[PCB_FORUM] Re: 0402 round pads

Jelena,

I agree. I love using micro vias, but it's hard to convince some folks
of the real value. Signal integrity plus high yield. What they see first
in the initial fabrication costs. Tis a shame.

 

Jim S. Wages / SR. PCB Layout Designer:  

Cary, NC - H: 919-466-1596 Cell: 919-484-2963

 

-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Jelena Larsen
Sent: Friday, January 05, 2007 8:16 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: 0402 round pads

 

Ah..the luxury of a micro via. If you get a chance look at an XBOX360
motherboard, bottom side under the CPU. An array of 0402 bypass caps
side by side tied to the plane with a standard via 10mil finished drill
size. No tombstone issues. Manufacturing tested. Patented design. Most
impressive for a 4 layer board. Oh..the 0402 pads are rectangle. You can
find pictures of it on the internet.

 

Jelena

 

  _____  

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Unruh Barry
Sent: Friday, January 05, 2007 4:24 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] 0402 round pads

 

Gary

     I feel that the significance of this discussion has been missed.

 

The fact that you can imbed termination resistors and decoup caps into a
1mm BGA via grid on the back side is a very BIG DEAL!

The round pads enable you to do this. Maybe some other shape works also,
but not square or rectangle.

For every 2 vias you can fit one 0402 component.

No vias need to be removed.

Short is better whether your talking about caps or termination
resistors.

This technique may delay or reduce the need of moving to 0201 packages.

 

Build your 0402 alt symbol with 1 mm pad to pad spacing.

 

What we use is....

Pad size is .022".

Via size is .019".

Via to pad is .007 min.

Make the solder mask cover most of the via.

 

Of course I can't guarantee yield, but so far so good.

 

It would make placement easier to be using a metric database but not
vital.

If your on an inch database use the rat going to the pad to enable you
to place the part to the closest .0001 inch.

 

Barry Unruh

 

 

 

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