Re: gEDA-user: QFN soldering
here's a video I found that answers a lot of questions - http://store.curiousinventor.com/guides/Surface_Mount_Soldering/QFN/ (scroll down just a little for the video) ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
gEDA-user: QFN soldering
does anyone have experience with this package? I want to know if they are hard to work with. The exposed pad underneath is a problem for hand soldering - but maybe could be left unsoldered for prototypes. Maybe just place some solder paste under there ? If the pcb pads are long enough, is it feasible to solder to the edge of the chip instead of getting it underneath the device? thanks gene ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: QFN soldering
get a stencil, get solder paste, apply paste over stencil, heatgun, done. super simple. dont even bother doing it manually pin to pin, it probably wont work. On Mon, Sep 13, 2010 at 10:46 AM, gene glick carzr...@optonline.net wrote: does anyone have experience with this package? I want to know if they are hard to work with. The exposed pad underneath is a problem for hand soldering - but maybe could be left unsoldered for prototypes. Maybe just place some solder paste under there ? If the pcb pads are long enough, is it feasible to solder to the edge of the chip instead of getting it underneath the device? thanks gene ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: QFN soldering
does anyone have experience with this package? Just did one today. I want to know if they are hard to work with. Harder than a QFP, but not impossible for home-fab. Pen flux the bottom of the chip before placing it on the paste - I wish I'd remember this more reliably :-) The exposed pad underneath is a problem for hand soldering - but maybe could be left unsoldered for prototypes. Depends on the chip. Some require an electrical connection, it may be the only ground for example. Maybe just place some solder paste under there ? If you have to solder an exposed pad manually, you have (IMHO) exactly two choices: 1. Put a via right under it, with a drill big enough to get your soldering iron in there to solder it from the back side. Keep in mind the big thermal sink this will be; your smallest iron tip might not be up to the task. Obviously, do this after soldering the edge pads :-) 2. Use a solder paste stencil of some sort and reflow it (heatgun, oven, hotplate). I make QFN stencils out of alumimum foil and UV film, I've done it with toner and thin brass too, and once with brass and a dremel drill press. But you can't just squeeze paste out of a tube and expect it to work - too little won't conduct and too much keeps the other pins from touching. Note that for home-etched boards, #1 requires a tiny wire, else you don't really have anything to solder to. Surface tension will keep the obvious idea from working :-) If the pcb pads are long enough, is it feasible to solder to the edge of the chip instead of getting it underneath the device? If you use #1 above, and the pads extend contiguously up the edges of the chip and not just on the bottom, yes. Use LOTS of pen flux and make sure the pcb's pads extend out far enough for a thermal connection with your iron. I've done this before, and the flux/iron trick can be used to fix reflow problems too. Note: some QFNs have copper on the side which is *not* contiguous with the pads on the bottom. The FT232RQ is such a chip. You have to reflow these, although the flux/iron trick can still repair them once there's *some* solder under the chip. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: QFN soldering
For quick breadboarding of an accelerometer I've deadbug soldered one successfully. Just superglued it upside down and soldered directly to the pads with very thin wire.. On Mon, Sep 13, 2010 at 12:04 PM, DJ Delorie d...@delorie.com wrote: does anyone have experience with this package? Just did one today. I want to know if they are hard to work with. Harder than a QFP, but not impossible for home-fab. Pen flux the bottom of the chip before placing it on the paste - I wish I'd remember this more reliably :-) The exposed pad underneath is a problem for hand soldering - but maybe could be left unsoldered for prototypes. Depends on the chip. Some require an electrical connection, it may be the only ground for example. Maybe just place some solder paste under there ? If you have to solder an exposed pad manually, you have (IMHO) exactly two choices: 1. Put a via right under it, with a drill big enough to get your soldering iron in there to solder it from the back side. Keep in mind the big thermal sink this will be; your smallest iron tip might not be up to the task. Obviously, do this after soldering the edge pads :-) 2. Use a solder paste stencil of some sort and reflow it (heatgun, oven, hotplate). I make QFN stencils out of alumimum foil and UV film, I've done it with toner and thin brass too, and once with brass and a dremel drill press. But you can't just squeeze paste out of a tube and expect it to work - too little won't conduct and too much keeps the other pins from touching. Note that for home-etched boards, #1 requires a tiny wire, else you don't really have anything to solder to. Surface tension will keep the obvious idea from working :-) If the pcb pads are long enough, is it feasible to solder to the edge of the chip instead of getting it underneath the device? If you use #1 above, and the pads extend contiguously up the edges of the chip and not just on the bottom, yes. Use LOTS of pen flux and make sure the pcb's pads extend out far enough for a thermal connection with your iron. I've done this before, and the flux/iron trick can be used to fix reflow problems too. Note: some QFNs have copper on the side which is *not* contiguous with the pads on the bottom. The FT232RQ is such a chip. You have to reflow these, although the flux/iron trick can still repair them once there's *some* solder under the chip. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: QFN soldering
There are a number of different QFN package styles. Some have pads only on the bottom, others have pads that wrap around the up the side a bit. These tend to be easier to hand solder since you have a place to contact with the solder iron. Sounds like yours don't have that plus they have a thermal pad on the bottom. If the thermal pad isn't required for an electrical connection, and you don't need to use the full power capability of the package, you can likely live without soldering the thermal pad for a prototype. But check the data sheet carefully. Sometimes they require you to provide an electrical connection. Is this a power supply devices? Those are the ones that are most demanding I've found. The assembly houses use a hot air tool. It heats up the entire part and everything in the immediate area such as the board. The solder flows, the part settles down onto the board and all is good. Rick At 09:46 PM 9/12/2010, you wrote: does anyone have experience with this package? I want to know if they are hard to work with. The exposed pad underneath is a problem for hand soldering - but maybe could be left unsoldered for prototypes. Maybe just place some solder paste under there ? If the pcb pads are long enough, is it feasible to solder to the edge of the chip instead of getting it underneath the device? thanks gene ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
