BGA Replacement - Part Placement
BGA Rework Process - BGA / LGA Part Placement
"Course: BGA Rework-A Primer-Placement"
Once the proper solder paste volume has been applied to the pads and cleaned off properly, the BGA can be placed onto the PCB using at the proper heat source for the placement job.
When the ball grid array is placed using a modern area array rework system, split prism optics is used to assist in the precision placement. Using a prism, optical images of both the solder balls on the device as well as the PCB pads corresponding to the BGA device pattern are superimposed in a stereomicroscope field of view on a monitor. The two images can then be aligned by X, Y and rotational adjustments. The device can then be placed onto the PCB after either paste flux or patterned solder paste is deposited onto the PCB.
BGA placement accuracy criteria is the same as the initial placement at the time of initial assembly. The ball grid array 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. This is the basic process for ball grid array placement.
Alternatively theball grid array 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. The stay in place stencil is first placed on to the board where the stencil apertures are aligned over the correct pads. After peeling back the release liner and placing the device either pressure or temperature can be used to cure the underlying adhesive on the stencil. The ball grid array placement process is completed when the device is tactily “fitted” in to the holes which have been filled with either paste flux or solder paste for the BGA placement process.
In either case the ball grid array placement can be confirmed with optical, endoscopic and x-ray inspection.