Method for protecting surface of flexible printed circuit board before epoxy potting

Abstract

The invention discloses a method for protecting the surface of a flexible printed circuit board before epoxy potting, which comprises the following steps of: coating a surface coating in advance, and then bending a flexible board, so as to ensure that the cured coating is matched with a bent substrate in form and stress. The coating capable of being reliably bonded with polyimide on the surface of the flexible substrate and pouring sealant can be formed, after the pouring sealant is adopted to conduct pouring on the bent flexible substrate, the pouring sealant does not make direct contact with the flexible substrate but makes contact with the coating, under the temperature change condition, the deformation stress of the pouring sealant is borne by the coating firstly, and the deformation stress of the pouring sealant does not make direct contact with the flexible substrate. Deformation stress caused by CTE difference on a material interface in a product when the temperature is changed is absorbed through a coating material, the deformation stress difference of the inner arc surface and the outer arc surface of the flexible substrate is balanced, a layered interface is prevented from appearing in a product encapsulation body, and the reliability of the product is improved. And the product pouring sealant is prevented from cracking along a layered interface in a high-impact state, so that the product reliability and the safety of internal components are ensured.

Description

Technical Field

[0001] This invention belongs to the field of advanced electronic packaging technology and relates to a method for surface protection of flexible printed circuit boards before epoxy potting. Background Technology

[0002] Rigid-flex substrates, which combine rigid and flexible substrates, have advantages such as high inter-board interconnect density and foldability. If the flexible substrate is folded and encapsulated with epoxy, the circuit size can be significantly reduced, the inter-layer interconnect density can be increased, and the size and weight of the circuit product can be reduced.

[0003] However, flexible substrates often use polyimide coatings as surface materials. While this material effectively protects the flexible substrate and wiring from damage, it inherently has poor adhesion to epoxy resin, resulting in a weak bonding interface between the potted flexible substrate and the potting compound. Furthermore, potting compounds developed to protect electronic components, especially those for protecting bonded bare chips, typically contain a large amount of SiO2 filler to reduce the coefficient of thermal expansion, giving them a low coefficient of thermal expansion and a high Tg value, which differs significantly from the mechanical properties of the flexible substrate. In addition, the curved surface formed after bending the flexible substrate exhibits different degrees of deformation between the inner and outer curved surfaces under temperature changes, leading to inconsistent stresses on the inner and outer curved surfaces during thermal expansion and contraction after potting. All of these factors contribute to the tendency for delamination at the interface between the potting compound and the flexible substrate during environmental temperature changes. This internal delamination can damage the structural strength of the product, posing a serious safety hazard, especially for products requiring high impact resistance. Therefore, a method is needed to address the mechanical compatibility issue between the potting compound and the flexible substrate. Summary of the Invention

[0004] The purpose of this invention is to solve the problem in existing technologies where the curved surface formed after bending of flexible substrates exhibits different degrees of deformation between the inner and outer arc surfaces under temperature changes. This leads to inconsistent stress between the inner and outer arc surfaces during thermal expansion and contraction after potting, easily causing delamination at the interface between the potting compound and the flexible substrate, thus compromising the structural strength of the product. This invention provides a method for surface protection of flexible printed circuit boards before epoxy potting, which can effectively enhance the reliability of the internal material interface bonding in electronic products potted with flexible substrates. This allows flexible substrates to be safely used in high-impact potted electronic products.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A method for surface protection of flexible printed circuit boards before epoxy potting includes the following steps: Obtain a rigid-flex substrate with assembled components; A flexible coating material is applied to the surface of a rigid-flexible substrate based on assembled components. The coated flexible substrate is bent, and the flexible coating material on the surface of the bent flexible substrate is cured. After curing, the entire component is potted.

[0006] A flexible coating material is attached to the surface of a flexible substrate, and then the coated flexible substrate is bent. After the flexible substrate is bent to the product design angle, the coating material is cured to form a modified coating on the surface of the flexible substrate. By first applying the surface coating and then bending it, it is ensured that the coating layer maintains the shape and stress matching with the bent substrate after curing.

[0007] A further improvement of the present invention is that: When applying a flexible coating material to the surface of the flexible substrate, the coating thickness of the flexible coating material is 100μm to 300μm.

[0008] The flexible coating material can be epoxy or silicone.

[0009] The Young's modulus of the cured flexible coating material is ≤1 GPa.

[0010] When the flexible coating material is cured, the curing time is greater than 8 hours.

[0011] The process of applying a flexible coating material to the surface of a flexible substrate includes: First, a flexible coating material is evenly applied to the inner surface of the flexible substrate, and then a flexible coating material is evenly applied to the outer surface of the flexible substrate.

[0012] The flexible coating material is applied to the surface of the flexible substrate by spraying or brushing.

[0013] A surface protective coating for flexible printed circuit boards, the coating being composed of a flexible material, the coating thickness being 100μm to 300μm, and the Young's modulus of the coating being ≤1GPa.

[0014] A rigid-flex printed circuit board assembly with a protective layer includes a rigid substrate and a flexible substrate connected in sequence. The flexible substrate is connected to the rigid substrate and is in a bent state. The surface of the flexible substrate is coated with the protective coating described in this invention.

[0015] An electronic component, characterized in that it includes the rigid-flex printed circuit board assembly described in this invention.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for surface protection of flexible printed circuit boards before epoxy potting. A flexible coating material is attached to the surface of the flexible substrate, and then the coated flexible substrate is bent. After the flexible substrate is bent to the product design angle, the coating material is cured to form a modified coating on the surface of the flexible substrate. By applying the surface coating first and then bending, it is ensured that the cured coating layer maintains the shape and stress matching with the bent substrate. When epoxy resin is used to pot the bent flexible substrate, the potting resin does not directly contact the flexible substrate, but rather contacts the coating layer. Under temperature change conditions, the deformation stress of the potting resin is first borne by the coating layer, which will not damage the flexible substrate or cause delamination inside the module. The coating material absorbs the deformation stress caused by the difference in CTE at the material interface inside the product when the temperature changes, balances the deformation stress difference between the inner and outer arc surfaces of the flexible substrate, prevents the formation of delamination interfaces inside the product potting body, and avoids cracking of the product potting resin along the delamination interface under high impact conditions. This ensures product reliability and the safety of internal components, making rigid-flexible substrates safe for use in high-impact potted electronic products. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 In this embodiment of the invention, the rigid-flexible substrate is assembled and awaits coating.

[0019] Figure 2 In this embodiment of the invention, a coating material is applied to the inner surface of the flexible substrate during bending.

[0020] Figure 3 In this embodiment of the invention, a coating material is applied to the outer surface of the flexible substrate during bending.

[0021] Figure 4 In this embodiment of the invention, 100% area coating is completed and inspected.

[0022] Figure 5 In this embodiment of the invention, the flexible substrate is bent and fixed at the designed angle, and then the coating layer is cured.

[0023] Figure 6 In this embodiment of the invention, epoxy potting is performed on the rigid-flexible substrate assembly. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0026] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0027] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0028] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0029] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1This invention discloses a method for surface protection of flexible printed circuit boards before epoxy potting, which can effectively enhance the bonding reliability of the internal material interface of electronic products potted with flexible substrates. It enables the safe application of flexible substrates in high-impact potted electronic products, solving the problem in the prior art where the curved surface formed after bending of the flexible substrate has different degrees of deformation between the inner and outer arc surfaces under temperature changes, and the stress on the inner and outer arc surfaces is inconsistent during thermal expansion and contraction after potting, easily leading to delamination at the interface between the potting adhesive and the flexible substrate, thus compromising the structural strength of the product.

[0031] Example 1 This invention discloses a method for surface protection of flexible printed circuit boards before epoxy potting. The method involves using a flexible coating material and applying it after bending the flexible substrate. This ensures that the coating layer, after curing, maintains a shape and stress match with the bent substrate. The coating is cured before potting and serves as a stress buffer layer between the flexible substrate and the potting compound. The method includes the following steps: Step 1: After assembling the components on the rigid-flex substrate, as follows... Figure 1 As shown; Step 2: Apply the coating material evenly to the inner surface of the flexible substrate during bending, ensuring that 100% of the inner surface area of ​​the flexible substrate is coated. Figure 2 As shown, when applying coating material to the inner and outer surfaces of the flexible substrate during bending, a uniform spraying method is used; Step 3: Flip the entire substrate over and apply a coating material evenly to the outer surface of the flexible substrate, ensuring that 100% of the outer surface is coated. Figure 3 As shown; Step 4: Inspect the substrate to confirm that 100% area coating has been completed, such as... Figure 4 As shown; Step 5: After bending and fixing the flexible substrate, cure the coating layer to determine the relative position and micromechanical state of the coating layer and the flexible substrate, such as... Figure 5 As shown; Step 6: Encapsulate the flexible substrate assembly with the cured coating, such as... Figure 6 As shown.

[0032] Furthermore, in step 5 of this embodiment, the coating material, after curing, is a flexible material with a thickness of 100μm to 300μm.

[0033] Example 2 This invention discloses a method for surface protection of flexible printed circuit boards before epoxy potting, comprising the following steps: Step 1: After assembling the components on the rigid-flex substrate; Step 2: Apply coating material evenly to the inner surface of the flexible substrate bend, so that 100% of the inner surface of the flexible substrate is coated. Specifically, when applying coating material to the inner and outer surfaces of the flexible substrate bend, the operation is carried out by uniform brushing.

[0034] Step 3: Flip the entire substrate over and apply the coating material evenly to the outer surface of the flexible substrate so that 100% of the outer surface of the flexible substrate is coated. Step 4: Inspect the substrate to confirm that 100% area coating has been completed, such as... Figure 4 As shown; Step 5: After bending and fixing the flexible substrate, cure the coating layer to determine the relative position and micromechanical state of the coating layer and the flexible substrate, such as... Figure 5 As shown, by first applying a surface coating and then bending the substrate, it is ensured that the cured coating maintains a shape and stress match with the bent substrate. The coating material absorbs the deformation stress caused by CTE differences at the material interfaces within the product during temperature changes, balancing the deformation stress difference between the inner and outer curved surfaces of the flexible substrate. This prevents delamination interfaces within the product's encapsulation, avoiding cracking of the encapsulation along these interfaces under high impact conditions. This ensures product reliability and the safety of internal components, allowing rigid-flex substrates to be safely used in high-impact encapsulated electronic products.

[0035] Step 6: Encapsulate the flexible substrate assembly with the cured coating, such as... Figure 6 As shown It should be noted that the coating layer is applied to 100% of the inner and outer surfaces of the flexible substrate before bending and fixing it.

[0036] Furthermore, in step 5 of this embodiment, the coating material, after curing, is a flexible material with a thickness of 200 μm.

[0037] Furthermore, in step 5 of this embodiment, the Young's modulus of the coating material after curing is ≤1 GPa.

[0038] Furthermore, in step 5 of this embodiment, the coating material can form a reliable bond with the polyimide on the flexible substrate surface and the potting compound.

[0039] Furthermore, in step 5 of this embodiment, the coating will not flow or accumulate during static standing before curing, and has a certain operating time window, for example, not less than 8 hours.

[0040] Furthermore, in this embodiment, the coating material has good adhesion to the polyimide surface, and the potting compound used in the product has good adhesion to the surface of the cured coating material.

[0041] Example 3 The present invention also discloses a surface protective coating for flexible printed circuit boards. The coating is made of a flexible material and has a thickness of 100μm to 300μm. The Young's modulus of the coating is ≤1Gpa. Under the bending and compression state of the flexible substrate, the coating disclosed in this embodiment is applied to the inner and lower surfaces of the flexible substrate.

[0042] This invention also discloses a rigid-flex printed circuit board assembly with a protective layer, comprising a rigid substrate and a flexible substrate connected in sequence, wherein the flexible substrate is connected to the rigid substrate and is in a bent state, and the surface of the flexible substrate is coated with the protective coating disclosed in this invention.

[0043] Furthermore, it should be noted that due to differences in potting compounds used in different products, the thickness and bending angle of the flexible substrate, and the resulting post-potting stress, the severity of the operating environment the products need to endure also varies. Therefore, the most suitable optional coating material also differs depending on the above conditions. It needs to simultaneously meet the requirements of effective adhesion with the selected potting compound and mechanical compatibility with the flexible substrate. This embodiment only discloses the following specific material applications: Furthermore, in this embodiment of the invention, the potting compound is E-500AH, and the coating material is SE4450.

[0044] Furthermore, in this embodiment of the invention, the potting compound is E-1033 and the coating material is Becoat 9067.

[0045] This invention employs a flexible coating material as a transition layer between the electronic component encapsulation potting compound and the polyimide coating. By applying the surface coating first and then bending, the cured coating layer maintains its shape and stress matching with the bent substrate. When the potting compound is applied to the bent flexible substrate, it does not directly contact the flexible substrate but rather the coating layer. Under temperature changes, the deformation stress of the potting compound is first borne by the coating layer, preventing damage to the flexible substrate or delamination within the module. A stress buffer layer is formed by utilizing a coating material that can reliably bond with both the polyimide on the flexible substrate surface and the potting compound. By applying the surface coating first and then bending, the cured coating layer maintains its shape and stress matching with the bent substrate. By absorbing the deformation stress caused by the difference in CTE at the material interface inside the product when the temperature changes, the coating material balances the deformation stress difference between the inner and outer arc surfaces of the flexible substrate, preventing the delamination interface from appearing inside the product potting body. This avoids the potting compound from cracking along the delamination interface under high impact conditions, thereby ensuring product reliability and the safety of internal components. This allows the rigid-flex substrate to be safely used in high-impact potting electronic products.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for surface protection of flexible printed circuit boards before epoxy potting, characterized in that, Includes the following steps: Obtain a rigid-flex substrate with assembled components; A flexible coating material is applied to the surface of a rigid-flexible substrate based on assembled components. The coated flexible substrate is bent, and the flexible coating material on the surface of the bent flexible substrate is cured. After curing, the entire component is potted.

2. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, When applying a flexible coating material to the surface of the flexible substrate, the coating thickness of the flexible coating material is 100μm to 300μm.

3. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, The flexible coating material can be epoxy or silicone.

4. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, The Young's modulus of the cured flexible coating material is ≤1 GPa.

5. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, When the flexible coating material is cured, the curing time is greater than 8 hours.

6. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, The process of applying a flexible coating material to the surface of a flexible substrate includes: First, a flexible coating material is evenly applied to the inner surface of the flexible substrate, and then a flexible coating material is evenly applied to the outer surface of the flexible substrate.

7. The method for surface protection of flexible printed circuit boards before epoxy potting according to claim 1, characterized in that, The flexible coating material is applied to the surface of the flexible substrate by spraying or brushing.

8. A surface protective coating for flexible printed circuit boards, characterized in that, The coating is made of a flexible material, with a thickness of 100μm to 300μm and a Young's modulus of ≤1Gpa.

9. A rigid-flex printed circuit board assembly with a protective layer, characterized in that, It includes a rigid substrate and a flexible substrate connected in sequence, the flexible substrate being connected to the rigid substrate, the flexible substrate being in a bent state, and the surface of the flexible substrate being coated with the protective coating as described in claim 8.

10. An electronic component, characterized in that, Includes the rigid-flex printed circuit board assembly as described in claim 8.

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