Because there is closed-loop temperature control, the reliability of reworked joints or PCBAs should be better.. The disadvantages of this method are that reflowing of nearby joints on c
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6 Since there is no moving gas, there is no built up of static
7 The method allows the use of the assembly robot’s gripper and vacuum suction heads, which can
be considered a major economic savings compared to the use of nozzles, which are all equipped
with vacuums
8 Despite the requirements of spot size adjustment and lens changing, the IR method eliminates
nozzle head design and manufacturing problems which are currently concerns for hot air/gas systems
9 Because there is closed-loop temperature control, the reliability of reworked joints or PCBAs
should be better
10 Noncontact heating eliminates tool marks
The disadvantages of this method are that reflowing of nearby joints on closely packed PCBAs is possible,
and reflow may occur at higher temperatures due to the use of short-wave IR
The solder fountain and VDI–SI couple-based reflow methods have been compared The study revealed that:
1 Solder fountain-based TH component rework is more effective because solder joints using a solder
fountain are reliable joints, and removal can be performed more safely due to the elimination of
sweated joints Furthermore, exclusion of sweated joints also eliminates the need for secondary
heating, which might degrade the PCB and take extra time
2 Even though the solder fountain method requires an X-Y-Z positioning table, the requirement of
an X-Y positioning table for all SM rework leaves only the need to justify a Z positioning table
This can indeed be justified, because the VDI–SI method requires a board reorientation facility
3 The use of a solder fountain and X-Y-Z positioning table eliminates the scattering of metal parts
on the PCBAs during leg cutting (removal)
4 The simultaneous desoldering and resoldering of the joints of the defective component decreases
the rework cycle time compared with sequential removal and resoldering of each leg
5 No adhesive dispensing is necessary This also eliminates adhesive curing and dispensing facilities
6 A solder fountain is less expensive than VDI–SI tooling
If double-sided mixed technology PCBAs are reworked, the method also has some disadvantages If any
insulated wire jumper exists in the vicinity of or just below a defective TH component, it may melt and
cause shorts If any SM components, such as micro-tabs, bobbins, or micro switches, which are not
resistant or suitable for wave soldering, are located in vicinity of or just below a defective TH component,
these can be damaged during removal Therefore, these components and jumper wires would need to
be removed during the preparation of the PCBAs for rework
6.7 Determination of Other Rework Requirements
Once decisions are made on the reflow methods for TH and SM components, analysis and decision
making based on rework requirements can be carried out to specify the other rework tooling necessary
for automation, and other related problems could be solved
Rework Tools
To achieve fully automated rework, the following needs to be considered [25]
Preparation of PCBAs for Rework
The cleaning of PCBAs and removal of conformal coatings are not necessary because the cell is designed
to rework assembly defects directly after manufacture when they are not covered by dust or other
contamination and conformal coatings (PCBAs are coated after the final test of the finished goods) and
are not subject to field defects The other problem when preparing a PCBA for rework is that of removing
obstructions (i.e., heat sinks, jumper wires, threaded fasteners, other components, etc.) The first three