GB2311416A

GB2311416A - Fixing structure for a printed circuit board

Info

Publication number: GB2311416A
Application number: GB9704013A
Authority: GB
Inventors: Hideki Watanabe
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1996-03-18
Filing date: 1997-02-26
Publication date: 1997-09-24
Anticipated expiration: 2017-02-26
Also published as: JPH09260884A; TW363337B; KR970068767A; DE19711325A1; DE19711325C2; GB9704013D0; CN1162899A; GB2311416B; CN1070684C

Description

7401GB 2311416 PRINTED STRUCTURE FOR A PRINTED CIRCUIT BOARD This

invention relates to a structure for fixing a printed circuit board to a metal frame in an electronic circuit apparatus such as an electronic tuner comprising a metal frame serving as a printed circuit board constituting an electronic circuit and a shield case.

A general electronic apparatus comprises a printed circuit board on which circuit elements such as a transistor, a diode, a capacitor, a register, and an inductor are mounted.

A printed circuit board is formed as follows. A copper-plated phenol multilayer is processed to have a predetermined shape, and a predetermined circuit pattern is formed on the multilayer. Circuit element attaching holes are formed, terminals of the circuit element are inserted into the attaching holes, and the terminals are connected to the circuit pattern with solder to constitute the circuit of an electronic apparatus.

An electronic apparatus such as an electronic tuner comprising a highfrequency oscillation circuit uses a structure for fixing a printed circuit board to a square metal frame having an opening in an upper surface to prevent unnecessary radiation to another circuit or another apparatus and to fix terminals or connectors for connection to another circuit. In order to electrically ground the metal frame, a conductive pattern formed by etching a copper foil on the peripheral portion of the printed circuit board is connected to the metal frame with solder.

Such a structure is described in Japanese Unexamined Utility Model Publication No. 62-178596. To illustrate an embodiment of the fixing structure,.Fig. 11 is a perspective view showing the relationship between a metal frame and a printed circuit board, and Fig. 12 is a sectional view showing a main part of connection between 7401GB - 2 the metal frame and the printed circuit board. As shown in Figs. 11 and 12, a side plate 2 of a metal frame 1 is punched into an "inverted U"- shaped punched portion 3 to form a tongue piece 5, and the side plate 2 is cut and bent below the tongue piece 5 to form a board engagement piece 8. When the printed circuit board 4 is incorporated in the metal frame 1, the printed circuit board 4 is inserted from an upper opening end of the metal frame 1 to be horizontally supported at a position where the printed circuit board 4 is brought into contact with the board engagement piece 8, and an end portion 5b of the tongue piece 5 is pressed inside the metal frame 1. At this time, a base portion 5a is brought into contact with the end face of the printed circuit board 4 and bent to fix the printed circuit board 4. Thermally melted solder 10 is filled in a portion between the tongue piece 5 and a conductive pattern 9 arranged at the peripheral portion of the printed circuit board 4, and is cooled and solidified. The solder 10 adheres to the tongue piece 5 and the conductive pattern 9 and fills a gap between the tongue piece 5 and the conductive pattern 9, so that the tongue piece 5 and the conductive pattern 9 are connected to each other with solder. In this manner, the printed circuit board 4 is fixed to the metal frame 1 by mechanical fixing and electrical connection.

However, in the prior art, when the tongue piece 5 is bent, as shown in Fig. 12, although the gap between the tongue piece 5 and the conductive pattern 9 is wide at the end portion 5b of the tongue piece 5, the gap becomes narrow toward the base portion 5a, and the gap is eliminated at the base portion 5a. For this reason, in soldering connection between the tongue piece 5 and conductive patter 9, the solder 10 on the conductive pattern 9 is filled on only the internal portion 9b, and a very small amount of solder 10 or no solder fills a

7401GB reservoir end portion 9a. Therefore, the connection of the conductive pattern 9 becomes disadvantageously poor toward the reservoir end portion 9a.

This presents the following problem. In a temperature cycle test (for example, a test in which exposure in an atmosphere of -200C to 600C is alternately performed in 10 cycles) for testing practical reliability, since the thermal expansion coefficients inherent in the materials used as the metal frame 1 and the printed circuit board 4 are different from each other, stress generated by the differences between the amounts of thermal expansion (or contraction) of the metal frame 1 and the printed circuit board 4 acts on the solder 10. When the amount of solder 10 is small, cracks are formed in the solder 10 which may lead to disconnection.

The present invention arose in consideration of the above problem and in an attempt to provide a fixing structure of a printed circuit board in which a large amount of solder is filled in a gap between the tongue piece 5 and the conductive pattern 9 to improve connection strength.

According to the present invention, there is provided a fixing structure of a printed circuit board, comprising a square metal frame having an opening in an upper surface, a printed circuit board which has a conductive pattern formed on a least one surface is stored in the metal frame, first and second tongue pieces which are formed at positions close to each other in a side plate of the metal frame by punching, wherein the first tongue piece is brought into contact with an end portion of the printed circuit board and bent inside the metal frame, the second tongue piece has an angle which is different from that of the first tongue piece with respect to the printed circuit board surface, and the first and second tongue pieces are connected to the conductive 7401GB 4 pattern with solder.

According to this structure, since the first and second tongue pieces face the printed circuit board at different angles, the first and second tongue pieces are soldered on the conductive pattern such that the first tongue piece has a proper gap between the end portion and the conductive patter, and the second tongue piece has a gap where soldering can be performed between the base portion and the conductive pattern. For this reason, the solder is filled at the end portion of the first tongue piece on the internal side, and the solder is filled at the base portion of the second tongue piece on the reservoir end portion side. In addition, since the first tongue piece and the second tongue piece are closed to each other and have different angles, solder for connecting the first and second tongue pieces to each other is filled, and an amount of solder is larger than the sum of amounts of solder filled in a portion between the conductive pattern and both the tongue pieces. The solder increases in area and thickness, and a fixing structure of a printed circuit board having high soldering connection strength can be provided.

The second tongue piece may be bent outside the side plate of said metal frame. The gap between the second tongue piece and the conductive pattern then increases, and a larger amount of solder is filled in the gap. A fixing structure of a printed circuit board having higher soldering connection strength can then be provided.

The first tongue piece may partially form the second tongue piece, in which case the second tongue piece need not be partially bent when the first tongue piece is bent. Thus, a fixing structure of a printed circuit board which can be easily bent can be provided.

Embodiments of the present invention will be described below, by way of example only, with reference to 7401GB the accompanying drawings, in which:

Fig. 1 is a sectional view showing a main part subjected to soldering connection according to a first embodiment of the invention; Fig. 2 is an upper view showing a main part of a soldering connection state according to the first embodiment; Fig. 3 is a front viewshowing a main part of metal frame sample 1 according to the first embodiment; Fig. 4 is a front view showing a main part of metal frame sample 2 according to the first embodiment; Fig. 5 is a front view showing a main part of metal frame sample 3 according to the first embodiment; Fig. 6 is a front view showing a main part of metal frame sample 4 according to the first embodiment; Fig. 7 is a sectional view showing a main part subjected to soldering connection according to a second embodiment of the invention; Fig. 8 is a front view showing a main part of metal frame sample 5 according to the first embodiment; Fig. 9 is a sectional view showing a main part subjected to soldering connection according to a third embodiment of the invention; Fig. 10 is a front view showing a main part of metal frame sample 6; Fig. 11 is a perspective view showing a connection structure between a metal frame and a printed circuit board according to the prior art; and

Fig. 12 is a sectional view showing a main part subjected to soldering connection according to the prior art.

Referring to Figs. 1 to 3, a side plate 12 - 6 constituting a metal frame 11 is punched into an "inverted U"-shaped hole at a position where an end face of a printed circuit board 4 is arranged to form a punched portion 13, and a first tongue piece 15 and a second tongue piece 17 are formed by a cut portion 16 on the tongue-shaped portion surrounded by the punched portion 13. The side plate 12 is partially bent inside the metal frame to form a circuit board engagement piece 18. The first tongue piece 15, the second tongue piece 17, and the circuit board engagement piece 18 are generally formed such that the metal frame 11 is punched by using a metal mold (not shown) when the metal frame 11 is processed.

A method of attaching the printed circuit board 4 to the metal frame 11 by the first tongue piece 15 and the second tongue piece 17 which are formed as described above will be described below.

The printed circuit board 4 is horizontally inserted from an upper opening end (not shown) of the metal frame 11 and stored at a position where the metal frame 11 is brought into contact with the circuit board engagement piece 18. When an end portion 15b of the first tongue piece 15 is pressed inside the metal frame 11 by using a proper jig (not shown), a base portion 15a is brought into contact with the end face of the printed circuit board 4 and bent to form a gap between the end portion 15b and the printed circuit board. That is, the first tongue piece 15 is arranged at an angle with respect to the printed circuit board surface. This angle may be properly set such that the first tongue piece 15 is brought into press contact with the printed circuit board 4 without breaking the printed circuit board 4. In this state, the base portion 15a of the first tongue piece 15 is in press contact with the end portion of the printed circuit board 4. For this reason, the printed circuit board 4 is mechanically fixed to the metal frame 1, the printed circuit board 4 is free from relief or unstableness. this time, the second tongue piece 17 and the printed circuit board surface form a right angle.

When thermally melted solder 10 is interposed between the conductive p attern 9 arranged on the printed circuit board 4 and the first and second tongue pieces 15 and 17, the solder 10 is adhered to the conductive pattern 9, the first tongue piece 15, and the second tongue piece 17. At this time, the amount of solder 10 filled in a portion between the first tongue piece 15 and the conductive pattern 9 increases because the gap between the first tongue piece 15 and the conductive pattern 9 increases 8 toward the endportion 15b. Since the second tongue piece 17 and the conductive pattern 9 form a right angle, the solder 10 is filled on a base portion 17a. In addition, the solders filled on -the end portion 15b of the first tongue piece 15 and the base portion 17a of the second tongue piece 17 are closed to each other, so that the solders are connected on the conductive pattern. When the thermally melted solder 10 filled as described above is cooled to be solidified, electrical connection can be obtained. As a method of interposing the melted solder 10 in the gap between the first tongue piece 15 and the second tongue piece 17 on the conductive pattern 9, a method of melting thread solder is generally used. A method of dipping the connection portion in a thermally molted solder tank or a method of coating cream solder on the connection portion and melting the cream solder by a point heater or a reflow furnace is also used. As a cooling and solidifying method, a method of leaving the soldered portion at room temperature is used. As a result, the solder 10 having a large area and a large thickness is filled on the end portion 9a and internal portion 9b of the conductive pattern 9 and on the intermediate portion therebetween. Therefore, connection strength can be improved.

- 9 In the first embodiment, Figs. 4 to 6 are front views showing main parts of metal frame samples 2 to 4. only different portions between metal frame sample 1 and metal frame samples 2 to 4 will be described below with reference to Figs. 4 to 6.

Metal frame sample 2 shown in Fig. 4 comprises a first tongue piece 25 and second tongue pieces 27 formed on a side plate 22 of a metal frame 21 by a punched portion 23 and cut portions 26. The second tongue pieces 27 are formed on both the sides of the first tongue piece 25 to sandwich the first tongue piece 25, and the second tongue pieces 27 are shorter than the first tongue piece 25.

In metal frame sample 3 shown in Fig. 5, a first tongue piece 35 and the second tongue piece 37 are formed at an interval such that a punched portion 33 is formed in a side plate 32 of a metal frame 31.

In metal frame sample 4 shown in Fig. 6, a first tongue piece 45 and a second tongue piece 47 are formed at positions close to each other such that punched portions 43a and 43b are formed in a side plate 42 of a metal frame 41.

-In Figs. 4 to 6, printed circuit boards 4 are fixed to the metal frames 21, 31, and 41 by the method described in the first embodiment, respectively, and the same soldering connection strength as that described in the first embodiment can be obtained.

Fig. 7 is a sectional view showing a main part subjected to soldering connection according to the second embodiment. A first tongue piece 55 and a second tongue piece 57 are formed on a side plate 52 of a metal frame 51 by the method described in the first embodiment, and the second tongue piece 57 is bent outside the side plate 52 as shown in Fig.. 7. This bending is performed in advance when the metal frame 51 is processed. Incorporation of a printed circuit board 4 in the metal frame 51, mechanical fixing of the printed circuit board 4 by the first tongue piece 55, and soldering between the conductive pattern 9 and the first and second tongue pieces 55 and 57 are performed by the method described in the first embodiment. As a result, the interval between the conductive pattern 9 and a base portion 57a of the second tongue piece 57 increases, and a large amount of solder is filled in the gap between the conductive pattern 9 and the base portion 57a. For this reason, according to the second embodiment, - 11 connection strength which is higher than that of the first embodiment can be obtained.

In the second embodiment, any one of metal frame samples 2 to 4 shown in Figs. 4 to 6 can be applied, and connection strength which is higher than that of the first embodiment can be obtained.

Fig. 8 is a front view showing a main part of metal frame sample 5 in the second embodiment. AS shown in Fig. 8, a first tongue piece 65 is formed on a side plate 62 of a metal frame 61 by an "inverted-U"-shaped punched portion 63, and a tongue piece 67 is formed on a part of the first tongue piece 65 by an "inverted-U"-shaped cut portion 66. At the same time, the second tongue piece 67 is bent outside the side plate 62 (not shown). As in this example, incorporation of a printed circuit board 4 in the metal frame 61, mechanical fixing of the printed circuit board 4 by the first tongue piece 65, and soldering between the conductive pattern 9 and the first and second tongue pieces 65 and 67 are performed by the method described in the first embodiment. As a result, solder 10 whose amount is larger than that in the first embodiment is filled, and connection strength can be improved. In this embodiment, when an end portion 65b of the first - 12 tongue piece 65 is pressed inside the metal frame 11, the following characteristic feature can be obtained. That is, a base portion 65a which is bent such that the base portion 65a is brought into contact with an end face of the printed circuit board 4 can be easily bent because no bending stress acts on the second tongue piece surrounded by the cut portion 66.

As the third embodiment, Fig. 9 is a sectional view showing a main part of soldering connection, and Fig. 10 is a front view showing a main part of-metal frame sample 6. Only different portions between the first embodiment and the second embodiment will be described below. Referring to Figs. 9 and 10, a first tongue piece 75 is formed on a side plate 72 of a metal frame 71 by an "inverted-U"-shaped punched portion 73, and a tongue piece 77 is formed on a part of the first tongue piece 75 by an "inverted-U"-shaped cut portion 76. At the same time, the second tongue piece 77 is bent outside the side plate 72 (not shown). As in this example, when a printed circuit board 4 is incorporated in the metal frame 71 by the method described in the first embodiment, and an base portion 75a of the first tongue piece 75 is pressed inside a metal frame 11, a base portion 75a is bent such that the base portion 75a is brought into contact with an end face of the printed circuit board 4. At this time, the second 13 - tongue piece 77 moves together with the end portion 75b of the first tongue piece 75, and an end portion 77 faces outside the metal frame 71, so that a gap is formed between the end portion 77 and the end portion of the printed circuit board 4.

When soldering is performed by the method described in the first embodiment, a large amount of solder 10 can be filled on the portion between the conductive pattern 9 and the end portions 75a and 77b of the first and second tongue pieces 75 and 77. For this reason, connection strength equal to that in the second embodiment can be obtained. In addition, because of the characteristic feature that the first tongue piece 75 can be easily bent in mechanical fixing of the printed circuit board 4, the same effect as in metal frame sample 5 of the second embodiment can be obtained.

[Advantages] The present invention is performed according to the above embodiments, and has the following advantages.

An amount of solder filled in a portion between the conductive pattern and the first and second tongue pieces to be soldered to each other can be increased. Since the soldering area of the connection portion can be increased, the-tensile strength between the tongue pieces and the conductive pattern is improved. Since the solder filled in a portion between the tongue pieces and the conductive pattern increases in thickness, the bending strength of the solder itself is improved. Therefore, connection strength can be advantageously improved.

Since the first and second tongue pieces are formed by forming a punched portion, in addition to an advantage that the above bending process can be easily performed, an advantage that solder can be prevented from flowing to the side plate in soldering can be obtained.

When soldering connection is generally performed by dip soldering, a disadvantage that solder is not entirely coated on the connection surfaces because air is filled in a narrow portion of the connection portion often occurs. In the present invention, even if the first tongue piece is bent to be in press contact with the printed circuit board, the second tongue piece is not in press contact with the end portion of the printed circuit board to keep a gap between the second tongue piece and the printed circuit board. For this reason, air is extracted from the gap in soldering connection between the second piece and the conductive pattern, and the solder is sufficiently filled in the portion between the second tongue piece and the conductive pattern, so that an advantage that soldering can be reliably performed can be obtained.

When cream solder is supplied to a portion between the tongue piece and the conductive pattern to perform reflow soldering, a nozzle can be vertically inserted from an opening of the upper portion of the metal frame in the first or second embodiment. For this reason, an attaching structure which is suitable for automation and has nozzles respectively arranged in a plurality of connection portions such that cream solder can be supplied to the plurality of connection portions at once can be obtained.

7401GB

Claims

1. A fixing structure of a printed circuit board, comprising a square metal frame having an opening in an upper surface, a printed circuit board, which has a conductive pattern formed on at least one surface, stored in said metal frame, and first and second tongue pieces which are formed at positions close to each other in a side plate of said metal frame by punching, wherein the first tongue piece is brought into contact with an end portion of said printed circuit board and bent inside said metal frame, the second tongue piece has an angle which is different from that of the first tongue piece with respect to the printed circuit board surface, and the first and second tongue pieces are connected to said conductive pattern with solder.

2. A fixing structure of a printed circuit board according to Claim 1, characterized in that the second tongue piece is bent outside the side plate of said metal frame.

3. A fixing structure of a printed circuit board according to one of Claims 1 and 2, characterized in that the first tongue piece partially forms the second tongue piece.

4. A fixing structure of a printed circuit board substantially as hereinbefore described with reference to, and as illustrated by, Figs. 1 to 10 of the accompanying drawings.