[chbot] Hot topic Solder paste.

[Marshland Engineering]

I did a test run and I could not see any flux till I use my microscope. The
joints look good. Much less less flux that hand soldering. 

http://www.marshland.co.nz/ftp/Misc/ReflowResults.JPG

I originally made single sided PCBs with my oven and used a suggested heat
profile. All worked fine. Now I playing with double sided ones. I ran a test
with 2 thermocouples, one top and one bottom of the board to see the
difference. The best I could do was a 10 degree differential. As this is quite
small, I guess I need to do both sides at once, not one then the other. If I
want to do that, I could use lead free for the first one and then leaded for
the second at the lower temperature. Still experimenting at the moment. 

Not sure if a quicker solder temp rise would increase the difference enough
after the initial preheat soak period to do one side then the other. Need to
try some component epoxy to do both at once. I guess capillary will hold
resistors at the bottom but not ICs, big caps or diodes.  

Just found this, 137 deg melting point. 

https://www.amazon.com/SRA-Temperature-Solder-Paste-SSLTNC-15G/dp/B005C6H26C

That looks like a solution. 

Cheers Wallace