Soldering LED light strips
- Thread starter Donald
- Start date
It does look close, but, gauging by the shadows in the soldermask, I think the black wire does connect to that side of the LED. So a solder bridge here won't matter. You need to verify that of course.
Looks like that leftmost LED cathode is probably tied to the "left" LED on all the other ones in this string. Looks like the bias resistor is in the middle of 4(?) LED's, then multiple strings in parallel? 17.4ohm bias resistor by the looks of it. 12V LED lighting?
So just because the solder melts at 361F does not mean I should set the temp of the solder station to that temp?
Nope. You don't want to heat it to where it boils--that'd be hazardous to your health!--but hotter is better, in the general case. I'm no SME on the subject, but, its like you want the copper pad to heat up really fast, solder really fast, then you're done. We don't think of FR4 as being a conductor of heat, but it does pull heat, it's not a perfect insulator.
Thought of differently: let's say your iron was 317F. You touch solder to it and it melts. Now you put the iron to the copper pad and touch the solder to it. What happens? nothing happens, because as soon as it touches, heat leaves the tip and now it's 315 or probably less, much less. As soon as the tip hits that copper pad, it starts losing heat. As soon as you touch solder to it, it's losing heat. As soon as the flux melts and starts flowing, it's "flowing" heat away from the iron.
How fast does the tip cool, and how much does it matter, eh, couldn't tell you, I've never tried to solder at low temperatures. I'm not an expert on PCB's but I will tell you, soldering temperatures, at any, degrades the plastic material that the laminate is. The longer you have it hot, the more damage occurs. Not only that but as you solder, the protective layer of metal above the copper trace is slowly absorbed into the solder joint itself. Once it disappears, the copper itself becomes next in line to be attacked--and it's going to degrade quicker than what was above it (often it's nickel). But this is happening at the same time that the FR4 is gassing out. And at the same time, you're well past the point where the FR4 is considered "solid", it's now above what's considered the glass temperature, where it's now "soft". Before long, the PCB pad will lift off the board, and it's game over.
Link to an article about Tg.
Another link about soldering temperature discussion.
Note, reflow soldering (where you apply solder paste to the pads, then place the SMT parts, then bake the assembly so that the solder paste melts) is done at lower temperatures, but as a process, it's different: the entire assembly is heated all at once, and even then, it's a quick ramp up, with a limited time at solder paste melting temperatures. Again, you're well past the temperature that the laminate is rated to live at, and it's outgassing at even these lower temperatures of 500F or so, so dwell time needs to be limited.
Thought of differently: let's say your iron was 317F. You touch solder to it and it melts. Now you put the iron to the copper pad and touch the solder to it. What happens? nothing happens, because as soon as it touches, heat leaves the tip and now it's 315 or probably less, much less. As soon as the tip hits that copper pad, it starts losing heat. As soon as you touch solder to it, it's losing heat. As soon as the flux melts and starts flowing, it's "flowing" heat away from the iron.
How fast does the tip cool, and how much does it matter, eh, couldn't tell you, I've never tried to solder at low temperatures. I'm not an expert on PCB's but I will tell you, soldering temperatures, at any, degrades the plastic material that the laminate is. The longer you have it hot, the more damage occurs. Not only that but as you solder, the protective layer of metal above the copper trace is slowly absorbed into the solder joint itself. Once it disappears, the copper itself becomes next in line to be attacked--and it's going to degrade quicker than what was above it (often it's nickel). But this is happening at the same time that the FR4 is gassing out. And at the same time, you're well past the point where the FR4 is considered "solid", it's now above what's considered the glass temperature, where it's now "soft". Before long, the PCB pad will lift off the board, and it's game over.
Link to an article about Tg.
Another link about soldering temperature discussion.
Note, reflow soldering (where you apply solder paste to the pads, then place the SMT parts, then bake the assembly so that the solder paste melts) is done at lower temperatures, but as a process, it's different: the entire assembly is heated all at once, and even then, it's a quick ramp up, with a limited time at solder paste melting temperatures. Again, you're well past the temperature that the laminate is rated to live at, and it's outgassing at even these lower temperatures of 500F or so, so dwell time needs to be limited.
Sounds like 600F is probably the right temp.
If you know your solder alloy, Kester has chart that shows range of melt temps.
Alloy Temperature Chart | Kester
www.kester.com
If you read the initial post of this thread I said it's 361F.
But I think the soldering pencil needs to be set a lot hotter than that.
My post was just to add general info, not to tell you where to set your temperature.
Yes, soldering temperature needs to be set higher than solder melt temps because of heat transfer, etc.
I one situation I have three back to back sections under the cabinets. The sections will be connected together via a short wire and the wire needs to go through a small hole between two cabinets.
The question is will I be able to solder properly where the light strip is installed under the cabinet and the soldering pencil and my hands are below the light strip. My head is looking up.
I try and solder as much as I can with the light strip on the counter and me sitting on a stool. But not in this one case. At least not both ends of this short wire.
The question is will I be able to solder properly where the light strip is installed under the cabinet and the soldering pencil and my hands are below the light strip. My head is looking up.
I try and solder as much as I can with the light strip on the counter and me sitting on a stool. But not in this one case. At least not both ends of this short wire.
