ARRANGEMENT FOR HOLDING A PRINTED CIRCUIT BOARD FIXED TO A FRAME

Abstract: The invention relates to an arrangement for retaining a printed circuit board (1) at a frame (5, 6). Connectors (2) are mounted on the PCB (1) and have electrical connection pins (3) connected to electrical conductors in the PCB (1). The connectors (2) are elongate and have end portions (4) bearing against the front of the PCB. In accordance with the invention, the frame (5, 6) has holders (7, 8, 9) coacting with the end portions (4), these holders retaining the connectors (2) and PCB (1). The frame (5, 6) has a tongue (7) engaging against the front of the end portion (4), and a movable support (8) is kept in engagement against the back of the PCB (1) behind the tongue (7) with the aid of a screw (9). The forces occuring when a means complementary to the connector (2) is connected to the connector are transferred to the frame (5) by the connector (2), and the invention thus allows the PCB to be made thin. This has, inter alia, the advantage that the capacitance between the different conducting layers of the PCB will be large, and the PCB will be well impedance-adapted and can have a high packing density of conductors without cross talk problems.

Description: ARRANGEMENT FOR HOLDING A PRINTED CIRCUIT BOARD FIXED TO A FRAME. TECHNICAL FIELD The invention relates to an arrangement for retaining a printed circuit board (PCB) at a frame, said arrangement including connectors with electrical connection pins connected to electrical conductors in the PCB, the connectors being elongate and having end portions, the backs of which bear against the front of the PCB. BACKGROUND ART Electronic equipment, e.g. for computers or telephone exchanges, is in many applications supported mechanically by a rack which is divided into compartments. The back of each compartment has a PCB, to which a plurality of other so-called daughter PCBs in each compartment are connected. Compartments of this type are to be found described in a brochure from Teradyne Connection Systems, Inc, Nashua, NH, USA under the name of STRONGHOLD ™ Card Guidance System. The brochure was printed in 1982 and revised in 1984 with the revision number REV. A 4-84. The implementation can be likened to a book shelf where the PCBs at the back of the compartments correspond to the back of the book case and the daughter PCBs correspond to the books. Each compartment has a frame retaining the PCB at the back of the compartment, and the daughter PCBs are thrust into grooved holders at the sides of the compartment. At their rear edges the daughter PCBs have electrical connection means, and the PCB at the back of the compartment has connectors with corresponding connection means, so that a daughter PCB can be connected to a connector when it is thrust into the compartment in its holders. The connectors have connection pins which are connected to electrical conductors in the PCB at the back of the compartment. The connectors are fastened to the PCB and, as mentioned, the latter is in turn fastened to the frame. The above described arrangement has the disadvantage that the PCBs at the back of the compartment must be very stable to withstand the forces occurring when a daughter PCB is thrust into its connector. The PCBs are therefore made thick, which increases expense in their manufacture. The different layers of electrical conductors in the PCB will be at a relatively large mutual spacing, resulting in that the capacitance between the layers will be small and the PCBs have poor impedance adaptability and poor cross talk properties when tightly packed. DISCLOSURE OF INVENTION The above-mentioned disadvantages are avoided by an arrangement in accordance with the invention in which the PCBs at the backs of the compartments are only subjected to small forces when the connectors on the PCBs are connected. The arrangement has the characterizing features disclosed in the accompanying claims. BRIEF DESCRIPTION OF DRAWINGS One embodiment of the invention will now be described in more detail below and in connection with the drawing, where Figure 1 is a perspective view of a PCB with connectors, Figure 2 is a cross section of a PCB with a connector retained in a frame by an inventive arrangement, Figure 3 is a perspective view of a part of the retaining means, Figure 4 is a cross section of an alternative embodiment of the retaining means, Figure 5 is a cross section of a further embodiment of a retaining means and Figure 6 is a perspective view of the retaining means in Figure 5. BEST MODE FOR CARRYING OUT THE INVENTION A known PCB 1 is illustrated in Figure 1 and is provided with connecors 2 in which electrical connection pins 3 are fixed. The connectors 2 have end portions 4, the backs of which bear against the front of the PCB, and the connection pins 3 are thrust (in a way not illustrated in the Figure) into holes in the PCB 1 and connected to its electrical conductors. The PCB 1 is, as is described above, Intended to be fastened to the back of a compartment, which has means for retaining daughter PCBs, which are connected to the PCB 1 via the connection pins 3 in the connectors 2. In Figure 2 there is illustrated an inventive arrangement for retaining the PCB 1 in a frame 5, which is placed at the back of a compartment in an unillustrated manner. According to this embodiment the frame 5 includes elongate rails 6, mutually joined at their ends by transverse elements. The rails, which may be extruded aluminium sections, have a longitudinal tongue 7. This bears against the front of the end portion 4 of the connector 2, and behind the end portion on the back of the PCB 1 there is a movable support 8 attached to the rail 6 by a screw 9. The movable supports 8 at the ends of the connector 2 are mutually connected in this embodiment by a bridging member 10, which extends at a distance from the PCB 1. The connector 2 and PCB 1 are kept against the rail 6 by the movable supports 8 being kept in engagement against the back of the PCB 1 by the screws 9, and the PCB 1 transfers the forces from the screws 9 to the end portions 4, the fronts of which are kept in engagement against the tongue 7. In an advantageous embodiment, the rail 6 has a further longitudinal tongue 11. which engages against the outer side 4a of the end portion 4. With the aid of this tongue the connector 2 is kept in a desired position laterally in a simple way. An advantageous embodiment of the displaceable supports 8 and the bridging member 10 is illustrated in Figure 3. The bridging member comprises a plate, e.g. of metal, with a flat central part 12 and upwardly folded longitudinal sides 13 with flanges. The latter have holes 14 for the screws 9, and the movable supports 8 comprise flaps punched out and folded upwards from the sides 13. An alternative embodiment of the invention is illustrated in Figure 4. In the manner described in connection with Figure 2, the front of the end portion 4 engages against the tongue 7 of the rail 6. The back of the end portion 4 bears against the front of the PCB 1 and on the back of the PCB, opposite the tongue 7, there is a displaceable support 15. The support 15 has a U-shaped cross-section, one flange of which engages against the rail 6 and the other flange engages against the back of the PCB 1. The support is kept against the rail 6 by the screw 9, with the aid of which the end portion 4 and PCB 1 are retained between the tongue 7 and support 15. A further alternative embodiment of the invention is illustrated in Figures 5 and 6. The frame 5, which retains the PCB 1 and connector 2, has rails 16 with holders, which have a fixed flange-like support 17 arranged at the back of the rail 16, and two projections 18 on the side of the rail. The back of the PCB 1 engages against the front of the support 17, and the connector 2 has an end portion 19 inserted between the projections 18. The back of the end portion 19 engages against the front of the PCB 1, and the end portion 19 is retained against the rail 16 by a screw 20, which passes through a hole in the rail 16. In the above-described arrangement for retaining the PCB 1 on the frame 5, the connectors 2 are also retained in the frame. The forces occurring when a daughter PCB is connected via the connector 2 to the PCB 1 are transmitted via the connector 2 directly to the frame. The PCB 1 can therefore be made thin. As mentioned above, the electrical connection pins 3 are thrust into holes in the PCBs. These holes are achieved by drilling, which is done with great precision and is therefore expensive. To keep costs down, several PCBs are placed one on top of the other and are drilled in packs. The thinner the PCB the more PCBs can be drilled simultaneously while maintaining the required precision. This is of course a production advantage in manufacturing the circuit boards. A functional advantage can also be obtained for the PCB if its thickness can be kept small, since the PCB has many layers with electrical conductors and a certain capacitance occurs between the layers. This capacitance shall have a minimum magnitude for the PCB 1 to be well impedance-adapted. The invention permits the PCB to be made so thin that this requirement for impedance adaptability is met.

Claims: C L A I M S 1 Arrangement for retaining a printed circuit board (PCB) at a frame, said arrangement including connectors with electrical connection pins connected to electrical conductors in the PCB, the connectors being elongate and at either end having an end portion, the back of which bears against the front of the PCB, and the frame having supports bearing against the back of the PCB, characterized in that the frame (5, 6) has tongues (7) coacting with the end portions (4) of the connectors (2), said tongues bearing against the fronts of the end portions (4), and in that said supports (8, 15) on the frame (5, 6) bear directly behind the end portions (4) of the connectors (2), the supports (8, 15) and tongues (7) retaining the end portions (4) of the connectors (2) in desired positions. 2 Arrangement as claimed in claim 1, characterized in that the supports (8, 15) are displaceable in relation to the tongues (7) on the frame (5, 6). 3 Arrangement as claimed in claim 2, characterized in that the movable support (8) at one end portion (4) of the connector (2) is connected to the support (8) at the other end portion (4) of the connector by a bridging means (10), which extends along the back of, and is spaced from the PCB (1).

Inventors: ERNOLF STIG CARL-OSKAR, KASSMAN BJOERN TURE, OLSSON KARL-GUSTAF, OLSSON ROLF TORBJOERN, ERNOLF, STIG, CARL-OSKAR, KASSMAN, BJOERN, TURE, OLSSON, KARL-GUSTAF, OLSSON, ROLF, TORBJOERN
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET L M ERICSSON
Application year: 1988
Main classification: H05K7
IPC codes: H05K7