Dragon Group China Bird AC-5K, Manual

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中龙集团
Dragon Group China Limited
BIRD
®
www.dragongroupchina.com
www.chinaemall.biz
No desoldering spots.
(3)Bridging and short-circuit.
When there is extra solder or the solder is not put on the right place, bridging and
short-circuit may happen. So no bridging or short-circuit.
(4)None paraposition.
The X-ray image will show very clearly whether the BGA solder ball is aimed at
the welding pad on PCB.
(5)Broken circuit and cold welding
When solder don't touch the relevant pad or the solder doesn
’
t flow very well, there
will be broken circuit or cold welding. It is absolutely not allowed.
4. BGA rework process
Most of the semiconductor device
’
s heat-resistant temperatures are between 240
°
C and
600
°
C. Therefore, the control of the temperature and uniformity are very important to
BGA rework systems. BGA rework process as follows:
a. Printed Circuit Board and BGA preheating
Printed Circuit Board and BGA
’
s preheating is meant to wipe off the moisture. If the
moisture was little, this step can be omitted.
b. Remove BGA
If the BGA will not be reused, and the PCB can endure high temperature, we can use
high temperature (shorter heating period) to remove it.
c. Clean the pad.
Pad cleaning is mainly clearing the solder paste and scaling powder remained on
the surface of PCB after BGA removal. For that process, it must use standard cleaning
agent. To ensure the reliability of the BGA solders, generally we cannot use the remained
solder paste in the pad, and we must clear away the used solder paste, except that solder
balls reform on the BGA. Because of the small size of BGA, especially CSP (or
μ
BGA
smaller), it is always difficult to cleaning the pad, so when reworking CSP, it needs to use
Rinse-free Flux if the space around CSP is very small.
d. Lay on BGA Flux Paste
Laying solder paste on the PCB has important influence on the result of BGA Rework. It
is convenient to lay solder paste on the PCB by selecting mould matched with BGA. For
CSP, there are three solder pastes for choice, including flux paste, clean-free and
water-soluble. If we choose the flux paste, the reflow time should be longer, if choose the
clean-free solder paste, reflux temperature should be lower.