Quote:
Originally Posted by VacioArconte
generously apply flux paste.
|
Flux, flux, and more flux.
For either through hole or surface mount the key to good solder joints is heat flow.
One thing that can get in the way of heat flow is oxidation. Do you know what helps oxidation form? Heat, like all that heat in your soldering iron. That's why most solder that you buy is actually a tube with a goopy core of a chemical called flux. The flux melts as the solder melts and helps clean the joint of any oxidation, vastly improving the heat flow.
I've seen a lot of people "paint" with the iron. That is, flowing some solder on the tip of the iron, and trying to spread that solder blob onto the joint. This doesn't work because all the flux in the solder has already burned off and none is left to clean the joint.
This is why it is best to heat the joint with the iron and let the joint melt the solder. This ensures that the joint is at the proper temperature to melt and bond with the solder and allows the flux to do its job.
However, this is difficult for surface mount components. You need a third hand to hold the small component with tweezers in addition to the iron and solder.
Here is where
flux paste or a
flux pen comes in handy. First, apply flux to the pin and pad you want to solder. Then flow some solder onto your iron tip. Next, hold the part in position with some tweezers and paint the crusty blob of solder from your iron to the joint. The applied flux will magically breath life into that crusty solder blob and beautifully wick it on to the joint.
With lots practice, you can solder QFP packages in no time with plenty of flux and the drag method:
https://www.youtube.com/watch?v=erb6-i54tbo
-David