We did investigate the solder flooding then wicking away technique...it looks OK, but produced consistent reliability problems once the boards were in the field. Admittedly, 'prototypes' are not supposed to go into live installations, but our production is too small to warrant the whole professional solder paste stencil / pick and place machine / reflow manufacture. The question was, "is the solder of the HASL surface sufficient for assembly?" The answer is yes...within certain limitations and provisos. On Thu, Apr 18, 2013 at 2:57 PM, Isaac Marino Bavaresco < isaacbavaresco@yahoo.com.br> wrote: > We assemble prototypes by hand-soldering down to 0.5mm pitch. > Just apply a lot of solder with the tip of the iron, short-circuiting > all the pads, then with a solder wick remove the excess. > Sometimes there are shorts that don't want to go, then scratch it with a > steel brush or add more solder and remove with the wick again. > > Isaac > > > Em 18/04/2013 02:53, Perry Curling-Hope escreveu: > > it's very much a prototype.? > > > > Then why are you attempting assembly by board reflow, which is very muc= h > a > > production technique? > > > > Hand soldering directly onto the HASL surface is practical given the > > following considerations: > > > > The land pattern is designed with hand soldering in mind > > The PCB has been produced for this purpose ( lead solder tinned ) > > A compatible liquid flux is applied > > The board is assembled promptly after manufacture ( oxidation minimized= ) > > > > This is workable with consistent results down to a pitch of 0.8mm (e.g. > > TQFP ) without any special equipment or skills. > > > > Prototyping with 0,65mm pitch (e.g. SSOP) packages is possible if one h= as > > an assembly stereo microscope, a micro tipped solder iron, a steady han= d > > and a lot of patience,,,,i.e. "very much a prototype" technique. > > > > The pads need to be longer than than that typically recommended, in ord= er > > to afford access to the pad beyond the package pin. > > The solder tip is touched here to reflow the HASL tinning, slid up to t= he > > pin and then on top of it, pressing the pin down into the molten > > hot leveled solder, and immediately withdrawn. > > > > > > > > > > > > On Thu, Apr 18, 2013 at 1:45 AM, Jesse Lackey >wrote: > > > >> Hi Josh, my 2c... > >> > >> 1) use a syringe with a fine tip and dab a little solder on each pcb p= ad > >> that way, instead of a stencil. > >> > >> 2) use iron to melt a little solder on each pcb pad, then to reflow > >> either with oven or (better) hot air gun. Or use iron to reflow one p= in > >> at a time. So you'll be melting the solder per pin twice, not > >> recommended in general, but these are prototypes. > >> > >> 3) metal stencils, I gave up on mylar long ago. If it is worth the > >> effort to get a stencil made etc., it is worth getting metal. I use > >> stencilsunlimited.com and have their prototype frame holder thingy, > >> recommended. The stencils are in the $125 range. > >> > >> 4) give up on being overly cautious about bridges; this is what the fi= ne > >> solder wick (0.025" wide, mg chemicals cat #423, for example) is for. > >> > >> Have a few extra pcbs and chips, and don't be in a hurry, try differen= t > >> techniques. If you don't have a hot air gun, now is definitely the ti= me > >> to invest. > >> > >> Making the pads on the pcb a bit longer to be hand-assemble-friendly i= s > >> a good idea. > >> > >> And of course have fun...! > >> J > >> > >> > >> Josh Koffman wrote: > >>> On Tue, Apr 16, 2013 at 10:31 PM, Marc Nicholas > >> wrote: > >>>> What package is the component in question? I have success without a > >> stencil on just about any part that has exposed pads/pins=85a fine lin= e of > >> solder paste across the pins is one trick, followed by a quick visit t= o > the > >> toaster over. > >>> Interesting. I'm currently designing a project for myself that will > >>> use an LFSCP package (reference here: > >>> > >> > http://www.analog.com/en/technical-library/packages/csp-chip-scale-packag= e/lfcsp/index.html > >>> ), which will be the first time I'm using such a fine pitch, lead fre= e > >>> device. I'm currently planning on making the pads a bit longer than > >>> usual, so I can try to touch an iron to them if things don't go well > >>> during reflow. I currently use laser cut mylar stencils, but the > >>> separation between the pads on fine pitch devices usually ends up a > >>> bit wonky, so I'm not sure what to do. I'm definitely afraid of too > >>> much paste causing a bridge. > >>> > >>> Josh > >>> -- > >>> A common mistake that people make when trying to design something > >>> completely foolproof is to underestimate the ingenuity of complete > >>> fools. > >>> -Douglas Adams > >>> > >> -- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Perry Curling-Hope Research and Development --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .