OSP PCB Finish Problems
OSP (Organic Surface preservative, not Oregon State Patrol) isn't all that commonly seen in our shop. It has been a pretty common pcb finish for high-volume, low-cost products for quite a while and I've heard that it's starting to show up more frequently on complex boards these days too. Some of the new formulations are pretty good for RoHS applications.
We got a set of OSP pc boards in just the other day with a lot of fine pitch parts and a few big, honkin BGA lands. Click on the two thumbnails for bigger images that do a good job of illustrating one of the potential pitfalls of OSP boards. In the close-ups, you can clearly see two different colors of copper land pads. That's not normal. It indicates an unsolderable, contaminated finish. If you look at an OSP board and see a pretty multi-colored pattern like that, get on the phone with your pcb fab shop and get the boards re-done.
Take a second look at the closer close-up here. This board also does a good job of illustrating the use of NSMD (Non Solder Mask Defined) pads. Most BGA manufacturers recommend the use of NSMD pads. This allows the BGA ball to sag down a little more and grip on the side of the pad too. It also illustrates the proper way to mask the trace between the pad and the via. That's very important too. That mask will keep the solder balls from being sucked off of the BGA.
Suddenly, State Patrol...