An inner-coated injection molded patch component

Abstract

This invention relates to the field of surface mount components (SMD) technology, specifically to an internally coated injection molded SMD component. It includes a capacitor and two SMD bases. Multiple connecting tabs are integrally formed on the outer wall of each SMD base. The capacitor is placed between the two SMD bases, with two connecting tabs positioned at the upper and lower electrodes of the capacitor, respectively. Soldering is then performed. A solder joint protective coating is applied to the solder joint. An adhesive layer is applied between the capacitor and the connecting tabs. The adhesive layer includes a low-viscosity layer and a high-viscosity layer. The low-viscosity layer is applied between the capacitor and the connecting tabs, and the high-viscosity layer is applied outside the low-viscosity layer. By adding a double-layer epoxy resin internal coating structure after the capacitor chip and connecting tabs are soldered and before injection molding, and finally using LCP material for rapid injection molding, the problem of traditional SMD components being susceptible to moisture, salt spray, and chemical corrosion, leading to insulation degradation, leakage, and breakdown failure, is solved.

Description

Technical Field

[0001] This invention relates to the field of surface mount components technology, and more specifically, to a surface mount component with internal coating injection molding. Background Technology

[0002] In high-voltage electrical equipment, switching power supplies, inverters, LED drivers, and industrial control circuits, surface-mount ceramic capacitors are commonly used as core protection components to ensure safe and stable circuit operation. They are mainly used for energy storage, filtering, bypassing, voltage regulation, and surge voltage suppression. They can effectively absorb instantaneous high voltage in the circuit, filter out noise interference, and prevent the circuit from being damaged by overvoltage and harmonic impacts. They are an indispensable basic component in high-voltage circuits.

[0003] The traditional production and assembly process of surface mount capacitors is as follows: first, the capacitor chip is welded and fixed to the metal connecting piece, then epoxy resin is directly used to mold and injection mold the outer side of the capacitor to form a package shell, and finally the packaged surface mount capacitor is welded onto the circuit board to achieve surface mount technology (SMT).

[0004] However, in harsh operating environments with high humidity, high salt spray, and strong chemical corrosion, the traditional structure is prone to micro-gaps at the interface between the epoxy resin encapsulation layer, ceramic capacitor chip, and metal base due to the mismatch in thermal expansion coefficients. External moisture, salt spray, and acid and alkali corrosive media can seep into the capacitor through these gaps, directly eroding the electrodes and solder joints. This leads to a decrease in capacitor insulation performance, increased leakage current, increased losses, and even breakdown failure, failing to meet the long-term use requirements of high-voltage and high-reliability equipment. Summary of the Invention

[0005] This invention provides a surface mount component with internal coating injection molding. By adding a double-layer epoxy resin internal coating structure after the capacitor chip and the connecting piece are soldered and before injection molding, and finally using LCP material for rapid injection molding, the problem mentioned in the background art of traditional surface mount components being susceptible to moisture, salt spray, and chemical corrosion, leading to insulation degradation, leakage, and breakdown failure is solved.

[0006] To achieve the above objectives, the internally coated injection molded surface mount component includes a capacitor and two surface mount bases, wherein the outer wall of the surface mount base is integrally formed with multiple connecting tabs.

[0007] Based on the above, during assembly, the capacitor is placed between two surface mount bases, with two connecting tabs positioned at the upper and lower electrodes of the capacitor, respectively. Then, the upper and lower electrodes of the capacitor are securely welded to the corresponding connecting tabs using resistance welding or laser welding. In the above technical solution, a weld point protective coating is applied to the welding position.

[0008] An adhesive layer is coated between the capacitor and the connecting piece. The adhesive layer includes a low-viscosity layer and a high-viscosity layer. The low-viscosity layer is coated between the capacitor and the connecting piece, and the high-viscosity layer is coated on the outside of the low-viscosity layer. Based on the above, firstly, a low-viscosity layer is coated at the tiny gap between the capacitor and the connecting piece. The low-viscosity layer uses low-viscosity epoxy resin adhesive, which can fully penetrate into all gaps to ensure that there are no voids left.

[0009] After the low-viscosity layer has initially solidified, a high-viscosity layer is then coated on top. The high-viscosity layer uses high-viscosity epoxy resin adhesive and may contain nanofillers. After being treated with a coupling agent, the nanofillers have good compatibility with the epoxy matrix and can form a stable organic-inorganic composite network.

[0010] In the above technical solution, after the adhesive coating layer has completely cured, an injection molding machine is used to injection mold a plastic encapsulation shell on the outside of the adhesive coating layer. Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By setting up a double-layer epoxy resin coating with low viscosity and high viscosity, the low viscosity layer first fills the gaps and then forms a dense protection, eliminating interface leakage at the source. The low viscosity epoxy resin can fully penetrate all micro gaps between capacitors, electrodes, and connecting pieces, eliminating voids and bubbles; then, a high-strength, highly dense protective layer is formed by high viscosity epoxy resin. The two layers of epoxy of the same material achieve chemical integration, completely blocking the intrusion of moisture, salt spray, and chemical media along the interface, solving the problems of micro gaps, insulation degradation, leakage, and breakdown that are easy to occur in traditional capacitor encapsulation.

[0011] 2. By using LCP material for injection molding to form the encapsulation shell, compared with traditional epoxy resin molding, LCP material has low water absorption, high heat resistance, and extremely fast molding speed. Injection molding can be completed within 2 seconds, which is 30 times more efficient than the traditional 60-second process. The cost of LCP-specific molds is only 70,000-80,000 RMB, which is far lower than the 500,000-600,000 RMB of traditional epoxy molds, significantly reducing production costs. At the same time, the LCP shell has stronger chemical stability and better weather resistance, forming a double protection with the inner epoxy coating, which increases the withstand voltage of components to over 6KV and the loss coefficient to less than 0.0250. Its durability and reliability far exceed international standards. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the capacitor structure of the present invention; Figure 2 This is a schematic diagram of the structure of the patch base of the present invention; Figure 3 This is a schematic diagram of the structure after the patch base and capacitor of the present invention are welded together; Figure 4 This is a schematic diagram of the structure of the protective coating applied to the solder joints according to the present invention; Figure 5This is a schematic diagram of the structure of the coating layer of the present invention; Figure 6 This is a schematic cross-sectional view of the adhesive layer of the present invention; Figure 7 A schematic diagram of the structure of the plastic encapsulation shell for this invention; Figure 8 This is a cross-sectional structural diagram of the plastic encapsulation shell of the present invention.

[0013] The meanings of the labels in the diagram are as follows: 1. Surface mount base; 11. Connector; 2. Capacitor; 21. Solder joint protective coating; 3. Adhesive layer; 31. Low viscosity layer; 32. High viscosity layer; 4. Plastic encapsulation. Detailed Implementation

[0014] The technical solutions of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0015] Traditional surface mount capacitors are encapsulated by direct injection molding of epoxy resin, which easily creates micro-gaps at the encapsulation interface. This allows moisture, salt spray, and chemical media to penetrate, causing the capacitor's insulation to deteriorate, leakage, and breakdown failure, making it unsuitable for long-term use in harsh environments.

[0016] Therefore, in view of the problems mentioned above, refer to Figure 1 As shown, the present invention illustrates a surface mount component with internal injection molding, including a capacitor 2, which is a high-voltage ceramic capacitor, typically used on the circuit boards of high-voltage equipment (such as switching power supplies, LED drivers, inverters, etc.), mainly for energy storage, filtering, bypassing or surge suppression, etc., and its operating voltage can reach several kilovolts.

[0017] To ensure that capacitor 2 can be safely and reliably mounted on the circuit board, this design includes two surface mount bases 1, such as... Figure 2 As shown.

[0018] The patch base (1) is made of conductive metal (such as iron-nickel alloy or copper alloy), and its outer wall is integrally formed with multiple connecting pieces 11.

[0019] The outer wall of the connecting piece 11 is pre-plated with a gold layer or a tin-bismuth alloy layer. Gold is an inert metal, and the tin-bismuth alloy is chemically stable. Neither of them reacts chemically with the subsequently coated epoxy resin or silicone protective coating. At the same time, they can prevent oxidation of the connecting piece surface, improve wettability and solderability during welding, ensure the quality of subsequent welding, and enhance the long-term reliability of the solder joint.

[0020] During assembly, capacitor 2 is placed between two surface mount bases 1, with two connecting tabs 11 positioned at the upper and lower electrodes of capacitor 2, i.e., the upper and lower end faces of the capacitor. Then, the upper and lower electrodes of capacitor 2 are firmly welded to the corresponding connecting tabs 11 using resistance welding or laser welding, forming a structure as shown below. Figure 3 The connection structure shown.

[0021] Next, along Figure 3 The two surface mount bases 1 are cut at the position indicated by the dashed line, dividing them into multiple independent surface mount capacitor units.

[0022] To prevent damage or corrosion of the weld joint in subsequent processes, a weld joint protective coating 21 is applied to the weld location, such as... Figure 4 As shown.

[0023] The solder joint protective coating 21 can be made of epoxy resin, polyurethane, or silicone to protect the solder joint from subsequent chemical treatments (such as solvents in the inner coating) and to buffer thermal stress, preventing solder joint cracking. Epoxy resin and silicone materials have good compatibility with the subsequently applied silane coupling agent; if polyurethane is used, it can be combined with an aminosilane coupling agent (such as KH550) to achieve the best bonding effect.

[0024] In traditional processes, after this step, an injection molding machine is used to directly encapsulate the capacitor 2 with epoxy resin to form a plastic shell 4.

[0025] However, with plastic encapsulation alone, micro-gaps can easily form at the interface between the plastic encapsulation material and the capacitor ceramic body and metal base due to thermal expansion mismatch or curing shrinkage. Moisture, salt spray and chemically corrosive substances can penetrate into the interior along these interfaces, leading to a decrease in insulation resistance, leakage, or even breakdown, which seriously affects electrical performance.

[0026] Therefore, this solution adds an internal coating process after welding and before injection molding: applying an adhesive layer 3 between capacitor 2 and connecting piece 11, such as... Figure 5 As shown.

[0027] The specific coating steps for adhesive layer 3 are as follows: Figure 6 As shown: First, a low-viscosity layer 31 is coated in the tiny gap between capacitor 2 and connecting piece 11. The low-viscosity layer 31 is made of low-viscosity epoxy resin, which has good fluidity and can fully penetrate into all gaps to ensure that there are no voids left.

[0028] After the low viscosity layer 31 has initially solidified, a high viscosity layer 32 is coated on top of it. The high viscosity layer 32 is made of high viscosity epoxy resin and can be filled with nanofillers (such as nano montmorillonite and graphene oxide). Both the low viscosity layer and the high viscosity layer are epoxy resins. Materials of the same type can be chemically bonded to form an integrated structure without interlayer delamination. After being treated with a coupling agent, the nanofillers have good compatibility with epoxy resins and can form a stable organic-inorganic composite network.

[0029] To further enhance the interfacial bonding strength, a layer of silane coupling agent can be coated on the surface of the solder joint protective coating 21 before coating the low viscosity layer 31. One end of the silane coupling agent can react with the active groups on the surface of the protective coating (epoxy / organosilicon), and the other end can crosslink with the epoxy resin to form a "chemical bridge", effectively preventing water vapor from penetrating along the interface.

[0030] The dual-layer structure of the adhesive layer 3 enables the low-viscosity layer to achieve perfect filling and the high-viscosity layer to form a strong waterproof barrier. The combination of the two can completely isolate external moisture and chemicals and prevent leakage.

[0031] The final adhesive layer 3 can bond and fix the capacitor and connecting piece, improve mechanical strength, form an electrical isolation layer, enhance insulation performance, block moisture and corrosive media, and ensure that the components work stably for a long time in harsh environments.

[0032] Finally, as Figure 7 and Figure 8 As shown, after the adhesive layer 3 has completely cured, an injection molding machine is used to inject and encapsulate a plastic shell 4 on the outside of the adhesive layer 3.

[0033] In this embodiment, liquid crystal polymer (LCP) is selected as the encapsulation material. LCP material has stable chemical properties and does not react with the fully cured epoxy coating. Utilizing its low water absorption, high heat resistance and rapid molding characteristics, injection molding can be completed within 2 seconds, and the mold cost is only about 1 / 7 of that of traditional epoxy molding molds.

[0034] Before injection molding, it is necessary to ensure that the adhesive layer 3 is completely cured to avoid the epoxy layer softening or degrading during high-temperature injection molding. After injection molding, the plastic shell 4 encapsulates and protects the entire internal structure, exposing only the bottom surface of the surface mount base 1 as the welding end, ultimately forming a surface mount high-voltage ceramic capacitor.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A surface mount component with internal injection molding, comprising a capacitor (2) and two surface mount bases (1), characterized in that: The outer wall of the patch base (1) is fixedly connected with multiple connecting pieces (11); The two connecting pieces (11) are welded to the upper and lower electrodes of the capacitor (2), and an adhesive layer (3) is coated between the capacitor (2) and the connecting pieces (11). A plastic shell (4) is injection molded on the outside of the adhesive layer (3). The adhesive layer (3) includes a low viscosity layer (31) and a high viscosity layer (32); The plastic encapsulation shell (4) is made of liquid crystal polymer to improve the moisture resistance of the encapsulation.

2. The surface mount component with internal coating injection molding according to claim 1, characterized in that: The low viscosity layer (31) is coated between the capacitor (2) and the connecting piece (11), and the high viscosity layer (32) is coated on the outside of the low viscosity layer (31).

3. The surface mount component with internal coating injection molding according to claim 2, characterized in that: The low-viscosity layer (31) is a low-viscosity epoxy resin adhesive that can penetrate into the gap between the capacitor (2) and the connecting piece (11).

4. The surface mount component with internal coating injection molding according to claim 2, characterized in that: The high-viscosity layer (32) is a high-viscosity epoxy resin adhesive used to form a dense waterproof barrier to prevent moisture and chemicals from penetrating.

5. The surface mount component with internal coating injection molding according to claim 4, characterized in that: Nanofillers are added to the high viscosity layer (32). The nanofillers are selected from at least one of nano-montmorillonite, graphene oxide, and boron nitride nanosheets to extend the water vapor permeation path and reduce the water absorption rate of the coating.

6. The surface mount component with internal coating injection molding according to claim 1, characterized in that: The outer wall of the connecting piece (11) is electroplated with a gold layer or a tin-bismuth alloy layer to prevent oxidation of the connecting piece surface and improve welding reliability.

7. The surface mount component with internal coating injection molding according to claim 1, characterized in that: After welding is completed, a solder joint protective coating (21) is applied between the capacitor (2) and the connecting piece (11).

8. The surface mount component with internal coating injection molding according to claim 7, characterized in that: After welding, a silane coupling agent is applied to the outer wall of the weld point protective coating (21).

9. The surface mount component with internal coating injection molding according to claim 1, characterized in that: The electrodes of the connecting piece (11) and the capacitor (2) are resistively welded or laser welded.

10. The surface mount component with internal coating injection molding according to claim 1, characterized in that: The patch base (1) is first subjected to plasma cleaning treatment before welding.

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