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| TQFP soldering troubles |
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| Rachie5272:
I've been having to rework a bunch of 0.5mm pitch TQFP chips lately, and for some reason they've been very difficult. Harder than QFN. The problem is solder bridging. Everything is swimming in really nice BGA rework flux gel, and I can very easily drag excess solder to one end of pins, but then what? The leads form a nice capillary channel, which preferentially holds the solder over the iron tip. I've tried sever tips: J hook, well, chisel, and even a big drag soldering tip. Solder wick is the only thing which works, but then I'm left with too little solder and mechanically weak joints. Any suggestions? I'm already switching to QFN for the next design. |
| Wilksey:
I use solder wick to remove excess solder, do you have any? Or use less solder to begin with, use thinner solder. |
| KL27x:
Either a tinned face-only bevel/hoof or a regular bevel/hoof. But it has to be 2.5mm plus or minus half a mm. With a regular hoof, carefully wipe the entire tip and only apply solder to the cut face. Don't hold the tip completely parallel with the pcb, because that will squish your solder reservoir. Tilt the tip to create clearance for this solder bead that you carry on the bottom cut face of this hoof tip. Try running the edge of the bevel just along the toe of the pins. Or you can try laying it on top of the pins. If you get a huge glob on the first few pins, just stop and do the other side, then finish this one when your iron is running lower on ammo. The TFO is the best at sucking out these big shoulder bridges. But only Hakko seems to make them. The regular bevel will do near the same thing, esp after months of use like this and the sides start of the tip start to oxidize a little. |
| james_s:
I use a regular 1/8" wide chisel tip. Try using less solder. Rather than dragging, I tend to melt a bit of solder onto the tip of the iron and then touch it to the tip of a few pins where they meet the pads and allow the solder to wick up under the pins. Occasionally I get a bridge at which point I either wipe the tip of the iron and use it to pick up the excess solder or use a bit of wick. It takes practice but it's not too hard. |
| KL27x:
The sharpness of the edge makes a big difference, too. E.g., the two "spoon/well" tips I have, I don't use, ever. The edges are way too rounded, and the utility of these tips is very limited for me. The hoof with a sharp edge is also better at doing the toe drag and for QFN's, you need a really crisp edge. This crisp edge also helps with solderwicking and keeping the bead on the face of the tip, rather than wrapping up the heel or side. This crisp edge is how my hoof tips die. When the edge gets too rounded to the point you can't get it back without wearing through to the copper, then it's done. Also, the angle of the cut face matters. You want it to be rounder. Something more closer to 45 than 60. |
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