There are several reasons that either BGAs or CSPs would need to be reballed. These include the need to reball a device after the device has been removed from the PCB and the exact same device needs to be placed back onto the PCB. In other instance, the device package has the incorrect solder alloy balls on it which means that the device balls need to be removed or deballed and replacement balls need to be placed back onto the device package. In still other instance, a new size solder ball may need to be placed onto the device in order for further processing requirements.
In such reballing cases for low volume reballing requirements less than a few hundred pieces the rework technician will typically use a solder reballing preform. The solder reballing preform has solder balls embedded in which correspond to the ball size, number and pattern of the device. After the balls are removed from the existing package and the pads are wicked or prepped otherwise as low and as flat as possible the package pads have solder paste flux applied to them. The solder reballing preform whether the solderquik preform or the EZReball preform is then placed with the device on top of the preform and is reflowed. Post reflow the preform remnants are removed , the device cleaned and inspected.
The solderquik preform has been around for many years and is well-suited for some applications. It consists of the solder balls embedded in a water soluble paper which after reflow is dissolved in DI water. The SolderQuik Preform is a stamped out design which means that any new patterns require some new tooling to be developed. This requires tooling charges and extended lead times for the solderquik preform to get in to the users’ hands.
There are several disadvantages inherent to the solderquik preform. One of them, citied above is the extended lead time and tooling cost associated with any of the new patterns. In addition, the mechanical tooling does not allow for very tight spacing in the solderquik preform design. In fact, pitches below 0.4mm are not currently available in the Solderquik preform.