eg
http://blog.makezine.com/_support.ga...00264_m0026 4
07.jpg

This package uses a secondary board , outlined in white square in the above
pic. On the periphery, just about visible in that pic, of this square board
there are traces , approximately 50 to a side. Not all have a corresponding
dot pad. Underlying array is 20 x 20 , not all pinned, and excluding
repeated grounds and power rails , maybe about 4x 50 active pins.
If you remove the lacquer covering, do each of these peripheral traces , go
to each active pin, hidden underneath?
Is there a structure to the order of these linear traces to the subset of
pin array row/col , corresponding to that edge ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Yes those peripheral cut traces do go inward, to the array, in a structured
manner, but not yet determined whether a regular pattern repeated around all
4 sides.

This is a 324 BGA , ball grid array, 324 solder balls
312 points come out to the periphery.
50 along each top edge and 28 on each underside edge.
tends to be outer 3 rows to the top and inner 2 rows to the bottom. Safest
to scratch away at the edge of this secondary pcb to expose the traces at
the sides, scratching-in from top or bottom may scratch through a trace.
Maybe just resin rather than glass reinforced board.
The underside line-up is more regular, tending to be 2 traces between each
grid ball. Upper edge is more erratic, the rings probably mean something ,
on some of the upper traces, but not decyphered


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/