GB2288912A

GB2288912A - Electrical device for surface mounting

Info

Publication number: GB2288912A
Application number: GB9507587A
Authority: GB
Inventors: Gerhard Strauss
Original assignee: Guentrher W GmbH
Current assignee: Guentrher W GmbH
Priority date: 1994-04-12
Filing date: 1995-04-12
Publication date: 1995-11-01
Also published as: GB9507587D0

Abstract

An electrical device for being mounted according to surface mounting device (SMD) technology includes an electrical component 1 having wirelike terminal ends 3 and an insulating housing 4 having dimensions suitable for handling by an automatic SMD assembly machine. The housing 4 comprises an insulating sheath in which the electrical component 1 is placed and has external metallized terminal pads 6 at opposite ends of the insulating sheath for electrically contacting contacts of a printed circuit board. The wirelike terminal ends 3 of the electrical component 1 are electrically connected to the metallized terminal pads 6 of the housing 4. … <IMAGE> …

Description

4 2288912 ELECTRICAL DEVICE FOR SMD TECEMOLOGY The invention relates to

SMD (surface mounted device) technology and particularly to an electrical component for SMD technology. and more particularly to a reed switch for SMD technology having wirelike terminal ends for electrically contacting the component with an external electrical circuit. Wires having circular. square. semicircular and other cross sections are known from BROCKHAUS NATURWISSERSCRAFTEN UND TECHNIK [Brockhaus Natural Sciences and Technology). Wiesbaden 1983. Volume One A- EK, page 270. ISBN 3-76530357-7.

For the assembly of printed circuits. electrical components are required to an increasing degree which can be processed by means of SMD technology. in particular. which can be handled by the available automatic SMD assembly 1 machines. Electrical components such as resistors, capacitors, reed switches and inductors. for example, are fabricated to be suitable for SMD technology.

An essential difference between conventional electrical components and electrical components that are suitable for SMD technology lies in the configuration of the electrical terminals of the component for its connection to the external electrical circuit. Conventionally, the terminals are wirelike terminal ends having circular cross sections. The terminal ends are plugged through associated through holes of a printed circuit or a printed circuit board. In SMD technology, such terminal ends are replaced by metallized component terminal pads. The SMD component or device is placed with its terminal pads on top of the associated electrical contact points (land points) of the printed circuit board.

In order to adapt an electrical component to the electrical contacting that is required in SMD technology at a reasonable cost, it is known, for example. in a reed switch (protective tube contact), to replace the circular cross section of its two wirelike terminal ends by a square cross section. These terminal ends are therefore configured like a flat band. They are angled multiple times with respect to the protective tube of the reed switch. The tube that is 3 - usually present. is preferably made of glass, so that the reed switch can be placed on top of the printed circuit board. With the exception of the terminal ends, the design of this SMD reed switch corresponds essentially to the design of a conventional reed switch. Within the protective tube. the two terminal ends are configured as electrically and magnetically conductive reeds which, depending on the relative position of an outside magnetic field. are either in contact with each other or separated from one another so as to close or interrupt a circuit. Usually. the protective tube encloses a protective gas surrounding the two reeds to reduce ignition sparks or electrode consumption. The drawback of this SMD reed switch is the fact that the protective tube is openly accessible and therefore entirely unprotected from mechanical damage. In addition. mechanical forces that act on the printed circuit board are directly conveyed onto the glass sheath. Furthermore, the handling of this reed switch by an automatic SMD assembly machine may be complicated due to the constructional configuration of the switch.

In a further prior art reed switch fabricated for SMD technology, the protective tube is covered by a usually black molded sheath made of a thermoset plastic, as Is also used for integrated circuits. This covering allows a certain

0 1 protection of the reed switch from mechanical damage. Such a covering, however, impairs the reliable functioning of the reed switch in"the course of its operating life because the temperature coefficients of the molded sheath and of the protective tube deviate from each other to such an extent that the molded sheath passes large mechanical forces into the protective tube, which can even result in the destruction of the reed switch.

DE-DM-8604096 discloses a plastic covering for an electrical component which is suitable for SMD technology. This electrical component is an inductor. A complex contour shape of the plastic covering is required In order to ensure that the component provides the terminal pads necessary for SMD technology in spite of its conventional terminal ends configured with a circular cross section. This requires complex fabrication tools and makes the fabrication of the electrical component very Involved. Furthermore. the handling of the electrical component must already be considered during the fabrication process of the plastic covering by using additional machines. because the component is placed. for example. into an injection inold and nolded in with plastic material. The complicated contour shape of the plastic covering involves the great risk that already minor fabrication-related dimensional tolerances result in unacceptable deviations from the specified dimensions of the plastic covering. A later processing of the plastic covering, however, is only possible under certain conditions or not at all. because the electrical component could be damaged or destroyed during this process. Therefore, the fabrication of this SMD component entails a large portion of rejects. This increases the fabrication costs of the SMD component further.

SUMMARY OF THE INVENTIO

It is an object of the invention to fabricate an electrical component suitable for SMD technology in a simple and cost- effective manner in terms of production engineering and to improve the component's functional reliability at the same time.

The above and other objects are accomplished according to the invention---by the provision of an electrical device for being mounted according to surface mounting device (SHD) technology, comprising: an electrical component having wirelike terminal ends; and an insulating housing having dimensions suitable for handling by an automatic SMD assembly machine and comprising an insulating peripheral sheath in which the electrical component is placed and metallized terminal pads at opposite ends of the insulating sheath for electrical contacting. the wirelike terminal ends of the electrical component being connected in an electrically conductive manner to the metallized terminal pads of the housing.

According to one embodiment of the invention. a conventional electrical component, in particular, a reed switch, is converted into an SMD component in a technically simple and cost-effective manner. For this purpose. the conventionally fabricated electrical component is simply placed into a separate insulating housing whose dimensions are chosen from the outset such that the insulating housing, and thus the entire SMD component,can be reliably processed by an automatic SMD assembly machine. Thus,, the component manufacturer can fabricate the SMD components on already available machines that are used for the fabrication of conventional components. This avoids a costly replacement of production lines. This also enables manufacturers of conventional components to quickly and cost- effectively adapt their production to the fabrication of SMD components at minor additional expenditure. The manufacturer can. at low cost. either obtain the separate insulating housings externally or produce them in- house.

The separate manufacture of the insulating housings allows for their uncomplicated mechanical reworking, if 4 necessary, which keeps the portion of rejects and thus the fabrication costs of the SMD component according to the invention at a low level.

The separate fabrication of the insulating housing also allows the selection of fabrication methods and materials which are not possible with state-of-the-art components because of the sensitive material properties of the electrical component which is intricately involved in the fabrication process of the molded sheath or the plastic -10 covering. The fabrication method for the insulating housing can be selected exclusively on the basis of cost considerations. The greater choice of materials ensures that, depending on the electrical component used, an insulating housing is made available which has a temperature coefficient that is well matched to the component and is sufficiently mechanically stable so as to protect the component from mechanical damage. The separately manufactured insulating housings therefore support the functional reliability of the electrical components.

The wirelike terminal ends of the component are connected to the metallized terminal pads of the insulating housing in an electrically conductive and therefore also mechanical manner. Because of this inevitable mechanical connection, additional fixing means for the stationary fixing of the component within the insulating housing can be dispensed with. As a consequence. the construction and fabrication of the insulating housing remains Inexpensive. Moreover. the SMD device of the invention, which is essentially composed of the conventional electrical component and the insulating housing, can be fabricated by means of a few process steps and thus cost-effectively.

There is provided a geometrically simple contour shape of the insulating housing or of the entire SMD component. Insulating housings of this type have a peripheral sheath which acts as a printing surface for the type-specific characteristics of the electrical component. Additionally. the peripheral sheath allows easy technical handling for the printing. Automatic SMD assembly machines can handle the insulating housings in a technically uncomplicated manner due to their simple contour shapes. Furthermore,, according to one embodiment of the invention, the contour shape of the housing is a right paralleleriped shape which supports the tilting stability of the insulating housing and thus of the entire SMD component after it has been placed on top of the associated contact points of a printed circuit board. The mechanically stable placement of the insulating housing is assisted by a solder paste, which is usually preapplied to a - 9 the land points of the printed circuit board in SMD technology. Thus, a sufficient adhesive bond between the land points and the metallized terminal pads of the insulating housing is created prior to the soldering process The insulating housing is made of ceramics or a high-temperature resistant plastic material. Such an insulating housing very effectively protects the electrical component. for example, the reed switch, from possible mechanical damage. Moreover.

these materials allow a close matching of the temperature coefficient of the insulating housing to the temperature coefficient of the electrical component, for example, to the temperature coefficient of the reed switch protective tube which is made of glass. Thus, the passage of undesirable temperature-dependent expansion forces of the insulating housing to the electrical component is prevented.

Furthermore. the light color of the ceramics or the free color choice for the plastic material of the insulating housing allows soldering of the entire SMD component by means of infrared lamps without excessively heating the insulating housing. in contrast to dark colors, the insulating housing absorbs only a very small amount of heat from the infrared lamp due to the light color of its peripheral sheath. As a consequence, the heating-related expansion forces of the - 10 insulating housing with respect to the inserted electrical component are kept low from the outset.

Other aspects of the invention support the mechanically stable seating of the electrical component within the insulating housing without additional complex fixing means. With its sheath. the receiving shaft into which the electrical component is inserted, also acts as a guide element during the insertion process. In this manner. faulty insertion positions of the component are prevented from the outset. This again assists a simple fabrication of the entire SMD component in terms of its assembly.

The receiving shaft extends along the longitudinal axis of the insulating housing and therefore has a large shaft length. This takes account of the fact that the same insulating housing can be used for electrical components of different constructional dimensions, in particular, of different lengths.

The receiving shaft surrounds the electrical component in an approximately form-fitting manner. This feature supports the desired precise insertion position of the component within the insulating housing.

1 c 1 n r k.

Preferably. the terminal pads are configured as selfcontained sheath segments. This simplifies the insertion and packaging of the individual insulating housings or the individual SMD components into magazine-like belt bands which must be handled by the automatic SMD assembly machines during the assembly process. In this manner. faulty packagings with a correspondingly faulty fixation by an automatic SMD assembly machine are prevented. The fact that the surface of such terminal pads is relatively large also assists the precise positioning of the SMD component and its electrical contacting with the associated contact points on the printed circuit board.

Further aspects of the invention relate to measures of low work intensity to produce the electrically conductive connection between the wirelike terminal ends of the component and the terminal pads of the insulating housing.

Preferably, short mechanical and electrical connecting paths between the terminal pads and the wirelike terminal ends are ensured. This makes it possible to maintain the electrically conductive connection without damage throughout a long operating life of the component.

The two shaft openings of the receiving shaft are formed by its two sheath segments that lie opposite one another, i. e., that are the outer segments along its longitudinal axis.

R These shaft openings are metallized as metallization zones. The component is inserted along the longitudinal axis of the receiving shaft so that its terminal ends which also extend approximately along the longitudinal axis are surrounded at a radial distance by one metallization zone each. The hollow space formed between the terminal end and the metallization zone is simply filled with a suitable electrically conductive material, e. g., with a high- temperature solder. This allows a simple technique for contacting the terminal ends with the terminal pads. The electrically conductive material which fills in the cited hollow space has the further function of serving as a fixing means for fixing the electrical component within the insulating housing without necessitating additional process steps and additional material expenditure.

The end faces of the housing bounding the receiving shaft are metallized. This ensures an electrically conductive through connection out of the receiving shaft toward the terminal pads. The terminal ends of the component inserted in the receiving shaft then merely need to be connected to the metallization zones of the receiving shaft in an electrically 1 9 t 1 1 conductive manner, e. g., by means of the measure according to claim 13.

Just like the end faces of the insulating housing. the netallization zones of the receiving shaft and the terminal 5 pads are also metallized, e. g., by means of tin-plating.

BRIEP DESCRIPTION OF TUB DRAWINGS

The subject matter of the invention is explained In greater detail by way of an embodiment illustrated in the drawings.

Fig. 1 is a perspective view of the insulating housing according to the invention.

Fig. 2 is an end view of the insulating housing in the direction of to arrow II in Fig. 1.

Fig. 3 is a side view of the SMD device according to the invention showing a partial section along cutting line IIIIII in Fig. 2.

Fig. 4 is-an end view of insulating housing similar to Figure 2, but showing a circular housing as opposed to a square or rectangular shaped housing.

- 14 DETAUBD D9SCRIPTION OP THE PREEMERM EMBODIMENTS Referring to Figure 3, there is shown an SMD device 12 which includes an electrical component. which for illustrative purposes is shown as a reed switch 1 provided with a protective tube 2 and with wirelike terminal ends 3 which project from the protective tube 2. The protective tube 2 made of glass surrounds two electrically and 'magnetically conductive reeds, which are not shown in the figures. Each reed is connected to a terminal end 3 in an electrically conductive 'manner. With the aid of a separate insulating housing 4, the conventional reed switch 1 produced by standard methods is suited for SMD technology in a simple manner. For this purpose. the dimensions (height,. width,, length) of the insulating housing 4 are chosen so that it can be handled easily by an automatic SMD assembly machine.

Insulating housing 4 includes an insulating peripheral sheath 5 provided with metallized, e. g., tin-plated. terminal pads 6 for the electrical contacting of the entire SMD device 12 with the associated contacting points (land points) of a printed circuit board (not shown). To establish the necessary electrical contacting of the reed switch 1 with the circuit on the printed circuit board, the terminal ends 3 are connected to the associated connecting pads 6 in an electrically conductivenanner.

The insulating housing 4 has the shape of a right parallelepiped with a rectangular cross section, i. e., Its two end faces 8 in the longitudinal direction 7 of the insulating housing 4. i. e., which lie opposite one another on the longitudinal axis,, are rectangular. In a further embodiment, the end faces 8 are square. Likewise, a cylindrically-shaped insulating housing 4 with circular end faces 81 is also possible as depicted in the end view of Figure 4.

The reed switch 1 is disposed in a receiving shaft 9 which extends through the insulating housing 4 and its two end faces 8 (Fig. 3). The receiving shaft 9 approximately form-fittingly surrounds cylindrical protective tube 2 of reed switch 1. For this purpose, receiving shaft 9 is configured as a bore which is arranged concentrically to the longitudinal center axis 10 of insulating housing 4.

The terminal pads 6 at each terminal end 3 form a selfcontained sheath segment of the peripheral sheath 5 (Fig. 1). In the case of the right parallelepiped insulating housing 4, four equally stable and tilt-resistant placement positions of SHD device 12 on a printed circuit board are thus created. In the case of a cylindrically-shaped insulating housing 4, as depicted in Figure 4, the terminal pads 6 are selfcontained cylinder sheath segments. This results in a t '.

16 - infinitely many equally stable placement positions of the SMD component 12 on the printed circuit board,, independently of the pivot position of the insulating housing 4 with respect to the longitudinal center axis 10.

The metallized terminal pads 6 are arranged at the outer regions of the peripheral sheath 5 with respect to the longitudinal axis and form the peripheral edge of the respectively associated end face 8. The two outer sheath segments of the receiving shaft 9. which lie opposite one another in longitudinal direction 7. 1. e., along the longitudinal axis, and which form the shaft openings, are configured as metallization zones 11, e. g., they are metallized by tin-plating. The metallization zone 11 extends in longitudinal direction 7 approximately as far as the terminal pads 6 and surrounds the associated terminal end 3 of the reed switch 1 at a radial distance as shown in Fig. 3. Since the end faces 8 are also metallized, a self-contained electrically conductive three- dimensional surface Is respectively created at the two end faces of the insulating housing 4 which lie opposite one another in longitudinal direction 7. This three-dimensional surface comprises the metallization zone 11. the end face 8 and the terminal pads 6.

1 h i, A In the fabrication of SMD device 12. reed switch 1 is inserted into receiving shaft 9 along longitudinal direction 7. During this process. the two wirelike terminal ends 3 are also oriented in longitudinal direction 7. If necessary, terminal ends 3 are shortened either before or after the insertion process so as not to protrude from the receiving shaft 9 (Fig. 3). The hollow space bounded by each metallization zone 11 is filled with an electrically conductive material, e. g. a high-temperature solder. This creates the required electrical contacting of the terminal end 3 with the- associated terminal pads 6.

Instead of reed switch 1, other conventionally fabricated electrical components such as resistors or capacitors can, of course, also be converted by means of simple fabrication techniques into an SMD device 12 which is suitable for SMD technology according to the principle of the invention. Instead of the hollow cylinder receiving shaft 9 shown in the figures, other cross sectional shapes of a receiving shaft 9 that are adapted to the respective contour shape of the conventional electrical component are also conceivable.

1 - is - The Insulating housing 4 preferably has a length in the longitudinal direction in the range 10 to 30 mm. The height d width of the two end faces of the insulating housing may each be in the range 1 to 5 x= if it Is rectangular or square In cross-section. Alternatively If the insulating housing in cylindrical then its diameter may be In the range 1 to 5 mm.

The invention has been described in detail with respect to preferred embodiments. and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in Its broader aspects, and the Invention. therefore. as defined in the appended claims is Intended to cover all such changes and modifications as fall within the scope of the invention.

1 --L-.

0 C L A 1 M S 1. An electrical device for being mounted according to surface mounting device (SKD) technology, comprising: an electrical component having wirelike terminal ends; and a housing having dimensions suitable for handling by an automatic SMD assembly machine and comprising an insulating peripheral sheath in which the electrical component is placed and metallized terminal pads at opposite ends of the insulating sheath for electrical contacting. the wirelike terminal ends of the electrical component being connected in an electrically conductive manner to themetallized terminal pads of the housing.

2. The electrical device according to claim 1. wherein the housing has a right parallelepiped shape.

3. The electrical device according to claim 1, wherein the housing has a cylinder shape.

4. The electrical device according to claim 1, 2 or 3, wherein the insulating sheath comprises a ceramic.

1 Z 5. The electrical component according to claim 1, 2 or 3, wherein the insulating sheath comprises a hightemperature resistant plastic material.

6. The electrical device according to any one of claims 1 to 5, wherein the housing has a receiving shaft extending therethrough in which the electrical component is inserted, and the housing has two end faces which lie opposite one another.

7. The electrical device according to claim 6, wherein the receiving shaft extends through the two end faces which lie opposite one another along a longitudinal axis of the housing.

8. The electrical device according to claim 6 or 7, wherein the receiving shaft surrounds the electrical component in an approximately form-fitting manner.

9. The electrical device according to claim 6, 7 or 8, wherein the receiving shaft extends approximately parallel to a longitudinal center axis of the housing.

10. The electrical device according to claim 9, wherein the receiving shaft is a bore which is disposed concentrically to the longitudinal center axis of the housing.

h 11. The electrical device according to any one of claims 6 to 10, wherein said receiving shaft has two outer sheath segments, each outer sheath segment being adjacent a respective one of the ends of the receiving shaft and being metallized to form metallization zones, and the terminal ends of the electrical component placed into the receiving shaft are surrounded by the metallization zones at a radial distance.

12. The electrical device according to claim 11, wherein the end faces of the housing bounding the receiving shaft are metallized.

13. The electrical device according to any one of claims 1 to 12, wherein the metallized terminal pads are self-contained sheath segments of the peripheral sheath.

14. The electrical device according to claim 13 when appendant to claim 6, wherein the metallized terminal pads form a peripheral edge of the end faces.

15. The electrical device according to any one of claims 1 to 14, wherein the electrical component comprises a reed switch.

16. An electrical device substantially as hereinbefore, described with reference to, and as illustrated in, the accompanying drawing.