Prototyping: Dead Bug construction

Last time (here) I was about to mount difficult little chip on my new board. Here is how it turned out:

So far my phone has been the best camera for taking photos through the microscope, but as you can see, it isn't exactly great for the job either, but sufficient for quick photo like this.

After some consideration and design re-check I decided against trying to reflow the plastic package on place - due to very low probability of success and the fact that two pins were actually flipped so it wouldn't have worked anyway. Next best thing was dead bug construction. Chip is placed/glued in suitable location upside down (so its legs point up, like dead bugs' legs, hence the name) and wired from there. Definitely not suitable for production but it can save some effort when prototyping (and round or two of boards before you get to final design.)

So I put some hot melt glue on board (not best for the job but other glues I had weren't any better), put chip on top of it and started soldering. Fortunately only four wires was needed so it wasn't too bad but it's difficult anyway.

Remember I said those pads are 0,25 x 0,25mm each? As it turns out, even the smallest, thinnest soldering iron tip I had is larger, making it very difficult to apply solder to chip pads without touching other pads at same time as often I ended up accidentially desoldering already placed wire.

This chip has two VCC pads (one for IO, one for analog parts) and one IO line had to be pulled high so that's three VCC pins. Now they're all same, dangling at the end of wires so noise performance won't as good as it could be but for quick testing it should be sufficient.

Then four ground pads, in somewhat difficult arrangement. Now those were a real PITA to solder as one pad tended to desolder when soldering another. Two IO pads were so very easy to solder compared to VCC and GND.

The tracks on board are mere 0,15mm wide. First I used one strand of thicker wire (in middle), but that was too rigid and working with it was way too difficult. For three others I took even thinner strand which was much easier to work with, but getting solder to stick still was difficult.

The end result is that chip responds to commands but so far I haven't had time to test it further (too busy at other functionality of the board so far), which means that some pad might still be badly soldered, causing it to behave unexpectedly or just wrong.

I'm still not looking forward to assembling next test boards...