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What Is This On This Board?


What Is This On This Board? | 5 December, 2000

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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Travis Slaughter


Re: What Is This On This Board? | 6 December, 2000

Sounds to me like they used conductive epoxy instead of plating the vias. I had to deal with boards like that when I was doing consumer electronics developed in Japan.

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Re: What Is This On This Board? | 6 December, 2000

I know what yer sayin', but this solder colored stuff sorta coats the barrel walls, not forming a glob by shrinking during cure, like most adhesives. Is that the way yours worked?

OK, here's some more information on the blue stuff => it's a "clear" material printed on top of each via [top & bottom side]. Apparantly, there is some color to it so it changes ... * Mask blue from green * Gray stuff in the vias to gray stuff colored [although it may be some other color and the clear coat changed it gray, hummmm?]

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Travis Slaughter


Re: What Is This On This Board? | 7 December, 2000

It sounds to me you have what I had it has been a few years though so things are a bit foggy. Grey in the hole seems like they tended to be plugged not just coated, and the blue ring around (I never did find out what that was). Is your board punched out, not routed? I don�t believe the ones I did had any PTH�s at all and I think all the holes their where had also been punched out.

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