Easist way to solder 400 SOIC-16 chips?! - Page 1
Forum section: electronics / projects

author: K3mHtH
author_rank: Regular Contributor
timestamp: October 26, 2022, 04:06:48 am
content: Hey everyone,I received a large order of boards back from JLC and one of the parts wasn't in stock, a SOIC-16 chip. I was able to find them and I have the parts, but now I'm trying to figure out the best way to solder these missing IC's onto the boards.It seems as though JLC excluded these chips from the solder mask, so no solder has been deposited on the pads (ENIG finish).I've soldered about a dozen already, using solder paste syringe and hot air... but I am getting bridging on almost every chip. I've ordered some narrower syringe tips, hoping this would deposit less solder on the pads and reduce the bridging.But I'm also considering having a tiny stencil made that is just the single SOIC-16 chip so I can use that deposit the paste on before I use the hot air gun. Wondering if maybe anybody's done that before, or if it's even worth it?

author: ataradov
author_rank: Super Contributor
timestamp: October 26, 2022, 04:23:36 am
content: Miniwave soldering iron tip and just solder by hand.I assembled 100 board with mini USB connector, SOIC-14 and some passives in a day by hand. And IC is the fastest and easiest part of this. You can do it in a couple days.It will take you longer to position the stencil and apply the solder paste than actually solder the whole IC.

author: Martian Tech
author_rank: Regular Contributor
timestamp: October 27, 2022, 02:56:28 pm
content: The hand-soldering technique is known as "drag soldering"https://classes.engineering.wustl.edu/ese205/core/images/0/0f/Soldering_Technician%27s_Refresher.pdf

author: fourfathom
author_rank: Super Contributor
timestamp: October 27, 2022, 03:29:19 pm
content: Quote from: K3mHtH on October 26, 2022, 04:06:48 amDrag soldering is probably the way to go.Pre-made stencils are available on Amazon (and elsewhere). These usually have several different footprints on the same stainless sheet, or an assortment of small stencils. But you're likely to have difficulty using a stencil on a partially-populated board. And if you trim the stencil to avoid interference from adjacent components it's going to be extremely hard to secure the stencil while you squeege the paste.As for hand-pasting the SOIC-16 pads, the syringes I have also put out too much paste, I put down a blob of paste nearby and use a toothpick or equivalent to transfer small paste dots to the board. This is tedious but it works. In some cases I just lay down a thin line of paste across a row of pads. The capillary action and solder mask generally do a good job of avoiding inter-pad shorts.

author: wraper
author_rank: Unknown
timestamp: October 27, 2022, 03:33:35 pm
content: Do not bother with solder paste unless you put a batch of them into reflow oven. But even then drag soldering will be faster. For me this job would take an hour at most. EDIT: misread number of boards, 3-4 hours.

author: tooki
author_rank: Super Contributor
timestamp: October 27, 2022, 07:51:23 pm
content: Quote from: wraper on October 27, 2022, 03:33:35 pmDid you misread the number of chips? It’s 400. For one hour, that’s 9 seconds per chip. You won’t have that speed unless you have someone else to position the chips, another person to flux them, and two more people to inspect the work.

author: John B
author_rank: Frequent Contributor
timestamp: October 27, 2022, 08:06:32 pm
content: Quote from: K3mHtH on October 26, 2022, 04:06:48 amDid you mean excluded from the stencil?Either way, 400 chips isn't too bad. Give yourself 1-2 mins per chip until you get into the flow. I prefer to to solder pin by pin with 0.35mm solder and a fine tip like a D08 0.8mm fine chisel tip. Mainly so that you can be sure the solder has taken to both the pin and pad, sometimes it will appear like a blob on the pin, but hasn't wetted the pad. You need to factor in inspection time as well as soldering so best to get it right the first time.Find 12 hours of podcasts you've been meaning to listen to.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 27, 2022, 08:15:19 pm
content: Aside from drag soldering, you could probably do it a bit quicker if you have a wide blade tip ( the width of the whole side of the package). First flux & tin all the pads, place the chip then flow each side in one go.5-10 seconds per chip pretty easily.A while ago I had to replace about 650 SO16s, don't think it took more than an afternoon, including removal

author: RogerThat
author_rank: Regular Contributor
timestamp: October 27, 2022, 08:15:50 pm
content: I use plenty of SOICs in my designs and they are easy/fast to hand solder correctly when you get the hang of it. I usually don't drag solder them but tap each pin one by one. Spread some flux on the land pattern, place IC, tack two diagonal corners down and then work your way one by one. Put the tip of the solder on top of the leg and then push the iron down on the solder. I would say about one minute per chip for high quality.

author: langwadt
author_rank: Super Contributor
timestamp: October 27, 2022, 08:37:59 pm
content: Quote from: mikeselectricstuff on October 27, 2022, 08:15:19 pmyou can also get tips like these,https://www.weidinger.eu/en/p/wl21480

author: wraper
author_rank: Unknown
timestamp: October 27, 2022, 08:53:18 pm
content: Quote from: tooki on October 27, 2022, 07:51:23 pmI misread 100 for some reason. Then I guess about 3-4 hours with all time wasting overheads. If boards are in panels and ICs prepared for past pick up, then IMHO 1 hour is completely possible if incentivized to try that. Out of interest I measured how fast it takes me to solder a 24 pin TH IDC connector (I needed to solder thousands of connectors many times). Was about 35-40 seconds with soldering pins individually and not low quality sort of drag soldering I've seen on Chinese videos.

author: wraper
author_rank: Unknown
timestamp: October 27, 2022, 09:00:48 pm
content: Quote from: mikeselectricstuff on October 27, 2022, 08:15:19 pmProperly sizedhollow point/well tip works the best IME. No need to pre-tin the pads, except pre-applying tin to one of corner pads will make it easier to fix IC in place before starting drag soldering. Adding flux helps a lot, if solder contains a relatively large amount of good flux, can be done without additional flux too.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2022, 03:12:19 pm
content: 1) Pre-tin one of the corner pads for all boards (or a few dozen boards) at once. 3-4 seconds per footprint.2) Tack the ICs to this one pre-tinned pad. 10 seconds per chip.3) Use tip like shown above by wraper to solder the remaining pins. Start from the opposite side of the pre-tinned pad so you don't accidentally unsolder the part. Maybe 20 seconds per chip (10 seconds per side).Total 200 minutes. Add some breaks etc. and it's a one-day job at most.

author: jmelson
author_rank: Super Contributor
timestamp: October 28, 2022, 04:43:11 pm
content: Quote from: K3mHtH on October 26, 2022, 04:06:48 amYou must be using WAY too much solder paste. A VERY thin line, spread by a small needle is all you need. SOIC is very forgiving. Just syringe a tiny line along each row of pads with as small a needle as will flow the paste is what you want. A good solder paste like GC10 will greatly help in reducing bridging. (Not sure that is available in syringes.) I use pots of GC10 and a stencil, and the results are great, even down to 0.5mm lead pitch. (SOIC is 1.27mm lead pitch.)Jon

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: October 28, 2022, 04:56:46 pm
content: Quote from: jmelson on October 28, 2022, 04:43:11 pm"Thinning" the paste with some flux also helps.

author: wraper
author_rank: Unknown
timestamp: October 28, 2022, 04:58:48 pm
content: Quote from: Ground_Loop on October 28, 2022, 04:56:46 pmI strongly suggest against that unless you want a bunch of small solder particles trapped in flux residues.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 28, 2022, 08:52:20 pm
content: Are you sure you need to solder them? About 9 years ago a researcher published a method to deposits nano silver particles using a modified Tollens reagent.* The modification essentially substituted classical Tollens reagents with reagents that were volatile at moderate temperatures (e.g, 60° to 100°C). The silver is claimed to be almost as conductive is pure silver and unlike other "conductive inks" is solderable. So, dip the SOIC device pads in a puddle of that or similar ink, place on a board and warm sufficiently.If you search on nanoparticle silver inks, you get a lot hits, like this one:https://www.daicel.com/smart/en/product/silver-nano-ink/#:~:text=Silver%20nanoparticle%20ink%20Picosil%E2%84%A2,cost%2Dsaving%20with%20Picosil%E2%84%A2.Come to think of it, it you want to solder, why not pat the device on a smear of solder paste, put it on the board, and reflow again? That's like ordinary reflow, except in your particular situation you put the paste the device's pins instead on the pads? (Can we call that "reverse stenciling?")*https://pubs.acs.org/doi/abs/10.1021/ja209267c Check Wikipedia for Tollens reagent. Its main use was silvering mirrors.