Contact spring for low resistance connection of a circuit board to a grounded subassembly carrier

A contact spring contained in a conforming recess in a guide channel has a U-shaped portion with projecting side tabs embracing the edge of a circuit board. The side tabs rest against conductors on the circuit board which carry circuit board potentials and establish a good electrical connection between the conductors and the contact spring. The contact spring also grips the circuit board. A spring leg on the contact strip goes through an opening in the guide channel and engages the subassembly carrier.

BACKGROUND OF THE INVENTION 
This invention relates to a contact spring for a low resistance chassis 
connection of a circuit board to a subassembly carrier. The circuit board 
is equipped with electronic components and is held, in at least one 
insulating guide channel, on a subassembly carrier which has a highly 
conducting surface and is connected to ground (a reference potential). 
As shown in DE-AS No. 26 53 216, one known device for equalizing the 
potential in electronic modular systems has a potential point on one 
subassembly which is connected, via a contact spring, to a corresponding 
reference potential point on the subassembly carrier. A contact bar 
connected to the subassembly carrier is provided as the reference 
potential point and is designed as a shielding housing, being realized as 
a copper strip or as an electrically highly conducting surface layer. The 
contact spring is held by a plastic part fastened to the subassembly. 
It is an object of the invention to provide a contact spring which is easy 
to handle and ensures a reliable contact between the potential of the 
circuit board and the subassembly carrier, which in turn is connected to 
ground (the reference potential). 
SUMMARY OF THE INVENTION 
According to the present invention, this problem is solved by means of a 
contact spring which is conformably accepted in a recess in the guide 
channel and which has a U-shaped portion. The legs of the U-shaped portion 
have reslient tabs or depressions embracing the edge of the circuit board. 
The tabs rest against conductors on the circuit board carrying the 
potential and establish a highly conductive electrical connection to them. 
At the same time, positive mechanical engagement of the contact spring 
with the circuit board is made. The contact spring also has a spring leg 
which passes through an opening in the channel and the guide member and 
either snaps into a cooperating depression on the subassembly carrier or 
engages (hooks) behind the subassembly carrier. 
According to the invention, the contact spring rests resiliently against 
conductors carrying the potential of the circuit board as well as resting 
against the highly conducting surface of the grounded subassemble carrier. 
This establishes a secure, electrical connection between them. 
Handling during assembly is simple. The contact spring provided by the 
invention is placed in the conforming recess of the guide channel with its 
leg passing through the associated, appropriately sized, opening on the 
guide channel. The circuit board is then pushed into the U-shaped portion 
of the contact spring, immediately establishing a secure mechanical 
connection between the circuit board and the contact spring. When this 
assemblage is pushed into the subassembly carrier, the leg of the contact 
spring either snaps into a corresponding depression in the subassembly 
carrier or engages behind it. This holds the guide channel on the 
subassembly carrier, and electrical connection between the conductors, 
which carry the reference potential of the circuit board, and the grounded 
subassembly carrier is established.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a circuit board 1, (only the edge is visible) on which some 
electronic components, not specifically designated, are arranged. Circuit 
board 1 is received in guide members 3 have suitable slots or channels 3' 
for receiving the circuit board. Guide members 3 carry posts 4 which 
engage in holes 6 in a subassembly carrier 5. A contact spring 7 is 
inserted into suitably shaped recess 7' (See FIG. 4) in guide channel 3. 
The design of contact spring 7 is best seen in FIGS. 2 and 4. In FIG. 2, 
the circuit board is omitted and in FIG. 4 it is inserted into the contact 
spring. Contact spring 7 has a U-shaped portion 8 which surrounds the edge 
of circuit board 1. U-shaped portion 8 is preformed and has several 
springy inwardly directed tabs or depressions 9a, 9b, and 9c. These 
resilient depressions extend into the slot and engage on circuit board 1, 
holding spring 7 in mechanical engagement with the board. Resilient spring 
depressions 9a and 9c project in from one side of the slot and rest 
against potential carrying conductors (conductor runs) 2 on circuit board 
1. This establishes a highly conducting electrical connection between 
contact spring 7 and conductors 2. Contact spring 7 also has a spring leg 
10 which passes through an opening in guide channel 3 and extends around 
and behind a projecting portion 12 of subassembly carrier 5. Subassembly 
carrier 5 is grounded and has, at least in those places where leg 10 of 
contact spring 7 rests against it, a highly conducting surface. For this 
purpose, subassembly carrier 5 may, for instance, be tinned. This assures 
a highly conducting electrical connection between contact spring 7 and 
grounded subassembly carrier 5. 
In summary, a low resistance chassis connection between conductors 2, which 
carry a potential of circuit board 1, and grounded subassembly carrier 5 
is provided, in a simple manner, via contact spring 7, the resilient 
depressions 9a and 9c of which rest against conductors 2 and via spring 
leg 10 which rests, under pretension, against subassembly carrier 5. Leg 
10 of contact spring 7 not only establishes a low resistance chassis 
connection to subassembly carrier 5, but secures guide member 3, with 
contact spring 7, on the subassembly carrier. End portion 11 of spring leg 
10 is reversed around formed end 12 of carrier 5. End 12 extends from 
carrier 5 perpendicular to the length of spring leg 10. By making end 
portion 12 thicker, a recess can be made in it into which part or all of 
the reversed portion 11 of spring leg 10 can engage, obtaining the same 
locking action. In either case, the subassembly carrier provides a 
detent-like surface on which reversed portion 11 of spring leg 10 rests.