JPS6222279B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetically shielded case for a magnetic bubble memory.

General electronic components and the like are protected by various packages such as plastic molds or canshields, and packaging measures are taken to stabilize component functions and facilitate handling during device assembly.

Regarding magnetic shielding, the can shield has a certain shielding effect due to the magnetic permeability of iron, which is the main material. However, bubble memory modules and the like that acquire memory functions by controlling magnetic domains may be subject to interference from weak external magnetic fields, resulting in malfunctions or, in some cases, loss of functionality.

The present invention provides attenuation of -40 dB or less (attenuation ratio 1/
This paper presents concrete measures to realize the magnetic shielding intended for 100).

The present invention is characterized by a magnetic shielding case for a magnetic bubble memory in which the shielding case material is a pipe with a rectangular cross section made of a highly magnetically permeable material, wherein the pipe is formed by forming the shielding case material into a pipe shape. The magnetic shield case is comprised of a seam-welded pipe with butt ends welded together, and the seam-welded joint is located within a flat plane along the longitudinal direction of the rectangular cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention and conventional structures will be described below with reference to the drawings.

FIG. 1A is a perspective view of a shield case having a conventional structure. The figure is formed by stacking two U-shaped cases 1 one above the other, and the joint 2 is located on a plane perpendicular to the long axis direction of the rectangular cross section. When the magnetic field strength ΔH _B in the internal space of the shield case is measured with the magnetic field strength Hex applied from the outside of the shield case in the direction shown, the hysteresis characteristic shown in FIG. 1B is obtained.

On the other hand, FIG. 2A is a perspective view of the basic shield case of the present invention. In this case, U-shaped case 1
The overlapping joint portion 3 is located on a flat surface along the long axis direction of the rectangular cross section of the shield case.

The magnetic field strength ΔH _B characteristic of the internal space with respect to the external magnetic field strength Hex is shown in FIG. 2B.

In comparing the shielding effects of both Figure 1 and Figure 2 above, except for the joint position, the same magnetic material (78Ni-Fe (78 Permalloy), Bm = 10000 Gauss) is used, the same shape and size and the same magnetic field. The annealing processing conditions were adopted. Nevertheless, there is a noticeable difference in the shielding effect, that is, △ at the former joint.
H _B /Hex = ±7/500, △H _B / at the latter junction
There is a significant difference of Hex=±1/500. However, the external magnetic field strength Hex was set to 50 Aersted (position indicated by the dotted line in the figure).

Note that from the viewpoint of only the shielding effect of the magnetic shield structure, it is effective to use a material with a high saturation magnetic density Bm. For example, for 45Ni-Fe (45 permalloy), which is the material for normal magnetic shielding cases, Bm=
Although 15,000 Gauss has an excellent effect, it has the disadvantage that the residual coercive force is large and induces magnetic interference in the target device inside the shield structure.

Therefore, a highly permeable material such as 78 permalloy, which has a low residual density, is effective as a magnetic shield case for a magnetic bubble memory module.

Next, an embodiment of the present invention according to the principles of the invention (FIGS. 2A and 2B) will be described with reference to FIG. 3.

By the way, the joints 2 and 3 of the magnetic shield case shown in Figs. 1 and 2 are overlapping joints, and the appearance is not good, and the assembly is complicated, so it is difficult to find a cheap one. You can't get it.

The present invention aims to solve these problems and provide a magnetic shielding case with good magnetic properties.

FIG. 3A shows a circular pipe material having a seam welded joint 8 in which the components constituting the shield case are formed into a pipe shape and the abutting ends are joined by welding means such as laser processing. Then, the pipe material shown in FIG. 3A is formed into a desired thin cross section as shown in FIG. 3B by hot drawing. In this state, the seam welded joint 8 becomes a seam welded joint 7 that is substantially seamless in appearance, as shown by the dotted line.
Thereafter, as shown in FIG. If the seam welded joints 7 are located on the respective corner parts, the magnetic properties will slightly decrease and the variation in characteristics will increase.
The magnetic shield case of the present invention can be obtained by forming the shield case into a rectangular cross section so that the magnetic shield case is preferably located inside the magnetic shield, and then magnetically annealing it in the same manner as in the prior art and cutting it to a predetermined size.

Incidentally, the seam welded joint 7 is in a state where the seam is not visible and the magnetic resistance is smaller than the joints shown in Figs. 1 and 2, but even this actually results in processing distortion and voids remaining during welding. There is.

Therefore, the seamless joint 7 also becomes a magnetoresistive part and deteriorates the magnetic shielding characteristics, and when it exists in a position as shown in FIG. 1A, it exhibits characteristics as shown in FIG. 1B.

On the other hand, the magnetic shield case according to the present invention shown in FIG. 3 exhibits good characteristics like the case shown in FIG. 2, that is, about ΔH _B /Hex=±1/500, and can be obtained at low cost.

As described above, according to the present invention, a shield case with good magnetic shielding properties and good appearance can be obtained by simple means, and its practical effects are remarkable.

[Brief explanation of the drawing]

Figures 1A and 1B are diagrams showing a conventional magnetic shielding case with a joint in which multiple U-shaped cases are stacked one on top of the other, and its shielding characteristics.
FIGS. 2A and 2B are diagrams showing the principle magnetic shielding case of the present invention and its shielding characteristics, and FIGS. 3A, B, and C are diagrams explaining the magnetic shielding case according to the embodiment of the present invention. In the figure, 1: U-shaped case, 2 and 3: overlapping joint, 5 and 6: flat surface, 7 and 8: seamless joint.

Claims (1)

[Scope of Claims] 1. A magnetic shielding case for a magnetic bubble memory in which the shielding case material is a pipe with a rectangular cross section made of a highly magnetically permeable material, wherein the pipe is formed by forming the shielding case material into a pipe shape, and the abutting ends thereof. A magnetic shielding case comprising a seam welded pipe, wherein the seam welded joint is located within a flat plane along the longitudinal direction of the rectangular cross section.