Assembly Inspection
Due to the area array format of the BGA, it is impossible to perform 100% inspection of all the solder joints. An
outer-row inspection can be used to verify the solder wetting, and alignment. X-ray can be used to identify solder
bridging. However, these techniques are often implemented on a sampling basis for high volume manufacturing. A
good SMT process control is the key to ensure high assembly yield and reliable product.
Rework
Rework should be performed using an industrial standard rework station such as SRT, SEC, PACE or equivalent.
a. BGA Package Removal. This process requires to preheat the PCB, from bottom side, to 80 °C to 120 °C
to enhance the temperature uniformity and process control. After the PCB has reached the set
temperature, the package can be locally heated with hot-gas nozzle to above solder liquidus temperature
(183 °C). Care should be taken to limit the temperature in solder joints to be less than 220 °C. Once all
solder joints melts, the package can be removed with a vacuum pick up tool.
b. Site Preparation. Hand-held solder vacuum tool or de-soldering braid can be used to remove residue
solder from the pads. No-clean flux is recommended to improve the cleaning efficiency.
c. Solder Paste or Flux Printing. If solder paste is used, the printing requirements should follow the
standard SMT process requirements. If flux is used, it can be printed on the PCB pads or applied on the
package BGA.
d. Component Placement. Utilize the pick and place feature of the rework station for accurate component
placement. Manual pick and place is not recommended.
e. Component Reflow. Similar to the package removal, the PCB should be preheated to 80 °C to 120 °C
and the hot-gas nozzle be used to apply thermal energy to the package. It is recommended the rework
profile should follow the same guidelines as the initial SMT assembly profile; or as close as possible.
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