JP2000299551A - Method for forming bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a bump having high profile at an electrode part by pouring an upper layer liquid into a solder tank to form a layer with molten solder and immersing a substrate into the upper layer liquid such that the electrode part touches the molten solder. SOLUTION: Eutectic solder 4 and an upper layer liquid, i.e., diethylene glycol 6, are poured into a crucible 3 and heated such that the diethylene glycol 6 is laminated on the solder 4 in molten state and two layers are formed. A printed board 1 is then immersed into the diethylene glycol 6 and the electrode part 2 of the printed board 1 is brought into contact with the surface of the molten solder 4 so that the molten solder 4 adhere to the electrode part 2. Since the difference of density between a ball bump 5 and the diethylene glycol 6 is extremely small as compared with that between the ball bump 5 and the atmosphere, surface tension of the ball bump 5 to the printed board 1 is increased. Consequently, contact angle between the ball bump 5 and the printed board 1 is increased and the height of the ball bump 5 is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a bump forming method. More specifically, the present invention relates to a bump forming method for forming a bump on an electrode portion of a printed circuit board.

[0002]

2. Description of the Related Art A bump forming method for forming a bump on an electrode portion of an electronic component is described in "Technique for forming a very fine pitch bump using a dipping method" (Yukiko Nakaoka et al., 25th Micro Joining Research Committee, Soldering Division Association, P51-61, July 1998, hereinafter referred to as Prior Art 1). Conventional technology 1
7A, the solder 4 is heated and melted in the crucible 3 as shown in FIG. 7A, and the electrode portion 2 of the printed circuit board 1 is brought into contact with the molten solder 4 in the crucible 3 as shown in FIG. 7 (c)
As shown in FIG. 1, the printed board 1 is pulled up from the crucible 3 to form ball bumps 5a (solder portions) on the electrode portions 2.

Further, Japanese Patent Application Laid-Open No. 09-237963 discloses a bump forming method for forming a bump on an electrode portion of a printed circuit board (hereinafter, this technique is referred to as Conventional Technique 2).
). In the prior art 2, first, a mask having a through hole is superimposed on a support member, a solder paste is filled in the through hole, and then a printed circuit board is arranged so that the through hole and the electrode portion are in contact with each other. Subsequently, the solder paste in the through holes was dissolved, and the solder paste was transferred to the electrode portions to form bumps on the electrode portions. Further, in the prior art 2, the printed circuit boards are positioned one by one with respect to the mask using a flip chip bonder, and then the substrates are pressurized and heated one by one by a bonder head.

[0004]

However, the prior arts 1 and 2 have the following problems.

[0005] First, the problem relating to the prior art 1 will be described. After lifting the printed board 1 from the crucible, the solder bumps 5a formed on the electrode portions 2 of the printed board 1 are exposed to the atmosphere 11 as shown in FIG. The contact angle α of the solder bump 5 with respect to the printed board 1 is
Density difference between air and air 11 (solder about 10, air about 1.3 × 1
0 ^-3) by is determined by the surface tension. That is, the amount of solder transferred to the electrode unit 2 depends on the density difference between the solder bump 5 and the atmosphere 11.

Since the density difference between the solder bump 5 and the atmosphere 11 is large and the amount of solder supplied to the electrode portion 2 is small, the height of the bump 5a formed in this way is only 30 μm. Therefore, the solder bumps 5a formed in the prior art 1
Is the FEGA Design Guide (EIAJ EDR-73)
It was impossible to satisfy 16).

In the prior art 2, the bonder head is
It is also used in the process of pressurization and heating. Therefore, in order to improve productivity by forming bumps on a plurality of printed boards, it is necessary to prepare a plurality of bonder heads.
However, in the manufacturing cost of the flip chip bonder, the ratio occupied by the bonder head exceeds 50%.
There was a problem that the cost of the flip chip bonder was increased.

A first object of the present invention is to provide a bump forming method capable of forming a bump having a large height on an electrode portion by supplying sufficient solder to the electrode portion.

A second object of the present invention is to provide a low cost and high productivity bump forming method.

[0010]

SUMMARY OF THE INVENTION The bump forming method of the present invention has been made in view of the above problems, and specifically, a method in which a substrate having a plurality of electrode portions is contacted with molten solder in a solder bath. A method for forming a bump on each electrode part, wherein an upper layer liquid is injected into the solder bath so as to form two layers with molten solder, and the electrode part contacts the molten solder with the substrate. As described above, the method is characterized in that the method includes immersing in an upper layer solution to form a bump. According to the method of the present invention, a sufficient amount of solder is supplied to the electrode portion by immersing the solder formed on the electrode portion in an upper liquid having a small density difference from the solder, and a bump having a sufficient height is provided. Can be formed on the electrode portion.

In the bump forming method of the present invention, the specific gravity of the upper layer liquid is preferably 0.5 or more.

Further, in the bump forming method of the present invention,
It is preferable that the solder bath is sealed so as to suppress vaporization of the upper layer liquid. By doing so, the solder can be heated to a temperature higher than the boiling point of the upper layer liquid, so that a solder having a higher melting point and an upper layer liquid having a lower boiling point can be used in combination. Specifically, it is preferable that the solder is Sn-3.5Ag eutectic solder and the upper layer liquid is diethylene glycol.

According to another bump forming method of the present invention, a concave portion is formed by superposing a mask having a through-hole corresponding to an electrode portion of a substrate on a support member and closing one opening end of the through-hole. A step of filling the recess with solder paste, a step of aligning the substrate so that the electrode portion of the substrate is positioned on the corresponding recess, and a step of attracting the substrate to the plate-like member; Including, between the solder paste filled in the concave portion and the corresponding electrode portion includes a step of bringing the substrate and the mask into close contact with each other, a bump forming method of forming a bump on the electrode portion of the substrate, the mask, By forming through holes corresponding to the respective electrodes of the plurality of substrates and simultaneously adsorbing the plurality of substrates to the plate-like member, bumps are simultaneously formed on the respective electrode portions of the plurality of substrates.

In another bump forming method of the present invention, the plate-shaped member has a substrate suction portion for sucking each substrate on one main surface and a penetrating region in a part of the substrate suction portion. Is preferably inserted from the other main surface side of the plate-shaped member, and each substrate on the one main surface side is moved and aligned by a bonder head, and then fixed at a predetermined position of the substrate suction portion.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 First, a bump forming method according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1 and FIG.
Are formed with a plurality of electrode portions 2, and a ball bump 5 is formed on each electrode portion 2. The printed circuit board 1 used in the present embodiment is made of, for example, glass epoxy,
For example, its outer dimensions are 16.0mm x 16.0mm x 1.
0 mm. Also, on one surface of the printed circuit board 1,
For example, the electrode section 2 having a diameter of 0.25 mm is formed at a pitch of 0.5 m.
1024 are formed with m. The electrode part 2 has a thickness of 16
made of Cu having a thickness of 0.5 μm
Ni and Au having a thickness of 0.1 μm are formed by plating.

In order to form a bump, first, FIG.
As shown in (a), dimensions 100 mm × 100 mm × 5
63% Sn-Pb in crucible 3 (solder tank) of 0 mm
Eutectic solder 4 (specific gravity about 9.6, melting point 183 ° C.) and diethylene glycol 6 (specific gravity 1.1, boiling point 244) as an upper layer liquid
° C). Further, the crucible 3 is heated to 210 ° C., and the solder 4 and diethylene glycol 6 are heated to 210 ° C. As described above, since the melting point of the solder is 183 ° C. and the boiling point of diethylene glycol 6 is 244 ° C., the solder 4 melts in the crucible 3 but the ethylene glycol 6 does not boil. Furthermore, since the specific gravity of the solder 4 is larger than the specific gravity of the ethylene glycol 6,
Without mixing ethylene glycol 6 and solder 4
As shown in FIG. 1A, ethylene glycol 6 is stacked on the molten solder 4, and in the crucible 3, the ethylene glycol 6 and the solder 4 form two layers.

In the first embodiment, ethylene glycol is used as the upper layer liquid 6 stacked on the molten solder 4. However, the present invention is not limited to this, and any liquid having a specific gravity smaller than that of the solder 4 may be used. . Specifically, when a liquid having a specific gravity of 0.5 or more was used as the upper layer liquid 6, bumps having a sufficient height were obtained.
The above liquid is preferably used as the upper layer liquid.

Furthermore, in the first embodiment, the crucible 3 is heated to 210 ° C., but the present invention is not limited to this, and the solder 4 and the upper liquid 6 are heated to a temperature higher than the melting point of the solder 4. As long as the liquid is held in the crucible 3 so as to cover the surface of the solder 4 in which the liquid 6 is dissolved, that is, the liquid 6 and the solder 4 form two layers, the same as in the present embodiment. Function and effect can be obtained.

Next, as shown in FIG. 1B, the printed circuit board 1 is immersed in ethylene glycol 6 so that the electrode portion 2 of the printed circuit board 1 is brought into contact with the surface of the molten solder 4 so that the electrode portion 2 is melted. The solder 4 is attached. By doing so, a ball bump can be formed on the electrode portion 2. further,
When the substrate 1 is lifted from the crucible 3, the substrate 1 passes through a liquid of ethylene glycol 6. That is, as shown in FIG. 2A, the substrate 1 is immersed in the ethylene glycol 6 so that the ethylene glycol 6 and the ball bump 5 formed on the electrode portion 2 are in contact with each other.

Since the density difference between the ball bump 5 and the ethylene glycol 6 is extremely small as compared with the density difference between the ball bump (solder) 5 and the atmosphere, the surface tension of the ball bump 5 on the printed circuit board 1 increases. As shown in FIG. 3, the contact angle α between the ball bump 5 and the printed circuit board 1 increases. That is, since the amount of solder adhering to the electrode portion 2 increases, the height of the ball bump 5 increases. Specifically, the solder bump height is 200 μm or more, and the FBGA design guide (EIAJ EDR-73
16).

As shown in FIG. 2B, the substrate 1 having the ball bumps 5 thus formed is pulled up from the crucible 3 to complete the ball bump forming step.

Embodiment 2 FIG. Further, in recent years, a method of using a Pb-free solder has been studied in preparation for the regulation of Pb use. Specifically, the use of Sn-3.5Ag solder or the like has been studied. However, the melting point of Sn-3.5Ag solder is as high as 221 ° C. as compared with the above-described Sn-Pb solder. Therefore, in the first embodiment, when Sn-3.5Ag solder is used as the solder and diethylene glycol having a relatively low boiling point is used as the upper layer liquid, the Sn-3.5Ag solder is heated to a temperature at which it is substantially melted. However, since diethylene glycol boils and evaporates, it does not serve as an upper layer liquid. For this reason, it is necessary to prepare an upper layer liquid having a boiling point corresponding to the melting point of the solder.
That is, it is necessary to replace the upper layer liquid in accordance with the melting point of the solder, so that the process becomes complicated. Embodiment 2 of the present invention
The bump forming method according to (1) addresses such a problem.

The bump forming method according to the second embodiment uses a closed crucible 3a as shown in FIG. The hermetic crucible 3a includes a crucible body 3b and a lid 3c. By closing the crucible body 3b with the lid 3c, the gas phase portion 7 of the crucible body 3b is sealed. In this embodiment,
The Sn-3.5Ag eutectic solder (melting point 2
21 ° C.) and diethylene glycol 6 and solder 4
a and diethylene glycol 6 heated to 250 ° C.
The bump formation is performed in the same manner as in the first embodiment.

Since the melting point of the solder 4a is 221 ° C., the solder 4a is melted in the crucible 3a. Also, since the boiling point of diethylene glycol 6 is 244 ° C., diethylene glycol 6 boils and evaporates in crucible 3a.
Further, when heating is continued, the vaporized diethylene glycol fills the gas phase 7, and the gas phase 7 is pressurized to an atmospheric pressure or higher. Thus, when the pressure of the gas phase part 7 becomes higher than the atmospheric pressure, the vaporization of the diethylene glycol 6 stops. Therefore, even if the solder 4a and the diethylene glycol 6 are heated to 250 ° C., which is equal to or higher than the boiling point of the diethylene glycol 6, as shown in FIG. 4, the liquid state diethylene glycol 6 remains so as to overlap the molten solder 4a. That is, since the vaporization of diethylene glycol 6 is suppressed by using the closed crucible 3a, it is possible to heat and melt the solder 4a to a temperature higher than the boiling point of diethylene glycol 6 with the liquid state of diethylene glycol 6 remaining. it can.

That is, according to the second embodiment, it is unnecessary to change the upper layer liquid depending on the melting point of the solder. Specifically, 63% Sn-Pb eutectic solder and Sn-3.5Ag
For any of the eutectic solders, diethylene glycol can be used as the upper layer liquid.

Embodiment 3 FIG. The bump forming method according to the third embodiment of the present invention forms electrodes on a plurality of substrates at the same time as described below with reference to FIGS.

In this embodiment, a SUS mask member 8 (0.15 mm thick) and a support member 10 are used. In the mask member 8, through holes 9 (φ0.4 mm) corresponding to the electrode portions 2 of the plurality of printed circuit boards 1 are formed. In order to form a bump, first, as shown in FIG.
The support member 10 and the mask member 8 are overlapped, and the through holes 9
The opening 11 is closed, and the recess 11 is formed by the through hole 9 and the surface of the support member 10. As described above, the through hole 9
Are formed so as to correspond to the electrode portions 2 of the substrate 1, so that the concave portions 11 are also formed to correspond to the electrode portions 2 of the plurality of substrates 1. Further, the squeegee 12 is used to fill the solder paste 13 into the recess 11 thus formed.

Next, as shown in FIG. 5 (b), a plurality of printed circuit boards (in this embodiment, one
6 (4 shown in the figure) are conveyed by the tray 14. Further, the plate-like member 15 is arranged above the printed board 1. The plate-like member 15 is for arranging a plurality of substrates 1 at predetermined positions of the mask 8 at a time, and includes a substrate fixing portion 20 for adsorbing and fixing the substrates 1 one by one. The substrate fixing portion 20 is formed on a surface of the plate-shaped member 10 on the substrate 1 side (hereinafter, referred to as a first main surface). Further, a suction groove 17 connected to the suction device is formed in each substrate fixing portion 20 so that the printed circuit board 1 is suctioned and fixed by a suction device (not shown). In addition, each substrate fixing portion 20 includes:
A plate-like member side through hole 16 is formed.

Next, each printed circuit board 1 is fixed to the plate member 15 by suction. As shown in FIG. 6A, the position of the concave portion 11 filled with the solder paste 13 and the position of the electrode portion 2 are detected by the half mirror 18, and the electrode portion 2 is positioned immediately above the concave portion 11. The printed board 1 is moved in the horizontal direction, and the printed board 1 is disposed immediately below the board fixing portion 16 of the plate member 15. Further, the bonder head 19 is passed through the plate-like member side through hole 16 from a main surface (hereinafter, referred to as a second main surface) opposite to the first main surface, and is disposed immediately below the substrate fixing portion 20. The printed board 1 located on the main surface side is sucked by the bonder head 19, the printed board 1 is moved upward, and placed on the board fixing section 16. Subsequently, the printed board 1 placed on the board fixing section 16 is vacuum-sucked by the suction groove 17, so that the printed board 1 is fixed to the board fixing section 20 of the plate member 15. After fixing the printed board 1 to the board fixing section 20, the half mirror 18 and the bonder head 19 move in the horizontal direction, and fix another printed board 1 to the board fixing section 20 of the plate member 15 by the above-described method.
By repeating such a suction fixing step, the printed circuit boards arranged on the tray 14 are simultaneously fixed to the plate member 15 by suction.

Further, as shown in FIG. 6B, the plate-like member 15 to which the printed circuit board 1 is fixed is moved directly below,
The plate member 15 and the mask member 8 are brought into close contact with each other. By doing so, the solder paste 13 filled in the through holes 11 can be brought into contact with the electrode portions 2 of the printed circuit board 1.
Subsequently, the plate member 15, the mask member 8, and the support member 10
Is heated while pressurizing, so that the solder paste 13 filled in the through holes 11 is melted, and the melted solder paste 13 is transferred to the electrode unit 2.

Finally, the plate member 15 adsorbed on the printed circuit board 1 is moved upward to separate the mask member 8 and the plate member 15 from each other, as shown in FIG. The bumps 5 can be simultaneously formed on the electrode portions 2 of the printed circuit boards 1.

In this embodiment, since the mask member 8 corresponding to the plurality of substrates 1 is used, bumps can be formed on the plurality of substrates 1 at the same time. Further, in the present embodiment, when transferring the solder paste 13 to the electrode portion 2 of the substrate 1, no bonder head is required, so that a large number of bonder heads 19 are not required, and the bumps 5 can be formed on a plurality of substrates 1 at low cost. Can be formed.

[0033]

According to the method of the present invention, a sufficient amount of solder is supplied to the electrode portion by immersing the solder formed on the electrode portion in the upper layer liquid having a small density difference from the solder.
A bump having a height sufficient to satisfy the A design guide (EIAJ EDR-7316) can be formed on the electrode portion.

In the bump forming method of the present invention, by setting the specific gravity of the upper layer liquid to 0.5 or more, a bump having a higher height can be formed.

In the bump forming method of the present invention, the solder bath is sealed so as to suppress vaporization of the upper layer solution, so that a solder having a higher melting point and an upper layer solution having a lower boiling point can be used in combination. That is, the same upper layer liquid can be used for both the low melting point solder and the high melting point solder.

In the bump forming method of the present invention, Sn-3.5Ag eutectic solder, which is Pb-free solder, can be used while using diethylene glycol as the upper layer solution.

Another method of forming a bump according to the present invention uses a mask and a supporting member having through holes formed so as to correspond to electrode portions of a plurality of substrates, so that bumps can be simultaneously formed on a plurality of substrates with high productivity. Can be formed.

In another bump forming method of the present invention, a bonder head is inserted from a penetrating region of a plate-like member, the substrate is aligned, and the number of bonder heads is reduced, thereby reducing the cost of bump formation.

[Brief description of the drawings]

FIG. 1 shows a bump forming method according to a first embodiment of the present invention, in which (a) shows a step of melting solder and (b) shows a step of bringing an electrode portion into contact with molten solder.

FIGS. 2A and 2B show a bump forming method according to the first embodiment of the present invention, wherein FIG. 2A shows a step of immersing a substrate on which bumps are formed in an upper layer liquid, and FIG. 4 shows a step of lifting a substrate from an upper layer solution.

FIG. 3 is an enlarged cross-sectional view of a step of immersing a substrate on which bumps are formed in an upper layer solution.

FIG. 4 shows a bump forming method according to a second embodiment of the present invention.

FIGS. 5A and 5B show a bump forming method according to a third embodiment of the present invention, wherein FIG. 5A shows a step of overlapping a mask member and a support member, and FIG. The following shows the steps performed.

6A and 6B show a bump forming method according to a third embodiment of the present invention, wherein FIG. 6A shows a step of fixing a substrate to a plate-like member, and FIG. 6B shows a step of bringing the plate-like member into contact with a mask. The step (c) shows the step of separating the plate member and the mask.

7A and 7B show a bump forming method according to the prior art, wherein FIG. 7A shows a step of melting solder, FIG. 7B shows a step of bringing an electrode portion into contact with molten solder, and FIG. Shows the step of contacting the substrate on which is formed with molten solder.

FIG. 8 is an enlarged cross-sectional view showing a step of exposing a bump formed on a substrate to the atmosphere, showing a bump forming method according to a conventional technique.

[Explanation of symbols]

Reference Signs List 1 board, 2 electrode section, 3 solder tank, 3a solder tank, 3b solder tank body, 3c lid 4 solder, 4a
Solder, 6 upper layer liquid, 8 mask member, 9 through hole, 10 support member, 11 concave portion, 12 squeegee,
13 Solder paste, 15 Plate member.

Claims (6)

[Claims] 1. A bump forming method in which a substrate having a plurality of electrode portions formed thereon is brought into contact with molten solder in a solder bath and bumps are formed on each of the electrode portions. An upper layer solution is injected so as to form two layers, and the method includes immersing the substrate in the upper layer solution to form the bumps so that the electrode portion contacts the molten solder. Bump formation method. 2. The bump forming method according to claim 1, wherein the specific gravity of the upper layer liquid is 0.5 or more. 3. The bump forming method according to claim 1, wherein the solder bath is sealed so as to suppress vaporization of the upper layer liquid. 4. The bump forming method according to claim 3, wherein said solder is Sn-3.5Ag eutectic solder, and said upper layer liquid is diethylene glycol. 5. A recess having a through hole formed so as to correspond to an electrode portion of a substrate, which is overlapped on a support member and one opening end of the through hole is closed to form a recess, and solder paste is applied to the recess. A filling step, an adsorption step of aligning the electrode portion of the substrate so as to be positioned on a corresponding concave portion, and adsorbing the substrate to a plate-like member, and a step between the support member and the plate-like member. A method of forming a bump on an electrode portion of the substrate, the method including: adhering the substrate and the mask so that the electrode portion corresponding to the solder paste filled in the concave portion is in contact with the electrode portion; Forming a through hole corresponding to each of the electrodes of the plurality of substrates on the mask, and simultaneously adsorbing the plurality of substrates on the plate-like member, thereby simultaneously forming bumps on each electrode portion of the plurality of substrates. Features Bump forming method. 6. The plate-shaped member has, on one main surface, a substrate suction portion for sucking each of the substrates and a penetrating region in a part of the substrate suction portion. The substrate is inserted from the other main surface side of the member, and the respective substrates on the one main surface side are moved and aligned by the bonder head, and then fixed at a predetermined position of the substrate suction portion. The bump forming method according to claim 5, wherein