[SI-LIST] Re: Search for the paper about minimum BGA pad size in PCB
- From: "Sol Tatlow" <Sol.Tatlow@xxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 16 Jun 2005 14:25:29 +0200
Hi Peter,
I would agree with Steve there - the pad sounds not quite right.
Normally, the pad size is dependant upon the corresponding pad
size on the BGA itself, and is not directly related to the ball
size - the idea is to get a symmetrical joint shape to maximise
resistance to sheer stresses once the BGA ball has melted, and
your pad will probably be smaller than the pad on the BGA. MIGHT
not be critical, but could lead to an increase in long term
failure rates, particularly in mechanically stressful environments.
So, due to the fact that different BGA manufacturers may (will)
use different size pads on their BGAs, it is a little difficult,
particularly for high volume manufacturing, to generalise.
However, I would think somewhere in the region of 16 to 19 mils
would be better - obviously, this is not going to fit to your
track width requirement, but I would suggest that you reduce
the track width and spacing (between tracks, first of all!!!)
to 4 mils and take a larger BGA pad.
If you do this, but keep to 5 mil spacing to pads (to avoid
shorts between tracks and pads in the case of offset solder
mask), you will come to a pad size of 17 mils, which, I
think, offers a good compromise. If you definitely need 5 mil
tracks for whatever reasons, like impedance, I would STILL
make them 4 mils in the area of the BGA pads, and then expand
once you are out of that area - the short track lengths inside
the BGA area are likely, in most normal commercial applications,
to have only a negligble impact on total impedance effects.
Hope this helps!
____________________________________
Sol Tatlow, M.Eng. (Oxon)
ProDesign Electronic & CAD Layout GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062-808-302
Fax: +49 (0) 8062-808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________=20
-----Urspr=FCngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
Im Auftrag von Pang Ning
Gesendet: Donnerstag, 16. Juni 2005 12:13
An: si-list@xxxxxxxxxxxxx
Cc: morris_yu@xxxxxxxxxxx
Betreff: [SI-LIST] Search for the paper about minimum BGA pad size in =
PCB
Dear Expert,
I encountered a problem about BGA pad size in PCB. The actual ball size =
is 0.6mm, and ball pitch is 1.0mm. We plan to route two 5mil traces =
between two adjacent pads, and reserve over 5mil spacing for =
trace/trace, trace/pad(or via). But in this way the BGA pad size in PCB =
will be only 14mil.
I'm wondering if 14mil BGA pad is too small for mass production. Is =
there any paper that demonstrates the guideline for BGA ball size vs. =
minimum pad size in PCB? Can anyone provide me the linkage for the =
paper? Thanks in advance!
Best Regards,
Peter Pang
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