OCX256 packaged 792-ball plastic TBGA package, SRAM-based bit-oriented

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OCX256 packaged 792-ball plastic TBGA package, SRAM-based bit-oriented

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OCX256 Layout Guidelines
OCX256 packaged 792-ball plastic TBGA package, SRAM-based bit-oriented switching device offering flow-through datarates 667Mb/s registered data modes 333MHz. Inputs Outputs each configured dedicated differential ports. ports connected each other through switch matrix, which supports one-to-one, one-tomany, one-to-all connections. proprietary RapidConfigureparallel interface allows fast configuration switch matrix. also allows readback device test verification purposes. OCX256 also supports industry standard JTAG (IEEE 1149.1) interface boundary scan testing. JTAG interface also used download configuration data device. Applications include telecom datacom switching, video switches servers, test equipment.
Package Dimensions
Figure
OCX256 Package Dimensions (Bottom View)
2002
AN500757
OCX256 Layout Guidelines
Figure
OCX256 Package Dimensions (Top Side Views)
Recommended Layout
OCX256's 792-pin package ball spacing (0.0394"). Ball spacing distance from center ball center adjacent ball. pads printed circuit board should circular. Fairchild Semiconductor recommends that following dimensions used printed circuit board pad:
Diameter: Solder Mask Diameter:
0.4572mm (0.018") 0.4318mm (0.017")
AN500757
2002
OCX256 Layout Guidelines
.018" Dia. (0.4572mm) .017" Solder Mask Dia. (0.4318mm) .005" Trace Width (0.127mm) .010" Dia. (0.254mm)
Figure
Solder Mask Diameters
Solder mask will cover outer 0.0127mm (0.0005") pad. This will help make placement OCX256 onto easier during manufacturing. common problem with BGAs solder migration away from pads. solder mask does cover trace leading from nearby via, then solder will migrate away from fill hole when BGA's solder ball melts during placement. This lead broken unreliable connections. highly recommended that solder mask used cover vias vicinity BGA. This sometimes referred "tenting" "tented vias", since solder mask forms protective tent over hole.
Layout Considerations
Fairchild Semiconductor OCX256 Evaluation Board manufactured with trace width spacing 0.127mm (0.005"). vias have diameter 0.254mm (0.010"). Bringing signal traces from requires careful planning routing, number layers, layer stackup. rule determining number signal layers that will required routing signals count number ball rows subtract one. Usually layer used break signals from outermost rings, additional layer will required route each additional ring. OCX256 rings balls, plan using five signal
2002
AN500757
OCX256 Layout Guidelines
layers. Careful planning could reduce this number four. Fairchild Semiconductor OCX256 Evaluation Board twelve-layer board with signal layers power planes. However, signal breakout around OCX256 required only four layers. Most signals routed from directly adjacent via. This must done very carefully order prevent creating wall vias that will plane layers board. Remember that internal power plane layers will fill copper open areas leave safety zone around vias. This safety zone usually wide enough that vias side-by-side they will adjacent pads) there will copper filled between them. This prevent area underneath from actually being connected power ground planes. some cases plane will incomplete, will leave center region connected very thin strip copper inner layer. order prevent this, leave space channels ground planes reach area underneath BGA.
Figure
OCX256 Signal Breakout (inner chip via's removed clarity)
area underneath connected printed circuit board's power planes several wide areas copper, then part able receive sufficient power susceptible power supply noise. OCX256 requires decoupling capacitors order
AN500757
2002
OCX256 Layout Guidelines
reduce noise power planes from affecting operation. These capacitors should placed side opposite many should placed directly beneath BGA's center. This makes connecting that region both power ground planes even more important. Fairchild Semiconductor recommends that least three power planes used supply power OCX256-one plane each VDD.CORE, VDD.IN, VDD.PAD. Using multiple power planes designing signal breakout such that channels inner area available will make OCX256 system more reliable. Fairchild Semiconductor OCX256 Evaluation Board three power planes three ground planes. with high-speed interface, RapidConfigure Interface OCX256 must carefully routed operated very high speeds. trace lengths signals should matched within approximately 12.7mm (0.500"). Clock signal should also routed directly from source OCX256, with T-junctions that could cause reflections line. OCX256 based switch system never include many decoupling capacitors. OCX256 approximately hundred power pins hundred ground pins. Fairchild Semiconductor recommends using small decoupling capacitor (typically 0603 size, 0.01µF) every power pins, approximately fifty small decoupling capacitors. decoupling capacitors should placed opposite side board from OCX256, should arranged underneath center chip. Decoupling capacitors should also placed same side board OCX256, routing permits.
References
Books:
Johnson, Graham, High-Speed Digital Design, 1993, Prentice Hall, 0-13-395724-1. Montrose, Printed Circuit Board, 1999, IEEE Press, 0-7803-4703-X.
Links:
(High-Speed Board Designs), ver. 3.01, December 1999
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OCX256 Layout Guidelines
Fairchild does assume responsibility circuitry described, circuit patent licenses implied Fairchild reserves right time without notice change said circuity specifications. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT FAIRCHILD SEMICONDUCTOR CORPORATIONS. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
www.fairchildsemi.com
AN500757
2002

OCX256 packaged 792-ball plastic TBGA package, SRAM-based bit-oriented

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