JP3245525B2 - Screen printing method of cream solder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of applying cream solder for soldering a chip onto a land of a substrate .
The present invention relates to a screen printing method for a solder paste.

[0002]

2. Description of the Related Art Since various types of chips are mounted on a substrate, lands corresponding to each chip are formed on the surface of the substrate. As a method of mounting a chip on a substrate, there are a method of soldering with cream solder, a method of bonding with a bond, and the like. The cream solder is generally applied onto the lands by a screen printing device.

FIG. 5 is a partially enlarged sectional view of a screen mask and a substrate of a conventional screen printing apparatus. In the figure, 1
Is a substrate, on its upper surface a land 2 for soldering a chip and a pad 3 for mounting a bare chip.
And pads 4 for connecting the electrodes of the bare chip with wires. Screen mask 5
Has a pattern hole 6 at a position corresponding to the land 2.

In screen printing, a cream squeeze 7 is applied to the land 2 through the pattern holes 6 by sliding a squeegee on the screen mask 5 with the upper surface of the substrate 1 approaching the lower surface of the screen mask 5. It is supposed to. FIG. 5 shows a state in which the substrate 1 is separated from the lower surface of the screen mask 5 after the squeegee is slid on the screen mask 5, whereby the cream solder 7 is applied on the lands 2.

[0005]

The cream solder 6 easily adheres to the lower surface of the screen mask 5. In FIG. 5, a, b, and c indicate cream solder attached to the lower surface of the screen mask 5. The main cause of the adhesion of the cream solders a, b, and c to the lower surface of the screen mask 5 is the adhesion of the screen mask 5 during cleaning. That is, at the time of screen printing, the cream solder 6 easily adheres to the lower edge of the pattern hole 6. In the drawing, d indicates the cream solder attached to the lower edge of the pattern hole 6.

[0006] The cream solder d tends to stain the surface of the substrate 1 during screen printing. Then, the cream solder d is cleaned by wiping with paper or the like. At this wiping, the cream solder adhered to the paper is unnecessarily transferred to the lower surface of the screen mask 5, and the cream solder a, b, c is removed. It causes stains. Further, the cream solder 7 applied on the land 2 may be scattered by some impact and adhere to the lower surface of the screen mask 5, thereby causing the cream solders a, b, and c to become dirty.

When the cream solders a, b, and c adhere to the lower surface of the screen mask 5 as described above, the cream solder 7 is applied to the lands 2 by bringing the upper surface of the substrate 1 close to the lower surface of the screen mask 5 as described above. At this time, the cream solders a, b and c are transferred onto the lands 3 and the pads 4. In the figure, a ', b', and c 'indicate the transferred cream solder.

[0008] By the way, a chip is mounted on the cream solder 7 on the land 2 of the substrate 1 in a later step, and then the cream solder 7 is heated and melted and solidified by a reflow process, so that the chip is placed on the land 2. Soldered. A bare chip is bonded on the land 3 with a bond, and the electrode on the upper surface of the bare chip and the pad 4 are connected by a wire. The cream solders b ′ and c ′ transferred onto the pad 4 are subjected to the reflow process. Since it is melted and solidified by the treatment and adheres to the pad 4, it is impossible to bond a wire on the pad 4. As described above, in the conventional screen printing apparatus, the cream solders b and c attached to the lower surface of the screen mask 5 are likely to be transferred onto the pads 4 of the substrate 1 for wire bonding the bare chip, so that a wire bonding error occurs. It was easy.

Therefore, the present invention provides an
It is an object of the present invention to provide a cream solder screen printing method that can surely prevent the transfer of cream solder that causes wire bonding failure.

[0010]

SUMMARY OF THE INVENTION For this purpose, the present invention provides a method of forming a solder paste on a land formed on a substrate in which a land for soldering a chip and a pad for wire bonding a bare chip are mixed. A cream solder screen printing method, wherein a pattern hole for applying cream solder on the land is formed, and a cream is formed on an inner surface on a lower surface facing the pad.
Solder is hard to adhere, or even if it adheres
A screen mask on which a relief groove in which the solder is not transferred by contact with the pad is overlapped on the substrate, and a squeegee is slid over the screen mask to apply cream solder to the lands through the pattern holes. Is cleaned by wiping the lower surface thereof.

[0011]

According to the present invention, cream solder does not easily adhere to the inner surface of the escape groove facing the pad,
Alternatively, even when the cream solder adheres, the cream solder does not contact the pad of the substrate and is not transferred.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a screen printing apparatus according to an embodiment of the present invention, FIG. 2 is a partially enlarged sectional view of the screen mask and a substrate, and FIGS. 3 (a), (b), (c), and (d).
(E) is a view of the screen printing process, and FIG. 4 is a partially enlarged view of the screen mask during cleaning.

In FIG. 1, reference numeral 10 denotes a mask holder, which holds a screen mask 11. Pattern holes 12 are formed in the screen mask 11. 13
Is a sliding plate erected on the screen mask 11,
A cylinder 14 stands on the upper surface. A squeegee 15 is connected to the rod of the cylinder 14. When the rod of the cylinder 14 projects, the squeegee 15 descends and lands on the upper surface of the screen mask 11. In this state, when the sliding plate 13 slides in the direction of the arrow, the squeegee 15 slides on the screen mask 11. The sliding mechanism of the sliding plate 13 and the like are omitted.

In FIG. 2, a substrate 1 is the same as the conventional substrate shown in FIG. 4, and lands 2, lands 3, and pads 4 are formed on the surface thereof in a mixed manner. The pattern holes 12 of the screen mask 11 are opened at portions corresponding to the lands 2. An escape groove 16 is formed in a portion of the lower surface of the screen mask 11 facing the land 3 and the pad 4.

This screen printing apparatus is configured as described above. Next, the operation will be described with reference to FIG. First, as shown in FIG. 3A, the upper surface of the substrate 1 is brought close to the lower surface of the screen mask 11, and the squeegee 15
On the screen mask 11 in the direction of the arrow. Then, the cream solder 7 on the screen mask 11 rolls over the screen mask 11 while pattern holes 12 are formed.
To be filled. With the upper surface of the substrate 1 approaching the lower surface of the screen mask 11 as described above, the land 3 and the pad 4 are located inside the escape groove 16 and the land 3
The upper surface of the pad 4 does not contact the screen mask 11.

When the squeegee 15 is slid on the screen mask 11 as described above, the substrate 1 is relatively lowered from the screen mask 11 and separated. Then, the cream solder 7 filled in the pattern hole 12 is transferred onto the land 2 as shown in FIG. Then, next, the chip 20 is mounted on the cream solder 7 (FIG. 3C). 21 are electrodes on both sides of the chip 20,
The electrode 21 lands on the cream solder 7.

Next, the substrate 1 is sent to a heating furnace, and the cream solder 7 is subjected to a reflow process. Then, the cream solder 7 is melted and solidified, and the electrodes 21 are soldered on the lands 2. FIG. 3D shows the state after reflow. Next (Fig. 3
As shown in (d)), a bond 22 is applied on the land 3 and a bare chip 23 is bonded on the bond 22. Next, the electrode on the upper surface of the bare chip 23 and the pad 4 are connected by wire 24 by wire bonding.
And the wire 24 is sealed with a resin 25 (see FIG. 3E). Next, if the resin 25 is cured by heating in a heating furnace,
The substrate 1 is completed.

As described with reference to FIG.
At the time of screen printing of the cream solder 7 shown in (a), the cream solder 7 easily adheres to the lower edge of the pattern hole 12. Therefore, the lower surface of the screen mask 11 must be cleaned by wiping it with paper.
FIG. 4 shows a state in which the paper 27 wound around the roll 26 is slid on the lower surface of the screen mask 11 in the direction of the arrow to wipe off the cream solder d attached to the lower edge of the pattern hole 12. ing. The cream solder which has been wiped off adheres to the surface of the paper 27, but the paper 27 does not contact the inner surface of the escape groove 16;
There is no transfer of the cream solder adhered to the substrate. Therefore, unlike the conventional example shown in FIG. 5, the cream solder 7 is not transferred onto the lands 3 and the pads 4 of the substrate 1,
The wire bonding shown in FIG. 3E can be performed without any trouble. Even if the cream solder 7 adheres to the inner surface of the escape groove 16 due to some reason such as the scattering of the cream solder 7 on the land 2, the land 3 and the pad are not printed during the screen printing shown in FIG. Since there is a gap between the upper surface of the groove 4 and the inner surface of the escape groove 16, the cream solder 7 does not contact the land 3 or the pad 4 and is not transferred.

[0019]

According to the present invention, since the escape groove is formed on the lower surface of the screen mask opposite to the pad, the cream solder hardly adheres to the inner surface of the escape groove, or even if the cream solder adheres. The cream solder is not transferred in contact with the pads of the substrate, so that wire bonding for connecting the electrodes of the bare chip and the pads by wires can be performed without any trouble.

[Brief description of the drawings]

FIG. 1 is a perspective view of a screen printing apparatus according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of a screen mask and a substrate of the screen printing apparatus according to one embodiment of the present invention.

FIG. 3A is a screen printing process diagram of a screen printing apparatus according to an embodiment of the present invention. FIG. 3B is a screen printing process diagram of a screen printing device according to an embodiment of the present invention. (D) Screen printing process diagram of a screen printing device according to an embodiment of the present invention (e) Screen printing process diagram of a screen printing device according to an embodiment of the present invention

FIG. 4 is a partially enlarged view of a screen printing apparatus according to an embodiment of the present invention when a screen mask is cleaned.

FIG. 5 is a partially enlarged sectional view of a screen mask and a substrate of a conventional screen printing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2, 3 Land 4 Pad 7 Cream solder 11 Screen mask 12 Pattern hole 16 Escape groove

Claims (1)

(57) [Claims] 1. A cream solder screen printing method for applying cream solder on a land of a substrate formed by mixing a land for soldering a chip and a pad for wire bonding a bare chip. hand,
While opening a pattern hole for applying cream solder on the land, on the lower surface facing the pad ,
Cream solder hardly adheres to or adheres to the inner surface
As even cream solder is transferred in contact with the pad
A cream mask is formed on the substrate by overlaying a screen mask having no escape groove on the substrate, and a squeegee is slid on the screen mask to apply cream solder to the lands through the pattern holes, and then wipe the lower surface of the screen mask for cleaning. Screen printing method for cream solder.