very weak wifi signal after getting phone wet

You can submerge the board for quite sometime..5-15 minutes is long enough but I've left it longer(hours...so don't panic). What you do need is something to try and clean any stubborn dirt/debris etc from in,around, under etc all the tiny components. I use an eye-makeup brush which is quite small, very soft. You can use an old soft toothbrush/paintbrush anything that isn't going to shred your components. You need to watch what you're doing, don't just wave the brush like a magician, try to direct it to the hard to get bits. water debris is greenish or white..look at the guide link for an idea(oldturkey's blue text up above) you can clean connectors/flex ends on the wifi antenna. The only reason not to submerge the LCD is it leaves watermarking behind your screen which is almost impossible to remove. You might find that having cleaned it there is still dirt etc, repeat again and sometimes again. let it dry a few hours before you reassemble it.