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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 2
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.
Version 1.0a, February 2004
† Other names and brands may be claimed as the property of others.
Copyright 2003, 2004 Intel Corporation. All rights reserved.
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 3
Revision History
Version Description Date 1.0 Initial release. September 2003 1.0 a Incorporated Errata A and other editorial changes. February 2004
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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............................................................................................................................... 13
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 EMC 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
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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. Reference Datums ....................................................................................................................... 11 Table 6. Board Size Options....................................................................................................................... 11 Table 7. Categories and Requirements for Motherboard Volumetric Zones ............................................. 14 Table 8. Categories and Requirements for Chassis Zones ....................................................................... 17 Table 9. Chassis Mechanical Interface Requirements............................................................................... 19 Table 10. Power Supply Connectors.......................................................................................................... 27 Table 11. PS_ON# Signal Characteristics ................................................................................................. 28 Table 12. PWR_OK Signal Characteristics................................................................................................ 29 Table 13. DC Output Voltage Tolerances .................................................................................................. 29
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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 Benefits Low profile options Easy integration in small, thin form factor systems In-line core layout Optimized for efficient system cooling Scaleable board dimensions
Multiple system sizes and configurations
Structural board support mechanisms
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) Motherboard geometry and mounting hole locations (mechanical)
Section 3.1
Motherboard volumetric zones (mechanical) Section 3.2
Chassis volumetric zones (mechanical) Section 3.2.2
Board/Chassis Interfaces
Rear panel chassis I/O locations and openings (mechanical)
Section 3.3.4 and Section 3.4.1
Main power connector (electrical and mechanical)
Section 4 Board/Power Supply Interfaces
+12V power connector (electrical and mechanical)
Section 4
Chassis interface to SRM (mechanical) Section 3.3.2 Chassis interfaces to other components
Chassis interface to Thermal Module (mechanical)
Section 3.3.3
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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1.1 Terminology Table 3 explains terms introduced in this specification.
Table 3. Terminology
Term Definition Support and Retention Module (SRM)
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.
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 Location PCI Express* Specifications http://www.pcisig.com/specifications/pciexpress/ Conventional PCI Specifications http://www.pcisig.com/specifications/conventional/ ATX and microATX Specifications http://www.formfactors.org
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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.
OM16305
Expandable Tower (Side View)
Note: Illustrations not to scale
Desktop (Top View)
Small Form Factor (Top View)
Rear Panel I/O
PowerSupply
Unit
Thermal Module
System/Processor Fan(s)
Cha
ssis
Hard Drive
Mobile OpticalDrive
System Memory
I/O Card Slots
Power Supply Unit
Thermal Module
System/Processor Fan(s)
I/O Card on Riser
Front Side I/OPeripherals
Cha
ssis
System Memory
OpticalDisk Drive
Rear Panel I/O
I/O Card Slots
Rea
r Pan
el I/
OSystem Memory
Processor
Thermal Module
Optical Disk Drive
Optical Disk Drive
Floppy Disk Drive
Hard Disk Drive
Power SupplyUnit
Syst
em/P
roce
ssor
Fan
(s)
Cha
ssis
Front Side I/OPeripherals
Processor
Processor
Figure 1. Example BTX Board and System Layouts
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3. Mechanical Requirements
This chapter describes the mechanical requirements of BTX system components and the associated interfaces.
Reference Datums are maintained throughout the drawings in this chapter. Table 5 lists the Datums and the figure in which they are defined.
Table 5. Reference Datums
Datum Defined A Figure 2 B Figure 2 C Figure 2 E Figure 7 G Figure 6 H Figure 6 J Figure 6 P Figure 7
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 6. Table 6 lists typical board sizes and the mounting holes required for the motherboard. A BTX chassis must provide mounting points and should provide add-in card apertures in the rear panel for the largest board that it is intended to support.
Table 6. Board Size Options
Board Designation
Maximum Board Width
Maximum Number of Add-in Card Slots Available
Required Mounting Hole Locations
Notes
picoBTX 203.20 mm 1 A, B, C, D 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
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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OM16309
Notes: 1. Card connector 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].
124.00[4.882]
(97.91)[3.855] 2
(35.04)[1.380] 3
Example PCIConnectors
313.
69[1
2.35
0]1
293.
37[1
1.55
0]1
232.
41[9
.150
]1
212.
09[8
.350
]1
273.
05[1
0.75
0]1
252.
73[9
.950
]1
191.
77[7
.550
]1
32
Add-in Card Connector X Direction Location
(39.09) [1.539](60.61) [2.386](60.61) [2.386](35.04) [1.380](35.04) [1.380]
X
50.59 [1.992]103.11 [4.059]83.11 [3.272]49.64 [1.954]97.91 [3.855]
X
PCI ExpressAGP 1.5VAGP 3.3VPCI 3.3VPCI 5V
Card type
Example PCI ExpressConnectors
203.20[8.000] 4
191.
77[7
.550
]
232.
41[9
.150
]
293.
37[1
1.55
0]
264.16[10.400] 5
325.12[12.800] 6
254.00[10.000]
C1.58 +0.20- 0.13
[0.062 ]+0.008- 0.005
A
(39.09)[1.539] 3
(50.59)[1.992] 2
266.70[10.500]
B6.35 ± 0.13
[0.250 ± 0.005]
0.000
Rear Panel I/O
5.08
± 0
.13
[0.2
00 ±
0.0
05]
0.00
0
X
Y
Mounting Holes
Ø 0.20 [0.008] A B C
10X Ø 3.96 +0.05- 0.03
[0.156 ]+0.002- 0.001
A E HC
F
GB D K
J
View Orientation Defined byThird Angle Projection
Figure 2. BTX Form Factor Board and Mounting Hole Dimensions
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 13
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.
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.
OM16311
Zone B
Zone C
Zone D
Zone A
Zone F
Zone G
Zone H
MotherboardZone H
Type IIType I
Figure 3. Chassis and Motherboard Volumetric Zones (not all zones are shown)
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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 7.
Table 7. Categories and Requirements for Motherboard Volumetric Zones
Category Examples Requirements Motherboard components
Memory modules, processors, rear panel motherboard connectors, rigid portions of motherboard-terminated cable assemblies, component heatsinks, components soldered to motherboard
Must fit completely within the motherboard volumetric zones (primary and secondary side)
Chassis components
Chassis walls, chassis pan, motherboard mounting features, peripheral mounting brackets
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.
Transition components
Add-in cards, air ducts, Thermal Module, SRM, flexible cabling from the motherboard to other system components, motherboard EMC grounding features
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 can reside across multiple zones (typically Zones A, C, F, G, and H. The Thermal Module should not intersect the top boundaries of any of the volumetric zones.
Other System components
Disk drives, front panel cards, system power supply, and other system components not listed above
Must not intersect the motherboard volumetric zone at any point. In addition, adequate clearance should be provided between installed system components and the motherboard volumetric zone to avoid component interference and/or damage during shipping or other dynamic conditions.
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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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.
OM16304
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.
A
2
B
0.000
C
162.80[6.409]
0.00
0
50.8
0[2
.000
]
176.
50[6
.949
]
(325.12)[12.800]
(266.70)[10.500]
Zone D34.30 [1.350]
Zone A86.00 [3.386] - Type I60.60 [2.386] - Type II
Zone B34.30 [1.350]
Zone C38.10 [1.500]
62.5
0[2
.461
] 10X Ø 10.92[0.430]
View Orientation Defined byThird Angle Projection
Figure 4. Motherboard Primary Side Volumetric Zone
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 16
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 EMC features. If needed, EMC 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.
No components or traces allowed
7.00 [0.276] height
7.00 [0.276] height. Height restriction does not applyto components maintaining conductive path betweenmotherboard and chassis for EMI purposes. Refer tocorresponding chassis requirements in Figure 6.
No components allowed(cone shape volume, Ref section A-A)
4.50 [0.177] height
A
Section A-A
10X Detail A8X Truncated Zones Near Board Edge
A A
(Ø 25.00)[0.984]
10.16[0.400](Ø 10.16)
[0.400]
See Detail A
(325.12)[12.800]
B
0.000
11.70[0.461]
2X 62.65[2.467] 2X 72.53
[2.856]
2X 102.53[4.037]
2X 82.65[3.254]
110.00[4.331]122.00
[4.803]
2X 97.00[3.819]
2X 157.00[6.181]
(254.00)[10.000]
C10X Ø 10.16[0.400]
10X (Ø 3.96)[0.156]
5.50[0.217]
(266.70)[10.500]
(124.00)[4.882]
0.00
0
34.3
2[1
.351
]
13.0
0[0
.512
]
41.3
2[1
.627
]35
.00
[1.3
78]
149.
17[5
.873
]
50.1
7[1
.975
]
78.1
7[3
.078
]
118.
67[4
.672
]10
8.67
[4.2
78]
177.
17[6
.975
]15
7.00
[6.1
81]
186.
02[7
.324
]
191.
20[7
.528
]
(191
.77)
[7.5
50]
197.
50[7
.776
]19
3.02
[7.5
99]
(232
.41)
[9.1
50]
(293
.37)
[11.
550]
OM16301
0.64[0.025]
0.64[0.025]
10X Ø 25.00[0.984]
A
View Orientation Defined byThird Angle Projection
Note: Main view as viewed from motherboard secondary side.
Figure 5. Motherboard Secondary Side Volumetric Zones
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 17
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 8. 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 8. Categories and Requirements for Chassis Zones
Category Examples Requirements Motherboard Components
Memory modules, processors, rear panel motherboard connectors and rigid portions of motherboard-terminated cable assemblies, component heatsinks, and components soldered to motherboard
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.
Chassis Components
Chassis pan, board mounting features, and drive bays
Must not intersect volumetric zones F, G, or H. Chassis features in Zone K must not cross the upper boundary of Zone K. Only the interface features called out in Figure 7 and Figure 8 are allowed in Zones F, G, H, and J. No other chassis features should intersect this zone. Board mounting features should stay within the zones specified for these features.
Transition Components
SRM and Thermal Module 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.
Other System Components
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.
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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97.75 [3.848] height off datum : Type I thermal moduleJ72.35 [2.848] height off datum : Type II thermal moduleJ
50.09 [1.972] height off datum J
0.000
305.35[12.022]
2X 302.85[11.923]
50.8
0[2
.000
]
41.0
3[1
.615
]
62.5
0[2
.461
]
176.
50[6
.949
]18
6.27
[7.3
33]Interface Plane
Zone F
Zone G
11.75 [0.463] height off datum Volume shared with chassis pan guide featuresas specified in Figure 7 (Ref Detail A).
J
3.16 [0.124] height off datum J
Zone H
3.16 [0.124] height off datum No feature placement with exception of thosefeatures defined in Figure 7.
J
Zone K
Zone J
Denotes cone shape chassis keep-in volume as depicted in Detail A.Motherboard mounting feature must stay within this volume.
OM16302
Zone
G
Zone F
Zone J
Zone K
J
Section A-A
10X Detail A8X Truncated Volumes
A A
(Ø 10.16)[0.400]
10.16[0.400]
(Ø 25.00)[0.984]
0.00
0
5.08
[0.2
00]
(191
.77)
[7.5
50]
(29.
21)
[1.1
50]
(232
.41)
[9.1
50]
(293
.37)
[11.
550]
320.
04[1
2.60
0]
6.35[0.250]
(124.00)[4.882]
260.35[10.250]
198.
12[7
.800
]
G
H
(260.35)[10.250]
(5.50)[0.217]
10X Ø 25.00[0.984]
10X Ø 10.16[0.400]
Zone KZo
ne H
Zone
H
See Detail A
J
Chassis PanPlanar
View Orientation Defined byThird Angle Projection
Figure 6. Chassis Volumetric Zones
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
Page 19
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 9.
Table 9. Chassis Mechanical Interface Requirements
Mechanical Interface Features Reference Areas on the chassis pan for interface with board EMC grounding features
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
Section 3.3.4, Figure 11
3.3.1 Chassis Interface for EMC Grounding 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 loads associated with 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 must include interfaces as defined by 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.
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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OM16310
4.45
[0.1
75]
0.00
0
157.
00[6
.181
]
191.
20[7
.528
](1
91.7
7)[7
.550
]19
7.50
[7.7
76]
(232
.41)
[9.1
50]
13.0
0[0
.512
]35
.00
[1.3
78]
J E
10.16 ± 0.10[0.400 ± 0.004]
Chassis RearPanel
0.000
See Detail B,Figure 8
185.00[7.283]
200.00 ± 0.50[7.874 ± 0.020]
160.10 ± 0.30[6.303 ± 0.012]
153.00 ± 0.30[6.024 ± 0.012]
Notes:1. Chassis datum axes and are coincident to motherboard datum axes and and simulated by chassis to motherboard fastening features. Chassis datum axis corresponds to motherboard elevation plane as simulated by chassis fastening features.
G HB C
E
2. 6-32 threaded standoff with height of 3.00 ± 0.15 [0.118 ± 0.006] above datum 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.
G
H
5.72[0.225]
11.70[0.461]
2X 97.00[3.819]
2X 157.00[6.181]
(254.00)[10.000]
(124.00)[4.882]See Detail C,
Figure 8
See Detail A,Figure 8
99.00[3.898]
272.53[10.730]
2X 7.91 ± 0.30[0.311 ± 0.012]
10.00 ± 0.50[0.394 ± 0.020]
55.88[2.200]
111.76[4.400]
2X 16.97[0.668]
57.7
9[2
.275
]
P
Ø 0.25 [0.010] J P
2X 145.70 ± 0.25 [5.736 ± 0.010]
Ø 0.25 [0.010] J G H
2X 2
6.38[0.251]
J
Flat EMI contact area at elevation of datum to be free of paint and coatingsthat would prevent electrical contact with motherboard enabled feature[s].
J
View Orientation Defined byThird Angle Projection
MotherboardElevation
4. Implement only on two front guide features. Omit on two rear guide features.
Figure 7. Chassis Interface to SRM Requirements
Balanced Technology Extended (BTX) Interface Specification Version 1.0a
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J
Section C-C
(2.32)[0.091]
3.80 Max[0.150]
20.00 Max[0.787]
J
(5.63)[0.222]
Section B-B
4X R0.75 Max [0.030]
(13.00)[0.512]
2X 3.69 ± 0.30 [0.145 ± 0.012]
2X 2.32 ± 0.20 [0.091 ± 0.008]
2X 2.00 ± 0.25 [0.079 ± 0.010]
J
4X Detail AGuide
(7.91)[0.311]
2X R1.0 Max [0.039]
4
2.20 ± 0.20[0.087 ± 0.008]
4
A
A
6.00 Max[0.236]
Section A-A
16.00 Max[0.630]
J
2.50 ± 0.25[0.098 ± 0.010]
4
3.50 ± 1.00[0.138 ± 0.039]
OM16313
Section D-D
3.00 ± 0.25[0.118 ± 0.010]
J
R0.50 Max [0.020]
26.00 Max[1.024]
BB
C
C
2X Detail BRetainer Slot
26.00 Max[1.024]
0.40 [0.016] J P
5.63 ± 0.20 [0.222 ± 0.008]
0.50 [0.020] J P
3.00 ± 0.50 [0.118 ± 0.020]
Detail CRetainer Tab
7.10 ± 0.30[0.280 ± 0.012]
(55.88)[2.200]
DD
1.00 [0.039] M J P
7.10 [0.280] Max
Notes:1. Chassis datum axes and are coincident to motherboard datum axes and and simulated by chassis to motherboard fastening features. Chassis datum axis corresponds to motherboard elevation plane as simulated by chassis fastening features.
G HB C
E
2. 6-32 threaded standoff with height of 3.00 ± 0.15 [0.118 ± 0.006] above datum 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.4. Implement only on two front guide features. Omit on two rear guide features.
J
View Orientation Defined byThird Angle Projection
Figure 8. Chassis Interface to SRM Requirement Details
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Page 22
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).
OM16312
Zone B
Zone C
Zone D
Zone A
Zone F
Zone G
Zone H
Zone H
Thermal Module
To ChassisInlet Vent
ChassisDuct Interface
Figure 9. Chassis to Thermal Module Interface and Relation to Chassis and Motherboard Zones
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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.
OM16303
Notes:1. Chassis datum axis and are coincident to motherboard datum axis and as simulated by chassis to motherboard fastening features. Chassis datum plane corresponds to bottom side of motherboard as simulated by chassis to motherboard fastening features. Chassis datum plane corresponds to the top surface of the chassis bottom.
G HB C
E
J
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 the thermal module interface plane side.4. All dimensions basic unless indicated otherwise.5. Applicable to Type I system.6. Applicable to Type II system.
305.
35 ±
0.5
0[1
2.02
2 ±
0.02
0]
System Front
J
E
JChassis Bottom
Motherboard Elevation
(98.00)[3.858]
92.00[3.622]
0.00
0
2X 3.00[0.118]
Interface area tothermal module 3
E
5
67.67[2.664]
6.00[0.236]
87.25[3.435]
661.85[2.435]
5(97.25)[3.829]
6(71.85)[2.829]Airflow Inlet Area
2X 4.00[0.157]
(2.00)[0.079]
Interface Plane 2
View Orientation Defined byThird Angle Projection
GH G
Figure 10. Chassis Requirements for Thermal Module Interface Definition
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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.
OM16307
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 is coincident to datum of motherboard. 3. Chassis datum plane corresponds to bottom side of motherboard as simulated by chassis fastening features. Chassis datum plane corresponds to the top surface of the chassis bottom.
E
8.46 ± 0.25[0.333 ± 0.010]
1.32 [0.052]0.79 [0.031]Allowable wall thickness
169.54 ± 0.20[6.675 ± 0.008]
2.16 ± 0.25[0.085 ± 0.010]
39.45 ± 0.20[1.553 ± 0.008]
1
2.47 ± 0.25[0.097 ± 0.010]
4X R1.0 [0.039] MaxTyp
Motherboardmount feature
Chassis I/O aperture should be a simple cutout of thechassis rear panel. Recessing the I/O aperture will
prevent the case from accepting compliant I/O shields.
2.29 [0.090] Min keepoutaround opening
J
Chassis I/O Aperture E
G
G
J
(10.16)[0.400]
G BE
J
View Orientation Defined byThird Angle Projection
Figure 11. Chassis Rear Panel I/O Aperture Requirements
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3.4 Motherboard Mechanical Interfaces
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.
OM16306
Notes: 1. Bottom of motherboard is coincident with datum . 2. Datum is coincident with datum .
A A
B 2
B 2
7.49 ± 0.20[0.295 ± 0.008]
(6.35)[0.250]
I/O ConnectorProtrusion Area
168.78 Max[6.645]Motherboard
1
E
GB
5.08 Min[0.200]
Connector's Protruding Feature
Connector Face
32.47 [1.278] Max
View Orientation Defined byThird Angle Projection
Figure 12. Motherboard Rear Panel I/O Aperture Requirements
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4. Electrical Interface Requirements
4.1 Motherboard Power Supply Connectors Figure 13 defines the required pinout for the required connectors listed in Table 10. 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 10. Power Supply Connectors
Connector Description
Status Board-mounted Header
Mating Power Supply Receptacle
Electrical Signal Implementation
Main Power Connector Required on all motherboards
Molex† 44206-0007 or equivalent
Molex† 39-01-2240 or equivalent
Per Figure 13 and Section 4.2
+12V Power Connector Required on all motherboards
Molex† 39-29-9042 or equivalent
Molex† 39-01-2040 or equivalent
Per Figure 13 and Section 4.2
OM16308
+3/3VDC
-12VDC
COM
PS_ON#
COM
COM
COM
NC
+5VDC
+5VDC
+3.3VDC
Pin 13 Pin 1
+3.3VDC
COM
+5VDC
COM
+5VDC
COM
PWR_OK
+5VSB
+12VDC
+5VDC
COM
+12VDC
+3.3VDC
+12VDC
+12VDC
COM
Pin 3 Pin 1
COM
+12V Power Connector
Main Power Connector
Figure 13. Power Supply Connectors
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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 11. PS_ON# Signal Characteristics
Min. Max. VIL, Input Low Voltage 0.1 V 0.8 V IIL, Input Low Current, Vin = 0.4 V -1.6 mA VIH, Input High Voltage, Iin = -200 µA 2.0 V VIH open circuit, Iin = 0 5.25 V
4.2.3 PWR_OK 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.
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Table 12. 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 < T3 < 500 ms PWR_OK rise time T4 ≤ 10 ms AC loss to PWR_OK hold-up time T5 ≥ 16 ms Power-down warning T6 ≥ 1 ms
OM16314
VAC
PS_ON#
PWR_OK
O/P's+12VDC+5VDC
+3.3VDC
T1
T4
T5
95%
10%
T3
T2
T6
Figure 14. Power Timing
4.2.4 Voltage Tolerances The system power supply shall guarantee that the tolerances for the main DC outputs comply with the values listed in Table 13, subject to the limits of the system power supply’s specified capabilities.
Table 13. DC Output Voltage Tolerances
Voltage Rail Tolerance +3.3VDC ± 5% +5VDC ± 5% +12VDC ± 5% -12VDC ± 10% +5VSB ± 5%
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5. Additional Information
For additional information beyond the requirements of this specification, refer to:
http:\\www.formfactors.org
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