I'm building a DIY DAC and had been dreading having to mount three 16 leg, SMT microchips (8 legs/side over 10mm). I decide to practice on a $7 Amazon kit. What a mess! Decided I've got nothing to lose; so I tried a technique I heard about. There were two 40 connector, square practice chips, 10 legs per 10 mm side. I soldered a couple of outer legs to keep the piece secure. Then I applied liquid flux liberally along one side then laid down a neat solder blob covering all ten legs. Let it set then, using my Hakko 630 de-soldering tool removed all the solder that wanted to come off. Perfect job: all legs connected, no solder bridges.
Probably everybody already knows about this; or someone will tell me why this is a bad idea because it fries the chip or something. If so, please advise. Thanks
Probably everybody already knows about this; or someone will tell me why this is a bad idea because it fries the chip or something. If so, please advise. Thanks
I refer to that as "slop soldering". Just make one big mess along
the chip and in my case, I use wick to remove the excess. Clean
off the flux and it looks and works great. As long as you don't use
some overheated tool you won't damage the chip.
G²
the chip and in my case, I use wick to remove the excess. Clean
off the flux and it looks and works great. As long as you don't use
some overheated tool you won't damage the chip.
G²
Pretty much the way you have to do it by hand, since SMT was designed only for machine assembly.
Not with some practice. I can solder the individual leads of a 0.65mm pitch IC by hand perfectly without causing any solder bridges. I use 0.015" solder and a Hakko 900M-T-I tip.
Heh, I'm no spring chicken. I will admit I can't control my hands well enough anymore if I have any coffee before soldering. Eyes are still good enough to solder without a magnifier if I really had too.
Doing one SMT joint by hand, you just can't heat up the pad and the lead at the same time and get the
kind of consistent results that won't raise your blood pressure. Instead, you have to press on the lead
to get some thermal conduction to the pad, or else feed in solder and hope that it will conduct the heat.
That's not the way to get good solder joints. Everything should be at the same temperature.
For prototype SMT boards, I've had to extend the standard footprint pad beyond the end of the lead
by a mm or two, so I can touch both with the iron tip before adding solder. Even then, I still have to
tin all the pads first to get reliable solder joints. And this is with fresh, gold plated boards.
kind of consistent results that won't raise your blood pressure. Instead, you have to press on the lead
to get some thermal conduction to the pad, or else feed in solder and hope that it will conduct the heat.
That's not the way to get good solder joints. Everything should be at the same temperature.
For prototype SMT boards, I've had to extend the standard footprint pad beyond the end of the lead
by a mm or two, so I can touch both with the iron tip before adding solder. Even then, I still have to
tin all the pads first to get reliable solder joints. And this is with fresh, gold plated boards.
Why waste the time ? - and it does take extra time to go pin-by-pin. On chips with 0.5 mm spacing
it's silly to go pin-by pin. As Rayma said, you get more consistent joints by vacuuming or wicking off
the excess. You don't get any extra points for doing it the hard way but if it makes you feel good, have
fun.
G²
Wick and the 62/36/2 solder I use has more value than the time it takes me, so I'd rather not waste supplies. Do whatever suits your goal best.
Why no paste and hot air advice here? Supplies are cheap and the process is easier then poking iron at the small leads and pads
Tiny (really tiny) amount of paste and slow air speed and that's it
Tiny (really tiny) amount of paste and slow air speed and that's it
A toaster oven can be adapted for SMT work - I made one by moving the bottom element to the top to give more even coverage, then used its built in timer and temp control - a little trial and error characterizing its performance and how its a simple process even without a thermostatic controller. Whole pcb done in one process, so easy and reliable.
However it can be a bit more expensive getting stencils cut for the boards, but it really helps with the finer pitches like 0.5mm
However it can be a bit more expensive getting stencils cut for the boards, but it really helps with the finer pitches like 0.5mm
I use the Pace trick with a large tip and use surface tension to pull off the excess solder. Two thirds the way through this video you'll see the technique:
No need for ovens, hot air or paste.
No need for ovens, hot air or paste.
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Problem is that technique doesn't work with many modern packages like DFN where the pads are underneath. Oven and hot air are definitely the way to go as chips with pins sticking out will become more and more rare (ie SOIC will eventually die).
If you want to see the cutting edge of manual SMT soldering this iPhone repair guy has some interesting videos: https://www.youtube.com/channel/UC39yMXOL0ubFxLWwF1RwelA
If you want to see the cutting edge of manual SMT soldering this iPhone repair guy has some interesting videos: https://www.youtube.com/channel/UC39yMXOL0ubFxLWwF1RwelA
I've used paste, hot air and a hot plate on packages with hidden pads but it's likely beyond the ability of most diyers.