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Once the proper solder paste volume has been applied to the pads and cleaned off properly, the device can be placed onto the PCB.
When the device is placed using a modern area array rework system, split prism optics can be used to assist in the proper placement of the device. Using a prism, optical images of both the solder balls on the device as well as the PCB pads are superimposed in a stereomicroscope field of view on a monitor. The two images can then be aligned by X, Y and rotational adjustments.
Placement accuracy criteria is the same as the initial placement at the time of initial assembly. The device should be placed with a force per the manufacturers' specifications such that the solder paste contacts 50% of the PCB pad and not be in contact with the vias. For test boards the placement accuracy can be confirmed using double-sided tape adhered to the PCB BGA site. The BGA can then be placed onto this site, firmly held in place and examined at an angle under a stereomicroscope for accuracy.
The BGA can be hand-placed when using the StencilQuik™ process for larger pitch sizes (1.00 and 1.27mm). Care must be taken in handling the parts at the edges while making sure the operator is properly grounded.
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