Symptoms of a Fried MCU

Go To Last Post
10 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,
I'm pretty new and was putting together a kit around the ATMega328P (Sparkfun's Simon SMT kit, yes the page says it's 168, but they shipped a 328 and it's identical PCB artwork to the pre-assembled kit featuring the 328). Wanted to try SMT soldering and, after much difficulty, I hobbled it together.

Among assembly notes, I tried spot soldering and drag soldering and left a mess of bridges in both cases. Pulled out the solder wick and to fix it and it looked pretty good, although I'm pretty concerned that there was so much solder to sop up that I kept my iron on it too long.

Tried programming with a known good programmer (got a basic hello world blinking LED working on a breadboard with the ATTiny13), but was surprised when I tried programming this kit and got the following:

avrdude: Device signature = 0x000000
avrdude: Yikes!  Invalid device signature.
         Double check connections and try again, or use -F to override
         this check.

I've done continuity checks on the board going from the chip to everywhere it connects to and it looks like, electrically, everything's the way it ought to be. Which brings me here instead of the forums there:

A) How tough are these little chips? Did I burn it out? Is there a way I can test that it's operational even though it doesn't have code on it?

B) The updated product page says the chip is preloaded with "Arduino Pro Mini bootloader". Could that be messing me up? I like to consider myself a pretty strong software guy and I'd like to start on the ground floor before using the shortcuts the Arduino environment provides.

Thanks in advance!
[/url]

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Did you check continuity using the actual chip leads, rather than the pads? Sometimes with QFP packages a joint can look OK, but the lead isn't actually soldered properly. It's caught me out a couple of times. Chips generally survive overheating when soldering, it's most likely a poor connection.

The secret of successful drag soldering is plenty of jelly flux.

Leon Heller G1HSM

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Trying to borrow a magnifying loupe for checking out the pins... I used the liquid rosin flux I've always used so maybe I wicked off all the solder since it wasn't jelly?

My meter probes aren't small enough to tap at the pad, but if they're crappy joints I guess I'll buy that the downward pressure is making "good" contact. Heh.

Just mostly curious to see if there's a simple way to rule out problems with the chip and try again with a fresh one (that would have to be ordered) instead of continually reworking and risking lifting the pads or delaminating the board... or else maybe I'm just paranoid about that. :)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Liquid flux isn't much use, get some of the jelly. I use a mini-hoof cartridge with my Metcal solder station for drag-soldering, it holds just enough solder.

I use tiny spring-loaded probes with my DVM for testing QFP connections. They are expensive but worth it.

Use Chip Quik for removing the chip if you don't have a hot-air rework station. It won't damage the pads.

Leon Heller G1HSM

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Leon,

Chip quick looks impressive - not used it myself.
Do you know of any UK based distributors? CPC are mentioned on the Chip Quick website, but can't find it listed.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Leon Heller G1HSM

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You're quite right. Many thanks.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

If you no longer need the chip, you can cut the legs with a sharp hobby knife close the body; the remaining pins are easy to remove in a few sweeps (they'll clump together on the iron tip), then clean it up with desoldering braid.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

As a follow up, looks like pretty much all my pins except the two at each corner of the package are dry joints. Yikes, talk about poor assembly. Ordered the chip quik and appropriate flux to give it a fresh go. :(

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I've had one or two like that, but never that many!

Leon Heller G1HSM