JP2000332153A - Method for cleaning solder bump forming surface of wafer-level csp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely clean the solder bump forming surface of a wafer-level chip size (scale) package (CSP) which is formed in the level of a wafer. SOLUTION: After solder bumps are formed on a wafer 13 and the bumps are reflowed, the wafer 13 is held by a spin chuck and rotated. The solder bump forming surfaces 10 of the wafer 13 are heated by blowing steam upon the surfaces 10 from a nozzle 16. When the surfaces 10 are heated, the residues of flux 11, scattered solder 12, etc., become soft. Then the residues are washed away by jetting a washing solution upon the softened residues with a high pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip size (scale) which is an IC package process in a semiconductor manufacturing process.
L) In connection with the cleaning of the package (CSP),
The present invention relates to a method for cleaning a solder bump forming surface of a wafer level CSP, in which, after a solder bump is formed, the formation surface is cleaned in a wafer level CSP in which the P process is performed on the wafer.

[0002]

2. Description of the Related Art In recent years, portable devices and small high-density mounting devices have been increasingly miniaturized and ultra-thin, and accordingly, integrated circuit (IC) packages used in these devices have been developed. Are also required to be ultra-small and ultra-thin. As an IC package process that meets such demands, a package that is equivalent to or slightly larger than the chip size is used.
A chip size (scale) package (CSP), which is a method of mounting, is known. Furthermore, such a CSP
As a process to perform all CSPs at the wafer stage
There is known a wafer level CSP in which processing is performed and then dicing is performed to obtain individual CSPs.

In the above wafer level CSP, for example, in the super CSP, Al pads are rearranged by multilayer wiring at the wafer level, and bumps which can be soldered to external terminal portions are formed. A protective resin is coated on the entire surface of the wafer, and after the solder bumps are formed, dicing is performed. Ultra CPS (Flip ChipTe
(Chnologies) forms an electrode conversion pattern and an electrode pad that can be soldered on an insulating resin layer at the wafer level, and forms a protective resin layer except for that part. After forming solder bumps on the CSP, it is diced into individual CSPs.

[0004] The formation of the solder bumps has a diameter of 0.3 to 0.3 mm.
The solder bump is soldered with a solder ball of about 5 mm or finer. However, a flux residue at the time of soldering and ultra-fine particles of about several μm to 100 μm are attached to the solder bump formation surface. Therefore, solder ball cleaning and flux cleaning must be performed after the formation of the solder bumps. Conventionally, cleaning of a printed circuit board is known as flux cleaning after soldering. In this process, a high-pressure jet method using a fluorocarbon, ethane or other solvent-based or water-based cleaning agent, a submerged jet system, an aerial jet system, a US (ultrasonic) dip system, or the like is used. In the case of flux cleaning of level CSP, as the solder ball becomes finer and denser, the flux residue at the edge and fine solder scattered matter are solidified and adhered to the protective resin layer of the package. Simply using the above-mentioned cleaning method has made it difficult to reliably clean.

[0005]

The problem to be solved by the present invention is as follows.
In the wafer level CSP, after forming solder bumps,
Wafer level C, which is capable of reliably cleaning the residue such as flux residue and solder fine particles adhered to the formation surface.
An object of the present invention is to provide a method of cleaning a solder bump forming surface of SP.

[0006]

According to the present invention, a wafer is provided.
In the level CSP, after the solder bump is formed, the solder bump forming surface is heated to such an extent that the residue existing on the forming surface is softened, the wafer is rotated, and a cleaning liquid is sprayed onto the heated solder bump forming surface to perform cleaning. A method for cleaning a solder bump forming surface of a wafer level CSP is provided, which solves the above problem.

The solder bump forming surface may be heated by spraying steam such as water vapor or a cleaning agent vapor, by spraying a heated cleaning solution or hot water, or by heating a heater such as a halogen lamp near the solder bump forming surface. -Heating,
These methods can be appropriately combined, and preferably, the wafer is pre-washed by immersing it in a heated washing solution before the heating step.

[0008]

FIG. 1 shows an example of a CSP.
Al pad (2) multi-layered in C chip (1)
Is connected to a barrier metal (5) via a Cu wiring (3) and a via post (4), and a solder ball (6) is soldered to the barrier metal (5) to form a solder bump. is there. SiN on the back surface of the IC chip (1)
(7) A polyimide layer (8) and a sealing resin layer (9) are provided. In the wafer-level CSP, these processes are performed at the wafer stage, and are finally diced to obtain individual CSPs.

On the surface (10) on which the solder bumps are formed, as shown in FIG. 2, for example, a flux residue containing rosin as a main component is present at the edge and the periphery of the solder ball (6).
Since the residue such as (11) and the ultra-fine solder scattered matter (12) is adhered, the wafer level CSP is washed after reflowing as described below.

[0010] As shown in FIG.
A spin cleaning apparatus is used in which the wafer (13) is held by the spin chuck (14) and washed while rotating the wafer, and pre-washing is preferably performed so as to enhance the washing effect of this step. The pre-cleaning is carried out in a pre-cleaning tank (15) containing a cleaning solution suitable for solder ball cleaning and flux cleaning.
C. (13) is immersed and washed in the washing tank by jet washing in liquid or ultrasonic washing as appropriate. At this time, if the liquid temperature in the cleaning tank is heated to, for example, about 60 ° C., the flux residue attached to the solder bump forming surface is easily dissolved or swelled. Can be washed. Thereafter, the wafer is rinsed or the like and transported to a spin cleaning unit.

In the spin cleaning section, the wafer is about 5
It is rotated at about 00 rpm. At this time, the wafer (1
The surface of 3), at least the surface 10 on which the solder bumps are formed, is heated to such a degree that the residue is softened when being cleaned with a cleaning liquid. The heating is performed by using steam such as steam, cleaning agent steam and a mixture thereof, preferably at a temperature of about 100-1.
This is performed by injecting steam at a temperature of 10 ° C. and a pressure of about 0.1 to 0.15 MPa from a nozzle. The nozzle (16) is
It is configured to oscillate diametrically along the surface of the wafer (13) so that the vapor particles (17) can be sufficiently sprayed on the surface on which the solder bumps are formed, and the injection angle can be varied as desired. And a plurality of them (not shown). For the heating, warming water may be injected, and the warming water may include a cleaning liquid or the cleaning liquid itself may be used as the warming water. Further, a heater (18) such as a halogen lamp may be provided near the formation surface (10), or a gas such as a heated nitrogen gas may be blown.

[0012] The degree of the heating is appropriately set according to the properties of the residue, and may be, for example, about 60 ° C to about 120 ° C. Blown away by the vapor particles. In addition, by appropriately changing the angle of the nozzle or adjusting the injection width, the steam can be reliably supplied to the edge of the solder ball, and the residue such as the flux residue at the corner can be sufficiently softened. It can be removed by the vapor particles.

After the residue is softened by the above heating,
A high-pressure cleaning liquid is sprayed on the forming surface (10). The discharge pressure of the cleaning liquid is, for example, about 1 MPa or more, and preferably about 3 to 7 MPa. Such a washing liquid may be pressurized to a predetermined pressure by a high-pressure pump, but for example, as shown in FIG. 3, the washing liquid is supplied from one flow path (19) to the nozzle (20) and the other is supplied to the nozzle (20). A pressurized gas such as pressurized air may be supplied to the nozzle (20) from the flow path (21) and pressurized by a two-fluid system. In addition, the above-mentioned cleaning liquid or pressurized gas is
It is good to heat so that it does not adhere to (10), for example,
The pressurized air is heated and pressurized to about 60 to 250 ° C., and the cleaning liquid ejected from the nozzle is heated to the optimum temperature for cleaning, for example, about 50 ° C.
It is preferable to heat to about 120 ° C. At this time, if steam is supplied to the air flow path, the formation surface can be heated and cleaned at the same time.
In addition, at the time of the steam injection, by supplying the cleaning liquid to the solder bump forming surface (10) in advance or continuously, the heating and cleaning of the forming surface can be performed together.

After washing with the washing solution, the wafer is optionally dried by a drying means such as combining an IPA jet and a nitrogen gas blow with a wafer pin, for example, at about 2000 to 3000 rpm. Thereafter, the wafer is diced to obtain individual CSPs.

[0015]

The present invention is constructed as described above,
In the level CSP, after the solder bumps are formed, the surface on which the solder bumps are formed is heated, and the wafer is rotated to spray a cleaning liquid onto the heated formation surface to clean the solder bumps. When soldering is performed, the flux residue mainly composed of rosin adhered to the forming surface and the residue such as fine particle scattered solder are softened by the above-mentioned heating, and the heating is performed by steam injection. The part is blown off with softening, and furthermore, a high-pressure cleaning solution is sprayed on the softened residue, so that the residue is reliably removed from the solder bump forming surface, and the wafer is immersed in the pre-cleaning tank. By performing the above-described cleaning process, the cleaning can be performed more efficiently.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a configuration of a CSP.

FIG. 2 is an explanatory view of a solder bump forming surface.

FIG. 3 is an explanatory view showing a cleaning step.

[Explanation of symbols]

 Reference Signs List 6 solder ball 10 solder bump forming surface 11 flux residue 12 solder scattered object 13 wafer 14 spin chuck 15 pre-cleaning tank 16, 20 nozzle

Claims (5)

[Claims] In a wafer level CSP, after a solder bump is formed, the surface on which the solder bump is formed is heated so as to soften the residue on the surface, and the wafer is rotated so that a cleaning liquid is applied to the heated solder bump formation surface. A method for cleaning a solder bump forming surface of a wafer level CSP, comprising: 2. The method for cleaning a solder bump forming surface of a wafer level CSP according to claim 1, wherein the heating of the solder bump forming surface is performed by injecting steam to the forming surface. 3. The heating of the solder bump forming surface is performed by heating and jetting the cleaning liquid.
3. The method for cleaning a surface for forming a solder bump of a wafer level CSP according to item 1. 4. The method for cleaning a solder bump forming surface of a wafer level CSP according to claim 1, wherein a heater is provided close to the solder bump forming surface of the rotatably supported wafer. 5. The solder bump of a wafer level CSP according to claim 1, wherein the wafer is pre-washed by immersing it in a heated cleaning solution before the step of heating the solder bump forming surface. Forming surface cleaning method.