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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


CBGA vs PBGA

Chris

#2656

CBGA vs PBGA | 25 October, 2000

I need to know the advantages or disavantages of a plastic or FR4/Flex based BGA over the ceramic based BGA. We have a BGA package we are going to have produced. Some want to have it made out of ceramic because they feel a ceramic package will be able to be reworked more often. I don't even think we will be reworking the BGA very often. I feel a plastic BGA package will provide better reliability due to CTE matching the substrate more closely. Does anyone know of any papers comparing CBGA to PBGA? Can a CBGA be reworked more often than a PBGA?

Thanks,

Chris

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Philip A. Reyes

#2657

Re: CBGA vs PBGA | 25 October, 2000

Hi Chris!

I hope this will help you! The CBGA uses an array of high melting point solder spheres(Sn10/Pb90) to connect its ceramic chip carrier to an epoxy glass (FR4) PCB using eutectic (Sn63/Pb37) solder joints at both ceramic and card interfaces. The solder shpere is nominally 0.89 mm in diameter and provides a noncollapsing standoff after board assembly. This package range from 14 to 3.25mm. The usable range of a CBGA is determined by the fatigue life of the eutectic solder joint, which in turn is affected by the size of the CBGA sphere array, the coefficient of thermal expansion (CTE) of the attached card, the temperature extremes the environment and system and the number of on/off cycles. All but the latter affect strain on the solder joint. This means that most problem occurs in CBGA will depend on the solderability of the joint. While PBGA solder joint has a potential reliability problem because the balls are near eutectic solder, the whole balls becomes liquid in the standard surface mount reflow process. One of the common problem of PBGA is voids, this was due to the flux tends to stay within the molten solder that causes voids. Another is CBGA is not moisture sensitive while PBGA is moisture sensitive that pre-baking process will be needed if packages were not consumed for 24 to 48 hours after removal from the pack. Pre-baking condition is 125degC for 24 hrs. Therefore Chris, the problem, its either CBGA or PBGA package you are going to use in your project or design, basically, based on the requirement/application (CBGA is for high temp application) it will always depend on your process capability. If your process is robust, well controlled, definitely you can eliminate those type of problems. Bye!!!

Philip

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