JP2004047670A - Flip chip mounting method and flip chip mounting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a flip-chip packaging method and a flip-chip packaging apparatus for obtaining flip chips with small amount of warpage. <P>SOLUTION: In the flip-chip packaging method, a substrate 5 is vacuum-chucked and retained on a stage, a flip chip 3, being vacuum-chucked and retained by a chip vacuum chuck block 1, is heated and is pressed onto the substrate, and at the same time, the substrate 5 is forcibly cooled from the side of the stage. The flip-chip packaging apparatus 21 comprises the chip vacuum chuck block 1 for incorporating a heating means 2; and a stage 23 having a substrate vacuum chuck means 27 and a substrate-cooling means 25, thus simultaneously operating the heating means 2, the substrate vacuum chuck means 27, and the substrate-cooling means 25. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flip chip mounting method and a flip chip mounting apparatus for thermocompression bonding a flip chip to a substrate.
[0002]
[Prior art]
FIG. 4 is a diagram showing an example of a conventional flip chip bonder. The flip chip bonder includes a chip suction block 1 having a built-in heater 2, a plunger 4, a substrate 5, a stage 6 for pressing a flip chip (IC chip) 3, and a vacuum suction pipe 7. The chip suction block 1 suctions the back surface of the IC chip 3 by vacuum and transfers the IC chip 3 to a predetermined position of the substrate 5 on the stage. Then, the plunger 14 is lowered, and the IC chip 3 is heated by the heater 2 while applying pressure. As a result, the thermosetting resin 5b previously applied to the upper surface of the substrate 5 shown in FIG. 5 is cured, the IC chip 3 and the substrate 5 are joined, and the bumps 3a of the IC chip 3 and the lands 5a of the substrate 5 are connected. Is done. Thereafter, the heater 2 is turned off, the plunger 4 is raised, and the connected IC chip 3 and substrate 5 are cooled and taken out.
[0003]
In the prior art, various measures have been taken to shorten the cycle time of the process and to perform resin curing in a short time or complete cooling after resin curing in a short time. For example, not only the heater head on the IC chip side but also the substrate stage is heated, or laser heating is performed instead of the heater, and the heating time is shortened by the steep rise of the temperature, thereby shortening the tact time of the process.
[0004]
By the way, in the flip chip mounting method of thermocompression bonding a flip chip to a substrate, there is a problem that deformation occurs after pressure bonding due to a difference in linear expansion coefficient between the flip chip and the substrate. Here, with reference to FIG. 6, the mechanism of deformation of the flip chip at the time of press bonding using a thermosetting resin will be described. However, the influence on the deformation due to the frictional resistance due to the pressurization is small, so it is not considered.
[0005]
Consider a case where the substrate 5 is placed on a stage at room temperature, IC chips 3 are stacked via a thermosetting resin, and heating is performed. The thermosetting resin is a liquid having a high viscosity at room temperature, but has a property of being cured when heated to about 150 to 200 ° C.
At the time of heating, both the IC chip 3 and the substrate 5 thermally expand. At this time, the linear expansion coefficient of the resin substrate is 10 to 50 ppm / ° C., whereas the IC chip 3 is made of silicon at about 3 ppm / ° C., and the displacement of the substrate 5 is larger than the displacement a of the IC chip 3 due to thermal expansion. The quantity b is much larger. In addition, while the thermosetting resin is in a liquid state, the IC chip and the substrate expand independently of each other, so that a large restraining force does not occur and no deformation such as warpage occurs.
[0006]
When the thermosetting resin is cured, the positions of the two are fixed at the interface between the IC chip 3 and the substrate 5.
Next, when the heater 2 is turned off and cooling starts, both the IC chip 3 and the substrate 5 try to shrink, but the thermosetting resin is hardened at the interface between them, and the positional relationship is fixed. The larger substrate has a larger shrinkage than the IC chip. Therefore, similarly to the bimetal, the bending deformation occurs so that the IC chip side becomes convex by the bending moment with the interface between the IC chip 3 and the substrate 5 interposed therebetween.
[0007]
If the deformation of the flip chip occurs in this way, the rate of occurrence of defects due to connection open and increase in electric resistance increases, so that it is necessary to minimize the amount of thermal deformation. Conventional methods for reducing the amount of thermal deformation include, for example, changing material constants such as the coefficient of linear expansion and glass transition characteristics of the resin substrate, and changing the temperature profile at the time of temperature rise.
[0008]
[Problems to be solved by the invention]
However, as for the change of the material constant, lowering the linear expansion coefficient of the resin substrate and using a material having a high glass transition temperature have been carried out. Change is difficult. The low expansion coefficient has a limit of about 8 ppm, which is far below 3 ppm of Si. In addition, although there are materials having a high glass transition point, production of a substrate (hot pressing) using the same becomes more difficult and does not lower the expansion coefficient itself. Thus, there is a limit to changing the material constant, and at present it is impossible to take measures.
When changing the temperature profile, if the IC bump and the land of the substrate are temporarily fixed at about 150 ° C. in advance and then heated, the temperature difference from the time of cooling to the return to room temperature is reduced, so that the warpage of the substrate is also reduced. However, there is a disadvantage that the tact time is increased and the productivity is reduced.
Furthermore, when bonding on a collective substrate using a flip chip bonder, since multiple IC chips are bonded on one interposer substrate, the heat of the previous bonding is transmitted to the stage, and the bonding is performed later. However, there is a problem that the bonding conditions are likely to vary within the collective substrate because the bonding temperature of the chip to be bonded increases.
The present invention has been made in view of the above situation, and a first object of the present invention is to provide a flip chip mounting method and a flip chip mounting method that can obtain a small warp flip chip without increasing the heater temperature or significantly extending the tact time. An object of the present invention is to provide a flip chip mounting device. A second object of the present invention is to provide a flip chip mounting method capable of reducing variations in the amount of warpage of individual flip chips even in the case of a collective substrate.
[0009]
[Means for Solving the Problems]
A flip-chip mounting method according to claim 1 of the present invention for achieving the above object is a flip-chip mounting method for thermocompression bonding a flip chip to a substrate, wherein the flip-chip mounting method holds a substrate on a stage by suction and holds the chip. The flip chip held by suction is heated and pressurized onto the substrate while being heated, and at the same time, the substrate is forcibly cooled from the stage side.
[0010]
In this flip chip mounting method, a large temperature gradient is formed between the substrate surface and the substrate back surface by simultaneously cooling the stage at the time of bonding in which the flip chip is heated and pressed onto the substrate while the flip chip is being heated, thereby curing the resin on the substrate surface. While maintaining the temperature, the back surface of the substrate is maintained at a temperature at which the amount of shrinkage decreases after cooling. As a result, a flip chip with a small warpage can be obtained without increasing the heater temperature or significantly increasing the tact time.
[0011]
A flip chip mounting method according to a second aspect is characterized in that, in the flip chip mounting method according to the first aspect, a plurality of flip chips are sequentially thermocompression-bonded to the same substrate.
[0012]
In this flip chip mounting method, the collective substrate is sucked and held on the stage, and the stage surface is uniformly cooled, so that the heat generated when the flip chip is bonded first is not accumulated on the collective substrate, so that the same Irrespective of the bonding position and order in the collective substrate, the variation in the amount of warpage of each flip chip is reduced.
[0013]
4. The flip chip mounting apparatus according to claim 3, further comprising: a chip suction block including a heating unit; and a stage including a substrate suction unit and a substrate cooling unit, wherein the heating unit, the substrate suction unit, and the substrate cooling unit. It is characterized in that the means operate simultaneously.
[0014]
In this flip-chip mounting apparatus, a coolant is flowed through the stage of the flip-chip bonder, and the stage is forcibly cooled, so that the temperature rise on the lower surface of the substrate during bonding is suppressed, and the warpage of the flip chip after cooling is reduced. .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a flip-chip mounting method and a flip-chip mounting apparatus according to the present invention will be described in detail with reference to the drawings. Note that the same members as those shown in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted.
FIG. 1 is a configuration diagram of a flip chip mounting apparatus according to the present invention.
[0016]
As shown in FIG. 1, a flip chip mounting apparatus (hereinafter, referred to as “flip chip bonder”) 21 according to the present embodiment has a cooling block structure capable of introducing a refrigerant into a stage 23 and forcibly cooling the stage 23. And That is, in the stage 23, a substrate cooling means (cooling pipe) 25 and a substrate suction means (vacuum pipe) 27 are provided. The cooling pipe 25 is connected to a substrate cooling means (refrigerant supply device) (not shown), and the refrigerant supply device can circulate and supply the refrigerant to the cooling pipe 25. The stage 23 is stabilized at a low temperature by circulating a refrigerant in the cooling pipe 25. In addition, as the refrigerant supplied to the cooling pipe 25, for example, cold water can be suitably used.
[0017]
A substrate suction means (vacuum pump), not shown, is connected to the evacuation pipe 27, and the vacuum pump can exhaust air in the evacuation pipe 27. The evacuation pipe 27 is opened as a substrate suction port 29 on the stage 23. The substrate suction port 29 is located between the cooling pipes 25 and has a structure in which substrate suction and cooling are performed alternately in position. Further, the stage 23 is formed of a material having a good thermal conductivity, so that the temperature of the lower surface of the substrate at the time of press bonding is cooled (decreased) satisfactorily by the high thermal conductivity.
[0018]
In the flip chip bonder 21 according to the present embodiment, the chip suction block 1 has the same configuration as the conventional one. That is, it has a heater 2 which is held at the lower end of the plunger 4 and serves as a heating means, and has a vacuum suction pipe 7 for vacuum suctioning the back surface of the IC chip 3.
[0019]
The flip chip bonder 21 is provided with a control unit (not shown), and the control unit controls the operation of the heater 2, the plunger 4, the vacuum pump, and the refrigerant supply device. Here, the control unit has an operation control mode for simultaneously operating the heater 2, the vacuum pump, and the refrigerant supply device.
[0020]
Next, the operation of the flip chip bonder 21 will be described.
FIG. 2 is a flowchart showing the procedure of the flip chip mounting method according to the present invention.
Prior to mounting the flip chip, a coolant is supplied to the cooling pipe 25 of the stage 23, and the stage 23 is cooled to a predetermined temperature in advance (st1). A transfer machine (not shown) of the flip chip bonder 21 places the substrate 5 on the stage 23 (st3), and a thermosetting resin for connection is supplied onto the substrate (st5). The method of supplying the thermosetting resin includes a method of bonding a film with resin, a method of injecting the film with a dispenser, and a method of printing at a predetermined position on the substrate. For example, ACF (anisotropic conductive film), ACP (anisotropic conductive paste), NCF (non-isotropic conductive film), NCP (non-isotropic conductive paste), etc. are used as bonding means. Can be used.
[0021]
Next, the chip suction block 1 sucks the IC chip 3 and moves onto the substrate (st7), and performs alignment of the bonding position of the IC chip 3 and the substrate 5 by a camera (st9).
Next, the pressurizing plunger 4 descends (st11), heats the heater 2 inside the chip suction block 1 to about 80 to 120 ° C. (st13), and pressurizes and heats the substrate 5 from above for several seconds (st13). st15). That is, cooling and heating of the substrate 5 are performed simultaneously.
[0022]
In this process, the thermosetting resin between the IC chip 3 and the substrate 5 is removed, and the IC bump 3a and the substrate land 5a (see FIG. 5) are pressed (st17).
Next, the heater temperature is raised to about 250 ° C., heating and pressurization are continued for several seconds (st19), and the thermosetting resin is cured (st21).
Finally, the heater 2 of the chip suction block 1 is turned off (st23), the plunger 4 is raised (st25), and the connected IC chip 3 is cooled (st27).
[0023]
The deformation of the substrate 5 after the compression starts from the moment of thermosetting of the thermosetting resin, and the amount of deformation increases in the cooling process due to the difference in the coefficient of thermal expansion between the substrate 5 and the IC chip 3. That is, the smaller the difference between the coefficients of linear expansion of the substrate 5 and the IC chip 3 and the lower the substrate temperature during curing of the thermosetting resin, the smaller the amount of contraction of the substrate 5, so the smaller the amount of warpage.
[0024]
In order to lower the temperature of the substrate 5 at this time, in the flip chip bonder 21, the temperature of the stage 23 is reduced. That is, the temperature of the lower surface of the substrate is lowered at the same time as the heating when the chip suction block 1 is pressed. Since the stage 23 for bonding the IC chip 3 and the substrate 5 to each other has a cooling block structure in which a refrigerant is introduced, the upper surface of the stage can be strongly cooled, and the upper surface has a large number of substrate suction ports 29. Adsorb. That is, the substrate 5 is cooled simultaneously with heating.
[0025]
Therefore, when the substrate 5 strongly adsorbed on the stage 23 is heated and pressed by the chip adsorption block 1, an increase in the lower surface temperature is suppressed. Since the temperature difference until the temperature returns to the normal temperature during cooling is reduced, the amount of contraction of the substrate 5 is also reduced, and the amount of warpage of the substrate 5 after bonding is reduced.
[0026]
When the substrate 5 is a collective substrate, since the stage surface is uniformly cooled, heat generated when the IC chip 3 is bonded first does not accumulate on the stage 23, and the bonding location is reduced. Irrespective of the order, the variation in the amount of warpage of each IC chip 3 can be reduced, and the connection reliability between the IC bump 3a and the substrate land 5a can be improved.
[0027]
【Example】
Next, the warp of the substrate was evaluated when the stage was not cooled using the flip chip bonder having the same configuration as the conventional technology and when the stage was cooled using the flip chip bonder having the same configuration as the embodiment. The following describes the results.
(1) The amount of deformation of the substrate when bonding was performed by the method shown in the prior art without cooling the stage was obtained by actual measurement.
The thicknesses of the IC chip and the substrate were 0.3 mm and 0.15 mm, respectively, and the linear expansion coefficients were measured when the IC chip was 3 ppm / ° C. and the substrates were 13 ppm / ° C. and 18 ppm / ° C.
The stage temperature was measured by attaching a thermocouple to a portion of the stage adjacent to the lower surface of the substrate.
After bonding, the substrate was naturally cooled to room temperature, and the warpage of the back surface of the substrate was measured with a non-contact laser displacement meter.
[0028]
(2) The stage is cooled by flowing cooling water into the stage so that the substrate lower surface temperature during bonding becomes 100 ° C., and the same IC chip and substrate as in (1) are used to cool the stage. Bonding was performed while performing.
Then, the warpage of the back surface of the substrate after cooling was measured.
[0029]
(3) Simulation was performed on the amount of warpage of the back surface of the substrate after bonding by the finite element method. For the simulation, a model in which the thermosetting resin of the IC chip and the substrate was sandwiched was created, and the transient heat conduction analysis and thermal stress analysis of the heating and cooling processes were performed. Taking the presence / absence of stage cooling as a parameter, the coefficient of linear expansion of the substrate was changed, and the calculation was performed under the same conditions as in (1) and (2), and compared with the measured values.
[0030]
FIG. 3 is an explanatory diagram in which the warpage after cooling the substrate is compared with the actually measured value and the simulation data depending on whether or not the stage is cooled.
FIG. 3 summarizes the above embodiments. As shown by the plot in FIG. 3, when the stage was not cooled, the stage temperature on the lower surface of the substrate was about 160 ° C., and the measured value of the amount of warpage after cooling the substrate was 39 μm. On the other hand, when the stage was cooled, the stage temperature under the substrate was about 100 ° C., and the warpage of the substrate after cooling was 22 μm. It can be seen that the amount of warpage of the substrate is reduced to about ２ compared to the case where the stage is not cooled.
[0031]
Further, a graph obtained by performing a simulation of the warpage of the substrate after bonding under the stage temperature condition is shown by a solid line in FIG. When the coefficient of linear expansion is 13 ppm / ° C., it is 33 μm without stage cooling and 16 μm with stage cooling, which is slightly smaller than the actually measured value, but the warpage amount of the substrate is about が, which is the same result as the actually measured value. Obtained.
[0032]
As described above, from the results of the actual measurement and the simulation, it can be said that as the stage temperature of the flip chip bonder is closer to room temperature, the amount of deformation of the IC chip after cooling can be reduced. That is, it has been found that by uniformly cooling the stage surface during bonding, the deformation amount of the IC chip and its variation can be reduced.
[0033]
Conventionally, there is an example in which, for example, a Peltier element is embedded in a stage portion, and heating and cooling are switched before and after flip chip bonding. However, there is no apparatus that cools the stage from the beginning of the flip chip crimping for the purpose of reducing the warpage of the substrate as in the configuration according to the present invention. If the mode is switched to cooling immediately after the thermosetting resin has hardened, the tact is shortened, but it is clear from the examples that there is actually no effect on warpage. In other words, it is understood that the effect of suppressing the warpage of the substrate is not effective unless the temperature of the substrate is lowered from the beginning during heating. In the present embodiment, as in the configuration according to the present invention, the stage is cooled at the time of flip chip bonding, and the temperature of the back surface of the substrate is suppressed to 100 ° C. or less while maintaining the adhesive at the curing temperature on the front surface side of the substrate. It turned out to be extremely effective for suppression.
[0034]
【The invention's effect】
As described above in detail, according to the flip-chip mounting method according to the first aspect of the present invention, by cooling the stage during bonding, a temperature gradient can be generated between the back surface of the substrate and the surface of the substrate, and the resin on the surface of the substrate can be cooled. While maintaining the curing temperature, the amount of shrinkage on the back surface of the substrate after cooling can be reduced. As a result, a flip chip having a small warpage can be obtained without increasing the heater temperature or significantly extending the tact time.
[0035]
According to the flip chip mounting method of the present invention, even in the case of a collective substrate, by cooling the stage surface uniformly, heat generated when the flip chip is bonded first does not accumulate, Irrespective of the location and order of bonding, there is an effect that variation in the amount of warpage of each flip chip is reduced and the process capability of flip chip connection performance is improved.
[0036]
ADVANTAGE OF THE INVENTION According to the flip-chip mounting apparatus which concerns on this invention, by making a structure which flows a refrigerant | coolant to the stage of a flip-chip bonder and cools a stage, the temperature rise of the lower surface of a board | substrate at the time of bonding is suppressed, and the warpage of the flip chip after cooling is carried out. Can be reduced. As a result, there is an effect that the connection reliability between the IC bump and the substrate land is improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a flip chip mounting apparatus according to the present invention.
FIG. 2 is a flowchart showing a procedure of a flip chip mounting method according to the present invention.
FIG. 3 is an explanatory diagram comparing warpage after substrate cooling with measured values and simulation data depending on whether or not stage cooling is performed.
FIG. 4 is a configuration diagram of a conventional flip chip bonder.
FIG. 5 is a structural conceptual diagram of a flip chip IC chip Au bump and a substrate land electrode connection portion.
FIG. 6 is an explanatory diagram of a mechanism of substrate warpage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Chip suction block, 2 ... Heater (heating means), 3 ... IC chip (flip chip), 5 ... Substrate, 21 ... Flip chip mounting apparatus, 23 ... Stage, 25 ... Cooling pipe (Substrate cooling means), 27 ... Vacuum pipe (substrate suction means)

Claims (3)

A flip chip mounting method for thermocompression bonding a flip chip to a substrate,
A flip chip mounting method, wherein a substrate is sucked and held on a stage, and the flip chip sucked and held on a chip suction block is pressed onto the substrate while being heated, and at the same time, the substrate is forcibly cooled from the stage side. The flip chip mounting method according to claim 1,
A flip chip mounting method, wherein a plurality of flip chips are sequentially thermocompression-bonded to the same substrate. A chip suction block with a built-in heating means,
A stage provided with a substrate suction means and a substrate cooling means,
The flip chip mounting apparatus, wherein the heating unit, the substrate suction unit, and the substrate cooling unit operate simultaneously.

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