ok i need to know how to solder some SMT leds they are 3mm length with 1mm wide and 1mm thick... eek?!!? how do i tell which is the anode and which is the cathode???? also the powering.. they are 3.8V what should i use?? the capacitors are 10V 22 micro farad edit:: they are actually smaller than that that was the packaging that i was measuring !!!
I have hand soldered more SMT parts than anyone I know. (Look at the reistors on your DDR and try doing 40 of those) ---------------- http://www.lcdexceltech.com/ledsur.jpg There should be a TINY dot marked on one side. Or one side may be beveled slightly. (I don't know which polarity it is, but once you figure one out you can use that for the rest) Are you soldering these to a PCB or trying to free hand them? (Like to the back of the membrane?) If free hand they will bust fast. If you don't want to do a PCB you need to use VERY thin wire (magnet wire works pretty good) You can then use a tiny amount of superglue to hold the LED down onto some lexan or some other plate. It is hard to tin SMT parts, but if you can tin them that would be best. (Applying fresh solder to each surface: wire/led) You need the smalled soldering tip you can get. A magnifying glass or microscope helps a lot too. If they are all 3.8volts I would power them off of 5 volts. (They were all in parallel right?) That way you can use a small SMT resistor also.
you could allways use an AA battery with a couple of leads to test for annode and cathode. As for the soldering, Good luck mate!! hehe maybe one of those helping hands doobries from mappers would be a godsend.
its FOR a mod?? the plexiglass keyboard?? still need help tho zap can i just use a needle in my soldering iron?
I'll agree with Zap from my experience working in QC and rework for SMT boards. He forgot to mention the tweezers though The tip should be fine enough that it feels fairly sharp, not as sharp as a nail or needle, but still pretty sharp. If it isn't you run the risk of getting too mch solder on the part. As for the wire, I usally use wire wrap wire myself. IMO, it's easier to work with because it's insulated and can be striped like other wire instead of trying to remove a varnish. I also reccomend at least some kind of adhesive. Somthing the the often mentioned blu-tac is good if you want some ability to rework the LEDs, otherwise, superglue is a bit more durable. SMT parts simply don't flex, the crack, tear off their pads, break in half, ect unless they are fastened to something. As for polarity, the marking usally indicates the cathode, but I'd still test it. Take a piece of take and make a loop with the sticky side out.Stich it to the table, and put the LED on it. It shouldn't go anyware easily now. Put three batteries in series so you have 4.5 volts, and use a 39 ohm current limiting resistor (assuming a 20mA current). Solder somthing like pins onto some wire, or use really fine wire and check the polarity. Clippings from componet leads also work instead of pins. Also, if you have any AT power supplies handy, they make a wonderful source for 5 volts specifically for testing stuff like this.
Get some Kynar wire if you want to solder wire to SMT parts, its the only way to go. Search for Kynar at http://www.rswww.com
i did it without solder-- just for testing purposes anyway-- i used some component wire and used double-sided sticky tape to keep it in place
Get some low-temperature solder for the job, thats what i use whenever i have to solder SMD's (very, very rare), much easier
You will need a very fine soldering iron bit (I use one of the maplin 'Antex' brand soldering irons with a 0.12 mm bit - Maplin don't sell these bits, you need to get them direct from Antex). If you are soldering to a PCB, I've found it helps to apply a tiny bit of solder to the pads first. This avoids the need to apply additional solder later. Attaching wires to SMDs is generally a bad idea - they are fragile and higher power devices, like LEDs, need the PCBs for heatsinking. The SMD LEDs I've used have the cathode marked, by a very subtle spot of ink near the terminal. The first board I assembled, I got 2 of 3 LEDs back to front. Doh! You should either check the datasheet to be sure, or use a power supply to test the polarity. Soldering SMDs is pretty tough - I recently built 10 boards, each with 30 SMDs (and I was careful to choose 'big' ones 0805 and 1206 sizes). You wouldn't believe the headaches and eye-strain I was left with. The boards all worked fine (apart from the last one where I ran out of parts because I dropped a couple of resistors and capacitors).
Hi For soldering SMD/SMT stuff use Solder Paste. U can find it at Farnell , search for "solder paste". The only problem with solder paste is "Refrigerated storage is recommended". But it gives really fine solder joints and only a small amount of heat is required.
If I read correctly in a couple other things, solder paste is a mix of granules of solder and a somewhat sticky flux, you put it on the solder pads, stick the SMT to it, and take something like a heat gun to melt it and solder it. It is how they do it commercialy with either wave soldering, or reflow. From what I read, they take either a 5 step infrared oven a heat the board, or hold it over a boiling liquid where the vapor is of sufficient heat.
Yeah okay i may have made it sound easy, this solder paste stuff... 1'st off take your solder paste out of the fridge and make sure that the paste hasen't exseeded the expiration date. Then the paste has to be left out for some time to reach a temp of 20 C. Apply the paste to the solder pads (not to much, not to little). Apply the SMD. And now for the soldering part: Preheat a oven (not one you inteend to use for cooking !!!! i have used a old toaster oven) Let it have a temp of 200 C (depending on paste) put in the board and watch it for 2-5 min. Take it out off the oven (auch HOT !!!) and let it cool slowly. Another way You have a heat gun speciallized for soldering and use that instead of the oven. Okay i hope this helped. BUT remember this stuff is poisonous wash hands and stuff. ALSO you should know the characteristics of the paste, there is a lot of this stuff out there and they have different temp and so one.... More ?'s ask....
Here's a good guide on using soldering paste. Bard, Don't you remember I gave you a link on soldering paste when you broke your soldering iron? [EDIT] You don't need to use an oven like in the guide, e.g a heat gun works very good [/]
