SOIC 28-pin chips (iron or hot air), and what solder - Page 1
Forum section: electronics / beginners

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 23, 2023, 07:29:16 am
content: I have to possibly solder several dozens of these ...I do have HAAKO FX-888D soldering station withseveral tips.I also have a TXINLEI 858D 110V Solder Station, Digital Display SMD Hot Air Rework Station Solder Iron Kit Heat GunI don't have an oven or electric food skillet.Solder commonly used on the workbench is shown; I have other spools (some thinner gauge).And I use a flux pen.What is good, reliable strategy for quickly soldering up several of these boards? For example ... what is best temp for HAKKO iron; what tip?If hot-air gun is used, what temp ... and should one hot-air with solder paste?

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2023, 10:08:15 am
content: Drag soldering with a spoon tip makes quick work of this. Hot air will take way longer.

author: Brianf
author_rank: Regular Contributor
timestamp: February 23, 2023, 10:25:12 am
content: Normal soldering, leg by leg, works fine and avoids having to clean up afterwards.I've done over 1000 of these on production PCBs. Lead-free solder 0.5mm, 340 degrees, using a 0.8mm chisel tip. A wipe of flux and you're away.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 23, 2023, 12:28:17 pm
content: Lots of suggestions here:https://www.eevblog.com/forum/beginners/fine-pitch-drag-soldering-tip/https://eevblog.com/forum/beginners/choice-of-soldering-iron-tips-for-smd/The Spoon tip is a "Bevel tip" with an indentation to hold a bit of solderJust drag it across one side of the IC, Then touch up with a Knife point, if there are any two leads that are joined by solder during the dragging.

author: Psi
author_rank: Super Contributor
timestamp: February 23, 2023, 12:34:07 pm
content: Use lots of flux.A flux pen isn't ideal but should work ok.Gel flux is better to cover the pins. Flux pens tend to dispense flux that's very runny and it's hard to put it on things in 3 dimensions.With enough flux you should be able to tap the iron onto the pin/pad and the 'correct' amount of solder will jump from the iron tip onto the pin and pad.

author: mariush
author_rank: Super Contributor
timestamp: February 23, 2023, 02:11:05 pm
content: If it's hundreds, order a STENSIL. It could be as small as the adapter board - if you make it the same size with holes where you have the through holes, you can center the stencil just by inserting some 0.1" headers.Then it's a matter of dragging something with solder paste over the soic footprint and you'll have paste appliedDo 5-10 of them in a batch, then use hot air iron to solder the chips .. don't make bigger batches because paste could dry out.

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 23, 2023, 06:08:07 pm
content: Only have to make up about a dozen. But that's still 28 pins x 12 !!!I've soldered several of these boards, years ago, including SSOP size. That was using Weller 25 or 35-w irons. Worked well enough with flux pen.Using GC brand flux.https://www.jameco.com/z/10-4202-GC-Electronics-Liquid-Solder-Flux-2-Fl-Oz-Bottle_615224.htmlOr this pen:https://www.jameco.com/z/83-1000-0951-Kester--33-oz-Low-Solids-No-Clean-Flux-Pen-reg-_2237634.htmlNow, even with upgraded Hakko fx-888d, I seem to be having issues with "sticky bridging" (must use wick) and some non-contacts. Have to use magnifier and DMM. 28 pins is not fun.I asked about soldering temps and solder types/widths which have yet to be mentioned. Or are they not critical for just using the iron.Also realize there is an art and skill-set to master. Like angling the board so gravity can help.

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2023, 06:40:06 pm
content: Quote from: mariush on February 23, 2023, 02:11:05 pmDoing them with hot air will take forever compared to just doing them with an iron.Who cares if the paste dries out (after the component is placed)? The first thing that happens in the reflow oven is for the paste to dry. (In fact, it needs to dry thoroughly so it doesn't cause solder balls and whatnot.)

author: Brianf
author_rank: Regular Contributor
timestamp: February 23, 2023, 06:44:42 pm
content: Quote from: 13hm13 on February 23, 2023, 06:08:07 pmSo about 30 minutes work.

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2023, 06:45:20 pm
content: Quote from: 13hm13 on February 23, 2023, 06:08:07 pmTemps vary by tip and iron, so it's hard to give a set number. But for what it's worth, this kind of stuff I'd do at around 300 for leaded solder, 320 for lead-free.Solder diameter doesn't matter because I'd use the spoon tip and drag solder, so the solder isn't applied onto the board.If you're having trouble with bridging:a) make sure your temperature is neither too low nor too high -- too high => more oxidation => more bridging.b) "rinse" your tip with fresh solder more frequently. That is, wipe it clean on your sponge/brass wool, apply fresh solder generously, wipe it clean again, then apply a bit of fresh solder to continue working. Do this right before you make the joint.c) flux.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 23, 2023, 07:19:10 pm
content: Only several dozen? With an iron.Leg by leg with a small tip, or with the edge of a large tip (both are OK) - maybe 15-20 minutes. Drag soldering multiple pins at once with large tip gets that down to maybe 10 minutes (you still need to tack corner pins first). But if you feel uneasy about drag soldering and are unwilling to experiment, then leg by leg gets the job done just fine.Just do it. In the time spent posting about it, you'd have done it already. If not, it's time to learn.

author: 13hm13
author_rank: Frequent Contributor
timestamp: February 23, 2023, 08:35:01 pm
content: Maybe we can make this easy since few of you want to commit in public to the OP .... if you have extensive experience in prototyping these types of boards and chips, how would you plug-n-chug?Iron temp:Iron tips: (chisel ??)Solder diameter (and formulation):Procedure:Rub flux on bare board padsPlace chip, position with tool or handTouch clean tip with solder to wet and pre-load a bitCarefully tack downdiagonalopposite pins -- wait a few secs. If all pins aligned to pads, then ...Bring wet (but not PRE-LOADED) tip to pins on one side of chip.Gently apply solder to pin that isalready being touched by hot iron tip. As solder melts, drag across pins.Do same for other side of chip.Helping hands device with board held at angle can help; esp. with light touch up.Stubborn bridges can be wicked away.Work can be double checked with magnifier and multi-meter with audible continuity (ohms) setting.

author: donlisms
author_rank: Frequent Contributor
timestamp: February 24, 2023, 03:28:18 am
content: I'm guessing more and better flux will help more than you might guess. I tried cheap pens and threw them away. I really like the syringes, and I think it's so important I'm okay with the expensive better ones, eg ChipQuik or genuine Amtech.I used to see flux as a vague factor; now I see it as Everything. Well, almost! But the rest is way easier with good flux.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 24, 2023, 06:17:46 am
content: Those legs and thin traces have so little thermal capacity that you can do it even with suboptimal tip type.For pin-to-pin soldering, I would recommend something 1.6mm or larger chisel tip. With a larger tip, just use the corner of the tip to touch the pin. The advantage of chisel is, it can't be too large because you can always use the edge or corner of the tip (unless the space is so cramped that the tip does not fit there due to nearby components).Temperature? 350degC for leaded or 400 for lead-free. I recommend leaded for beginners because it's marginally easier, but lead-free is fine, too, it's not too difficult.

author: Infraviolet
author_rank: Super Contributor
timestamp: February 25, 2023, 09:52:12 pm
content: In an ideal world you'd put solder paste on these, using a little foot-switch controlled needle dispenser, then put them through a temperature controlled soldering oven of one type or another.In a not so ideal world, you could paste them, then heat the paste with a normal iron tip (which works quite well for small quantitiy use) to solder it, or heat the paste with a hot air soldering "iron".If you can't get paste so easily then normal* solder and a fine tipped iron will work fairly easily for SOIC (1.28mm pitch), make sure you've got comfortable magnification to work under. I'd think nothing of using that method for one such 28pin SOIC chip, but for many it could be a bit time consuming and tiring.*Unless you're making something which is going in to a production device where the presence of lead is forbidden, I'd always recommend leaded 60/40 (63/37 is virtually identical too) rosin cored solder from any decent brand. And you'll want the finest type, 0.3 to 0.4mm diameter (different sellers do 0.3/0.32/0.35/0.37/0.38/0.4, use whichever of the sizes you can get) solder wire if I remember rightly. I don't do anything myself where I have to suffer lead-free solders, so can't recommend types amongst them, but if you're using those, you'll still want the 0.3 to 0.4mm sizes though.