Josh, I've done a large number of small quantity SMT board runs as follows: 1. Using a syringe of solder paste with the smallest tip provided, put tiny dabs on pads of Rs, Cs, Qs. For ICs, run a thin line of paste over the pads on each side. 2. Hand place the parts with reasonable alignment using tweezers and magnifier. The paste will hold the parts in place. I made a parts holder using a bunch of small tin cups mounted to a board. Each cup has a ref designator next to it and the parts go in the tins before I start placing. 3. Stick the boards in a toaster oven at the highest temp it will go to. 4. Through the window, watch the solder melt (turn shiny) starting at the back of the oven and progressing to the front. It's kind of fascinating to watch! 5. Surface tension of the melted solder near always aligns all parts perfectly. It's magic! 6. Magic comes with a price: 7. Once you've seen all the solder melt, turn off the oven and open the door. 8. After the boards cool down enough to handle inspect with a magnifying lens. 9. You may have to use thin solderwick to remove the solder bridges on some ICs. This is really much easier to do than write about. It has always worked very well for me. If you always use a tiny amount of solder for the pads and the ICs, you will produce very few solder bridges. Good luck old friend! On Thu, Apr 18, 2013 at 12:26 AM, Josh Koffman wrote: > Hi Jesse, > > > 1) use a syringe with a fine tip and dab a little solder on each pcb pa= d > > that way, instead of a stencil. > > Do you do a little dab or are you a proponent of the "thin line" techniqu= e? > > > 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. > > So I'm melting the solder that I just applied with the syringe, right? > Is the goal to end up with a small bump on each pad? Then do I apply > any more solder paste or flux before reflowing onto the actual chip? > > If I'm reflowing in an oven without applying some sort of goo, what > keeps the chip in place? So far, in the boards I've done this way, the > solder paste holds the component in place. > > > 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. > > I'll check them out. It's so quick and convenient to get the mylar > stencils cut that it's hard to justify the comparatively huge expense > and time to get a metal stencil. I am considering trying to get my > laser guys to cut the stencil in two passes, doing alternate pads each > time (ie cut apertures for all the odd pins, then come back and do the > even pins). My thought there is that it would give the material some > time to cool in between passes, and would perhaps mean that the > interstitial plastic bits won't overheat and warp. > > > 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. > > Bridges that are somewhere I can see aren't usually that concerning, > but I'm worried I'll get bridges just under the edge of of the chip > that I won't be able to get out. Luckily I have a hot air station and > I'll be sure I have the right tip to desolder if I need to. > > > Making the pads on the pcb a bit longer to be hand-assemble-friendly is > > a good idea. > > Ok, good to know I'm on the right track there. > > Thanks for the advice! > > 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 > --=20 Carey Fisher Chief Technical Officer New Communications Solutions, LLC 678-999-3956 careyfisher@ncsradio.com --=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 .