projections is precisely adjusted by surface grinding after the projections are set. The height (Tb) of the solder ball 15 from the lower surface 5 is smaller than the diameter of the solder ball because the suction hole 15 is chamfered. Assuming that the height of the projection 17 from the lower surface 5 is Tp, Tp is larger than Tb, specifically, 2 to 30% larger, and more preferably 5 to 15% larger. The thickness of the flux printed on the substrate before the solder balls are mounted or the thickness of the flux applied to the solder balls is 1
0-200 microns. When a solder ball is mounted on a substrate, the adhesiveness of the flux is used, so it is necessary to push the solder ball into the flux in an appropriate amount. The amount of the solder ball pushed into the flux, the pushing speed, the separation speed between the pickup head and the substrate, and the addition to the pickup head so that the solder ball does not bite into the suction hole due to the pressing force and sufficiently receive the adhesive force of the flux. It is important to appropriately determine the mounting conditions such as the magnitude and number of vibration amplitudes and the timing of vibration application.

FIG. 3 is a partial cross-sectional view of the mounting table used in the present invention. Reference numeral 18 denotes a mounting table provided on the XYZθ table 13 for mounting a substrate, 19 denotes a vacuum suction pad for vacuum-sucking the substrate, Reference numeral 20 denotes a recess for the vacuum suction pad 19 to escape, and reference numeral 21 denotes a supply / exhaust passage for vacuum suction. The supply / exhaust passage 21 is connected to the vacuum pump 10. The vacuum suction pad 19 is made of silicone rubber. Although the number of vacuum suction pads provided is preferably one at the center of the mounting table, it is preferable to provide a plurality of vacuum suction pads. In the case where the substrate is relatively flat and has a small amount of warpage, the substrate is sucked by the vacuum suction pad and is brought into close contact with the upper surface of the mounting table without being pressed when the substrate is transferred to the mounting table. However, if the amount of warpage or rigidity of the substrate is large, the substrate does not adhere to the upper surface of the mounting table even if the substrate is placed on the mounting table and vacuum-sucked. In this case, after the substrate is placed on the mounting table, the substrate must be pressed against the mounting table. Note that the pressing method may be pressing with a projection disposed on the lower surface of the head, the lower surface of the head, another pressing jig, or the like, and the pressing method is not particularly limited.

FIG. 4 is a flowchart of a first solder ball mounting method according to the present invention. Except in special cases,
Soldering requires solder and flux, and the flux is applied to the substrate in any process unless the flux and solder are integrated. The method of applying the flux includes a method of screen-printing the flux on a required portion of the substrate by screen printing using a mask, and a method of applying a flux by dipping the lower part of the solder ball adsorbed on the pickup head into the flux. FIG. 4 shows the former, and FIG. 5 shows the latter. In the former ball mounting method of screen printing a flux, a step of printing a flux on a substrate, a step of transferring the substrate to a mounting table, a step of fixing the substrate to the mounting table with a vacuum suction pad, and suctioning a solder ball to a pickup head Moving the pickup head over the substrate, lowering the pickup head, pressing a projection provided on the lower surface of the pickup head against the substrate to flatten the substrate, and removing the solder balls adsorbed by the pickup head. The method includes a step of mounting on a substrate, a step of raising a pickup head and moving it onto a ball supply unit, and a step of unloading and transferring the substrate to a next step such as a reflow step. Performing the flux printing step and the step of attracting the solder balls to the pickup head in parallel is effective for shortening the tact time. There are two methods for defect inspection in the process of adsorbing the solder ball to the pickup head and the process of mounting the solder ball on the substrate, image processing and light detection processing. Defect inspection by image processing is a method of comparing image information of a substrate read by a CCD with set reference data and inspecting for the presence or absence of a defect. Defect inspection by light detection processing is a method of determining the presence or absence of a mounting defect based on the presence or absence of light shielding by a ball. If it is found that there is a defect in the solder ball mounting, the part in process is regarded as defective, and the process is returned to the initial stage and restarted. In the process of mounting the solder ball on the board, the solder ball is vacuum-adsorbed to the pickup head, so first break the vacuum, then slowly raise the pickup head and apply vibration to the pickup head as necessary, The substrate is separated from the pickup head. As described above, since the solder ball is mounted on the substrate from the pickup head while the pickup head is separated from the substrate, the step of mounting the solder ball on the substrate from the pickup head and the step of separating the pickup head from the substrate partially overlap. .

FIG. 5 is a flowchart of a second solder ball mounting method according to the present invention, in which a lower portion of a solder ball adsorbed by a pickup head is immersed in a flux to apply a flux. The method includes a step of transferring a substrate to a mounting table, a step of pressing and flattening the substrate and fixing the substrate to the mounting table, a step of moving a pickup head onto a ball supply unit, and a step of attracting a solder ball to the pickup head. Immersing the lower part of the solder ball in the flux and applying the flux to the solder ball, moving the pickup head onto the substrate, mounting the solder ball adsorbed by the pickup head on the substrate, raising the pickup head And a step of unloading the substrate and transferring it to the next step such as a solder reflow step. In this method, when the projections 17 are provided, the flux is simultaneously applied to the projections 17 in the step of applying the flux to the solder balls. Therefore, it is preferable to use a pickup head in which the projections 17 are not provided on the lower surface.
Since the flux applied to the projections 17 remains until after the ball is mounted on the substrate, the next time the ball is picked up, the ball adheres to the remaining flux in a dango-like manner, causing actual harm. Further, a jig other than the pickup head may be used to press the substrate against the mounting table.

On the other hand, when the mounting table of the substrate used in the flux printing step is continuously used in the ball mounting step, it is not necessary to flatten the substrate again in the ball mounting step. Therefore, this ball mounting method includes a step of pressing the substrate to flatten and fix it to the mounting table, a step of adsorbing the solder ball to the pickup head, a step of moving the pickup head onto the substrate, and a step of moving the solder ball adsorbed to the pickup head. The method includes a step of mounting on a substrate, a step of separating a pickup head from the substrate, and a step of unloading the substrate and transferring the substrate to a next step such as a solder reflow step. The operation of mounting the solder balls adsorbed on the pickup head on the substrate includes operations of vacuum break, lifting of the pickup head, and vibration of the head.

In the present invention, the term “substantially flat” means to correct a substrate to a flatness that does not cause inconvenience in mounting a solder ball. The amount of warpage in the range where the probability of inconvenience in mounting the ball is small depends on the diameter of the solder ball, but is approximately 10% or less of the ball diameter or １ ／ or less of the thickness of the printed flux. When the diameter of the solder ball is 760 microns and the thickness of the flux is 120 microns, the allowable limit of the amount of warpage of the substrate is approximately 60 microns. The smaller the solder ball diameter, the smaller the amount of warpage allowed for the substrate. Specifically, the amount of warpage of the substrate is preferably 5 microns to 76 microns, and more preferably 30 microns or less. Theoretically, the best warpage of the substrate is zero, and the next best warpage is the range in which the ball is immersed in the flux at a non-uniform depth but does not touch and press the substrate. The worst warpage is when the ball directly presses the substrate. It goes without saying that an appropriate amount of flux is applied to the ball and must not exceed the appropriate amount limit.

The proper pressing force in the present invention is a force capable of substantially flattening the substrate, and is, for example, 0.3 to 2.5 kg for a tape substrate, and 0.5 to 2.5 kg for a glass epoxy substrate and a semiconductor wafer. 10 kg. At this time, the force acting on the ball is mainly the viscoelastic force of the flux, and the viscoelastic force can be controlled by the composition of the flux, the operating temperature, the load speed, etc., so the force applied to the ball can be easily controlled arbitrarily. it can. Also, since the rigidity of the substrate is proportional to the cube of the plate thickness, depending on the thickness of the multilayer resin circuit substrate or semiconductor wafer, the warped substrate may not be flat unless a greater pressing force is applied. In this case, the only applied force is the viscoelasticity of the flux.

FIG. 1 shows a state in which balls are stacked in the ball supply section 1 in multiple layers. However, it is preferable to control the amount of balls inserted into the ball supply unit to be the number of balls that can be separated from each other in one layer without the balls being stacked, so that the balls are not so many that they interfere with each other. Also,
The ball may be vibrated by the vibrator 3 or by blowing dry air or nitrogen gas from below to float the ball. Furthermore, to prevent oxidation of the ball surface,
It is also possible to supply a reducing gas or to apply a voltage of 5 volts or less to the ball through an electrode provided on the ball supply unit or the pickup head. The applied voltage may be obtained by superimposing an alternating current on a direct current, and further inverting the direct current at a predetermined cycle.

The ball in the present invention refers to a metal ball, a ceramic ball, a plastic ball, a ceramic ball coated with a metal, a plastic ball coated with a metal, and the like, in addition to the solder ball. Solder balls include lead-tin eutectic solder, high-temperature solder, low-temperature solder, lead-free solder, and gold solder. The diameter of the ball is 100 to 760 microns, and 200 to 500 microns is frequently used. The shape of the ball may be a polygon or an aspherical curved surface in addition to a sphere.

In the present invention, it is essential that the height of the projection is higher than that of the solder ball. However, the height of the projection must satisfy the condition that the ball is not directly pressed onto the substrate and that the flux can be applied sufficiently and sufficiently to the ball. It is important that the height should be 2 to 30% higher than the height of the solder ball.
More preferably, it is higher by ~ 15%.

In the present invention, the composition of the flux requires that the shape of the flux printed by adding a thixotropic agent for squeegee printing does not collapse at room temperature. On the other hand, a mixture of solder powder and flux, that is, a cream solder, good. In the case of cream solder, the solder ball may not be a solder ball such as a metal ball.

[0023]

According to the ball mounting apparatus and the mounting method of the present invention, even if the substrate is warped, the ball is mounted in a state where the substrate is flat, so that the ball digs into the suction hole of the pickup head. There will be no mounting error and no ball mounting position shift. Furthermore, since the relationship between the ball and the flux is uniform when the ball adsorbed by the pickup head is mounted on the substrate, uniform application of the flux, high yield and high precision ball mounting can be easily performed. For this reason, the ball mounting apparatus and mounting method according to the present invention enable the ball to be mounted on a large wafer or a large circuit board for the first time industrially, and the contribution to the progress of the semiconductor mounting technology is extremely large.

[Brief description of the drawings]

[Figure 1] Front view of solder ball mounting device

FIG. 2 is a cross-sectional view of the pickup head of the present invention.

FIG. 3 is a partial sectional view of a mounting table.

FIG. 4 is a flowchart of a first solder ball mounting method according to the present invention.

FIG. 5 is a flowchart of a second solder ball mounting method according to the present invention.

6A is a plan view of the tape substrate during mounting, and FIG.
(B) is a front view and (c) is a bottom view.

FIG. 7 is a measurement result of a warpage amount of a tape substrate during mounting.

FIG. 8 is a part of a conventional ball mounting device.

[Description of Signs] 1 Ball supply unit 2 Ball 3 Vibrator 4 Pickup head 5 Lower surface of pickup head 6 Cavity 7 XYZθ table 8 Base 9 Z direction driving device 10 Vacuum pump 11 Light source 12 Substrate 13 XYZθ table 14 Piping 15 Solder ball 16 Suction Hole 17 Projection 18 Mounting base 19 Vacuum suction pad 20 Vacuum suction pad recess 21 Supply / exhaust passage 22 Tape substrate 23 IC (semiconductor chip) 24 Sealing resin 25 Pressurized rubber 26 Sword pin 27 Spring 28 Pressure device 29 Ball mounting portion

Claims (4)

[Claims] 1. A ball mounting apparatus comprising a ball supply unit, a table for mounting and positioning a substrate, a pickup head having a plurality of suction holes on a lower surface, and a moving mechanism for moving the pickup head. A ball mounting device, wherein a projection is provided on the lower surface of the pickup head. 2. A ball mounting method for mounting a ball on a substrate after adsorbing the ball to a plurality of suction holes provided on a lower surface of a pickup head, wherein a flux is printed on the substrate, and the substrate is mounted on a mounting table. Transferring, picking up the ball on the lower surface of the pickup head, moving the pickup head over the substrate, pressing a projection provided on the lower surface against the substrate to substantially press the substrate. A ball mounting method, comprising: flattening, mounting the ball on the substrate from the suction hole, and separating the pickup head from the substrate. 3. A method of mounting a ball on a substrate after the ball is sucked into a plurality of suction holes provided on a lower surface of the pickup head, wherein the substrate is substantially flattened. A step of adsorbing the ball on the lower surface, a step of applying a flux to a lower portion of the ball, a step of moving the pickup head over the substrate, a step of mounting the ball on the substrate from the suction hole, and a step of picking up A method for mounting a ball, comprising a step of separating a head from the substrate. 4. A ball mounting method for mounting a ball on a substrate after the ball is sucked into a plurality of suction holes provided on the lower surface of the pickup head, wherein the substrate is substantially flattened. A ball mounting method comprising: a step of adsorbing the ball on the lower surface; a step of mounting the ball on the substrate from the suction hole; and a step of separating the pickup head from the substrate.