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Jan/Feb, 2024 Trends in BGA/CSP Reballing By Bob Doetzer, Circuit Technology, Inc. T
he trend in the electronics interconnect industry towards “Area Array Pack - ages” (BGAs, CSPs, CGAs etc.) and
away from high pin count leaded packages (primarily Quad Flat Packs) has increased dramatically over the last several years. The primary reasons for this are:
high BGA I/O (Input/Output) density (up to and exceeding 1,000 I/Os, compared with the largest QFP packages of 304 pins).
Additional reasons include increased reliability/robustness in all PCB assem- bly processes, improved electrical and thermal characteristics, higher first pass yield over conventional QFPs, easier and more reliable rework if the proper equip- ment is used, and the ability to touch up (re-ball) and reuse BGAs after removal in the rework process. BGA packages are fundamentally
different from other types of surface mount devices (SMDs) in that they do not allow visual inspection of solder joints unless the user has very specialized equipment. This is due to the intercon- nects being hidden “under” the package. Therefore all parameters of the BGA rework process, including the consistency of the interconnect balls on the package must be precise and consistent. For example, in the re-balling process of
a 1,000 I/O package, if just one ball size is incorrect (a 99.9% accuracy), the rework will
Trends toward “area array” packages have increased dramatically in recent years.
small and therefore did not make contact with the corresponding pad. So, the re- balling process must be 100%, there is no room for error.
Common BGA Packages The plastic BGA is the most common of
the BGA package types. It uses an overmold-
look good but will not work properly. Even under simple 2D X Ray, an insufficient ball size will not be noticeable. It will require a much more time-consuming 3D X-ray analy- sis to reveal that the solder ball was too
ed resin substrate to encapsulate the die/chip and either SN63/PB37 eutectic solder bumps or SN62/PB36/AG2 solder bumps are used for attachment to the mounting site. These solder bumps collapse during reflow creating the electromechanical connection to the PCB. Most PBGA’s use a solder bump diameter of 0.03 in. so the same 0.03 in. size is best for re- balling. PBGA overmold epoxies are generally moisture sensitive (hydroscop- ic) in that they absorb moisture from the surrounding environment. This can lead to a condition termed
“popcorning” during the reflow/re- balling process as the entrapped mois- ture turns to steam and expands. Popcorning is the delamination of the plastic packaging material or the delam- ination of the plastic material from the die itself and needs to be avoided at all costs. Therefore dry storage or pre-bak- ing the PBGA in an oven at 257°F (125°C) for 24 hours is necessary for the re-balling process. Next, micro BGAs and chip scale
packages (CSPs) are actually the same thing. Tessera Inc. trademarked the term µBGA, and CSP is the term used by the rest of the industry. A µBGA or CSP is commonly defined as a package that is no more that 1.2 times the size of the actual chip in the package. Pitch, or the center-to-center bump/ball
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