Introduction

Also referred to as micro BGA’s, Chip Scale Packages (CSP) although similar to traditional BGA components differ in overall size and diameter of solder spheres. Their size is typically smaller and solder spheres are about ½ the diameter of BGA’s which range from 0.55mm to 0.75mm. This article details rework of a CSP on a test board using an AT-GDP Rework Station. A Lead Free profile has been applied during removal and installation processes.

Components

The CSP measures 7mm x 6mm and contains 46 spheres (Figure 1). Solder spheres measure 0.35mm in diameter with a pitch of 0.75mm. Test board measures 70mm x 165mm.

Figure 1: CSP on a test board

Removal

After securing the test board by the board holder’s clamps, an operator installs a vacuum pick up tip and nozzle suitable for the CSP device. Implementing machine’s optics, the nozzle is aligned over the component. A pre-established profile is selected from the software’ library and Start icon is selected. At this point the process is hands-off. Rework station automatically drives the nozzle down to a board and covers the CSP. Machine then activates vacuum pick up tip so as to remove the component once reflow is achieved and the heating cycle is initiated. Figure 2 shows a nozzle covering the device during reflow. Heating is precisely controlled by the software (Figure 3). It mimics an original profile with heat applied from both top and bottom sides of a board. Source of bottom heating is Quartz IR while the top side is forced air or nitrogen convection. As is shown in the video of removal, upon completion of reflow, the machine lifts a CSP off a board and moves nozzle up along Z axis to its starting point. Figure 2: Nozzle covering CSP during reflow Figure 3: Screenshot of a profile Residual solder remains on the board after removing a component. It takes the shape of Hershey’s kisses candy due to surface tension of molten solder (Figure 4). As a result of its uneven shape and volume, solder must be removed prior to installing a new component. This is commonly performed using a solder wick method... see more in attached pdf file