[PCB_FORUM] Re: 0.5 mm BGA, whew!

From: "Budathoki, Trilok (GE Consumer & Industrial)" <trilok.budathoki@xxxxxx>
To: <icu-pcb-forum@xxxxxxxxxxxxx>
Date: Mon, 1 Nov 2004 12:55:05 +0530
Natalie,
 
I want to know if you have have any problem from manufacturing dept.
Sometime back,we did created a BGA matrix (37 * 37) with microvias in pads, 
unfortunately we couldn't make it as manufacuting dept found problems doing 
prototype.
The reason, reduced solder area for BGA. This was confirmed after viewing X ray 
film of Board (done at Singapore).
It's interesting topic & would like to hear from all experienced folks in 
design, manufacturing & Signal Integrity.
 
Trilok Budathoki
GE- India Business Centre
Email: trilok.budathoki@xxxxxx
 

-----Original Message-----
From: Degennaro, Natalie N [mailto:natalie.n.degennaro@xxxxxxxxx]
Sent: Friday, October 29, 2004 10:29 PM
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
[PCB_FORUM] Re: 0.5 mm BGA, whew!

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