JP2000062136A - Method for printing metallic paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a metallic paste to be smoothly supplied into a recessed part and prevent a joint failure from occurring. SOLUTION: In a metallic paste printing method by which a metallic paste 6 is printed on an electrode 2 formed at the bottom of a recessed part 3 through a stencil mask 4, the stencil mask 4 with a smaller opening size than the opening size D of the recessed part 3, is used when the recessed part 3 is a recessed part whose ratio obtained by dividing the depth (t) of the recessed part 3 by an opening size D is a depth aspect ratio exceeding 0.2. Consequently a deaeration passageway for an air remaining in the recessed part 3 during printing the metallic paste 6 is secured without the edge part 1E part of the recessed part 3 being hermetically sealed by the metallic paste 6 and therefore an unfilled part to be caused by a residual air in the recessed part 3 is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal paste printing method for printing a metal paste on an electrode in a recess provided in a work.

[0002]

2. Description of the Related Art A printing method is known as a method for applying a metal paste such as cream solder used for joining electronic parts to electrodes. This method, by mounting a stencil mask provided with an opening corresponding to the electrode that is the printing target site on the printing object, after supplying the metal paste on the stencil mask, by sliding the squeegee on the stencil mask Since the metal paste is imprinted through the openings, it is characterized in that a fixed amount of metal paste can be supplied only to the printing target portion.

[0003]

By the way, the shape of the target portion on which the metal paste is printed is various, and the electrode formed on the bottom of the recess provided in the work such as the substrate may be the target. . In such a case, especially in the case of a recess having a deep aspect ratio in which the depth of the recess is deeper than the opening size, it is difficult to completely fill the metal paste into the recess, and the inside of the metal paste is not filled. Easy to create gaps.
This phenomenon occurs when the metal paste is imprinted with a squeegee so that the metal paste completely imprints the opening of the recess, so that the air at the bottom of the recess does not escape from the opening and enters the recess. It is caused by remaining. If solder joining is performed while leaving such an unfilled gap, the gap hinders the joining between the solder mounted on the recess and the electrode of the recess, and a problem that a joint failure easily occurs. there were.

Therefore, an object of the present invention is to provide a method for printing a metal paste which can supply the metal paste satisfactorily into the recesses and prevent defective bonding.

[0005]

A method of printing a metal paste according to a first aspect of the present invention is a method of printing a metal paste in which a metal paste is printed on an electrode formed on the bottom of a recess of a work through a stencil mask. Then, when the ratio obtained by dividing the depth of the recess by the opening size exceeds a predetermined ratio, a stencil mask having an opening size smaller than the opening size of the recess is used.

A method for printing a metal paste according to a second aspect is the method for printing a metal paste according to the first aspect,
The predetermined ratio is 0.2.

According to the invention described in each claim, by using the stencil mask having the opening size smaller than the opening size of the recess, the degassing route in the recess at the time of printing the metal paste is secured, and the air in the recess is secured. There is no unfilled portion due to the remaining.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1 (a), (b), (c),
(D), (e), FIG. 2 (a), (b), (c), (d)
FIG. 4 is a process explanatory diagram of a solder bump forming method according to an embodiment of the present invention. In FIG. 1A, a substrate 1 as a work is provided with a recessed portion 3, and an electrode 2 is provided on the bottom of the recessed portion 3.
Are formed. Here, the ratio t / D obtained by dividing the depth t of the concave portion 3 by the opening dimension D of the concave portion 3 is larger than 0.2, and the concave portion has a deep aspect ratio shape having a large depth with respect to the diameter.

Next, a stencil mask 4 for printing a metal paste in the recess 3 is mounted on the surface of the substrate 1. The metal paste is a flux component containing conductive particles. As shown in FIG. 1B, the stencil mask 4 is provided with an opening 4 a at a position corresponding to the recess 3, and the dimension d of the opening 4 a is set smaller than the opening dimension D of the recess 3. In the present embodiment, the dimension d is set in the range of 70 to 90% of the opening dimension D of the recess 3.

As shown in FIG. 1B, the metal paste 6 is supplied onto the stencil mask 4, and the squeegee 5 is slid on the stencil mask 4, so that the metal paste 6 is opened in the concave portion 3 a 4 a. Is printed through. The behavior of the metal paste 6 during this printing process will be described below. When the squeegee 5 is gradually slid to the right, the metal paste 6 is scraped on the stencil mask 4,
As shown in FIG. 1C, the stencil mask reaches the opening 4a.

At this time, since the metal paste 6 is a highly viscous paste-like substance, it does not immediately droop vertically downward even when it reaches the opening 4a, and the squeegee 5 moves in the traveling direction as shown by the arrow a. It penetrates into the concave portion 3 with a velocity component. That is, the metal paste 6 is not evenly filled in the recesses 3, but the filling of the metal paste 6 progresses in the form of leaving the voids 3a inside the recesses 3 on the side opposite to the advancing direction of the squeegee 5.

The air remaining in the void 3a is pushed out through the gap between the stencil mask 4 and the substrate 1. As described above, the opening dimension d of the stencil mask 4 is the opening dimension D of the recess 3. 1 (c) because it is smaller than
The edge portion 1E of the concave portion 3 shown in FIG. 3 does not contact the metal paste 6 but contacts only the lower surface of the stencil mask 4. That is, from the time when the filling of the metal paste 6 into the recess 3 is started to the time when the inside of the recess 3 is completely filled through the state shown in FIG. It is not sealed by the paste 6, and therefore, the air remaining in the recess 3 is not pressed by the metal paste 6 and leaks to the outside from the gap near the edge point 1E. As a result, FIG. 1 (e)
As shown in FIG. 3, after the printing of the metal paste 6 into the recess 3 by the squeegee 5 is completed, an unfilled gap due to air remaining inside the recess 3 does not occur, and the inside of the recess 3 is filled with the metal paste 6. Fills well with no gaps.

Next, after the printing is completed, as shown in FIG. 2 (a), with respect to the concave portion 3 filled with the metal paste 6,
Solder balls are mounted. As shown in FIGS. 2B and 2C, the solder balls 7 are aligned and mounted on the concave portions 3 by the suction tool 8. After that, the substrate 1 is sent to the reflow process and heated. By this heating, the solder balls 7
Melts and is soldered to the surface of the electrode 12 at the bottom of the recess 3. At this time, due to the flux component in the metal paste 6, the oxide film on the surfaces of the solder balls 7 and the electrodes 2 is removed,
Good solder joining is achieved. Further, since the conductive particles in the metal paste 6 are present in the concave portion 3, the solder balls 7
The molten solder, which has melted, moves downward while wetting the conductive particles in the recess 3 and reliably reaches the surface of the electrode 2. At the time of this movement, since there is no unfilled portion of the metal paste 6 due to air remaining inside the concave portion 3, the molten solder surely fills the concave portion 3 to form a good solder joint with the electrode 2. Can be formed.

[0014]

According to the present invention, since the stencil mask having the opening size smaller than the opening size of the recess is used, the deaeration path of the air remaining in the recess during the printing of the metal paste is secured, An unfilled portion of the metal paste due to air remaining in the recess does not occur. Therefore, the solder mounted on the recess and the electrode in the recess can be soldered well.

[Brief description of drawings]

FIG. 1A is a process explanatory diagram of a solder bump forming method according to an embodiment of the present invention. FIG. 1B is a process explanatory diagram of a solder bump forming method according to an embodiment of the present invention. (D) Process explanatory drawing of the solder bump forming method of one embodiment of the present invention (e) Process explanatory drawing of the solder bump forming method of one embodiment of the present invention

FIG. 2A is a process explanatory diagram of a solder bump forming method according to an embodiment of the present invention. FIG. 2B is a process explanatory diagram of a solder bump forming method according to an embodiment of the present invention. (D) Process explanatory drawing of the solder bump forming method of one embodiment of the present invention

[Explanation of symbols]

1 substrate 2 electrodes 3 recess 4 stencil mask 4a opening 6 Metal paste

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05K 3/12 610 H05K 3/12 610N 3/34 505 3/34 505C (72) Inventor Shoji Sakami 1006, Kadoma, Kadoma City, Osaka Prefecture F-term within Matsushita Electric Industrial Co., Ltd. (reference) 2C035 AA06 FD01 FF22 2H113 AA02 BA10 BB22 BC12 CA17 EA06 EA07 5E319 BB04 BB05 CD29 GG03 5E343 BB03 EE23 GG18

Claims (2)

[Claims] 1. A method for printing a metal paste in which a metal paste is printed on an electrode formed on the bottom of a recess of a work through a stencil mask, which is obtained by dividing the depth of the recess by the opening size. A method of printing a metal paste, wherein a stencil mask having an opening size smaller than the opening size of the recess is used when the ratio exceeds a predetermined ratio. 2. The method for printing a metal paste according to claim 1, wherein the predetermined ratio is 0.2.