SMD soldering - components blowing away - Page 1
Forum section: electronics / beginners

author: djd_oz
author_rank: Contributor
timestamp: July 21, 2020, 12:49:41 pm
content: Hey there,I'm new to SMD soldering. I purchased an AOYUE 968A hot air rework station, a practice solder kit and the below solder paste from Jaycar.https://www.jaycar.com.au/solder-paste-smd-syringe-15g/p/NS3046Firstly, I apply some solder paste on the pads, place the SMD components, heat the hot air gun to around 375 C with the lowest air flow setting. When I point the hot air gun onto the component, I can see the solder slowly melting and then it reaches a point where it is almost liquidy and then sometimes the components gets blown away from the pads.What are some tips from preventing the components blowing away?

author: Unixon
author_rank: Frequent Contributor
timestamp: July 21, 2020, 01:04:05 pm
content: Probably move the fan a little bit away and be more patient and wait a little longer?Also, 375C is kind of hot, how fast do you melt solder at your setting?

author: djd_oz
author_rank: Contributor
timestamp: July 21, 2020, 01:34:51 pm
content: Maybe around 5 secs? If I have time, I might do a video.

author: Unixon
author_rank: Frequent Contributor
timestamp: July 21, 2020, 01:51:17 pm
content: Quote from: djd_oz on July 21, 2020, 01:34:51 pmThat's way too fast, you can damage components at this rate. Look at typical thermal profiles in datasheets, preheating takes 2-3 min, then 10-30 sec soldering phase then cooling down about 1 min. Don't bring the fan too close until solder melts and components soak terminals in liquid solder.For Pb/Sn solder I usually set 260-270C, do 1-1.5 min preheating from the bottom side of the board, then 10-30 sec from the top until solder melts and components settle.Preheating can take more or less time depending on the board, I would suggest to keep heating the board until solder is just about to melt and you see it starting to change (matt<->gloss). Dry solder without flux may not change appearance, keep this in mind and watch time.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 21, 2020, 03:23:30 pm
content: You may use a glue with a fan soldering (there is special ones. But it is a bit tricky).A solder paste is good for use with a solderingoven.As for me, I use fan only for desoldering, especially for multy-legged parts. It seems to me much convenient to use a (T12-type) soldering station (iron) to solder.

author: ercapoccia
author_rank: Regular Contributor
timestamp: July 21, 2020, 08:09:39 pm
content: Temperature and flow figures don't make much sense with hot air station. You can adjust for both flow and temperature moving the hand piece closer or farther from the components you want to solder.With small component you want hold it with fine tip tweezers while the solder is not melt yet after surface tension will kick in and it will magically slip in the right place. It needs some practice. You can watch Louis Rossmann's channel on YouTube, it will be very informative.

author: tooki
author_rank: Super Contributor
timestamp: July 22, 2020, 09:03:47 am
content: Quote from: Vovk_Z on July 21, 2020, 03:23:30 pmOh please. Tons of people use solder paste with hot air for rework, it’s a well established method. You don’t need glue, you just need to use hot airproperly, with fresh paste.

author: mayor
author_rank: Regular Contributor
timestamp: July 22, 2020, 10:11:34 am
content: What has vastly improved this issue for me has been using a hot plate in conjunction with hot air. Barring that, I would pre-heat the board with air from below, slowly, then move to the top once there is a fair amount of heat in the board. I mostly work on fairly small boards, so this method might not be practical on a large one.

author: tooki
author_rank: Super Contributor
timestamp: July 22, 2020, 10:15:36 am
content: Do you have a name-brand one, or a Chinese cheapie? (If the latter, is it any good?)

author: tautech
author_rank: Super Contributor
timestamp: July 22, 2020, 10:18:05 am
content: Not how many do it but it works !Further tips here:https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/

author: mayor
author_rank: Regular Contributor
timestamp: July 22, 2020, 10:31:52 am
content: Quote from: tooki on July 22, 2020, 10:15:36 amNot sure if this question was for me, but it's a cheap one (https://www.ebay.ca/itm/NEW-Electronic-Hot-Plate-Preheat-Preheating-Station-946C-110V/312691707496?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649)The relay is off ~50% of the time all the way up to temp, so it's slow. But, in conjunction with air, it works well.

author: tooki
author_rank: Super Contributor
timestamp: July 22, 2020, 11:43:40 am
content: Quote from: mayor on July 22, 2020, 10:31:52 amYes, sorry, I meant you! :pThanks! Does it actually get hot enough to reflow without added air? (Essentially, the “frying pan method”.)We are looking to get some kind of reflow tool at work (technical training center), and I had seen both these plate type preheaters as well as the IR ones, and the little reflow ovens. Not sure which is the right one for what.

author: Shock
author_rank: Super Contributor
timestamp: July 22, 2020, 01:07:17 pm
content: I've deduced that IR with fan is better suited for oven reflow (even heat distribution and efficiency) and plain hot air is fine for underside pcb preheating, which can be localized easily and unlike plates doesn't need to directly contact with the PCB. Happy to hear otherwise though.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 22, 2020, 01:30:18 pm
content: If you heat up fast enough you can make the flux explode! Blowing the component away. It is dangerous and you should be wearing goggles.Anyway, to prevent this, heat up slooooowly.

author: mayor
author_rank: Regular Contributor
timestamp: July 23, 2020, 11:13:08 am
content: Quote from: tooki on July 22, 2020, 11:43:40 amIt will get hot enough, but you can forget about following any reflow profiles. It is too conservative in the way it gets to the temperature you set. Haven't looked inside yet, but I'm tempted to add manual control of the relay.

author: djd_oz
author_rank: Contributor
timestamp: July 25, 2020, 11:21:38 am
content: Quote from: Unixon on July 21, 2020, 01:51:17 pmThanks for the tip, after lowering the temperature to about 280C, it is a lot more managable.

author: Teledog
author_rank: Regular Contributor
timestamp: July 26, 2020, 05:27:48 am
content: Never bothered with the oven thing in the lab..For low run PCBs, we used to just hand solder (PbSn) down to 0402.Clean the board, wipe with rosin flux.Make tiny dots on the pads with solder, then wipe again with flux pen.Place components on the sticky solder dots (they stick) & solder with 2 (yes two) irons in unison.Used JBCs with fine tips.Done a few 1,200 component boards that way (make a roadmap first)Do the BGA (preheat underneath, then hot top)beforethe passives..BTW..G'luck!try some crap boards/old parts to practice!