[sdiy] DIP LM13700 discontinuation

cheater cheater cheater00social at gmail.com
Thu May 20 19:25:48 CEST 2021

One thing being forgotten here is that SMT allows much easier repair
if parts are spaced the same as they would be on a through-hole board.
If you make a board with footprints for both TH and SMD, and populate
it with SMD, that's super spacy. The "difficulty" of repairing SMT
boards is that they are extremely miniaturized, which means they are
super packed. Obviously you'll have problems repairing those. But if
you're choosing TH only because it forces you to use a larger PCB, you
might as well use a PCB of that same size with SMD, and they'll
actually be easier to work on because of the additional space margins.

In addition to hot air, wick, and wire methods, I'd like to mention
the following.

First of all, when using wick, make sure you don't just unroll it. It
comes compressed. You have to spread it out so that all the tiny
strands are separate, rather than one solid bundle. So make sure to
press it together length-wise so it spreads apart radially.

There's also quartz pre heaters. Those are great. You can just use a
toaster oven with a PID.

There are those rubberized heating elements. You stick it on the
underside of the PCB, and it heats it. Similar to the things used for
heating the oil pan in a truck, but here they're much smaller.

Finally, there's desoldering foil. I've never seen it demonstrated. I
think it's spring steel foil, and what it does is it acts like a knife
that you slide under the pins to get parts off.

By far the most common thing I've seen is hot air. You point a hot air
gun on whatever you want to desolder, and slightly poke it with a
stick every now and then until it's ready to move. Then you just move
it off. Doesn't matter how much solder is present - it'll melt, and
then you move the part off to the side a little, and then you pick it
up and off, either with tweezers or with a vacuum grabber.

Good luck

On Thu, May 20, 2021 at 11:20 AM Roman Sowa <modular at go2.pl> wrote:
> With special tip I'm able to desolder SOIC16 within 5 seconds or so. Not
> doable with DIP, although there are also special tips for DIP, at least
> I have seen one in the 80's.
> It's hard to have every possible tip for every possible package, so hot
> air comes handy. Recently I have desoldered a few TQFP44. Took a minute
> or two, no damage to traces, which is important as and it was done
> several times on the same PCB.
> I have tried also the thin stainless wire method, but it takes more
> practice and needs room around the chip to operate the wire.
> At one trade show years ago I have seen a guy desoldering SOIC with
> DenOn SC7000 but I was never able to do that.
> Roman
> W dniu 2021-05-20 o 11:04, chris pisze:
> > On Thu, 20 May 2021 10:07:19 +0200 Steve via Synth-diy <synth-diy at synth-diy.org> wrote:
> >
> >>> And at that scale, the rework is also not hard, and I think it's far
> >>> easier to actually properly desolder SMT parts than through hole.
> >> There it would seem that smaller parts are easier - heat it all up with
> >> the hot air station (the cheap ATTEN 858D+ does it),
> >> which would seem difficult with SOIC of that pin count. (OK it's also
> >> not fun with e.g. UFQFPN with a nasty thermal sink in the middle)
> >>
> >> IIRC I never de-soldered a SOIC - how *do* you do that? Flux and wick
> >> still leaves a little bit of connecting solder on many pins at the same
> >> time?
> >> I faintly remember once using a piece of lacquer insulated copper wire,
> >> dragging it under the first heated pin in line, then the next, and so
> >> forth, where the wire keeps the pins from the pads. That was not as big
> >> a part, though.
> >
> > Using hot air this is easier than I had expected.
> >
> > I once had to desolder a finger nail sized TQFP Atmel Mega 64, and it
> > was a breeze. I had suspected everything around would float away, but it
> > was possible to work exactly where I wanted. Only took a couple of
> > seconds.
> >
> > I'd rather do that than suck-wicking a DIL-40.
> >
> > Chris
> >
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