TWI861607B - Packaging structure and mass production method thereof for roll-type solid electrolytic capacitor - Google Patents

Abstract

This invention describes a packaging structure and a mass production method thereof for roll-type (wound-type) aluminum conductive polymer capacitor. Two protective substrates are applied to sandwich a roll-type capacitor element in between with an insulating material surrounding the capacitor element also in between the protective substrates. The protective substrates comprise electrically separated anodic conductive pad and cathodic conductive pad on their surfaces and through holes that pass through the conductive pads. The capacitor element is oriented with its axis perpendicular to the two substrates. The anodic and cathodic leads of the capacitor element pass through the through holes. An anodic external terminal is plated over the anodic conductive pad and a cathodic external terminal is plated over the cathodic conductive pad so that the anodic external terminal is electrically connected to the anodic lead and the cathodic external terminal is electrically connected to the cathodic lead.

Description

Packaging structure of wound solid electrolytic capacitor and its mass production method

Cross-reference to related applications: This application claims the benefit of U.S. Provisional Application No. 63/283,222 filed on November 25, 2021 by the inventors, the entire contents of which are incorporated by reference into this application.

The present invention relates to a packaging structure and method for a capacitor core, and in particular to a packaging structure and method for a winding capacitor core.

Existing methods for packaging rolled solid electrolytic capacitors have defects in terms of component size and shock resistance, and therefore have limitations in specific application areas. FIG. 1 shows several common roll-type or wound-type solid electrolytic capacitor cores manufactured using existing commercial equipment and parts. Among them, 10F and 10G are the most typical types. A typical rolled (wound-type) solid electrolytic capacitor core includes a cylindrical capacitor core body 13, an anode lead 11, and a cathode lead 12. The capacitor core body is made by rolling an etched aluminum foil strip and a spacer layer into a cylindrical shape, and then filling it with a polymer-based solid electrolyte. The lead is usually a three-section structure composed of three materials: the root section (11D, 12D) is an aluminum sheet (tab) or aluminum wire directly welded to the anode or cathode aluminum foil strip in the capacitor core body, the end section (11DC, 12DC) is a copper-clad steel core lead, and the root section and the end section are welded to each other. Lead connection section (11W, 12W). For convenience of explanation, this is called a standard lead. It is also possible to obtain a capacitor core that uses only aluminum wire as a lead, as shown in 11D and 12D in type 10D and 10E in Figure 1. The two leads of types 10F and 10D are at the same end of the body, while the leads of types 10G and 10E are at both ends of the body. The existing packaging method for wound solid electrolytic capacitors is to use a can-shaped aluminum shell to contain the capacitor core body, and seal it at one or both ends by clamping the aluminum shell with a sealing material (such as plastic or rubber). The existing packaging method includes multiple separate parts that must be manufactured separately using special machines, and usually must be done one by one, and parallel processing is not possible. In many packaged capacitors, the sealing material occupies a considerable portion of the total volume of the component. In addition, this can-shaped packaging method allows the capacitor core to be supported only by aluminum leads at one or both ends, and the core body has no mechanical support. Therefore, in applications in the automotive and transportation industries, fatigue of aluminum lead materials caused by frequent vibrations can cause reliability issues.

Because solid electrolytic capacitor cores are fragile, some common electronic packaging processes are difficult to apply. Traditional packaging processes, such as transfer molding molding compounds, are high-viscosity materials that flow under high pressure. In order to make thin insulation layers to reduce component size, the distance between the mold wall and the capacitor core needs to be reduced, resulting in increased hysteresis stress on the capacitor core while maintaining the same flow rate. Compression molding can reduce pressure flow, but it does not completely eliminate it. Sheet molding compound compression molding involves high pressure. Therefore, an improved packaging structure and method would be beneficial.

The present invention describes a packaging structure for a roll-type or wound-type aluminum conductive polymer capacitor element. A wound-type capacitor element is surrounded by an insulating material and sandwiched between two protective substrates. The axis of the capacitor element is perpendicular to the two protective substrates. The anode lead and cathode lead of the capacitor element are shortened, passed through through holes to the outside of the protective substrate, and are connected and electrically connected to the anode and cathode external terminals on the outer surface of the protective substrate. For capacitor cores with aluminum leads only, the external terminals and the electric connection from the terminals to the aluminum leads of the capacitor core are usually completed by a multi-step electroplating process that includes a zinc substitution step to enable the aluminum leads to receive plating. For capacitor cores with standard leads, that is, capacitor cores with the typical three-material three-section structure described above and copper-clad lead end sections, the electrical connection between the leads and the external terminals is basically completed by electroplating after welding. The aluminum sheet portion (root section) of the lead is bent so that the connection section is rotated approximately 90 degrees, which allows the body of the capacitor core to be close to the surface of the protective substrate or package, thereby reducing the overall component size. The copper-clad portion (end section) of the lead is also bent to facilitate connection with the external terminal. The electrical connection between the external terminal and the copper-clad end section of the lead from the terminal to the capacitor core is basically completed by welding, surface treatment and electroplating.

The filling of insulating material can be done through a capillary filling process or a simple pouring and flooding process. Generally, a low to medium viscosity liquid insulating material is used and the flow rate is kept low to avoid damaging the capacitor core. After filling, the insulating material hardens in the curing process and bonds the components into a whole.

[Prior Art]

10D, 10E, 10F, 10G: Different types of wound capacitor cores

13: Cylindrical capacitor core body

11: Anode lead

12: Cathode lead

11D, 12D: Lead root segment

11DC, 12DC: Lead end section

11W, 12W: Lead connection section

[Implementation method]

10D: Single capacitor core (wound solid electrolytic capacitor core)

20U: Upper protection substrate (upper substrate)

20L: Lower protective substrate (lower substrate)

11D: Anode lead (root section)

12D: cathode lead (root section)

21: Electrically insulating substrate body

22A: External surface (external conductive pad, copper pad, conductive pad, anode conductive pad)

22C: External surface (external conductive pad, copper pad, conductive pad, cathode conductive pad)

28A, 28C: Through hole

52: Adhesive

22T: Metal pad

60S: Gap

60: Insulation material

40A: External terminal (anode terminal, terminal)

40C: External terminal (cathode terminal)

42: Insulated body

11DA, 12DA: Tip surface

13: Cylindrical capacitor core body

70: Small capacitors

23C, 23A: External conductive pad (conductive pad)

23CI, 23AI: Internal conductive pad

29C: Conductive hole (electroplating perforation)

29A: Conductive hole (electroplating through-hole)

54: Conductive glue

41C, 41A: External terminals

10E: Main body (capacitor core body)

20UF, 20LF: Large full-size substrates

D1-D5: components

CLH, CLV: cutting line

11W, 12W: Lead connection section

11DC, 12DC: Lead end section

22AI, 22CI: Internal conductive pad

55: Solder (welding material)

20UM: Metal (copper) substrate

20LM: Lower copper substrate

20G: Gap

Figure 1 shows several common wound solid electrolytic capacitor cores manufactured using existing commercial equipment and parts.

Figures 2(a), (b) and (c) show one of the packaging structures and packaging processes of the wound solid electrolytic capacitor core proposed in the present invention, in which the aluminum leads are all located at the same end of the capacitor core body.

Figure 3 is a cross-sectional view of the package structure in Figure 2.

Figures 4(a) and (b) show an exemplary packaging structure proposed by the present invention, which includes a wound solid electrolytic capacitor core and a small capacitor.

Figure 5 is a cross-sectional view of the package structure of Figure 4.

Figures 6(a) and (b) show the packaging of the wound solid electrolytic capacitor core proposed by the present invention, in which the aluminum leads are located at both ends of the capacitor core body.

Figures 7(a) and (b) show the method of batch manufacturing of multiple capacitor components proposed by the present invention.

Figures 8(a), (b), (c), (d) and (e) show the packaging structure and packaging process of the wound solid electrolytic capacitor core proposed in the present invention, and the standard leads are all located at the same end of the capacitor core body.

Figure 9 is a cross-sectional view of the package structure of Figure 8.

FIG10 is a cross-sectional view of the packaging structure based on the all-conductor protective substrate proposed by the present invention.

The details of the invention will be described in detail through the following examples:

[Example 1]

Wrap-around capacitor core package with aluminum leads at one end of the core body, using a protective substrate with conductive pads on the non-conductive surface.

FIG2(a) is an exploded view of the package structure of a wound capacitor core with the anode lead and cathode lead at the same end, showing the main parts. The capacitor core 10D is placed between the upper protective substrate 20U and the lower protective substrate 20L in an axially perpendicular manner to the protective substrate. The leads on the capacitor core have been shortened in advance so that the remaining anode lead (root section) 11D and cathode lead (root section) 12D are both aluminum wires. The upper protective substrate 20U is composed of an electrically insulating substrate body 21 and conductive pads (22A, 22C) on its outer surface. Two through holes (28A, 28C) penetrate the substrate body and the conductive pad. During assembly, the anode lead (root section) 11D passes through the through hole 28A, and the cathode lead 12D passes through the through hole 28C, as shown in the cross-sectional view of Figure 2(b) and Figure 3. During assembly, the capacitor core is fixed to the upper protective substrate with adhesive 52. There is a metal pad 22T on the inner side of the lower protective substrate 20L, which serves as an anti-moisture shield during packaging.

The protective substrate can be made of a copper clad printed circuit board (PCB copper clad board). The copper clad printed circuit board is usually composed of an electrically insulating substrate body 21 made of glass fiber reinforced epoxy resin and a single-sided or double-sided copper clad layer. The copper conductive pad can be made by printing the copper clad layer through a standard PCB printing process. Through-hole electroplating can also be processed through a standard PCB printing process.

Figure 2(b) shows the state of the main components after assembly. The space 60S between the two protective substrates surrounding the capacitor core is filled with insulating material 60, as shown in the perspective view of the packaged capacitor core in Figure 2(c). The insulating material fills the through hole and wraps the lead and the entire capacitor core, as shown in the cross-sectional view of Figure 3. The protruding parts of the two leads on the upper surface are first cut, and then coated or electroplated with conductive material to form external terminals. The perspective view of the packaged capacitor core in Figure 2(c) shows that the external terminals 40A (anode) and 40C (cathode) are located at the top of the insulating body 42. The external conductive pads (22A, 22C) are covered with electroplated conductive material. This allows the external anode terminal 40A and cathode terminal 40C to be electrically connected to the anode lead (root section) 11D and cathode lead (root section) 12D of the capacitor core.

Next, the formation of the external terminals and their electrical connection with the conductive pads on the protective substrate are further explained. After the insulating material 60 is filled and solidified and before the external terminals 40A and 40C are plated, the tips of the leads (anode lead (root segment) 11D, cathode lead (root segment) 12D) that slightly protrude from the conductive pads (22A, 22C) are processed to flatten the surface and expose the tip surfaces (11DA, 12DA) of the leads. Then, a layer of first conductive material is deposited on the tip surfaces. For example, a layer of nickel is deposited on the tip surfaces by a zinc substitution process and an electroless nickel strike process. In this example, the electroless nickel strike is generally not plated on the exposed surface of the electrically insulating substrate body 21 or the insulating material 60, nor on the copper pads (22A, 22C) because copper does not have a catalytic effect on the electroless nickel. Next, an electroless copper plating process and an electrolytic plating process are performed to increase the thickness to form the external terminals 40A and 40C. Appropriate masks are used in the process to protect the areas that need to be maintained non-conductive. The zinc substitution process (also known as the zinc activation process or zinc-nickel process) is an electroplating process for coating aluminum. Examples of this process can be found in K. Murakami et al.'s article "Effect of Zincate Treatment on Adhesion of Electroless Nickel-Phosphorus Coating for Commercial Pure Aluminum", Materials Transactions, Vol. 47, No. 10 (2006) pp. 2518-2523, or S. Court's article "Monitoring of zincate pre-treatment of aluminium prior to electroless nickel plating", Transactions of the Institute of Metal Finishing 95 (2): 97-105, which are hereby incorporated by reference in their entirety.

[Example 2]

A wound capacitor core with the anode lead and cathode lead at the same end is packaged together with an accompanying component.

It is convenient in some applications to package one or more accessory components and the wound capacitor core in the same package, that is, to combine the two into a circuit and package them together.

For example, in order to stabilize the supply voltage at the power connection of each component, the power supply system of the circuit board requires a set of capacitors with various capacitance specifications. These include bulk capacitors close to the power connection part of the circuit board, with specifications ranging from a few microfarads to hundreds of microfarads, as well as local filtering and bypass capacitors, with specifications generally ranging from 0.01 to 0.1 microfarad. The current practice is to assemble individual capacitors of different types and capacity specifications onto the circuit board one by one. For mass-produced circuit boards, packaging a combination of several capacitors in one package will reduce the total footprint and assembly time, which is more convenient. For example, aluminum solid electrolytic capacitors of several hundred microfarads are often used near power connectors, along with tantalum capacitors of several hundred to tens of microfarads. Smaller capacitors, such as film or multilayer ceramic capacitors (MLCC), are used in local locations. Therefore, for a denser layout design, these capacitors can be packaged together. Since aluminum solid electrolytic capacitors are the largest in volume, it is reasonable to package a wound aluminum solid electrolytic capacitor with one or more smaller capacitors.

FIG. 4( a) shows an exploded view of an exemplary package structure, including a wound solid electrolytic capacitor core 10D and a small capacitor 70. The wound solid electrolytic capacitor package, connection method and parts are basically the same as those in FIG. 2( a). However, the upper substrate is additionally provided with a second set of external conductive pads 23C and 23A and internal conductive pads 23CI and 23AI. FIG. 20UL shows the inner structure of the upper substrate at a lower angle. The internal conductive pad and the external conductive pad are conductively connected through vias 29C and 29A, i.e., plated through holes. The small capacitor is electrically connected to the second set of conductive pads from the inside by welding or conductive paste 54. The vias and their connections to the small capacitors can be completed in advance in a separate process. After the parts are assembled, the insulating material is filled to wrap the two capacitors, as shown in Figure 4(b). Figure 5 is a cross-sectional view of Figure 4(b) at section A-A, showing the connection of the small capacitors. Therefore, this package contains two independent capacitors with separate external terminals (40C, 40A and 41C, 41A) that are plated on corresponding conductive pads (22C, 22A and 23C, 23A). When applied, the two capacitors can be used as two independent components and the external terminals can be connected to the power/ground layer/node of the circuit board as required.

[Example 3]

A wound capacitor core (10E) package with anode and cathode leads located at both ends.

The package structure and process are basically similar to Figure 2, with the only difference being that the through hole 28A, the anode conductive pad 22A and the terminal 40A will be located on the upper substrate 20U, while the through hole 29A, the cathode conductive pad 22C and the terminal 40C will be located on the lower substrate 20L. Figure 6 shows the packaged capacitor in this case. Figure 6(a) shows the anode side of the package, while Figure 6(b) shows the cathode side. 28A and 28C indicate where the leads are connected to the terminals.

[Example 4]

Batch manufacturing using parallel processing.

One of the advantages of this new packaging structure and process is that a large number of capacitor cores can be mass-produced simultaneously through parallel manufacturing. Although the construction shown in Figures 2 to 5 is a single package component, this construction can be extended to a two-dimensional matrix. Figure 7 (a) (b) describes this concept. At the beginning, the protective substrate is two large full-size substrates (20UF, 20LF), and the conductive pads and holes have been pre-processed at the corresponding positions of multiple components. Then several capacitor cores are placed (glued) to these positions and assembled to the substrate.

The insulating material 60 can be filled as a whole between the two full-size substrates. The filling of the insulating material can be carried out through a capillary filling process or a simple pouring and flooding process. Generally, low to medium viscosity insulating materials are used and the flow rate is kept low to avoid damaging the capacitor core. After filling, the insulating material hardens during the curing process and bonds the assembly into a whole. The curing/hardening process inevitably causes uneven expansion and contraction between the insulating material and the protective substrate. By sandwiching the insulating material between the two protective substrates, the bending deformation of the assembly after curing can be minimized.

The electroplating of all component external terminals (such as 40A, 40C) can also be performed simultaneously. Finally, cutting is performed along the cutting lines CLH and CLV to separate the individual components.

[Example 5]

Wrap-around capacitor core (10F) package with standard leads located on the same end of the capacitor core body, using a protective substrate with conductive pads on the non-conductive surface.

The extension of the standard lead is coated with a copper layer, making it easier to connect to the external terminal. Because it can be directly soldered, no zinc replacement is required. Figure 8 shows the package structure and process. Figures 8(a) and 8(b) show the assembly process of the main parts. The process is similar to Figures 2(a) and 2(b), except that the leads of the capacitor core are bent or folded. The aluminum sheet portion of the lead (anode lead (root section) 11D, cathode lead (root section) 12D) is bent, so that the lead connection section (11W, 12W) is rotated 90 degrees. This allows the body of the capacitor core to be close to the protective substrate during assembly, thereby reducing the overall component size. The copper-clad portion (11DC, 12DC) of the lead (the end section of the lead) is also bent so that it points to the corresponding hole on the upper protective substrate 20U. The bending of the lead can be completed in a separate process using a forming mold before assembly with the protective substrate.

The protective substrate can be made of a copper clad printed circuit board (PCB copper clad board). In Figure 8(b), the capacitor core is glued to the bottom surface of the upper protective substrate 20U, and its leads pass through two vias or plated through-holes (29A, 29C). The plated through-holes connect the external conductive pads (22A, 22C) and the internal conductive pads (22AI, 22CI) of the anode and cathode respectively. In other words, the inner surface of the through-hole, the top outer side and the bottom outer side, and the leads passing through the holes are all copper. Therefore, a spot welder can be used to weld the leads to the conductive pads on the upper side of the upper substrate. With proper use of flux, solder 55 can flow into the plated through-hole and solder the lead to the through-hole and conductive pad, as shown in Figure 8(c).

Then, the insulating material 60 is filled and cured, so that the assembly hardens into a complete solid. The protruding leads are then cut and the residues are polished. Figure 8(d) describes this concept. Then, a layer of copper is electroplated onto the copper pads (22A, 22C) and the remaining solder 55 on the copper pads to form external terminals (40A, 40C), as shown in Figure 8(e). Figure 9 shows a cross-sectional view of the completed structure.

It is best to use high temperature solder to ensure that the external terminals of the packaged capacitor do not melt during the reflow soldering process.

[Example 6]

Wrap-around capacitor core (10F) package with standard leads located at the same end of the capacitor core body, using an all-conductor protection substrate.

The protective substrate may also only have a conductive substrate and conductive pads, without an insulating substrate body. For example, an all-conductor substrate may be made of a thin copper sheet. This package can further reduce the overall component thickness. Taking the structure of a printed circuit board (PCB) as an example, a typical printed circuit board (PCB) may include an insulating core material made of glass fiber reinforced epoxy resin with a thickness of 4 to 8 inch (or 0.1 to 0.2 mm), and a 1 ounce or even half ounce copper clad on both sides, which corresponds to a thickness of 1.4 to 0.7 inch (or 0.035 to 0.018 mm). The total thickness of two protective substrates made of printed circuit boards (PCBs) is about 0.27 to 0.54 mm. On the other hand, if 0.1 mm copper foil is used, the total thickness of the two substrates can be reduced to 0.2 mm. If only copper clad sheets are used, the total thickness of the two substrates can be further reduced to 0.035 to 0.07 mm.

FIG10 shows a cross-sectional view of a package structure based on an all-conductor protective substrate. This structure is basically similar to FIG9, with the only difference being that the PCB copper clad board is replaced by an upper metal (copper) substrate 20UM and a lower copper substrate 20LM. The through holes (28A, 28C) can be direct through holes. The packaging process is also similar to FIG8, with the only difference being that the copper pads 22A and 22C need to be made by an etching process after the lead welding and the curing of the insulating material, and a gap 20G is opened to separate the two electrodes.

[Example 7]

Wrap-around capacitor core (10G) package with standard leads located at both ends of the capacitor core body.

This example is similar to Example 5 or Example 6, the only difference being that the anode lead and cathode lead are connected to external terminals located on opposite sides of the package, on the upper and lower substrates, respectively. The final component looks similar to the component shown in Figure 6.

The present invention disclosed herein is described above through multiple specific embodiments and multiple process steps. However, technicians in this field can make many modifications, changes and improvements to it without departing from the spirit and scope of the present disclosure as set forth in the claims.

11D: Anode lead (root section)

12D: cathode lead (root section)

21: Electrically insulating substrate body

22A: External surface (external conductive pad, copper pad, conductive pad, anode conductive pad)

22C: External surface (external conductive pad, copper pad, conductive pad, cathode conductive pad)

28A, 28C: Through hole

52: Adhesive

60: Insulation material

40A: External terminal (anode terminal)

40C: External terminal (cathode terminal)

11DA, 12DA: Tip surface

13: Cylindrical capacitor core body

Claims (10)

A packaging structure of a wound solid electrolytic capacitor comprises: two protective substrates, including a lower substrate and an upper substrate, wherein the substrates have an anode conductive pad and a cathode conductive pad at predetermined positions on their surfaces, wherein the two conductive pads are non-conductive to each other, and the protective substrates further comprise a plurality of through holes passing through the conductive pads; a wound solid electrolytic capacitor core, wherein the winding axis is perpendicular to the protective substrates and is disposed between the upper substrate and the lower substrate, wherein the capacitor core comprises an anode lead and a cathode lead, wherein the anode lead passes through the anode lead. The through hole on the cathode conductive pad, and the cathode lead passes through the through hole on the cathode conductive pad; an insulating material, filling the space between the substrates and surrounding the capacitor core, so that the protective substrate, the capacitor core, and the insulating material form an integrated solid; an anode external terminal coated on the anode conductive pad and a cathode external terminal coated on the cathode conductive pad, the anode external terminal is electrically connected to the anode lead, and the cathode external terminal is electrically connected to the cathode lead. The packaging structure as described in claim 1, wherein the external terminal is copper-plated, the anode lead and the cathode lead are aluminum leads, and the leads are electrically connected to the corresponding external terminals through an internal nickel layer. The package structure as described in claim 1, wherein the anode lead and the cathode lead are standard leads with copper-clad end sections, the through-holes are copper-plated through-holes, the copper-clad end sections of the leads are electrically connected to the corresponding conductive pads through a solder, and the external terminals are copper plated on the conductive pads and the solder. A packaging structure as described in claim 3, wherein the anode lead and the cathode lead are bent to reduce the distance between the capacitor core and the protective substrate. The packaging structure as described in claim 1, wherein the protective substrate is a fully conductive substrate including a thin copper sheet, and the conductive pad is formed by separating the thin copper sheet into mutually non-conductive parts by selective etching. The package structure as described in claim 1 further includes at least one accessory component located in the same package. In the package structure described in claim 1, the accessory element is another capacitor used for voltage regulation applications. A mass production method of a package structure of a wound solid electrolytic capacitor comprises: (a) providing a first substrate as an upper substrate, the surface of which comprises a plurality of conductive pads and a plurality of through holes at predetermined positions; (b) arranging a plurality of wound solid electrolytic capacitor cores on the lower surface of the upper substrate, the electrode leads of the capacitor cores passing through the through holes; (c) providing a second substrate as a lower substrate, clamping the plurality of capacitor cores Between the lower substrate and the upper substrate, a liquid insulating material is filled in the space between the two substrates, and then the insulating material is hardened to combine the upper substrate, the lower substrate, and the plurality of capacitor cores into an integrated component; (d) Copper is plated on the plurality of conductive pads to form a plurality of external terminals, and the plurality of external terminals are electrically connected to the electrode leads of the plurality of capacitor cores. As described in claim 8, the electrical conduction connecting the multiple external terminals and the electrode leads uses aluminum wires as the electrode leads, and a nickel layer is first plated on the tip of the aluminum wire using a zinc replacement process, and then copper is plated to form the external terminals. As described in claim 8, the electrical conduction connecting the multiple external terminals and the electrode leads includes: copper plating the multiple through holes to form multiple copper-plated through holes; using a lead having a copper-plated end section as the electrode lead; and welding the copper-plated end section of the electrode lead to the conductive pad and the copper-plated through hole.