The CDROM player in my personal computer just died and I replaced it with a more lively unit.
Being an inveterate gearhead, of course I had to field strip the old CDROM player as soon as I pulled from my PC [and got the new one running]. There are some curious things on the board that I could use your help in understanding.
First, some background on the board: * Double sided, CEM-1 substrate. * Solder mask is green, who knows what, probably LPI over bare copper, but not a screenable. * Insides of vias are coated with a solder colored material that closes the secondary side of most vias.
Second, assembly of the board: * QFP (5) and SMT what not on the primary side. * Second side SMT [all fly shit] is glued. * Most PTH on primary side [except a couple hand soldered ECO caps] is wave soldered. * Afore mentioned caps and secondary operation potentiometers and such hand soldered.
OK, here�s the part that has me scratching my head: * Each via has a blue colored material that is donut shaped [~0.1" wide between inner and outer diameter with the inner diameter just touching the outside of the via pad] that are on both sides of the board. It is very thin [~solder mask thickness]. What is the material and its purpose? * Primary side global fiducials [located within 0.2" of the board edge] have a trace that runs from the fid to the edge of the board. The trace is perpendicular to the edge of the board and covered with mask [fids are not coated]. What is the purpose of this trace? * Also, what�s your guess on the material in the vias?
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