[SI-LIST] Re: 0.8mm BGA routing
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <vincenzo@xxxxxxxxxxxxxx>
- Date: Mon, 29 Dec 2003 10:31:08 -0500
Vincenzo,
In addition to what you listed in your mail, you will also need
to consider the clearance hole (antipad) around the pad, which
may be at least 8 to 10 mils bigger than the pad. Adjacet
signal vias would completely perforate the plane.
I agree with Lee's comment he made earlier on this thread:
0.8-mm BGA is tough on conventional PCBs with through
holes. You may need a build-up process or sequential
lamination to get your routing properly.
Regards,
Istvan Novak
SUN Microsystems
----- Original Message -----
From: "Vincenzo Kreft-Kerekes" <vincenzo@xxxxxxxxxxxxxx>
To: "Tayyab Jamil" <tayyab@xxxxxxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Monday, December 29, 2003 9:25 AM
Subject: [SI-LIST] Re: 0.8mm BGA routing
> Tayyab,
>
> You're right, I apologize. It looks like you need a 16 mil via pad to
route
> 5/5 between two vias which in turn makes for a tiny drill hole (8 mil
> probably) and all its associated plating problems. Could someone comment
> please? Thanks.
>
> Regards,
> Vincenzo
>
> -----Original Message-----
> From: Tayyab Jamil [mailto:tayyab@xxxxxxxxxxxxxx]
> Sent: Monday, December 29, 2003 12:54 AM
> To: Vincenzo Kreft-Kerekes
> Cc: si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] Re: 0.8mm BGA routing
>
>
> Vincenzo,
>
> you are perfactly alirght when you mention the space left for pads. but
you
> did not talk about the tracks escaping between vias.
>
> but when i place vias a matrix form, there is only 31.496 mil distance
> between the centers of adjacent via pads. keeping via pad of 20 mil there
is
> only 11.496 mil space left between the pads of adjacent vias.
>
> Now if i use 5/5 routing this means i need 5+5+5 = 15 mils total space for
> routing atleast one track between the pads of adjacent vias, which in our
> case is only 11.496. Even 4/4 routing scheme does not allow me to
> route/escape one track between the pads of adjacent vias.
>
> I am attaching the rough diagram for reference.
>
> What you say in this regard?
>
> Also please let me know the links/documents reffering to the design of
BGAs
> with 0.8 mm pitch.
>
> Thanks
> Tayyab
>
> -----Original Message-----
> From: Vincenzo Kreft-Kerekes [mailto:vincenzo@xxxxxxxxxxxxxx]
> Sent: Friday, December 26, 2003 10:19 PM
> To: tayyab@xxxxxxxxxxxxxx
> Subject: [SI-LIST] Re: 0.8mm BGA routing
>
>
> Tayyab,
>
> You place escape vias diagonally in the 0.8 mm raster which means you have
> 0.8 * sqrt(2) = 1.13 mm (44.5 mil) to work with. If you're using a 20 mil
> via pad and have an etch capable of resolving 5 mil spaces between copper
> structures then you need a 30 mil zone around your via hole center (for
pad
> and clearance) which leaves 44.5 - 30 = 14.5 mil as pad diameter for the
> ball. As was already mentioned, Xilinx has escape diagrams for most if not
> all of their packages so you can look at what we're talking about, Altera
> also has a good application note on this topic and both have recommended
> values for the via and etch parameters in these documents.
>
> Regards,
> Vincenzo
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Tayyab Jamil
> Sent: Thursday, December 25, 2003 11:35 PM
> To: Stephen Chavez
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: 0.8mm BGA routing
>
>
> Hi,
>
> I could not understand your scheme, for me it is not possible what you
> suggest as
>
> 0.8 mm pitch means there is only about 31 mil distance between via pads of
> adjacent pins. 24 mil pad of via leaves only around 7.xx mils space in
> between. If we use 5 mil trace this leaves only around 2.xx mils in total
on
> both sides of the trace, means 1.xx mil clearence on each side of trace.
>
> What i was thinking of is 18mil via pad and 8mil via hole finished, and
4mil
> trace and 4mil clearnce. This allows one trace to be escaped between
> adjacent pades. Any suggestions about this.
>
>
> Please let me know if I am wrong.
>
> Regards
> Tayyab
>
>
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