Testing components with power as soldering before entire circuit is built.  - Page 1
Forum section: electronics / beginners

author: Websteria
author_rank: Contributor
timestamp: August 27, 2019, 04:34:40 pm
content: Let me say my level of experience is building 2 smd kits. Watching lots of videos about how to solder qfp44. I’ve been doing this about 4 months now. No formal training. I’ve been working on a rather elaborate rgb led clock. I have gone through about four kits now after what seemed to be a critical failure in the processor.I’ve removed these processors using hot air. 300 degrees. About 30-45 seconds. Too hot?Here’s the real question:I built the clock circuit and began to work on the 60 leds. Having had problems with shorts in the past I was soldering them with the power on to the clock, to ensure all points made contact and the colors were correct.Could this have contributed to problems? Is this a no no? If so, why?In the instructions they say to solder all 60 leds on the front of the board before building the clock circuit on the back. This feels dangerous as I can’t really test the processor output without having a processor in there.Why do shorts seem to happen so easily with this kit? I’ve made other smd things that worked fine?I’m flabbergasted, at the end of my rope. Have ordered 10 more kits. I’m not giving up but I figure somewhere someone here has been where I’ve been.Btw to see the clock google ds3231 rainbow.

author: mikerj
author_rank: Super Contributor
timestamp: August 27, 2019, 04:43:45 pm
content: You certainly shouldn't be soldering anything with power applied, this an absolute no. Do those LEDs have the WS2812 controllers on board or are they just dumb RGB LEDs, since the former are very heat sensitive.

author: Websteria
author_rank: Contributor
timestamp: August 27, 2019, 04:53:26 pm
content: theyre just dumb 5050 leds. I can apply 20ma across each segment and it lights.

author: Websteria
author_rank: Contributor
timestamp: August 28, 2019, 01:41:29 pm
content: As an aside, is it safe to solder each LED with the power off while the MCU is in? Or should all RGBs be soldered before testing. I have a feeling it's the second because of expected resistances and voltages, etc.

author: IanB
author_rank: Super Contributor
timestamp: August 28, 2019, 01:54:59 pm
content: I think you should follow the instructions. If they say to assemble things in a certain order, there will be a reason for that. Also, do not assemble anything with power supplied, ever. It's a very bad idea. Don't even think of it.In the old days a sensitive component like a processor might be socketed. You would install the processor in the socket at the very end after assembling the rest of the circuit and checking to make sure it looks good. If there is no socket you still might install the processor last to minimize the risk of damage.

author: Websteria
author_rank: Contributor
timestamp: August 28, 2019, 02:24:02 pm
content: Thank you. This is what I needed to hear. I have fear of the circuit failing with no reason, and having no documentation really on the application the processor is running I can't even tell what the problem is if it just doesn't power. Off to solder 60 SMD LEDs (at 280C) !