Frame for printed circuit cards

Chassis comprising cross members joined by slides intended to hold printed circuit boards. The end of the slides is shaped to engage in, and be centered between the arms of an extruded section, the cross-section of which resembles a spring clamp.

The invention concerns a chassis for a printed circuit board, comprising 
two side walls, between which are arranged two pairs of parallel 
cross-members, each with regular perforations which accomodate centering 
devices placed near the ends of the slides, which serve to guide and 
support the boards by their paralled edges. 
Such chassis are used, in particular, in electronic, digital or analogue 
data processing systems. 
Chassis already exist in accordance with previous art, defined above, in 
which the slides are made of a plastic material. 
These chassis have the disadvantage that, owing to the high coefficient of 
expansion of the plastic materials, a deformation takes place when the 
circuits located in the chassis dissipate a certain quantity of heat; the 
rigidity of these slides may also be a disadvantage when, with a view to 
increasing the liability, increasing numbers of components are arranged on 
a single large printed circuit board, which leads to a significant 
increase in weight; finally, the heat dissipated by the increasing number 
of components has to be removed by natural or artificial ventilation, heat 
transfer to the metal of the chassis being made insignificant, owing to 
the extremely poor coefficient of conductivity of the plastic materials 
used for making the slide. 
Chassis also exist in which all the slides are formed by stamping from a 
metal plate, with perforations through which the cooling air may 
circulate. A criticism of such an approach is that the area of the 
perforations is always smaller than the area of the space which can exist 
between two neighbouring slides and, secondly, using such a chassis 
implies that all the slides will be used, otherwise the production cost 
will be out of proportion with the density of equipment the chassis is to 
carry. 
An object of the invention is, then, to provide a chassis consisting of 
separate metal slides in order to benefit from their advantages of good 
heat transmission, "as required" fitting, simple and rapid fitting and 
rigidity usually unsatisfactory in prior art involving such individual 
slides. 
According to the invention, this result is obtained by means of the fact 
that the cross-section of the cross-members is in the form of a metal, 
spring clamp comprising rims 15, 16, and that at least one of the ends of 
each metal slide has at least one taper 8, 11, and one groove 9, 12, 
designed to open the arms 13, 14, of the clamp and engage on the bead.

Referring to FIGS. 1 and 2, 1 is one of the side walls of the chassis, 2 
and 3 are the two upper parallel cross-members joining the two side walls, 
and 4 the upper slide, 5 indicating the printed circuit board, to simplify 
the drawing, the lower slide and the two lower cross-members have not been 
shown. 
The metal body of the slide 4 has lateral lugs at a certain interval as 
shown on the rotated section shown by 6. These lateral lugs serve to guide 
and hold the edge of the printed board in the vertical and transverse 
direction of the chassis, other means (not shown) being provided to 
prevent the board from sliding in the direction parallel to the slide. 
Each end of the slide has at least one taper, such as 8, followed by a 
groove 9. The latter may be placed in close proximity to a shoulder 10. 
Preferably, other tapers and grooves 11, respectively 12, are located 
symmetrically with respect to a longitudinal axis XX' of the slide. 
In section, the metal cross-member 2 appears as a clamp formed of two 
parallel arms 13, 14, at the end of each is a bead 15, 16 respectively, 
these two beads facing one another. The base of each arm is linked to a 
front part 17 by a wall, such as 18, of relatively low thickness, in order 
to give the clamp the necessary elasticity. In the example shown, this 
wall is curvilinear, which results first in the arm being longer, thus 
facilitating its deformation, and secondly in the formation of a 
cylindrical channel 19, parallel to the longitudinal axis of the 
cross-member. This channel will be used for attaching the ends of the 
cross-member to the lateral walls by means of 20 mm screws, the threaded 
part of which will be housed in the said channel. 
The front part 17, of the cross-member has a series of equidistant openings 
21, each of which houses an extention 22, of the end of the slides it is 
decided to use. The extension is visible in particular in FIG. 2. 
In the example shown, the openings of the cross-member clamps are directed 
towards each other. It may be easily conceived that the clamps, instead of 
being arranged thus, could be arranged perpendicularly, on condition that 
the end of the slides were shaped accordingly. 
In order to fit the slides to the cross-members, the number of slides 
chosen for a given application, are first arranged parallel on the working 
surface of a simple machine, and the two cross-members intended to retain 
them are then placed opposite their ends; a chuck device with two jaws is 
then moved in the direction of the arrows, F1 and F2 in order to put the 
clamps on the ends. During this operation, the arms of the clamps open out 
as they slide on the tapers so that the end beads finally engage at the 
grooves; the extent of penetration of the ends may be determined by the 
grooves themselves, or by the shoulder 10, while the penetration of the 
extentions 22, into the openings 21, retains the slide in a satisfactory 
position. 
The contact between these parts is such as to give efficient grip and 
excellent rigidity, together with good heat transfer properties. 
In the example illustrated on FIG. 3, the taper and the groove of the slide 
has been broken down into a series of teeth 24, while the series of beads 
25, of complementary shape is provided on the arms of the clamp. 
The slides are made by a casting process such as to give dimensional 
accuracy, for example, pressure molding; while the cross-members are made 
using the extrusion process, which is perfectly suited for the relatively 
complicated shape of the section. 
The presence of the open channels 19, the opening of which is in a plane 
perpendicular to the longitudinal axis of the slides, may also be used for 
retaining other parts of the chassis, for example, they may support a wall 
23, forming the bottom of the chassis on which will be arranged the 
connectors 26 for the printed circuits. The movements of such a wall may 
be limited by the lateral walls and the cross-members, if it is possible 
to tolerate reduced clearance which is, nevertheless, adequate to allow 
the ends of the printed circuit board to penetrate the connectors. 
The parts of the chassis described above may be the subject of 
modifications without departing from the scope of the invention, for 
example, by a kinematic inversion whereby the arms of the clamp would be 
designed to be pressed together instead of being spread apart.