SMD soldering for a 3030 led. - Page 1
Forum section: electronics / beginners

author: 6PTsocket
author_rank: Regular Contributor
timestamp: November 09, 2018, 06:48:35 pm
content: I just removed/ butchered a bad led off a pc board. This is my first experience with a device that is soldered on the back as opposed to the edge. I assume it is to get the best heat sinking to the copper on the pc board. The board has some high temp coating in both sides of the board with vent? holes around the led on both sides of the board. The only damage my soldering pencil heat did was discolor it. What is the best way to install the new led, hot air from the front, the back? Hopefully I can put the soldering iron next to the led and conduct enough heat under it to the pre tinned pads. See attached photos of front and back. The entire light fixture is around 60 bucks and I am sure going to try replacing the led first. The fixture worked at room temp and quit when it got cold in my freezer so it was probably a bad solder joint to begin with but I blew the led "testing" it. My bad.I posted a question earlier about how to calculate the correct size led. I measured open circuit at 14.86 volts. I soldered in a 169.5 ( measured) resistor in for the led and measured 11.81 across it. That makes the series resistor 43.77 ohms. Assuming the 3030 drops 3 volts. That works out to 270ma or a 1watt led. I did, at one point, have the old led led pretty bright with a little under 3 volts so I am pretty sure it is not a 6 volt double led. Thanks.Sent from my SM-G900V using Tapatalk

author: t1d
author_rank: Super Contributor
timestamp: November 09, 2018, 10:41:28 pm
content: YouTube has videos on soldering techniques, for this very type LED project. So, maybe check there.I learned tons, about soldering, on YT. NASA even has soldering tuts, on there! It is easy to spot the folks that don't know what they are doing. Just move on, to the next one.Plus, there are a lot of DIY work-around solutions, for tough problems, with limited specialty tools. Heat gun, hot plate, clothes iron, homemade reflow oven...See "Mr. Carlson's Lab," for how to easily make a special tip, for the pistol-style soldering irons, that dumps a lot of heat, to a flat surface, in a hurry.I made my own DIY reflow oven. It works, well enough.See if there is a MakerSpace club, in your area. They often have great equipment, for the members to use. And, expertise, too.Isopropyl alcohol and a static-free brush (An old toothbrush would be okay, here, because the component has been removed.) will help with cleaning the board. You can get it at most any pharmacy. Get the highest percentage of alcohol, that they have... 99%, but not all stores have it.Do you have flux and solder paste (not solder wire?) If not, read up on those, too.Please remember to post your solutions, to help the next guy... I would like to know what you do, myself.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: November 10, 2018, 01:33:14 am
content: Quote from: t1d on November 09, 2018, 10:41:28 pmThanks for all the suggestions. I have a plastic welder that is basically a soldering iron. One of the tips is a flat pad that might do the trick. I'll have to check with the IR gun or thermocouple bead tip that came with my dmm to see if it gets hot enough. I think my old Weller gun has a spreader tip, too. I guess it is best to use a lot of heat and get out quick.Sent from my SM-G900V using Tapatalk

author: Brumby
author_rank: Unknown
timestamp: November 10, 2018, 03:31:18 am
content: Quote from: 6PTsocket on November 10, 2018, 01:33:14 amJust be careful about "a lot of heat" - you can go too far (as I'm sure you know). The "get out quick" part is the right thinking, but make sure you don't get outtooquick. An extra half second for the solder to flow properly on your first attempt isfar less riskythan having to go back and heat the whole joint for a second (or third, or fourth) time.This type of board is made as a heatsink and it will draw heat away quite effectively, so my advice would be to preheat the board with a hot air gun (if you have one) so the soldering iron doesn't have to doallthe work (which will likely take longer). This also minimises the time the LED spends at elevated temperatures.

author: t1d
author_rank: Super Contributor
timestamp: November 10, 2018, 05:23:29 am
content: Quote from: Brumby on November 10, 2018, 03:31:18 amExcellent point. And, with solder that is not completely liquid and just a little too much lifting force, you can pull the copper pads off.Quote from: Brumby on November 10, 2018, 03:31:18 amGreat suggestion.

author: t1d
author_rank: Super Contributor
timestamp: November 10, 2018, 05:45:50 am
content: Quote from: 6PTsocket on November 10, 2018, 01:33:14 amHey, now you are thinking outside the box and you're going to test the idea, before trying it with the board. Atta-boy.As far as how hot the plastic welder will get, you also have to consider how much mass its tip has. I imagine that it is thin. If so, the board will probably suck all the heat out of it, before the job is done.Quote from: 6PTsocket on November 10, 2018, 01:33:14 amYes, this should be the gun-style iron that I was referring to. Carlson's tip is just a piece of bare (12 gauge, IIRC) copper wire, bent in a special shape, to work with the gun.I have a friend that needed to cut and heat seal the seam of a great quantity of synthetic cloth. Own his own, he came up with the copper wire tip idea. He flattened the curve, of the wire, to make a knife blade. It does both jobs at once, extremely well, easily and lightning fast. You might flatten the tip, to give it a broader face, to increase the contact area.