We’ve hit a few challenges in the hardware project. Here is an e-mail that Brian, the Electrical Engineer on the Falstaff project sent to our internal mailing list yesterday:

Well…The build of 20 units has not gone as cleanly as I had hoped.

There has been pretty low yield on the two PCBs. Less than 50% on the Main board and ~75% on the Button board.

For the Main PCB there are a lot of boards that have processor bus data lines shorted to each other.

For example one of the boards looks to have D8 and D10 shorted together.

If you look at the layout of the board, you’ll see that D8 and D10 are adjacent to each other at the board to board connector and under the SDRAM BGA. See the image below.

If you look at the left side, you’ll see two pins on the connector that are colored yellow. These are D8 and D10.

I suspect that they are shorted either under the J2 connector or under the U7 BGA.

I’m taking 10 boards over to PCA to morrow to have them x-rayed to see if we can locate the shorts, then fix them.

The fallout on the Button board seems to be a bit more random. On one board, the Left Illumination LED doesn’t work, on another the SM Bus data line is shorted to ground.

That being said, I’ve give 7 working board sets to Dave to get assembled into units. We’ll work on getting more working and assembled ASAP…

We’ve been using the name Falstaff to refer to our first prototype of the oPen. Falstaff will have three printed circuit boards (PCBs) to connect all of its electronic components: a processor board that has the processor, RAM, and ROM; an input/output board that has the buttons and lights; and an image-sensor board that, you guessed it, holds the image sensor and illumination lights.

Here’s a picture of Rev 1 of the Falstaff processor board which was completed on Wednesday. This board has eight layers of electrical connections through wires that are only 3 thousandths of an inch wide. The next step in the manufacturing process is to solder all the components onto this “bare” board.

Why isn’t this PCB green?

The color of a circuit board comes from the outer layer which is called a “solder mask.” The solder mask covers all the wires to protect them, but leaves holes where the components are soldered to the board. Without solder mask, PBCs are a dirty-yellow color. For some reason, most circuit boards are made with green solder mask, but the manufacturers have many colors to choose from. Since future revisions of this board may look very similar, it is handy to make each revision of the board a different color so that it is easy to tell them apart.

By Ian MacDuff