:: One of my DIP chips came with a notice saying that it should be
:: "cooked" at 125 degrees Celsius prior to reflow soldering

this shouldn't be a problem for a hobby, non commercial item. Where I 
once worked - some baking would take 24 hours and included baking flex 
pcb's as well. - I've used Ds1337 which come with a bake before you 
use - and a nice pink (well it was blue to start with) age disk - for 
proof of concept and one off hobby stuff I wouldn't bother - 
commercial and medical equipmen

:: How do I apply solder paste on pads?t most definitely.

As others have said a small syringe - there are different size 
hyperdermics and you need to get one that is large enough to only have 
to apply slight pressure to move the solder paste otherwise add a air 
pump with foot switch to your list-.


:: Should I use flux? Should I pre-flux the pads or apply flux
:: and then solder paste?

Yes - make sure that you get the flux that goes with the brand of 
solder you are using - 

Solder paste is the most carcianogenic form of solder as it is small 
balls of solder combined in a wetting agent. It will feel and look a 
bit like graphite paste, being small it can be absorbed by the skin.

Surgical/medical/household disposable gloves will be fine. Make sure 
that you wear clothes that you won't use for anything else or wash the 
clothes afterwards as solder paste can get EVERYWHERE surprisingly.

Solder pastes should eb kept in a fridge - not a fridge used for food 
due to contamination. The paste from a fridge will need upt o 4 hours 
to get to working temperature. Again though as you are not producing 
medical or military goods you probably don't need to worry about the 
fridge bit, the solder just won't last as long.  

Music to your ears - find a local board/manufacturing company, if they 
make medical equipment they will probably have whole buckets of solder 
they can't use anymore, which they are often willing to either give 
away or for a small consideration - the solder will probably be 
'dirty' and may have flux already mixed into it.

Colin
--
cdb, colin@btech-online.co.uk on 27/03/2009
 
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