Q&A for Work. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Hi Bill, I was thinking the same thing, so last night I deleted all symbols, and vias in a copy of the design, purged unused pad stacks, ran a dbcheck, and still COVERLAY was there. The bigger problem that I was not going to get into is I believe this layer is interfering with a proper usage of COVERLAYTOP and COVERLAYBOTTOM.
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If you are using a via on a high speed net, chances are - it has excessive capacitance. The main source of the excess capacitance is the coupling between the via pads and the nearby power plane.
One quick way to reduce the via capacitance is to reduce the size of the pad. You start with the minimum drill size, which is typically 8 mils for most inexpensive PCB Fabrication processes. Now you need a minimum 4 mil trace for common inexpensive process which sets the minimum Via diameter size as 16 mils.
Even with the reduced pad size, the via is capacitive. The next step to reduce the capacitance is to increase the Antipad size. If you do not specify the antipad size, the separation between the via and the power plane is determined by the design rule of clearance between power plane flood and the nearest trace. 2001 headlines jay abraham pdf download. For example if this clearance is set to be 4 mils, the diameter of the antipad can be assumed to be 24 mils or 8 mils more than the pad diameter of 16 mils. Typically if the antipad diameter is set to be 12 mils more than the pad size, we get reduced capacitance from via.
One final important way of reducing the via capacitance is the by removing the internal unused pads from via. These unused pads are more popularly called non functional pads. In a typical design, the pads are almost always present in the top and the bottom layers. Simplified via design has pads connected to all internal layers. So if a trace is going from top layer to bottom layer, the internal via pads are present even if not used. These internal unused pads add to the via capacitance. If you care for high speed designs, it is a good idea to consider removing these internal pads from the via. The separation between the via barrel and the power and ground plane increases, reducing the via capacitance.
You may extend the same concept by defining a new via from top layer to an internal layer. For example if you have an 8 layer board and you you are jumping from layer 1 to layer 6, you may remove via pad from all layers, except from 1( top) , 6 and 8 ( bottom). Each internal signal layer will require separate via definition(s).
Manufacturing Considerations
I am not a manufacturing expert, but there is one aspect that is certain - removing the Non Functional pads, does reduce the separation between the pads and the power plane and thereby reduces the chance of short, especially in the dense BGA areas. The PCB house, therefore, like to remove the Non Functional pads and potentially improve the yield.
There have been other discussion about the via barrel cracking and there are discussion about how the additional pads help keeping the barrel together. It appears that removal of the non functional pads does not create any disadvantage from manufacturing, yield or long term reliability perspective.
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The removal of the Non Functional pad works at the design level ( or the gerber level). Another way to reduce the additional Capacitance is back drilling the pads. If a trace is going from Layer 1 to Layer 3 in a 8 Layer PCB, we have an extra stub from Layer 3 to Layer 8. Ipulse 3 0 5 download free. Even if we remove the internal non functional pads, we have pads on layer 8. Back drilling is the process to remove the extra stub and the pad. This serves dual purpose - removal of the pad and the removal of the extra stub.
How about Non Functional Pads on Via for Power connections
Power connections are a totally different from high speed. In via for power plane, we wish to keep the length of the via drill to the minimum and we wish to keep capacitive coupling ( between power and ground ) high. The pad size in power via should be kept large to provide more capacitance. There is little discussion about the design of the via for delivering power nets. The design of via for the power nets will be guided by two basic principles - reducing the via drill inductance and more capacitive coupling between power and ground nets.
We expect your comments on this serious discussion.
By Vikas Shukla
Related posts:
- AL_ID — Converts four 8 bit values to a packed 32 bit integer ID.
- ALLEGRO_DATE — Defined to a number with the release date of Allegro.
- ALLEGRO_DATE_STR — Defined to a string with the year Allegro was released.
- allegro_error — Stores the last Allegro error message.
- allegro_exit — Closes down the Allegro system.
- allegro_id — String containing date and version number of Allegro.
- allegro_init — Macro to initialise the Allegro library.
- allegro_message — Used mainly to show error messages to users.
- ALLEGRO_SUB_VERSION — Defined to the middle version of Allegro.
- ALLEGRO_VERSION — Defined to the major version of Allegro.
- ALLEGRO_VERSION_STR — Defined to a string with the full Allegro version number.
- ALLEGRO_WIP_VERSION — Defined to the minor version of Allegro.
- check_cpu — Detects the CPU type.
- cpu_capabilities — Contains the capability flags of the CPU.
- cpu_family — Contains the CPU type.
- cpu_model — Contains the Intel CPU submodel.
- cpu_vendor — Contains the CPU vendor name.
- desktop_color_depth — Finds out the desktop color depth.
- END_OF_MAIN — Macro to put after your main() function.
- get_desktop_resolution — Finds out the desktop resolution.
- install_allegro — Initialise the Allegro library.
- MAKE_VERSION — Create a 32 bit integer from the Allegro version
- os_multitasking — Indicates if the OS is multitasking.
- os_revision — Version of the OS currently running.
- os_type — Stores the detected type of the OS.
- os_version — Version of the OS currently running.
- set_close_button_callback — Handles the user clicking on the close button of the window.
- set_window_title — Sets the window title of the Allegro program.
See readme.txt for a general introduction, copyright details, and information about how to install Allegro and link your program with it.
Initialises the Allegro library. You must call either this or allegro_init() before doing anything other than using the Unicode routines. If you want to use a text mode other than UTF-8, you can set it with set_uformat() before you call this. The other functions that can be called before this one will be marked explicitly in the documentation, like set_config_file().
The available system ID codes will vary from one platform to another, but you will almost always want to pass SYSTEM_AUTODETECT. Alternatively, SYSTEM_NONE installs a stripped down version of Allegro that won't even try to touch your hardware or do anything platform specific: this can be useful for situations where you only want to manipulate memory bitmaps, such as the text mode datafile tools or the Windows GDI interfacing functions.
The `errno_ptr' and `atexit_ptr' parameters should point to the errno variable and atexit function from your libc: these are required because when Allegro is linked as a DLL, it doesn't have direct access to your local libc data. `atexit_ptr' may be NULL, in which case it is your responsibility to call allegro_exit() manually. Example: Vectorworks free mac.
Return value: This function returns zero on success and non-zero on failure (e.g. no system driver could be used). Note: in previous versions of Allegro this function would abort on error.
See also:allegro_init,allegro_exit,set_uformat,set_config_file.
See also:install_allegro,allegro_exit.
Examples using this:Available Allegro examples.
See also:install_allegro,allegro_exit.
Examples using this:Available Allegro examples.
Closes down the Allegro system. This includes returning the system to text mode and removing whatever mouse, keyboard, and timer routines have been installed. You don't normally need to bother making an explicit call to this function, because allegro_init() installs it as an atexit() routine so it will be called automatically when your program exits.
Note that after you call this function, other functions like destroy_bitmap() will most likely crash. This is a problem for C++ global destructors, which usually get called after atexit(), so don't put Allegro calls in them. You can write the destructor code in another method which you can manually call before your program exits, avoiding this problem.
See also:install_allegro,allegro_init,destroy_bitmap.
Examples using this:ex3d,exscn3d,exswitch,exxfade,exzbuf.
In order to maintain cross-platform compatibility, you have to put this macro at the very end of your main function. This macro uses some `magic' to mangle your main procedure on platforms that need it like Windows, some flavours of UNIX or MacOS X. On the other platforms this macro compiles to nothing, so you don't have to #ifdef around it. Example:
See also:Windows specifics,Unix specifics,MacOS X specifics,Differences between platforms.
Examples using this:Available Allegro examples.
Text string containing a date and version number for the library, in case you want to display these somewhere.
Text string used by set_gfx_mode(), install_sound() and other functions to report error messages. If they fail and you want to tell the user why, this is the place to look for a description of the problem. Example:
See also:set_gfx_mode,install_sound.
Examples using this:Available Allegro examples.
Defined to the major version of Allegro. From a version number like 4.1.16, this would be defined to the integer 4.
Defined to the middle version of Allegro. From a version number like 4.1.16, this would be defined to the integer 1.
Defined to the minor version of Allegro. From a version number like 4.1.16, this would be defined to the integer 16.
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Defined to a text string containing all version numbers and maybe some additional text. This could be `4.2.1 (SVN)' for an Allegro version obtained straight from the SVN repository.
Defined to a text string containing the year this version of Allegro was released, like `2004'.
Defined to an integer containing the release date of Allegro in the packed format `yyyymmdd'. Example:
This macro can be used to create a packed 32 bit integer from 8 bit characters, on both 32 and 64 bit machines. These can be used for various things, like custom datafile objects or system IDs. Example:
See also:DAT_ID.
This macro can be used to check if some Allegro version is (binary) compatible with the current version. It is safe to use > and < to check if one version is more recent than another. The third number is ignored if the second number is even, so MAKE_VERSION(4, 2, 0) is equivalent to MAKE_VERSION(4, 2, 1). This is because of our version numbering policy since 4.0.0: the second number is even for stable releases, which must be ABI-compatible with earlier versions of the same series. This macro is mainly useful for addon packages and libraries. See the `ABI compatibility information' section of the manual for more detailed information. Example:
See also:ALLEGRO_VERSION,ALLEGRO_SUB_VERSION,ALLEGRO_WIP_VERSION.
Set by allegro_init() to one of the values:
See also:allegro_init,os_version,os_multitasking.
The major and minor version of the Operating System currently running. Set by allegro_init(). If Allegro for some reason was not able to retrieve the version of the Operating System, os_version and os_revision will be set to -1. For example: Under Win98 SE (v4.10.2222) os_version will be set to 4 and os_revision to 10.
See also:os_type,os_multitasking.
Set by allegro_init() to either TRUE or FALSE depending on whether your Operating System is multitasking or not.
See also:os_type,os_version.
Outputs a message, using a printf() format string. Usually you want to use this to report messages to the user in an OS independent way when some Allegro subsystem cannot be initialised. But you must not use this function if you are in a graphic mode, only before calling set_gfx_mode(), or after a set_gfx_mode(GFX_TEXT). Also, this function depends on a system driver being installed, which means that it won't display the message at all on some platforms if Allegro has not been initialised correctly.
On platforms featuring a windowing system, it will bring up a blocking GUI message box. If there is no windowing system, it will try to print the string to a text console, attempting to work around codepage differences by reducing any accented characters to 7-bit ASCII approximations. Example:
See also:allegro_init,install_allegro,set_uformat.
Examples using this:Available Allegro examples.
On platforms that are capable of it, this routine alters the window title for your Allegro program. Note that Allegro cannot set the window title when running in a DOS box under Windows. Example:
See also:set_close_button_callback,set_uformat.
Examples using this:exunicod.
On platforms that have a close button, this routine installs a callback function to handle the close event. In other words, when the user clicks the close button on your program's window or any equivalent device, the function you specify here will be called.
This function should not generally attempt to exit the program or save any data itself. The function could be called at any time, and there is usually a risk of conflict with the main thread of the program. Instead, you should set a flag during this function, and test it on a regular basis in the main loop of the program.
Pass NULL as the `proc' argument to this function to disable the close button functionality, which is the default state.
Note that Allegro cannot intercept the close button of a DOS box in Windows.
Also note that the supplied callback is also called under MacOS X when the user hits Command-Q or selects 'Quit' from the application menu. Example:
Return value: Returns zero on success and non-zero on failure (e.g. the feature is not supported by the platform).
See also:set_window_title.
Finds out the currently selected desktop color depth. You can use this information to make your program use the same color depth as the desktop, which will likely make it run faster because the graphic driver won't be doing unnecessary color conversions behind your back.
Under some OSes, switching to a full screen graphics mode may automatically change the desktop color depth. You have, therefore, to call this function before setting any graphics mode in order to retrieve the real desktop color depth. Example:
Stronghold crusader hd mac download. Return value: Returns the color depth or zero on platforms where this information is not available or does not apply.
See also:get_desktop_resolution,set_color_depth,set_gfx_mode.
Finds out the currently selected desktop resolution. You can use this information to avoid creating windows bigger than the current resolution. This is especially important for some windowed drivers which are unable to create windows bigger than the desktop. Each parameter is a pointer to an integer where one dimension of the screen will be stored.
Under some OSes, switching to a full screen graphics mode may automatically change the desktop resolution. You have, therefore, to call this function before setting any graphics mode in order to retrieve the real desktop resolution. Example:
Photoscape x pro 2 6. Return value: Returns zero on success, or a negative number if this information is not available or does not apply, in which case the values stored in the variables you provided for `width' and `height' are undefined.
See also:desktop_color_depth,set_gfx_mode.
Detects the CPU type, setting the following global variables. You don't normally need to call this, because allegro_init() will do it for you.
See also:cpu_vendor,cpu_family,cpu_model,cpu_capabilities,allegro_init.
Removal Of Unused Vias In Stack Allegro For Sale
On Intel PCs, contains the CPU vendor name if known. On Mac OSX systems this contains the PPC subtype name. On other platforms, this may be an empty string. You can read this variable after you have called check_cpu() (which is automatically called by allegro_init()).
See also:check_cpu,cpu_family,cpu_model,cpu_capabilities,allegro_init.
Contains the Intel type, where applicable. Allegro defines the following CPU family types: You can read this variable after you have called check_cpu() (which is automatically called by allegro_init()).
See also:check_cpu,cpu_vendor,cpu_model,cpu_capabilities,allegro_init.
Contains the CPU submodel, where applicable. Allegro defines at least the following CPU family types (see include/allegro/system.h for a more complete list): You can read this variable after you have called check_cpu() (which is automatically called by allegro_init()). Make sure you check the cpu_family and cpu_vendor so you know which models make sense to check.
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See also:check_cpu,cpu_vendor,cpu_family,cpu_capabilities,allegro_init.
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Contains CPU flags indicating what features are available on the current CPU. The flags can be any combination of these: You can check for multiple features by OR-ing the flags together. For example, to check if the CPU has an FPU and MMX instructions available, you'd do: You can read this variable after you have called check_cpu() (which is automatically called by allegro_init()).See also:check_cpu,cpu_vendor,cpu_family,cpu_model,cpu_capabilities,allegro_init.
