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Problems of welding BGA
Problems of welding BGA
After a chip welding, from the outside, there is nothing different, but from the internal analysis, there will
be a big difference.
1, blow hole
Blow hole is in the reflow process, the surface of the ball appear hole type or a circular pit, the porous may
be very small, very likely to see how much gas in the solder ball. Appear this kind of phenomenon from the
outside to see, will be able to see the ball around the ball, ball caused by incomplete, so there are may chip
and the motherboard contact is not good. Cause blowing hole is in the reflow process, solder balls have
overflow gas formation of blow hole, the source of the solution is best to control the ball, strengthen solder
quality. This is generally used to weld the people can see.
Cold is the surface of the ball usually dull, caused by incomplete welding, the general was no problem, a
long time will appear weld and other issues. Caused by cold welding is insufficient heat, in solder balls did
not melt completely stops heating. This general and operator's practical experience. The solution is to
increase the temperature of the heating curve, increase the welding temperature, prolong the welding
time and improve the operation level of the operator.
Crystalline fracture is ruptured surface of the ball, not the normal shape, solder ball like explosion, surface
rupture trace. Cause crystalline fracture is the main reason for the solder ball polluted, solder balls contain
other substances, in the melting point is not the same heating will rupture. The solution is in the solder pad
solder joints tin, followed by an increase in temperature or temperature of the time, to extend the time of
heating and cooling can be achieved to prevent the crystallization of the problem. Because of the time and
energy of the relationship, this time to write these three phenomena, and the rest I will make up the next
time, I hope you can put forward suggestions.
Flux residue is in the reflow process, due to the unevenness of the surface of the PCB, the flux residue will
residues between the solder ball, may will have some bad problems. Caused by the residual flux residues
many in solder balls between the maximum possible flux is use too much, there is some flux relatively thick.
In addition, different PCB layer and temperature curve also certain relationship. Solution is welding solder,
it is best to wash, of course, remain inside the chip can not be cleaned, which requires a flux, prevent flux in
the chip solder balls form a connection, in addition, improve welding temperature and prolonging welding
time can also reduce the flux residue.
5,Incomplete welding solder
Solder ball incomplete welding is flux and solder balls not reaching reflow temperature, solder ball for
melting stopped heating the, which makes part of solder ball stays in the pad and the motherboard fully
connected, the formation of cold welding. Resulting in solder balls attached for three reasons: one is the
welding temperature is not high enough and the welding time is not long enough, the second is likely no
brush flux pads, PCB board is not smooth, resulting in the whole welding surface is not at the same level.
The solution is to improve welding temperature and prolonging the time of the welding, strengthen the
training of operating personnel, careful flux coating, pay attention to try to put the flat motherboard and
prevent the deformation of the motherboard. As long as the above points, cold welding phenomenon is
6,To prevent the migration of solder ball
In the BGA chip on the motherboard, due to the absence of the placed position, resulting in solder ball
did not put on the pad or migration, is a direct result of the chip without welding on the motherboard.
Caused by the migration of a tin ball are operator does not put good motherboard is operator carelessness.
In addition, welding platform deflection will cause chip offset. So to avoid such problems, then to improve
the level of the operator, this technology requires time of accumulation, not one or two days will be able
to put good, in addition to regularly check the BGA welding station, check the support frame, to prevent
deformation, improve welding quality.
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