[Arm-netbook] iMX6 EOMA-68 CPU Card
joem at martindale-electric.co.uk
Wed Feb 27 11:25:18 GMT 2013
On Wed, 2013-02-27 at 10:47 +0000, luke.leighton wrote:
> On Wed, Feb 27, 2013 at 10:32 AM, luke.leighton <luke.leighton at gmail.com> wrote:
> #>> 1. What via hole sizes do you use inside the BGA area?
> > 10mil. i think i made it 10mil with a very narrow surround
> it's juuust about possible to do this, because freescale have a very
> sensible rule of doing a 0.8mm pitch on BGA for precisely the reason
> that many older PCB factories cannot do anything more accurate.
> less than 10mil drill, the bits have to be carbide, and they break;
PCB makers are ok to 0.2mm. After that its at least x5 price for 0.15mm
and if they use laser drilling, it is at least x10 price for 0.15mm.
(Laser drills are OK if making own BGAs with a chip bonded to one side
of the PCB and the other side is all BGA pads, because the PCB will then
be just postage stamp size. Definitely worth doing if say the ARM and
the DDR memory and flash can be obtained in dice form. The high
pinout of a big chip can be replaced with a smaller pin out with own BGA
pin out with RAM and flash on board of custom BGA - good for EOMA type
projects where space is mega restricting.)
Narrow girth around drill hole has its risks - drills can slip and the
hole get slightly out of alignment with the pad, and it cuts up the pad
into a crescent shape.
> less than 6mil clearance and they end up having to x-ray the board, or
> just hope like hell. also, below 6mil, BGA moves about, causes solder
> to bridge across tracks and pads. whoops.
> i *may* be able to use a little company in saffron waldon, it will
> be touch-and-go because of the 5mil clearance on the DDR3 RAM.
5 mil should be ok.
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