JPH03269512A - Formation of bump - Google Patents

Abstract

PURPOSE:To obtain bumps having high accuracy on a PLZT substrate, etc., by forming holes of bump patterns on a coated photoresist, packing conductive paste therein, thermally curing the paste and then peeling the photoresist to form the bumps at the prescribed points on a substrate surface. CONSTITUTION:The substrate 1 is coated with the photoresist film 3 at a prescribed thickness and the bump patterns 4 are patterned on this photoresist 3 by a photolitho graphic stage; thereafter, the resulted mask is used as the screen of a screen printing method. The conductive paste 5 which is an adhesive material of a cold curing type is packed into the holes (bump patterns) 4 of the mask by this screen printing method. This conductive paste 5 is thermally cured to form the bumps 2 of the prescribed shape on the substrate 1. The bumps of the high accuracy are formed on the substrate regardless of the viscoelastic characteristic of the conductive paste in this way. In addition, the stage is simple and the cost thereof is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is useful for forming bumps on PLZT (transparent ceramic) substrates or for forming bumps on PLZT (transparent ceramic) substrates.
The present invention relates to a bump forming method used to connect a substrate (hip) to a substrate, and more specifically to a bump forming method that allows highly accurate bumps to be formed on a substrate by a screen printing method.

[Conventional example] In recent years, transparent ceramic P made by adding La to PZT has been developed.
LZT (PbO, LaO, ZrO2, Tie) is about to be used in optical shutters and display devices. When using this PLZT as a display device,
Electrodes are formed inside the PLZT substrate to form pixels,
It is necessary to connect the internal electrodes to an external drive circuit.

Therefore, a transparent surface electrode and a wiring pattern are provided on the front surface of the PLZT substrate, and the wiring part is led out to the drive circuit through the wiring pattern. In this case, bumps are formed on the surface of the PLZT substrate to connect the internal electrodes and the transparent electrodes.

Examples of methods for forming bumps include plating, screen printing, sputtering, and vapor deposition. Methods other than screen printing can form fine bumps with high precision, but the process is Screen printing is generally adopted because of its complexity and high cost [Problem to be solved by the invention] However, the process of forming bumps using screen printing is simple. Although the cost can be reduced, there is a problem in that highly accurate bumps cannot be formed due to the viscosity of the conductive paste used as the material for the bumps. That is, as shown in FIG. 6, for example, there are at most 120 at on the PLZT substrate 1.
μIl-200p L height h is 10 μml to 200 μ
It was possible to form only a bump 2 of about m. Even in the on-contact mode using a high-precision metal mask, when the metal mask with a fine bump pattern is filled with the conductive paste and the metal mask is peeled off from the PLZT substrate 1, the Since the bump pattern is minute, the metal mask peels off while the conductive paste remains attached to the bump pattern, that is, it becomes clogged, making it difficult to form highly accurate bumps.

This invention was made in view of the above problems.

The purpose is to provide a bump forming method that allows highly accurate bump formation on a PLZT substrate or the like by screen printing.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a bump forming method for forming bumps on the surface of a substrate by a screen printing method in order to draw out electrodes of the substrate to the outside.
The surface of the substrate is coated with a photoresist with a film thickness corresponding to the height of the bumps to be formed on the surface, and after forming holes in the bump pattern in the coated photoresist by a photolithography process, a low-temperature curing type is applied to the holes. The gist is that after filling a conductive paste as an adhesive and curing the filled conductive paste with heat, the photoresist is peeled off to form bumps at predetermined locations on the surface of the substrate. .

[Operation] Since the method described above is used, when forming bumps at predetermined locations on a PLZT substrate (for example, a PLZT substrate) in order to draw out the internal electrodes of the substrate, the height of the bump is approximately the same as that of the intended bump. A thick film of photoresist is coated on a PLZT substrate, and then holes of a bump pattern are formed in the photoresist film by a photolithography process, and the photoresist film with the holes formed becomes a screen for screen printing. That is, the surface of the PLZT substrate is masked except for the bump, and the depth of the hole in the bump is approximately the same as the height of the intended bump. Therefore, without placing a screen with a bump pattern on the PLZT substrate, the conductive paste can be filled into the holes by screen printing, and by peeling off the photoresist film after filling, the PLZT substrate can be filled with conductive paste. Bumps of conductive paste can be formed on the substrate, and the bumps can be formed with high precision using a photolithography process.

In addition, when a low-temperature curing type conductive paste is used as the conductive paste, if the conductive paste is filled into the hole and heat-treated, and then the photoresist film is removed, bumps will be formed on the PLZT substrate. .

[Embodiments] Hereinafter, embodiments of the present invention will be described based on FIGS. 1 to 5. In the figure, the same parts and corresponding parts as in FIG. 6 are denoted by the same reference numerals, and redundant explanation will be omitted.

As shown in FIG.
In forming the bumps 2 (50 μl), in the present invention, first, as shown in FIG. 2, the surface of the PLZT substrate 1 on which the internal electrodes are formed is coated with a photoresist film 3. In this case, the thickness of the photoresist film 3 is determined according to the height of the intended bump.

Subsequently, as shown in FIG. 3, a bump pattern is patterned by a photolithography process, and the patterning is performed according to the shape of the bump at a predetermined location connected to the internal electrode of the PLZT substrate 1. This is done by forming a hole 4. That is, the photoresist film 3 formed on the PLZT substrate 1 serves as a screen in the screen printing method.

Subsequently, as shown in FIG. 4, conductive paste 5 is filled into the holes 4 by screen printing.
When a low-temperature curing adhesive is used as the conductive paste 5, it is heated after filling. As a result, the hole 4
Since the conductive paste 5 filled in the PLZT substrate hardens, even if the photoresist film 3 on the PLZT substrate 1 is peeled off, the hardened conductive paste remains as bumps 2 on the PLZT substrate, as shown in FIG. It will remain on top.

According to the above method, the middle height is 5 μm to 25 μm, and @T
However, it is possible to obtain a highly accurate bump 2 with a weight of 30 μm to 50 μm. That is, the photoresist film 3 can be coated with an accuracy of 30 .mu.l to 50 .mu.m, and the bump pattern can be patterned with an accuracy of 30 .mu.l to 50 .mu.l.

As described above, since the bumps 2 can be formed on the PLZT substrate 1 with the patterning accuracy of the photoresist film 3 by the screen printing method, the bumps 2 can be formed with high precision without being restricted by the viscous characteristics of the conductive paste. Furthermore, the bump formation process is simple and the cost can be reduced. Moreover, as the conductive paste 5, for example, a low temperature curing type epoxy type A is used.
The use of g paste has the advantage that it causes almost no damage to the PLZT substrate 1 and does not affect the optical characteristics of the PLZT substrate 1.

In the above embodiment, the bumps 2 are formed on the PLZT substrate 1. However, it may also be possible to connect a pair of chips to the substrate, and in this case, the parts mounted on the substrate may be damaged. Never give up.

[Effects of the Invention] As explained above, according to the bump forming method of the present invention, when forming bumps on a substrate by screen printing, the substrate is coated with a photoresist film to a predetermined thickness, and a photolithography process is performed. After patterning the bump pattern on the photoresist, the mask obtained by the patterning is used as a screen for screen printing, and the holes (
The conductive paste (bump pattern) is filled with a conductive paste that is a low-temperature curing adhesive, and the filled conductive paste is heated and cured to form bumps of a predetermined shape on the substrate. High-precision bumps can be formed on a substrate regardless of the viscosity characteristics of the paste, and since the screen printing method is used, the process is simple and the cost can be reduced.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and is a schematic side sectional view of a bump according to the bump forming method, and FIGS. 2 to 5 are schematic process diagrams of bump formation for explaining the above bump forming method. FIG. 6 is a schematic side sectional view of a bump formed by a conventional screen printing bump formation method. In the figure, 1 is a PLZT substrate, 2 is a bump, 3 is a photoresist film, 4 is a hole, and 5 is a conductive paste (low-temperature curing type, epoxy-based Ag paste).

Claims (1)

[Claims] (1) In a bump forming method in which bumps are formed on the surface of a substrate by screen printing in order to draw the electrodes of the substrate to the outside, a film thickness corresponding to the height of the bump formed on the surface of the substrate is provided. After forming bump pattern holes in the coated photoresist using a photolithography process, the holes are filled with a conductive paste of a low-temperature curing adhesive, and the filled conductive paste is heated. 1. A method for forming a bump, characterized in that after curing, the photoresist is peeled off to form a bump at a predetermined location on the surface of the substrate.