[PCB_FORUM] Re: 0402 round pads
- From: Jelena Larsen <jelenal@xxxxxxxxxxxxx>
- To: "icu-pcb-forum@xxxxxxxxxxxxx" <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Fri, 5 Jan 2007 17:15:38 -0800
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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