JP2010056098A - Surface mounting discharge tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface mounting discharge tube which is capable of suppressing positional deviation at the time of soldering and has sufficient PCT property. <P>SOLUTION: The surface mounting discharge tube includes a structure in which both ends of a cylindrical ceramic envelope are sealed with sides of electrodes, respectively, and the tube is directly soldered onto a mounting board. Each electrode has rectangular portions at the both ends that are extended outward from the ends of the ceramic envelope and tapered portions or stepped portions for soldering at the peripheral edges of sides of the electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface mount discharge tube that is soldered directly onto a printed circuit board.

  In general, a discharge tube has a structure in which both ends of a cylindrical ceramic envelope are sealed with the side surfaces of electrodes, and mounting on a printed circuit board is conventionally performed via lead wires provided on the end surfaces of the electrodes. It was.

  Mounting via lead wires is performed for each discharge tube, but there is a strong demand for mounting a large number of discharge tubes at the same time. For this reason, the surface to be directly bonded on the printed circuit board without using lead wires Implementation has become necessary.

  At that time, if the cylindrical discharge tube is simply placed on the printed circuit board as it is, it will roll and positioning will be difficult, so a flat portion is provided on a part of the electrode (Patent Documents 1 and 2). Yes. Further, in a surge absorber having the same basic structure as the discharge tube, the electrode is made polygonal with the same purpose (Patent Document 3).

  In surface mounting, solder pellets are placed at each mounting location on the printed circuit board, and the solder joint flat portions of the electrode periphery of the discharge tube are aligned and placed in the heating furnace. Then, after the solder pellets are dissolved, the solder pellets are taken out of the furnace and solidified to complete the joining.

  However, the discharge tube that has been surface-mounted in this manner has a problem that positional displacement occurs with respect to a predetermined mounting position at the time of solder joining, and reliability such as pressure cooker test (PCT) characteristics is insufficient. It was.

Japanese Utility Model Publication No. 59-33690 (claims for registration of utility model, FIGS. 2 to 5) JP 2003-151716 A (Claims, FIGS. 1 and 3) JP 2001-135453 A (Claims, FIG. 3)

  An object of the present invention is to provide a surface-mount discharge tube that suppresses the occurrence of misalignment during solder bonding and has sufficient PCT characteristics.

In order to achieve the above object, the surface-mount discharge tube of the present invention is formed by joining the side surfaces of each electrode to both ends of a cylindrical ceramic envelope, thereby sealing the both ends with the side surfaces of the electrodes. A surface mount discharge tube that is directly soldered onto a mounting board,
The electrodes connected to the both ends are square and project outward from the end of the ceramic envelope to the central axis of the ceramic envelope and are joined to the ceramic envelope. A taper or a step for soldering at the periphery of the electrode side surface of the electrode
Discharging is performed at the facing portions of both electrodes at the center of the discharge tube.

  The inventor makes the electrodes at both ends square, projects outward from the end of the ceramic envelope, and provides a solder joint taper or step on the periphery of the electrode side surface. The present invention has been completed by finding that the occurrence of misalignment at the time can be suppressed and at the same time sufficient reliability (particularly PCT characteristics) can be secured.

  Furthermore, since the discharge tube of the present invention does not require a lead wire, the steps for forming the lead wire can be omitted in the manufacturing process, so that the productivity is improved.

FIG. 1 is a (1) longitudinal sectional view and (2) a transverse sectional view showing an embodiment of a discharge tube having a taper on the electrode side surface according to the present invention. FIG. 2 is a (1) longitudinal sectional view and (2) a transverse sectional view showing an embodiment of a discharge tube having a step on the electrode side surface according to the present invention.

  Embodiment 1 FIG. 1 shows an example of a surface mount discharge tube according to the present invention. FIG. 1 (1) is a longitudinal sectional view cut along a plane including the central axis of the cylindrical ceramic envelope of the discharge tube, and FIG. 1 (2) is cut along the line XX shown in FIG. 1 (1). FIG.

  The discharge tube 110 shown in FIG. 1 has a structure in which both ends of a cylindrical ceramic envelope 102 having a central axis C are sealed with side surfaces S of circular electrodes 104. The electrode 104 has a square shape and projects outward from the end of the ceramic envelope 102 with respect to the central axis C. The electrode 104 includes a taper T for solder bonding on the periphery of the side surface S of the electrode 104.

  In addition, a material for reliably generating a discharge and maintaining it stably is applied or filled in the recesses 106 with a large number of recesses formed respectively on the facing portions of both electrodes 104, 104 at the center of the discharge tube. . The multiple recesses in the recess 106 are multiple recesses each shown in a hemispherical shape in FIG. 1A (not shown in FIG. 1B).

  Since the electrode 104 is square, it can be mounted anywhere on the four sides during surface mounting. This eliminates the need for orientation by positioning and potting during mounting.

  Since the electrode 104 projects outward from the end of the ceramic envelope 102 with respect to the central axis C, the surface of the printed circuit board and the ceramic envelope 102 of the discharge tube 110 when mounted on the printed circuit board. Since a space is secured between them, the PCT characteristics are improved.

  As one effect of ensuring the space, it is possible to prevent the solder melted at the time of surface mounting from penetrating into the joint interface between the ceramic envelope 102 and the electrode 104 due to a capillary phenomenon, thereby causing a short circuit failure due to migration of the solder when energized. Can be prevented.

  Since the taper T for soldering is provided on the periphery of the side surface S of the electrode 104, when surface mounting using solder pellets, molten solder tends to crawl up to the electrode due to surface tension, and misalignment occurs during soldering. Is suppressed and the soldering strength is improved.

  The taper angle θ (see FIG. 1 (1)) provides the above effect within a range of 0 ° <θ <90 °, and the effect is particularly remarkable when 0 ° <θ <45 °, and around θ = 25 °. The largest effect has been confirmed.

  A large dimple 108 is formed in the central portion of the outer surface of the electrode 104 and can be used as a chuck portion when the discharge tube 110 is transported. At the same time, the volume of the electrode 104 is reduced and the surface area is increased to improve heat dissipation. It is increasing.

  Embodiment 2 FIG. 2 shows another example of a surface mount discharge tube according to the present invention. FIG. 2 (1) is a longitudinal sectional view cut along a plane including the central axis of the cylindrical ceramic envelope of the discharge tube, and FIG. 2 (2) is cut along the line XX shown in FIG. 2 (1). FIG.

  The discharge tube 120 shown in FIG. 2 has the same structure as the discharge tube 110 of FIG. 1 except that the peripheral edge of the side surface S of the electrode 104 is provided with a step D for soldering. The portions corresponding to those of the discharge tube in FIG.

  The discharge tube 120 according to the present embodiment includes a step D for solder bonding at the periphery of the side surface S of the electrode 104, and similarly to the solder bonding taper T of the discharge tube 110 according to the first embodiment, the position at the time of soldering. A slip prevention effect and a soldering strength improvement effect are obtained. When expressed by the dimension measured from the outer periphery of the electrode, the solder joint step is generally about 0.1 to 5 mm, preferably about 1 to 2 mm, and preferably larger than the thickness of the solder pellet used for solder joining.

  Other effects, that is, the effect of the electrode 104 having a square shape, the effect of securing the space between the surface of the printed circuit board and the ceramic envelope 102, the central portion of the outer surface of the electrode 104, described in the first embodiment The effects of the dimples 108 provided in the above are also obtained in the same manner as in the first embodiment.

  [Reduction effect of lead wire forming step] In order to form a lead wire on an electrode, the following steps (1) to (4) are generally required.

  (1) Lead wire spot welding (join the lead wire to the center of the outer surface of the electrode) (2) Lead wire processing (lead wire bending to form legs for joining to the substrate) (3) Leak check (4) Ignition confirmation Since the discharge tube of the present invention does not use lead wires, the above steps (1) to (4) can be omitted.

  Furthermore, resistance welding by 10 kg pressurization is standard for the step (1) lead wire spot welding. However, since this method gives an impact to the discharge tube main body, a load is applied to the brazing surface that joins the ceramic envelope and the electrode, which causes leakage of the sealed gas due to the occurrence of microcracks. . Since the present invention does not perform the lead wire forming step, such a problem does not occur.

  In each of the above embodiments, the example in which the taper T and the step D of the electrode 104 are provided on the periphery of the inward side surface S of the electrode 104 has been described. However, if migration due to solder creep does not occur, the taper T and the taper T and the step D are not provided on the periphery of the inward side S, and the taper T and A step D may be provided.

  Further, the taper T and the step D of the electrode 104 may be provided on both the periphery of the inward side surface S of the electrode 104 and the periphery of the outward side surface opposite to the side surface S.

  [Example 1] A surface mount test using solder pellets was performed on the discharge tube of the present invention in which the side surface of the electrode was tapered and a conventional discharge tube without a taper, and the displacement during soldering was measured.

  The taper angle θ shown in FIG. 1 (1) is θ = 0 ° in the conventional example (however, two types of electrode overhang (conventional example 1) / existing (conventional example 2)), and in the present invention example, θ = Three levels of 25 °, 45 °, and 75 ° were set. The sample shape was as follows.

<Sample shape>
Ceramic envelope: Outer diameter φ0.8mm x Length 6.0mm (cylindrical)
Electrode: □ 12.0 mm, outer edge thickness 2.0 mm
(Conventional example 1 is □ 8.1 mm)
Spacing with printed circuit board: 2.0 mm (Conventional example 1 has a spacing of 0)
The surface mounting test was performed according to the following procedure.

<Surface mount test procedure>
(1) A solder pellet (length 12.5 mm, width 2.0 mm, thickness 1.5 mm) is placed on a printed circuit board.

  (2) A sample discharge tube is placed on the solder pellet, and the initial positions in the discharge tube cylindrical axis direction (X direction) and the discharge tube direct direction (Y direction) are measured.

  (3) Charge in a solder welding furnace and heat to 350 ° C.

  (4) After taking out from the solder welding furnace and cooling to room temperature, the X direction position and the Y direction position of the sample are measured. Calculate the positional deviation during soldering from the difference from the initial position.

  The above test was performed on five samples of the same type (repetition number: n = 5). The test results are shown in Table 1.

  All of the tapered samples according to the present invention have significantly reduced misalignment at the time of soldering as compared with the conventional samples without taper.

  Conventional example 1 has no taper and no electrode overhang, and there is no space between the ceramic envelope and the printed circuit board. The positional deviation is most significant, and the X direction (the direction of the discharge tube cylindrical axis) is 1.1 to 3.6 mm, the Y direction (discharge tube diameter direction) is 1.2 to 3.3, and the variation in misalignment is large.

  Conventional example 2 has no taper, and as with the present invention example, with an electrode overhang, a space of 2 mm is secured between the ceramic envelope and the printed circuit board, and the positional deviation is 1.2-2 in the X direction. .2 mm, 1.3 to 2.5 mm in the Y direction, and there is less positional deviation and less variation compared to Conventional Example 1.

  On the other hand, in the example of the present invention, in the tested range, the taper angle θ = 25 ° has the smallest positional deviation, 0.1 mm to 0.2 mm in the X direction, and 0.1 mm to 0.3 mm in the Y direction. It is reduced to the level of 1/10. As the taper angle θ increases to 45 ° and 75 °, the positional deviation tends to gradually increase. However, even in the present invention example where the positional deviation is the largest, the taper angle θ = 75 ° is several minutes of the conventional example. 1 level, which is 0.3 to 0.6 mm in the X direction and 0.8 to 1.1 in the Y direction.

  [Example 2] With respect to the discharge tube of the present invention in which the electrode side surface is tapered and the conventional discharge tube without taper, surface mounting is performed using solder pellets in the same manner as in Example 1, and the pressure cooker test ( PCT).

  The taper angle θ of the side surface of the discharge tube electrode is θ = 0 ° in the conventional example (however, there are two types of electrode overhang (conventional example 1) / existing (conventional example 2)), and the present invention example is θ = 25 °, 75 Two levels of ° were set.

  The discharge tube sample shape was the same as in Example 1.

  The PCT test was performed under the following conditions.

<PCT test conditions>
Temperature: 120 ° C
Humidity: 100% (saturated state)
Pressure: 0.150 MPa
Energization: DC500V always applied Time: 100 hours to 800 hours (cumulative)
Evaluation: To maintain an insulation resistance of 1000 MΩ or more at an acceptable standard (standard) / 500 hours.

  The results of measuring the insulation resistance after the PCT test are shown in Table 2.

  In all the samples of the conventional example and the example of the present invention, 10000 MΩ (measurable upper limit value) or more was maintained until after 100 hours.

  Conventional Example 1 (no taper, no space) has already dropped to 600 MΩ in 200 hours, and Conventional Example 2 (no taper, space secured) has dropped to 500 MΩ in 500 hours, and none of them passed the acceptance criteria.

  On the other hand, the examples of the present invention (with a taper, ensuring space) maintain an insulation resistance of 10000 MΩ (measurable upper limit) or more after 500 hours, and show excellent characteristics exceeding 10 times the acceptance standard. ing. In particular, when the taper angle θ = 25 °, the insulation resistance of 10000 MΩ or more is maintained even after 800 hours. Even when the taper angle θ = 75 °, the insulation resistance of 7000 MΩ corresponding to 7 times the acceptance criterion is maintained after 600 hours.

  According to the observation after the surface mounting, as a phenomenon peculiar to the conventional example in which there is no taper on the side surface of the electrode, bubbles remain between the joint portion of the electrode and the ceramic envelope and between the ceramic envelope and the printed circuit board. It was. Since this was not observed in the example of the present invention in which the side surface of the electrode was tapered, in the conventional example, the presence of bubbles may have contributed to the promotion of insulation deterioration.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing generation | occurrence | production of position shift at the time of solder joining, the discharge tube for surface mounting provided with sufficient reliability (especially PCT characteristic) is provided.

110, 120 Discharge tube of the present invention 102 Cylindrical ceramic envelope 104 Electrode 106 Recess 108 Dimple C Central axis of cylindrical ceramic envelope 102 S Side surface of electrode 104 T Solder provided on peripheral edge of side surface S of electrode 104 Taper for joining θ Taper angle (reference is electrode side S)
D Step for solder joint provided on the periphery of the side surface S of the electrode 104

Claims (5)

A surface-mount discharge tube that has a structure in which the side surfaces of each electrode are joined to both end portions of a cylindrical ceramic envelope so that the both end portions are sealed by the side surfaces of the electrodes, and is soldered directly onto the mounting substrate. Because
The electrodes connected to the both ends are square and project outward from the end of the ceramic envelope to the central axis of the ceramic envelope and are joined to the ceramic envelope. A taper or a step for soldering at the periphery of the electrode side surface of the electrode
A discharge tube for surface mounting, wherein discharge is performed at the facing portions of both electrodes at the center of the discharge tube.   2. The surface-mount discharge tube according to claim 1, wherein a taper angle θ with respect to the electrode side surface periphery is 0 ° <θ <90 ° with respect to the electrode side surface.   3. The surface-mount discharge tube according to claim 2, wherein the taper angle θ is 0 ° <θ <45 °.   2. The surface-mount discharge tube according to claim 1, wherein the step for solder joint at the peripheral edge of the electrode is 0.1 to 5 mm.   5. The surface mount discharge tube according to claim 4, wherein the step is larger than a thickness of a solder pellet used for the solder joining.

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