. COMPONENTS (8 questions)
. HAND SOLDERING AND DE-SOLDERING (3 questions)
. INSPECTION (3 questions)
. PRINTED BOARD DESIGN (3 questions)
. PRINTED CIRCUIT BOARDS (6 questions)
. REFLOW SOLDERING (5 questions)
. REWORK (1 questions)
. SCREEN PRINTING (2 questions)
. WAVE SOLDERING (4 questions)
. X-RAY INSPECTION (1 questions)
1 . Are there any changes to reworking joints chip components with lead-free alloy?
Are there any changes to reworking joints chip components with lead-free alloy?
The basic procedures that you follow for any surface mount process are the same. Obviously slightly higher temperatures are used for lead-free alloys. A no clean flux is applied to the joints and the joints are then reflowed, most commonly with a hot air pencil. When the joints reflow you lift the component off the surface with a pair of fine pitch tweezers. Normally when reflow takes place it can be seen.
The flux protects the solder on the pad during heating. The solder will normally collapse back to the pad without leaving spikes. This allows a small amount of flux to be applied again a new component placed and reflowed in place. Normally there is no need to add solder and provided the air pressure of the hot air tool is controlled you can use the procedure on components down to 0201 chips.
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