中龙集团
Dragon Group China Limited
BIRD
®
(5)Good electrical property. The pins are small, the selfinductance and mutualinductance
of the conductivity is low, and the frequency characteristic is good.
(6)The tension between solder points produces good self-centration effect in
solder-reflow, allowing 5% error of patch precision.
(7)Compatible with original SMT mount technology and machines. The original screen
printer machine, mounter and solder-reflow machine all can be used. The comparison
between BGA and QFP is shown in Table 1. The main defect of BGA is the necessity of
X-ray detection after welding.
c. Welding of BGA
The success of welding BGA is affected by the assembly of PCB. So 3 key factors must
be considered in the layout of PCB.
Features
BGA
QFP
Package size S/m
2
525
1600
Pin space L/mm
1.27
0.50
fault rate (
×
10
-6/ pcs
)
0.60
100
(1)Thermal management Thermal management must be considered when we design the
assembly of PCB. If many pieces of BGA gather on a small area of PCB, it will cause the
imbalance of PCB in the reflow oven. If many big pieces of BGA gather on a certain area
of PCB, longer heating period will damage some of the BGA. The areas with fewer
components have reached the welding temperature, while those areas with BGA are still
in low temperature. So the welding period is over before the flux paste withdraws from
the welding spots, thus there may be poor soldering or no-melting of welding balls.
(2)Rabbet
The design of rabbet on PCB should stick to relevant standards strictly. Any rabbet
near BGA welding pad must cover the solder mask very well. If not, the extra welding
paste will flow from the welding pad to the rabbet, then leads to short circuit between
welding pad and rabbets nearby.
The geometric shape and diameter of welding pad:
The compactness of pins has immediate impact on the geometric shape and diameter of
welding pad. Similarly, BGA has different sizes, shapes and complexity. As the package
size decreases, the geometric shape and diameter of the welding pad calls for higher
precision in detection.
Summary of Contents for Bird AC-5K
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