soldering on PCB help - Page 1
Forum section: electronics / beginners

author: jonny_w
author_rank: Contributor
timestamp: January 20, 2014, 12:59:33 am
content: I recently purchased one of those cheap Elenco training kits to practice my soldering. I'm using leaded 63/37 solder. I've got a Hakko FX-888, running at 650F.What I'm noticing is that the solder isn't flowing on to the PCB pad, and it's just balling up. However, once I remove the solder from the pad (using a solder sucker), and reapply the solder, it flows BEAUTIFULLY to the joint.Is this an indication that I should clean the PCB before soldering? For some reason the solder just isn't flowing nicely, right off the bat. I attached some photos of my work.Any suggestions welcome.

author: Rory
author_rank: Frequent Contributor
timestamp: January 20, 2014, 01:09:05 am
content: Sounds like it needs more flux.

author: rexxar
author_rank: Frequent Contributor
timestamp: January 20, 2014, 01:11:37 am
content: I'll assume you mean 650C. I'd back that down a bit for leaded, I usually put mine about 550C.Are you using flux? If you got one of these kits from RadioShack or similar, it's probably been on the shelf for a long time, and the pads are oxidized. Flux will help a lot. Make sure your tip is clean and well tinned, and you should be good to go.Remember that you want to heat the pad and component, not the solder. It's fine to put a bit of solder on the tip of your iron to help contact, but you really want to be applying solder directly to the pad.

author: Rudane
author_rank: Regular Contributor
timestamp: January 20, 2014, 01:15:44 am
content: Can you describe your process? Hopefully it's something like this:1. Tin your tip with a small amount of solder2. Bring the tip to the pad.3. While holding the iron onto the pad, add a little more solder.4. Drag your iron up the leg of the component and inspect for the proper solder shape.

author: rdl
author_rank: Super Contributor
timestamp: January 20, 2014, 01:16:05 am
content: Quote from: rexxar on January 20, 2014, 01:11:37 amNo, I think he means F, the FX-888 only goes to 480C. 0ver 600C is way high for soldering.

author: sleemanj
author_rank: Super Contributor
timestamp: January 20, 2014, 01:43:49 am
content: Quote from: rexxar on January 20, 2014, 01:11:37 am550 Fahrenheit is what you are using (290 Celsius), if you were using 550 Celsius, you wouldn't be having any success at all.To the OP, drop the temperature a bit, 300 Celsius or so, wipe clean the board before you start, and use flux. Make sure the tip of the iron is clean and tinned.

author: jonny_w
author_rank: Contributor
timestamp: January 20, 2014, 01:51:39 am
content: Thank you all for your replies. I'll drop the temperature to 300C, clean the next board & use flux.As for the cleaning, I'm assuming isopropyl alcohol applied with a toothbrush is okay? And for flux, should I buy a flux pen & apply the flux to the pad before soldering?

author: Psi
author_rank: Super Contributor
timestamp: January 20, 2014, 02:30:38 am
content: 350C is a good default temp300C tends to be a bit low for bigger components

author: rexxar
author_rank: Frequent Contributor
timestamp: January 20, 2014, 02:38:38 am
content: Quote from: rdl on January 20, 2014, 01:16:05 amIt would seem that I can't read the temperature scale on my iron (and also don't understand Celsius). Carry on.

author: GreyWoolfe
author_rank: Unknown
timestamp: January 20, 2014, 01:14:24 pm
content: Quote from: jonny_w on January 20, 2014, 01:51:39 amI use MG CHemicals rosin flux liquid applied with a hypodermic needle for precise placement. You can also get small squeeze bottles with hypo needles on them, which I have, but I find I have better control with the hypodermic needle.

author: nanofrog
author_rank: Super Contributor
timestamp: January 20, 2014, 01:57:41 pm
content: Quote from: GreyWoolfe on January 20, 2014, 01:14:24 pmI also have a needle bottle. Small, precise paint brush works really well too (few drops on a spot plate, and dip as needed). Even keeps costs lower and waste down IMHO.Stumbled across aBON-102 refillable pen(fine point brush tip; sold empty), and seriously considering giving it a go. Seems it would be very convenient. FWIW, they have a few other tip shapes as well.

author: GreyWoolfe
author_rank: Unknown
timestamp: January 20, 2014, 10:19:23 pm
content: Nanofrog, I use a 10 ml syringe with a 21 ga needle cut flat. With just a little practice I am able to drop a tiny bead on a pad and spread it with the tip of the needle. I probably do use a bit more than using a fine paintbrush or a refillable pen, but the syringes and needles are free. My wife works at a Dr. office and brings them as I need them. I might try the paint brush, what size do you use? I would think at least a 4-0. If you decide to get one of those pens, let us know what you think.

author: nanofrog
author_rank: Super Contributor
timestamp: January 20, 2014, 11:21:48 pm
content: Quote from: GreyWoolfe on January 20, 2014, 10:19:23 pmDon't have access to free syringes (must be nice), and I'm not sure of a good source that's inexpensive. Does seem like you'll have a lot of control though.Not sure on the size (bench is completely cleared for the shelving project & stuffed in boxes or wherever I could find a hole), but based on a chart I found, it's probably a #2 round (2/32"). Waste isn't bad due to size. Chisel type, would probably be another story if it's a small job or taken in spells, which is more of how I tend to do things (rely on the solder wire most of the time).They do require cleaning though, so it's as convenient as a disposable pen or the refillable model mentioned. I really like the brush idea better than the hard felt or plastic nibs, and when I saw refillable, that got my attention.Found a source on eBay for one ($5.99), and the box it's photographed with looks genuine. But I'm not sure due to the cost, as they're $15+ everywhere else I've looked. Might use it as a filler item from All-Spec. If I do go ahead and get one, I'll let you know.I usually only use a needle bottle for tinning wire & drag soldering, so not that big a deal.I found a seller on eBay that sells small quantities of Kester 186 if you're interested (sells 951 too). The 186 seems to be genuine to me (behaves well, and smells as I remember). Can't justify buying it by the gallon (would need to sell of the majority of it), so I gave the seller a chance (~$6 IIRC for the size I got). Previously, I'd use MG Chemicals liquid rosin, as they sell a 125ml bottle. The Kester is a bit lower in solids (36% vs. 50%, so it's a bit easier to clean IMHO). Not as active though IIRC, so YMMV, depending on if you're repairing stuff that's heavily oxidized or building on boards that are relatively new.

author: wilheldp
author_rank: Regular Contributor
timestamp: January 20, 2014, 11:34:10 pm
content: I have a nearly unlimited supply of 1/2cc syringes with 29 gauge needles. I'm not sure if they are appropriate for solder past or flux, but if anybody is nearby, you can have some. It wouldn't be cost effective to ship them anywhere because they only cost 25 cents each. Look up U-40 insulin syringes if you want some.

author: GreyWoolfe
author_rank: Unknown
timestamp: January 21, 2014, 02:05:12 am
content: Quote from: wilheldp on January 20, 2014, 11:34:10 pmI think that 29 ga will be too small for practical use. I believe that the paste will be too thick to pass and from playing with the MG chemicals flux, I think that the flux will be thick enough that it will really require some pressure which will either shoot out like projectile vomit ( sorry for the reference) or you could possibly pop the needle off of the syringe which will make an even bigger mess. I have had that happen trying to push marvel mystery oil through too small of a needle. We used to use this to lubricate parts of a proprietary printer. The stuff would also degrade the seal on the plungers after awhile. I don't know if this will happen with liquid flux. Time will tell.Nano, I did buy the 2 for $7 squeeze bottles with the needles on them off of eBay and those are great for tinning or soldering Western Union splices. I also think the liquid flux/squeeze bottle combo will work well for soldering the shields of RG8X style coax to PL-259 connectors. I played with both for soldering pcb and decided to stick with the syringe.

author: sleemanj
author_rank: Super Contributor
timestamp: January 21, 2014, 02:24:48 am
content: Quote from: GreyWoolfe on January 21, 2014, 02:05:12 amAs a diabetic, I have to agree, I don't think that insulin syringes would work that well, the capacity is miniscule, really they are only intended for single use (the plunger won't stand up to much abuse), the gauge is microscopic. They would be no good at all for solder paste, for flux... nah I don't think so, even liquid flux would probably have trouble. I haven't used them in years (I use pens) but might have one or two somewhere, if I stumble across one I'll try it out.Large syringes and needles of various gauges are available readily on ebay for very little, I bought some last year with long needles for de and re filling inkjet cartridges, I think I paid $6.50 US for 10 (10cc) syringes and needles (eg like this:http://www.ebay.com.au/itm/10x-10ml-syringe-for-ink-jet-cartridges-of-HP-Canon-Lexmark-Brother-syringes-/111249909202?pt=AU_Computers_Printer_Accessories&hash=item19e702e5d2&_uhb=1but I didn't buy from there, the seller I did buy from must be on Chinese New Year holiday)

author: IanB
author_rank: Super Contributor
timestamp: January 21, 2014, 03:16:28 am
content: Quote from: jonny_w on January 20, 2014, 12:59:33 amI had exactly the same experience last time I soldered a kit. Same iron, same temperature.My conclusion was the same as yours. Clean the PCB before starting. I'd suggest giving it a wipe over with IPA to remove any grease, then give it a once-over with an abrasive pad such as a hard pencil eraser or a purpose designed contact cleaning tool to make each of the solder pads shiny.For through hole soldering you should find that the flux in the solder core is sufficient. If people added extra flux to every solder pad before soldering then assembling a board would take forever.

author: sleemanj
author_rank: Super Contributor
timestamp: January 21, 2014, 04:08:22 am
content: Quote from: IanB on January 21, 2014, 03:16:28 amFlux on cottonbud or finger tip, swipe pads and pins with flux, job done.

author: nanofrog
author_rank: Super Contributor
timestamp: January 21, 2014, 06:21:50 am
content: Quote from: GreyWoolfe on January 21, 2014, 02:05:12 amIf it uses thinners such as acetone or xylene for example, I would expect so (possibly soften or solve the syringe body as well).

author: Rerouter
author_rank: Super Contributor
timestamp: January 21, 2014, 06:51:29 am
content: solder forming balls on leads is generally a sign that the board is just old, (oxidized in free air) so increasing flux is the general rework option, otherwise if you have more boards to make, 15 seconds with a bit of wet and dry sandpaper to bring it back to a shine can be the better way when starting fresh,

author: Rick Law
author_rank: Super Contributor
timestamp: January 21, 2014, 08:30:05 am
content: Quote from: Psi on January 20, 2014, 02:30:38 amI found that to be true also, and 350C is also what Dave Jones' solder video suggests. But I am a bit confused. Many datasheet I've seen had soldering info with something like 270C for up to x seconds where x is typically 2 to 3 seconds and I don't recall seeing any x > 5 seconds.I suppose 350C is relying on shorter contact time?(I have little success with 270C, but with datasheet saying 270C for up to X seconds, I keep thinking perhaps I should get good at soldering at around 270C.)

author: Rerouter
author_rank: Super Contributor
timestamp: January 21, 2014, 08:51:06 am
content: When you first touch the iron to the joint the joint is at ambient (25 degrees C for example) and the iron tip is at 330-350, now when these 2 piece of metal become coupled with a good thermal contact (wetted by solder) one will shoot down and one will shoot up until the wattage can correct it back up to set point,Now this amount is dependent on the 2 thermal masses (how much thermally conductive material) so a pissy little 25W iron with a massive tip may perform better than a 75W iron with a tiny tip as long as the mass your soldering is not too big, however if you where to compare apples to apples and give them both the same tip you would generally run the 25W hotter than you would the 75W to counteract the cooling when meeting a joint to keep the time in contact to a minimum (time is money and ratings are only given for a few seconds)Another view point on this is where the newer Very compact and very high wattage irons come in, there fast response and massive peak wattage demand means they see essentially no drop until you get to some very big masses, and with these you can set the iron on the dot and trust that what you see is what you get.

author: Psi
author_rank: Super Contributor
timestamp: January 21, 2014, 09:59:20 am
content: Typical solder melts at ~190C, so when you touch the iron to the pad and see the joint begin to flow it's WELL under the 350C of your ironPut simply, if you solder something for 2 seconds with the iron at 350C the joint may only ever get to 300C and the semiconductor inside the component may only get to 270C for example.Side note: 300C is a good temp to solder wires onto small connector terminals, its low enough to avoid the problem where the wire insulation starts to melt and pull away from the terminal

author: jonny_w
author_rank: Contributor
timestamp: January 22, 2014, 02:01:15 am
content: Thanks for all the tips, guys! Much appreciated

author: Rick Law
author_rank: Super Contributor
timestamp: January 22, 2014, 02:56:03 am
content: Me too... thanks for the advice! Mr. Psi and Mr. Rerouter.I think I will get more practice, first get my contact time lower at about 350C. I was practicing with a 8pin micro-soic at 350-360C last week. If I ignore bridges, soldering that on properly aligned took me less than 2 seconds, BUT cleaning up the bridges took me a few minutes - perhaps even 10. If that was for real, the IC would have cooked for sure. I did get it very well aligned with good quality joints - just took forever for me to clean up the bridges.After I get better practiced (ie: down to time I consider what I can expect of myself and my equipment), I will then try reducing the temperature a bit and see if I can do the darn thing at 300C and under 5 seconds including cleaning up bridges. That may be the range I need to solder on a living IC instead of a dead one.Quote from: Psi on January 21, 2014, 09:59:20 am

author: scientist
author_rank: Frequent Contributor
timestamp: January 22, 2014, 03:11:14 am
content: When applying flux, does it matter that each pad's flux is separate? For instance, if I smear flux all over all of the pins, will the fact that flux connects multiple pins be a problem? Applying flux to each individual pad is tedious especially with <SSOPs.

author: nanofrog
author_rank: Super Contributor
timestamp: January 22, 2014, 03:27:28 am
content: Quote from: scientist on January 22, 2014, 03:11:14 amNo, you don't have to get it on each pad precisely at all. Down side per se, is it makes for a messier board the more flux you use. So if you want it to look nice, you'll have to clean it off afterwards (or if there's a technical requirement for cleaning, such as using water soluble flux).The flux between the pins on the solder mask actually helps avoid bridges for small pitch devices during drag soldering for example. You'll be able to see what I'm talking about if you watch a few drag solder videos on youtube.

author: sleemanj
author_rank: Super Contributor
timestamp: January 22, 2014, 03:43:59 am
content: Quote from: scientist on January 22, 2014, 03:11:14 amNo, more the merrier as far as I'm concerned, flux is cheap, no need to be stingy

author: MrAureliusR
author_rank: Unknown
timestamp: January 22, 2014, 08:25:11 am
content: Anybody who lives in Ottawa Canada, and wants large size syringes for flux use for free, just shoot me a PM on here. Where I work I can get an unlimited supply.

author: Psi
author_rank: Super Contributor
timestamp: January 22, 2014, 08:58:59 am
content: Quote from: Rick Law on January 22, 2014, 02:56:03 amUnlikely, it's pretty hard to damage a chip from a typical soldering temperature like 350C.I've never had a chip fail that could be attributed to excessive soldering time or temp.And i've soldered 100+ tiny 3mm DFN by repeatedly dragging the iron tip across each side until the side pads all look to be soldered good.Being quite a small IC it will heat up really fast internally, so should be more prone to damage and i've never seen a failure.

author: Rick Law
author_rank: Super Contributor
timestamp: January 22, 2014, 04:44:04 pm
content: Quote from: Psi on January 22, 2014, 08:58:59 amAh, that must have been my old irons (RIP) being too hot then!I killed an LM35Z (TO-92 package) and an MC34063 (DIP) with my two old irons. Neither of them had temperature control. That was almost a year ago when I first "return" to playing with electronics. I have been paranoid about overheating components since. Both I know were heat related deaths since it was working and I resoldered them for one reason or another.