On 4/18/2013 8:57 AM, Isaac Marino Bavaresco 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 much= 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 ha= s >> an assembly stereo microscope, a micro tipped solder iron, a steady hand >> and a lot of patience,,,,i.e. "very much a prototype" technique. >> >> The pads need to be longer than than that typically recommended, in orde= r >> to afford access to the pad beyond the package pin. >> The solder tip is touched here to reflow the HASL tinning, slid up to th= e >> 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 hot leveled solder, and immediately withdrawn.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 pa= d >>> 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 pi= n >>> 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 fin= e >>> 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 different >>> techniques. If you don't have a hot air gun, now is definitely the tim= e >>> to invest. >>> >>> Making the pads on the pcb a bit longer to be hand-assemble-friendly is >>> 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 line= of >>> solder paste across the pins is one trick, followed by a quick visit to= 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-pack= age/lfcsp/index.html >>>> ), which will be the first time I'm using such a fine pitch, lead free >>>> 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 >>> >> In my experience, HASL is very workable while the PCB is fresh, but in a=20 few weeks the tin./lead surface begins to oxidize. If you store unpopulated PCBs for long periods, you should store them in=20 an airtight container. Years ago, I dabbled in the oil exploration business. and on shipboard,=20 the environment was extreme. We sometimes had to cobble up some special=20 filter circuits. The proto PCBs we used were coated with plastic from=20 the home office to protect the surface from oxidation or corrosion. When=20 we needed the board, we just dissolved the plastic coating with acetone,=20 so the surface was always pristine and easily solderable. --Bob A --=20 The only place success comes before work is in the dictionary. VINCE LOMBARDI --=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 .