Apparatus for compliantly retaining a circuit board in a housing

Abstract: An apparatus compliantly retains a circuit board (14) including a housing comprising two portions (10,12). Within the hosing is a seat (22) for supporting the printed circuit board (14). When the two housing portion (10,12) are brought together a snap retainer (18) engages. A flexible tab (16) urges the circuit board (14) between it and the seat (22) holding the circuit board (14) in place.

Description: The present invention relates generally to printed circuit board assemblies and more particularly to means for securing a printed circuit board within a housing. Numerous methods are available to secure printed circuit (PC) boards in a housing. Such methods include the use of screws or rivets which are labour intensive, as well as expensive. Another method currently used includes a cover which snaps onto a housing. The PC board is sandwiched into a fixed space provided between the cover and the housing. Such a printed circuit board housing is disclosed in DE-U-9115002. However, a problem arises because the manufacturing process for printed circuit boards leads to some variability in the board thickness. Because of the inflexibility of the cover and the housing, the outer cover has a tendency to crack if the PC board is too thick. Conversely, if the PC board is too thin it vibrates in the housing, causing noise and durability problems. DE-A-4106077 discloses a housing for a low noise converter which housing includes two parts and in which a projection formed on one part is received in a recess formed in the other part. It is therefore a primary object of the present invention to provide a flexible PC board housing to secure the PC board in a fixed position in such a manner as to compensate for the variability in PC board thicknesses. The apparatus for retaining a printed circuit board, according to invention as defined in claim 1 includes a housing having a first and second portion. The first housing portion has a flexible bent tab portion. The second housing portion has a seat for supporting a printed circuit board. The first housing portion is engaged with the second housing portion in a fixed relationship such that when the first housing portion is secured to the second housing portion, the flexible bent tab portion urges the printed circuit board against the housing seat with a sufficient force to hold the printed circuit board in a fixed relationship within the housing. An important advantage of the present invention is that it provides a flexible PC board retaining mechanism resulting in fewer unit repairs resulting in less cost. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an isometric view of the preferred embodiment. Figure 2. is a cross section of the present invention before the cover is snapped into place. Figure 3. is a cross section of the present invention with the cover snapped into place. Referring now to Figure 1, a preferred embodiment of the present invention is shown enclosing a circuit board. A housing for the circuit board comprises two pieces, a housing 12 and a housing cover 10 which are preferably made of a thermoplastic. Cover 10 has an L-tab 16 and snap tang 18 which can be made of a plastic material. L-tab 16 can be either recessed into cover 10 as shown or can extend beyond the outer edge of cover 10. A preferred relationship between L-tab 16 and cover 10 is to have one leg of L-tab 16 flush with the surface of cover 10 and the other leg of L-tab 16 perpendicular to the surface of cover 10. L-tab 16 should be recessed into cover 10 such that no part of either leg protrudes past the perimeter of cover 10. L-tab can be molded into cover 10 or can be cut into cover 10 after the molding process. Typically one or two L-tabs are provided per printed circuit board edge depending on size. For example, one housing has been made using six L-tabs for a 90mm. by 110mm. circuit board, two on each edge excluding one 110 mm. edge so as not to interfere with a connector incorporated on the circuit board. Snap tang 18 extends form the cover 10 in a parallel direction to the surface of cover 10 and is shaped so that it will secure housing 12 to cover 10 at snap opening 20. Snap tang 18 may be formed to be compliant in the same manner as L-tab 16 is formed. Housing 12 has snap opening 20 and housing seat 22 which may be integrated thereinto. Seat 22 is a protrusion or formed surface on the interior of housing 12 to provide support printed circuit board 14. Snap opening 20 is formed in wall 11 of the housing 12 to accept snap tang 18 when cover 10 is placed on housing 12. Cover 10 is fixedly attached to housing 12 when snap tang 18 engages snap opening 20. Once cover 10 is placed onto housing 12 and snap tang 18 engages snap opening 20, L-tab 16 flexes so as to compliantly retain printed circuit board 14 between seat 22 and L-tab 16. Snap tang 18 may also flex to help compensate in variations in thickness of printed circuit board 14. During the assembly process, printed circuit board 14 is first inserted into housing 12. Cover 10 is then placed over housing 12 and pressed toward housing 23 so that snap tang 18 engages snap opening 20. L-tab 16 applies adequate force to hold printed circuit board 14 against housing seat 22 without vibration. L-tab 16 is made to flex as the thickness of printed circuit board 14 varies without causing the cover to stress or fracture. Snap tang 18 may also flex to help compensate in variations in thickness of printed circuit board 14. Fig. 2 shows a cross section of the interface prior to final assembly between cover 10, housing 12 and printed circuit board 14 and undeformed L-tab 16. L-tab 16 in its undeformed states is preferably flush with the surface of cover 10. A force in direction of 26 is applied to cover 10 until snap 18 engages snap opening 20. Fig. 3 shows a cross section of the interface after final assembly between cover 10, housing 12, printed circuit board 14, and deformed L-tab 16. When cover 10 is snapped into place on housing 12, L-tab 16 is flexed by a small angle 24. Angle 24 varies as the thickness of printed circuit board 14 varies. L-tab 16 when flexed will provide sufficient force to hold printed circuit board 14 against housing seat 22 which is shown as an integral part of housing 12. For example, a nominal value for the force exerted by the L-tab 16 on the printed circuit board 14 is about 13.75 pounds.

Claims: An apparatus for retaining a printed circuit board comprising: a housing having a first and second portion (10,12) said first portion (10) having a flexible bent tab portion (16), said second portion (12) having a seat (22) _ for supporting a printed circuit board (14): and means (18,20) for engaging said first housing portion (10) to said second housing portion (12) in a fixed relationship such that when said first housing portion (10) is secured to said second housing portion (12) the flexible bent tab portion (16) urges the printed circuit board (14) against the housing seat (22) with a sufficient force to hold the printed circuit board (14) in a fixed relationship within said housing. An apparatus as claimed in claim 1, wherein said engaging means (18,20) for holding said first housing portion (10) in a fixed relationship to said second housing portion (12) comprising a snap tab (18) integrally formed on said first housing portion (10) and a means (20) for receiving said snap tab (18) integrally formed on said second housing portion (12) such that when the first housing portion (10) is placed in said second housing portion (12), the snap tab (18) engages the means (20) for receiving the snap tab. An apparatus as claimed in claim 1 or 2, wherein said bent tab portion is an L-tab (16) integrally formed on said first housing portion (10).

Inventors: BELANGER THOAMS DUDLEY JR, BELANGER, THOAMS DUDLEY, JR.
Applicants: FORD MOTOR CO, FORD MOTOR COMPANY
Application year: 1993
Main classification: H05K7
IPC codes: H05K5, H05K7