JP2004273654A - Surface-mounting method of mounting component and method of repairing mounted article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of surface-mounting a mounting component almost without void in the solder connected part between the mounting component and a substrate, and to provide a method of simply repairing a mounted article having a void in a solder ball discovered by an inspection by simply removing the void. <P>SOLUTION: (1) The method of surface-mounting the mounting component 1 on the substrate 4 by using a solder includes the steps of removing the void existing in the molten solder ball 2 by heat treating the substrate and the mounting component in a standing state in a reflow furnace, and then cooling to solidify the solder ball. (2) The mounted article in which the mounting component 1 is surface-mounted on the substrate 4 and which has the void in the solder ball 2, is heat-treated in the standing state in the reflow furnace to remove the void existing in the solder ball, and to then cool to solidify the solder ball. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a method for surface-mounting a mounted component on a substrate using solder. More specifically, the present invention relates to a method of surface mounting a mounted component on a board in which defects due to voids in a solder joint are improved, and a method of repairing a mounted component in which a mounted component is surface mounted on a board having a void in a solder joint.
[0002]
[Prior art]
2. Description of the Related Art Electronic devices represented by semiconductor integrated circuits are becoming smaller and more highly integrated. As one of the high-density technologies, mounting components are three-dimensionally stacked and mounted on a substrate.
[0003]
Such mounting techniques include area array mounting such as CSP (Chip Scale Package) and BGA (Ball Grid Array), which have terminals coming out from the bottom of the mounting component body, and fine pitch FBGA (Fine pitch Ball). (Grid Array) implementation.
[0004]
In these electronic devices, after applying flux onto a wiring pattern provided on a substrate, mounting parts such as CSP and BGA are arranged, and heat is applied in a reflow furnace to melt solder balls and connect to the wiring pattern. Is used.
[0005]
In the above-described conventional mounting method for mounting components, since there is a mounting component on the upper part of the solder ball, when a reflow process is performed, a flow path of a gas generated by the applied flux entering the solder ball and evaporating is generated. There is a possibility that voids may be generated in the solder ball after the reflow process because of the blockage. As a result of investigations by the present inventors, it has been found that, in the area array mounting and the bare chip mounting, there is a considerable percentage of voids at the solder joints, and therefore, there is a problem that cracks are generated at the joints. .
[0006]
Conventionally, this solder shape evaluation has been performed visually or using an X-ray photograph or the like after actually mounting the mounted components on the surface of the substrate. If a defect occurs, the solder is peeled off, the mounted component and / or the solder ball is replaced, the reflow process is performed again, and the mounted product is evaluated. This is repeated until the solder shape becomes appropriate. Needed. For this reason, there has been a problem that it takes a lot of time and money to repair the defective solder.
[0007]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method of surface-mounting a mounted component having almost no void at a solder joint between the mounted component and a substrate. Another object of the present invention is to provide a method for easily removing and repairing a void in a mounted product having a void in a solder ball portion found by inspection.
[0008]
[Means for Solving the Problems]
That is, the present invention provides a method of surface mounting a mounted component on a substrate using solder, in a state where the substrate and the mounted component are set up, removes voids present in the molten solder ball by performing a heat treatment in a reflow furnace. After that, a solder ball is cooled and solidified.
[0009]
The mounted component is preferably a BGA (Ball Grid Array) or a CSP (Chip Scale Package).
[0010]
The heat treatment temperature is preferably in the range of the melting point temperature of solder + 20 ° C to the melting point temperature of solder + 60 ° C.
[0011]
Solder can also be applied to cream solder.
[0012]
In the reflow step, it is preferable to melt the solder while applying vibration to the mounted component and the substrate.
[0013]
The vibration is preferably vibration by ultrasonic waves.
[0014]
Another invention of the present invention is a mounted product in which a mounted component is surface-mounted on a substrate, and a mounted product having a void in a solder ball portion is heated in a reflow furnace in an upright state, thereby forming a solder ball. This is a method for repairing a mounted product, which comprises cooling and solidifying a solder ball after removing an existing void.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail.
The board in the present invention is a board on which a mounted product such as a semiconductor is mounted. This substrate is required to have a low coefficient of linear expansion, high rigidity, and heat resistance. For example, a paper phenol laminate, a glass fiber / epoxy resin laminate, a glass fiber reinforced polyimide resin plate, a glass fiber reinforced polyamide-imide resin plate, or the like is used.
[0016]
The mounting component according to the present invention refers to an integrated circuit such as an IC, an LSI, a VLSI, and an ULSI mounted on a substrate. The mounting component is preferably a bottom terminal lead-out mounting component such as CSP or BGA.
[0017]
The solder ball in the present invention is, for example, a metal having a composition having a low melting point, such as Pb-Sn, Sn-Zn, Pb-Sn-Ag, or Sn-Ag-Cu, having a diameter of 10 to 800 m, preferably 50 to 500 m. Refers to a spherical object. As the solder, it can be applied to a case where cream solder is used. The cream solder is a creamy material in which a solder powder, a fluxing agent, a thixotropic agent such as carnauba wax and the like are mixed as is known.
[0018]
The solder cream preferably contains about 5 to 15% of a flux agent for cleaning a metal surface to be joined. The fluxing agent is an auxiliary material containing rosin, a solvent and an activator for improving the adhesiveness of solder, and plays a role of removing oxides on the metal surface. In the soldering step, it is considered that volatile components in the flux enter the metal of the solder and form voids.
[0019]
The mounted product in the present invention refers to a product in which mounted components are fixed on a board by soldering.
[0020]
An example of a method for surface mounting a mounting component on a substrate according to the present invention will be described step by step. In the method of the present invention, first, a solder cream is applied to one or both of a substrate and a mounted component. The solder cream is preferably applied in a pattern by applying a mask on the substrate using a printing machine. The amount of application at this time should be adjusted so that the amount of solder becomes an appropriate amount. If the amount is too large, there is a problem that the solder flows in the heat treatment step. If the amount is too small, the adhesion between the two becomes poor.
[0021]
In BGA and CSP, a flux is first applied onto a substrate by a printing process, and then a BGA or CSP mounting component having solder balls is pressed onto the applied substrate, and solder balls are applied to the ends of the flip chip pads via the flux. Temporarily. Next, the mounted component substrate to which the chip has been temporarily attached is placed in a reflow furnace and subjected to reflow processing at a predetermined temperature. In the present invention, the heating reflow process is performed in an upright state.
[0022]
In the present invention, erecting a substrate / mounted component means a state in which an angle is formed with respect to a horizontal plane. It includes not only the vertical state as shown in FIG. 1 but also the oblique state as shown in FIG. The angle with respect to such a horizontal plane is 30 degrees or more, preferably 45 degrees or more, and particularly preferably 90 degrees (upright). By setting the board / mounted component in such a state, the gas can easily escape from the molten solder.
[0023]
In the present invention, it is not necessary that the board / mounting component is melted in the upright state in the state where the entire process is upright, but may be performed in some steps, for example, after the solder is melted in the latter half of the melting step. Good. Further, the angle may not be constant, and may be changed with time from a horizontal state to a certain angle and from a certain angle to another angle. In order to prevent the uneven distribution of the solder, a so-called swing may be performed in the middle of the process, for example, by lowering the right direction or by changing the direction in which the substrate / mounting component stands in the opposite direction.
[0024]
In the method of the present invention, it is necessary to stand up for a certain period of time so that voids in the solder are removed. For example, it is preferably 5 seconds to 5 minutes, preferably about 10 seconds to 2 minutes.
[0025]
In the above heating step, when the board / mounted component cannot be held, the angle is set to 45 degrees or less, and placing the mounted component at the soldering position does not cause a problem that the mounted component falls off. The surface may be temporarily fixed with a bond or the like. During the process, the board and the mounted component may be sandwiched by some jig.
[0026]
The operation of removing the voids by heating and melting the solder is preferably performed while applying vibration, because bubbles in the solder are easily removed. As the vibration, fine vibration by an ultrasonic wave, a low frequency or the like is preferable.
[0027]
In the present invention, the reflow furnace is a furnace used for heating and melting the board / mounting component solder. The reflow furnace may be a batch heating furnace or a continuous tunnel furnace. A continuous tunnel furnace is preferred from the viewpoint of processing efficiency. The atmosphere of the furnace may be air, but is preferably a nitrogen atmosphere in order to prevent oxidation of solder and the like. Further, reflow under reduced pressure is more preferable.
[0028]
The heating method of the reflow furnace in the reflow step may be an infrared radiation heating method or a hot air heating method. Further, another method may be used. The processing temperature must be higher than the temperature at which the solder melts, so that the oxidation of the solder surface does not proceed significantly, and the substrate and the mounted parts are not damaged by heat. The temperature is preferably in the range of + 20 ° C to the melting point temperature of solder + 60 ° C.
[0029]
The board / mounted component soldered by the solder melted in the reflow furnace is taken out after solidifying the molten solder in a subsequent cooling step, or is taken out as a product, or is further carried to the next step to be a product.
[0030]
The method of the present invention also includes a mounting component in which a mounting component is surface-mounted on a board, and a mounting component having a void in a solder ball portion is heated in a reflow furnace in an upright state to be present in the solder ball. Also, the present invention relates to a method of repairing a defective mounting product in which a solder ball is cooled and solidified after removing a void.
[0031]
A mounted product having a void can be detected by inspection using X-rays or the like. The mounted products that were found to be defective with many voids as a result of the inspection are collected, and the mounted products are set up and reheated in a reflow furnace to discharge the voids in the solder out of the solder. Can be repaired.
[0032]
The reheating temperature, time, heating rate, furnace, and atmosphere in the furnace in the reflow furnace in the repair method of the present invention can be performed under the same conditions as described in the first invention.
[0033]
【The invention's effect】
According to the method of the present invention, the gas generated during the heating reflow process and existing in the solder balls moves upward in the molten solder balls and is released to the atmosphere. As a result, it is possible to reliably prevent voids from being generated in the solder ball. In addition, even if a defective product has a void, the reflow treatment of the present invention allows the gas in the solder ball to escape, and it is possible to obtain a good product without voids.
[0034]
【Example】
Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
[0035]
Embodiment 1
《Test material》
The following members were used.
Substrate: a length L of 25.0 mm, the width W is 21.0 mm, used as a rectangular parallelepiped plate shape having a thickness of t is 0.8 mm, the diameter _{d 0} of the electrode pads is 0.4 mm, N is 360 Flip Chip pads were formed.
Mounting component: Silicon wafer Solder ball: 0.6 mmφ Sn-Pb eutectic solder ball Flux: Rosin
《Application of flux to substrate》
Screen printing was performed.
[0037]
《Heating reflow device》
The following equipment was used.
Manufacturer: Malcolm Inc. Heating method: Hot air heating method
《Reflow test》
As shown in FIG. 2, a heating reflow process was performed under the following conditions while maintaining the temperature at 60 degrees.
Heating rate: 4 ° C / sec Maximum temperature: 230 ° C
Holding time at the maximum temperature: 30 seconds Cooling rate: 300 ° C./min
FIG. 3 shows an X-ray photograph of a solder ball in the obtained mounting product. It can be seen that the solder ball has almost no void.
[0040]
Embodiment 2
In Example 1, a 0.6 mmφ Sn—Ag (3%) — Cu (0.5%) solder ball was used instead of a 0.6 mmφ Sn—Pb eutectic solder ball, and the maximum temperature was Was carried out in the same manner as in Example 1 except that the temperature was changed to 250 ° C. X-rays of the solder balls showed similar results.
[0041]
[Comparative Example 1]
Example 1 was carried out in the same manner as in Example 1 except that the substrate / mounting component was placed horizontally and treated in a reflow furnace. FIG. 4 shows the results.
[0042]
Embodiment 3
Four mobile phones (model D502i) were disassembled, and the mounting board was taken out. Heat reflow treatment was performed under the following conditions with the solder ball portion having the largest number of voids (90% of the solder balls containing voids) vertically arranged as shown in FIG.
Furnace: Tamura Seisakusho Nitrogen atmosphere reflow system (TNS40-50H)
Heating rate: 2.2 ° C./sec Maximum temperature: 220 ° C.
Holding time at the maximum temperature: 10 seconds Cooling rate: 300 ° C./min
FIG. 5 shows a photograph of the condition of the voids in the solder ball portion before the treatment, and FIG. 6 shows a photograph of the condition of the voids in the solder ball portion after the treatment. As is clear from these photographs, voids were significantly reduced by the reflow treatment of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing one embodiment when a mounted product is surface-mounted by the method of the present invention.
FIG. 1 is a schematic diagram showing another embodiment when a packaged product is surface-mounted by the method of the present invention.
FIG. 3 is an example of an X-ray fluoroscopic image showing a state of a solder ball of a BGA package manufactured by the method of the present invention.
FIG. 4 is an example of an X-ray fluoroscopic image showing a state of a solder ball of a BGA package manufactured by a conventional method.
FIG. 5 is an example of an X-ray fluoroscopic image showing a state of a solder ball of a BGA package before performing a repair method of the present invention.

Claims (7)

In the method of surface-mounting a mounted component on a board using solder, the board and the mounted component are heat-treated in a reflow furnace in an upright state to remove voids present in the molten solder balls, and then the solder is removed. A method for surface mounting a mounting component, which comprises cooling and solidifying a ball. 2. The method according to claim 1, wherein the mounted component is a BGA or a CSP. 3. The method according to claim 1, wherein the heat treatment temperature is in a range from a melting point temperature of solder + 20.degree. C. to a melting point temperature of solder + 60.degree. 4. The method according to claim 1, wherein the solder is cream solder. 5. The method according to claim 1, wherein in the reflow step, the solder is melted while applying vibration to the mounted component and the substrate. The method according to claim 5, wherein the vibration is an ultrasonic vibration. After removing the voids in the solder balls by performing a heat treatment in a reflow oven in a standing state, the mounted products with the voids in the solder ball part are mounted on the board with the mounted components surface-mounted. A method for repairing a mounted product, characterized by cooling and solidifying the product.

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