BGA Package Removal
Best Practices
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2. BGA Removal – An accurate thermal profile needs to be established for the component removal process. This will determine the exposure duration and the maximum component/board temperatures.The profile should be adapted to each board and component to be removed. Although the typical profile should provide a peak temperature between 210°C to 220°C (at the solder joint) for a maximum of 75 seconds. It is best, however, to consult with equipment manufacturer for the recommended profile. Research also indicates that a short delta T and a short dwell time above 183°C are preferred to minimize intermetallic growth and control board warpage. It is also important to ensure that the component and the board are not overheated and that all balls are re flowed on the specific component being removed. In general, preheat the entire board to a minimum of 85°C to avoid large temperature differentials and potential board war page. In terms of the equipment and tools available, hand-held as well as automatic hot gas rework systems with vacuum suction have been developed for BGA removal. First, position the nozzle (same size as component or smaller) around 100 mils from the top of the component and apply heat from the top side using the rework profile developed (ramp the temperature for 45-60 seconds with a maximum temperature between 210°C to 220°C). Finally, remove the component using a vacuum tip. Do not attempt to remove a partially re flowed component from a board by prying it off as this could likely damage the component and potentially destroy the board. 3. Site Preparation – After the reworked component has been removed, some excess solder might remain on the board. The excess solder can be removed using a vacuum de-soldering system or a soldering iron with a solder wick. Special care must be taken to avoid damaging the solder mask material and the solder pads. As a final step, alcohol can be used with a brush to clean the rework area. Allow the board to dry and inspect to ensure a clean solder able surface. The specific steps used here can be different from board to board and from company to company. As a minimum, the removal of the excess solder is an essential requirement. 4. Solder Paste Application – There are several options available to apply the solder paste to the component site. The BGA package itself can be screened with paste prior to placement. In addition, the site can receive solder paste with a dispensing method. Finally, the application of flux to a prepared pre-tinned site can produce acceptable results in most situations. 5. BGA Placement and Re flow – The next step is to replace the component on the board. The replacement component should be baked prior to assembly to the board if the component has been exposed to the environment for more than the allotted time. Place the component on the site observing all the alignment precautions. Reflow the balls using hot air in a manner similar to the removal process. Again observe total board temperature to avoid any thermal gradients that can result in board warpage. Allow the board to sufficiently cool before lifting the nozzle to avoid any chances of misalignment. For larger BGA components that are more sensitive to heat, extra precautions are necessary to ensure successful results. It is critical to minimize the temperature gradient on the part. A high temperature gradient creates thermal shock that leads to package warpage. The temperature delta between the following locations should be 5°C or less than the solder balls on the corners, the solder balls at the center of the package, and the top surface side of the package. To achieve a minimal temperature gradient, a slower ramp up rate (0.5°C/s) and a lower peak reflow temperature (195°C to 200°C as measured at the solder balls) is recommended. Additionally, the parts should be allowed to cool down by ambient air instead of blowing cool air on the parts with the nozzle. Blowing cool air on the component while it is still hot at the solder ball locations creates an undesired temperature gradient which might lead to package warpage. 6. Cleaning – Remove all residue from the board. However, if no-clean solder paste/flux is
used, cleaning is not required. See Also 7. Inspection – This is the final step in the process. Visually inspect the outer rows of the
solder joints to check for gross misalignment, joint quality, wrong orientation, board delamination, and damage of adjacent components. If detailed inspection is required,
X-Ray can be used to inspect for solder bridging and missing balls. See Also See Also: Reworking BGA & QFN Devices on the DENON RD500 Series Platform Call (858) 536-5050, for more information |
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