CN118629735A - Varistor module and method for manufacturing a varistor module - Google Patents

Abstract

The present invention relates to a varistor module and a method for manufacturing a varistor module. A varistor module is provided, comprising a varistor (1), a contact element (2, 3) fixed to the varistor (1), and a terminal (4) comprising a metal contact (7, 8), wherein the contact element (2, 3) is fixed to the metal contact (7, 8), and wherein the metal contact (7, 8) comprises a lower surface (14) which faces away from the varistor (1) and is configured for surface mounting.

Description

Varistor module and method for manufacturing a varistor module

Technical Field

The invention relates to a varistor module and a method for manufacturing the varistor module.

Background Art

In applications where high surge capability is critical, especially for ESD protection, it is common to use a monolithic disc-type varistor, which can be soldered via two lead terminals. However, problems arise when this type of varistor module is used in SMD (surface mount device) applications. The soldered connections of the lead terminals to the varistor disc are susceptible to damage by the high temperatures that occur during the SMD process. If the lead contacts are soldered to the varistor disc, and the final device is then used in the SMD process, the heat applied during the SMD process may loosen the soldered contact between the lead contacts and the varistor, resulting in device failure.

Summary of the invention

The object of the present invention is to provide an improved varistor module and a method for manufacturing the same.

A varistor module is proposed, which includes a varistor, a contact element fixed to the varistor, and a terminal including a metal contact, wherein the metal contact is fixed to the contact element and wherein the metal contact includes a lower surface facing away from the varistor and configured for surface mounting.

The contact element itself is not intended to be used as a contact surface for surface mounting. Instead, the contact element is fixed to the metal contact of the surface-mountable terminal, i.e. it is configured to be used as a contact surface for surface mounting. Thereby, it can be ensured that the high temperatures occurring during the SMD process are not applied directly to the contact element, but only indirectly to a slightly reduced extent via the metal contact. This design protects the fixing of the contact element to the varistor and prevents the connection of the contact element to the varistor from melting.

The addition of the terminals can make a varistor having a contact element including leads compatible with surface mounting technology. Even an existing varistor having a contact element can be combined with the terminals, thereby making the varistor surface mountable, which was not previously possible.

The varistor may be a monolithic disk having electrodes on its upper surface and on its lower surface. The contact element may be a strip-shaped element, which is fixed to the electrodes of the varistor, for example by soldering or welding. The contact element can be used to apply an electrical signal to the varistor. The electrical signal is applied to the varistor from the outside via the metal contacts and the contact element. In particular, high voltages and/or high currents can be applied to the varistor via the contact element.

The contact element may include a lead. The contact element may consist of a lead. The contact element may be covered by a coating comprising or consisting of copper. The contact element may be covered by a coating comprising or consisting of tin. Using leads is advantageous in ESD applications because the leads can withstand high surge loads. The contact element may include copper-coated steel, tin-coated steel, copper-plated steel, or tin-plated steel.

The contact element can be fixed to the varistor by soldering or by welding.

Preferably, the contact element is welded to the metal contact. Alternatively, the contact element is brazed to the metal contact. In particular, a high-temperature solder having a melting temperature above 250° C. can be used to braze the contact element to the metal contact. Both welding and brazing offer the advantage that the high temperature is only applied locally at the location where the contact element is fixed to the metal contact. This local occurrence of high temperature does not detach the connection of the contact element and the varistor.

The terminal may include a plastic base, wherein the metal contact is integrated in the plastic base. The plastic base may include a plastic material that can withstand high temperatures, particularly high temperatures that occur during reflow soldering. For example, the plastic base may include a liquid crystal polymer (LCP) or may consist of an LCP. Alternatively, the plastic base may include another plastic material.

The metal contact integrated in the plastic base may be arranged in the plastic base such that a lower surface of the metal contact is arranged at a lower surface of the terminal facing away from the varistor and such that an upper surface of the metal contact is arranged at an upper surface of the terminal facing the varistor.

The metal contact may include an upper surface and a welding area. The upper surface may be parallel to the lower surface and may face the varistor when the varistor is fixed to the terminal. The welding area may be perpendicular to the upper surface and may protrude toward the varistor. The contact element may be welded to the welding area.

The varistor and the contact element may be covered by a coating. For example, the varistor and the contact element may be covered by a coating comprising a plastic material or a glass material. The coating may provide additional heat protection for the connection between the varistor and the contact element.

The varistor module may further include a housing, wherein the varistor and the contact element are arranged in the housing, and wherein the terminals and the housing surround a cavity, in which the varistor and the contact element are arranged. The housing may protect the varistor from environmental influences, such as moisture or dust. In addition, air may be arranged between the inner surface of the housing and the varistor. The air layer may provide thermal protection that prevents heat transfer to the connection between the contact element and the varistor during the SMD process, thereby also improving the heat resistance of the varistor module.

The varistor module may include more than one varistor. For example, at least a second varistor may be provided, comprising a second contact element fixed to the second varistor, wherein the terminal comprises a second metal contact fixed to the second contact element (e.g., by welding or soldering), wherein the second metal contact comprises a lower surface that faces away from the second varistor and is configured for surface mounting. Thus, two or more varistors may be fixed to one terminal by soldering or soldering the corresponding contact elements to the corresponding metal contacts of the terminal. Thus, the terminal may protect the connection between each varistor and each contact element from melting during the SMD process.

Another aspect relates to a method for manufacturing a varistor module. The varistor module manufactured by the method may be the above-mentioned varistor module. The method comprises the following steps:

- providing a varistor having a contact element fixed to the varistor,

- providing a terminal comprising a metal contact including a lower surface configured for surface mounting, and

- Fixing (eg soldering) the contact element to the metal contact such that the lower surface of the metal contact faces away from the varistor.

The method may further include the step of placing a housing over the varistor and the contact element such that the housing and the terminals surround a cavity.

The contact element can be fixed to the varistor by soldering or by welding.

The method may further comprise the following steps:

- providing a second varistor having a second contact element fixed to the second varistor, wherein the terminal comprises a second metal contact including a lower surface configured for surface mounting, and

- fixing (for example welding) the second contact element to the second metal contact such that a lower surface of the second metal contact faces away from the second varistor.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Each of FIG. 1 and FIG. 2 shows a varistor module in a perspective view.

FIG3 shows the terminals.

FIG. 4 shows a metal contact.

FIG. 5 shows a perspective view of a varistor module including a housing.

FIG. 6 shows a varistor module according to a second embodiment, in which a plurality of varistors are arranged on a single terminal.

FIG. 7 shows the welding method of the welding process.

DETAILED DESCRIPTION

Each of FIG. 1 and FIG. 2 shows a varistor module in a perspective view.

The varistor module comprises a varistor 1 , two contact elements 2 , 3 and a terminal 4 .

The varistor 1 has a first external electrode at its upper surface and a second external electrode at its lower surface. The varistor 1 is a monolithic varistor disc. The varistor 1 is constructed as a monolithic varistor disc. The monolithic varistor disc has a very high surge capability. The varistor 1 is intended for surge protection. For example, the varistor module can be part of an ESD (ESD=electrostatic discharge) protection device.

The contact elements 2 , 3 are ribbon or lead terminals. One of the contact elements 2 is connected to a first external electrode of the varistor 1 , and the other contact element 3 is connected to a second external electrode of the varistor 1 .

The contact elements 2, 3 are fixed to the varistor 1 by soldering. In particular, a first end of each strip-shaped contact element 2, 3 is fixed to the varistor 1, for example by soldering. As an alternative to the soldered connection, the contact elements 2, 3 can be welded to the varistor 1. Compared with mechanical connections (such as clamped connections), soldered connections and welded connections can withstand higher surge loads.

The contact elements 2, 3 consist of leads which are tinned copper leads or tinned highly conductive metal leads.

The varistor 1 and the contact elements 2, 3 are covered by a coating 5, which can be applied by overmolding. The coating 5 comprises a material with high moisture resistance, such as epoxy or silicone. The coating 5 provides protection against external influences such as dust, moisture, etc. In addition, the coating reduces the heat transfer from the outside to the varistor 1.

The varistor modules are intended for surface mounting.

As will be described below, the varistor is constructed so that the heat applied during the SMD process, in particular during reflow soldering, does not loosen the contact between the contact elements 2, 3 and the varistor 1. Otherwise, loosening the contact between the contact elements 2, 3 and the varistor 1 will lead to failure of the varistor module. In particular, the addition of the terminal 4 ensures that the connection of the contact elements 2, 3 and the varistor 1 is not overheated during the SMD process, so that the contact between the contact elements 2, 3 and the varistor 1 is prevented from loosening.

The contact elements 2, 3 are not directly surface mounted on an application, such as a printed circuit board. Instead, the varistor module comprises a terminal 4, to which the contact elements 2, 3 are fixed. In particular, the ends of the strip-shaped contact elements 2, 3 opposite to the ends fixed to the varistor 1 are fixed to the terminal 4. The contact elements 2, 3 are fixed to the terminal 4 by welding or by soldering with a high-temperature solder having a melting point above 250°C.

FIG3 shows a more detailed view of the terminal 4. The terminal 4 comprises a plastic base 6 and two metal contacts 7, 8. The terminal 4 is arranged at the bottom side of the varistor module. The varistor 1 is fixed to the terminal 4 via contact elements 2, 3 fixed to the terminal 4. The terminal 4 is surface mounted to an SMD application, for example to a printed circuit board.

The plastic base 6 of the terminal 4 includes a plastic material capable of withstanding high temperatures, such as a liquid crystal polymer (LCP). In particular, the plastic base 6 can withstand the high temperatures occurring during reflow soldering.

The plastic base 6 includes two spring arms 9 that are configured to snap into openings 10 of the housing 11 in order to attach the terminal 4 to the housing 11 .

Two metal contacts 7, 8 are integrated into the plastic base 6. Each metal contact 7, 8 is connected to one of the contact elements 2, 3. Figure 4 shows a more detailed view of one of the metal contacts 8. The metal contacts 7, 8 consist of a tinned copper sheet or a tinned highly conductive metal.

Each metal contact 7, 8 comprises a lower surface 14 which faces away from the varistor 1 when the terminal 4 is fixed to the varistor 1. The lower surface 14 of the metal contacts 7, 8 is intended to be surface mounted to the application.

The metal contacts 7, 8 further include an upper surface 15, which is parallel to the lower surface 14 and faces the varistor 1 when the varistor 1 is fixed to the terminal 4. Each metal contact 7, 8 is U-shaped, wherein the lower surface 14 and the upper surface 15 of the metal contact are connected by a short connection 16, which is perpendicular to the lower surface 14 and perpendicular to the upper surface 15.

The metal contacts 7, 8 comprise a soldering area 17 formed by a wall arranged on and perpendicular to the upper surface 15. The soldering area 17 protrudes from the upper surface 15 towards the varistor 1. Each contact element 2, 3 of the varistor 1 is soldered to the soldering area 7 of the respective metal contact 7, 8.

During soldering, high temperatures occur only locally at the locations where the contact elements 2, 3 are soldered to the soldering area 17. Therefore, high temperatures occur locally at the ends of the strip-shaped contact elements 2, 3 opposite to the ends of the contact elements 2, 3 fixed to the varistor 1. Since the heat must propagate along the contact elements 2, 3 before reaching the connection with the varistor 1, the heat is partially radiated to the environment and is only partially applied to the connection between the contact elements 2, 3 and the varistor 1. The strip-shaped contact elements 2, 3 are constructed to be long enough so that a sufficient amount of heat is radiated to the environment and the heat applied during the soldering of the contact elements 2, 3 to the terminal 4 does not damage the connection between the contact elements 2, 3 and the varistor 1.

In an alternative embodiment, each contact element 2, 3 of the varistor 1 is soldered to the soldering area 7 of the corresponding metal contact 7, 8 using a high-temperature solder that does not melt during reflow soldering in the SMD process. During soldering with the high-temperature solder, heat is also applied only locally at the ends of the strip-shaped contact elements 2, 3 opposite to the ends at which the contact elements 2, 3 are fixed to the varistor 1. The strip-shaped contact elements 2, 3 are constructed to be long enough so that a sufficient amount of heat is radiated to the environment and the heat applied during soldering of the contact elements 2, 3 to the terminals 4 does not damage the connection between the contact elements 2, 3 and the varistor 1.

Fig. 5 shows a perspective view of the final product of the varistor module. The varistor module comprises a housing 11 which is not shown in Figs.

The housing 11 is attached to the terminal 4. The housing comprises two openings 10, wherein the spring arms 9 of the terminal 4 snap into the openings 10.

The housing 11 and the terminals 4 surround a cavity in which the varistor 1 and the contact elements 2 , 3 are arranged. The varistor 1 and the contact elements 2 , 3 are protected by the housing 11 .

The housing 11 has a cubic shape in which there is no bottom. When the housing 11 is attached to the terminal 4, the terminal 4 forms the bottom of the cavity, and the housing 11 forms the other walls of the cavity. The lower surface 14 of the metal contact 8 can be contacted as a mounting partner for surface mounting. In particular, during the SMD process, in particular during reflow soldering, the lower surface 14 can be fixed to the printed circuit board.

The housing 11 may comprise a plastic material. For example, the housing 11 may comprise the same plastic material as the plastic base 6 of the terminal 4. For example, the housing 11 and the plastic base 6 may both comprise LCP.

Alternatively, the housing 11 may comprise a different material than the plastic base 6 .

When the housing 11 is fixed to the terminal 4, an air layer is formed inside the housing 11, between the inner surface of the housing 11 and the varistor 1. Therefore, neither the varistor 1 nor the contact elements 2, 3 abut against any inner surface of the housing 11.

The air layer inside the housing 11 partially absorbs the heat occurring during the SMD process (e.g. during reflow soldering), so that a lower amount of heat is applied to the connection between the contact elements 2, 3 and the varistor 1. The air layer inside the housing 11 thus reduces the heat transfer to the connection between the contact elements 2, 3 and the varistor 1 during the SMD process.

Fig. 6 shows a varistor module according to a second embodiment. According to the second embodiment, a plurality of varistors 1 are arranged on a single terminal 4. In the embodiment shown in Fig. 6, three varistors 1 are arranged on the terminal 4. However, any other number of varistors 1 may also be used.

The terminal 4 comprises a single plastic base 6 and two metal contacts 7, 8 for each varistor 1. The metal contacts 7, 8 are formed and arranged in the same manner as described above with respect to the first embodiment. Each metal contact 7, 8 is configured to be surface mounted, and each metal contact 7, 8 comprises a welding area 14, which is configured to be welded or brazed to the corresponding contact element 2, 3 using a high temperature solder. In addition, a housing 11 may be provided, which is fixed to the terminal 4, so that the terminal 4 and the housing 11 surround a cavity in which the varistor 1 and the contact elements 2, 3 are arranged.

Compared to varistor modules in which the contact elements are directly used as mounting partners for surface mounting on SMD applications, the varistor module according to the invention can better withstand the heat during the SMD process. In particular, the connection between the contact elements 2, 3 and the varistor 1 is better protected from melting.

In both embodiments, various measures prevent or reduce heat transfer to the connection between the contact elements 2, 3 and the varistor 1 during the SMD process. By providing the terminals 4 for surface mounting to the SMD application, the contact elements do not serve as mounting counterparts during surface mounting, so that heat is not applied directly to the contact elements 2, 3, but to the terminals 4.

Furthermore, by providing an air layer between the inner surface of the housing 11 and the varistor 1, additional isolation of the connection of the varistor 1 and the contact elements 2, 3 is provided. Furthermore, by providing a coating of the varistor 1 and the contact elements 2, 3, the connection is made more heat resistant.

The terminal 4 can be combined with an existing leaded varistor to form a surface-mountable package. The varistor module is a low-cost varistor module with high surge capability. The connection of the contact elements 2, 3 with the corresponding metal contacts 7, 8 can withstand the high temperatures of reflow soldering and also the high-frequency vibrations common in automotive applications. In general, the varistor module has a simple structure, which is easy to integrate into automated production.

FIG. 7 shows the welding method of the welding process.

Reference numerals

1 Varistor

2Contact elements

3 Contact elements

4 terminals

5. Coating

6 Plastic base

7Metal contacts

8Metal contacts

9 Spring Arm

10 Opening

11 Shell

14 Lower surface

15 Upper surface

16 Connectors

17 welding area

Claims (15)

1. A varistor module comprises

A varistor (1),

-A contact element (2, 3) fixed to the varistor (1), and

-A terminal (4) comprising a metal contact (7, 8), wherein the contact element (2, 3) is fixed to the metal contact (7, 8), and wherein the metal contact (7, 8) comprises a lower surface (14) facing away from the varistor (1) and configured for surface mounting.

2. The varistor module of claim 1,

Wherein the contact elements (2, 3) comprise copper or tin coated leads.

3. The varistor module of claim 1,

Wherein the contact element (2, 3) is fixed to the varistor (1) by soldering or by welding.

4. The varistor module of claim 1,

Wherein the contact element (2, 3) is fixed to the metal contact (2, 3) by soldering or by soldering using a high temperature solder.

5. The varistor module of claim 1,

Wherein the terminal (4) comprises a plastic base (6),

Wherein the metal contacts (7, 8) are integrated in the plastic base (6).

6. The varistor module of claim 5,

Wherein the plastic base (6) comprises a liquid crystal polymer or another plastic material.

7. The varistor module of claim 1,

Wherein the metal contact (7, 8) comprises an upper surface (15) and a soldering region (17),

Wherein the upper surface (15) is parallel to the lower surface (14) and faces the varistor (1),

Wherein the soldering region (17) is perpendicular to the upper surface of the metal contact (7, 8) and protrudes towards the varistor (1),

Wherein the contact elements (2, 3) are welded to the welding areas of the metal contacts (7, 8).

8. The varistor module of claim 1,

Wherein the varistor (1) and the contact elements (2, 3) are covered by a coating (5).

9. The varistor module of claim 1,

Further comprises a shell (11),

Wherein the terminal (4) and the housing (11) enclose a cavity, and wherein the varistor (1) and the contact elements (2, 3) are arranged in the cavity.

10. The varistor module of claim 9,

Wherein air is arranged between the inner surface of the housing (11) and the varistor (1).

11. The varistor module of claim 1,

Comprising at least a second varistor (1), wherein a second contact element (2, 3) is fixed to said second varistor (1), and

Wherein the terminal (4) comprises a second metal contact (7, 8), wherein the second metal contact (7, 8) is fixed to the second contact element (2, 3), and wherein the second metal contact (7, 8) comprises a lower surface (14) facing away from the second varistor (1) and configured for surface mounting.

12. A method of manufacturing a varistor module, comprising the steps of:

providing a varistor (1), the varistor (1) having contact elements (2, 3) fixed to the varistor (1),

Providing a terminal (4) comprising a metal contact (7, 8) comprising a lower surface (14) configured for surface mounting,

-Fixing the contact element (2, 3) to the metal contact (7, 8) such that a lower surface (14) of the metal contact (7, 8) faces away from the varistor (1).

13. The method of claim 12, further comprising the step of:

-placing a housing (11) over the varistor (1) and the contact elements (2, 3) such that the terminals (4) form the bottom side of the housing.

14. The method according to claim 12,

Wherein the contact element (2, 3) is fixed to the varistor (1) by soldering or by welding.

15. The method according to claim 12,

Wherein the method comprises the steps of:

Providing a second varistor (1) with a second contact element (2, 3) fixed to the second varistor (1),

Wherein the terminal (4) comprises a second metal contact (7, 8) comprising a lower surface (14) configured for surface mounting,

-Fixing the second contact element (2, 3) to the second metal contact (7, 8) such that a lower surface (14) of the second metal contact (7, 8) faces away from the second varistor (1).