METHOD FOR PRODUCEING A WATERPROOF CONDUCTOR PLATE

Abstract

Method for producing a water-resistant substrate (20), wherein the method comprises the steps: Providing a substrate (22); Mounting the substrate (22) with at least one component; Purifying the substrate (22) containing the at least one component to form a purified substrate (22); and Deposition of a multilayer waterproof coating (24, 26, 28) onto the cleaned substrate (22); wherein the multi-layer waterproof coating (24, 26, 28) consists exclusively of silicone; wherein the deposition step comprises a step of spraying a first water-resistant layer (24) onto the cleaned substrate (22) and curing the first water-resistant layer (24); wherein the deposition step further comprises a step of spraying a second waterproof layer (26) onto the first waterproof layer (24) and curing the second waterproof layer (26); and wherein the deposition step further comprises a step of spraying a third waterproof layer (28) onto the second waterproof layer (26) and curing the third waterproof layer (28) to produce the multilayer waterproof coating (24, 26, 28).

Description

AREA OF INVENTION

[0001] The present disclosure relates to a method for producing a waterproof substrate and in particular a method for producing a waterproof printed circuit board populated with at least one component. BACKGROUND

[0002] Automotive OEMs have expressed a desire for a water-resistant coating applied to printed circuit board assemblies used in electronic power steering systems (EPS systems) for vehicles equipped with advanced driver assistance systems (ADAS). Industry research indicates that Parylene C and Parylene F are common materials used to waterproof printed circuit board assemblies (CCAs), where a CCA is a printed circuit board (PCB) containing at least one electronic component. This material is used in many industries, including, but not limited to, automotive, aerospace, medical technology, and military applications.

[0003] A conventional method for waterproofing CCA involves creating a dam around the CCA and filling the dam with silicone gel to produce a waterproof silicone layer approximately 1 / 4 inch thick, covering the entire surface of the CCA. Another conventional method for creating a waterproof CCA involves a first step in placing the CCA on custom-made racks, and then placing the custom-made racks, including the CCA, in an oven.

[0004] The process continues by placing a raw material for a waterproof coating, such as Parylene C or Parylene F, into an evaporator of the oven. The raw material is then heated in a pyrolyzer of the oven, converting it from a solid to a vapor. The vapor is then deposited onto the CCA (carbon composite material) in a deposition chamber of the oven. After deposition, the vapor forms a uniform, thin-film polymer barrier around the device, including the CCA and all its components, thus waterproofing the printed circuit board and all electrical components.

[0005] There are some undesirable problems with the conventional methods described above. First, these methods can only reliably prevent electrical failure for 8 hours when the circuit boards are immersed in a 5% saline solution. The canary circuit is a single board with multiple switches (MSBs) in a package that was previously uncoated and would fail, shutting down the system before any damage to the electronics occurred. The disadvantage of the aforementioned coating is that the dam function and application process require a significant amount of space, making it impossible to use in a two-board system.

[0006] In other words, it's understood that conventional methods are not designed to provide water protection that allows the ADAS EPS to function underwater indefinitely, but rather to apply a coating that makes the ADAS EPS system impervious to water for a limited period. The idea is that during this period, the system first detects water ingress using a device such as a canary-shaped circuit (an uncoated circuit board with multiple switches). Once water ingress into the ADAS power supply is detected, the vehicle drives to a safe point, sets fault codes, and shuts down safely.

[0007] Furthermore, the deposition (or application) times for the conventional process range from 12 hours (for Parylene C) to 18 hours (for Parylene F), making the conventional process difficult to streamline. Therefore, it would be desirable to provide an alternative to the conventional process for manufacturing a waterproof CCA that encompasses the printed circuit board with all its electrical components.

[0008] WO 02 / 031 027 A1 discloses a water-repellent coating comprising a composition of urethane, acrylic, and silicone resin, which can be used as a coating for printed circuit boards. Further prior art is known from DE 196 11 407 A1, US 2 683 767 A, and US 5 981 043 A. SUMMARY

[0009] The object of the invention is to provide an improved method for producing a waterproof substrate.

[0010] To solve the problem, a method with the features of claim 1 is provided. Advantageous embodiments of the invention can be found in the dependent claims, the description, and the drawings.

[0011] The present disclosure provides a method for producing a waterproof substrate that overcomes the shortcomings of the conventional method. The present disclosure also provides a method for producing a waterproof substrate that has low production costs and can be easily rationalized. Furthermore, the present disclosure provides a method for producing a waterproof substrate wherein the waterproof substrate can withstand a wide operating temperature range.

[0012] According to the present disclosure, a method for producing a waterproof substrate comprises a first step of providing a substrate. The method continues with a step of depositing at least one component onto the substrate. Next, the method comprises a step of cleaning the substrate, including the at least one component, to form a cleaned substrate. Then, the method continues with the application of a multilayer waterproof coating to the cleaned substrate. The multilayer waterproof coating consists exclusively of silicone. The deposition step comprises a step of spraying a first waterproof layer onto the cleaned substrate and curing the first waterproof layer.The deposition step further includes spraying a second waterproof layer onto the first waterproof layer and curing the second waterproof layer. The deposition step further includes spraying a third waterproof layer onto the second waterproof layer and curing the third waterproof layer to produce the multi-layer waterproof coating.

[0013] These and other advantages and features will become clearer from the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The subject matter considered to be the invention is specifically highlighted and clearly claimed in the claims at the end of the description. The foregoing and other features and advantages of the invention will become apparent from the following detailed description in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic flowchart showing a process for producing a waterproof substrate according to one aspect of the present disclosure; Fig. 2 is a schematic flowchart showing a process for producing a waterproof substrate according to another aspect of the present disclosure; Fig. 3 a perspective view of a waterproof substrate according to an aspect of the present disclosure; Fig. 4 a cross-sectional view of the waterproof substrate along lines 4-4 in Fig. 3 is; and Fig. 5 a cross-sectional view of the waterproof substrate with a first waterproof layer according to one aspect of the present disclosure. DETAILED DESCRIPTION

[0015] Now, with reference to the figures in which the invention is described with reference to certain embodiments, without limiting them, it is in Fig. 1 generally a method for producing a water-resistant substrate 20 according to one aspect of the present disclosure.

[0016] Referring to Fig.1. The method comprises a first step of providing a substrate 22. The step of providing the substrate 22 can be defined as providing a printed circuit board (“PCB”) without screen printing. Screen printing consists of white and legible letters used to identify components, test points, and the PCB, as well as warning symbols, company logos, date codes, and manufacturer's marks. According to one aspect of the present disclosure, PCBs must not have screen printing, as this would impair the optimal flow properties of a water-resistant coating. Accordingly, without the screen printing, the water-resistant coating can flow freely on the PCB, allowing the water-resistant coating to form a uniform layer on the PCB.

[0017] The process then proceeds with a step of placing at least one component onto the substrate 22. The step of placing the substrate 22 can be defined as placing the at least one component onto at least one surface of the substrate 22 to form a printed circuit board assembly (“CCA”). The at least one component can include, for example, capacitors and processors, but is not limited to these. The at least one component can also be placed on a variety of surfaces of the printed circuit board to form the CCA. The CCA can be dry and free of moisture. If the CCA has just undergone a dual reflow (also known as reflow soldering) or a single / dual selective wave process, it would not be necessary to bake the CCA, as the temperatures occurring during these processes are sufficient to remove the moisture from the CCA.If the CCA needs to be stored overnight, it can be stored in an inert atmosphere, such as, but not limited to, a nitrogen atmosphere. If an inert atmosphere cannot be achieved, the CCA can instead be baked in an oven at a minimum of 120 °C for at least 6 hours to remove the moisture.

[0018] Optionally, after the step of placing at least one component onto the substrate 22, the process can include a step of covering a portion of the at least one surface of the substrate 22, including the at least one component. The covering step can be defined as applying a masking material to the portion of the at least one surface of the substrate 22 that contains the at least one component, in order to cover and protect the portion. In other words, during the covering step, portions of the surface of the substrate 22 are protected by a masking material, which can be cured by ultraviolet light to form a protective layer over the portion of the substrate 22's surface.

[0019] The process then proceeds with a cleaning step of the substrate 22, including the at least one component, to form a purified substrate. The cleaning step can be defined as the removal of particulate contaminants from the substrate 22, including the at least one component, using an air knife system. In addition to removing particulate contaminants, the air knife system can rapidly remove residual water or other liquids from the substrate 22, including the at least one component. The air knife system converts a low-pressure volume of air into a targeted, high-velocity, high-effect airflow that exits the air knife system through a narrow slit. The air knife system generates a uniform and consistent airflow, which in turn eliminates many quality control problems, such as…Staining and discoloration, which can lead to surface coating failure, are prevented. Furthermore, the air knife system offers flexibility in positioning the airflow, enabling the removal of particulate contaminants from irregularly shaped areas, such as holes and crevices.

[0020] According to one aspect of the present disclosure, the cleaning step following the removal of particulate contaminants can include a plasma treatment step of the substrate 22, including the at least one component, using a plasma treatment system. During the plasma treatment step, the plasma treatment system operates at zero volts, such that the surface energy of the substrate 22, including the at least one component, is greater than or equal to 72 dyn, or a wetting angle measured with a goniometer is less than or equal to 20°. If the surface energy of the substrate 22 is greater than or equal to 72 dyn, this indicates a high surface tension of the substrate 22, which prevents the penetration of liquid.Additionally, a wetting angle α of the substrate 22 that is less than or equal to 20° indicates that the substrate 22 is wettable, which facilitates the formation of a uniform film of the waterproof coating on the surface of the substrate 22.

[0021] The process then proceeds with the deposition of a multilayer waterproof coating 24, 26, 28 onto the cleaned substrate to protect the substrate and the at least one component, i.e., the CCA, from water and / or moisture damage. Each layer of the multilayer waterproof coating 24, 26, 28 can be arranged over an adjacent layer of the multilayer waterproof coating 24, 26, 28. According to one aspect of the present disclosure, the deposition step can be defined as the application of a plurality of three waterproof layers 24, 26, 28 to the cleaned substrate to prevent water and / or moisture damage to the CCA.

[0022] Many materials can be used to form the waterproof layers, such as Parylene C, Parylene F, or silicone (e.g., DOW SIL CC 8030), but these are not the only options. Currently, Parylene C is the most widely used material in the industry for forming a waterproof conformal coating for products like pacemakers and iPhones. Since the operating temperature of Parylene C is in the range of 85°C to 100°C, a variant of Parylene C, such as Parylene F, which has an operating temperature range of 150°C to 200°C, can be used for electronic components operating in a higher temperature range, e.g., above 100°C. However, switching from Parylene C to Parylene F can significantly increase production / manufacturing costs.In addition, Parylene C and Parylene F are applied to components via a special process, whereby the application of Parylene requires a deposition time of 12 hours (Parylene C) to 18 hours (Parylene F).

[0023] According to the invention, each waterproof layer of the multilayer waterproof coating 24, 26, 28 consists exclusively of silicone. The use of silicone eliminates the need for special application equipment, thus reducing the cost of producing a waterproof substrate 20. In other words, standard coating systems such as Asymtek and PVA systems can be used to deposit the multilayer waterproof coating 24, 26, 28 onto the substrate 22. Furthermore, the silicone for each waterproof layer can be deposited onto the cleaned substrate by spray coating and cured within approximately 30 seconds, enabling efficient deposition of successive waterproof layers.

[0024] Furthermore, the operating temperature of silicone can be at least 200°C during continuous use. Therefore, silicone can be used to form the multilayer waterproof coating 24, 26, 28 for a variety of components, which can operate from 85°C to 200°C. Additionally, silicone can exhibit high thermal conductivity (up to approximately 4.3 W / m*K) compared to parylene (0.082 W / m*K for parylene C and 0.1 W / m*K for parylene F). Accordingly, due to the thermal conductivity properties of silicone, areas of the substrate 22 that come into contact with a heat sink via a gap filler can contain the waterproof layers and would not impair heat transfer.

[0025] Depending on the complexity of at least one component, the multilayer waterproof coating 24, 26, 28 can be deposited onto the cleaned substrate by spraying or dipping. For example, a single-board CCA configuration can be more easily coated with the waterproof layers 24, 26, 28 by dipping (also known as immersion coating), whereas a configuration with two stacked boards may require deposition of the multilayer waterproof coating 24, 26, 28 by spraying (also known as spray coating). The immersion and spray coating processes also offer different advantages. For example, spray coating uses only half the material, while immersion coating can also cover hidden areas on the cleaned substrate. Furthermore, spray coating offers the simplest process control and raw material management.

[0026] According to the invention, the step of depositing the multilayer waterproof coating 24, 26, 28 is carried out by spraying a first, second, and third waterproof layer 24, 26, 28 onto the cleaned substrate. In particular, after cleaning the substrate 22, the process continues with spraying a first waterproof layer 24 onto the cleaned substrate. After spraying the first waterproof layer 24, the first waterproof layer 24 is cured using ultraviolet light. After the first waterproof layer 24 has cured, the process continues with spraying a second waterproof layer 26 onto the first waterproof layer 24. After spraying the second waterproof layer 26, the second waterproof layer 26 is cured under ultraviolet light. Subsequently, the process continues with spraying a third waterproof layer 28 onto the second waterproof layer 26.After spraying on the third waterproof layer 28, the third waterproof layer 28 is cured under ultraviolet light to produce the multilayer waterproof coating 24, 26, 28. Any ultraviolet light can be used to cure the first waterproof layer 24, the second waterproof layer 26, and the third waterproof layer 28. According to one aspect of the present disclosure, the ultraviolet light used to cure the first waterproof layer 24, the second waterproof layer 26, and the third waterproof layer 28 can have a wavelength of 280 nm and an intensity of 2 J / cm². 2 exhibit.

[0027] In other words, during spray coating, each waterproof layer of the multilayer waterproof coating 24, 26, 28 can be cured after spraying onto the clean substrate. This arrangement ensures zero holding time between the deposition of each waterproof layer, thereby streamlining the process for producing a waterproof substrate 20. Accordingly, when the cleaned substrate is treated by spray coating, the final product can be shipped immediately, as each waterproof layer is fully cured after each step of the spray coating process.

[0028] According to a non-inventive example, the step of depositing the multilayer waterproof coating 24, 26, 28 can be carried out by immersing the cleaned substrate in a solution containing the waterproof layer to form first, second, and third waterproof layers 24, 26, 28 on the cleaned substrate. In particular, the non-inventive method proceeds, after cleaning the substrate 22, by immersing the cleaned substrate in the solution containing the waterproof layer to form a first waterproof layer 24 on the cleaned substrate. After the formation of the first waterproof layer 24, it is cured under ultraviolet light for a first duration. The first duration can vary considerably depending on the amount of solution applied to the cleaned substrate to form the first waterproof layer 24.The first duration might be approximately 24 hours, for example.

[0029] After the first waterproof layer 24 has cured, the non-inventive method continues by immersing the purified substrate, including the first waterproof layer 24, in the solution to form a second waterproof layer 26 on top of the first waterproof layer 24. After the formation of the second waterproof layer 26, it is cured under ultraviolet light for a second duration. After the curing of the second waterproof layer 26, the non-inventive method continues by immersing the purified substrate, including the second waterproof layer 26, in the solution to form a third waterproof layer 28 on top of the second waterproof layer 26. After the formation of the third waterproof layer 28, it is cured under ultraviolet light for a third duration to produce the multilayer waterproof coating 24, 26, 28.The second and third durations can vary considerably depending on the amount of solution deposited onto the purified substrate to form the second waterproof layer 26 and the third waterproof layer 28. For example, the second and third durations can be approximately 24 hours. Additionally, any ultraviolet light can be used to cure the first waterproof layer 24, the second waterproof layer 26, and the third waterproof layer 28. The ultraviolet light used to cure the first waterproof layer 24, the second waterproof layer 26, and the third waterproof layer 28 can have a wavelength of 280 nm and an intensity of 2 J / cm². 2 exhibit.

[0030] Similar to spray coating, in dip coating each waterproof layer of the multilayer waterproof coating 24, 26, 28 can be cured after each dip coating step. Typically, the curing time for each waterproof layer is approximately 24 hours. This allows each waterproof layer to be fully cured before another waterproof layer is formed by dip coating. After the formation of the third waterproof layer 28, the cleaned substrate with the first, second, and third waterproof layers 24, 26, 28 can be cured for at least 5 days before shipment. This allows the areas between the at least one component that is not exposed to ultraviolet light to cure wet. Depending on the layout of the substrate 22, the dip coating process may also require secondary masking and mask removal steps to protect solder joints on the substrate 22 after the process.

[0031] Although the invention has been described in detail in connection with only a limited number of embodiments, it is easy to understand that the invention is not limited to these disclosed embodiments. Rather, the invention can be modified to include any number of variations, changes, substitutions, or equivalent arrangements not described here, but which are appropriate to the spirit and scope of the invention. Furthermore, although various embodiments of the invention have been described, it is understood that aspects of the invention may encompass only some of the described embodiments. Accordingly, the invention should not be considered as limited by the foregoing description.

Claims

[1] Method for producing a water-resistant substrate (20) wherein the method comprises the steps: Providing a substrate (22); Mounting the substrate (22) with at least one component; Purifying the substrate (22) containing the at least one component to form a purified substrate (22); and Deposition of a multilayer waterproof coating (24, 26, 28) onto the cleaned substrate (22); wherein the multi-layer waterproof coating (24, 26, 28) consists exclusively of silicone; wherein the deposition step comprises a step of spraying a first water-resistant layer (24) onto the cleaned substrate (22) and curing the first water-resistant layer (24); wherein the deposition step further comprises a step of spraying a second waterproof layer (26) onto the first waterproof layer (24) and curing the second waterproof layer (26); and wherein the deposition step further comprises a step of spraying a third waterproof layer (28) onto the second waterproof layer (26) and curing the third waterproof layer (28) to produce the multilayer waterproof coating (24, 26, 28). [2] Method according to claim 1, wherein the step of providing the substrate (22) is defined as providing a printed circuit board without any screen printing. [3] Method according to claim 1, further comprising a step of covering a part of a surface of the substrate (22), including the at least one component, after the step of placement. [4] Method according to claim 3, wherein the covering step is defined as applying a masking material to the part of the surface of the substrate (22) which contains the at least one component to cover and protect the part. [5] Method according to claim 1, wherein the cleaning step is defined as the removal of particulate contaminants from the substrate (22) including the at least one component using an air knife system. [6] Method according to claim 5, wherein the cleaning step comprises a plasma treatment step of the substrate (22) including the at least one component using a plasma treatment system after the step of removing particulate impurities. [7] Method according to claim 6, wherein the plasma treatment system is operated at zero volts such that the surface energy of the substrate (22) including the at least one component is greater than or equal to 72 dyn or a wetting angle measured with a goniometer is less than or equal to 20°.

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