US-20260129765-A1 - METHOD FOR FORMING STENCIL MASK

Abstract

A method for forming a stencil mask is provided. The method includes: providing a reinforcement base frame; and etching a portion of the reinforcement base frame to form a non-reinforcement portion, such that a remaining portion of the reinforcement base frame forms a reinforcement portion. The non-reinforcement portion has a mask surface configured to contact a substrate surface. The reinforcement portion has a thickness greater than that of the non-reinforcement portion, and includes: an embossed surface for insertion into a cavity of the substrate and configured to contact a cavity bottom surface when the stencil mask is placed onto the substrate for stencil printing; and at least one first stencil window that allows a fluid material to flow therethrough, wherein the at least one first stencil window is aligned with at least one printing region within the cavity when the stencil mask is placed onto the substrate for stencil printing.

Inventors

• KyoWang Koo
• Kicheol Lee
• BoLee LIM

Assignees

• STATS ChipPAC Pte. Ltd.

Dates

Publication Date

20260507

Application Date

20251230

Priority Date

20220414

Claims (14)

1. 1 . A method for forming a stencil mask, wherein the stencil mask is configured for printing a fluid material onto a substrate, and the substrate comprises a substrate surface, a cavity having a cavity bottom surface below the substrate surface, and at least one printing region within the cavity; and wherein the method comprises: providing a reinforcement base frame; and etching a portion of the reinforcement base frame to form a non-reinforcement portion of the stencil mask, such that a remaining portion of the reinforcement base frame forms a reinforcement portion of the stencil mask, wherein the non-reinforcement portion has a mask surface configured to contact the substrate surface, and wherein the reinforcement portion has a thickness greater than that of the non-reinforcement portion, and comprises: an embossed surface for insertion into the cavity of the substrate and configured to contact the cavity bottom surface when the stencil mask is placed onto the substrate for stencil printing; and at least one first stencil window that allows the fluid material to flow through the reinforcement portion, wherein the at least one first stencil window is aligned with the at least one printing region within the cavity when the stencil mask is placed onto the substrate for stencil printing.
2. 2 . The method of claim 1 , wherein the at least one first stencil window has at its bottom a cross-sectional shape the same as a shape of one of the at least one printing region.
3. 3 . The method of claim 2 , wherein the at least one first stencil window has a vertically straight sidewall.
4. 4 . The method of claim 2 , wherein the at least one first stencil window has an inward inclined sidewall.
5. 5 . The method of claim 2 , further comprising: forming a coating layer with anti-stick properties on a sidewall of the at least one first stencil window.
6. 6 . The method of claim 1 , wherein the non-reinforcement portion comprises at least one second stencil window that allows the fluid material to flow through the non-reinforcement portion.
7. 7 . The method of claim 1 , wherein the thickness of the reinforcement portion is greater than that of the non-reinforcement portion by a depth of the cavity of the substrate.
8. 8 . A method for forming a stencil mask, wherein the stencil mask is configured for printing a fluid material onto a substrate, the substrate comprises a substrate surface, a cavity having a cavity bottom surface below the substrate surface, and at least one printing region within the cavity; and wherein the method comprises: providing a non- reinforcement base frame; providing a reinforcement layer; and attaching the reinforcement layer onto a portion of the non-reinforcement base frame to form a reinforcement portion of the stencil mask, such that a remaining portion of the non-reinforcement base frame which is not attached with the reinforcement layer forms a non-reinforcement portion of the stencil mask, wherein the non-reinforcement portion has a mask surface configured to contact the substrate surface, and wherein the reinforcement portion has a thickness greater than that of the non-reinforcement portion, and comprises: an embossed surface for insertion into the cavity of the substrate and configured to contact the cavity bottom surface when the stencil mask is placed onto the substrate for stencil printing; and at least one first stencil window that allows the fluid material to flow through the reinforcement portion, wherein the at least one first stencil window is aligned with the at least one printing region within the cavity when the stencil mask is placed onto the substrate for stencil printing.
9. 9 . The method of claim 8 , wherein the at least one first stencil window has at its bottom a cross-sectional shape the same as a shape of one of the at least one printing region.
10. 10 . The method of claim 9 , wherein the at least one first stencil window has a vertically straight sidewall.
11. 11 . The method of claim 9 , wherein the at least one first stencil window has an inward inclined sidewall.
12. 12 . The method of claim 9 , further comprising: forming a coating layer with anti-stick properties on a sidewall of the at least one first stencil window.
13. 13 . The method of claim 8 , wherein the non-reinforcement portion comprises at least one second stencil window that allows the fluid material to flow through the non-reinforcement portion.
14. 14 . The method of claim 8 , wherein the thickness of the reinforcement portion is greater than that of the non-reinforcement portion by a depth of the cavity of the substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation of U.S. Application No. 18/299,072, filed on April 12, 2023, which claims priority to Chinese Patent Application No. 202210400953.1 filed on April 14, 2022, the entire content of which is incorporated herein by reference. TECHNICAL FIELD The present application generally relates to semiconductor technology, and more particularly, to a stencil mask and a stencil printing method. BACKGROUND OF THE INVENTION The semiconductor industry is constantly faced with complex integration challenges as consumers want their electronics to be smaller, faster and higher performance with more and more functionalities packed into a single device. One of the solutions is the cavity printed circuit board (PCB) technique, in which cavities are formed in a PCB, and then electrical components are disposed in the cavities to reduce the thickness of the total package. However, a stencil mask for printing solder paste into the cavities of the PCB is easy to bend, bringing down the yield of the electrical components mounted in the cavities of the PCB. Therefore, a need exists for a more reliable stencil mask. SUMMARY OF THE INVENTION An objective of the present application is to provide a stencil mask with higher reliability. According to an aspect of embodiments of the present application, a stencil mask for printing a fluid material onto a substrate is provided. The substrate includes a substrate surface, a cavity having a cavity bottom surface below the substrate surface, and at least one printing region within the cavity. The stencil mask includes: a non-reinforcement portion having a mask surface configured to contact the substrate surface of the substrate; and a reinforcement portion having a thickness greater than that of the non-reinforcement portion, wherein the reinforcement portion includes: an embossed surface for insertion into the cavity of the substrate and configured to contact the cavity bottom surface when the stencil mask is placed onto the substrate for stencil printing; and at least one first stencil window that allows the fluid material to flow through the reinforcement portion, wherein the at least one first stencil window is aligned with the at least one printing region within the cavity when the stencil mask is placed onto the substrate for stencil printing. According to another aspect of embodiments of the present application, a stencil printing method is provided. The method includes: providing a substrate, wherein the substrate includes a substrate surface and a cavity having a cavity bottom surface below the substrate surface; providing a stencil mask, wherein the stencil mask includes a non-reinforcement portion and a reinforcement portion having a thickness greater than that of the non-reinforcement portion, and wherein the non-reinforcement portion has a mask surface, and the reinforcement portion has an embossed surface and at least one first stencil window; placing the stencil mask onto the substrate, such that the embossed surface is inserted into the cavity of the substrate and is in contact with the cavity bottom surface; depositing a fluid material on the stencil mask such that the fluid material can flow through the at least one first stencil window onto at least one printing region in the cavity bottom surface; and planarizing the fluid material using a squeegee. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention. Further, the accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain principles of the invention. BRIEF DESCRIPTION OF DRAWINGS The drawings referenced herein form a part of the specification. Features shown in the drawing illustrate only some embodiments of the application, and not of all embodiments of the application, unless the detailed description explicitly indicates otherwise, and readers of the specification should not make implications to the contrary. FIG. 1A is a cross-sectional view of a printed circuit board (PCB). FIG. 1B is an enlarged view of a portion of the PCB shown in FIG. 1A. FIG. 2A is a top view of a stencil mask according to an embodiment of the present application. FIG. 2B is a cross-sectional view along a section line of the stencil mask shown in FIG. 2A. FIG. 3 is a flowchart illustrating a method for forming a stencil mask according to an embodiment of the present application. FIGS. 4A and 4B are cross-sectional views illustrating various steps of the method for forming a stencil mask illustrated in FIG. 3 according to an embodiment of the present application. FIG. 5 is a flowchart illustrating a method for forming a stencil mask according to another embodiment of the present application. FIGS. 6A to 6C are cross-sectional vie