JPH09116257A - Solder bump forming method - Google Patents

Abstract

The present invention relates to a solder bump forming method which is applied when manufacturing a circuit board or the like having solder bumps for connecting various electronic parts and the like, and uses equipment for ordinary screen printing. (EN) A plurality of solder bumps can be easily formed at a low cost at a necessary place at the same time. In a method of forming solder bumps on a surface of a circuit board for an electronic circuit, a step of preparing a solder paste molding sheet 1 having an opening 1a for filling a solder paste at least at a predetermined position; A step of filling the above-mentioned opening portion 1a of the sheet 1 with the solder paste 3;
The step of aligning and superposing the sheet 1 on the electrode 6 position of the circuit board 5 and the like, the step of reflowing the solder paste 3 filled in the opening portion 1a of the sheet 1, and the sheet 1 the circuit board 5 and the like. And a step of removing the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder bump forming method applied to, for example, manufacturing a circuit board having solder bumps for connecting various electronic components.

[0002]

2. Description of the Related Art Conventionally, as a method of mounting a silicon chip on a circuit board, for example, a wire bonding method in which an electrode pad of the silicon chip and an electrode pad on the circuit board are conductively connected with a thin metal wire, or a chip is mounted on a lead frame. The method of packaging and connecting to the circuit board by using solder is adopted.

However, with the recent miniaturization and high density of electric products, the flip-chip method has attracted attention. In the flip chip method, electrodes on a circuit board and electrodes on a silicon chip are connected by bumps such as solder provided on the electrodes of the silicon chip.

Furthermore, BGA (ball grid array)
Also when connecting these to the circuit board, solder bumps (solder balls) in which the electrodes of the BGA and the electrodes on the circuit board are formed on the electrodes of the BGA are used.

As a method of forming the solder bumps (or solder balls) as described above, conventionally, for example, a solder is processed into a ball shape, and a flux or the like is applied onto an electrode as an adhesive and then reflowed. In the case of small solder bumps, a solder wire is bonded to the electrode using a wire bonder, and a ball that can be used for bonding is used, or a molten solder is sprayed from a nozzle to directly form a solder bump. Etc. have been proposed and implemented.

[0006]

However, each of the above methods requires large-scale mechanical equipment, and as a result, an increase in the cost of the mounting process cannot be avoided. Further, as described above, the method of using the wire bonder or the molten solder has a problem that the point-by-point bumps are formed, resulting in a long working time. When the size becomes small, there is a problem that handling becomes difficult.

The present invention has been proposed in view of the above problems, and it is possible to easily form a plurality of solder bumps simultaneously at low cost and at required locations by using a facility for ordinary screen printing. It is an object to provide a solder bump forming method.

[0008]

In order to achieve the above object, the solder bump forming method according to the present invention is as follows.

That is, in the method of forming solder bumps on the surface of a circuit board for electronic circuits, the step of preparing a solder paste molding sheet having openings for filling the solder paste at least at predetermined positions, and the sheet. A step of filling a solder paste in the opening portion, a step of aligning and superimposing the sheet at an electrode position of a circuit board or the like, and a step of reflowing the panda paste filled in the opening portion of the sheet, And a step of removing the sheet from the circuit board or the like.

[0010]

When the solder paste is filled in the openings formed in the solder paste molding sheet as described above, it can be easily filled by using, for example, a screen printer. In addition, by simply stacking the solder paste molding sheet filled with the solder paste on the circuit board, etc. and performing reflow, the solder bumps can be easily and surely placed at desired positions on the electrodes of the circuit board, etc. Then, it is possible to form them simultaneously.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A method of forming a solder bump according to the present invention will be specifically described below with reference to the drawings, taking an example of forming a solder bump on an electrode of a circuit board or the like.

First, as shown in FIG. 1 (a), a solder paste molding sheet 1 in which openings 1a for filling solder paste are formed in advance at positions corresponding to electrodes of a circuit board or the like on which solder bumps are to be formed, is formed. prepare. As the solder paste molding sheet, a green sheet in which ceramic particles are dispersed is preferably used. However, for example, a soft or hard heat-resistant synthetic resin sheet or metal such as a metal mask may be used.

The opening 1a may be formed corresponding to the electrode position of the circuit board or the like on which the solder bumps are to be formed, and when there are a plurality of electrodes, they may be formed correspondingly. The opening area of the opening 1a and the thickness of the sheet 1 may be appropriately set in consideration of the size of the solder bump to be formed on the electrode of the circuit board or the like.

Next, as shown in FIG. 1B, when the solder paste is filled with the solder paste molding sheet 1 having an opening 2a at the same position as the opening 1a of the sheet 1 as required. The mask sheets 2 are laminated. Then, the solder paste 3 is placed on the mask sheet 2 and pressed from above to fill the solder paste into the openings 1a and 2a of both sheets 1 and 2 described above, and then, as shown in FIG. ), The mask sheet 2 is separated from the solder paste forming sheet 1. In the figure, 4 is a mask for pressing the paste.

Then, the sheet 1 in which the opening 1a is filled with the solder paste as described above is placed on the electrode 6 of the circuit board 5 or the like as shown in FIG. 3D, and the solder paste is reflowed. By doing so, after the solder bumps 7 are formed on the electrodes 6 as shown in FIG. 6E, the sheet 1 is removed as shown in FIG. When the sheet 1 is removed, if the shape of the sheet is maintained, it can be removed simply by peeling. Thereafter, if necessary, the solder bumps 7 may be heated again on the electrodes 6 to adjust the shape of the solder bumps 7.

As described above, the solder bumps can be satisfactorily formed on the electrodes of the circuit board or the like, and a large number of solder bumps can be easily formed at the same time. For example, the solder paste is directly printed on the circuit board or the like to form the bumps. When forming, there are problems such as excess and deficiency of the amount of solder and variations in the height of the bumps. However, in the present invention, the solder paste is filled in the openings formed to have a predetermined size, The amount is kept almost constant and there is almost no excess or deficiency.

When the solder paste forming sheet is filled with the solder paste, the sheet is inspected, for example, the filling amount of the solder paste is confirmed by the unevenness of the solder filling portion to correct the excess or deficiency of the solder amount, or By changing the thickness of the solder paste molding sheet and the size and shape of the openings, etc., when the solder bumps are formed on a silicon chip, circuit board, etc.
Alternatively, the occurrence of defects such as bump height variations can be prevented in advance, and the product yield can be improved.

In the above embodiment, the mask sheet 2 can be repeatedly used, and the solder paste molding sheet 1 can also be repeatedly used for materials other than the green sheet that are not deformed or deteriorated during the reflow. can do.

When a green sheet is used, a mask sheet 2 having no openings 2a is used as an underlay when the green sheet is formed by the doctor blade method or the like, and the green sheet is placed on the mask sheet 2. After molding the solder paste molding sheet 1, both sheets 1
It is also possible to simultaneously form the openings 1a and 2a in 2 with a mold or the like, turn them upside down and fill the solder paste from there.

When a sheet other than the green sheet is used as the solder paste forming sheet 1, the solder paste 3 is placed directly on the upper surface of the solder paste forming sheet 1 without using the mask sheet 2 and opened. The hole 1a may be filled with solder paste, and the solder paste remaining on the sheet 1 may be scraped off with a scraper or the like.

[0021]

EXAMPLE As an example of the present invention, a green sheet in which ceramic particles were dispersed was used as a solder paste molding sheet, and solder bumps were formed on the electrodes of the circuit board according to the process of FIG.

First, alumina powder was used as the ceramic particles, and 10 parts by weight of butyral resin, 70 parts by weight of dibutyl phthalate as a plasticizer, and 5 parts of isopropyl alcohol as a solvent were used with respect to 100 parts by weight of the alumina powder.
Add 0 parts by weight and 50 parts by weight of methyl ethyl ketone and add
A slurry was prepared by mixing with a ball mill for 8 hours, and a green sheet having a thickness of 250 μm was prepared on a PET film by a doctor blade method.

An opening portion 1a for filling a circular solder paste having a diameter of 200 μm is formed on the green sheet by using a mold.
1 are formed by forming a large number of them at intervals of 500 μm pitch.
The solder paste molding sheet 1 in (a) was used.
A PET film having an opening 2a at the same position as the opening 1a of the sheet 1 was prepared as a mask sheet 2 at the time of filling the solder paste.

As shown in FIG. 1 (b), the mask sheet 2 is superposed on the solder paste molding sheet 1 and the solder paste 3 using Pb / Sn = 60/40 solder is placed above the mask sheet 2. Place and press from above to open hole 1
After a and 2a were filled with the solder paste, the mask sheet 2 was peeled from the solder paste molding sheet 1 together with the solder paste remaining thereon as shown in FIG.

Next, the ceramic substrate 5 made of 96% alumina.
A circuit board on which a large number of circular electrodes 6 having a diameter of 300 μm were formed at a pitch of 500 μm using Ag / Pd paste was prepared. After applying flux onto the electrodes 6, solder was applied as shown in FIG. The paste forming sheet 1 was aligned and superposed so that the solder paste 3 filled in the openings 1a was located on the electrodes 6.

In this state, the solder bumps 7 were formed on the electrodes 6 by heating for 5 seconds at 220 ° C. and reflowing, as shown in FIG. 1 (e). Then, after removing the solder paste molding sheet 1 as shown in FIG.
The solder bumps 7 were ball-shaped by heat treatment at a temperature of ℃ for 5 seconds.

Solder bump 7 obtained as described above
The height of each of the 200 solder bumps was measured and found to be 110 μm ± 15 μm without any variation in height, and no defects such as bridges occurred in the 200 solder bumps. It was possible to form solder bumps on.

As a comparative example, a solder paste was printed using a metal mask on an alumina substrate provided with the same Ag / Pd electrode as described above and reflowed to form solder bumps. When the height of the obtained bump was measured in the same manner as in the invention example, it was 60 μm ± 30 μm.

[0029]

As described above, according to the present invention, it is possible to easily form a plurality of solder bumps at a necessary position at a low cost by a simple operation without using a large-scale equipment. This is effective for improving the efficiency and accuracy of the solder bump forming work, and has an effect of being able to sufficiently cope with recent miniaturization and high density of various electronic devices and the like.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing an example of steps of a solder bump forming method according to the present invention.

[Explanation of symbols]

 1 Solder Paste Molding Sheet 2 Mask Sheet 1a, 2a Openings 3 Solder Paste 5 Circuit Board 6 Electrode 7 Solder Bump

Claims (2)

[Claims] 1. A method of forming a solder bump on a surface of a circuit board for an electronic circuit, the step of preparing a solder paste molding sheet having an opening for filling a solder paste at least at a predetermined position, and the sheet. A step of filling a solder paste in the opening part, and a step of aligning and superimposing the sheet on an electrode position of a circuit board or the like,
A solder bump forming method, comprising: a step of reflowing a solder paste filled in an opening of the sheet; and a step of removing the sheet from a circuit board or the like. 2. The solder bump forming method according to claim 1, wherein a green sheet in which ceramic particles are dispersed is used as the solder paste forming sheet.