20
Because of counterpoint by hand will cause deviation between chip and welding plate,
surface tension of tin ball will have a process of automatic correction between BGA
chip and welding pad Once heating, BGA falls not evenly, which will cause that the
chip drops not evenly It will cause the phenomenon of missing weld and false weld if
stop reflowing at this time, the chip will not fall normally So it is necessary for you to
extend heating time of third .forth temperature zones or add the bottom pre-heating
temperature to make the tin balls meltdown and drop evenly
(2) short-circuiting
：
When the ball reached the melting point, it is in a liquid state , if too long or too high
temperature and pressure, it will destroy surface tension of solder balls and the
supporting role, resulting in short-circuit phenomenon when reflows, the chips fall
entirely on the PCB pads the , so we need to appropriately reduce the heating section
of the third and fourth soldering temperature and time , or reduce the bottom of the
preheat temperature
Attention:
It will cause occur odor in the normal working process In order to assure
safe and healthy operation environment, please keep ventilation in and out of the room
G Outer temperature measurement couple usage
（
A
）
the function of external temperature sensor
a To measure actual temperature more accurately during the welding process
b Because it can move freely, it is more convenient to measure different parts of ready
to be measured component
c It has correct function, which can make the temperature of welding parts is more
familiar with the setting temperature
(B)The installation of couple
a Check that whether the couple line is in good condition
b Put the plug of couple line in the socket of external couple
c After right installation of couple, the touch screen will show the current temperature
of couple
(C)Use the couple to measure actual temperature
a Put the PCB board on the BGA Rework station Use tinfoil paper to fix the couple
line on the PCB board
b Adjust the detector and make it 1-2mm higher than the ready to be measured parts
