PCB Assembly Services - Screaming Circuits: What's Wrong With This Picture?


What's Wrong With This Picture?

Questions for the day:

  1. What are we looking at here? (Come on, you can be more specific than that)
  2. What's wrong with it?
  3. Where are we going?
  4. When?
What is wrong

And... will it work? Or is it just scrap? Stay tuned. Answers will appear on the Screaming Circuits blog either in the comments or in a new post.

Duane Benson
It flies like a truck.


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1) This looks like a BGA layout using plated-through hole vias as pads.

2) Some pads are oxidized and are now un-reliable for assembly.

3) We are going to the QA Team for immediate investigation and corrective action. Check handling, storage and vendor as indicated by the root cause findings.

4) NOW - assume there needs to be immediate corrective action.

So the finish looks inconsistent. That could be a problem, or just lighting.

The other thing I note is the holes seem rather large for the annular rings.

1. It looks like a BGA land pattern (not mask-defined pads) connected to inner layers with vias that are "encroached" with mask but not tented.

2. It looks like some of the pads are oxidized, might not solder/wet

3. We are going back to Immersion Silver!

4. next revision... which needs to start right now

1. Bga, hopefully 1mm or bigger spacing
2. I believe that's Black pad, there may be a process to etch them or refinish?
3. Nowhere fast :-)

Where's the ENIG? Unless this has OSP you could have some solderability issues with bare copper! And even then OSP isn't all that great is it? How often do you see it?

(I confess I didn't get it until I saw the category was PCB finishes!)

Is the problem that that part of the pads on some of the vias are not completely covered with soldermask? Maybe they artwork had soldermask openings for the vias with diameters equal to the vias' finished hole size. Any tiny registration or finished hole size tolerances cause part of the pad to be exposed.

I might naively think that this is fine as long as there's enough soldermask around the BGA pads to keep the solderpaste from flowing to the via. I also worry that if I leave no opening in the soldermask for the via, the soldermask material will fall into the via hole during fabrication and cause problems (assuming the fab house doesn't add openings for me). So my approach is to use a soldermask opening w/ a diameter a few mils less than the finished hole size. Is that the correct policy? What exact soldermask diameter should I be using?

Newbie guesses:
1) It's a BGA of some kind, with non-solder-mask-defined pads.

2) The vias aren't completely covered with solder mask, so there might be bridging that occurs between balls and vias...?

3) We're going back...to the future!

4) Tout de suite

I think it will work, but that's only because I wouldn't have thought there was anything wrong with it if you didn't point it out :) I guess if solder bridging is a problem it would work with a good stencil. Make the stencil openings smaller than the pads so that you use less solder?

I'll let someone more knowledgeable tackle the first two questions, but I'd like to answer to the last two:

3. Planet Ten!
4. Real Soon!

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