JP4764976B2 - External case for module type semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exterior case for a module type semiconductor device, and more particularly, is referred to as a power transistor module used for a converter or inverter such as a switching power supply device, a constant voltage constant frequency control device (CVCF) or a variable voltage variable frequency power supply device (VVVF). The present invention relates to an outer case for housing a semiconductor device to be used.
[0002]
[Prior art]
As a form in which the power transistor module is incorporated in a device such as the aforementioned switching power supply device, as shown in FIG. 5, a control circuit or the like is provided on an outer case 1 containing a power transistor chip (not shown in the figure). May be attached by a tapping screw 3. FIG. 6 is a plan view of the outer case 1, and the outer case 1 is provided with a protruding (tubular) screw hole 4 for receiving the tapping screw 3. FIG. 7 is a plan view of the printed board 2, and a tapping screw 3 is also shown in order to make it easy to imagine the state of being attached to the exterior case 1.
[0003]
Conventionally, the outer case 1 is made of a polybutylene terephthalate resin that is excellent in mechanical properties, particularly in toughness. When the tapping screw 3 is M2.6, as shown in FIG. 8, the outer diameter and inner diameter of the protruding screw hole 4 are 4.5 mm and 2.1 mm, respectively, and the wall thickness is 1.2 mm. . Moreover, the depth of the screw hole 4 is 6 mm. By the way, recently, environmental problems have been attracting attention, and a halogen-free free of halogen elements and a lead-free free of lead are being promoted.
[0004]
[Problems to be solved by the invention]
However, the polybutylene terephthalate resin conventionally used as the material of the outer case 1 uses a halogen substance as a flame retardant. Further, higher heat resistance is required with the lead-free solder, but the polybutylene terephthalate resin has a low solder heat resistance, and therefore cannot satisfy the high heat-resistance requirement with lead-free.
[0005]
Therefore, the present inventors have focused on polyphenylene sulfide resin that has high heat resistance and does not use a flame retardant as a material for the exterior case. However, since polyphenylene sulfide resin has lower toughness than polybutylene terephthalate resin, it is necessary to increase the thickness of the protruding screw holes.
[0006]
As a result of the examination by the present inventors on the dimensions of the protruding screw holes of the outer case made of polyphenylene sulfide resin, in order to ensure the same strength as the protruding screw holes 4 of the outer case 1 made of polybutylene terephthalate resin. 9, the outer diameter, inner diameter, wall thickness and depth of the protruding screw hole 5 with respect to the M2.6 tapping screw are 6.5 mm, 2.2 mm, 2.15 mm and 6.5, respectively. 5 mm. In other words, the outer diameter of the protruding screw hole is increased by 2 mm, so that there is a problem in that polyphenylene sulfide resin cannot be used as a material for the outer case depending on the product due to external dimension restrictions.
[0007]
The present invention has been made in view of the above problems, and has a protruding shape having sufficient strength with the same outer diameter as compared with a protruding screw hole of a conventional outer case made of polybutylene terephthalate resin. An object is to provide an exterior case made of polyphenylene sulfide resin having a screw hole.
[0008]
[Means for Solving the Problems]
To achieve the above object, the present invention is to provide an exterior case made of polyphenylene sulfide resin, a protruding threaded bore for receiving a tapping screw, at least twice the depth of the thread pitch, and nominal diameter of the screw and A guide portion having the same inner diameter and a screw diameter of 5 times the screw pitch; It is composed of a pilot hole with a depth equal to or greater than the value obtained by adding 5 times. The guide portion is provided on the upper side of the prepared hole portion and has an inner diameter wider than the inner diameter of the prepared hole portion. According to the present invention, since the guide portion having an appropriate depth and inner diameter is provided in the protruding screw hole, the tapping screw is prevented from entering the lower hole portion obliquely. In addition, since the depth of the pilot hole is optimized, the number of screw threads to be screwed into the pilot hole is optimized, and a waste pool is secured at the bottom of the hole.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partially enlarged cross-sectional view showing an enlarged screw fastening portion of an exterior case according to the present invention.
[0010]
The outer case 6 is made of polyphenylene sulfide resin, and the shape thereof is the same as that of the conventional case 1 shown in FIGS. Therefore, the illustration of the outer case 6 corresponding to FIGS. 5 and 6 is omitted. The projecting screw hole 7 for receiving the tapping screw 3 is constituted by a guide hole 72 for inserting the tapping screw 3 straight without being inclined to the pilot hole 71 into which the screw thread of the tapping screw 3 is screwed and the pilot hole 71. Is done. In FIG. 1, reference numeral 8 denotes a washer.
[0011]
The inner diameter of the pilot hole 71 is slightly smaller than the nominal diameter of the tapping screw 3. The depth of the pilot hole 71 is a dimension equal to or larger than a value obtained by adding approximately 1.5 times the nominal diameter of the screw to approximately 5 times the screw pitch of the tapping screw 3. Here, with respect to the depth of the pilot hole portion 71, about five times the screw pitch of the tapping screw 3 is the number of threads (5 threads) regulated in common with the former Electrical Appliance and Material Control Law and Table 8 of the technical standards. ) Is ensured. Therefore, unless this restriction is used, the screw pitch is not limited to about 5 times. Further, the depth of the pilot hole 71 is approximately 1.5 times the nominal diameter of the tapping screw 3 in order to secure a dust pool at the bottom of the screw hole 7, and as a result, it has been found that A nominal diameter of about 1.5 times is appropriate.
[0012]
The inner diameter of the guide portion 72 is substantially the same as the nominal diameter of the screw. As described above, since the guide portion 72 is for inserting the tapping screw 3 straight, it is preferable that the tapping screw 3 does not wobble when the tip portion of the tapping screw 3 is inserted into the guide portion 72. In general, the outer dimension of the thread is slightly smaller than the nominal diameter of the screw. Therefore, if the inner diameter of the guide part 72 is substantially the same as the nominal diameter of the screw, the tapping screw 3 is inserted into the guide part 72 without shaking. Accordingly, the tapping screw 3 is inserted straight into the prepared hole 71.
[0013]
Further, the depth of the guide portion 72 is approximately twice or more the screw pitch. The reason will be described with reference to FIGS. 2 and 3, the left and right ends of the third thread from the bottom of the tapping screw 3 are P1 and P3, respectively, and the left and right ends of the second thread from the bottom are P2 and P4, respectively. To do.
[0014]
As shown in FIG. 2, when the depth of the guide portion 72 is approximately twice or more the screw pitch, P1, P2, P3, and P4 are in contact with the inner peripheral surface of the guide portion 72. That is, since the two screw threads reliably contact the inner peripheral surface of the guide portion 72, the tapping screw 3 does not tilt. On the other hand, as in the screw hole 7 ′ shown in FIG. 3, if the depth of the guide portion 72 ′ is less than about twice the screw pitch, P3 does not contact the inner peripheral surface of the guide portion 72 ′. For this reason, there is a case where there is one crest that contacts the inner peripheral surface of the guide portion 72 ′, and the tapping screw 3 is inclined by about 2 °, for example.
[0015]
When the tapping screw 3 is M2.6, an example of the dimension of the screw hole 7 is shown in FIG. The inner diameter and depth of the guide portion 72 of the screw hole 7 are (about) 2.6 mm and (about) 3 mm, respectively. The inner diameter and depth of the pilot hole 71 are (about) 2.25 mm and (about) 9 mm, respectively. Further, the thickness of the pilot hole 71 is (about) 1.125 mm, and therefore the outer diameter of the screw hole 7 is the same (about) 4.5 mm as the screw hole of the conventional outer case made of polybutylene terephthalate resin. Become.
[0016]
According to the embodiment described above, the guide screw 72 having an appropriate depth and inner diameter is provided in the protruding screw hole 7, so that the tapping screw 3 is prevented from entering the lower hole portion 71 obliquely. The Moreover, since the depth of the pilot hole part 71 is optimized in consideration of the waste accumulation, the number of screw threads to be screwed into the pilot hole part 71 is optimized and the dust accumulation is secured at the bottom of the hole. Therefore, the outer case 6 made of polyphenylene sulfide resin having the projecting screw holes 7 having the same outer diameter and sufficient strength as compared with the projecting screw holes of the outer case made of polybutylene terephthalate resin. Is obtained.
[0017]
The present invention can be variously modified as described above, and is not limited to the above description of the embodiment, the illustrated examples, the illustrated dimensions, and the like.
[0018]
【The invention's effect】
According to the present invention, an outer case made of polyphenylene sulfide resin having a protruding screw hole having the same outer diameter and sufficient strength as compared to the protruding screw hole of a conventional outer case made of polybutylene terephthalate resin Is obtained.
[Brief description of the drawings]
FIG. 1 is a partially enlarged cross-sectional view showing a screwed portion of an exterior case according to the present invention in an enlarged manner.
FIG. 2 is a view for explaining a depth of a guide portion of a screw hole provided in an exterior case according to the present invention.
FIG. 3 is a view for explaining a depth of a guide portion of a screw hole provided in an exterior case according to the present invention.
FIG. 4 is a schematic view showing an example of the dimensions of the screw holes of the exterior case according to the present invention.
FIG. 5 is a front view showing an appearance of a power transistor module.
FIG. 6 is a plan view showing an outer case of the power transistor module.
FIG. 7 is a plan view showing a printed board attached to an exterior case.
FIG. 8 is a schematic diagram showing the dimensions of a screw hole of a conventional exterior case.
FIG. 9 is a schematic diagram showing the dimensions of screw holes in a polyphenylene sulfide resin outer case investigated by the present inventors.
[Explanation of symbols]
2 Printed board 3 Tapping screw 6 Exterior case 7 Screw hole 8 Washer 71 Pilot hole 72 Guide part

Claims (3)

An exterior case used for a module-type semiconductor device that houses a semiconductor device and has a configuration in which a printed board is attached to the upper surface of the case by a tapping screw,
It has a protruding screw hole for receiving the tapping screw, and is made of polyphenylene sulfide resin.
The protruding screw hole is
A pilot hole portion for meshing with a screw portion of the tapping screw;
A guide portion provided on the upper side of the pilot hole portion, having an inner diameter wider than the inner diameter of the pilot hole portion and having a depth of twice or more the screw pitch of the tapping screw,
Module type semiconductor device outer casing for, characterized in that the diameter of the guide portion is a same size and a nominal diameter of the tapping screw. The protruding screw hole is
The outer case for a module type semiconductor device according to claim 1, comprising the guide portion for inserting the tapping screw into the lower hole portion so as not to tilt. The depth of the pilot hole is 5 times the screw pitch of the tapping screw and 1 . 3. The exterior case for a module type semiconductor device according to claim 1, wherein the outer case has a dimension equal to or larger than a value obtained by adding 5 times.

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