Solder Mask Patterns using BGAs

Replying to mine own thread for clarification. We are having some issues with solder mask shifts on memory boards using fine pitch BGAs. At times the etch to etch distance does not leave room for a solder mask annular ring to be shifted or it will cause exposed copper on adajacent traces. Is there solder mask methodology that will help this situation?

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Jim,

There are 2 thoughts to this technology. SMDP (Soldermask Defined Pads) Can achieve more uniform opening of the land, yet as you know Regisration shift of mask can become a problem. Also there has been debate as to whther SMDP cause crack propagation as the BGA balls collapse over the Mask. NSMDP (Non Soldermask defined Pads) require that the copper "etching" be uniform, which early technologies this was difficult. Now with all the new platings and process control of developing a PWB, it is not that much of a problem.

http://www.priorartdatabase.com/IPCOM/000008472/

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