BGA Re-balling Demands a Precise and Controlled Process
Re-balling BGA-packaged devices such as FPGAs, highly complex ASICs, and µPs is becoming increasingly more popular. That’s because OEMs much prefer to watch the bottom line by taking the less costly route of BGA re-balling than the considerably more expensive replacement of these highly advanced and expensive devices.
At PCB assembly, x-ray inspection can spot a BGA or two that have poor ball collapse. X-ray inspection can also show voids or cracks within the collapsed balls, as well as opens or shorts between different balls. Further, an array of flaws or defects can be associated with an imperfect BGA. For instance, Fig. 1 below shows excessive solder paste applied and this creates bridging between BGA balls, also called ball shorts.
Check this link to read our SMT Magazine article on BGA re-balling and get all the important details associated with this PCB assembly process.
One thing to keep in mind is that BGA re-balling requires a precise step-by-step process that is straightforward, but highly complex. It’s imperative that you work directly with an experienced EMS provider or contract manufacturer (CM) to assure your BGA-packaged devices are correctly re-balled.
Here are some tips to help you achieve that objective:
- Don’t be fooled into thinking BGA re-ball incurs only a few simple steps.
- Get a basic understanding of the main steps required to perform re-balling.
- Put equal focus on the other aspect of BGA re-balling ñ moisture sensitivity level (MSL) and find out what role it plays in the overall process.
- Keep in mind flux can be corrosive. Completely cleaning package surface is required to remove all residue.
- Place special considerations on ball size and type ñ whether eutectic or lead free. Varying ball size requires specific solder paste.
- Don’t let your CM or EMS provider downplay stencil importance. A high quality stencil ensures the solder properly adheres to the board site during re-population.
Lastly, BGA re-balling incurs extra time when the job is done correctly. That means OEM PCB shipment schedules can be adversely affected. In some cases, short cuts are taken to make up for lost time. Also, in some cases, inexperienced technicians may inadvertently skip certain re-balling steps to pose subsequent assembly issues, further extending shipment time. The most damaging shortcut is failing to subject final BGA re-ball to a high-powered x-ray and completely overlooking voids within the balls. Here again, a well-equipped and experienced EMS provider can eliminate potential problems, which otherwise result from inexperience and shortcuts.