System for connecting a module comprising a plurality of...

Details System for connecting a module comprising a plurality of... System for connecting a module comprising a plurality of...

1999-12-08

2002-06-11

Gandhi, Jayprakash N. (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S752000, C361S758000, C361S759000, C361S801000, C174S13800J, C211S041170

Reexamination Certificate

active

06404650

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to modular electronic equipment such as computers or communication systems, which need to achieve a maximum of connectivity and more particularly, to a system for precisely positioning a plurality of electronic cards with the aim of plugging them into a backplane.
BACKGROUND ART
In most instances, large electronic systems are made of a set of electronic cards providing internal and peer to peer connection through a backplane. With the electronic technology progress, it is often interesting to enhance the performance and the function of an electronic system by adding cards. One or more daughter cards can be connected on a mother card or additional cards can be directly connected to the backplane. This process has been widely deployed across the industry to save development efforts and preserve customers investments. However, because the need of connecting additional cards to a backplane cannot always be foreseen during the design or installation phase, the upgrading of large electrical systems may lead to some mechanical problems in particular for mating cards and backplane connectors.
FIG. 1
, FIG.
2
and
FIG. 3
describe the background art related to electronic cards and backplane connectors.
FIG. 1
is a perspective view of an electronic module (
100
) comprising a plurality of cards (
102
) connected to a backplane (
101
) according to prior art. The electronic module (
100
) comprises a mechanical housing (
103
), one or more mother board cards (
102
) or Printed Circuit Boards (PCB).The mother cards (
104
) directly connected to the backplane, and daughter cards (
105
) connected to mother cards and/or directly to the backplane (
107
).
The backplane (
101
) comprises one or a plurality of connectors (
106
) for receiving said one or plurality of cards equipped with connectors. Mother cards (
104
) are connected peer to peer through the back plane. Daughter cards (
105
) are connected either internally on mother cards or directly through the back plane.
FIG. 2
is a section view of the system according to prior art showing two particular embodiments, the first being with the daughter card (
201
) directly plugged (via connector
208
) on an associated mother card (
202
) which is connected to the backplane (
200
). The second embodiment comprises a daughter card (
203
) connected to its mother card through the backplane (
200
).
A set of spacers (
205
,
206
) is installed between cards (
201
,
202
,
203
,
204
) to guarantee the mechanical rigidity of the electrical module, the parallel positioning of the electronic cards, and the spacing between the card connectors (
207
).
FIG. 3
is a section view of the system described in FIG.
1
. The electronic module (
300
) comprises within its mechanical housing (
310
), a plurality of electronic cards with connectors. Three cards are shown, mother cards (
302
,
303
) and daughter card (
304
) plugged on mother card (
303
) by means of connector (
305
). Cards are stacked together using spacers (S
1
, S
2
, S
3
. . . ). In general, the first card (
303
) is fastened to the housing (
310
) by means of one or a plurality of posts (
308
) or equivalent means. This first card is generally used as “reference card” (
309
) for positioning the other cards. The problem raised by the prior art is related to the plugging of the electronic module on the backplane (
301
) and more particularly to the alignment of the card connectors (
306
) with the backplane connectors (
307
) taking into account the mechanical tolerances of the various elements.
To evaluate the mechanical tolerance one can refer to
FIG. 3
where the spacing between backplane connectors is defined by A
1
, A
2
, An, and the spacing between card connectors is defined by X
1
, X
2
, Xn. To simplify the description, it will be supposed that:
A
1
=A
2
=An
X
1
=X
2
=Xn
It will be also assumed that tolerances on connectors are insignificant and negligible (close to zero).
For aligning electronic cards connectors with backplane connectors, a reference card and reference planes must be defined. The first electronic card (
303
) can be defined as “reference card” (
309
) (in general, the card fastened to the housing is chosen as reference card). For each card, the side where the card connector is located is defined as “reference plane” (R
1
, R
2
, R
3
). There is one reference plane per card. The reference planes in a module comprising a plurality of cards are arranged parallel and are generally oriented towards the same direction. In prior art, the first spacer (S
1
) is fixed between the reference plane (R
1
) of the first card and the opposite side of the second card (
304
).
From a theoretical standpoint we have the following equations.
A
1
=X
1
,A
2
=X
2
,An=Xn
From an industrial and realistic standpoint, industrial tolerances of the various mechanical elements must be taken in account. The equation becomes:
X
1
min
<X
1
<X
1
max
where
X
1
min
=X
1
−x
1
and X
1
max
=X
1
+x
1
with
X
1
max
=S
1
max
+T
2
max
=(S
1
+s
1
)+(T
2
+t
2
)
X
1
min
=S
1
min
+T
2
min
=(S
1
−s
1
)+(T
2
−t
2
)
where:
S
1
, S
2
, Sn: dimension of spacers
1
,
2
, n
T
1
, T
2
, Tn: thickness of electronic cards (Printed Circuit Boards PCB)
1
,
2
, n
s
1
, s
2
, sn: tolerance on spacer dimension
1
,
2
, n
t
1
, t
2
, tn : tolerance on card thickness
1
,
2
, n
S
1
max
=S
1
+s
1
S
1
min
=S
1
−s
1
T
2
max
=T
2
+t
2
T
2
min
=T
2
−t
2
The spacing tolerance on second card connector is equal to:
x
1
=s
1
+t
2
For the third connector, the equation becomes:
X
1
min
+X
2
min
<X
1
+X
2
<X
1
max
+X
2
max
with
X
1
max
+X
2
max
=(S
1
max
+T
2
max
)+(S
2
max
+T
3
max
)
X
1
min
+X
2
min
=(S
1
min
+T
2
min
)+(S
2
min
+T
3
min
)
The spacing tolerance on third card connector is equal to:
x
1
+x
2
=s
1
+s
2
+t
2
+t
3
The spacing tolerance on the connector of the nth electronic card is equal to:
x
1
+x
2
+ . . . +xn=(s
1
+s
2
+ . . . +sn)+(t
2
+t
3
+ . . . +t(n+1)).
The spacing and thickness tolerances are cumulative, they must be added with each additional card. It becomes more of a problem for systems using a larger number of electronic cards.
This problem can be illustrated with an example. The commercial tolerance for the spacing of the backplane connectors A
1
, A
2
, An is +/−0.025 mm and the tolerance range is 0.05 mm.
The regular industry thickness tolerance for a Printed Circuit Card (PCB) is 10% with a nominal tolerance of +/−5%. The current nominal thickness used nowadays in most industries for ongoing developments is 2.2 mm (+/−0.11 mm).
The regular tolerance on commercial spacers S
1
, S
2
, Sn is +/−0.05 mm and the tolerance range is 0.1 mm. This tolerance is generally given in millimetres and is not function of the spacers length or dimension.
Applying numbers to the equations:
X
1
max
=(S
1
+0.5)+(T
2
+0.11)
x
1
upper tolerance is 0.16 mm.
X
1
min
=(S
1
−0.05)+(T
2
−0.11)
x
1
lower tolerance is 0.16 mm.
X
1
tolerance is equal to +/−0.16 mm, and the tolerance range is 0.32 mm.
This result must be compared to the tolerance on the spacing between backplane connectors. If we call a
1
, a
2
, an: the tolerance on spacing between backplane connectors
1
,
2
, n and assume:
x
1
=0.32 mm
a
1
=0.05 mm
The ratio x
1
/a
1
between tolerance is 6.4:
x
1
/a
1
=0.64 mm
With such a ratio, trying to match an electronic module comprising two cards with a backplane will result in damaging connectors contacts. If the electronic module is upgraded with a third card, the situation will be worst because tolerances are cumulative. Thus, the analysis of tolerances sh

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