Patent Application
20240421104
Development of electronics is increasing rapidly driven by accelerated technological revolution, innovation, and commercialization of new products. Increased demand has also brought the attention about efficiency, quality, and durability of electronics manufacturing. Electronic parts are intensively used in vast range of applications which still capitalize on their competent efficiency and life-span. A common application is motherboard, defined as circuit board or logic board, which is the biggest component for a computer system that controls links between all components. It usually contains different components, such as read-only memory (ROM), central processing unit (CPU), random-access memory (RAM), peripheral component interconnect (PCI) slots, universal serial bus (USB) ports, etc.
Photolithography is a process used in microfabrication to pattern parts on a thin film or the bulk of a substrate, e.g., a semiconductor wafer. A photoresist is a light-sensitive material used in photolithography to form a patterned coating on a surface. A photoresist developer is a solvent to selectively remove the photoresist to form the patterned coating. As an example, photolithography may be applied in the process of exposing a pattern into photoresist, depositing a thin film over the entire area, then washing away the photoresist to leave behind the deposited thin film only in the patterned area. The step of washing away the photoresist along with the underlying portion of the thin film is referred to as “lift-off.”
In one aspect, embodiments of the present invention relate to a method for water drainage of a substrate. The method includes creating, on a surface of the substrate, a designated hydrophobic region having hydrophobic surfaces of a hydrophobic film, wherein electronic circuitries are fabricated in the designated hydrophobic region of the substrate, creating, on the surface of the substrate, a designated hydrophilic region having hydrophilic surfaces of the substrate, wherein a drainage channel is formed in the designated hydrophilic region, and facilitating, based on capillary imbibition of the drainage channel, fluid flow from the designated hydrophobic region to a drainage/evaporation port to prevent damage of the electronic circuitries by moisture accumulation in the designated hydrophobic region.
In one aspect, embodiments of the present invention relate to a substrate with improved water drainage. The substrate includes a designated hydrophobic region comprising hydrophobic surfaces of a hydrophobic film, wherein electronic circuitries are fabricated in the designated hydrophobic region of the substrate, and a designated hydrophilic region comprising hydrophilic surfaces of the substrate, wherein a drainage channel is formed in the designated hydrophilic region, wherein the drainage channel facilitates fluid flow from the designated hydrophobic region to a drainage/evaporation port of the silicon-based substrate to prevent damage of the electronic circuitries by moisture accumulation in the designated hydrophobic region.
In one aspect, embodiments of the present invention relate to a circuit module with improved water drainage. The circuit module includes a substrate comprising a designated hydrophobic region comprising hydrophobic surfaces of a hydrophobic film, and a designated hydrophilic region comprising hydrophilic surfaces of the substrate, wherein a drainage channel is formed in the designated hydrophilic region, a drainage/evaporation port of the substrate, and electronic circuitries fabricated in the designated hydrophobic region of the substrate, wherein the drainage channel facilitates fluid flow from the designated hydrophobic region to a drainage/evaporation port of the silicon-based substrate to prevent damage of the electronic circuitries by moisture accumulation in the designated hydrophobic region.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skills in the art that the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.
Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as using the terms “before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.
Embodiments disclosed herein present a method to improve drainage of a substrate to protect electronic components fabricated on the substrate from damage due to contact with liquid. In one or more embodiments, the substrate includes a silicon-based substrate where surface wettability alteration technique is used to facilitate removal of trapped water and/or moisture from the silicon-based substrate embedded in electronics and integrated circuits. In one or more embodiments, hydrophobic surfaces and hydrophilic channels are formed in selected regions of the silicon-based substrate using photolithographic techniques with precision controlled at micro-scales and/or nano-scales. Specifically, thin film deposition is performed on silicon substrate surface to obtain desired wetting properties. Embodiments may be applied to electronics and semiconductors applications where silicon wafers are used for the fabrication of integrated circuits and photovoltaic solar cells. Embodiments may also be applied to electronics and semiconductors applications where semiconductors or other electronic components are installed on fiber glass printed circuit boards to produce electronic device assemblies in various electronic products. In one or more embodiments, hydrophobic surfaces and hydrophilic channels are formed in selected regions of the fiber glass printed circuit board. For example, hydrophobic and hydrophilic materials may be printed on, painted on, or otherwise applied on the printed circuit board in a selective manner to form the drainage channels.
One main issue associated with reliability of electronic devices or computer systems, e.g., containing or based on the silicon-based circuit module (110), is their high sensitivity to moisture. Electronic parts may be damaged by water contact. Surface wettability or fluid affinity to substrate may vary dramatically depending on the type of substrate material and fluid. Accordingly, adjusting wetting properties of surface present an impact on water displacement, characterized by drainage or imbibition. Even with coating the electronic parts with hydrophobic material to repel fluids/water, any water droplet that enters the electronic device or computer system can be trapped and still cause damage to interior electronic parts. As illustrated above, wetting surfaces are selectively created in the designated hydrophilic region (111b) of the silicon-based substrate (111) to act as water drainage channels. In one or more embodiments, by tuning the wetting states of these channels, these channels become more hydrophilic while maintaining the remaining surface hydrophobic in the designated hydrophobic region (111a). Any water droplet, referred to as wetting-phase, touching those hydrophilic channels network will be drawn into the drainage/evaporation port (113) and escape or be removed from the silicon-based circuit module (110). Mechanism of water removal is based on capillary imbibition (or absorption) by the action of capillary forces.
To create a fully hydrophobic coated surface, any stable hydrophobic coating may be used using physical or chemical deposition techniques. In one or more embodiments, Perfluorodecyltrichlorosilane (FDTS) material may be used as a hydrophobic coating using a thin film deposition procedure, such as atomic layer deposition (ALD), molecular vapor deposition (MVD), pulsed laser deposition (PLD), physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, or evaporation, etc. Selective deposition of hydrophobic FDTS is achieved using a selective wettability control mask. The FDTS-coated regions of the surface shift the localized wetting state of the silicon towards hydrophobic, while wettability of un-coated silicon substrate remains unchanged. In one or more embodiments, the electronic circuitries (110a, 110b, 110c, 110d, 110e) are fabricated on the silicon-based substrate (111) throughout the designated hydrophobic region (111a) prior to fabricating the hydrophobic coated surface and the hydrophilic drainage channels of the silicon-based substrate (111). In one or more embodiments, the hydrophobic coated surface and the hydrophilic drainage channels depicted in
Although the description above relates to the embodiments based on the silicon-based substrate and specific drainage channels formed on the silicon-based substrate, one skilled in the art will appreciate that alternative fabrication techniques may be employed to form drainage channels on other types of substrate, such as the fiber glass printed circuit board. As noted above, hydrophobic and hydrophilic materials may be printed on, painted on, or otherwise applied on the printed circuit board in a selective manner to form the drainage channels.
Initially, in Step 200, a designated hydrophobic region is created that has hydrophobic surfaces of a hydrophobic film. In one or more embodiments, the designated hydrophobic region is created by selectively coating (e.g., printing, painting, depositing, or otherwise applying) hydrophobic material to form a patterned film on the substrate. For example, the patterned film may be defined by a pattern on a screen or a mask used in the printing, painting, depositing, or other application procedure. In particular, the pattern is determined for forming the drainage channel. In some embodiments, electronic circuitries are fabricated in the designated hydrophobic region of the substrate.
In Step 201, a designated hydrophilic region is created that has hydrophilic surfaces of the substrate. In one or more embodiments, the designated hydrophilic region corresponds to the remaining uncoated areas that are not covered by the hydrophobic patterned film. In one or more embodiments, a drainage channel is formed in the designated hydrophilic region.
In Step 202, fluid flow is facilitated from the designated hydrophobic region via the drainage channel to a drainage/evaporation port to prevent damage of the electronic circuitries by moisture accumulation in the designated hydrophobic region. In one or more embodiments, fluid flow from the designated hydrophobic region toward the drainage/evaporation port is facilitated based on capillary imbibition of the drainage channel.
In one or more embodiments, the fabrication method includes photolithography and thin-film deposition. The photolithography is a process of transferring pattern from a mask to a photoresist layer on top of a substrate. The thin-film deposition is a process to place a very thin layer of material on top of the substrate surface.
Initially, in Step 210, a designated hydrophobic region of the silicon-based substrate is covered with a first photoresist using a first photolithographic technique. Separate from the designated hydrophobic region, a designated hydrophilic region of the silicon-based substrate is not covered with the first photoresist.
In one or more embodiments, the designated hydrophobic region of the silicon-based substrate is covered with the first photoresist by performing the following sub-steps 200a through 200e using the first photolithographic technique.
In a first sub-step 210a, the top surface of the silicon-based substrate is covered with the first photoresist, e.g., by a spinning method.
In a second sub-step 210b, the top of the first photoresist is covered with a photomask having a pattern transparent to UV light. The pattern delineates the designated hydrophobic region and the designated hydrophilic region. In particular, the designated hydrophilic region corresponds to the pattern of intended drainage channels. In this context, the photomask is referred to as a wettability control mask. In the case where the first photoresist is a positive photoresist, the transparent pattern of the photomask defines the designated hydrophilic region. In the opposite case where the first photoresist is a negative photoresist, the transparent pattern of the photomask defines the designated hydrophobic region.
In a third sub-step 210c, the covered top of the first photoresist is exposed to UV light that selectively changes a first chemical property of the first photoresist according to the transparent pattern of the photomask. In the case where the first photoresist is a positive photoresist, the exposed first photoresist under the transparent pattern of the photomask becomes degraded and soluble to a photoresist developer while the unexposed first photoresist remains undegraded and insoluble to a photoresist developer. In the opposite case where the first photoresist is a negative photoresist, the exposed first photoresist under the transparent pattern of the photomask becomes strengthened and insoluble to a photoresist developer while the unexposed first photoresist remains un-strengthened and soluble to a photoresist developer.
In a fourth sub-step 210d, the photomask is removed to apply the photoresist developer to the silicon-based substrate coated with the first photoresist.
In a fifth sub-step 210e, the degraded or un-strengthened first photoresist is removed across the designated hydrophilic region based on the changed first chemical property of the first photoresist. In contrast, the remaining designated hydrophobic region remains covered with the first photoresist.
In Step 211, a drainage channel is created by deep dry etching into the designated hydrophilic region of the silicon-based substrate that is not covered with the first photoresist.
In Step 212, all remaining first photoresist is removed from the silicon-based substrate using a lift-off solvent, such as N-methyl pyrrolidone (NMP).
In Step 213, the drainage channel is covered with a second photoresist using a second photolithographic technique. Separate from the drainage channel in the designated hydrophilic region, the designated hydrophobic region of the silicon-based substrate is not covered with the second photoresist.
In one or more embodiments, the drainage channel is covered with the second photoresist by performing the following sub-steps 203a through 203e using the second photolithographic technique.
In a first sub-step 213a, the top surface of the silicon-based substrate is covered with the second photoresist, e.g., by a spinning method.
In a second sub-step 213b, the top of the second photoresist is covered with the photomask that is aligned to the drainage channel. In the case where the first photoresist and the second photoresist have the opposite polarities (i.e., one is positive and the other one is negative), the same version of photomask is used for both the first photolithographic technique and the second photolithographic technique. In the opposite case where the first photoresist and the second photoresist have the same polarities (i.e., both being positive or both being negative), inverse versions of photomask are used for the first photolithographic technique and the second photolithographic technique. Specifically, the transparent pattern in the photomask for the first photolithographic technique becomes the non-transparent pattern in the photomask for the second photolithographic technique.
In a third sub-step 213c, the covered top of the first photoresist is exposed to UV light that selectively changes a second chemical property of the second photoresist according to the transparent pattern of the photomask.
In a fourth sub-step 213d, the photomask is removed to apply the photoresist developer to the silicon-based substrate coated with the second photoresist.
In a fifth sub-step 213e, the degraded or un-strengthened second photoresist is removed across the designated hydrophobic region based on the changed second chemical property of the second photoresist. In contrast, the drainage channel in the designated hydrophilic region remains covered with the second photoresist.
In Step 214, the top surface of the silicon-based substrate is coated with a hydrophobic film using a thin film deposition technique. For example, the hydrophobic film may include Perfluorodecyltrichlorosilane (FDTS) material. In one or more embodiments, the thin film deposition technique includes atomic layer deposition (ALD), molecular vapor deposition (MVD), pulsed laser deposition (PLD), physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, or evaporation, or other suitable deposition technique.
In Step 215, the second photoresist material is removed from the drainage channel using the lift-off solvent, such as N-methyl pyrrolidone (NMP). In response to removing the second photoresist material, the hydrophobic film is removed along with the second photoresist material from the drainage channel. Accordingly, the designated hydrophobic region of silicon-based substrate now includes hydrophobic surfaces of remaining hydrophobic film, while the drainage channel includes hydrophilic surfaces of the silicon-based substrate. to facilitate fluid flow to a drainage/evaporation port external to the silicon-based substrate, and
In Step 216, fluid flow is facilitated by the drainage channel to a drainage/evaporation port of the silicon-based substrate to prevent moisture accumulation from the designated hydrophobic region.
In the first section (300) shown in
In Step 302, initial surface pretreatments are applied to the silicon-based substrate (320), which include: (1) dehydration of the silicon-based substrate (320) by baking at high temperature (150° C.) to remove any moisture on the wafer surface; (2) surface treatment with adhesion promoter to facilitate adhesion of the photoresist (322) to the substrate surface; and (3) oxygen plasma may be used before applying the adhesion promoter for surface activation.
In Step 304, photoresist (322) is applied on the top surface of the treated substrate (320). In the scenario illustrated in
In Step 306, the wettability control mask (324) is aligned with the photoresist coated substrate (324).
In Step 307, UV exposure is performed using the partially transparent wettability control mask (324) that allows UV light to shine through a transparent pattern (325) of the wettability control mask (324). The transparent pattern (325) defines a designated hydrophilic region of the silicon-based substrate (320) where drainage channels (326) are created. In this context, the pattern (325) is also referred to as the channel pattern. The exposure to intense UV light “prints” the channel pattern (325) of the wettability control mask (324) onto the photoresist (322). The term “print” refers to changing a chemical property (i.e., solubility in a photoresist developer) of the photoresist (322). Using the positive photoresist (322), a portion of the photoresist (322) covering the transparent pattern (325) becomes soluble to the positive photoresist developer after the UV exposure. Feature size of the printed pattern may be as fine as 1 μm.
In Step 308, development process is performed to remove soluble photoresist material after UV exposure. The development is based on photoresist material type (referred to as polarity such as positive type or negative type) that are used. Since positive photoresist is used, the exposed areas of the photoresist corresponding to the channel pattern (325) become soluble (degraded by UV light) to the photoresist developer. The unexposed areas (covered under non-transparent portions of the mask) of the photoresist remains insoluble to the photoresist developer.
In Step 310, deep dry etching is performed to etch away substrate material uncovered with the remaining photoresist to create the drainage channels (326) in the substrate. Etched drainage channels (326) are created by engraving the silicon substrate (320) into a patterned silicon-based substrate (328).
In Step 312, the remaining photoresist is removed from silicon surface using a lift-off solvent, such as N-methyl pyrrolidone (NMP). Piranha solution, a mixture of sulfuric acid and hydrogen peroxide, may be used for further cleaning of the patterned silicon-based substrate (328).
In the second section (350) shown in
In Step 351, initial surface pretreatments are applied to the patterned silicon-based substrate (328), which include: (1) dehydration of the patterned silicon-based substrate (328) by baking at high temperature (150° C.) to remove any moisture on the wafer surface; (2) surface treatment with adhesion promoter to facilitate adhesion of the photoresist (322) to the substrate surface; and (3) oxygen plasma may be used before applying the adhesion promoter for surface activation.
In Step 352, photoresist (368) is applied on the top of the patterned silicon-based substrate (328). In the scenario illustrated in
In Step 354, a photomask is aligned with the channel pattern (325) previously engraved in the photoresist coated patterned silicon-based substrate (328). In one or more embodiments, the wettability control mask (324) used in Step 306 above is used as the photomask in this step.
In Step 356, UV exposure is performed using the same wettability control mask (324) used to transfer the channel pattern (325), After the UV exposure, the portion of the negative photoresist covering the channel pattern (325) becomes strengthened and insoluble to the negative photoresist developer.
In Step 358, the photoresist coated patterned silicon substrate (328) is soft baked after UV exposure at 110° C. for one minute.
In Step 360, development process is performed to remove photoresist material after the UV exposure. Development is based on the type of photoresist material used. Since negative photoresist is used in this step, the exposed areas of the photoresist corresponding to the channel pattern (325) become insoluble to the photoresist developer. On the other hand, the unexposed areas of the negative photoresist is dissolved by the photoresist developer to expose the underlying surface of the silicon-based substrate (320).
In Step 362, the surface of the photoresist coated patterned silicon-based substrate (328) is coated with FDTS (372) using MVD or other suitable techniques to create a hydrophobic coating. A very thin layer is deposited with few nanometers thickness.
In Step 364, the remaining photoresist covering the etched drainage channels (326) is removed using a lift-off process. The thin layer of FDTS (372) covering the etched drainage channels (326) is lifted off along with the photoresist to restore the original substrate surface in the area of the etched channels (326). This is done using a lift-off solvent, such as N-methyl pyrrolidone NMP. Accordingly, the drainage channels (326) now has hydrophilic surface of the silicon-based substrate (320) while the remaining surface covered with FDTS (372) are hydrophobic.
As illustrated above, embodiments allow wetting surfaces to be selectively created in the designated hydrophilic region of a silicon-based substrate of silicon-based circuit module to act as water drainage channels. In one or more embodiments, by tuning the wetting states of these channels, these channels become more hydrophilic while maintaining the remaining surface hydrophobic in the designated hydrophobic region. Any water droplet, referred to as wetting-phase, touching those hydrophilic channels network will be drawn into a drainage/evaporation port and escape or be removed from the silicon-based circuit module. Mechanism of water removal is based on capillary imbibition (or absorption) by the action of capillary forces in the hydrophilic drainage channels. It is further contemplated that the alternating hydrophilic and hydrophobic line/square patterns may be used to facilitate water/moisture flow along non-linear (e.g., at a turning angle) portions of the drainage channels based on the hysteresis or alternating wettability behaviors.
Embodiments disclosed herein are directly applicable for manufacturing in various industries, such as electronic, electrical, computer system, information technology (IT), telecom, devices manufacturing companies. Expected commercial applications include generation of mixed wettability surface which may be used in many fields of application such as environmental engineering, biomedical, and electronics.
Embodiments disclosed herein exhibit at least the following advantages: (i) providing a simple fabrication procedure, (ii) causing less chemistry interference and uncertainty in the fabrication outcomes, (iii) causing less complexity in term of pattern creation, (iv) generating clean surface, and (v) providing better protection for electronic parts from water or liquids.
While one or more embodiments have been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope as disclosed herein. Accordingly, the scope should be limited only by the attached claims.
