Okay, I was having quite a bit of trouble figuring out how to hand-apply solder paste to SSOP pads without stencils, but I got some very good insight here. One method of soldering fine pitch pads is the “pool of solder” method, whereby you flood the pads and pins with solder, then you use solder wick to remove the excess. You’ll have nice, cleanly separated pads.
So, that’s really great to hear! The technique can be extended to using solder paste too. You apply the solder paste such that the pads are bridged together, but then you can use solder wick to remove the excess. But, the good things don’t stop there. Thanks to surface tension magic, most bridges across pads will break apart on their own because the molten, liquid solder wants to stick to the metal pad surfaces more so than the insulative solder mask surface. That leaves less work for solder wick cleanup, not to mention less likelihood of failure to properly clean up the overflow.
That being said, this technique of course doesn’t work with Quad-Flat-No-Leads (QFNL) or Ball Grid Array (BGA) components due to the lack of exposed leads where you can do cleanup with solder wick.
20200815/DuckDuckGo hand apply solder paste tssop pads
20200815/http://skywired.net/blog/tutorials/how-to-solder-qfp-tssop-soic-surface-mount/
20200815/https://electronics.stackexchange.com/questions/145271/whats-the-easiest-way-to-solder-tssop-parts
So, I put my hypothesis to the test. The result? I am quite impressed! Re-positioning a fine-pitch chip is very easy when you have solder paste smeared across the pads because you do not worry about accidentally creating bridges when doing so, they’ll be broken away anways after your rework. And then, after I’ve done the reflow, indeed there were only a few fine-pitch pads bridged together, and I was able to clean these up with solder wick without much issue.
My main concerns were that I either (1) may have not cleaned up enough solder, somehow hiding deep on the pads may be a bridge I just cannot reach, or (2) I may have damaged the chip from too much heat from the soldering iron from solder wick cleanup. Reflow ovens are nice because you don’t use as high of a point temperature as soldering irons, so heat damage is less likely. That being said, I was of course trying to be very careful to avoid overheating when using the soldering iron, and my hope was that the thermal mass of the solder wick also helped for softer and gentler treatment to the chip itself.
Finally, the question of testing for bridges? Basically, the only reliable way to do this with integrated circuits is optical inspection. Often times the internal circuits may use buffers or default ground termination of some sort that render basic electrical continuity testing pretty much useless in informing you of solder bridges.