Xilinx device packages must be placed accurately according to their geometry outline. Positioning packages manually via hand mounting is not recommended. Typical component placement accuracies of ±50 μm can be achieved using standard pick and place equipment with vision system. The PCB and components are optically checked and measured by the pick and place vision system. The pick and place machine detects the fiducial on the PCB immediately prior to the placement of the Versal device. Recognition of the packages is performed by the vision system, to ensure correct centering of the Versal device placement on the PCB pad array. BGA packages with solder balls can self-align during the reflow process because of the solder high surface tension that enables the pulling and centering of the device, and where a slight offset of the placement is still allowed. For guidance, the maximum tolerable offset of device placement is around 30% of the pad diameter on the PCB for typical non-solder mask defined pads. This means that the misalignment of solder ball device packages to the PCB pad must be better than 150 μm to assure a robust mounting process. Generally, this is achievable using a wide range of modern pick and placement systems. The following setup conditions are important for the pick and placement systems:
- The pick and place nozzle type should be selected based on the dimensions of the Versal device. The nozzle needs to firmly hold the device package during the pick and place stage. The appropriate nozzle type for the device package can be chosen from the manual provided by the pick and place equipment manufacturer.
- The ball recognition capabilities of the placement system should be used and package outline centering should be avoided. This eliminates the solder ball to package edge tolerances of the package. Refer to the specific package outline drawing for details.
- To ensure the proper identification of the device package during vision recognition, prior to its placement, a suitable lighting system and the correct choice of the features of the measuring method are essential. The most suitable settings can be chosen from the manual provided by the pick and place equipment manufacturer.
- To avoid solder bridging or solder smear, ensure the proper placement force of the device package during placement on the PCB. Excessive placement force can lead to excess solder paste and cause solder bridging. However, a slight placement force can lead to insufficient solder paste contact between the device package solder balls and the solder paste, causing solder defects including open solder joints, badly centered packages, or even head-in-pillow (HIP) defects.