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![[SI-LIST] Backdrill under BGA](http://www.fpgacentral.com/group/iconimages/si-list/si-list-backdrill-under-bga_ltr.gif)
07-22-2009, 02:46 AM
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[SI-LIST] Backdrill under BGA
SI Gurus,
Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu 
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07-22-2009, 04:12 AM
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[SI-LIST] Re: Backdrill under BGA
Sam,
The critical factors missing here*are*your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias*require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the*manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam * * * ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: * * * * * * * * http://www.si-list.net List archives are viewable at:* * *** *** http://www.freelists.org/archives/si-list or at our remote archives: *** *** http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: *** *** http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 06:15 PM
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[SI-LIST] Re: Backdrill under BGA
Sam,
Yes we have back drilled in GHz boards. It works pretty well. Cadence has a built in feature to define back drills and their depths. If you are using Mentors (PADs) you might have to manually locate the vias (or use a separate drill size than the others). The antipad and layer stackup plays the main role. I can send you an example setup if you are interested to take a look. -Qazi -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of cygnul (AT) yahoo (DOT) com Sent: Tuesday, July 21, 2009 5:46 PM To: si-list (AT) freelists (DOT) org Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 06:35 PM
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[SI-LIST] Re: Backdrill under BGA
Sam,
I do not have experience with backdrilling under BGAs specifically. My suggestion would be to avoid putting vias on the signal at BGA in the first place, or if you must have vias to transition from layer 1 to layer N and avoid the stub. I realize this doesn't exactly address your question, but if you avoid having a via/stub altogether, you will avoid the added complexity and cost of having to backdrill and account for the items David mentions below. Just thought I would throw it out there. Bill Stube Hardware Engineer Plexus - http://www.plexus.com The Product Realization Company -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of David Mullenex Sent: Wednesday, July 22, 2009 4:13 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, The critical factors missing here*are*your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias*require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the*manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 06:40 PM
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[SI-LIST] Re: Backdrill under BGA
We looked at backdrilling an 82 mil thick pcb under a 1mm (40 mils) pitch
BGA once. Almost all of the low cost PCB suppliers said no. Aubrey Sparkman Aubrey.K.Sparkman (AT) ieee (DOT) org -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Bill Stube Sent: Wednesday, July 22, 2009 11:36 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, I do not have experience with backdrilling under BGAs specifically. My suggestion would be to avoid putting vias on the signal at BGA in the first place, or if you must have vias to transition from layer 1 to layer N and avoid the stub. I realize this doesn't exactly address your question, but if you avoid having a via/stub altogether, you will avoid the added complexity and cost of having to backdrill and account for the items David mentions below. Just thought I would throw it out there. Bill Stube Hardware Engineer Plexus - http://www.plexus.com The Product Realization Company -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of David Mullenex Sent: Wednesday, July 22, 2009 4:13 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, The critical factors missing here*are*your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias*require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the*manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 06:54 PM
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[SI-LIST] Re: Backdrill under BGA
What is the data rate , rise time , maximum stub length, and dielectric constant . For an 82 mil board and reasonable data rates , you may not have to worry about back drilling at all because stub length may not be significant as compared to rise time wave length.
Justin Tabatchnick SI , Intel -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Aubrey Sparkman Sent: Wednesday, July 22, 2009 9:41 AM To: 'Bill Stube'; cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA We looked at backdrilling an 82 mil thick pcb under a 1mm (40 mils) pitch BGA once. Almost all of the low cost PCB suppliers said no. Aubrey Sparkman Aubrey.K.Sparkman (AT) ieee (DOT) org -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Bill Stube Sent: Wednesday, July 22, 2009 11:36 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, I do not have experience with backdrilling under BGAs specifically. My suggestion would be to avoid putting vias on the signal at BGA in the first place, or if you must have vias to transition from layer 1 to layer N and avoid the stub. I realize this doesn't exactly address your question, but if you avoid having a via/stub altogether, you will avoid the added complexity and cost of having to backdrill and account for the items David mentions below. Just thought I would throw it out there. Bill Stube Hardware Engineer Plexus - http://www.plexus.com The Product Realization Company -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of David Mullenex Sent: Wednesday, July 22, 2009 4:13 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, The critical factors missing here*are*your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias*require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the*manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 06:57 PM
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[SI-LIST] Re: Backdrill under BGA
Sam,
It depends on how many multi gig traces/via are needed in BGA design. You could try eliminating stub altogether by transition from top to last layer; and design a transparent via to account for capacitance using a 3D field solver. Other options - use coreless substrates or build-up substrates with blind/buried vias. -Vijaya -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Aubrey Sparkman Sent: Wednesday, July 22, 2009 9:41 AM To: 'Bill Stube'; cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA We looked at backdrilling an 82 mil thick pcb under a 1mm (40 mils) pitch BGA once. Almost all of the low cost PCB suppliers said no. Aubrey Sparkman Aubrey.K.Sparkman (AT) ieee (DOT) org -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Bill Stube Sent: Wednesday, July 22, 2009 11:36 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, I do not have experience with backdrilling under BGAs specifically. My suggestion would be to avoid putting vias on the signal at BGA in the first place, or if you must have vias to transition from layer 1 to layer N and avoid the stub. I realize this doesn't exactly address your question, but if you avoid having a via/stub altogether, you will avoid the added complexity and cost of having to backdrill and account for the items David mentions below. Just thought I would throw it out there. Bill Stube Hardware Engineer Plexus - http://www.plexus.com The Product Realization Company -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of David Mullenex Sent: Wednesday, July 22, 2009 4:13 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, The critical factors missing here are your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-22-2009, 07:11 PM
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[SI-LIST] Re: Backdrill under BGA
Justin,
You are correct in that an 82 mil board with 6.4GT/s or less data rates doesn't need back drill for the usual reasons. Aubrey Sparkman Aubrey.K.Sparkman (AT) ieee (DOT) org -----Original Message----- From: Tabatchnick, Justin [mailto:justin.tabatchnick (AT) intel (DOT) com] Sent: Wednesday, July 22, 2009 11:54 AM To: Aubrey Sparkman; 'Bill Stube'; cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: RE: [SI-LIST] Re: Backdrill under BGA What is the data rate , rise time , maximum stub length, and dielectric constant . For an 82 mil board and reasonable data rates , you may not have to worry about back drilling at all because stub length may not be significant as compared to rise time wave length. Justin Tabatchnick SI , Intel -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Aubrey Sparkman Sent: Wednesday, July 22, 2009 9:41 AM To: 'Bill Stube'; cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA We looked at backdrilling an 82 mil thick pcb under a 1mm (40 mils) pitch BGA once. Almost all of the low cost PCB suppliers said no. Aubrey Sparkman Aubrey.K.Sparkman (AT) ieee (DOT) org -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of Bill Stube Sent: Wednesday, July 22, 2009 11:36 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, I do not have experience with backdrilling under BGAs specifically. My suggestion would be to avoid putting vias on the signal at BGA in the first place, or if you must have vias to transition from layer 1 to layer N and avoid the stub. I realize this doesn't exactly address your question, but if you avoid having a via/stub altogether, you will avoid the added complexity and cost of having to backdrill and account for the items David mentions below. Just thought I would throw it out there. Bill Stube Hardware Engineer Plexus - http://www.plexus.com The Product Realization Company -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of David Mullenex Sent: Wednesday, July 22, 2009 4:13 AM To: cygnul (AT) yahoo (DOT) com; si-list (AT) freelists (DOT) org Subject: [SI-LIST] Re: Backdrill under BGA Sam, The critical factors missing here*are*your BGA pitch and location of the proposed back-drills relative to the BGA grid and each other. This as Back-drilled vias*require larger anti-pads to accomodate the larger diameter of the back-drill head that assures removal of the matal stub, as well as the minor mis-alignment tollerace for the back-drill. Note, that you will also lose routing channels on the back drilled layers due to the larger antipad and back-drill diameter. Looking at the drill size, anti-pad, routing channels, board thickness, and ground/power plane coverage under the BGA, may indicate that back-drilling is not the preffered solution for fine pitch BGAs. Also, selection of the right routing layers and pad stack may allow you to get by with negligable stubs... assuming you do not have a boat load of multi-gig signals on a poorly pinned-out BGA. Porvide more details here or work with your fab house to arrive at the*manufacturable solution. cheers, - David. ----- Original Message ---- From: "cygnul (AT) yahoo (DOT) com" <cygnul (AT) yahoo (DOT) com> To: si-list (AT) freelists (DOT) org Sent: Tuesday, July 21, 2009 5:46:21 PM Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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07-27-2009, 09:58 PM
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[SI-LIST] Re: Backdrill under BGA
Hi Sam,
It is definitely achievable. Please check your PCB vendors. They will be able to tell the exact manufacturing limit for via size, back-drilling size and antipad clearance. BR Tony -----Original Message----- From: si-list-bounce (AT) freelists (DOT) org [mailto:si-list-bounce (AT) freelists (DOT) org] On Behalf Of cygnul (AT) yahoo (DOT) com Sent: Tuesday, July 21, 2009 5:46 PM To: si-list (AT) freelists (DOT) org Subject: [SI-LIST] Backdrill under BGA SI Gurus, Has anybody done back drilling on BGA vias for multi gig traces? is that achievable? If so, what was the via structure? -Sam ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request (AT) freelists (DOT) org with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
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