The reballing process: using preforms, balls can be removed and reattached in an hour.

Position:TECH TIPS

REMOVING AND REWORKING the BGA is often an economically attractive alternative to replacement with a new part. If the intent is to reuse the BGA, the solder balls must be replaced before it can be resoldered to the circuit board. The BGA removal process renders existing solder balls unusable.

Starting with a BGA removed from the board, the first step is to bake the moisture out of the component to prevent a defect known as popcorning. This defect appears as craters in the BGA package, caused by the explosive expansion of absorbed water vapor during reflow. It is easy to see on the top and sides of components, but after the solder balls have been reflowed, it can be more difficult to see on the underside of the component.

Next, remove the existing solder balls and clean the surface. Solder balls can be removed using a soldering iron with a blade tip attached. Uniform heating of the part with auxiliary heating is necessary to avoid localized thermal shock to the BGA from the hot blade. This method is adequate for bulk solder removal. Care must be taken not to scratch the BGA surface. Generous use of flux increases the effectiveness of the heat transfer and also removes any oxides. Solder braid is used next to remove smaller flecks of solder, also with generous flux.

As a final cleaning and preparation, the BGA is carefully washed with isopropyl alcohol (IPA) to remove flux. The part is then inspected. Cleanliness can be confirmed using standard resistivity of solvent extract (ROSE) or SEC (solvent extract conductivity) testing.

Specify the BGA type and part number to BGA reballing vendors in order to obtain the correct preform parts.

Continuing with a clean, solder-free BGA, the next step is to perfectly position the balls under the BGA. With hundreds of solder balls to be exactly positioned, a mechanical device is required to maintain the alignment and position the solder balls under the chip...

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