SPECIFICATION OF THE INVENTION
1. Title of the Invention:

Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB of avionics Computer application.

2. Field of Invention:

The invention relates to backplane and Front block PCBs for avionics computer for management of huge number of signals of different types including video channels to communicate with other avionics LRUs and sensors. Particularly it is more related to the backplane of a mission computer having several segments that also follow to the Compact Peripheral Component Interconnect Specification. Backplane and Front block PCB are connected through a Flexi PCB to make continuous signal routing.

3. Prior art and Drawback

In conventional arrangement, backplane and Front block PCBs (with MIL Grade connectors) have separate PCBs for such large no of input signals. The PCBs are thick and connected by rigid arrangement.

4. Aim of the Invention:

An optimized design of backplane and Front block PCBs for large no. of input signals including different types of video signals with Flexi-rigid arrangement.

5. Summary of the Invention:

cPCI backplanes are used in many applications. Conventionally all the inserted boards are cPCI based so a standard cPCI backplane caters to the purpose. In the present invention cPCI signals along with local processor's address and data bus signals are also used to enhance the features of the cPCI backplane and give a reason to be called as hybrid cPCI backplane. Along with the hybrid feature the numbers of 10 signals were too high (more than 500) which demands for proper placement of the connector to ease the routing of the signals. As the IOs includes a large number of video signals (8DVI and 8composite), it demanded for the routing of such signals having minimum length and no via to match signal impedance and video quality. To caters this requirement Rigid -Flexi-Rigid PCB concept is used. Due to the use of Flexi-Rigid PCB, combination of micro-strip routing and strip-line routing, both concepts are used.

6. Brief Description of the Drawings:

Fig 1: Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB Fig 2: Backplane Stack-up

7. Detailed description of the invention:

Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB has three major segments.
• Hybrid Backplane
• Flexi PCB
• Front Block PCB

Backplane segment of Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB consists of seven slots for different modules as follows:
I. Slots S1 for SBC1
II. Slots S2 for SBC2
III. Slots S3 for Video
IV. Slots S4 for Serial Communication
V. Slots S5 for Discrete l/O's
VI. Slots S6 for Spare l/O's
VII. Slots S7 for Power Supply

7.1 Hybrid Backplane:

First cPCI Slot (S1) is used as System Controller Slot or Master Slot and next other three cPCI Slots (S2-S4) are peripheral slots. Communication between Master and Peripherals will be happening via PCI interface. PCI Interface works on 32/64 bit at 66 MHz Slot 4 is based on cPCI as well as on Local bus. S5 and S6 are completely on Local bus of S4 and communicate via local address and data lines. This is how the backplane caters the Hybrid feature of the Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB between Slots-S4 and non-cPCI Slots-S5/S6. Refer Fig.1 7.2Optimized placement of cPCI connectors in Backplane Segment and MIL-grade Circular Connectors in Front Block PCB: This backplane uses a high quality 2 mm metric pin and socket connector that meets IEC standards. All Compact PCI, Discrete IQs and Power Supply boards will be inserted vertically from the top of the chassis through card guides on both sides (front and rear) and locked by tightening the wedge locks. Signals from all the boards are routed to backplane and running via flexi to Circular connectors (C1-C7) which are soldered on Connector block Segment on front side of chassis.

Placement of cPCI connectors in Backplane Segment and MIL-grade Circular Connectors in Front Block PCB Segment has been done in such a way that routing become so easy without criss-cross and shortest routing length of IO Signals dedicatedly from P3, P4, and P5 connector of cPCI connectors to MIL-grade Circular Connectors Segment via 20 layer of rigid PCB and 16 layer of flexi PCB of the backplane. Refer Fig.1 7.3Micro Strip-line and Strip-line Stack-up planning: cPCI backplane is based on 20 layers of stack-up for controlled impedances of 50 Q, 75 Q, 65 Q & 100 Q of strip line and micro-strip line design (two layers are dedicated to ground planes - External surfaces designed as GND planes). Top and bottom ground planes with 02 oz copper are used to fully shield the backplane to minimize EMI/RFI emissions susceptibility, minimize crosstalk, and maximize power distribution. Refer Fig.2

7.4 Video Signals are routed inner layers: cPCI backplane have 8 no. of DVI Video and 8 no. of Composite video Signals, which are routed to inner layers of backplane to achieve the good quality of video and shielding to EMI/EMC.

7.5 Provision of non-cPCI spare slot-6: Slot-6 is having 100 pins of non-cPCI spare connector to cater any analog signals requirement in future. These signals are routed to different circular connectors.
7.6 Provision of ATX connector for giving power to the entire system.
7.7 Hybrid cPCI Flexi-Rigid Complex Backplane and Front Block PCB specification:
Material Used : FR4 & Polyamide
Thickness of Board : 3.6 mm
Size of the Backplane Segment : 161 mm (W) x244mm (L)
Size of the Front Block PCB Segment : 152.5mm (W) * 155mm (L)
Type : Strip-line and Micro Strip-line Design
No. of Layers : 20 layers
Impedance of Bare PCB : 65±3 Q
Critical Impedances of Signals : 50Q, 65Q, 75Q and 100Q
Ohmic Resistance of Signal Line : <1 Q

CLAIMS

We claim

1. Signal routing management of more than 550 lOs with different electrical characteristics from IO connector of cPCI connectors to Circular Connector of MIL grade Circular Connector Segment. The "Hybrid feature" [1] of motherboard supports communication of non-cPCI standard PCB boards to cPCI standard PCB boards. This motherboard is having "Optimized placement of cPCI connectors in Backplane Segment and MIL-grade Circular Connectors in Front Block PCB" [2] to ease the signal routing. "Micro Strip-line and Strip-line Stack-up planning" [3], both are used in this motherboard. To reduce the EMI/EMC effect and to maintain the quality the "Video signals are routed in the inner layers" [4]. To cater the need of analog signals as future growth requirement "Provision of non-cPCI spare slot-6" [5] is given.

2. Hybrid feature claimed in claim 1) of cPCI Based Hybrid Flexi-Rigid Motherboard between Slots-S4 and non-cPCI Slots-S5. Refer Fig.1

3. Optimized placement of cPCI connectors in Backplane Segment and MIL-grade Circular Connectors in Front Block PCB claimed in claim 1), for easy and shortest routing of IO Signals dedicatedly from P3, P4, and P5 connector of cPCI connectors to MIL-grade Circular Connectors Segment via 20 layer of rigid PCB and 16 layer of flexi PCB of the motherboard. Refer Fig.1

4. Micro Strip-line and Strip-line Stack-up planning claimed in claim 1) to achieve four different types of signal impedances 50 Q, 75 Q, 65 O & 100 Q of various signals for the 3.6 mm thickness of motherboard. Refer Fig.2

5. Video Signals are routed inner layers claimed in claim 1) of motherboard to achieve the good quality of video and shielding to EMI/EMC.

6. Provision of non-cPCI spare slot-6 claimed in claim 1) for analog signals future use.