Feng Yi,

BGA (Ball Grid Array) is the "next generation" of surface mount. Rather than "surrounding" a
package with leads in which the count is limited by the lead pitch vs. perimiter, BGA utilizes
spheres placed on pads on the bottom of the device in a matrix pattern. A 50MM square part can
accomodate 2400 balls on 1 mm centers. That allows denser packaging.You can download drawings from
the JEDEC website (hotlinked from my site under "Useful links") which are viewable using Acrobat
Reader(also downloadable for free).

Screen print and placement is not dissimilar to conventional SMT however, you will find that
reflow and cleaning is a bit more critical as the device "shields" the interconnects. Inspection
can only be done with X-Ray since most defects will lie within the core of the array. Rework is
another story altogether. If a component is to be removed/replaced, specialized equipment will be
needed to remove, desolder, re-paste, reball, re-paste the PCB, then reposition the part and
reflow.

Regards,

Ed Popielarski
QTA Machine
10 Mc Laren, Suite D
Irvine, Ca. USA 92618
Ph: (949)581-6601
Fx: (949)581-2448
E-Mail: [log in to unmask]
http://www.qta.net
ASK ABOUT OUR BGA REBALLER!

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