Inge,
If the big slab of metal in the device isn't connected to the PWB ground
then it can make things worse, not better. If it is, then I agree with
you that it will have a shielding effect.
Regards,
Terry Kozlyk wrote:
> Hi Inge;
>
> Disturb away ! I find your 2 questions very good. Very good points !!!
>
> TDKtalks (Terry)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Terry D.Kozlyk ACS, CL, C.E.T.
> TDKtalksTM PodCast
> TDKtalksTM Blog
> Silver Springs Toastmasters - Club #3987
> [log in to unmask]
> [log in to unmask]
> home (403) 239-7939
> work (403) 295-6773
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
> Sent: Thursday, September 17, 2009 2:33 AM
> To: [log in to unmask]
> Subject: Re: [TN] Ground Pour Under BGA
>
> Hi,
> CADing boards is not my job, but I became curious when I read your pingpong.
> We have a board with a number of SuperBGAs, number of balls about 660.Vias
> in pad. I have two questions for you professionals. 1)what's the benefit
> with a groundplane (that looks more like a copper net)under chip, when the
> whole BGA has a thick metal plate all over the BGA. That metal sheet is
> mainly for cooling and stabilizing the body mechanically, but isn't this
> cover also a effective ground plane and a electrostatic shield? 2)will such
> an extra groundplane under chip make 3D X-raying even harder to read, e.g.
> bond wires, which are already hard to inspect due to the massive top metal
> plate.
> Sorry for disturbing you with such trivia.
> /Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
> Sent: onsdag 16 september 2009 17:26
> To: [log in to unmask]
> Subject: Re: [TN] Ground Pour Under BGA
>
> yes. If BGA pitch is large enough then it makes nice little pwr/gnd island
> with some distributed capacitance directly under the device (available with
> very low inductance).
> When picking and choosing which of several device voltages to locate thusly,
> for greatest benefit use it for the heavy fast currents (e.g.
> core voltages).
>
> At 07:16 AM 9/16/2009, Kenneth Wood wrote:
>
>> Keep in mind that on HDI designs you are not JUST adding a few micro
>> vias and pouring GND on the top layer...you are using via-in-pad on all
>> devices so to try and minimize top side pour cuts. Also, you are
>> routing as many nets on internal layers as possible.
>> The top layer GND is not usually the only GND plane too, there is
>> usually an internal plane to back up the top layer.
>> This does reduce EMI significantly, shorter runs and external shielding
>> works.
>> Ken
>> Saturn PCB Design, Inc.
>> www.saturnpcb.com
>>
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
>> Sent: Wednesday, September 16, 2009 10:07 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Ground Pour Under BGA
>>
>> Ken,
>>
>> With all the BGA pads and possible vias I don't see how a top side
>> can have a better mesh of copper paths than an internal layer. I would
>> think a poor copper mesh plane would be a generator of large GND return
>> loops. Aka antennas.
>>
>> As for a GND plane being a few mils closer to the BGA and this
>> reducing EMI, that sounds like hog wash. Consider that conductor
>> lengths from a ball to chip is probably about 1/2 inch at times. How is
>> adding 10 mils going to affect anything?
>>
>> I am open to Hog Wash ideas but they need to be well defined.
>>
>> Thanks,
>> Bob Kondner
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Kenneth Wood
>> Sent: Wednesday, September 16, 2009 9:54 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Ground Pour Under BGA
>>
>> It is an technique used in HDI designs that utilize micro vias.
>> Top layer is GND and layer 2 can be a power layer. It also helps with EMI.
>> Ken
>> Saturn PCB Design, Inc.
>> www.saturnpcb.com
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
>> Sent: Wednesday, September 16, 2009 8:42 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Ground Pour Under BGA
>>
>> Hi,
>>
>> What would be the goal of placing atop side GND plane under the BGA?
>>
>> Low Z Gnd return? Electrostatic shield?
>>
>> Having a plane under the BGA vs another layer is not going to make a
>> difference in plane Z.
>>
>> Sounds like a good chance of creating shorts if the solder mask chips
>> or is damaged during rework.
>>
>> Bob Kondner
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
>> Sent: Wednesday, September 16, 2009 7:43 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Ground Pour Under BGA
>>
>> IPC 7095, BGA Technology by Lau.
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Toby Carrier
>> Sent: Tuesday, September 15, 2009 8:45 PM
>> To: [log in to unmask]
>> Subject: [TN] Ground Pour Under BGA
>>
>> Hello all,
>>
>> Is it a good idea to create a top layer ground flood under a BGA
>> package? I am guessing that the fanout will not allow much area for the
>> ground pour, am I correct in thinking so? Does anyone have any good
>> reference info on this topic?
>>
>> Also, if you don't have a ground pour under the BGA, how will that
>> affect the impedance control of the traces going to the BGA ball?
>>
>> Thanks for the help,
>>
>> Toby
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at [log in to unmask]
>> or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at [log in to unmask]
>> or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at [log in to unmask]
>> or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at [log in to unmask]
>> or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at [log in to unmask]
>> or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to
>> [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>> per day of all the posts: send e-mail to
>> [log in to unmask]: SET Technet Digest
>> Search the archives of previous posts at:
>> http://listserv.ipc.org/archives Please visit IPC web site
>> http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
>> information, or contact Keach Sasamori at [log in to unmask] or
>> 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
> unsubscribe, send a message to [log in to unmask] with following text in the
> BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
> (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
> NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
> e-mail to [log in to unmask]: SET Technet Digest Search the archives of
> previous posts at: http://listserv.ipc.org/archives Please visit IPC web
> site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
> ext.2815
> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
> for additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-615-7100 ext.2815
> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
> -----------------------------------------------------
>
>
--
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
