[sdiy] pros and cons of SMT in DIY

Sun May 21 13:27:04 CEST 2017

Yeah i know you can put th footprints on a board you'll populate with smd,
that's the whole point. I posted about this here maybe 10 years ago already.

Good to know about the experiences with magnet wire. Thanks.

Charlie what lenses do you suggest for the ps eye? Do you have video demos?

On Sat, 20 May 2017 18:59 charlie wallace, <charlie at finitemonkeys.com>
wrote:

> a few of us are putting together 400 boards this week/end, it is
> mostly smd 0805 with lqfp (which i personally dislike but i was
> outvoted, i prefer qfn since it solders better)
>
> we have a stencil printer
>
> http://www.ebay.com/itm/332130477725?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
> it is not great but once you get it dialed in it works, in the past we
> just put hinges on a piece of MDF and the stencil, then cut out an
> outline of the pcb to be made , and use those as guides
>
> the stencil comes from the pcb people or we laser cut or cnc one out,
> these are generated from the tcream layer in eagle, with cheap ebay
> 40w laser i use the engrave method rather than cut , it gives better
> edges; if i cnc then i use brass shims, usually 3mil and i schrink the
>  tcream a little first.
>
> the paste is applied using a thin spring steel metal scraper that i
> used for clay sculpting, it works the best of anything i've found so
> far, i use aim leaded water soluble solder the no clean stuff is no
> good for these boards, and its a nightmare to clean if you have too
>
> then to a small pnp the neoden tm220a, though wish i'd gone for the
> 240a at the time (bought by generating litecoins with old gpus a few
> years ago) there is a nice ulp dp-tm220a.ulp that handles it, once its
> up and running it does pretty good but not a lot of components can fit
> it, we have a modified juki as well but its in storage.
>
> once as many parts as the pnp can place, the board goes into the
> kitchen and the others place the few smd components, and then it goes
> on to the madell hot plate, for a 170o cycle, after the thru hole
> parts are added with the metal under either the amscope microscopes or
> the mantis (all ebayed or bought from amscope directly during sales)
>
> then the board is de-briged if needed, usually the lqfp arm chips
> since this time i let the board house do the stencil gerber and they
> didn't shrink it.
>
> there are about 60 parts placed, the good thing about smd is that part
> placement only has to be pretty close, the surface tension of the
> solder will pull the parts in (usually)
>
> with two of us we can do about 10 boards an hour at a relaxed pace,
>
> qfn's i like since you can practically throw them onto the board and
> they'll self right, and they tend not to bridge, we did a test where
> we could see how lax the part could be placed and it'll still solder
> in properly.
>
> smd size doesn't really matter if you're hot plating, once you get
> down to like 0201 and such its all about magnification and a steady
> hand, and if you don't have that then use a manual xy pick and place
> tool, or an automatic one. manually soldering them is also straight
> forward you can glue them in place then solder if you're not steady, a
> small tipped iron with the right temperature it goes well , takes a
> little bit of practice on how best to hold them and avoid tombstones
> if not glued, again you can also use the xy tool to place and hold a
> part while you hand solder it.
>
> we've taught 100s of people to smd aver the years, some have never
> even picked up an iron before and they're placing chips, 0602s with no
> bother , though occasionally people have soldered chips upside down
> before ,another good argument for qfn
>
> basically you just need a good iron, good microscope (amscope rp type
> is fine) i'd avoid most usb microscopes since too much lag so hard to
> solder and stick to glass, but you can $5 a playstation eye , mod the
> lense and and get an ok picture at 180fps, flux and a 10/5ml tube of
> solder paste.
>
>
>
> On Sat, May 20, 2017 at 8:15 AM, Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
> > Paula, when you say "working with 0402", do you mean replacing the odd
> > component here and there, or soldering 100s of SMT parts on?  And how are
> > you actually doing the soldering?  With a fine tipped soldering iron and
> a
> > steady hand?  ...heater tweezers?  ...or stencilling solder paste onto
> the
> > board then placing components into the paste and ovening the board?  Just
> > curious what methods you're using, particularly to get consistent results
> > with those tiny QFNs.
> >
> > I can also vouch for the structural integrity of super-gluing down
> > wire-wrapping wire or polyurethane enamelled copper (magnet wire) for
> mods
> > to PCBs.  Never seen one fail, and they're almost impossible to rip up if
> > you need to.  I've never felt entirely happy with the fumes given off
> when
> > someone has to solder in an area of the board polluted with dried
> > Cyanoacrylate glue though.  I remember doing this once and leaping
> backwards
> > with my eyes and nose stinging!  Can any of the chemists on this list
> > comment on what vapours are liberated when a hot soldering iron touches
> > cured Cyanoacrylate glue?  (I appreciate that I should already have been
> > soldering in an area with positive airflow away from me, extraction to
> > outdoors, etc...)
> >
> > -Richie,
> >
> > -----Original Message----- From: paula at synth.net
> > Sent: Saturday, May 20, 2017 3:45 PM
> > To: cheater00 cheater00
> > Cc: Synth DIY
> > Subject: Re: [sdiy] pros and cons of SMT in DIY
> >
> > On 2017-05-20 03:42, cheater00 cheater00 wrote:
> >>
> >> Yes, a TH pcb will be able to hold a daughter pcb just by the
> >> through-holes, whereas SMD pads will not hold one. So you can easily
> >> change topology using an extra pcb on a TH circuit but not on an SMT
> >> circuit.
> >
> >
> > You know you can use both SMT and through hole if you need?
> > My current project for work has around 100 SMT parts, and 7 through
> > hole, some of which are for PCB interconnect.
> >
> > At the end of the day, the choice is up to the designer.
> > I'm really comfortable working with 0402 and QFN (3mm x 3mm) packages,
> > and with modding them with mod wires if needed (for the record super
> > gluing a mod wire makes it rock solid).
> > I'm considering trying 0201 for some parts, just as a personal challenge
> > :)
> >
> > So it's up to each person.
> > There's no "right or wrong" or "this way is better", it's just
> > different.
> >
> > Paula
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