SMD soldering advice - Page 1
Forum section: electronics / beginners

author: dan-esc
author_rank: Newbie
timestamp: April 29, 2021, 11:31:35 am
content: Hi all,I've done a bit of soldering and have purchased some parts for an OSSC (Open Source Scan Converter)I have soldered the QFP's and main chips however I am having a hard time with the small 0603 0.1uf capacitors.My current setup isSmall magnification (x3?)Jewlers Loupe to check jointsHakko FX888DAn assortment of tips including small chisel, hoof tip, etcI'm young so my eye sight is fine but for a reliable and flat solder connection for the 0603 parts capacitors it seems quite hard from what I can see looking through the jewellers loupe on every part.AA

author: knapik
author_rank: Regular Contributor
timestamp: April 29, 2021, 11:41:34 am
content: What I like to do is put a small amount of solder on one pad only and let it cool, then heat up the joint again and then slide your component to be soldered on that one side. From there I reposition my pair of tweezers on the top of the component and press down slightly and heat up the joint again to position the component flat on the PCB. Finally, I solder the other side of the component normally.I wouldn't say that a loupe is necessary for 0603 components, but a pair of sharp tweezers definitely is. I would be a lot more worried with all those fine pitch QFPs, they're always a pain for me.

author: jmelson
author_rank: Super Contributor
timestamp: April 29, 2021, 03:15:43 pm
content: Quote from: knapik on April 29, 2021, 11:41:34 amYes, this is about my technique, too, but I do it in less steps. I use curved-tip serrated tweezers and put some heat shrink in the finger grip area to get more friction. I put solder on one pad, often doing all components of the same value at once. Then, spill that number of parts in a handy spot, and then pick one part, place one end on the soldered pad and heat. let the tweezers move down as the part settles into the solder. Do all parts of same value on one end.Then turn board 180 degrees and apply solder to other end of all parts. it goes pretty quick.Jon

author: jmelson
author_rank: Super Contributor
timestamp: April 29, 2021, 03:21:53 pm
content: Quote from: knapik on April 29, 2021, 11:41:34 amAh, for the QFPs, here my system:Using a fine-tip iron and fine (0.5mm or smaller, if you can get it) solder, place a little solder on two diagonal corner pads.Place component on pattern and line up corner leads. Reflow one corner with iron, check alignment. Reflow other corner. Check alignment of pins on all sides. If alignment is off, You can "walt" the chip by alternately reheating one pad and then the other. When all pins are properly aligned, use a fine wire to dip out liquid flux and wipe down all rows of pins. I use water washable solder for easy clean-up. Then, just run the soldering iron down the rows of pins. Generally the board has enough solder plating on it so that no additional solder needs to be applied. If you get a bridge, remove with fine desoldering braid.I have done down to 0.4 mm lead pitch 128-pin, and 0.5mm 144-pin chips, by the hundreds.Jon

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 02, 2021, 09:16:10 pm
content: For resistors & capacitors I do the (nearly) the same as jmelson.First put a dab of solder on all left pads, then put the SMT resistors / capacitors on a flat surface, so your tweezers do not go beyond the bottom of the components when you pick them up. Then first place the component on the pad and then re-heat the solder and position the component.When applying the first dab of solder, it is very important to heat it as short as possible. For every second it's hot, more flux evaporates, and without flux there simply is no soldering.When done, put the soldering iron in your other hand, and solder all the right pads of the footprints.The thing of "left" and "right" handed is mostly a fallacy (except for writing and some other things). The first few times you do it it feels very weird, but the more you practice the less the difference becomes. And it tickles your brain cells in a particular way that makes them active. Has something to do with neuro plasticity.For QFP's, I put a dab of solder in one corner (2 to 4 pads) with a fat iron. then position the part and solder that corner. Then another corner. Next step is to add flux and drag the iron slowly over a whole row of pins. If you do this correctly it works very well. Have a look at youtube for some drag soldering examples. With drag soldering it's extremely important to position your parts very accurately. Pins have to be smack in the middle of the pads. If they are even 0.05mm to the side of the pad, that reduces the clearance and makes the chance of shorts bigger.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 02, 2021, 09:36:57 pm
content: Hot air.Get a decent hot air rework station.