The first step to testing the CC1120 dev board was to assemble a few of them. For myself (Kaveet), this was my first time soldering, let alone hand-soldering 0402 components. If you can’t easily trust your soldering skills, try and assemble a few boards rather than just one. Having multiple boards increases your sample size and makes it easier to identify issues.
During assembly, you can validate that any given passive (caps, inductors, resistors) has been soldered correctly. To do this, you’ll need to set a DMM (digital multimeter) to the X function and probe the board. Connect one end to either side of the capacitor and the other end to a nearby VIA. If you get a reading of Y, then the capacitor is correctly soldered to the board. Obviously, this is tedious to do for every capacitor, so maybe try it for the first few, until you’re comfortable with soldering. Eventually, you’ll be able to check for a good connection either visually or by feeling. For now, the DMM is a perfectly reasonable way to check.
Once the boards were assembled, some of the pre-existing firmware was run on them. It’s important to note that this firmware should be previously developed beforehand. You need to know the firmware actually works before trying to run it on the board. For the CC1120s, this meant running them on the ccRF3 development boards we purchased. These software tests were attempting to read the registers on the CC1120 IC, and will be explained further below.
Additionally, you can optionally look at your boards under a microscope before/after running firmware. There's one inside the RPC (E5-2002). You can use this to take a closer look at the connections. You want to be able to visibly see the solder connecting the pad to the passive/component. If you can’t see this under the microscope, there's probably not enough solder. Here's a diagram of what you should see:
If you ran firmware and everything worked, that's great! Your design works as-is and you can start characterizing the outputs and making little changes to optimize other things (e.g increasing the value of a capacitor to optimize filtration). However, chances are, it won’t work the first time around and with the CC1120, that was the case. We got complete failures on our readings (registers reading 255). In this situation, it isn't always clear what to do, so I’ll walk you through some of the things we did to try and diagnose the issue as well as the lessons we learned.
If you haven't already, the first thing you should do is examine the connections. You can likely use some of the methods described earlier, like checking a few with a DMM, or taking a closer look under the microscope. The good news about this is that it's super easy to fix, you just need to redo a few connections.
Next up, you probably want to check for shorts in any closely packed spaces and any components with small pins. If you have a short, it’s probably most likely on one of the ICs. To identify these, you can look at them closely under the microscope. This usually does the trick, but sometimes you might want even more confirmation. You can use a DMM to check for continuity, probing the two adjacent pads that you think might be shorted. If you get a reading, then they are. From there, you can find whichever method you want to resolve the short (resolder, reflow, etc.).