JP2000340931A - Solder mask forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for forming a solder mask. SOLUTION: A method for forming a solder mask includes a step, in which a board 100 which has a plurality of wires 102 with a plurality of bonding pads 102a is prepared, a step in which a 1st solder resist layer is formed to cover a plurality of wires 102 and the board 100, a step in which the 1st solder resist layer is partially removed to expose the plurality of wires 102, a step in which a 2nd solder resist layer is formed to cover the plurality of wires 102 and the remaining 1st solder resist layer, and a step in which the 2nd solder resist layer is partially removed to expose the plurality of bonding pads 102a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder mask. More particularly, the present invention relates to a method for forming a solder mask by performing two printing steps.

[0002]

2. Description of the Prior Art In a conventional method for forming a solder mask, a solder resist layer is formed on a printed circuit board. Next, a part of the solder resist layer covering the region of the plurality of bonding pads is entirely removed. That is, no solder mask is formed between the bonding pads. This causes a short between the bonding pads. In addition, an electroplating layer is typically formed on each bonding pad to couple with other components. Since no solder mask is formed between the bonding pads, a short circuit easily occurs. Pitch
If less than 8 mil (ie 0.2 mm), then
Shorts occur more easily. As a result, the reliability and yield of the printed circuit board are reduced.

[0003]

SUMMARY OF THE INVENTION The present invention provides a method for forming a solder mask. In this way, a solder mask is formed by performing two printing steps. Thus, unwanted electrical coupling is avoided. Further, the reliability and yield of the substrate are increased.

[0004] The present invention provides a method for forming a solder mask. A substrate is provided with wires having a plurality of bonding pads for coupling with other elements. The first solder resist layer is formed on the substrate so as to cover the wires and the substrate. A pre-curing step is performed. First
The solder resist layer is removed, exposing the wires,
Next, the remaining solder resist layer is cured. The second solder resist layer is formed so as to cover the remaining first solder resist layer and the wire. After the pre-curing, a part of the second solder resist layer is removed and a plurality of bonding resists are removed.
Expose the pad.

In the present invention, a solder mask is formed by performing two printing steps. The solder mask avoids unwanted electrical coupling. As a result, the reliability and yield of the printed circuit board is increased. Further, since only each bonding pad needs to be exposed, it is easy to form an electroplating layer for coupling to other elements.

It is to be understood that the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are provided to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. Each drawing shows an embodiment of the present invention, and serves to explain the principle of the present invention together with the description of the embodiment.

In the drawings, FIGS. 1 to 5 are schematic sectional views of a method for forming a solder mask according to the present invention, and FIG. 6 is a schematic top view of a solder mask formed according to the present invention. is there.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used in the drawings and detailed description for the same or similar parts.

FIGS. 1 to 5 are schematic sectional views of a method for forming a solder mask according to the present invention. FIG.
FIG. 3 is a top view of a solder mask formed according to the present invention.

Referring to FIG. 1, a substrate 100 such as a printed circuit board (ie, chip carrier) is provided. The substrate 100 is formed of a prepreg such as FR-4 or BT (bismaleimide-triazine) resin. Each wire 102 is formed on the substrate 100, and a plurality of trenches 110 are present between each wire 102. Each wire 102 comprises copper or other conductive material. Further, bonding pads 102a (FIG. 6) for coupling with other elements are formed on each wire 102.

In FIG. 1, each wire 102 is connected to a substrate 10
0. This configuration is used only for illustrating the present invention, and the present invention is not limited to this configuration. Other configurations are suitable for the present invention.

Referring to FIG. 2, the solder resist layer 10
4 is formed so as to cover each wire 102 and fill each trench 110. The solder resist layer 104
It has an insulating material such as a UV type solder resist. The step of forming the solder resist layer 104 includes roller coating, curtain coating, screen printing, dip or dry film. Next, a pre-curing step is performed to remove the solvent in the solder resist layer 104.

Referring to FIG. 3, the solder resist layer 10
4 is removed to expose the wires 102 and a lower solder mask 104a is formed in each trench 110 (FIG. 1) to isolate each wire 102. This lower solder mask 104a has substantially the same thickness as the wire 102. The step of removing a part of the solder resist layer 104 includes mechanical polishing. When the solder resist layer 104 (FIG. 2)
When a V type solder resist is used, a developing device is used to remove a part of the solder resist layer 104, and a lower solder mask 104a is formed. Next, the lower solder mask 104a is cured by UV light.

Referring to FIG. 4, the solder resist layer 10
6 are formed so as to cover each wire 102 and the lower solder mask 104a. The material of the solder resist layer 106 and the step of forming the solder resist layer 106 are the same as in the case of the solder resist layer 104, and a detailed description thereof will be omitted. Next, the solder resist layer 106
A pre-curing step is performed to remove the solvent therein. The adhesion between the solder resist layer 106 and other layers can be improved by this pre-curing step.

Referring to FIGS. 5 and 6, the solder resist layer 106 is irradiated with UV light. Therefore, the patterns of the wires 102 and the bonding pads 102a are transferred onto the solder resist layer 106 (that is, the solder resist layer 106 is shaped). The solder resist layer 106 is removed, and then the upper solder mask 106a is formed. Upper solder mask 106a exposes each bonding pad 102a. Solder mask 108 is made from lower solder mask 104a and upper solder mask 106a. Next, an electroplating layer (not shown) is formed on the bonding pads 102a for bonding with other components. Electroplating layer materials include gold, nickel, or other conductive materials.

Referring to FIG. 6, a portion of each wire 102, indicated by a dashed line, is covered by a solder mask 108 and each bonding pad 102a is exposed for bonding with another element. After the solder mask 108 is formed, the cross-sectional view of the bonding pad region is as shown in FIG.

In the present invention, a solder mask comprising a lower solder mask and an upper solder mask is formed by performing two printing steps. First, a lower solder mask is formed between each wire, and then an upper solder mask is formed on each wire and exposes each bonding pad. The solder mask avoids unwanted electrical coupling between each bonding pad.
As a result, both the reliability and the yield of the printed circuit board are increased. Furthermore, since each bonding pad is only exposed, it is easy to form an electroplating layer for coupling to other elements.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing description, it is to be understood that the invention includes modifications and variations of this invention, assuming that they fall within the scope of each of the foregoing claims and their equivalents.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a method for forming a solder mask according to the present invention, showing a stage in which wires are being formed on a substrate.

FIG. 2 is a schematic cross-sectional view of a method for forming a solder mask according to the present invention, showing a step of forming a solder resist layer.

FIG. 3 is a schematic cross-sectional view of a method for forming a solder mask according to the present invention showing the step of removing a solder resist.

FIG. 4 is a schematic cross-sectional view of a method for forming a solder mask according to the present invention, further illustrating a step of forming a solder resist layer.

FIG. 5 is a cross-sectional view of a region where a bonding pad is formed.

FIG. 6 is a schematic top view of a solder mask formed according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 100 Substrate 102 Wire 102a Bonding pad 104 First solder resist layer 106 Second solder resist layer

Claims (27)

[Claims] Providing a substrate having a plurality of wires having a plurality of bonding pads; forming a first solder resist layer to cover the plurality of wires and the substrate; Removing a portion of the first solder resist layer to expose the plurality of wires; and forming a second solder resist layer to form the plurality of wires and the remaining first solder resist layer. A method for forming a solder mask, comprising: covering; and removing a portion of the second solder resist layer to expose the plurality of bonding pads. 2. The method of claim 1, wherein forming the first solder resist layer comprises roller coating. 3. The method of claim 1, wherein forming the first solder resist layer comprises curtain coating. 4. The method of claim 1, wherein forming the first solder resist layer comprises screen printing. 5. The method according to claim 1, wherein the step of forming the first solder resist layer has a dip.
The described method. 6. The method of claim 1, wherein forming the first solder resist layer comprises a dry film. 7. The method of claim 1, wherein removing a portion of the first solder resist layer comprises mechanical polishing. 8. The method of claim 1, wherein said first solder resist layer comprises a UV type solder resist. 9. The method of claim 8, wherein a pre-curing step is performed before removing a portion of the first solder resist layer. 10. The method of claim 8, wherein removing a portion of the first solder resist layer comprises a developing device. 11. The method according to claim 8, wherein the first solder resist layer is irradiated with UV light before the second solder resist layer is formed. 12. The method of claim 1, wherein forming the second solder resist comprises a roller coating. 13. The method of claim 1, wherein forming the second solder resist layer comprises curtain coating. 14. The method of claim 1, wherein forming the second solder resist layer comprises screen printing. 15. The method of claim 1, wherein forming the second solder resist layer comprises a dip. 16. The method of claim 1, wherein said step of forming a second solder resist layer comprises a dry film. 17. The method of claim 1, wherein said second solder resist layer comprises a UV type solder resist. 18. A step of pre-curing the second solder resist layer after the second solder resist layer is formed, and using UV light to irradiate the second solder resist layer. 18. The method of claim 17, further comprising: 19. The method of claim 17, wherein the step of removing the second solder resist layer comprises a developing device.
The described method. 20. Forming a lower solder mask between a plurality of wires; forming an upper solder mask exposing a bonding pad to cover the plurality of wires and the lower solder mask; A method for forming a solder mask applied to a substrate comprising a plurality of wires having bonding pads comprising: 21. A step of forming the lower solder mask, comprising: forming a first solder resist layer to cover the plurality of wires and the substrate; and forming a part of the first solder resist layer. Removing the wire to expose the wire. 22. The method of claim 21, wherein removing a portion of the first solder resist layer comprises mechanical polishing. 23. The method according to claim 21, wherein said first solder resist layer comprises a UV type solder resist. 24. The method of claim 20, wherein removing a portion of the first solder resist layer comprises a developing device. 25. The method of claim 25, wherein forming the upper solder mask comprises forming a second solder resist layer to cover the plurality of wires and the lower solder mask. 21. The method of claim 20, further comprising: removing a portion to expose the plurality of bonding pads. 26. The method according to claim 25, wherein said second solder resist layer comprises a UV type solder resist. 27. The step of removing a part of the second solder resist layer, the step of patterning the second solder resist layer by UV light; and the step of removing a part of the second solder resist by a developing device. 27. The method of claim 26, comprising: