[PCB_FORUM] Re: 0.5 mm BGA, whew!

All;

 

My mistake this was not to go out to the forum.

 

My apologies.

 

 

-----Original Message-----
From: Roberto Torres [mailto:robertotorres@xxxxxxx] 
Sent: Saturday, October 30, 2004 1:05 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: 0.5 mm BGA, whew!

 

Don't really like this answer.

 

-----Original Message-----
From: Degennaro, Natalie N [mailto:natalie.n.degennaro@xxxxxxxxx] 
Sent: Friday, October 29, 2004 9:59 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: 0.5 mm BGA, whew!

 

Gary,

 

1)       We use micro vias in pad (built into padstack used, and are
through hole).

2)       Decide ahead of time and build them into the symbol. Otherwise
"replace padstack" for when you do know what layers you need to connect
to. That will get you out of the DRC quandary. You can use the
blind/buried via wizard to generate them automatically.

3)       Why are you still using a .brd in mils? Your parts are
dictating that you need to switch to millimeters (like we have). Or is
this just a personal thing? (LOL). Parts built in millimeters and then
read into a mils .brd will have round off.

4)       Why do this?

5)       Why not have a micro via in pad set for 1-4, in your example?
Your three mv's are going to connect anyway, if they are at same center.

 

It doesn't have to be as hard as you think. Just change the way you
think and try something new (LOL). It can be fun! 

 

Natalie

 

  _____  

From: Gary MacIndoe [mailto:gary.macindoe@xxxxxxx] 
Sent: Friday, October 29, 2004 9:06 AM
To: Allegro Forum
Subject: [PCB_FORUM] 0.5 mm BGA, whew!

 

All,

 

Well, it seems to be a slow day on the Forum, so I'll through out a
relatively involved set of questions!

 

We are looking into using a 0.5 mm BGA in a very dense design, so big
time HDI practices will come into play: micro vias (MVs), probably even
stacked micro vias (SMVs), in order to fan out on several layers.

 

-  would you use the micro vias in pad or not?  Why?  Build them into
the symbol?

 

-  how can you have the micro vias built into the symbol if you don't
know which balls will go down to which layer?

 

-  I will make the 0.5 mm BGA Allegro symbol with the drawing units set
to Millimeters, but would like to keep the design database set to Mils.
Is this the way most of you have done it?

 

-  if the symbol is set to Millimeters and the design set to Mils, this
makes dropping the micro vias (in pad or not) after the BGA symbol is
placed in the design tricky.  Any other way to get around this?

 

-  So, setting up blind/buried micro vias should be the same as any
blind/buried via.  How about SMVs?  If you have a micro via set up for
layers 1-2, 2-3, 3-4, etc., how do you avoid the DRCs when you stack
them (same X,Y)?

 

My head is about spinning trying to comprehend all of this micro
via/stacked micro via stuff!

 

Any help from someone that has already used a 0.5 mm BGA on a very dense
design with stacked micro vias would be greatly appreciated!!

 

Thanks in advance,

Gary E. MacIndoe
PCB Design Engineer
Advanced Micro Devices, Inc.
Longmont, Colorado

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