Hot-Air Rework, First Try

I wanted to try adjusting the current limiting resistors on my register boards to improve the readability in videos. So it was time to try out hot air rework.
I purchased an 858D on ebay, it arrived today so I rushed home to give it a try. You get to see my first attempt and initial thoughts on the process.

[@weirdboyjim]

amzn.to/3qdXG97 (Amazon.com) amzn.to/3nCTHRZ (Amazon.co.uk)

[@spartan456]

Definitely get some flux! MG8341 is a really solid brand, it even comes in a syringe tube, along with a needlepoint tip, for easy dispensing. Any electronics-grade flux will do, I'm just partial to 8341 because I've used it for years with no trouble. You'll want one that is in some kind of paste form. The pen you've got looked like it was doing a good job, but a lot of the flux from that will get burned away when you add it to an already-hot board. Paste flux on the other hand will basically ooze everywhere and coat a large region of the board as it heats up, so more of it will stick around for soldering purposes. Adding flux will make soldering these things much, much easier. It will also make desoldering them easier, because it gives you an indication of when the components are "ready" to be lifted away. For desoldering, the flux will gradually begin to bubble as it reaches activation temp, which is always right around the window where solder melts. So when the flux starts bubbling, that's when you know the component is really close to being safe to lift. I usually give it a few more seconds after it begins to bubble just for good measure. For soldering, the flux acts almost like a glue. It will help keep the component mostly in the right spot, and when both of the solder pads finally melt, the component will "snap" into place almost like magic. Going back to my first point with the paste flux, you'll have a huge pool of it over the area, so other parts should "stick" as well and be less likely to just fly away. I actually DO NOT recommend solder paste for this, the only reason why is because you have to be veeeeeery precise with your application of it to the pads. I've tried using solder paste before on a number of electronics repairs (I work in a repair shop), and it ended in disaster. Basically ONLY THE PAD has to have paste on it. Any excess paste out on the sides of the pad is a massive no-no. When you go to heat up the area, any errant paste will form little itty bitty solder balls that can get trapped and clumped together near other solder pads, and possibly even work their way underneath the component and short the pads together. I've had this happen several times with similarly sized components that you're dealing with. It was a total nightmare. I only recommend solder paste if you have a fresh board with absolutely no solder on it, and an accompanying solder paste stencil to go with it. The stencil will allow you to "squeegee" solder paste onto the pads, and when you lift the stencil away, only the pads will have solder paste. From there you can drop your components in, then heat them all up. This is actually how many PCBs are professionally soldered during the manufacturing process, and depending on where you're sourcing your boards from, you can probably ask if they can make you a stencil for them. You only need two stencils, one for the top and one for the bottom, and you can re-use the stencils as often as you'd like. EDIT Also, just a tip, that PCB holder you're using is total garbage. I used to use one exactly like that and I ended up getting so angry at working with it that I threw it against the wall. No matter how much you fannagle it, it doesn't work quite right. Takes far too long to get it to hold the board just right. On the other hand, I was also working with quite oddly shaped boards so that might have something to do with it. Either way, I realized the best way to hold the board is to....tape it to the work mat. Yep. Just kapton tape. That's all it needs. The board won't go anywhere while you're working on it. I even spent $60 on a Hakko Omnivise before I came to this extremely cheap realization. The Omnivise is now a very interesting paperweight.

[@weirdboyjim]

Thanks for the recommendations, I've ordered a syringe of the MG8341. I know the pcb holder isn't great, i've found it grips my rectangular boards quite well but it slips on the rotation unless I constantly tighten it. Interesting suggestion about the kapton tape I'll give it a try some time. For my register boards most of the soldering was done by putting the pin headers in first, then just dropping it into a breadboard to secure it. I'm familiar with the paste/stencil approach (in so far as I've watch videos), some of the future boards for my cpu build will be larger than the smaller boards I've been hand soldering so I'm intending to investigate some of the other soldering methods in future. Expect a diy reflow oven project at some point.

[@AaronBonBarron]

I've got the same hot air station in a smaller form factor, I'm pretty happy with it. Flux and solder paste really help!

[@weirdboyjim]

I didn't see a smaller one or I would have been tempted. This hobby is starting to consume space!

[@AaronBonBarron]

@@weirdboyjim I know what you mean, I've been collecting electeonic junk since I was about 5 years old! The smaller form factor has the heat and blower controls integrated into a power brick the size of a regular laptop power supply.

[@tinygriffy]

i don't use paste for low component count boards anymore.. makes no sense without stencil because it takes so much time to apply -.- I just tin the pads with a soldering iron and blow them on afterwards... I would like to have a hot plate though... i think heating the whole board to 120°C or so would make this process much more .. fluid well okay, for some sensors and certain LED's i have bismuth paste with a melting point @ 180°C but other than that...

[@tablatronix]

Good job, might want to use some paste flux for rework it will go much faster without damaging your pcb

[@weirdboyjim]

Thank! I have some paste type flux on order, I'll give it a go when I get it.

[@DigicoolThings]

Nice effort, for your first hot air rework experience! Looks like you have a silicone mat protecting your bench. Good idea with a hot air gun! I now use a 5 diopter magnifying LED desk lamp for all my SMD work, infact for all of my hand soldering work. Nothing wrong with my close-up vision, but it helps having everything enlarged, and I have great tweezer control with the direct visual depth perception (rather than via a 2D camera image). But, for videoing your work, I guess the video microscope is needed for sharing the close-up view. :-)

[@weirdboyjim]

It is odd the way making videos tends to skew the methods I use.

[@HenryLoenwind]

I'm using cheap magnifying glasses, the advantage is that I can look any direction as they are fixed to my head, the disadvantage is that the my depth of view is quite limited and fixed. A second disadvantage is that they remind my how old I am, as I need them for stuff I did without any aid in my youth...

[@tinygriffy]

if you don't want parts flying .. put the biggest nozzle on and turn down air to lowest setting... at least that's what i did ;) I think there is no point in having a small nozzle since the hot air will spread over the whole board anyways ;) With hot air it is flux flux flux ... cant have enough of it ... I bought raw Rosin on ebay ground and solved it in IPA, maybe add a couple drops of very light machine oil (it doesn't harden like candy then and is easier to remove afterwards)... works a treat, there are videos here on YT that show how its done.

[@weirdboyjim]

Yeah! I’ve switched back to a larger nozzle, the small one seems to heat slower, maybe it was restricting the airflow?

[@GeorgeJFW]

New subscriber I definitely feel like I am going to fit right in!

[@weirdboyjim]

Welcome! I'm sure you will.

[@sillymel]

As of the end of this video, I'd say the red LEDs are fine, but the green LEDs could use their resistors raised even higher.

[@weirdboyjim]

Subjective!

[@AmauryJacquot]

the solution to this is to wick out the solder, apply solder paste, put the components back on and use the air to reflow the paste on the new components.

[@weirdboyjim]

Oddly enough, I had to reword some led's on a later board that had been originally soldered with paste, it was far easier. Something about the solder paste blend re-flows easier with hot air.

[@AJB2K3]

You need some Rossman group Flux! And a co2 fire extinguisher!

[@azyfloof]

Don't delay, buy today!

[@weirdboyjim]

From Adam's post I had a creeping feeling there was a joke I'd missed the reference to, from Azy's post I'm sure of it.

[@AJB2K3]

@@weirdboyjim Check out the lewis rossman channel, he loves his flux!

[@rafikben7829]

what is your opinion of solder wire Type (billiton cw) SVP

[@weirdboyjim]

I don’t have experience with that brand sorry.

[@AJB2K3]

The hot air tools are cheep and easy to replace should they go wrong.

[@weirdboyjim]

Indeed. I know I'll end up with a reflow oven sooner or later but I think a scope would make a difference to my builds in the near term, the price on a decent one is a big investment though.

[@AJB2K3]

@@weirdboyjim I have a duel station and I have personally experienced a hot air tool going up in flames (was brand new) fortunately (like you) I know enough to be able to replace the air tool!

[@weirdboyjim]

I bought separates, I didn't think I'd need the hot air initially and desk space is at a premium. I expect the solder station will still get a lot more use. Did you work out why it went up in flames?

[@AJB2K3]

@@weirdboyjim Yup same issue as with inferno my 3d printer. The temperature sensor failed, there was no thermal runaway detection so the PSU kept pumping current into the heating elements until it went pop! BTW, both have been repaired and still work!

[@AaronBonBarron]

@@weirdboyjim you can buy a quite useful scope for $30 on AliExpress called a DSO150. It's handheld and runs on an external power supply, but I've fit a li-ion battery and boost converter + usb charger inside mine to make it truly portable.