BACKLOG 20180202: PCB Issues & Fixes

A project log for M.O.S.A.I.C. LS

Modular Open Source Adjustable Intelligent Control Lighting System

slisgrinderslisgrinder 04/05/2018 at 02:090 Comments

I Did This To Myself...

So I placed an order with OSH Park for the PCBs on January 13th and I wasn't expecting them to be here so soon!

1st Cell Prototype
Figure 1: 1st cell prototype
1st Cell Prototype Backside
Figure 2: 1st cell prototype backside

The silkscreen turned out fabulous; the soldermask and hole registrations are VERY good. And then I noticed something...

If you look carefully at the soldermask in Figure 2, notice the lack of copper pads where the ground pads and screw pads are. A quick continuity check further confused me as all the IO connections were shorted together along with the power pads on the side and the corner ground pads.

Looking further at Figure 2, you can see that the vias seem raised and bumpy. The same can be said about the power pads and IO connectors. Compared to Figure 1, all seems well on the top side of the board.

Cell Edge Inspection Top
Figure 3: cell edge inspection top
Cell Edge Inspection Bottom
Figure 4: cell edge inspection bottom

A quick look under the inspection scope shows a potential problem in the IO connector. Figure 3 shows the top side (LED side) on the left and in focus. Figure 4 shows the bottom side on the right and in focus. The IO pads seem to be connected on the bottom layer and on the top they are isolated as they should be. Also of note are the internal layers visible in both inspection pictures.

Cell Prototype Missing Plane
Figure 5: cell prototype missing plane

It seems that the ground plane on the bottom later is entirely missing (as outlined in Figure 5). However, the IO connector pads are all shorted together. Weird...

The Fix...

I informed OSH Park about the issue and their response was quick and quite unexpectedly detailed. They were so awesome in fact that they dug deep to figure out the problem and over the weekend at that! It turns out it was partly my fault although I didn't know it at the time.

Cell Ground Plane Over Extended
Figure 6: cell ground plane over extended

The internal planes were initially setup as an equilateral triangle but my board outline cut through them. This meant that there were parts of the planes outside the board as shown in Figure 6 (top portion of plane visible above and past the center "GND" screw pad). When the gerbers were processed by OSH Park, the over extending parts of the plane were removed. However because they are part of the same plane entities, the entire plane was removed and funkiness ensued.

The folks at OSH Park were very thorough in their investigation and offered a very concise explanation in a timely manner. They were nice enough to rerun the boards for me at no cost and even offered expedited shipping!

Thank you OSH Park!

OSH Park, thank you very much for the help. I learned something new and I hope other companies follow your lead...