JP3540901B2 - Method of transferring flux to electrode and method of manufacturing bump - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates flux transfer method to the electrodes, the method for producing a fine bump made of a low melting point alloy or metal.
[0002]
[Prior art]
2. Description of the Related Art With the spread of portable information devices and portable video cameras, small semiconductor packages have been required. The number of electrodes tends to increase as the performance of LSIs increases. As a method of realizing such a small and multi-terminal mounting, there is a flip chip in which a chip is directly mounted on a substrate electrode having a narrow pitch. Also, a BGA (ball grid array) or a CSP (chip size package) has been developed in which the terminal arrangement is changed from the peripheral arrangement to the plane arrangement, thereby increasing the number of terminals without extremely narrowing the pitch.
[0003]
In any of the above cases, it is necessary to form a connection terminal (bump) made of a low melting point alloy such as solder or a metal on an electrode such as a substrate. A method of forming a bump using a ball made of a low melting point alloy such as solder or a metal is an effective bump forming method. When forming a bump from a ball, it is necessary to transfer flux to the electrode and temporarily fix the ball to ensure sufficient bonding with the electrode, and then heat and melt the ball at a temperature equal to or higher than its melting point to join the ball to the electrode There is.
[0004]
However, if the flux is transferred to a portion other than the electrode, there is a problem that the ball flows down from the electrode during heating and melting. This can be avoided by transferring the flux only to the electrode portion. That is, U.S. Pat. No. 5,284,287 discloses the following method. A solder having a diameter of 500 to 700 μm is held by an array substrate, and the array substrate is moved onto a flux bath filled with flux while holding the ball, and the array substrate is pushed down and a part of the ball held there is placed in the flux. Soak and apply flux to it. Next, the ball to which the flux is adhered is pressed from the array substrate to the substrate electrode, and is temporarily fixed. Therefore, the flux is supplied only to the electrode to which the ball is temporarily fixed. Even if the temporarily fixed ball is heated and melted, the ball does not flow down from the electrode.
[0005]
[Problems to be solved by the invention]
The method of transferring the flux only to the above electrodes becomes difficult when the diameter of the ball is less than 500 μm. In other words, as the size of the ball becomes smaller, the distance between the array substrate holding the ball and the tip of the ball immersed in the flux becomes shorter, and the flux adheres to the array substrate when the ball is immersed in the flux bath. The adhesion of the flux to the array substrate may cause the adhesion of the ball to that part at the time of the next ball holding, which causes a decrease in the reliability of the formation of the bump on the electrode. Further, when the ball diameter is small, it becomes difficult to adhere the flux to only a part of the ball with good controllability. That is, if the ball has too much flux, the ball will fall from the array substrate into the flux bath due to the adhesive force.
[0006]
The present invention is to provide a method of forming a bump on the electrode of the substrate or the like of the ball is less than 500μm in diameter, a method of transferring a reliably flux only in the electrode portion, and a method for manufacturing a bump using the same .
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is a method for transferring a flux to an electrode of a semiconductor chip, a film carrier, or a substrate by using a transfer device, wherein a parallelizing mechanism made of an elastic material is added to the transfer device. The transfer substrate held by the transferred transfer head has projections corresponding to the electrodes, and the tips of the projections of the transfer substrate are immersed in a flux bath to allow the flux to adhere to the tips, and thereafter, the tips of the projections and the electrodes And then transferring the flux to an electrode to be transferred.
In addition, the present invention transfers the flux to the electrodes by the above method, and thereafter, holds the fine metal balls made of a low melting point alloy or a metal collectively on the array substrate corresponding to the electrodes, and then transfers the flux to the array substrate. After aligning the held fine metal ball with the electrode to which the flux has been transferred, the fine metal ball is pressed against the electrode to which the flux has been transferred and temporarily fixed collectively, and then the temporarily fixed fine metal ball has its melting point. A method for producing a fine metal bump made of a low melting point alloy or a metal on an electrode, characterized by being heated and melted at the above temperature and joined to the electrode.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, a transfer substrate having a projection corresponding to the substrate electrode is used. The tip of the projection of the transfer substrate is immersed in a flux bath, the flux is adhered to the tip of the projection, the tip is aligned with the electrode, and then the flux is transferred to the electrode to be transferred.
The present invention is directed to a ball having a diameter of less than 500 μm, but can be effectively applied to a ball having a diameter larger than that (for example, 760 μm).
[0009]
Although various structures can be considered as the structure of the projection, a sufficient amount of flux necessary to cover the electrode needs to be attached to the tip portion. Therefore, it is desirable that the cross-sectional area near the tip of the protrusion is equal to that of the electrode pad. In addition, in order to easily immerse only the tip in the flux bath, the height must be 200 μm or more, preferably 500 μm or more, as shown in FIG. The shape of the projection tip of the transfer substrate may be flat or may have a curvature.
[0010]
Any material can be used as the material of the flux transfer substrate as long as it can form a protruding structure, and it can be made of ceramic such as glass, metal such as stainless steel, or plastic. The target on which the electrode for transferring the flux is formed is a semiconductor chip, a film carrier, a substrate, or the like. Here, the substrate may be a printed substrate made of glass epoxy, glass, ceramics, or the like, or a flexible substrate made of polyimide or the like. As the material for the fine bumps, solders of various compositions and so-called low melting point alloys or metals having a melting point of 400 ° C. or less can be used.
[0011]
To realize the above transfer method of the present invention, it is possible to use the following mechanism.
1. A transfer substrate having a projection for transferring flux to a position corresponding to an electrode.
2. A mechanism that immerses only the tips of the projections on the transfer substrate in a flux bath.
3. A mechanism that recognizes the positions of the tips of the protrusions of the transfer substrate and the electrodes by image processing and matches the positions of the electrodes.
4. A mechanism that transfers the flux to the electrode by moving the transfer substrate with the flux attached to the tip of the projection to the position of the electrode.
[0012]
Here, as shown in FIG. 2A, a parallelizing mechanism including an elastic body 62 is added to the transfer head 61 that holds the transfer substrate 11 having the protrusions 12. In this case, even if the degree of parallelism of the object to which the flux is applied, such as a substrate, is poor, the transfer head 61 can maintain the degree of parallelism with the object 63 as shown in FIG. Can be applied. Here, the elastic body may be a spring or a polymer material such as rubber.
[0013]
Further, if the flux is applied many times, the flux may adhere to the tip of the protrusion 12 of the transfer substrate 11 in some cases. In such a case, a bath made of a solvent for dissolving the flux is provided, and the tip of the transfer substrate can be immersed therein to remove the fixed flux. At this time, if ultrasonic waves are applied to the solvent, the removal efficiency increases.
[0014]
【Example】
A method for transferring a flux to only an electrode portion and a method for manufacturing a fine bump using the same according to the present invention will be described in detail with reference to the drawings.
1 (a) to 1 (j) show a method of transferring a flux to only an electrode portion and a method of manufacturing a solder bump using the same according to the present invention. On a printed board made of glass epoxy to be transferred, 350 electrodes are formed. One electrode pad has a square shape of 50 μm square. The 350 electrode pads are formed at intervals of 100 μm. Bumps are manufactured using eutectic solder balls (Sn: 60 wt%, Pb: 40 wt%, melting point: 188 ° C., diameter: 45 μm).
To transfer the flux only to the electrode portion, a flux transfer substrate having a protrusion at the same position as the substrate electrode is used. In this embodiment, the flux transfer substrate is manufactured using glass. The projection structure has a columnar shape with a cross-sectional diameter of 50 μm and a height of 500 μm.
[0015]
Hereinafter, a flux transfer method to the electrodes in the order shown, described a method for manufacturing a fine ball bumps to the electrode.
(A) The flux transfer substrate 11 is moved onto the flux bath 21 filled with the flux 22.
(B) The flux transfer substrate 11 is lowered toward the flux 22, and only the tip of the projection 12 of the transfer substrate 11 is immersed in the flux 22.
(C) The transfer substrate 11 is pulled up and the flux 23 is attached only to the tip of the protrusion 12.
(D) The transfer substrate 11 is moved above the electrode portion 32 of the substrate 31, and the tip of the protrusion 12 and the electrode pad 32 are aligned.
(E) The transfer substrate 11 is lowered toward the electrode 32, and the flux 23 is brought into contact with the electrode pad 32.
(F) The flux 23 attached to the tip is transferred to the electrode pad 32, and the transfer substrate 11 is retracted.
(G) After the eutectic solder balls 51 are collectively sucked and held on the array substrate 41 having holes 42 smaller than the ball diameter corresponding to the electrodes, the electrode pads 32 on which the balls 51 and the flux 24 are transferred are formed. Adjust the position.
(H) is lowered towards the arranged substrate 41 to the printed circuit board 31 to press the ball 51 in the arranging substrate 41.
(I) The balls 51 are temporarily fixed collectively to the electrodes to which the flux 24 has been transferred , and the array substrate 41 is retracted.
(J) the ball 51 transports the substrate 31 is temporarily fixed to the electrode 32 in a furnace, heated and melted at 200 ° C. above the melting point of the solder balls 51 and thereafter cleaning the flux, substrate electrode portion and fully bonded to fine A simple solder bump 52 can be formed.
[0016]
【The invention's effect】
As described above, according to the present invention, when a fine metal ball of less than 500 μm is bonded to an electrode using a flux to produce a fine bump, the adhesion of the flux to the array substrate and the fine Metal balls can be prevented from falling off. A fine bump can be manufactured on the electrode onto which the flux has been reliably transferred by using a fine metal ball made of a low melting point alloy or a metal. By using a semiconductor chip, a film carrier, or a substrate to which such fine bumps are connected, an electronic component having an extremely small area can be mounted with high productivity.
[Brief description of the drawings]
FIG. 1 is a view schematically showing a flux transfer step ((a) to (f)) and a bump manufacturing step ((g) to (j)) of the present invention.
FIG. 2 is a diagram illustrating a parallelizing mechanism using an elastic body of a transfer head that holds a projecting transfer substrate according to the present invention.
[Explanation of symbols]
11: Flux transfer substrate 12: Projection structure 21: Flux bath 22: Flux 23: Flux attached to projection 24: Flux transferred to electrode 31: Printed substrate 32: Electrode pad 41: Array substrate 42: Adsorption hole 51: Low melting point Metal or alloy ball 52: low melting point metal or alloy bump 61: transfer head 62: elastic body 63: flux coating target

Claims (2)

A method for transferring a flux to a semiconductor chip, a film carrier, or an electrode of a substrate by a transfer device, wherein the transfer substrate held by a transfer head having a parallelizing mechanism made of an elastic body, which constitutes the transfer device, Having a projection corresponding to the electrode, the tip of the projection of the transfer substrate is immersed in a flux bath, flux is adhered to the tip, and then the projection of the transfer substrate and the electrode are aligned. And thereafter, transferring the applied flux to the electrode, wherein the flux is transferred to the electrode. The method according to claim 1, wherein the flux is transferred to an electrode of a semiconductor chip, a film carrier, or a substrate, and thereafter, fine metal balls made of a low melting point alloy or a metal are collectively held on an array substrate, and thereafter, the array is formed. Align the fine metal balls held on the substrate and the electrode to which the flux has been transferred, and then temporarily fix the fine metal balls held on the array substrate to the electrodes to which the flux has been transferred, Thereafter, the temporarily fixed fine metal ball is heated and melted at a temperature equal to or higher than its melting point and joined to the electrode, and a method for producing a fine metal bump made of a low melting point alloy or metal on the electrode.

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