JP2788694B2 - Method of forming bump electrode in electronic component - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for connecting a semiconductor chip to a circuit board or a lead frame or the like via a metal bump electrode. And a method for forming the bump electrode.

[0002]

2. Description of the Related Art Conventionally, bump electrodes of this type have generally been formed by metal plating such as gold or silver. However, this method requires a large number of steps, and thus costs are reduced. In addition to a significant increase, there was a problem of pollution such as treatment of a plating solution. Therefore, Japanese Patent Application Laid-Open Nos. 59-48941 and 1-251 as prior arts are disclosed.
No. 643 discloses that, instead of the method using metal plating, the bump electrode is formed by applying a metal paste such as solder or silver to an electrode pad by screen printing, and then appropriately controlling the temperature. Has proposed a method of forming by heating and baking.

[0003]

However, in this prior art method, a metal paste is applied to the electrode pads.
In order to apply by screen printing, a screen mask in which a cutout window is formed in the electrode pad portion is superimposed on one of the semiconductor chip and the circuit board, and the metal paste supplied on the upper surface of the screen mask Is reciprocated along the upper surface of the screen mask to fill the opening in the screen mask and then remove the screen mask.

In the above-mentioned screen printing method of the prior art, the height of the bump electrode is determined by the thickness of the screen mask. When the thickness of the screen mask is increased, the height of the screen mask is reduced. When the metal paste is removed, the metal paste that has been filled in the opening window and adhered to the electrode pad is lifted together with the screen mask.

For this reason, the thickness of the screen mask cannot be increased, and in addition to this, the metal paste applied to the electrode pads is heated and heated.
During firing, it spreads so that its diameter increases,
Since the height becomes smaller, the height of the bump electrode cannot be made sufficiently high. Therefore, there has been a problem that a connection error frequently occurs in connection with the bump electrode.

Therefore, Japanese Patent Laid-Open No. 2-15 as a prior art is disclosed.
No. 0031 proposes that the bumps are raised by repeating the formation of the bumps by a screen mask twice, but in this method, screen printing and heating / firing are repeated twice. The cost is greatly increased from within the necessity.

An object of the present invention is to provide a method for forming a bump electrode which solves these problems.

[0008]

In order to achieve this technical object, the present invention provides a method of forming a photoresist film on a surface of a semiconductor substrate, a circuit board or the like having an electrode pad formed on the surface thereof. Then, a hole is formed in the photoresist film at the electrode pad portion by photoetching. Then, a metal paste is formed in the hole in the photoresist film, and the hole is formed. By screen printing using a screen mask having a cutout window communicating with the metal mask, the metal paste is filled so as to fill the cutout window in the screen mask, and after heating and firing at a predetermined temperature, the photoresist film is removed. It is characterized by being removed. "

[0009]

[Operation] By doing so, the height of the metal paste applied to the electrode pads is set to a value obtained by adding the thickness of the photoresist film to the thickness of the screen mask. In other words, the size of the photoresist film can be increased by a single screen printing by the thickness of the photoresist film as compared with the prior art.

On the other hand, when the metal paste is heated and baked, the spread of the metal paste in the diameter direction can be surely reduced by the photoresist film. In other words, the height dimension of the metal paste is reduced by the metal paste. Since the reduction in height due to the spread of the paste in the diameter direction can be reduced, the height of the bump electrode can be made sufficiently higher than in the prior art.

[0011]

Therefore, according to the present invention, the bump electrode can be formed at a low cost without using metal plating as in the prior art, but the height dimension is sufficiently increased. This makes it possible to reliably reduce the occurrence of connection errors when connecting using the bump electrodes. Since only one screen printing and one heating and firing are required, the cost can be significantly reduced. Has an effect.

Further, the bump electrode can be formed into a mushroom-like shape by making the inner diameter of the hole in the photoresist film smaller than the inner diameter of the window in the screen mask. Of these, since the diameter of the portion to be joined to the electrode pad can be reduced, the size of the electrode pad can be reduced by this amount, and the density of various circuits on a semiconductor substrate, a circuit board, or the like can be increased. Has an effect that can be.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings in the case where bump electrodes are formed using a solder paste. In the drawing, reference numeral 1 denotes a semiconductor substrate formed by forming a plurality of electrode pads 2 and a passivation film 3 for various semiconductor elements (not shown) on the upper surface, and the surface of each electrode pad 2 has a conventional case. Similarly, a barrier film (not shown) composed of a titanium layer and a copper layer is formed.

Then, on the upper surface of the semiconductor substrate 1, FIG.
As shown in (1), a mixture of xylene and cyclized rubber is applied to an appropriate thickness to form a photoresist film 4 so as to cover the electrode pads 2. Then
A hole 5 is formed in the portion of the photoresist film 4 at each of the electrode pads 2 by exposing the portion using a photomask and then performing an etching process.

Next, on the upper surface of the photoresist film 4, a screen mask 6 formed by piercing a window 7 at a position corresponding to each of the holes 5 is superimposed. After supplying a solder paste containing eutectic solder grains of 500 mesh or less, each squeegee 8 is moved along the upper surface of the screen mask 6 as shown in FIG. The solder paste 9 is filled in the inside 5 and in the opening 7 in the screen mask 6.

When the filling of the solder paste 9 is completed,
As shown in FIG. 3, after removing the screen mask 6, the entire semiconductor substrate 1 is placed in a heating furnace and baked to be heated to a temperature (about 220 ° C.) higher than the melting point of the eutectic solder. Thus, the eutectic solder particles of the solder paste 9 are melted and integrated with each other, and are also welded to the electrode pads 2 on the semiconductor substrate 1 side.

Then, the photoresist film 4 is peeled and removed by using a parallel plate type plasma asher or by using oxygen plasma, as shown in FIG. The bump electrode 10 made of solder can be formed on the pad 2. As described above, the photoresist film 4 is formed on the surface of the semiconductor substrate 1, and the solder paste 9 is filled in the holes 5 formed in the photoresist film 4 by photoetching using the screen mask 6. ,heating·
Since the baking electrode 10 is formed by firing, the height of the bump electrode 10 can be made higher than that of the prior art by the thickness of the photoresist film 4. It is.

In the above embodiment, the bump electrode is formed by soldering. However, the present invention is not limited to soldering, and can be applied to the case of forming a bump electrode made of silver or gold. Alternatively, in the case of forming a bump electrode of gold, since a baking temperature is high, a photosensitive polyimide resin having heat resistance is used for forming the photoresist film 4).
Needless to say, the present invention can be applied to a case where bump electrodes are formed on a printed circuit board, a flexible circuit board, or a lead frame.

Next, FIGS. 5 and 6 show a second embodiment. In the second embodiment, the inside diameter of the hole 5 formed in the photoresist film 4 is smaller than the inside diameter of the window 7 in the screen mask 6, and as a result,
Since the mushroom-shaped bump electrode 10a can be formed and the diameter of a portion of the bump electrode 10a that is joined to the electrode pad 2 can be reduced, the size of the electrode pad 2 can be reduced by that much. It is possible to increase the density of various circuits on the semiconductor substrate 1 or the circuit board.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing a state in which a photoresist film is formed on a surface of a semiconductor substrate and a hole is formed in the photoresist film in the first embodiment of the present invention.

FIG. 2 is a vertical sectional front view showing a state in which a through hole in the photoresist film is filled with a solder paste using a screen mask.

FIG. 3 is a vertical sectional front view showing a state where a screen mask is removed after the solder paste is filled.

FIG. 4 is a longitudinal sectional front view showing a state where the photoresist film is peeled and removed after the heating and baking.

FIG. 5 is a vertical sectional front view showing a state in which a screen mask is overlaid on a photoresist film in a second embodiment of the present invention.

FIG. 6 is a vertical sectional front view showing a state where bump electrodes are formed according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Electrode pad 3 Passivation film 4 Photoresist film 5 Drilled hole 6 Screen mask 7 Drilled window 8 Squeegee 9 Solder paste 10, 10a Bump electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/60

Claims (2)

(57) [Claims] 1. A photoresist film is formed on a surface of a semiconductor substrate or a circuit substrate having an electrode pad formed thereon so as to cover at least a portion of the electrode pad.
A screen provided with a hole through which a hole is formed in the photoresist film after the hole is formed in the electrode pad portion by photoetching, and then the metal paste is formed in the hole in the photoresist film. This metal paste is screened by screen printing using a mask.
A method of forming a bump electrode in an electronic component, wherein the photoresist film is removed after filling so as to fill the opening window in the thermal mask, heating and baking to a predetermined temperature. 2. A method for forming a bump electrode in an electronic component according to claim 1, wherein the inner diameter of the hole in the photoresist film is smaller than the inner diameter of the window in the screen mask.