Some small solder balls would appear around the solder joint during the reflow soldering process (only occur in the air atmosphere).
The whole TEST reflow process is:
a. Place solder paste onto stencil/screen and print the terminal pattern onto the test substrate by wiping paste over the stencil/screen in one smooth motion using rubber or metal squeegee.
b. Remove the stencil/screen carefully to avoid smearing the paste print.
c. Verify a paste print equivalent in geometry to the terminal of the device to be tested.
d. Place the terminals of the component being tested onto the solder paste printed pattern.
e. Verify the component placement by appropriate magnification.
f. Place the test substrate into the applicable reflow equipment and conduct the reflow process.
g. After reflow, carefully remove the substrate with the component(s) and allow to cool to room temperature.
h. Remove the component(s) from the substrate. The component leads may adhere slightly to the substrate due to the flux
residue.
i. Before examination, all leads shall have all visible flux residues removed. Care should be exercised in the flux residue removal process to not damage the leads or terminations.
Now I doubt that this problem may be caused by the wettability of the solder paste( for we change the solder paste component).
Can anyone tell me what is the reasons of this "satellite balls" phenomenon?
