Balanced Technology Extended
(BTX) Interface Specification
Version 1.0a
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
IMPORTANT INFORMATION AND DISCLAIMERS
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BALANCED TECHNOLOGY EXTENDED (BTX) SPECIFICATION (“SPECIFICATION”),
AND IN PARTICULAR DOES NOT WARRANT OR REPRESENT THAT THIS
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INFORMATION AND DISCLAIMERS” SECTION (PARAGRAPHS 1-4) IS PROVIDED IN
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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.
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
Revision History
Version
Description
Date
1.0
Initial release.
September 2003
1.0 a
Incorporated Errata A and other editorial changes.
February 2004
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
Contents
1. Introduction ...................................................................................................................7
1.1
1.2
Terminology ....................................................................................................................................... 8
Related Documents ........................................................................................................................... 8
2. Form Factor Overview .................................................................................................. 9
3. Mechanical Requirements............................................................................................ 11
3.1
3.2
3.3
3.4
Motherboard Size and Mounting Hole Placement............................................................................. 11
Volumetric Zones............................................................................................................................... 13
3.2.1 Motherboard Volumetric Zones ............................................................................................ 14
3.2.2 Chassis Volumetric Zones.................................................................................................... 17
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
Motherboard Mechanical Interfaces .................................................................................................. 25
3.4.1 Motherboard Rear Panel Interface Requirements ............................................................... 25
4. Electrical Interface Requirements ............................................................................... 27
4.1
4.2
Motherboard Power Supply Connectors ........................................................................................... 27
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
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Balanced Technology Extended (BTX) Interface Specification
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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
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Balanced Technology Extended (BTX) Interface Specification
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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)
Board/Chassis Interfaces
Motherboard geometry and mounting hole
locations (mechanical)
Section 3.1
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)
Section 3.3.4 and Section 3.4.1
Main power connector (electrical and
mechanical)
Section 4
+12V power connector (electrical and
mechanical)
Section 4
Chassis interface to SRM (mechanical)
Section 3.3.2
Chassis interface to Thermal Module
(mechanical)
Section 3.3.3
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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)
Rear Panel I/O
Optical Disk Drive
I/O Card Slots
Power Supply
Unit
Power Supply Unit
Optical Disk Drive
System Memory
Floppy Disk Drive
I/O Card on Riser
Processor
Chassis
System/Processor Fan(s)
Chassis
System Memory
Rear Panel I/O
Hard Disk Drive
Optical
Disk Drive
Processor
Thermal Module
Thermal Module
System/Processor Fan(s)
I/O Card Slots
Front Side I/O
Peripherals
Front Side I/O
Peripherals
Small Form Factor (Top View)
Rear Panel I/O
Power
Supply
Unit
Hard Drive
Processor
Mobile Optical
Drive
Chassis
System Memory
Thermal Module
System/
Processor Fan(s)
Note: Illustrations not to scale
OM16305
Figure 1. Example BTX Board and System Layouts
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Balanced Technology Extended (BTX) Interface Specification
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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 Addin Card Slots
Available
Required Mounting
Hole Locations
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
Notes
Page 11
0.000
A
(39.09)
[1.539] 3
Y
1
1
1
1
1
C
E
313.69
[12.350] 1
Rear Panel I/O
212.09
[8.350]
232.41
[9.150]
252.73
[9.950]
273.05
[10.750]
293.37
[11.550]
B
6.35 ± 0.13
[0.250 ± 0.005]
A
191.77
[7.550] 1
5.08 ± 0.13
[0.200 ± 0.005]
0.000
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
H
(35.04)
[1.380] 3
X
(50.59)
[1.992] 2
(97.91)
[3.855] 2
266.70
[10.500]
F
J
Example PCI
Connectors
Example PCI Express
Connectors
G
203.20
[8.000] 4
K
+0.05
10X Ø 3.96 - 0.03
+0.002
[0.156 - 0.001 ]
Ø 0.20 [0.008] A B C
Mounting Holes
293.37
[11.550]
D
232.41
[9.150]
+0.20
C
1.58 - 0.13
+0.008
[0.062 - 0.005 ]
B
191.77
[7.550]
254.00
[10.000]
124.00
[4.882]
264.16
[10.400] 5
325.12
[12.800] 6
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].
Add-in Card Connector X Direction Location
Card type
X 2
X 3
97.91 [3.855] (35.04) [1.380]
PCI 5V
49.64 [1.954] (35.04) [1.380]
PCI 3.3V
83.11 [3.272] (60.61) [2.386]
AGP 3.3V
103.11 [4.059] (60.61) [2.386]
AGP 1.5V
50.59 [1.992] (39.09) [1.539]
PCI Express
View Orientation Defined by
Third Angle Projection
OM16309
Figure 2. BTX Form Factor Board and Mounting Hole Dimensions
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
eD
Zon
eB
Zon
eA
Zon
eF
Zon
eC
Zon
Motherboard
Zone H
Type I
Zone H
Type II
Zone G
OM16311
Figure 3. Chassis and Motherboard Volumetric Zones (not all zones are shown)
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
3.2.1.1 Motherboard Primary Side Volumetric Zones
A
(325.12)
[12.800]
176.50
[6.949]
0.000
50.80
[2.000]
Motherboard primary side volumetric zones are defined in Figure 4 . All areas are defined from the
top surface of the motherboard.
B
0.000
Zone B
34.30 [1.350]
Zone C
38.10 [1.500]
(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
62.50
[2.461]
C
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.
View Orientation Defined by
Third Angle Projection
OM16304
Figure 4. Motherboard Primary Side Volumetric Zone
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
13.00
[0.512]
0.000
35.00
34.32 [1.378]
[1.351]
50.17
[1.975]
41.32
[1.627]
78.17
[3.078]
(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]
See Detail A
(293.37)
[11.550]
(325.12)
[12.800]
0.64
[0.025]
A
B
0.000
11.70
[0.461]
2X 62.65
[2.467]
(266.70)
[10.500]
2X 82.65
[3.254]
2X 72.53
[2.856]
2X 97.00
2X 102.53 [3.819]
[4.037] 110.00
[4.331]
122.00
[4.803]
(124.00)
[4.882]
10X Ø 25.00
[0.984]
2X 157.00
[6.181]
0.64
[0.025]
(254.00)
[10.000]
5.50
[0.217]
No components or traces allowed
4.50 [0.177] height
No components allowed
(cone shape volume, Ref section A-A)
10X Ø 10.16
[0.400]
10X (Ø 3.96)
[0.156]
C
10.16
[0.400]
(Ø 10.16)
[0.400]
A
(Ø 25.00)
[0.984]
7.00 [0.276] height
Section A-A
7.00 [0.276] height. 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.
A
View Orientation Defined by
Third Angle Projection
A
10X Detail A
8X Truncated Zones Near Board Edge
Note: Main view as viewed from motherboard secondary side.
OM16301
Figure 5. Motherboard Secondary Side Volumetric Zones
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
Page 17
320.04
[12.600]
(293.37)
[11.550]
(191.77)
[7.550]
198.12
[7.800]
(232.41)
[9.150]
(29.21)
[1.150]
0.000
5.08
[0.200]
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
6.35
[0.250]
0.000
G
Zone K
Zone K
(124.00)
[4.882]
Zone J
See Detail A
Chassis Pan
Planar
H
(260.35)
[10.250]
Interface Plane
Zone H
Zone F
176.50
[6.949]
186.27
[7.333]
Zone H
Zone G
41.03
[1.615]
50.80
[2.000]
62.50
[2.461]
J
2X 302.85
[11.923]
305.35
[12.022]
260.35
[10.250]
Zone F
97.75 [3.848] height off datum J : Type I thermal module
72.35 [2.848] height off datum J : Type II thermal module
Zone G
50.09 [1.972] height off datum J
Zone H
Zone J
Zone K
10X Ø 25.00
[0.984]
10X Ø 10.16
[0.400]
(5.50)
[0.217]
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 25.00)
[0.984]
10.16
[0.400]
(Ø 10.16)
[0.400]
J
Section A-A
3.16 [0.124] height off datum J
A
Denotes cone shape chassis keep-in volume as depicted in Detail A.
Motherboard mounting feature must stay within this volume.
A
10X Detail A
8X Truncated Volumes
View Orientation Defined by
Third Angle Projection
OM16302
Figure 6. Chassis Volumetric Zones
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
Page 19
(232.41)
[9.150]
197.50
[7.776]
(191.77)
[7.550]
191.20
[7.528]
99.00
[3.898]
157.00
[6.181]
G
6.38
[0.251]
35.00
[1.378]
0.000
Chassis Rear
Panel
13.00
[0.512]
4.45
[0.175]
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
5.72
[0.225]
0.000
11.70
[0.461]
Motherboard
Elevation
See Detail B,
Figure 8
2X 97.00
[3.819]
(124.00)
[4.882]
2X 157.00
[6.181]
See Detail C,
Figure 8
200.00 ± 0.50
[7.874 ± 0.020]
185.00
[7.283]
160.10 ± 0.30
[6.303 ± 0.012]
153.00 ± 0.30
[6.024 ± 0.012]
(254.00)
[10.000]
272.53
[10.730]
H
10.16 ± 0.10
[0.400 ± 0.004]
J
55.88
[2.200]
10.00 ± 0.50
[0.394 ± 0.020]
See Detail A,
Figure 8
E
2X 2
111.76
[4.400]
57.79
[2.275]
Ø 0.25 [0.010] J G H
P
2X 7.91 ± 0.30
[0.311 ± 0.012]
2X 16.97
[0.668]
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.
4. Implement only on two front guide features.
Omit on two rear guide features.
View Orientation Defined by
Third Angle Projection
OM16310
Figure 7. Chassis Interface to SRM Requirements
Page 20
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
C
5.63 ± 0.20 [0.222 ± 0.008]
0.40 [0.016] J P
3.50 ± 1.00
[0.138 ± 0.039]
(2.32)
[0.091]
6.00 Max
[0.236]
A
2.50 ± 0.25 4
[0.098 ± 0.010]
3.00 ± 0.50 [0.118 ± 0.020]
(7.91)
[0.311]
0.50 [0.020] J P
B
20.00 Max
[0.787]
B
16.00 Max
[0.630]
26.00 Max
[1.024]
2X R1.0 Max 4
[0.039]
2.20 ± 0.20 4
[0.087 ± 0.008]
A
J
3.80 Max
[0.150]
4X Detail A
Guide
Section A-A
J
C
26.00 Max
[1.024]
Section C-C
2X Detail B
Retainer Slot
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.
4. Implement only on two front guide features.
Omit on two rear guide features.
View Orientation Defined by
Third Angle Projection
3.00 ± 0.25
[0.118 ± 0.010]
J
R0.50 Max
[0.020]
(5.63)
[0.222]
2X 2.32 ± 0.20
[0.091 ± 0.008]
Section D-D
J
4X R0.75 Max
[0.030]
J
2X 3.69 ± 0.30
[0.145 ± 0.012]
(13.00)
[0.512]
Section B-B
D
D
7.10 [0.280] Max
1.00 [0.039] M J P
7.10 ± 0.30
[0.280 ± 0.012]
2X 2.00 ± 0.25
[0.079 ± 0.010]
(55.88)
[2.200]
Detail C
Retainer Tab
OM16313
Figure 8. Chassis Interface to SRM Requirement Details
Page 21
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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
eB
Zon
eD
Zon
A
one
Z
eF
C
one
Zon
Z
Zone H
To Chassis
Inlet Vent
Chassis
Duct Interface
Zone H
Zone G
OM16312
Figure 9. Chassis to Thermal Module Interface and Relation to Chassis and Motherboard Zones
Page 22
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
305.35 ± 0.50
[12.022 ± 0.020]
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.
2X 3.00
[0.118]
0.000
Interface Plane
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.
Airflow Inlet Area 2
(2.00)
[0.079]
E
Motherboard Elevation
Chassis Bottom
67.67
[2.664]
Interface area to
thermal module 3
System Front
H
(98.00)
[3.858]
92.00
[3.622]
G
J
J
2X 4.00
[0.157]
(97.25)
[3.829] 5
(71.85)
[2.829] 6
87.25
[3.435] 5
61.85
[2.435] 6
6.00
[0.236]
E
G
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.
View Orientation Defined by
Third Angle Projection
OM16303
Figure 10. Chassis Requirements for Thermal Module Interface Definition
Page 23
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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
8.46 ± 0.25
[0.333 ± 0.010]
4X R1.0 [0.039] Max
Typ
39.45 ± 0.20
[1.553 ± 0.008]
Chassis I/O Aperture
J
169.54 ± 0.20
[6.675 ± 0.008]
1.32 [0.052]
0.79 [0.031]
Allowable wall thickness
(10.16)
[0.400]
E
E
J
2.47 ± 0.25
[0.097 ± 0.010]
G
2.16 ± 0.25
[0.085 ± 0.010]
Motherboard
mount feature
G
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.
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.
View Orientation Defined by
Third Angle Projection
OM16307
Figure 11. Chassis Rear Panel I/O Aperture Requirements
Page 24
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
Connector Face
B 2
Connector's Protruding Feature
A
32.47 [1.278] Max
1
Motherboard
7.49 ± 0.20
[0.295 ± 0.008]
B 2
I/O Connector
Protrusion Area
5.08 Min
[0.200]
168.78 Max
[6.645]
A
(6.35)
[0.250]
Notes:
1. Bottom of motherboard is coincident with datum E .
2. Datum B is coincident with datum G .
View Orientation Defined by
Third Angle Projection
OM16306
Figure 12. Motherboard Rear Panel I/O Aperture Requirements
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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Page 26
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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
Pin 13
Pin 1
+3/3VDC
+3.3VDC
-12VDC
+3.3VDC
COM
PS_ON#
COM
Pin 3
+5VDC
Pin 1
COM
+12VDC
COM
COM
+5VDC
+12VDC
COM
COM
COM
COM
NC
PWR_OK
+5VDC
+5VSB
+5VDC
+12VDC
+5VDC
+12VDC
COM
+3.3VDC
+12V Power Connector
Main Power Connector
OM16308
Figure 13. Power Supply Connectors
Page 27
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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.
VIL, Input Low Voltage
0.1 V
IIL, Input Low Current, Vin = 0.4 V
VIH, Input High Voltage, Iin = -200 µA
VIH open circuit, Iin = 0
Max.
0.8 V
-1.6 mA
2.0 V
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.
Page 28
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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
T5
T1
VAC
PS_ON#
+12VDC
+5VDC
+3.3VDC
95%
O/P's
10%
T2
T3
PWR_OK
T6
T4
OM16314
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%
Page 29
Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
5. Additional Information
For additional information beyond the requirements of this specification, refer to:
http:\\www.formfactors.org
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Balanced Technology Extended (BTX) Interface Specification
Version 1.0a
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Page 32