Printed circuit board connector system

A system for connecting printed circuit boards to card cages. In addition to a conventional pin-and-socket connector arrangement for making signal and main power connections, the printed circuit board has a conducting pad coupled to the power traces of the board. A clip mounted in the card cage and connected to a first power source isolated from the main power source engages the pad before the conventional connectors make contact. Thus, the board is powered up first. As the board is fully seated and the conventional power and signal connections made, the power clip slides off the pad to break contact, leaving the main power source supplying power to the board.

BACKGROUND OF THE INVENTION 
The present invention relates to the field of connector systems for circuit 
boards and, more particularly, to a printed circuit board connector system 
which permits the board to power up before mounting into a structure is 
complete. 
FIELD OF THE INVENTION 
Electronic systems are typically made from individual devices, such as 
hybrid circuits, integrated circuits and individual components, including 
resistors, capacitors, and inductors. These individual devices are 
typically mounted on a printed circuit board which has a pattern of 
conductive traces on the board substrate to electrically couple the 
devices together in a desired configuration. 
Normally, the printed circuit boards are mounted in slots in a mounting 
structure, such as a card cage. At one edge of the printed circuit board 
there are connectors which are connected to the wire traces on the printed 
circuit board. When the printed circuit board is inserted into the card 
cage, the connectors mate with complementary connectors attached to the 
card cage in a pin-and-socket configuration. The complementary connectors 
are wired to a bus, or backplane, of the card cage. Through each line of 
the bus, the connectors of each board in electrical contact with the wires 
are connected together in parallel. A line in the bus may supply power to 
the connected printed circuit boards. A line may also supply a 
communication path between the boards or between a board and the outside 
world. 
The card cage with its mounted printed circuit boards form an electronic 
unit, such as a computer. The unit depends upon the design of the circuits 
on the printed circuit board and their interconnections. In many such 
units, there is a requirement that the boards be inserted and removed 
while the electronic unit is operating. Examples of such units include 
central office switching systems and private branch exchanges (PBXs) in 
telephone systems. The requirement, however, is not limited to telephone 
systems. 
There are a few major problems, however, which must be surmounted when a 
board is inserted into or removed from the card cage. The first problem is 
that the installed board must not affect the operation of the other boards 
in the system by generating unsynchronized interactions on the backplane 
or common bus of the system. The second problem is that board insertion 
and removal must not create electrical conditions which might damage the 
components on the board. The final problem is that the insertion of the 
board must not create transient interactions on the common power bus. 
The present invention solves or substantially mitigates these problems in 
an incisive and economical way not contemplated heretofore. 
SUMMARY OF THE INVENTION 
The present invention provides for a system for electrically connecting a 
printed circuit board having a plurality of connector contacts at an edge 
of the printed circuit board to a mounting structure having a plurality of 
mating connector contacts for engaging the connector contacts when the 
board is mounted in the mounting structure. The system comprises a 
conducting pad on the board coupled to electrical devices on the board for 
supplying power thereto, and a slidable contact on the mounting structure 
coupled to a first power source. The contact engages the pad before the 
connector contacts engage the mating connectors as the board is mounted in 
the structure and disengages when the board is fully mounted in the 
structure. 
The conducting pad is substantially coincident with a surface of the board 
and the slidable contact comprises a clip which resiliently contacts the 
board's surface. The clip contacts the pad when the board is placed in a 
first position for mounting the board into the structure and does not 
contact the pad when the board is placed in its final mounted position in 
the structure. The conductor pad is of such shape that the clip loses 
contact with the pad when the board is seated into the mounting structure. 
One of the connector contacts is also coupled to the electrical devices on 
the printed circuit board for supplying power thereto and its mating 
connector contact is coupled to a second power source electrically 
isolated from the first power source.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
Heretofore, attempts to solve the problems above have not been completely 
successful. To prevent unsynchronized interaction on common signal 
connectors, a printed circuit board is powered up before its signal 
connectors make contact with the bus. The powering up stage requires only 
a fraction of a second typically, but it must occur prior to the signal 
connector contact. Similarly, if the board is kept powered up as the 
signal connector contacts are broken, then erroneous signals are not 
generated on the bus when the board is removed. 
A prior art solution to this problem has been multi-level pins so that a 
power pin and its complementary socket mate before the signal pins do when 
the printed circuit board is inserted. Moreover, the power pin and socket 
stay mated as the signal pin contacts are broken when the board is 
removed. 
Another solution in the prior art has a mechanical lever attachment which 
opens and closes the connections in sequence, somewhat in the fashion of a 
zipper, so that the power connections are made first and broken last. 
Still another solution uses an umbilical cord which is manually connected 
to a special power connector of the printed circuit board before the board 
is pushed into contact with the main connectors. The umbilical power cord 
is then manually removed. For board removal, the umbilical cord is 
attached, the board removed and the cord disconnected. 
These solutions also typically solve the second problem. When a printed 
circuit board is inserted, a ground contact should be made first or 
coincident with the power contacts. If not, the power contacts with no 
ground reference may have unintended electrical paths through the printed 
circuit board. Integrated circuit components are often electrically 
fragile; the unexpected voltages across device leads may lead to 
destruction of the component. Therefore, when a printed circuit board is 
removed, a ground contact should be the last to be broken. The solutions 
above typically have a ground connector which is one of the first to make 
or last to break contact upon board insertion or removal respectively. 
These solutions solve the first two problems but still do not attack the 
third problem of the harmful voltage transients caused by the initial 
surge of current when the board is initially coupled to a power source. 
After the capacitance of the board is charged, the power supply returns to 
a stable state. This power source current surge causes voltage 
fluctuations with potentially serious consequences to the other printed 
circuit boards already in place and operating. 
Two approaches have been used to solve this third problem. The first 
solution reduced the amount of in-rushing transient current into the newly 
connected board by having an impedance in series with the power connection 
so that the resulting voltage transient is reduced to a harmless level. 
This solution has some drawbacks, however. A special component, such as a 
resistor or inductor, must be mounted on the card. Since this component is 
in series with the power connection, it limits the current to the printed 
circuit board so that the board does not receive the full operating 
voltage to power the printed circuit board. A modification to this 
approach has been to add more power sequencing levels to the connector so 
that the card is powered in steps. This just adds extra complexity to the 
problem. 
The other approach has been the use of two power sources which are isolated 
from one another. The first source powers up the printed circuit board 
before the board has been fully inserted into the card cage. Though the 
voltage level of the first power source may fluctuate, it does not affect 
the operating cards which are being powered by the second or main power 
source. In the prior art the first power source has been coupled to the 
printed circuit board by an umbilical cord before insertion into the card 
cage. After the card was mounted into the card cage, the umbilical cord 
was removed. While solving two problems discussed above, this system still 
required effort beyond the straight-forward insertion and removal of the 
printed circuit board into the mounting structure. The umbilical cord must 
first be attached and after the card is fully seated, the cord must be 
removed. The same procedure must be followed to safely remove the board. 
The present invention also uses the two separate power sources, which are 
isolated from one another. The printed circuit board has its normal 
connecting system, typically a pin-and-socket arrangement at an edge of 
the board with the mating connectors in the board mounting structure, in 
the card cage. The connectors at the printed circuit board edge are 
connected to the wire traces of the board. 
The present invention is illustrated in FIGS. 1A-1D of the present 
invention. The printed circuit board 20 has several electrical components, 
here shown as multi-pin integrated circuits 12 which are attached to the 
board substrate 10. These components 12 are electrically interconnected by 
wire traces (not shown) on the surface of the board substrate 10. The 
board 20 and its components 12 are coupled to other printed circuit boards 
through connectors 13 located at one edge of the board substrate 10. The 
connectors 13 are sockets which are protected by a socket housing 18. The 
connectors 13 mate with complementary connectors 14 in the form of pins 
protected by a housing 19 when the board 20 is connected to a backplane 
board 21. One or more of the connector sockets 13 is a power connector 
which has its corresponding complementary connector pin connected to a 
main power source to drive the components 12. This is a typical 
arrangement found in electrical systems. 
The present invention also has a power pad 15 which is also connected to 
the power wire traces of the board 20. Corresponding to the power pad 15 
is a specially adapted connector 16 which has leads in the form of a clip. 
The connector clip 16 with its protective housing 17 is mounted to the 
backplane board substrate 11 in the same manner as the complementary 
connector contacts 14. The housing 17 has a slot 24 to receive the 
substrate 10. The clip 16 is longer than the complementary contacts 14 so 
that it resiliently engages the power pad 15 before the connector contacts 
13 mate with the complementary connector contacts 14. FIG. 1B illustrates 
this relationship. 
The clip 16 is coupled to a first power source which is electrically 
isolated from the main power source coupled to the complementary connector 
contact 14. Since the power pad 15 first engages the clip connector 16, 
the first power source first supplies power to the board 20. Even though 
the first power source may suffer from transient fluctuations, it does not 
affect the other printed circuit boards since it is electrically isolated 
from the main power source. As the board 20 is inserted, the connector 13 
and complementary connectors 14 mate, as shown in Fig. lC. At this point 
the second or main power source is also supplying power to the board 20 
through the power connector in the set of connector pins 13. 
Finally, as shown in Fig. lD, the power pad 15 is of such a shape that the 
clip leads of connector 16 slide off the power pad 15 thus breaking 
contact when the board substrate 10 is fully seated. Hence the board 20 is 
now supplied by power through the second power source only. 
FIGS. 2A-2D show a top view of the power pad-connector slip connection and 
correspond respectively to FIGS. 1A-1D. Besides the clip 16, a second clip 
23 is shown. The connector clip 16 coupled to the first power source 
engages the power pad 15 when the board substrate 10 is inserted into a 
card for mounting. The clip 23 is coupled to ground. A ground pad 22, like 
the power pad 15, which is nearly coincident with the surface of the 
substrate 10 engages the clip 23 when the board 20 is inserted. 
The pad 22 is coupled to all of the ground terminals of the printed circuit 
board 20. When the clips 16, 23 respectively resiliently engage the pads 
15, 22, a path is made to supply electrical power to the board 20. 
Unlike the pad 15, however, the pad 22 need not be shortened in the 
direction of board travel. Since the pad 22 is a grounded contact, the pad 
22 and clip 23 contact may remain even after board mounting is complete 
and one of the pin-socket 13, 14 connections provides a conventional 
grounded connection for the board 20. 
It should be noted that the main connectors for the printed circuit board 
connection may also be of the sliding clip-and-pad construction as the 
power pad and clip previously described. The clips may then be integrated 
into one housing with a possible savings in manufacturing costs. Of 
course, the clip lengths, pad sizes and placement must be adjusted to 
maintain the function of the power pad and complementary clip. 
In this manner, the present invention permits the inserted printed circuit 
board to be powered before the critical signal contacts are coupled into 
the overall system. Power down under the present invention occurs after 
the signal contacts are broken. Secondly, a ground contact is made 
initially for the power up stage to provide a proper reference for all 
voltages to the board. A ground contact is also assured in the power down 
stage. Thirdly, the board 20 is first powered up by a first power source 
which is electrically isolated from the main power source so that 
transient voltage fluctuations in the initial stages of board mounting do 
not affect the operations of the electronic system. 
Accordingly, while the invention has been particularly shown and described 
with reference to the preferred embodiments, it would be understood by 
those skilled in the art that changes in form and details may be made 
herein without departing from the spirit of the invention. It is therefore 
intended that an exclusive right be granted the invention as limited only 
by the metes and bounds of the appended claims.