Balanced Technology Extended (BTX) Interface Specification
IMPORTANT INFORMATION AND DISCLAIMERS 1. INTEL CORPORATION MAKES NO WARRANTIES WITH REGARD TO THIS BALANCED TECHNOLOGY EXTENDED (BTX) SPECIFICATION ( SPECIFICATION ), AND IN PARTICULAR DOES NOT WARRANT OR REPRESENT THAT THIS SPECIFICATION OR ANY PRODUCTS MADE IN CONFORMANCE WITH IT WILL WORK IN THE INTENDED MANNER. NOR DOES INTEL ASSUME RESPONSIBILITY FOR ANY ERRORS THAT THE SPECIFICATION MAY CONTAIN OR HAVE ANY LIABILITIES OR OBLIGATIONS FOR DAMAGES INCLUDING, BUT NOT LIMITED TO, SPECIAL, INCIDENTAL, INDIRECT, PUNITIVE, OR CONSEQUENTIAL DAMAGES WHETHER ARISING FROM OR IN CONNECTION WITH THE USE OF THIS SPECIFICATION IN ANY WAY. 2. NO REPRESENTATIONS OR WARRANTIES ARE MADE THAT ANY PRODUCT BASED IN WHOLE OR IN PART ON THE ABOVE SPECIFICATION WILL BE FREE FROM DEFECTS OR SAFE FOR USE FOR ITS INTENDED PURPOSE. ANY PERSON MAKING, USING OR SELLING SUCH PRODUCT DOES SO AT HIS OR HER OWN RISK. 3. THE USER OF THIS SPECIFICATION HEREBY EXPRESSLY ACKNOWLEDGES THAT THE SPECIFICATION IS PROVIDED AS IS, AND THAT INTEL CORPORATION MAKES NO REPRESENTATIONS, EXTENDS NO WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, ORAL OR WRITTEN, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR WARRANTY OR REPRESENTATION THAT THE SPECIFICATION OR ANY PRODUCT OR TECHNOLOGY UTILIZING THE SPECIFICATION OR ANY SUBSET OF THE SPECIFICATION WILL BE FREE FROM ANY CLAIMS OF INFRINGEMENT OF ANY INTELLECTUAL PROPERTY, INCLUDING PATENTS, COPYRIGHT AND TRADE SECRETS NOR DOES INTEL ASSUME ANY OTHER RESPONSIBILITIES WHATSOEVER WITH RESPECT TO THE SPECIFICATION OR SUCH PRODUCTS. 4. A NON-EXCLUSIVE COPYRIGHT LICENSE IS HEREBY GRANTED TO REPRODUCE THIS SPECIFICATION FOR ANY PURPOSE PROVIDED THIS IMPORTANT INFORMATION AND DISCLAIMERS SECTION (PARAGRAPHS 1-4) IS PROVIDED IN WHOLE. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY OTHER INTELLECTUAL PROPERTY RIGHTS IS GRANTED HEREIN. Intel is a trademark or registered trademark of Intel Corporation or its subsidiaries in the United States and other countries., September 2003 Other names and brands may be claimed as the property of others. Copyright 2003 Intel Corporation. Page 2
Revision History Version Description Date 1.0 Initial release. September 2003 Page 3
Contents 1. Introduction...7 1.1 Terminology... 8 1.2 Related Documents... 8 2. Form Factor Overview...9 3. Mechanical Requirements...11 3.1 Motherboard Size and Mounting Hole Placement... 11 3.2 Volumetric Zones... 12 3.2.1 Motherboard Volumetric Zones... 14 3.2.2 Chassis Volumetric Zones... 17 3.3 Chassis Mechanical Interfaces... 19 3.3.1 Chassis Interface for EMI Grounding... 19 3.3.2 Chassis Interface to Support and Retention Module... 19 3.3.3 Chassis Interface to Thermal Module... 22 3.3.4 Chassis Rear Panel I/O Interface Requirements... 24 3.4 Motherboard Mechanical Interfaces... 25 3.4.1 Motherboard Rear Panel Interface Requirements... 25 4. Electrical Interface Requirements...27 4.1 Motherboard Power Supply Connectors... 27 4.2 Motherboard Power and Control Signal Definitions... 28 4.2.1 +5VSB... 28 4.2.2 PS_ON#... 28 4.2.3 PWR_OK... 28 4.2.4 Voltage Tolerances... 29 5. Additional Information...31 Page 4
Figures Figure 1. Example BTX Board and System Layouts... 9 Figure 2. BTX Form Factor Board and Mounting Hole Dimensions... 12 Figure 3. Chassis and Motherboard Volumetric Zones (not all zones are shown)... 13 Figure 4. Motherboard Primary Side Volumetric Zone... 15 Figure 5. Motherboard Secondary Side Volumetric Zones... 16 Figure 6. Chassis Volumetric Zones... 18 Figure 7. Chassis Interface to SRM Requirements... 20 Figure 8. Chassis Interface to SRM Requirement Details...21 Figure 9. Chassis to Thermal Module Interface and Relation to Chassis and Motherboard Zones... 22 Figure 10. Chassis Requirements for Thermal Module Interface Definition... 23 Figure 11. Chassis Rear Panel I/O Aperture Requirements... 24 Figure 12. Motherboard Rear Panel I/O Aperture Requirements... 25 Figure 13. Power Supply Connectors... 27 Figure 14. Power Timing... 29 Tables Table 1. BTX Feature Summary... 7 Table 2. Specification Quick Reference... 7 Table 3. Terminology... 8 Table 4. Related Documents... 8 Table 5. Board Size Options... 11 Table 6. Categories and Requirements for Motherboard Volumetric Zones... 14 Table 7. Categories and Requirements for Chassis Zones... 17 Table 8. Chassis Mechanical Interface Requirements... 19 Table 9. Power Supply Connectors... 27 Table 10. PS_ON# Signal Characteristics... 28 Table 11. PWR_OK Signal Characteristics... 29 Table 12. DC Output Voltage Tolerances... 29 Page 5
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1. Introduction The Balanced Technology Extended (BTX) interface specification was developed to provide standard interfaces and form factor definitions to address the electrical, thermal, and mechanical attributes of desktop computer systems. The specification is intended to allow for a wide variety of product differentiation that can be adapted to multiple applications and usage models. This specification describes the critical mechanical and electrical interfaces for the design of chassis, motherboard, power supply, and other system components necessary for hardware vendors and integrators to build and integrate compliant components, systems, and devices that are interoperable with each other. The intention of this document is not to provide all requirements necessary to design any one of these components, but instead to provide standard interfaces for the components to be designed around. Table 1 summarizes some of the key features enabled by the BTX specification. Table 1. BTX Feature Summary Features Low profile options In-line core layout Scaleable board dimensions Structural board support mechanisms Benefits Easy integration in small, thin form factor systems Optimized for efficient system cooling Multiple system sizes and configurations Mechanical characteristics to support high-mass motherboard components Table 2 details the interfaces defined in this specification and the section(s) that address each. Table 2. Specification Quick Reference Interfaces Features Defining Interface Related Section(s) Board/Chassis Interfaces Motherboard geometry and mounting hole Section 3.1 locations (mechanical) Motherboard volumetric zones (mechanical) Section 3.2 Board/Power Supply Interfaces Chassis interfaces to other components Chassis volumetric zones (mechanical) Section 3.2.2 Rear panel chassis I/O locations and openings (mechanical) Main power connector (electrical and mechanical) +12V power connector (electrical and mechanical) Section 3.3.4 and Section 3.4.1 Section 4 Section 4 Chassis interface to SRM (mechanical) Section 3.3.2 Chassis interface to Thermal Module (mechanical) Section 3.3.3 Page 7
1.1 Terminology Table 3 explains terms introduced in this specification. Table 3. Terminology Term Support and Retention Module (SRM) Thermal Module Definition System component that is assembled to the chassis beneath the motherboard to provide structural support for motherboard and components as well as retention for a thermal module. A system component with the primary role of dissipating heat from the core components. A typical thermal module includes a heatsink for the processor, an air mover such as an axial fan, and a duct to isolate and direct airflow through the system. The flexibility to adapt to many applications is offered through the option to integrate a range of cooling technologies and components to create a thermal module. Modules will be one of two types based on which Zone A component height maximum (see Figure 4, page 15) is selected: Type I (Standard Height ) or Type II (Low Profile). 1.2 Related Documents Table 4 lists documents related to this specification. Table 4. Related Documents Specification PCI Express* Specifications Conventional PCI Specifications ATX and microatx Specifications Location http://www.pcisig.com/specifications/pciexpress/ http://www.pcisig.com/specifications/conventional/ http://www.formfactors.org Page 8
2. Form Factor Overview This specification allows the processor, chipset, memory, add-in cards, and other components to be designed and located in a way that facilitates both efficient motherboard routing and cooling of the components. It also allows options for system layouts that can accommodate a range of profiles and sizes from compact systems and devices to large, very expandable systems. The power supply connectors and interfaces are defined to be compatible with those defined for the ATX family of form factors. For more information on standard power supply definitions and the ATX form factor family, see the references listed in Chapter 5. Figure 1 shows three examples of the many layouts possible with the BTX form factor. Expandable Tower (Side View) Desktop (Top View) Optical Disk Drive Optical Disk Drive Power Supply Unit Power Supply Unit Rear Panel I/O I/O Card Slots Floppy Disk Drive Hard Disk Drive Chassis System/Processor Fan(s) Processor Thermal Module System Memory Rear Panel I/O Chassis System Memory Hard Disk Drive I/O Card on Riser Processor Thermal Module I/O Card Slots Optical Disk Drive System/Processor Fan(s) Front Side I/O Peripherals Front Side I/O Peripherals Small Form Factor (Top View) Rear Panel I/O Power Supply Unit Hard Drive I/O Card Slot Chassis System Memory Processor Mobile Optical Drive Thermal Module System/Processor Fan(s) Note: Illustrations not to scale OM16305 Figure 1. Example BTX Board and System Layouts Page 9
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3. Mechanical Requirements Balanced Technology Extended (BTX) Interface Specification This chapter describes the mechanical requirements of BTX system components and the associated interfaces. 3.1 Motherboard Size and Mounting Hole Placement A BTX board must adhere to the mechanical details depicted in Figure 2. All boards must be 266.70 mm deep. The board width may range from 203.20 mm to 325.12 mm per Table 5. Table 2 lists example board sizes and the mounting holes required for the motherboard. A BTX chassis should provide mounting points and add-in card apertures in the rear panel for the largest board that it is intended to support. Table 5. Board Size Options Board Designation Maximum Nominal Board Width Typical Number of Add-in Card Slots Available picobtx 203.20 mm 1 A, B, C, D Required Mounting Hole Locations microbtx 264.16 mm 4 A, B, C, D, E, F, G BTX 325.12 mm 7 A, B, C, D, E, F, G, H, J, K Notes Page 11
A B 6.35 ± 0.13 [0.250 ± 0.005] 0.000 (39.09) [1.539] 3 (50.59) [1.992] 2 5.08 ± 0.13 [0.200 ± 0.005] 0.000 Rear Panel I/O 191.77 [7.550] 1 212.09 [8.350] 1 232.41 [9.150] 1 252.73 [9.950] 1 273.05 [10.750] 1 A Y C E H X 293.37 [11.550] 1 313.69 [12.350] 1 (35.04) [1.380] 3 266.70 ± 0.25 [10.500 ± 0.010] F J (97.91) [3.855] 2 124.00 [4.882] Example PCI Express Connectors Example PCI Connectors 254.00 [10.000] 1.58 +0.20-0.13 +0.008 [0.062-0.005 ] C B D G K 203.20 ± 0.25 [8.000 ± 0.010] 4 264.16 ± 0.25 [10.400 ± 0.010] 5 Notes: 1. Connector card slot centerline. 2. Connector key centerline. 3. Connector pin 1 reference. 4. picobtx board (maximum 1 slot) 5. microbtx board (maximum 4 slots) 6. BTX board (maximum 7 slots) 7. Tolerance unless otherwise noted ± 0.25 [0.010]. 191.77 [7.550] 232.41 [9.150] 325.12 ± 0.25 [12.800 ± 0.010] 6 293.37 [11.550] Add-in Card Connector X Direction Location Card type X 2 X 3 PCI 5V 97.91 [3.855] (35.04) [1.380] PCI 3.3V 49.64 [1.954] (35.04) [1.380] AGP 3.3V 83.11 [3.272] (60.61) [2.386] AGP 1.5V 103.11 [4.059] (60.61) [2.386] PCI Express 50.59 [1.992] (39.09) [1.539] 10X Ø 3.96 +0.05-0.03 +0.002 [0.156-0.001 ] Ø 0.20 [0.008] A B C Mounting Holes OM16309 Figure 2. BTX Form Factor Board and Mounting Hole Dimensions 3.2 Volumetric Zones Volumetric zones are defined to provide a definition for mechanical requirements for each of the key system components areas. These definitions allow components in these areas to be designed separately and integrated without interference. This section describes volumetric zones based from the motherboard planar (referred to as motherboard zones Section 3.2.1), volumetric zones based from the chassis (referred to as chassis zones Section 3.2.2), and the placement requirements for all system components with respect to the zones. These requirements ensure that key system components do not mechanically interfere when they are integrated into a system. Page 12
Figure 3 shows some of these zones. Zones A, B, C, and D are motherboard zones and Zones F, G, and H are chassis zones. Not shown in this figure are chassis zones J and K (under the motherboard). Note that some zones, like Zone A and Zone F, have two heights associated with them. This is to accommodate the two types (heights) of thermal modules and the corresponding system designs. Type I (Standard Height) is intended to be utilized where space is available to maximize the volume available for the thermal module solution design, while Type II (Low Profile) is included as an option for designs where lower profile components in this area are highly valued. Zone D Zone B Zone C Zone A Zone F Motherboard Zone H Type I Zone H Type II Zone G OM16311 Figure 3. Chassis and Motherboard Volumetric Zones (not all zones are shown) Page 13
3.2.1 Motherboard Volumetric Zones Sections 3.2.1.1 and 3.2.1.2 define the footprint and height constraints that comprise the overall motherboard volumetric zones. All components in a BTX-compatible system must adhere to the motherboard volumetric zones according to the requirements in Table 6. Table 6. Categories and Requirements for Motherboard Volumetric Zones Category Examples Requirements Motherboard components Chassis components Transition components Other System components Memory modules, processors, rear panel motherboard connectors and mating cable connectors, component heatsinks, components soldered to motherboard Chassis walls, chassis pan, motherboard mounting features, peripheral mounting brackets Add-in cards, air ducts, Thermal Module, SRM, cabling from the motherboard to system components, motherboard EMI grounding feature Disk drives, front panel cards, system power supply, and other system components not listed above Must fit completely within the motherboard volumetric zones (primary and secondary side) Must not intersect the motherboard volumetric zone at any point. In addition, adequate clearance should be provided between the chassis, the motherboard volumetric and installed system components to avoid component interference and/or damage during shipping or other dynamic conditions. May cross the outer boundary of the motherboard volumetric zone. Some of these components, such as add-in cards, may have their own mechanical volumetric specifications which should be considered by the designer in addition to those specified in this document. The Thermal Module should not intersect the top boundary of Zones A and C, but will intersect the boundaries adjacent to chassis Zones F and G to extend into these zones. Must not intersect the motherboard volumetric zone at any point. In addition, should provide adequate clearance between installed system components and the motherboard volumetric zone to avoid component interference and/or damage during shipping or other dynamic conditions. Page 14
3.2.1.1 Motherboard Primary Side Volumetric Zones Motherboard primary side volumetric zones are defined in Figure 4. All areas are defined from the top surface of the motherboard. (325.12) [12.800] A 0.000 50.80 [2.000] 176.50 [6.949] B 0.000 Zone C 38.10 [1.500] Zone B 34.30 [1.350] (266.70) [10.500] 162.80 [6.409] Zone D 2 34.30 [1.350] Zone A 86.00 [3.386] - Type I 60.60 [2.386] - Type II C 62.50 [2.461] 10X Ø 10.92 [0.430] Notes: 1. No components or traces allowed in the crosshatched areas. 2. To avoid mechanical interference, motherboard and chassis designers who choose to support add-in cards in zone "D" should observe additional mechanical constraints imposed by the add-in card specifications. OM16304 Figure 4. Motherboard Primary Side Volumetric Zone Page 15
3.2.1.2 Motherboard Secondary Side Zones Motherboard secondary side volumetric zones are defined in Figure 5. All areas are defined from the bottom surface of the motherboard. Also defined in Figure 5 are areas for inclusion of optional EMI features. If needed, EMI grounding features extending from the motherboard to the chassis should only be designed within these areas to ensure contact with the corresponding areas reserved in the chassis below the board for this purpose. All zone boundaries are defined to avoid interference with components in the assembled condition. Additional clearances based on target assembly processes may need to be incorporated. (325.12) [12.800] See Detail A (293.37) [11.550] (232.41) [9.150] 197.50 [7.776] 193.02 [7.599] (191.77) [7.550] 191.20 [7.528] 186.02 [7.324] 177.17 [6.975] 157.00 [6.181] 149.17 [5.873] 118.67 [4.672] 108.67 [4.278] 78.17 [3.078] 50.17 [1.975] 41.32 [1.627] 35.00 [1.378] 34.32 [1.351] 13.00 [0.512] 0.000 0.64 [0.025] B A 0.000 11.70 [0.461] (266.70) [10.500] (124.00) [4.882] 10X Ø 25.00 [0.984] 2X 62.65 [2.467] 2X 72.53 [2.856] 2X 82.65 [3.254] 2X 102.53 [4.037] 122.00 [4.803] 2X 157.00 [6.181] 2X 97.00 [3.819] 110.00 [4.331] 0.64 [0.025] No components or traces allowed 4.50 [0.177] height off datum A No components allowed (cone shape volume, Ref section A-A) 7.00 [0.276] height off datum A 5.50 [0.217] 7.00 [0.276] height off datum A. Height restriction does not apply to components maintaining conductive path between motherboard and chassis for EMI purposes. Refer to corresponding chassis requirements in Figure 6. 10X Ø 10.16 [0.400] 10X (Ø 3.96) [0.156] (Ø 10.16) [0.400] A A Section A-A (254.00) [10.000] (10.16) [0.400] (Ø 25.00) [0.984] 10X Detail A 8X Truncated Zones Near Board Edge C A OM16301 Figure 5. Motherboard Secondary Side Volumetric Zones Page 16
3.2.2 Chassis Volumetric Zones Figure 6 defines the footprint and heights that comprise the chassis volumetric zones as referenced from the top surface of the chassis pan. All components in a BTX-compatible system must adhere to the chassis volumetric zones according to the requirements in Table 7. Note that although Figure 6 shows the zones for the widest motherboard (seven slot board), rules for Zone J scale according to the width of the motherboard being used. Requirements in this section do not affect the volume beyond the extensible edge of the motherboard that the system is designed to accommodate. Table 7. Categories and Requirements for Chassis Zones Category Examples Requirements Motherboard Components Chassis Components Transition Components Other System Components Memory modules, processors, rear panel motherboard connectors and mating cable connectors, component heatsinks, and components soldered to motherboard Chassis pan, board mounting features, and drive bays SRM and Thermal Module Disk drives and system power supply Must not intersect any of the chassis volumetric zones at any point. In addition, adequate clearance should be provided between installed system components and the chassis volumetric to avoid component interference and/or damage during shipping or other dynamic conditions. Must not intersect volumetric zones G, H, or F. Chassis features in Zone K must not intersect the upper boundary of Zone K. Only the features called out in Figure 6 and Figure 7 are allowed in Zone J. No other chassis features should intersect this zone. Board mounting features should stay within the zones specified for these features. May cross the outer boundary of some chassis zones. Components such as an SRM may have their own requirements which should be considered by the designer in addition to those specified in this document. Must not intersect any of the chassis volumetric zones at any point. In addition, adequate clearance should be provided between installed system components and the chassis volumetric to avoid component interference and/or damage during shipping or other dynamic conditions. Page 17
Chassis Rear Panel 5.08 [0.200] 0.000 (29.21) [1.150] (191.77) [7.550] 198.12 [7.800] (232.41) [9.150] (293.37) [11.550] 320.04 [12.600] 0.000 6.35 [0.250] G Zone K Zone K Zone J (124.00) [4.882] See Detail A H (260.35) [10.250] 260.35 [10.250] 10.16 ± 0.10 [0.400 ± 0.004] J E 2X 302.85 [11.923] 305.35 [12.022] Zone F 41.03 [1.615] Zone H Zone G 50.80 [2.000] 62.50 [2.461] Zone F Interface Plane Zone H 176.50 [6.949] 186.27 [7.333] 97.75 [3.848] height off datum J : Type I thermal module 72.35 [2.848] height off datum J : Type II thermal module (5.50) [0.217] (10.16) [0.400] 10X Ø 25.00 [0.984] 10X Ø 10.16 [0.400] Ø 25.00 [0.984] J Zone G Zone H Zone J 50.09 [1.972] height off datum J 11.75 [0.463] height off datum J Volume shared with chassis pan guide features as specified in Figure 7 (Ref Detail A). 3.16 [0.124] height off datum J No feature placement with exception of those features defined in Figure 7. (Ø 10.16) [0.400] Section A-A E Zone K 3.16 [0.124] height off datum J A A Denotes cone shape chassis keep-in volume as depicted in Detail A. Motherboard mounting feature must stay within this volume. 10X Detail A 8X Truncated Volumes OM16302 Figure 6. Chassis Volumetric Zones Page 18
3.3 Chassis Mechanical Interfaces In addition to the other mechanical requirements in this specification, a BTX chassis should provide the interface features listed in Table 8. Table 8. Chassis Mechanical Interface Requirements Mechanical Interface Features Areas on the chassis pan for interface with board EMI grounding features Reference Figure 7 Attach features for a Support and Retention Module (SRM) Figure 7 and Figure 8. Common interface to a thermal module Section 3.3.3, Figure 10 Rear panel aperture for interface with the motherboard rear panel connectors 3.3.1 Chassis Interface for EMI Grounding Section 3.3.4, Figure 11 The chassis should allow areas as shown in Figure 7 to interface with the grounding features on the motherboard. These areas must be unpainted and allow conduction to chassis for grounding. 3.3.2 Chassis Interface to Support and Retention Module A Support and Retention Module, or SRM, is a system component that can be used to support an area of the motherboard and loads upon the motherboard such as a thermal module. An SRM can reside in chassis volumetric zone J and also may share chassis zone K as well as the secondary side motherboard zone. A BTX chassis should include the features shown in Figure 7 to provide a standard interface for SRMs. Accordingly, an SRM for a BTX chassis and motherboard should be designed to fit into and mate with these features. The interface between the SRM and the motherboard will vary depending on the motherboard and thermal module design. Page 19
4.45 [0.175] 13.00 [0.512] 6.38 [0.251] 99.00 [3.898] 191.20 [7.528] 197.50 [7.776] Chassis Rear Panel G 0.000 0.000 35.00 [1.378] 157.00 [6.181] (191.77) [7.550] (232.41) [9.150] 5.72 [0.225] See Detail B, Figure 8 11.70 [0.461] 2X 97.00 [3.819] 200.00 ± 0.50 [7.874 ± 0.020] 185.00 [7.283] See Detail C, Figure 8 (124.00) [4.882] 2X 157.00 [6.181] 153.00 ± 0.30 [6.024 ± 0.012] 160.10 ± 0.30 [6.303 ± 0.012] 10.16 ± 0.10 [0.400 ± 0.004] J E 272.53 [10.730] H See Detail A, Figure 8 10.00 ± 0.50 [0.394 ± 0.020] 55.88 [2.200] 2X 16.97 [0.668] 2X 7.91 ± 0.30 [0.311 ± 0.012] (254.00) [10.000] P 2X 2 Ø 0.25 [0.010] J G H 57.79 [2.275] 111.76 [4.400] 2X 145.70 ± 0.25 [5.736 ± 0.010] Ø 0.25 [0.010] J P Flat EMI contact area at elevation of datum J to be free of paint and coatings that would prevent electrical contact with motherboard enabled feature[s]. Notes: 1. Chassis datum axes G and H are coincident to motherboard datum axes B and C and simulated by chassis to motherboard fastening features. Chassis datum axis E corresponds to motherboard elevation plane as simulated by chassis fastening features. 2. 6-32 threaded standoff with height of 3.00 ± 0.15 [0.118 ± 0.006] above datum J and Ø 7.11 ± 0.12 [0.280 ± 0.005] required. 3. All critical interface features are dimensioned. All other features shown for reference only. OM16310 Figure 7. Chassis Interface to SRM Requirements Page 20
(2.32) [0.091] C 5.63 ± 0.20 [0.222 ± 0.008] 0.40 [0.016] J P 3.50 ± 1.00 [0.138 ± 0.039] 2.50 ± 0.25 [0.098 ± 0.010] 4 6.00 Max [0.236] A 3.00 ± 0.50 [0.118 ± 0.020] 0.50 [0.020] J P (7.91) [0.311] 20.00 Max [0.787] B 26.00 Max [1.024] B 16.00 Max [0.630] 2X R1.0 Max [0.039] 4 J Section C-C 3.20 Max [0.126] C 27.00 Max [1.063] 2X Detail B Retainer Slot J J Section A-A 3.00 ± 0.25 [0.118 ± 0.010] 2.20 ± 0.20 [0.087 ± 0.008] 4 A 4X Detail A Guide 2X 2.32 ± 0.20 [0.091 ± 0.008] (5.63) [0.222] 4X R0.75 Max [0.030] R0.50 Max [0.020] Section D-D J 2X 3.69 ± 0.30 [0.145 ± 0.012] (13.00) [0.512] Section B-B Note: 4. Required on two guide features only. J D 7.10 [0.280] Max 1.00 [0.039] M J P (55.88) [2.200] Detail C Retainer Tab D 7.10 ± 0.30 [0.280 ± 0.012] 2X 2.00 ± 0.25 [0.079 ± 0.010] OM16313 Figure 8. Chassis Interface to SRM Requirement Details Page 21
3.3.3 Chassis Interface to Thermal Module In order to provide a standard interface between a thermal module and the chassis, a common physical interface plane and geometry are required. Figure 9 shows the relationship between the motherboard zones (Section 3.2.1), the thermal module, the chassis/thermal module interface, and the chassis zones (Section 3.2.2). Thermal Module Zone C Zone B Zone A Zone F Zone D Zone H Zone G To Chassis Inlet Vent Zone H Chassis Duct Interface OM16312 Figure 9. Chassis to Thermal Module Interface and Relation to Chassis and Motherboard Zones Page 22
Figure 10 defines both a plane relative to the motherboard datums as well as the surface geometry that should be provided on that plane by the chassis (and designed for the thermal module). The surface consists of a frame of minimum width around the window defined for airflow to the thermal module. The primary purpose for this interface and connection is to provide external air from a vent in the chassis to the thermal module. For this reason, the air channel and the chassis vent should be designed so that there is minimal impedance to airflow from outside the chassis to the defined interface. 305.35 ± 0.50 [12.022 ± 0.020] System Front Motherboard Elevation 2X 3.00 [0.118] Interface area to thermal module 3 Interface Plane Airflow Inlet Area 2 0.000 E (2.00) [0.079] (98.00) [3.858] 92.00 [3.622] 67.67 [2.664] (97.25) [3.829] 5 (71.85) [2.829] 6 87.25 [3.435] 5 61.85 [2.435] 6 E Chassis Bottom J J 2X 4.00 [0.157] 6.00 [0.236] Notes: 1. Chassis datum axis G and H are coincident to motherboard datum axis B and C as simulated by chassis to motherboard fastening features. Chassis datum plane E corresponds to bottom side of motherboard as simulated by chassis to motherboard fastening features. Chassis datum plane J corresponds to the top surface of the chassis bottom. 2. Airflow volume between interface plane and chassis airflow inlet shall be isolated from internal chassis volume to prevent re-circulation of air. 3. Do not place any topographical features in this area on this side. 4. All dimensions basic unless indicated otherwise. 5. Applicable to Type I system. 6. Applicable to Type II system. OM16303 Figure 10. Chassis Requirements for Thermal Module Interface Definition Page 23
3.3.4 Chassis Rear Panel I/O Interface Requirements Figure 11 defines the chassis cutout window and associated margins for interface with the rear panel I/O shield. Chassis I/O aperture should be a simple cutout of the chassis rear panel. Recessing the I/O aperture will prevent the case from accepting compliant I/O shields. 2.29 [0.090] Min keepout around opening 1 4X R1.0 [0.039] Max Typ 8.46 ± 0.25 [0.333 ± 0.010] 1.32 [0.052] 0.79 [0.031] Allowable wall thickness 39.45 ± 0.20 [1.553 ± 0.008] Chassis I/O Aperture E (10.16) [0.400] E J J 169.54 ± 0.20 [6.675 ± 0.008] 2.16 ± 0.25 [0.085 ± 0.010] 2.47 ± 0.25 [0.097 ± 0.010] G G Motherboard mount feature Notes: 1. Do not place any topographical features in this area on either the inside or the outside surface of chassis rear panel. Do not paint this area. 2. Datum axis G is coincident to datum B of motherboard on Figure 12. 3. Chassis datum plane E corresponds to bottom side of motherboard as simulated by chassis fastening features. Chassis datum plane J corresponds to the top surface of the chassis bottom. OM16307 Figure 11. Chassis Rear Panel I/O Aperture Requirements Page 24
3.4 Motherboard Mechanical Interfaces Balanced Technology Extended (BTX) Interface Specification 3.4.1 Motherboard Rear Panel Interface Requirements All rear panel external motherboard connectors (and their mating cable connectors) must pass through the motherboard rear panel I/O shield within the shaded window depicted in Figure 12. Connector Face Connector's Protruding Feature B 2 7.49 ± 0.20 [0.295 ± 0.008] A 32.47 [1.278] Max I/O Connector Protrusion Area B 2 A 1 Motherboard 168.78 Max [6.645] 5.08 Min [0.200] (6.35) [0.250] Notes: 1. Bottom of motherboard is coincident with datum E on Figure 11. 2. Datum B is coincident with datum G on Figure 11. OM16306 Figure 12. Motherboard Rear Panel I/O Aperture Requirements Page 25
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4. Electrical Interface Requirements Balanced Technology Extended (BTX) Interface Specification 4.1 Motherboard Power Supply Connectors Figure 13 defines the required pinout for the required connectors listed in Table 9. The connectors provide a standard interface between a BTX motherboard and a compatible system power supply. Further information on critical signals is defined in Section 4.2. For additional information on the design of compatible system power supplies, refer to the design guides at the location listed in Section 5. Table 9. Power Supply Connectors Connector Description Status Main Power Connector Required on all motherboards +12V Power Connector Required on all motherboards Board-mounted Header Molex 44206-0007 or equivalent Molex 39-29-9042 or equivalent Mating Power Supply Receptacle Molex 39-01-2240 or equivalent Molex 39-01-2040 or equivalent Electrical Signal Implementation Per Figure 13 and Section 4.2 Per Figure 13 and Section 4.2 Pin 13 Pin 1 +3/3VDC -12VDC COM PS_ON# COM COM COM NC +5VDC +5VDC +5VDC COM +3.3VDC +3.3VDC COM +5VDC COM +5VDC COM PWR_OK +5VSB +12VDC +12VDC +3.3VDC Pin 3 Pin 1 +12VDC COM +12VDC COM +12V Power Connector Main Power Connector OM16308 Figure 13. Power Supply Connectors Page 27
4.2 Motherboard Power and Control Signal Definitions 4.2.1 +5VSB +5VSB is a standby voltage supply that is active whenever AC power is present to the system power supply. It provides a power source for circuits that must remain operational when the three main DC outputs (+12VDC, +5VDC, +3.3VDC) are in a disabled state. Example uses include soft power control, Wake on LAN technology, wake-on-modem, intrusion detection, or suspend (sleep) state activities. The maximum current available from the +5VSB output depends on the design of the system power supply. 4.2.2 PS_ON# PS_ON# is an active low, TTL-compatible signal that allows the motherboard to enable the three main system power supply DC output rails (+3.3VDC, +5VDC, +12VDC). PS_ON# is pulled up to +5VSB via a 10 kω resistor internal to the system power supply. When PS_ON# is pulled to TTL low, the DC outputs are enabled by the system power supply. When PS_ON# is held to TTL high by the motherboard or left open circuited, the system power supply shall not deliver current at the main DC outputs and shall hold them at zero potential with respect to ground. Table 10. PS_ON# Signal Characteristics 4.2.3 PWR_OK Min. Max. V IL, Input Low Voltage 0.1 V 0.8 V I IL, Input Low Current, V in = 0.4 V -1.6 ma V IH, Input High Voltage, I in = -200 µa 2.0 V V IH open circuit, I in = 0 5.25 V PWR_OK is a power good signal asserted by the system power supply to indicate that the +5VDC, +3.3VDC, and +12VDC outputs are above the undervoltage thresholds of the power supply. When this signal is asserted high, the system power supply has sufficient energy stored by the converter to guarantee continuous power operation for a minimum hold-up time per the system power supply s specification. Conversely, when one or more of the output voltages fall below their undervoltage threshold, or when mains power has been removed for a time sufficiently long so that power supply operation is no longer guaranteed beyond the hold up time, PWR_OK will be de-asserted to a low state by the power supply. Page 28
Table 11. PWR_OK Signal Characteristics Parameter Value Signal type +5 V TTL compatible Logic level low < 0.4 V while sinking 4 ma Logic level high Between 2.4 V and 5 V output while sourcing 200 µa High-state output impedance 1 kω from output to common PWR_OK delay 100 ms < T 3 < 500 ms PWR_OK rise time T 4 10 ms AC loss to PWR_OK hold-up time T 5 16 ms Power-down warning T 6 1 ms T1 VAC ~ T5 +12VDC +5VDC +3.3VDC PS_ON# } O/P's PWR_OK 95% 10% T2 T3 ~ ~ T4 T6 PWR_OK Sense Level = 95% of nominal timing_3_5_12b 4.2.4 Voltage Tolerances Figure 14. Power Timing The system power supply shall guarantee that the tolerances for the main DC outputs comply with the values listed in Table 12, subject to the limits of the system power supply s specified capabilities. Table 12. DC Output Voltage Tolerances Voltage Rail Tolerance +3.3VDC ± 5% +5VDC ± 5% +12VDC ± 5% -12VDC ± 10% +5VSB ± 5% Page 29
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5. Additional Information Balanced Technology Extended (BTX) Interface Specification For additional information beyond the requirements of this specification, refer to: http:\\www.formfactors.org Page 31
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