Have an issue with some legacy system - need to replace throughhole parts on PCB in situ while PCB is sandwiched between two sheets of acrylic with only small holes to access the leads on one side (i.e the back access is through a 3mm wide hole through a 10mm sheet of acrylic) and the front access is also tight (but just able to get a fine soldering tip in).
What we've been doing so far is prewarm the PCB to about 80C while trying to shield as much acrylic as possible. Then warm the leads (these have been soldered w leaded solder, (Sn60/Pb40) and remove but it is extremely difficult to get enough heat in due to the tight access and large ground planes and is causing issues with pad removal etc.
So I was considering using a low temp solder alloy but I am not experienced with them and from what I have seen, most are used mostly for when you want to reuse the IC not the PCB.
I'm sure it will work well for removal but its when we add the replacement part I am concerned that leftover low temp solder will produce a weak joint? I have read that many low temp solders alloy with leaded solder to produce brittle alloys - are there any that don't? Cost is not a major issue.