Hi, Edri,
It's not uncommon for PCB fab houses to change pad sizes like that, due to design constraints....however, it always aggravates me when they do it without checking with me first. In my mind, that's the first sign of potential bad issues with a fab house...if they don't communicate about something like this, I'm always concerned about what other potential issues they may not tell me about.
On to your questions. 1. The potential effect is for an inconsistent joint between the balls and the pad. 2. This is a potential reliability issue...with such small targets, you could end up with poor connections. After looking at the pictures, I'd be concerned about some boards possibly having solder mask over the smaller pads, as it looks like they've gotten particularly small. 3. I can't help you make that determination...I'm not fully versed in BGA's. On the surface, I can tell you that I don't like it! 4. Yes, if rejecting, I'd reject the entire lot, and remake the boards I'd try working with the designer, fab house, and BGA manufacturer to get to a determination of what is allowable, functional, and process controllable. It's possible that you could use these boards with no issues...but, I'd definitely work to get all parties to sign off on that before running the boards.
Cheers, ..rob
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